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An evaluation of soil and water management practices on a lowland soil with poor natural drainage Heinonen, John Stanley 1992

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AN EVALUATION OF SOIL AND WATER MANAGEMENT PRACTICES ON A LOWLAND SOIL WITH POOR NATURAL DRAINAGE by JOHN STANLEY HEINONEN B.Sc., The University of Toronto, 1978.  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIRMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Soil Science)  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA DECEMBER, 1992 © JOHN STANLEY HEINONEN  In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.  Department of  ,S002.).2LL--CS2_  The University of British Columbia Vancouver, Canada  Date )a e& ,  DE-6 (2/88)  /8  ii Abstract Low-lying areas of the Lower Fraser Valley tend to have poor natural soil drainage. Excess moisture, because of a high water table and ponded surface water, restricts the range of crops that can be grown and influences farm management decisions regarding the nature and timing of field operations. When economic considerations lead farmers to commence field operations when the soil is too wet, the result can be structural degradation of the soil, leading to the formation of surface seals and crusts and a compact ploughpan. The aim of this study was to evaluate the effectiveness of various management practices in controlling the water table, to gain an understanding of the mechanisms governing excess water accumulation, persistence, and removal from lowland soils, and to make management recommendations from these. Monitoring was conducted on two adjacent farms on Westham Island. They differed in their management of excess water: one relied on surface ditching, subsoiling, mole drains, and cover crops, while the other used a system of perforated subsurface drainlines emptying into a ditch that was pumped to keep the water level low. Soil-water pressure potentials were measured automatically and manually with piezometers located in selected depressions and surrounding slightly higher ground from February to April 1981. Depth of ponded surface water and water level in the ditches draining each farm were monitored. Rainfall was recorded with four rain gauges. Bulk densities  and saturated hydraulic conductivities of the surface crust, ploughpan, and subsoil were measured. Soil penetration resistances and aggregate stabilities (wet sieving) were measured as indices of compaction and structural stability. Earthworm numbers and biomasses were measured in both farm. Land drainage through a system of subsurface drainlines was found to lower the water table more rapidly after rainfall, and reducing the depth and duration of ponding compared to undrained land. Drainage resulted in more trafficable and opportunity days for field operations. Drainage dramatically increased earthworm populations which in turn improved the drainage via the pathways for water movement provided by burrows. Although there was a more severe ploughpan in the undrained farm there was no evidence that it impeded water movement. There were no differences in aggregate stabilities between farms. The presence of ponded water in depressions was found to be due mainly to a low permeability surface seal which was more severe in the undrained farm. The presence of the seal resulted in surface runoff to low areas and slowed water infiltration there. Subsoiling and moling may also aggravate excess water problems by directing water to low areas. Surface ditches were found to be ineffective in removing ponded water. Using a cover crop, which reduced the severity of crusting and ponding, was a more effective practice than subsoiling when the soil was undrained.  iv TABLE OF CONTENTS Page ABSTRACT TABLE OF CONTENTS^  iv  LIST OF TABLES^  vi  LIST OF FIGURES^  vii  LIST OF APPENDICES^  ix  ACKNOWLEDGMENTS CHAPTER 1 - INTRODUCTION 1 Introduction and Purpose ^ Literature Review^ 6 6 1. Drainage^ a. Drainage Design Criteria ^ 7 b. Subsurface Drainage and Water-Table Depth ^8 c. Water-Table Control: TrafficabilityWorkability and Timeliness ^ 9 d. Subsoiling^ 13 14 e. Mole Drainage^ 2. Aggregate Stability^ 15 18 3. Soil Sealing and Crusting ^ 4. Earthworms and Drainage ^ 19 CHAPTER 2 - MATERIALS AND METHODS 21 1. Soil and Landscape Descriptions ^ a. Topography, Elevation, and Drainage ^21 21 b. Parent Material and Texture ^ 2. Site Description and Location ^ 22 3. Piezometers and Ditch Water-Level Recorders^28 4. Surface Crust Saturated Hyraulic Conductivity^31 and Bulk Density 5. Soil Profile Saturated Hydraulic Conductivity^33 34 a. Large Core Method^ b. Auger-Hole Method^ 35 6. Earthworm Numbers and Biomass ^ 38 7. Penetration Resistance Profile ^ 38 8. Bulk Density Profiles ^ 39 9. Aggregate Stability^ 39 41 10. Rainfall^  V  Page CHAPTER 3 - RESULTS AND DISCUSSION Introduction^ 42 1. Piezometer Data^ 42 2. Surface Ponding in the Lowest Spots in Each^44 Site 3. Analysis of Recording Piezometer Graphs^47 4. Comparison of Water-Table Behavior in^52 Depressional Areas i. Sites D1 and D2^ 52 ii. Sites D2 and U2^ 56 iii. Sites Ul, U2, and U3 ^ 56 5. Variations in T with Depth ^ 61 i. Depressional Sites^ 61 ii. High Sites^ 68 6. Water Table - Trafficability Relationships^68 7. Ditch Water Levels^ 80 8. Profile Hydraulic Conductivity ^ 80 9. Surface Crust Ks^ 86 10. Surface Crust and Soil Profile Bulk ^ 89 Density 11. Earthworms^ 93 12. Water-Stable Aggregates^ 96 13. Penetration Resistance and Compaction^99 14. Effects of Moling, Subsoiling, and Subsurface ^101 Drainage on the Water Regime of Depressional Areas i. Moling^ 101 ii. Subsoiling^ 102 iii. Subsurface Drainage^ 102 15. Surface Ditching to Remove Ponded Water ^104 CHAPTER 4 - SUMMARY AND CONCLUSIONS ^  107  BIBLIOGRAPHY^  111  APPENDICES^  116  vi LIST OF TABLES Page Table 1  Crescent Soil Description  23  Table 2  Westham Soil Description  24  Table 3  Surface Ponding Data for Depressions  45  Table 4  Saturated Hydraulic Conductivity Data: Large Core Method (plough layer removed)  82  Table 5  Auger Hole Method Hydraulic Conductivity Data  83  Table 6  Surface Crust Saturated Hydraulic Conductivity  87  Table 7  Surface Crust Bulk Density  90  Table 8  Profile Bulk Density (Core Method)  91  Table 9  Earthworm Numbers and Biomass  94  Table 10  Water Stable Aggregation Data  97  vii LIST OF FIGURES Page Figure 1  Map of Low-Lying Portions of the Lower Fraser Fraser River Valley  2  Figure 2  Climate Data for Vancouver International Airport  3  Figure 3  Pea Harvesting Equipment and Compacted Soil from potatoe harvesting under wet conditions  17  Figure 4  Location of the Research Site on Westham Island in relation to British Columbia  25  Figure 5  Location of Research Sites on adjacent drained and undrained farms  26  Figure 6  Pumphouse in Farm D with float on right  27  Figure 7  Examples of the two piezometer designs used  30  Figure 8  Laboratory Aparatus for Measuring Soil Crust K,  32  Figure 9  Large Core Technique for measuring K,  36  Figure 10 Field measurement of K, using large core method  37  Figure 11 Recording piezometer "T data from depressional portions of sites Dl and Ul  48  Figure 12 Comparison of manual and recording piezometer AFT data for site Ul  53  Figure 13 Water table comparison from manually read piezometers in Site D1  53  Figure 14 Comparison of water table heights from sites Dia and Dld  54  Figure 15 Comparison of water table heights from sites D2a, 55 D2b, and D2c Figure 16 Comparison of water table heights from sites U2a and D2a  57  Figure 17 Comparison of water table heights from sites Ula and Ule  58  viii  Page Figure 18 Comparison of water table heights from sites U2a 59 and U2b Figure 19 Comparison of water table heights from sites U3a, 60 U3b, and U3c Figure 20 4 7, vs Z (depth) graphs for Sites U2a, D2a, ^62 and U3a ,  Figure 21 4rT vs Z (depth) graphs for Sites Ula, Dla,U1b, ^64 and Dlb Figure 22 4%. vs Z (depth) graphs for Sites D2c, Did,^69 U3c, and Ule Figure 23 Relationships between ponded days, trafficable ^72 days, opportuity days and days on which rain was recorded Figure 24 Total Ponding-Trafficability relationships for^73 all Sites Figure 25 Ditch water level data for Farm D and Farm U^81 Figure 26 Crust properties and Earthworm Behavior during^95 Wet Periods Figure 27 Penetration Resistance Profiles  ^  Figure 28 Effects of mole draining at a constant depth below the soil surface  ^  100  103  Figure 29 Unsuccessful surface ditch installation^105  ix LIST OF APPENDICES Page Appendix 1 UBC Evaporation Pan Data  ^  Appendix 2 Westham Island Rainfall Data  ^  116 117  ACKNOWLEDGEMENTS My wife Yiolanne, and children Julia and Keith, have provided me with continual support and encouragement which was needed to complete this project. I thank my thesis committee for the direction given, and Jan deVries for framing the problem and his many suggestions about approaches to take. Martin Driehuyzen proposed the use of piezometers for the study and this proved invaluable. Many people helped with the field work but none more than Trevor Murrie. Thanks to the Reynolds and Swenson families for allowing me to conduct my field research on their farms. Bernie von Spindler and Bill Cheang assisted in many ways. The community of the Soil Science Department provided enthusiasm and comradeship. Thanks to Jack Dobb, Peter Mills, Charlie Arshad, and Alan Stewart for helping to lighten the load in the last phase of my M.Sc. program. I am also grateful for the support my boss John Payne has shown. Finally, I deeply appreciate the positive approach of Andy Black and Mike Novak and their help in hurdling a myriad bureaucratic barriers. Where there's a will there really is a way! Free at last, free at last, .  1  CHAPTER 1  INTRODUCTION  Introduction and Purpose  Low-lying portions of the Lower Fraser River Valley, as shown in Figure 1, generally have poor natural drainage. This is due to a number of factors including the deltaic nature of the area, the proximity to the Fraser River and sea level, and runoff originating from adjacent forested and urbanized upland areas. The region's humid maritime climate (see Figure 2) is also a major contributing factor. Nearly level to gently undulating topography and medium- to fine-textured soils combine with the above factors to produce a fluctuating, but generally high, regional water table in the lowland areas. Excess water can accumulate in and on the soils in these areas at any time of the year as a result of poor natural drainage; this most commonly occurs in the off-season from November 1 to March 1. Fraser Valley farmers find that surface water (flooding and ponding) reduces soil trafficability and workability and thereby reduces the timeliness with which land preparation, planting, harvesting and manure spreading can be carried out. It is a major cause of soil structure degradation  2  Figure 1: Generalized map of the agricultural lowland areas in the Lower Fraser Valley of British Columbia. Based on information from Winter (1966) and Luttmerding(1980).  3  Figure 2: Climatic normals based on the period from 1951-1980 for Vancouver International Airport (Atmospheric Environment Service, 1980,1984).  4 leading to the formation of a surface seal (Abbaspour, 1988). Excess water can also lower crop yields and quality, or result in complete crop failure. Although lowland areas of the Lower Fraser Valley are protected from flooding by over 500 km of river and sea dykes (Victoria, 1968) regional water management is generally inadequate. It relies heavily on passive methods of water removal such as gravity operated flood boxes that open only at low tide and close during high tide. Most pumping stations are located around urbanized lowland areas and as a result the removal of excess water on a regional scale is not sufficient to meet agricultural requirements. Whenever this regional problem is combined with runoff from uplands and inadequate on-farm water management, soil water-logging and surface ponding often occur throughout the rainy winter months. Water frequently covers the soil surface in local depressions, sometimes to depths of 0.25 m or more. This tends to discourage cultivation of overwinter crops such as cabbage and cauliflower, made possible by the area's mild climate. If this surface water persists into March, April, or even May, significant delays in tillage operations may result since the decision to commence land preparation usually depends on how dry these depressional areas are. Farmers are generally reluctant to bypass wet depressions in their fields except in the wettest springs because of the difficulties caused for plowing.  5 When wet conditions continue, economic and other conditions lead farmers to begin land preparation when the soil is too wet. This can degrade soil structure in the surface layer, and, in the case of plowing and rotovating, also results in the formation of a compacted plowpan. Sohne (1958) found that compaction from surface applied pressures can occur down to depths of up to 0.60 m. Surface structure degradation can increase the susceptibility to surface sealing and crusting, which decreases infiltration rates, causing local surface runoff and ponding. If the plowpan remains intact it can also restrict vertical water movement and result in wet surface soil conditions. The problem is therefore somewhat cyclic in nature. The difficulties associated with the accumulation of excess water in and on lowland soils are of considerable agricultural importance in the Lower Fraser valley. Good soil and water management practices can alleviate many of the negative consequences of poor regional drainage, however adequate regional drainage is required before the full benefits of proper on-farm management practices can be attained. The primary aim of this study was to evaluate the effectiveness of various management practices in controlling the behaviour of the water table, since water table depth greatly affects surface trafficability and workability. A  6 broader purpose was to gain an understanding of the mechanisms governing excess water accumulation, persistence, and eventual removal from lowland soils. This information is used to recommend soil and water management practices best suited for the control of excess water, and to suggest improved drainage design criteria. Differences in soil physical properties resulting from variations in management were also studied, as they indicated how to optimize management practices.  LITERATURE REVIEW  1. Drainage Drainage of agricultural land is practiced in humid areas in order to reduce the water content of wet soils and thereby increase their aeration, temperature and strength (Marshall and Holmes, 1979). ^ Most permanent subsurface drainage^involves installation of perforated plastic drain pipes in conjunction with drainage ditch water level control. The depths, spacings, and lay-out of the drainpipes vary according to design criteria. Short term subsurface drainage improvements can also be achieved by subsoiling and moling. Surface drainage, which is done by land levelling, or shaping to form temporary shallow ditches, can be used to remove excess surface water.  7 a.  Drainage Design Criteria The agricultural function of a drainage system is to  help increase the economic returns from the farm enterprise (Bouwer, 1974). Economic criteria have to be included into the design process of farm water management systems. It is obvious that in every circumstance a point is reached beyond which equal increments of increased benefit are achieved only at the expense of increasing additional costs. The optimum drainage design is one which maximizes the difference between annual benefits and annual costs (Buras, 1974). However, our present state of knowledge is such that an assessment of the full economic implications of better drainage is not yet possible (Morris and Calvert, 1976). In practice, drainage criteria are based on a combination of environmental conditions (climate, soil, weather, etc.) and management concerns (eg. crop requirements, trafficability - workability and timeliness). In each case the design choice is made within the general economic constraints as perceived by the farm manager. Given all the variables, there is considerable potential for sub-optimal drainage designs. It is therefore essential to assess the effects of various drainage systems in order to obtain appropriate drainage criteria that will result in improved design (Oosterbaan, 1980). According to Bouwer (1974), the drainage design criterion expresses the drainage deficiency of a field to be  8 corrected by a drainage system. Drainage criteria can be evaluated for a variety of conditions depending on the main function of the drainage system (Bouwer, 1965). The lack of adequate design criteria constitutes the weakest link in rational drainage design (Bouwer, 1974). Dieleman (1979) stated that the cause of failure in drainage design is more often a lack of understanding of the broad inter-relations between drainage and other farm or water management matters than the lack of precise data. Drainage is therefore more than just the determination of the correct dimensions of the system. Optimum depths and spacings are probably strongly dependent on local conditions (Oosterbaan,1980).  b. Subsurface Drainage and Water-Table Depth Shkinkis (1979) presented results showing significant lowering of water tables due to drainage, the effect increasing with drain depth and reduced spacing (sandy loam to sandy clay soils, 0.9-1.8 m drain depths, and 12-45 m spacings). Trafford and Oliphant (1977) concluded, however, that relatively shallow drainage systems alone caused no decrease in mean water table levels, but when combined with subsoiling or moling the mean depth of the water table was increased from 0.23 to 0.40 m ('heavy' clay soil, 0.80 m drain depth, 15-60 m drain spacings,subsoiling at 0.45 m and 1.5 m spacings, moling at 0.55 m and 2 m spacings).  9 They also found that the effect of decreased drain spacings was small especially when drainage was combined with moling or subsoiling, likely due to the drain depth being shallow. Wind (1976) demonstrated the influence of drainage depth on soil workability in the spring under climate conditions in the Netherlands. He showed a significant increase in the number of work or opportunity days in March and April as drain depth is increased from 0.9 to 1.1 m. A drain depth of 1.5 m appeared to give optimum water-table control for workability. These varying results serve to confirm that the effectiveness of a drainage system is partially dependent on local soil and hydrologic conditions. The depth of the regional water-table is an example of a local condition which could be important in this regard. The average depth of the water-table resulting from on-farm water management is however, generally an excellent indicator for trafficability, workability, and plant growth conditions and it can serve as a good criterion for evaluating the effectiveness of a drainage system (Oosterbaan,1980).  c. Water-Table Control: Trafficability-Workability and Timeliness Timeliness in the performance of farming operations is a major objective of drainage. Draining excess water from a soil reduces drying time and causes an increase in soil  10  strength and therefore trafficability, thereby making additional time available for carrying out farming operations and lessening the risk of soil compaction and structural degradation. A long-term loss in productivity potential may result from too much traffic or soil manipulation at times when the soil is not trafficable or workable (Reeve & Fausey, 1974). Paul and deVries (1979b) established linear relationships between water-table depth and cone penetration resistance (a soil strength index) of the plow layer, and used these relationships to establish critical water-table levels for trafficability of drained mineral soils. They defined trafficability as "the ability of a soil to support traffic without receiving structural damage beyond the limits for good crop growth". Paul and deVries (1979b) found that cultivated mineral soils became trafficable as much as 25 days earlier in the spring where effective subsurface drainage systems lowered the water-table rapidly in comparison with the same soils in their natural poorly-drained state. Similar results were reported by Fausey and Schwab (1969) who found that for a clay soil, the moisture content in the upper 0.3m was 4-5% higher throughout the spring with surface drainage than with subsurface drainage. This resulted in a 17-day delay in planting date. Subsurface drainage can therefore significantly improve the timeliness of farm operations, with  11 consequent gains in crop yields (due to earlier and more flexible planting dates) and hence in farm income. The additional number of trafficable days can be critical on clay soils, in some years being the difference between normal yields and total crop failure (Armstrong, 1978). The definition of trafficability given by Paul and deVries (1979b) should, for most practical purposes, be normally extended to include workability. Their definition is satisfactory for cases where machinery rides on the soil as with manure spreading, but it does not adequately apply where tillage or planting are involved. Workability, in a general context, refers to the ease with which the soil may be manipulated and the relative success of the manipulation in achieving the desired results. Since the types and purposes of soil manipulation are so varied, and the methods of characterizing the soil inadequate, it is difficult to generally define workability in a quantitative manner. The workablility criteria developed by van Wijk and Feddes (1986) was a soil and crop specific value (a workability limit). If the pressure potential ("I') at 5 cm depth in the clay soil they studied was below a threshold value of 4rp = -70 cm, then moderate to good field conditions for potatoe planting prevailed. On days with ir p higher than the threshold value, planting could not be accomplished without damaging the soil structure. Van Lanen et al (1992) used this criteria and simulated pressure potentials to  12 calculate workable days. A higher probability of workable days was found to result in the possibility of a longer growing season. Trafficability and workability are sometimes used interchangeably in an agricultural context. If an agricultural soil is workable it is certainly also trafficable, however, the reverse is not always true, eg. a hard dry soil is quite trafficable but marginally workable. For tillage and planting the range of moisture contents where a given soil is both workable and trafficable is of most interest. This range extends from the moisture content where the soil becomes friable rather than hard, to the plastic limit. The optimum part of the range is likely somewhat removed from its wetter or drier ends. Wind (1975) stated that the most important factor governing workability is weather. In humid regions the timing of farming operations is highly dependent on weather, particularly in the early and late season operations. Since moisture inputs to the soil are mainly from precipitation, the most practical means of gaining control over soil moisture conditions in humid areas is to provide drainage (Reeve & Fausey 1974). Since the time suitable for field work is directly related to the weather, there is an element of risk in all farming operations. By reducing weather-induced uncertainty, drainage can provide a more predictable environment for farm  13 management decisions. The number and distribution of workable days in spring is important for the choice of type and size of farm machines and for the organization of farm work (Wind,1976). The drainage investment can help towards minimizing the considerable 'hidden' costs of untimeliness in farm practices and as a result reduces the necessity to over-invest in farm machinery system capacity as a hedge against the vagaries of weather (Morris & Calvert, 1976). Since soil moisture is directly related to the weather, the concepts of risk and uncertainty associated with weather should be logically incorporated in the design of drainage systems (Reeve & Fausey, 1974). Where drainage systems are designed for trafficability control, a random-type layout is used whereby drain lines are located so as to drain as many low areas or wet spots in the field as possible (Bouwer, 1974). In lowland areas a partial random layout may be used to augment a system of parallel spaced drains. By increasing water-table draw-down in depressions a partial random layout can affect the desired control without requiring major, and possibly expensive, adjustments to the drainage system as a whole.  d.Subsoilinq Subsoiling is a form of deep tillage which disrupts the subsoil without inverting it or bringing it to the surface (Wells, 1956). The basic aim of subsoiling is to loosen  14 compacted soil such as a plowpan, and thus improve vertical water movement and the growth of plant roots. In order to be effective subsoiling should only be carried out when the soil is dry and brittle, for maximum shattering. The distance between subsoiler blades should also be at least equal to, or less than, the depth of subsoiling to ensure overlap of lifting zones (Swain, 1975). Subsoiling is only beneficial in soils with a compacted layer that restricts root development or water movement, and where there is a better structured or drained horizon below (Wells,1956). Compaction can also be alleviated by using a recently introduced slant-legged soil loosening implement, the Paraplow. It works to depths of 0.25 to 0.35 m; soil passing over the slanting legs is placed under tension causing cracking to occur along natural planes of weakness. The degree of soil disturbance and fracturing is varied by adjusting the spacing between the legs and by a flap hinged to the trailing edge of the leg, the amount of soil lifting and cracking being altered by the angle between the flap and the leg (Chaney and Hodgson, 1984).  e.Mole Drainage The aim of mole drainage is to create a channel, usually cylindrical, at a depth of 0.5 to 0.7 m, with cracks radiating from it, that will conduct water laterally to a drain line or open ditch. Mole drains will not persist for  15 more than a few months unless the clay content is greater than 40% and the soil is structurally stable under saturated and near-saturated conditions. The operation is also only successful in clay if the soil consistence is plastic at moling depth and friable above (Swain, 1975). Spoor et al (1982b) identified clay mineralogy and soil bulk density at moling depth as being factors influencing the suitability of soils for mole drainage. They identified numerous factors important in the formation, stability, and failure of mole drainage channels. It is evident from their results that it is difficult to accurately predict the suitability of soils to mole drainage.  2. Aagreciate Stability Soil structure can change in response to different agricultural practices and can, in turn, influence the productivity arising from agricultural practices. Artificial drainage diminishes the length of time that the soil has high water contents and low structural stability and enhances the extent of wetting and drying (Kay, 1990). Differences in trafficability also result in the potential for structural degradation being greater on undrained fields, given similar tillage or harvesting dates. The problem of soil degradation has also become more serious generally, because of the trend to more intensive field traffic by heavier machines (Raghvan et al, 1978). These points are illustrated by the photographs  16 in Figure 3. Aggregate stability, as determined in the laboratory, is commonly used as an index of soil structure stability in the field. The type of disrupting force exerted on aggregates during laboratory experiments depends on the situation of interest in the field (Kemper, 1965). In humid areas, such as coastal British Columbia, the water-stability is a measure of the relative susceptibility of the soil to compaction, surface sealing and crusting, and is a factor in the infiltrability and aeration of the rootbed. Comparatively little research has been done on the effects of drainage treatments on soil structure. Wesseling and van Wyk (1957) concluded that improvements to soil structure due to drainage are small. Leyton and Yadav (1960) working in Great Britain found a significantly higher proportion of water-stable aggregates after five years of drainage. This difference was attributed to lower water-table levels. Sieben (1974) reported deterioration of soil structure caused by persistance of water-table levels near the soil surface. Fausey and Schwab (1969) noted adverse soil structure and more severe crusting on undrained plots where there were long periods with ponded water. Kay (1990) stated that there is little information on the rate of change in structural characteristics when artificial drainage is introduced in agricultural soils.  18 3. Soil Sealing and Crusting Soil seals form where the aggregated structure near the surface is more or less destroyed and the primary particles are rearranged. This change can come about under the influence of externally applied mechanical pressures such as raindrop impact or vehicle traffic (Bonsu, 1984), or through spontaneous slaking of soil aggregates in the course of natural wetting-drying cycles (Hillel, 1960). Soil crusts form as the seal dries and becomes harder and more compact. Surface seals can form at the soil surface when sediment fills in surface pores and builds up a layered, dense soil (Abbaspour, 1988). Sediment can originate from erosion and rainsplash in adjacent higher areas surrounding a depression or from wave action where there is surface water. One of the most significant effects of a surface seal is the decrease in infiltrability, resulting in ponding. Surface seals and crusts also inhibit seedling emergence and aeration of the rootbed. McIntyre (1958) found that surface crusts reduced the hydraulic conductivity of the soil profile by as much as a factor of 10 4 . When rainfall rates exceed the infiltrability of a seal excess water either accumulates or runs off. In individual fields both may occur. The water accumulating in surface sealed depressional areas, may be augmented by runoff generated from surrounding higher areas with surface seals. The depth of water accumulated in the depression may be  19 several times the amount of actual rainfall depending on the severity of sealing, and the effective catchment area. Upon drying, higher areas will develop a network of cracks which breach the seal. These cracks permit entry of water into the soil until the infiltrability is exceeded or the cracks are closed by swelling, infilling due to rainsplash and erosion, and the reformation of a continuous seal. In the ponded depressions cracks cannot form until the water is removed by infiltration through the seal and evaporation. The water may also be removed through construction of a shallow surface ditch, or direct pumping from a sump into the main ditch using a portable pump.  4. Earthworms and Drainage Earthworms require reasonably aerated conditions and hence do not thrive in poorly drained soils prone to waterlogging or where the soil surface is covered by ponded water (Guild, 1948). They can, however, survive for a time in water provided that it is sufficiently oxygenated (Russell, 1973). Two reasons why the presence of earthworms in a soil is desirable are: (1) they contribute to the formation of water-stable aggregates (Hopp and Hopkins, 1946; Dawson, 1947; Dutt, 1948, Evans, 1948), and (2) their burrowing activities improve air and water movement in the soil by providing non-capillary pore space (Guild, 1955). Bouma et al  20 (1977) and Bouma (1981) studied the effects of macropores, including earthworm burrows on soil hydrology. The influence of earthworm burrows increases dramatically with the number, diameter, and vertical continuity of burrows. Bouma's research has demonstrated that earthworms can significantly benefit agriculture where they are found on finer-textured soils with poor natural drainage. Earthworm populations have been shown to be particularly sensitive to crop rotations and their associated tillage operations (Russell, 1973). Earthworm numbers have been found to decrease after plowing and discing, but increase in barley-clover rotations which leave the soil undisturbed for periods sometimes greater than one year (Carter et al, 1981). Qualitative field observations have indicated dramatic differences in the number of earthworms between drained and undrained farmland in the Lower Fraser Valley. In undrained land significant residual earthworm populations are only present along ditches where the soil is better aerated during the wet months. In drained land earthworms are more evenly distributed throughout the fields. These differences in earthworm populations appear to have significant effects on soil physical properties, especially hydraulic conductivity.  21  CHAPTER 2  MATERIALS AND METHODS  1.^Soil and Landscape Description The soils in this study consisted of a Crescent and Westham series complex. (a)Topography. Elevation and Drainage The topography of the complex varies from nearly-level to gently-undulating with slopes up to two percent. The relief is generally 0.5 m or less. Westham soils are poorly drained and sometimes have slightly depressional topography. The Westham soils usually occur at slightly lower elevations than the adjacent Crescent soils which are moderately poorly to poorly drained. Elevations are all less than 5 m above sea level. (b)Parent Material and Texture The parent materials of the Crescent and Westham soils are medium to moderately-fine textured, stone-free, deltaic deposits of the Fraser River, usually deeper than 1 m and underlain by sand. Moderately- to strongly-saline materials are usual below 1 m in the Crescent series and below 0.5 to 1 m in the Westham series. Sulfurous compounds are also usually present at these depths(Luttmerding, 1981a). The Crescent soil  22 is described in Table 1, the Westham soil in Table 2. 2.^Site Description and Location Five sites were established at Westham Island (located as shown in Figure 4) on two adjoining farms with the same soil types but having contrasting soil and water management practices (see Figure 5). Two of the sites were on Farm D (D for drained) which has perforated plastic drainpipes installed at an average depth of 1.2 m and spaced 18 m apart. These drainpipes empty into a central ditch in which the water level is controlled by a pump (Figure 6) automatically triggered by a float switch. The water is pumped into a drainage canal. This drainage system was installed nine years prior to the study. Farm D had also not been subsoiled for a period of at least eleven years and had no shallow surface ditches in place during the study. Site D2 was in an area beyond the end of the central ditch where the drain lines fan out, so the spacing is consequently greater than 18 m. The remaining three sites were located on Farm U (U for undrained) which had no permanent subsurface drainage system. The problem of excess water and poor drainage was dealt with in three ways in Farm U: (1) subsoiling to break up the plow pan and speed vertical water movement, (2) mole drains to move water laterally, and (3) shallow surface ditches to remove excess surface water. Site Ul had been subsoiled and a cover crop of fall rye was planted to protect the soil surface from raindrop impact and hence reduce the degree of crusting. Site  23 Table 1: Crescent Series - Profile Description Horizon^Depth Description ^ 0-18cm^Dark greyish brown (10YR4/2,moist) Ap silty clay loam. Weak medium to coarse subangular blocky structure. Friable hard. Abundant fine roots. pH 5.4. ^ 18-30cm Grey (10YR5/1,moist) silty clay loam. Bg Massive to coarse angular blocky structure. Slightly sticky, firm, slightly plastic. Few fine roots. pH 4.8. ^ 30-48cm Grey (10YR5/1,moist) silt loam. Cgl Massive structure. Slightly sticky, firm, slightly plastic. Very few fine roots. pH 4.4. ^ 48-97cm Dark Grey (5Y4/1,moist) silt loam. Cg2 Massive^structure.^Non-sticky, friable, slightly plastic. Common rhyzo-concretions. pH 3.9. ^ 97+ cm Dark Grey (2.5Y4/l,moist). Massive Cg3 structure. Non-sticky, non-plastic. Common rhyzo-concretions. pH 3.4. (from Luttmerding, 1981a)  24 Table 2: Westham Series - Profile Description Horizon  Depth^Description  Ap2  0-15cm^Dark^grayish^brown (10YR4/2,moist) silt loam. Fine to medium subangular blocky stucture. Friable when moist. Many roots in grassed areas. pH 6.1.  Ap2  15-25cm Grayish brown (2.5Y5/2,moist) silt loam . Medium subangular blocky structure. Friable when moist. Abundant roots in grassed areas. pH 5.3. Abrupt boundary at plow pan.  Cgl  25-40cm Gray (5Y5/1,moist) silt loam. Massive structure. Firm when moist. Yellow (5Y8/6, moist) mottles. pH 4.1  Cg2  40-95cm Dark gray (5Y4.5/l,moist) silt loam. Massive to weak subangular blocky structure. Reddish-brown mottles; rhyzo-concretions. pH 3.4  Csg  95+ cm Dark-gray (5Y4/1,moist) sandy loam. Massive. Friable when moist. pH 3.4.  (from de Vries, J. and C.L. Paul, 1978)  25 Figure 4: Location of the research site on Westham Island in relation to British Columbia.  26 Figure 5: Schematic plan view of the research sites on Westham Island. The letter "a" is located in the lowest spot in a depressional area and each subsequent letter indicates progressively higher areas.  27  Figure 6: Pumphouse in Farm D with float on right.  11111111111/61+Lh _  „...„„...„  28 U2 was located in a field which was not subsoiled in the fall of 1980 and where the soil surface was severely crusted. Site U3 had been subsoiled, however, the soil was left bare and as result had a severe surface crust. The ditches surrounding Farm U are connected to large regional drainage ditch that flows into the south arm of the Fraser River at low tide via a sluice gate. These ditches had not been properly cleaned for several years. The sediment and vegetation in them prevented optimum water flow.  3. Piezometers and Ditch Water-Level Recorders Piezometer nests were installed at each of the five sites in late January and early February of 1981. The piezometers are referred to by the abbreviation assigned to them, for example: Dia, where "a" is a location within Site Dl. Each site was located in a depression where ponding had been observed. Nests of two to six piezometers, with the test sections located at a various depths in the 0.10 m - 0.80 m range were installed in the lowest point in each depression and also on adjacent higher areas where there was no prolonged surface water accumulation. Another piezometer nest was located at an intermediate position in all sites except U2. Piezometer nests and a recording piezometer were located in sites Dl and Ul, for more intensive monitoring. Stevens water-`level recorders were installed on the ditches in both farms in order to relate ditch water-levels to water-table  29 behavior in the field. The recording piezometers consisted of an 0.18 m diameter aluminum tube with a removeable covered platform containing a Stevens water-level recorder. The lower (open) end of the tube was covered with fibreglass window screening bound on with baling wire. The other piezometers consisted of 0.04 m inside diameter galvanized steel pipes pressed together at one end. In the test section slits were sawed into the bottom 0.05 m. An alternate design employed fibreglass window screening and bailing wire as in the recording piezometer (see Figure 7). All piezometers were installed in auger holes 0.04 m larger in diameter, with gravel placed around the test section to prevent clogging. The pipes were then sealed in with concrete. Small tins were placed over the tops of the piezometers to prevent rainwater entry. Before measurements commenced each piezometer was emptied once or twice to remove mud which had entered through the test section during installation. The water level in each manual piezometer was measured with a float tube and a calibration was carried out to account for the volume of water it displaced. The recording piezometers and ditch water-level recorders were checked regularly to ensure accurate time and water-level.  30  Figure 7: Examples of the two piezometer designs used.  31 4.^Surface Crust, Saturated Hydraulic Conductivity & Bulk Density Saturated hydraulic conductivity (KJ measurements were made on nine field-moist samples of the 0.03-0.04 m thick crust taken from site U3. Samples were taken after the onset of cracking so the main sampling criteria was that there be approximately a 0.15 m X 0.15 m area unbreached by cracks. Each sample was carefully carved into an 0.11 m X 0.11 m block. Care was also taken to level the bottom of each block without smearing the soil. The crust was placed on a porous plate composed of closely-packed, very-fine sand, and a plexiglass chamber with internal dimensions 0.12 X 0.12 X 0.07 m high was put over it (see Figure 8). A water-tight seal was obtained by pouring molten paraffin around the sample to the top of the crust. Once cooled the wax-plexiglass interface was further sealed with stop-cock grease. The sample was then flooded and inflow measured using a marriot device which also maintained atmospheric pressure at about the crust surface. A suction of 0.06 - 0.07 m of water was imposed at the base of the sample by lowering the outlet. The hydraulic gradient across the crust sample was measured using manometers connected to the inflow and outflow ports, and K, was calculated using Darcy's Law. Measurements were taken at intervals during periods ranging from 42 to 70 hours. The hydraulic conductivity of the surface crust was also measured by performing a water balance calculation ((depth of  32  Figure 8: Laboratory apparatus for measuring soil crust K 5 .  Qy  rryriot device air bubbler intake air vent q - -  ■••  • ‘'• • •", •  gasket ax  AL  •••^ow  LH screen  sand outlet  q  Yanometers  33 water on the surface) = rainfall - evaporation - drainage) for the ponded area in site U3. Changes in the height of ponded water were accurately measured by counting the number of turns required to bring a sharpened screw with a known thread pitch into contact with the water. The hydraulic gradient across the crust was determined by measuring the depth of surface water and the hydraulic pressure at a depth of 0.14 m using a piezometer. AL in Darcey's Law was taken to be 0.14 m rather than the thickness of the crust, because the exact hydraulic gradient across the crust itself was not measured. The evaporation data was obtained from class A evaporation pan measurements (Appendix 1) at the University of British Columbia climate station located 21 km north of Westham Island. Calculations were only made for sunny days in order to insure more comparable evaporation regimes between site U3 and the evaporation pan location and to avoid errors due to surface runoff into the depressional area during rain. Bulk density of the surface crust was measured using the clod method after Blake (1965). Three samples were taken from both the 0-0.015 m and 0.015-0.03 m layers of each of the nine laboratory Ks crust blocks.  5.^Soil Profile Saturated Hydraulic Conductivity Profile saturated hydraulic conductivity (Kd was measured using two techniques:  34 (a)Large Core Method In July 1980 K, was measured in both farms D and U. In farm U two sites were established in the general vicinity of site Ul. One of these had been subsoiled the previous autumn (blade spacing i m and depth approximately 0.5 m), the other had not been subsoiled for more than one year. The site on farm D (near site D1) had not been subsoiled for more than eleven years. Sample locations at each site were randomly located in a 20 x 50 m area. The plow layer was removed to the surface of the plowpan and a 0.25 m diameter, 0.30 m high column of soil carefully carved out, after the technique of Bouma (1978), with an upper surface at the top of the plowpan. The smeared areas of the upper surface were picked clean with a knife to re-open pores and the soil particles were removed with a battery-powered portable vacuum cleaner. The sides of the column and a 0.05 m deep trough dug around its base were painted with puddled Haney clay to prevent infilling of pores with plaster or concrete. The trough was filled with a slurry of quick setting dental plaster and a 0.35 m high tube of plastic-covered singlefaced corrugated paper was placed so that its base was set in the plaster around the base of the column. The top of the corrugated paper tube was even with the top of the soil column. The space between the tube and the soil column was filled with concrete mixed at three parts sand to one part  35  Portland cement. Plaster had originally been used to encase the soil after Bouma (1978) but it was found to be too weak and prone to leaks. A 0.30 m diameter, 0.10 m high, metal collar (a cut-off pail top) was set in the concrete on an angle and a plexiglass top with water inflow and air outflow ports was clamped onto the rim of the collar. The soil was then flooded and the air outflow port clamped off once all the air was displaced. Inflow was syphoned from a small bucket whose water height was kept level with the soil surface using a float valve, i.e. a condition of "just ponding" infiltration was maintained to ensure the water entered the soil at atmospheric pressure. Inflow into the bucket was measured for one hour using a one litre graduated cylinder, and this was assumed to be equal to inflow into the soil column. The measurements were taken after three to four hours when steady infiltration was reached (as indicated by nearly constant readings over one hour) K, was calculated assuming a hydraulic gradient of unity. The experimental procedure is illustrated in Figures 9 and 10. (b)Aucter-Hole Method Profile K, measurements were also made in the low areas in each site in the spring of 1981 using the auger-hole method as described by van Beers (1965). Ten centimetre diameter holes were augered to depths of between 1.2 and 1.6 m and the water level in them allowed to equilibrate with the water  36 Figure 9: Large core technique for measuring K.  grgduated cylinder  outlet stopper  air vent gasket pail rim —cardboard oncret e clay plaster  37  Figure 10: Large core method of K, measurement in the field. Plaster has been used to encase the soil in the example shown.  38 table for at least 24 hours before measurements commenced. Water was baled out of the hole and then the rate of refilling measured. The number of measurements per site were roughly proportional to their relative areas. Sample locations were randomly chosen along a line transect. 6.  Earthworm Numbers and Biomass Earthworm numbers and biomass were measured in adjacent  barley fields in both farms. Sampling was carried out in the high unponded areas of both farms. No attempt was made to differentiate between earthworm populations in higher areas and those in lower areas prone to periods of ponding. A 0.25  m2 quadrat frame was used to sample the top 0.15 m of soil. Six samples were randomly taken along a line transect in each field in early January 1981. Samples from farm U were hand-sorted in the field, those from farm D were partially hand sorted in the field with the remainder hand sorted in the laboratory. Earthworm biomass was determined on a dry weight basis for five of the earthworm samples for farm A (one earthworm escaped during storage). No biomass measurements were made on Farm U (only one worm was sampled). Qualitative observations of earthworm behavior made in the field also appeared to be of importance.  7.  Penetration Resistance Profile Shortly after the disappearance of ponded surface water,  cone penetration resistance was determined with a Gouda type  39 HSA-5, 0.05 m2 base, 60 ° tip cone penetrometer. Measurements  were made at depths between 0 and 0.55 m at 0.05 m intervals. Three measurements were made at each of ten locations randomly chosen along a line transect through the area of ponding in sites Ul, U2, D1, D2, for a total of thirty replicates per site. Water content was determined gravimetrically for 0.10 m depth intervals at each of the ten locations. It was assumed that the effects of differences in water management practices on trafficability and compaction would be most apparent in these low areas.  8.  Bulk Density Profiles Bulk density samples of the 0 - 0.50 m depth were taken  at 0.10 m intervals using the core method after Blake (1965). Five locations randomly selected along a line transect were sampled in sites Ul, U2 and D1 and two in site D2 (this site was disturbed by tillage before completion of sampling).  9.  Aggregate Stability Ten 500 g samples of the plowlayer (0 - 0.15 m) were  taken from the areas subject to surface ponding in sites Ul and D1, and an additional ten were taken in both sites from adjacent higher areas not subject to ponding. The samples were randomly chosen along line transects when the soil water content was just below the plastic limit. Each sample was passed through an 0.008 m sieve and the  40 portion greater than 0.00475 m collected on a sieve below after shaking by hand. Fifty grams (moist weight) of field moist soil from the 0.00475 m - 0.00800 m fraction was placed on a nest of four 0.15 m diameter sieves with mesh openings of 0.00475, 0.00200, 0.00118 and 0.000212 m. The gravimetric water content was determined for part of the remaining sample. The samples were allowed to moisten slowly before immersion but were not completely protected from slaking. Four nests of sieves were raised and lowered 0.038 m through water thirty times per minute, for ten minutes, on a Yoder (1936) type wet sieving machine. A sliding mechanism attached to the drive shaft caused the nest of sieves to rotate through an angle of 20 ° on up and down strokes. The size distribution of water-stable aggregates was expressed as the mean weight-diameter:  MWD = Ex i wi  where^MWD is the mean weight-diameter of aggregates (m), n is the number of size fractions, x i is the mean diameter (m) of each size fraction , and w; is the proportion of the total sample (dry weight) occurring in the corresponding size fraction (Kemper and Chepil, 1965).  41 10. Rainfall Rainfall was measured with four 0.12 m diameter plastic funnel rain gauges. Two of these rain gauges were located in each of sites Dl and Ul.  42  CHAPTER 3  RESULTS AND DISCUSSION  1.^Piezometric Data Piezometers measure the pressure potential  MO  soil-water only below the water table. In this region 4  of  ,  1  ,  is  always greater than atmospheric pressure, ie. ir p >0, and the soil is saturated. The total potential of soil-water, ir T , is the sum of 4 1, and the gravitaional potential ,  NFG ,  ie.  * ..110-4 . 1  -  0  ,  The gravitational potential is generally taken to equal zero at the soil surface. Water movement in saturated soil is described by Darcy's Law: q = -KdART dZ where q is the discharge through a cross sectional area per unit of time, K s is the saturated hydraulic conductivity, diri. is the total potential difference over distance Z (dZ) in the saturated soil (Hillel, 1971). When (d* r /dZ)=0 there is no discharge, in other words the soil is hydostatic. When (d4ydZ)=-1 the soil is draining freely at rate equal to  K.  For saturated soil, K s is at a  maximum and is fairly constant in time. Saturation also ensures that large  'T  gradients common in drier soil do not  normally occur. In the absence of artificially imposed  43 gradients, the dominant driving force causing water movement is gravity, so that pore water in saturated soil moves much as it does in bulk free water (Childs, 1969). Where ditches and subsurface drains are present significant horizontal flow can occur in response to resultant horizontal pressure gradients (Luthin, 1957). The position of the water table is mainly determined by the rate of water percolation through the layers of soil overlying it. A rise or fall of the water-table indicates a net recharge or discharge of groundwater respectively (Hillel, 1971). The location of the water table has been calculated from the piezometer data. The water table was taken to be the highest point in the soil where 'I', the pressure potential, equals zero. The depth of ponded water (if any) is irp at the soil surface. It was assumed that the soil between two piezometers in a nest, both containing water, was saturated. For practical purposes, the water table was taken to be located at the water surface when there was water on the soil surface. On days where no readings were taken the water table was assumed to be at the mid-point between the previous and subsequent values. The two exceptions to this were the rain-free periods, March 17 to March 24 and March 26 to March 28, where the water table was assumed to be equal to the reading on the last day.  44 2. Surface Ponding in the Lowest Spots on Each Site Figures 11 to 19 clearly show that no surface water was recorded at any of the high spots in the four sites, which is an obvious consequence of their topographic position. A film of water was noted on the surface of each high spot during and shortly after some rainfall events when the surface infiltrability had been exceeded. This was observed to result in surface runoff at a rate dependent on the slope, the severity of surface crusting and other antecedent conditions. In the high areas in the drained sites some runoff was apparently intercepted by cracks and worm burrows connected to the surface, which were common. In the undrained sites very few worm burrows were observed and it therefore appeared that a higher proportion of surface runoff flowed into the low, ponded areas. The severity of the surface crust appeared greater in the undrained farm which may have resulted in more runoff. It was also noted that the surface runoff sometimes carried with it sediment in varying amounts. The mechanism of sediment generation was not studied, but was thought to be a combination of rainsplash and sheet erosion. The duration and average depth of water ponding differed considerably between Farms U and D as shown in Table 3. The low areas at sites Ul and U2 had a mean ponding duration of 46.5 days during the fifty-five day period from February 12 to April 7th. During the same period sites D1 and D2 had a mean ponding duration of 18 days. The absence of adequate land  45 Table 3:  Surface Ponding Data for Depressions  Site^ Average Depth of Ponded Water (cm)  when ponded -■ over measurement-* period  Period with Ponded Water ^11-+ from Feb. 12 to Apr. 7 (days):  Ul U2 U3 D1 D2 12.5 10.3  6.5  2.7  2.7  8.4 10.3  6.5  0.9  0.9  38  55*  38*  17  19  The average depth of ponding is expressed in two ways: (i) the average depth of ponded water over the period February 12 to April 7th, (ii) the average depth of ponded water for the days with ponding. *ponding during entire period of measurement  46 drainage resulted in an average of 2.6 times more days with surface water in the low areas of Farm U. No primary seedbed preparation such as ploughing can be initiated when there are any ponded areas in a farmer's field, so that times of ponding can be viewed as "no go" periods. The longer ponding period in site U2 (when compared to site Ul) can be attributed to its more severe crust which resulted from poor surface cover. The data suggest that cover cropping is more effective than subsoiling, if undrained. The fact that there were 17 to 19 days of ponding in the drained farm suggests that the drainage system was not operating properly, or that weather conditions exceeded the system's capacity. It was observed that the pump was often switched off for up to fifteen minutes due to lowering of the float, even though the water level in the ditch feeding it was above the level of the drain outlets. This was due to the culverts under the machinery crossing being too small and the ditch being too filled with sediment and weeds to efficiently conduct water to the pump. It should be noted that the average depth of ponded water is in part a function of the geometry of the low spot and how much water it can hold before overflowing. The average depth of ponded water, when present, ranged from a mean of 11.4 cm for sites Ul and U2 to a mean of 2.7 cm for sites D1 and D2. The average depth of ponded water over the entire 55 day period was 9.4 cm for sites Ul and U2 and 0.9 cm for sites D1 and D2. The latter is an order of  47 magnitude less than the former due to the combined effects of smaller depth of ponding and the presence of worm burrows connected to the surface in low areas which allowed surface water to enter the soil, bypassing the crust. This process has been referred to as "short-circuiting" by Bouma and Dekker (1978). The capacity of each ponded area did not appear to have been exceeded during the period of data collection. It can therefore be concluded that the data were likely not influenced by overflow. The data for sites U2 and U3 are quite similar in that there was ponded water on the surface throughout the respective periods of measurement. The average depth of water at site U3 between March 1st and April 17 was 6.5 cm.  3. Analysis of Recording Piezometer Data The difference in the behaviour of soil water between Farm U and Farm D is clearly represented in the recording piezometer plots shown in Figure 11. The 4%. in the recording piezometers at Sites Ul and D1 commence rising quickly after the beginning of rain following prolonged dry periods, such as on February 13 and March 29. There are greater fluctuations at Site D1 after the initial rise in ir T , which indicates that it is more responsive to rainfall inputs, even with surface water present. It also indicates that water is being removed more effectively through the system of subsurface drains between rainfalls.  ^  W 0. hi Z 0 HO, (-h0 0 0 - II i-I^(D  • tr  O Fa rt1-• 0" ••  II (D (D W i-, 31iL O n H. II  r  < a mZ H  -  rt. "1  Oro  rt- N. • M (D N 0  I-, 0 O M  O ft^.It• pi M^03 I-, li DI  o -i I-i- gv ,  Z (fl (I 0  li rn  M0 ID pi O ti,  M gu ' 0 0  M 11 °a 0 IV  rt  cn M 1-- '1 It  Oa ul m to o rtI-.  49 At both sites 4%., as measured by the recording piezometers, increased to greater than zero during mid- to late February, though it rose higher and longer in Site Ul. The 4 1. at Site D1 increased by about 0.20 m with the rainfall ,  on March 3. The rate of rise was significantly greater than the 0.04 m increase at Site Ul. This relatively sluggish and smaller rise at Site Ul can be attributed to poorer hydraulic contact between the soil and the water overlying it due to the presence of a surface crust. The additional rain input went primarily into storage on the surface along with the existing surface water. The fact that the surface water-level at Site Ul rose 0.05 m in response to an 18 mm rainfall was probably a result of surface runoff inputs from surrounding higher areas. The presence of a surface crust in higher catchment areas can therefore result in a greater depth of water ponding on the surface of low areas. The increments at site Ul, shown in Figure 11, were greater on March 15, 16, and 25, despite the relatively low and falling water table and absence of surface water, due to the wetter conditions than in Site D1 in the soil above the water table. At Site D1, for the same rainfall, water that might otherwise have contributed to a rise in  AFT  at depth went  into storage in the unsaturated soil above the water table. Ponding also resulted from the 29.4 mm rainfall on March 29, but only at site Ul. Ponded water was last observed at site D1 on March 3, and then it was a relatively minor amount.  50 The period of ponding at site Ul following March 29 differed from the earlier one; the depth of ponded water in this case closely reflects the rainfall inputs. This was apparently due to the extensive cracks which were observed to breach the surface crust during the preceding rain-free period. The consequent increase in the surface infiltrability resulted in little runoff into the ponded area. The general pattern of  'T  behaviour during this time was similar to the earlier and more severe period of ponding. The drop in skr at site Ul after the April 5 rainfall trails the recession in site D1, however, the rate at which the 'YT dropped was very similar. The lag time for site Ul was directly related to the difference in the length of time water was present on the surface. At the end of the two periods of ponding'YT was,-0.20 m at 1.21 m depth at site Ul on the last day water was recorded on the surface. The same was true of Site D1 on February 27. When there was water on the surface AFT generally did not drop to lower than -0.20 m. In view of this it is advisable that all possible measures be taken to eliminate, or at least reduce the depth and duration of ponding. Drainage as practiced in Farm D was more successful in eliminating surface water and in reducing in low areas after the cessation of rain. Figure 12 shows the manually collected data from piezometer Ula plotted with the recording piezometer chart from site Ul. There is close agreement between the two which  i-s- DI IV 04 M 0 0 P.. 11 P, th1j M 1-t) < Al 0) Pi 10 ID 0+ M Pi M ■ MN O II tv ct 11) 0 .. • 0M II ,  -a  (al 0  1  i)  I—.• ct ° ct M 15 M Pi Pi 11 1-"  a  ~b . ori 0 (-I- 0 ril  0 I—'^0  oa  1-1)  co III M rt 0 ru w  0 ... 0 LEI 0 11 tr pi M i..., M ct El 0' gu M O 11 a rt M I—, ^ 0) ll M tt M tt I-a- 0 • 0 M M Pi M ,  .  o  a  'Q  rt l'4 * 0  ft • rt M 0'1s M 1.-■rt M 1-1 N O 0 0 O El El pi m M 1-, re  rt m  0" co ii o o aw l, co 1—• .-1  52 indicates that the recording piezometer data can be used to interpolate  'PT  and water table behaviour between readings from  manually recorded piezometers in comparable locations. Similar close agreement was found in the piezometric data from site Dl. This agreement occurred despite the differences in test-section depth and the greater diameter of the recording piezometers, which required that twenty times more water be displaced from or into the soil for each unit rise or fall in the water table. That the greater diameter of the recording piezometers did not influence the comparison is likely due to the test-sections being located in the relatively highly permeable sandy subsoil. The similarity in * 1. beneath about 0.70 m depth seems to indicate that it does not vary much vertically below this depth under saturated conditions. Figure 13 shows the close agreement which existed between piezometers Dlb and Dlc which were located about 8 m apart. The data are similar in spite of minor differences in well point depth and surface elevation, which indicates that the water table is nearly level, at least over short distances.  4. Comparison of Water-Table Behaviour in Depressional Areas  (i) Sites Dl and D2 Figures 14 and 15 show that the respective water-tables at Dla and D2a behaved similarly throughout the period of measurement.  •  E Nei  ▪  Fa-  rt ctiq  mm  II CI) 11  ct  C7 N  • H tr tr  CD gu •  .  o •  1.4 pci  Cr), 0 pi  • ti I-A-  tr 1-3 (a a' PI 0 0 p. 0 I 0 frt)  • cu o o  H • m • o o 0^L..) o rt (D rt 0, 0 • 0, rt M  "  a rt a s  • tr zm 0 N m E  1-1-  "11  a rt  O 01  rf 0) it  i i i i E  56 ii) Sites D2 and U2 The water tables for sites U2a and D2a are plotted together in Figure 16. At the lower piezometer the 4%. at U2a was higher than D2a with the exception of the periods associated with the onset of prolonged rainfall in midFebruary and late March. On both these occasions the  '"T  at  D2a increased more quickly to rainfall inputs due to better hydraulic contact between the soil surface and lower portions of the profile. This is especially due to the absence of a continuous slowly permeable surface crust at D2a. On several occasions there is a rise of 0.1 m or more at D2a while there a continued decline or slight rise at U2a for similar reasons; for example refer to March 3 and 16, and April 5. The 4 1, decline after March 3 is initially much faster at ,  D2a, with its rate of fall slowing somewhat after March 5. The fall in 4%. at U2a generally trails D2a by about ten days. There was ponded water on the surface crust at U2a throughout the measurement period, and this dominated the hydrologic behaviour of the soil. (iii) Sites Ul, U2, and U3 The piezometric data for sites Ul, U2, and U3 are shown in Figures 17, 18 and 19 respectively. Sites U2a and U3a were very similar in that they both had ponded water on the surface throughout the entire period of measurement, and the depth of that water followed a similar pattern over time. In both cases dropped to -0.50 m in mid-March despite the presence of the  ^O  •  w •) I-- lai ...t O 1•) • 14) H. 0 ,  I 0 l't  ui p)  o a  0 t• 1-4  O  P MH.' • 0^vi 0^--.1 0 1--1  art H' (D  it 0., HO Z 0 M rt.  1:D M Pi "  as m tr • M 1E1 M 0.  as  /""  1.  0  m z 61rt  • gli a) ct  rt N a gir- 1....; I-1 •• 1:11 01 Z a 0 e' 0 O H p0  0mw In • 11 1-Cr 1-3 co  .  M i-at0i 0  0i-r,0  E rb 1_,. I 0 11)  Ill ill 0 tr 0 O I-I gli ig ID I-'  •^0^U1 0 0 03 O i-, o 1:11 13, fl1-, - (1) ft 1:1, 1-, • 0 Zm U1 rt go M II " ft 13) 0 U1 tr U1 I-, .-  0 (7) (D o• as  •  E C  • I-'ID  G kg  til  rt  1.4 t:r^03 •• M^  a  H  •  a  0 tEi  ▪ tr N••  ti  tr H )-•M 11 0 O M B p.  I 0 • 1)) 0 0' 0 • M • O 0 •  it  0 W 0 0 1:11  • rt  • a P-  O 4 O pi  rt • M  Pi Pi (1• W (11 er M  A. (D J. 0"4 M  tn  rt  0'a M rt  61 ponded water, although this occurred four days earlier at site U2a. The rate of decrease in AFT was similar at both sites prior to this time. U3a is more responsive to rainfall inputs than U2a, eg. March 16 and 29. This may be due to site U3 being a smaller, more pronounced depression. The latter may also account for the rise of AF T above zero at U3a on March 30th and thereafter. The water ponded on the surface crust at U3a dominates the hydrologic behaviour of the soil as it does at U2a. Site Ula, in contrast to U2a and U3a, was free of ponded water in early February, mid- to late March and in mid-April. The presence of a cover crop prevented formation of a surface crust severe enough to reduce infiltration to the point where ponded water persisted throughout. Yet despite this, and the fact that it had been subsoiled, the water table did not fall below 0.21 m in the dry period in mid-March. Even with subsoiling and a cover crop the absence of adequate drainage resulted in excess soil moisture in this depressional area. Some of these differences remains unaccounted for; they may be due to the inherent landscape variations between the sites.  5.^Variations in AFT with Depth  (i) Depressional Sites The  "T  vs. Z graphs for depressional sites are shown in  Figures 20 and 21.  62 Figure 20: iri. vs. Z (depth) graphs for Sites U2a, D2a, and U3a. Missing data points occur when the piezometer tube contains no water ie.*.<0. • Site U2a^■ Site U3a^• Site D2a  63  Figure 20 continued: 4 1. vs. Z (depth) graphs for Sites U2a, D2a, and U3a. Missing data points occur when the piezometer tube contains no water ie.ir<0. ,  0  Ma r18^I^Mar 25  Mar.29^  Mar. 31  le  II  50^  50  I^ I 'U  0  0 Apr.5^ Apr.9^ Apr.16  • Site U2a  ■ Site U3a^• Site D2a  64 Figure 21: i./. vs. Z (depth) for Sites Ula, Dla, Ulb, and Dib. Missing data points occur when the piezometer tube contains no water ie.ir<0. • Site Dia ■ Site Ulb • Site Ula 0 Site Dlb 4' 1' (cm of water)  0 -4^-10 0 .1^0 10 20 ? 30 - 40 :9- 50 ° 60 70 80  50  65  Figure 21 continued: 'T vs. Z (depth) for Sites Ula, Dla, Ulb, and Dib. Missing data points occur when the piezometer tube contains no water ie.irp <0.  ? E. 50  -  a  0  ^t  Mar.16  o  Mar18  • 1I0  50-  50-  • Mar.29^ Mar.31  Apr.3  ?•  of 50  506  •  /  /  0 Apr.5^  Apr.9  AprI6  •  •  AO  In  50  50-  •  1 1  • • Site D1a ■ Site Ulb • Site Ula 0 Site Dlb  66 These graphs show that there is a general trend, especially in the upper portion of the profile, towards a lower 1T in the drained low sites (Dia and D2a), and a shorter period when free water is present, when compared with the depressional sites in Farm U. The differences in the depth and duration of ponding certainly accounts for part of this. As long as ponded water persists there is a source of water continually supplying the surface soil, keeping it saturated. This is aggravated by the fact that the supply rate is governed by the K, of the surface layer which is low, to a degree dependent on the severity of surface crusting. The surface crust in the drained sites was less severe, and was also extensively perforated by worm holes, and in some instances breached by cracks, which meant that the supply rate of water into the soil was higher. Water was also more effectively removed by the system of subsurface drains in Farm D and this also accounted for the drier conditions. Figures 20 and 21 clearly show that decreases in AFT within the profile of the drained soil after rain are much more rapid than in the undrained. Figure 22 illustrates that this also applies to the high sites, and in both cases decreases in 4%. are also faster in the drained, ie. there are greater fluctuations in 4r.r . This may be partially due to the hydraulic contact between the surface and the upper profile in the undrained being poor due to the presence of a surface crust. The direct addition of rain waters, as well as surface  67 runoff, added to the reservoir of ponded water in depressions. This ponded water receded slowly through evaporation and infiltration through the crust. The differences between the drained and undrained farms appears to be due mainly to the much shorter periods of ponding on the drained farm. There was a general trend to hydraulic gradients of near zero in the low areas. In the drained farm at site D2a the water levels in the piezometer nest rose and fell with only very slight vertical gradients indicating good hydraulic contact within the profile. In the undrained sites vertical gradients of up to 0.6 developed in the lower profile during dry periods when water was ponded on the soil surface. This is both an indication of the effect of the surface water on the energy state of the soil water in the upper profile and of the influence of the regional water table as transmitted through the underlying sandy. strata. In late March the 4%. below 0.20 m depth at site U2a is larger negative than at D2a. This is a reflection of the poor hydraulic contact between the surface and the soil profile and the consequent lack of response to rainfall on March 29, 30, and 31st at U2a. While the data clearly indicate the influence of the surface crust on soil hydrologic behaviour in Farm U, there is no consistent evidence of there being other soil layers, for example a ploughpan, restricting vertical water movement. Any influence the ploughpan may have is masked by the effects of the layer at the soil surface which most restricts water  68 flow. It is the surface crust on which attention must be focused. (ii) High Sites Figure 22 contains the ir T vs Z graphs for the high sites. It is clear that the decline of 4 1, in the profile after wet ,  periods is faster in the drained sites. This was likely due to the more effective removal of water from the soil by subsurface drainage. Hence there was a longer period when free water is present in the upper 0.50 m of the profile in undrained high areas and therefore fewer opportunity days. There was a trend towards higher 4 1, in the profile at D2c ,  than at Dld. This may have been a result of D2c being situated where the drain lines fan out and the drain spacing is consequently greater. This was most evident during wetter periods.  6. Water table - Trafficability Relationships Paul and deVries (1979) used traction efficiency as a criterion for trafficability, and cited general agreement among researchers that maximum traction efficiency is achieved at about 20% wheelslip. They used this relationship to establish critical water table levels for trafficability. It was found that critical water table levels were 0.45 m and 0.60 m for Hallart SiCL for grassland and cultivated conditions respectively. Steinhardt and Trafford (1974) also recommended water table depth of 0.50-0.60 m as being required  69 Figure 22: 4 ./. vs. Z (depth) graphs for Sites D2c, Dld, U3c, and Ule. Missing data points occur when the peizometer tube contains no water ie.ir p <0. ,  70  Figure 22 continued: iri. vs. Z (depth) graphs for Sites D2c, Dld, U3c, and Ule. Missing data points occur when the peizometer tube contains no water ie.ir p <0.  71 to minimize structural damage of clay soils in England. In analyzing the water table data collected in this study it will be assumed that the critical water-table level for trafficability is 0.50 m. It will be further assumed that the water table is located at the highest point where 'I' equals zero in a piezometer, or on the soil surface. The water table is defined as that level in the soil at which the hydrostatic pressure of soil water is zero Childs, 1969). It should be noted that Paul and deVries measured the water table using open wells and not with piezometers. Using the trafficability-water table assumption discussed above, Figure 23 shows when each site had ponded water on the soil surface, was not trafficable, and those days on which the site was trafficable. Figure 24 focuses on some of the points illustrated in Figure 23 for the fifty-five day period from February 12 to April 7 when the majority of sites were in "operation". The concept of "opportunity day" is introduced and used to illustrate differences in management options resulting from soil-water phenomena. An opportunity day is one on which a site is trafficable based on the critical water table depth, has no water ponded on the soil surface, and has not recorded any rainfall. The latter is included because it is assumed that the farmer is a good manager who would not attempt tillage or traffic on a day that it has rained, due to wet conditions in the surface layer and the consequent risk of soil structure degradation, ie. soil is untrafficable. This  ••  •  H) rt 0 it O 0"1:1 M •11 0 ttN ti ^'! • rt rt M M 0 0 ,-'  L.)  •  "  co^ft '• "CI `'‹ la,^m  p. m  O h<rt •Cl^C0 N. M •^0 ti^z Z 0 0 0, rt M a Pa Cr^0) rt^tr  0“11  rt M rt 0 M^M rr,  xo  rt 1-■• •CI PI a) 0 0 0 a LJ^(p 0) •  WiM'  • Cr  as  --  1"‹  •  133  rfi "'  rt  ul 11 I-I  i•-■•^M  fg 0 pt 0 0 HI  •^ 0, rt m O 0, ty CD^m  o 11 01 64w  -  •  O 04 PI ,-4 O fD M Hi-, tr 1-1 (0 .4 1-1 0 O (1- li 1-1) fu Fa- (D o 1- 1 o 1-1 ,.< 0 i--. CA N3 rt e%) 0' 0. 0" H. •• (D 1:1) PEI O M (.4 0,^ 1-3 °I) ...., it 0 0, 1::$ ii 0  a ti^i_, •< I-J• pi I^ 1^ 1:1^F.,  M -4^,,, NJ ri •^u  oZ  a o  Aa  (  14. 1-1 *  rt rt 0  tr m m  4  m ti) I (-1- rt^/-3^■I • 0' /-1) 11^(4 Mr00 0) al r t ti I-b 1-I) O En t 1-ix 1.... 04 0 11) (-1- m 131 1-i M tr 0 0 H0' 0 0 1-1 L4^If,: t...).-..^IT gu 0,1-4 fu te• 0 1 • 0.40 a., its Pc1 V >1 f D 0 1:5 fu 11 11 PI fil 1-" rt I-1. 0 0 1-, 1E1 cl. 0 14 * o tr , rt •^ ).- m --• ,i  o  ft rt  o i.i m ti m m OP 0. 0 1.<  74 is assumed to be the case even when there is no ponded water and the water table is below 0.50 m. Figure 23 shows that there were consistently more trafficable days at drained sites than at comparable undrained sites between February 12 and April 7. There were fewer days where ponded water was present on the surface of depressional drained sites and there also was a higher proportion of non-trafficable days, where ponded water was not present, in the drained farm. This points to the significance of ponded water resulting from surface crusting in prolonging periods of untrafficable conditions on the undrained sites. The number of trafficable days, and also of opportunity days, is maximum in the highest sites and minimum in the depressional sites. The difference in the number of opportunity days between high and depressional locations means that a portion of the opportunity days in higher locations are "lost" to primary tillage operations such as ploughing. These opportunity days would not be lost to tillage operations like discing (which commonly precedes ploughing in the Lower Fraser Valley) or to manure spreading, both of which could more easily be carried out while bypassing untrafficable depressions. It is interesting to note that while site Dld had two more opportunity days available than at Ule, all opportunity days at Ule were "lost" for an operation such as ploughing due to untrafficable conditions in the depression while there  75  were six "full" or "unrestricted" opportunity days at Dld. It is obviously desirable to maximize the number of "full" opportunity days since this leaves open the widest range of management options. The soil and water management practices, particularly the system of subsurface drains and the associated water removal system, on the drained farm have been successful in providing six and twelve "full" opportunity days at sites D1 and D2 respectively. All "full" opportunity days (FODs) occurred between March 11 and March 24. FODs during this period are generally more important than ones in February for the farms studied since primary tillage operations and planting of early potatoes (an important crop on both farms) could reasonably begin in March. It should be noted, however, that fertilization of the overwinter cauliflower and cabbage crops on the drained farm was carried out in February to correct nutrient deficiencies so opportunity days can be significant throughout the year. There were no full opportunity days at any of the undrained sites from February 12 to April 7 either due to ponding, untrafficable conditions based on the critical water-table levels, or both. This does not mean the drained sites physically could not be ploughed, it simply suggests that there is a greater potential for compaction and structure degradation if they were ploughed on non-opportunity days, especially in the depressional areas which comprise approximately 10 to 15 percent of the field.  76 It is significant not only that full opportunity days were obtained only in Farm D but also that the lag time between the high and depressional areas becoming trafficable was short. It is highly desirable that this time be minimized, for example, to avoid a situation where ploughing takes place when the depressions are trafficable, but the high areas have become too dry. While it is apparent that Farm U would benefit from installation of a drainage system in this regard, drained land would also benefit from any changes in management which would expand the period of full opportunity days. In the case of the soil being studied any management practices in addition to drainage that would further reduce crusting, runoff, and ponding would be desirable. The experimental results clearly illustrate the hydrologic results of topographic variations at the Westham Island sites. There is an uneven distribution of infiltration water due to runoff, followed by its accumulation in depressions. As a result there is great spatial variability of trafficable conditions, ponding and opportunity days on both farms. The effect of a subsurface drainage system is, on a relative scale, to either insufficiently drain depressional areas or excessively drain high areas to a degree largely dependent on weather conditions. It seems that most of these problems could be lessened, or eliminated, if systematic land-levelling were undertaken. This would involve stripping off the existing Ap horizon and adjusting the levels of the  77 subsoil materials followed by respreading of the Ap soil. At no point would it be acceptable to bring saline and acidic subsoil closer to the final levelled land surface, than it was prior to levelling. Although low areas comprise at most 10% to 15% of the land area, their elimination through land levelling would appear to be worthwhile. If anything was surprising in the water-table data it was not that there were differences between the drained and the undrained farms, rather it was that the differences, especially after cessation of ponding at site U1 as compared to site D1, were less extreme than anticipated. This may be accounted for by one or more of the following reasons: (i) There were indications that the drainage system in Farm D was not functioning at desired efficiency levels during the study period. It was noted that the pump would shut off for over ten minutes during the wettest periods while at the same time ditch water-levels farther out in the field remained above the drain outlets as illustrated in Figure 25. The pump switched on for about seven minutes so in effect the capacity of the pump wasn't even tested since it was shut off more than half of the time. As a result, during peak rainfall periods when it was needed most the drainlines were not flowing freely, although they were always observed to be flowing to some extent. This appeared to be caused by a restriction of flow in the ditch due to the presence of too much sediment and weeds,  78 and culverts being too small and possibly high. The level of the pump intake may not have been low enough as well. The damlocated at the pump also seemed to be leaking since water was observed welling up into the ditch when the water level in the adjacent drainage canal was high at high tide. Remedying these problems is recommended. (ii) The Westham soil is underlain by sand at a depth averaging about 1 m. The thickness of this sandy layer is not known but it is thought to be several metres. The effect of having this permeable sand underlying the entire area may be to counteract or retard some of the beneficial effects of the drainage system in Farm D. Water may flow upwards into the "drained" surface soil in the drained farm from this sandy layer. The driving force would result from the elevation difference between the regional water table and the artificially lowered water table in Farm D. This may be one of the problems in attempting to improve drainage on a spot basis in an area where the regional drainage is inadequate. In effect a portion of the water being pumped from the ditch in Farm D may have originated from below the drainlines rather than the soil above. The influence of the regional water table appeared when the recession of the water table seemed to slow down when the latter reached approximately 0.50 m in depressions.^Further research into the nature of these interactions is required. (iii) Large scale "macro-cracks", 0.02 m or more wide  79  extending over tens of metres, and up to 1 m into the soil have been observed in the Westham soil. These macro-cracks form as a result of soil shrinkage during drying and their location and orientation seem to be influenced by tillage and cropping patterns eg. some cracks were located between, and parallel to potato rows. To the extent that they remain open, these macro-cracks provide an important lateral pathway for transporting ground water to drainlines. They may account for part of the differences between drained and undrained land since, by keeping moisture levels down, a drainage system improves the chances of the macro-cracks remaining at least partially open while at the same time providing a pathway (the drain-line) for removal of groundwater from the cracks. There is a "positive feedback loop" in that, as long as they are open, the macro-cracks can transfer water to the drain-line. It was suggested by the farmer (Bob Reynolds) that the macro-cracks had closed up in Farm D the winter of the study as a result of the persistent wet weather that began in mid-October 1980, thereby removing their benefits. The wet weather likely combined with problems with the functioning of the drainage system discussed above to bring this situation about. The issue of macro-cracks and their effects on soil drainage is highly speculative at this point, and further research into the question seems worthwhile.  80 7.  Ditch Water Levels The changes in ditch water levels with rainfall are  illustrated in Figure 25. The generally faster and greater rise and fall in the ditch water level in Farm D is a reflection of the more efficient delivery of water through the subsurface drainage system. Ideally, however, the water level in the Farm D drainage ditch should remain fairly constant and certainly not rise above the level of the drain outlets as it did after March 29. This points to problems with the drainage system in Farm D, and these are discussed later. The smaller rise in the water level in the Farm D ditch is likely due to the drier conditions there which resulted in a greater portion of the rain going into storage. It may also be the case that water was delivered to the ditch and pump at a slower rate which permitted more efficient pumping.  8.  Profile Hydraulic Conductivity The data from the core method are shown in Table 4, and  the auger-hole K, data are presented in Table 5. The core data indicate higher mean K, values on the drained site, 3.4 times greater than the undrained subsoiled and 5.0 times greater than the undrained unsubsoiled. This difference is attributable to the more abundant macropores, especially worm burrows, which provided preferred pathways for vertical water movement on the drained site. Differences in worm populations are discussed in Section 11.  hi H.  trl 0 11 M  NJ tn •• 0 I-.• rt 0 E 03 rt (1) 11 I--, (D  <  M I-i  a a  rt II 1-t) 0 11 1'1  iu  d gl) Z  a It gu Pi 0  oo i-i  82  Table 4: Profile saturated hydraulic conductivity - largecore method (plough-layer removed) FARM U (In Site Ul area)  FARM D (in Site Dl area)  K s (m/s) not subsoiled 1.50x10 4 24.0x10 4 3.40x10 4 13.3x10 4 6.70x10 4 4.10x10 4 5.10x10 4 12.9x10 4 1.00x10 4  USILal subsoiled^not subsoiled 10.0x104 15.7x104 13.5x104 2.70x10-6 14.0x104 8.70x104 14.7x1e 13.4x10  1.90x104 56.8x104 33.6x104 0.35x104 60.3x104 47.6x104 71.9x104 44.1x104  mean=8.00x10 4m/s^mean=11.6x104m/s^mear.39.6x1T6m/s  83  Table 5: Profile hydraulic conductivity data; auger-hole method Hydraulic Conductivity (m/s) Site R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 R16 R17 R18 R19 MEAN  Ul  U3^U2  5.1x104 46x10 23x10-6 32x10 2.6x10-6 38x10 4 13x10-6 21x10 4 0.8x10-6 18x10 45 4.2x104 55x10 4 20x104 0.9x10 4 3.2x10-6 52x10 3.7x10-6 9.4x10 17x104 9.5x104  11x1045  33x10 4  39x10 70x104 17x104 17x104 40x10 16x104 11x1045 24x104 18x10 91x104 47x10  36x104  D1  D2  12x104 4.2x104 2.1x104 6.0x1045 10x1045 8.9x104 20x104 22x10 4.3x104 6.4x104 14x104 30x104  20x10 4.6x104 26x104 9.0x104 4.1x10 21x10 13x104 4.8x10 22x104 2.4x104 28x10 13x104 13x104 3.7x10 6.0x104 14xle 13x10-6 28x104 20x104  10x10  14x10  84  Subsoiling evidently increased the K, of the ploughpan and its homogenizing effects can be seen in the lower sample variance when compared to the unsubsoiled plot. It is also important to note that while almost all the core method K, data are high relative to expected rainfall rates, they were likely increased over true winter conditions due to the influence of summer soil cracking (seasonal macropores). They cannot therefore be used to directly explain ploughpan hydrologic behaviour in the winter. The auger-hole method data show that there is no significant difference (95% level) in K, between sites Ul and Dl, between U2 and U3, or between Dl and D2. In the other cases the sites that performed poorly had significantly higher (95% level) auger-hole K, when compared to sites that performed better in terms of the water status of the soil and ponding. This result might at first sight seem to discount the influence of earthworm burrows in water movement, however, measurements were made when the water table was 0.40 to 0.60 m below the surface. This range is below the depth of most winter earthworm activity and also of most tillage operations and so should not be expected to strongly reflect earthworm modification of soil hydrologic behaviour. Some earthworm channels may have been present at these depths. It is likely that differences between the measurement techniques used had a strong influence on the results. Water movement in the core method was primarily vertical due to the  85 barrier imposed by the concrete sleeve. In this case flow would be dominated by vertically continuous series of cracks and worm burrows. Flow into an auger hole, however, is three-dimensional (Boersma, 1965). If deep worm holes were present they likely would not contribute to higher K, values using the auger-hole method for two reasons: (i)a worm hole would have to connect into the auger hole in just the right way in order to empty its water directly into the hole, and it is improbable that many holes would be so connected, and (ii) any such worm hole would also tend to drain rapidly and therefore be included in the error (due to water running down the walls of the auger-hole after bailing water out) which is corrected for by discarding the initial one or two readings. It is possible that horizontal flow along lithologic discontinuities was important in the auger-hole method indicative of matrix K . Flow along these ,  roughly horizontal discontinuities would be important when considering the delivery of water to drainlines. The auger-hole K, data therefore most likely reflect the K, of the soil matrix surrounding any macropores. The auger-hole K, data are consistently quite high relative to expected winter rainfall rates. It is evident from this that the K, of the lower part of the profile is not a limiting factor in the movement of water in these soils. If a drainline were present at a depth of 1.3 m, and a pressure near atmospheric maintained there, water would be removed from  86 the soil fairly rapidly and the water table kept low. This would necessarily involve the proper functioning of the entire drainage system i.e. prompt delivery of water from the soil to the ditch via the drain, and constant maintenance of ditch water-levels below the drainline outlets. 9. Surface Crust K, Laboratory and water balance K, data are given in Tables 6a and 6b. The mean saturated hydraulic conductivities calculated by the two methods are quite close which gives confidence in their accuracy. The data indicate that the water flux through the crust at site U3 would be in the range from 0.0018 to 0.0020 m/day under gravity drainage. This is slightly lower than the rates reported by McIntyre (1958) on artificial crusts formed on a fine sandy-loam soil. It is interesting that on soil having a crust with K, in the order of 0.0020 m/day it would take 50 days to remove 0.10 m of ponded water by gravity drainage alone. Data from the U.B.C. climate station (Appendix 1) show that evaporation during March and April often equalled or exceeded 0.002 m/day. The removal of ponded water from site U3 was therefore roughly equally partitioned between drainage and evaporation. The low infiltration rates into the surface crust resulted in surface runoff flowing into local depressions where it accumulated. This was less prone to happen in drained farms where worm holes bypassed the crust in both depressions and the surrounding upland areas. The continuity  87  Table 6: Surface Crust Saturated Hydraulic Conductivity (a) Water Balance Calculations ^Drainage irT (Ocm) 'YT(-14cm)^clIFT-^K, Date^mm/day cm H 2O^cm H 2O^dZ mm/day m/s +4 81-3-17 2.5 -14 1.3 1.9 2.3x10-8 81-3-20 0.6 +3 -14 1.2 0.5 5.8x10-9 81-4-1 2.6 +6.5 8.1 + 2 0.32 9.4x104 81-4-15 0.5 +4* -12.5* 1.2* 0.4 4.6x104 +4 81-4-16 0.9 -12.5 1.2 0.75 8.7x10 4 81-4-17 0.9 +3 -14 1.2 0.75 8.7x10 4 mean = 2.4x10 -8 m/s *data not available, assumed to be same as 81-4-16 Note: lmm/day = 1.16x10 4 m/s (b) Laboratory Measurements Crust Sample^K, (m/s) R1 R2 R3 R4 R5 R6 R7 R8 R9  5.9x10 3.6x104 5.3x10 6.3x10-9 8.2x10 8.2x10-9 6.7x104 2.6x10 5.9x104 mean= 2.1x10 4m/s  88  of the crust in the relatively higher areas was dependent on the extent of surface cracking. Since the soil dried out faster there cracks formed first in higher areas. Cracks wereobserved to close up generally within 24 hours of the commencement of rain after swelling of the soil, so for a period at the beginning of a rainfall event water infiltrated by bypassing the crust via cracks. Later surface runoff was produced when the cracks closed up. In low areas subject to prolonged ponding, cracks did not form and so the surface seal remained intact with its low  K, controlling drainage. The surface seal is therefore responsible for the delivery of water to low areas, and for its retention there. The growth of a cover crop can prevent crust formation. The crop should be high and dense enough at the onset of the rainy season so that it completely covers the soil surface when matted down by rain. Cover crops protect the surface by absorbing the energy of falling raindrops. Provision of surface cover does not entirely protect the surface from slaking due to wetting-drying cycles, however these cycles are less extreme since infiltration is promoted, and surface drying retarded, by the presence of the cover crop. In order to obtain satisfactory cover the crop must be planted early enough to grow the required amount. This is not always possible however, where the cash crop is harvested late in the growing season or when the rains begin early in the  89 autumn. Where a surface crust forms it can be bypassed by cracks or worm channels. It was noted in the field that cracks tended to first form parallel to, and at the base of ridges left as the result of various tillage operations. The cracks formed first were generally the last to close after rain resumed since they were widest, having been subject to the cracking process for the longest time. Further research into the hydrology of surface cracking in relation to surface geometry is required and it appears that some important management recommendations may result. It appeared, on the basis of field observations, that ridging of the soil induced earlier and more extensive cracking in addition to the beneficial effects ridging had on earthworm survival. Since worms are more abundant in drained fields, drainage directly and indirectly alleviates much of the ponding problem by promoting surface crust perforation.  10. Surface Crust and Soil Profile Bulk Density Surface crust bulk density data are shown in Table 7. All the samples (which were also used in the crust K, measurements) were taken from Site U3 which was not sampled for profile bulk density. It appeared reasonable to assume that the severe crusting at Site U3 can be taken as a fair representation of the "worst-case" crusting that could be expected on the soils studied. If this assumption is  90  Table 7: Surface Crust Bulk Density Data for Site U3 Crust Sample  Depth Range  Bulk Density (kg/m3 )  R1  0 - 0.0015m 0.0015 - 0.003m  1310^1360 1330 1320  1380 1320  R2  0 - 0.0015m 0.0015 - 0.003m  1350 1410  1360 1400  1320 1402  R3  0 - 0.0015m 0.0015 - 0.003m  1400 1320  1390 1320  1350 1330  R4  0 - 0.0015m 0.0015 - 0.003m  1370 1390  1400 1380  1350 1380  R5  0 - 0.0015m 0.0015 - 0.003m  1390 1400  1410 1390  1420 1420  R6  0 - 0.0015m 0.0015 - 0.003m  1330 1380  1380 1400  1350 1360  R7  0 - 0.0015m 0.0015 - 0.003m  1350 1410  1410 1410  1320 1410  R8  0 - 0.0015m 0.0015 - 0.003m  1350 1340  1670 1360  1200 1430  R9  0 - 0.0015m 0.0015 - 0.003m  1380 1400  1420 1370  1360 1400  mean bulk density = 1380 kg/m 3 ; range = 1200 to 1670 kg/m3  ^  91  Table 8: Profile Bulk Density Data (Core Method) Bulk Density (kg/m 3 ) Site Depth^  Replicate  R1^R2^R3^R4^R5^Mean Di^0 -10 cm 1108^1014^1062^1144^1190^1100 10-20^1158^1077^1062^1044^1210^1110 20-30^1177^1077^1062^901^1270^1100 30-40^1087^1122^1032^1038^1250^1110 40-50^948^1053^966^977^1110^1010 D2^0 -10 cm 1250^1250^----*^----^1250 10-20^1000^1220^----^----^1110 20-30^1170^960^----^ 1070 30-40^1120^950^----^ 1040 40-50^990^1020^----^ 1010 U1^0 -10 cm 1180^1170^1060^1064^1080^1130 10-20^1330^1275^1096^1080^1000^1160 20-30^1150^1262^1122^1105^1000^1130 30-40^1017^1131^982^1090^1010^1050 40-50^922^1170^1010^980^1020^1020 U2^0 -10 cm 1260^1320^1230^1340^1180^1270 10-20^1320^1350^1250^1260^1350^1310 20-30^1315^1260^1239^1270^1260^1270 30-40^1198^1035^1060^1140^1140^1110 40-50^1252^1080^980^1150^1090^1110 *Note: the field was disturbed by tillage prior to completion of sampling  92 accepted, the data in Table 7 can be compared with the profile bulk density shown in Table 8 which were collected at the other four sites. The crust bulk densities for the upper 0.03 m of soil at site U3 ranged from 1,200 to 1,670 kg/m 3 , and the mean bulk density was 1,380 kg/m 3 . The mean crust bulk density is significantly higher (5% level) than the mean bulk densities for the. upper 0.5 m as shown in Table 8. Where it is present, therefore, this thin surface layer has a closer particle packing and lower porosity than most of the soil underlying it. The crust pore-size distribution is also different, although this is not revealed in the bulk density data. The crust has only very small pores which do not transmit water and air easily except where a worm burrow or crack passes through it. The highest mean profile bulk density was found in the upper 0.20 m in each of the four sites sampled. There is a trend towards a decrease in bulk density with increasing depth, which suggests that agricultural use of the plough layer has resulted in closer packing of soil particles. This pattern is apparent despite the tendency for relatively organic rich soil such as the surface layer to have lower bulk densities. Differences in bulk density may be attributed to variations in tillage history and the degree of compaction; mean bulk densities in site Ul which was subsoiled are lower than those for site U2 which was not. In general, though, the  93  small sample size and its variability prevents the making of any broad conclusions with confidence.  11. Earthworms The data in Table 9 are in general agreement with qualitative field observations. There were an average of 573 earthworms per square metre on the drained farm. The mean for the undrained farm was only three earthworms per square metre. The mean biomass for the drained field was 19.9 g/m 2 (dry weight) or approximately 100 g/m 2 wet weight. These data for the drained field are among the highest recorded in the literature. It was observed that when depressions in the drained farm became waterlogged, earthworms left their flooded burrows and retreated to higher areas on the soil surface as shown in Figure  26.  In this case the higher areas were ridges formed  during the planting of over-winter cauliflower and cabbage. Such variation in surface microrelief appeared to be an important factor in improving earthworm survival rates during very wet periods. The surface crust in the drained field was extensively perforated by worm burrows. Their number and extent varied markedly with conditions, becoming less numerous during periods of rain, due to infilling by rainsplashed and surface transported sediment, especially in low areas. Surface water was removed much more rapidly where worm holes connected with  ^  94  TABLE 9: Earthworm Data Farm U ^Sample^No. Earthworms/m 2^Dry Weight 16 ^Q1^ 0 Q2^ 0 Q3^ 0 Q4^ 0 ^Q5^ 0 Q6^ mean = 2.6/m2 -  Farm D  ^Sample^No. Earthworms/m 2^Dry Weight ^Ql^ 14.1 g/m 2 Q2^ 512^ 15.1 Q 3^544^ 38.3 Q4^ 544^ 15.9 ^512^ Q5 16.0 Q6^ 752^ mean = 573/m 2^mean = 19.9 g/m 2  95 Figure 26: Surface crust perforated by earthworm burrows in Farm D. Earthworms escape to drier ridges during very wet periods.  96 the surface since they effectively bypassed the relatively impermeable crust. The improved water movement through the surface layer in turn enhanced aeration and the environment forearthworms. It is recommended, on the basis of the above observations, that farmers ridge the soil by fall-ploughing in low areas. Fall-ploughing of low areas in undrained fields should be attempted, in connection with earthworm inoculation where existing earthworm populations are low. Increased earthworm survival is of benefit under both drained and undrained conditions because worm burrows bypass the surface crust.  12. Water-Stable Aggregates Data in Table 10 show no significant differences (5% level) in water-stable aggregates between ponded and non-ponded areas, or between drained and undrained fields. The results are quite variable indicating that perhaps greater replication is needed to adequately characterize a soil. Sample water content also varied considerably, however only weak positive correlations existed between MWD and water content, which tends to discount these variations as a determining factor in MWD results. The mean percentage of sample passing through the smallest sieve opening is greater for the non-ponded areas in both the drained and undrained fields. This is in apparent  O 4 1-3 M tr <  WATER-STABLE AGGREGATE ANALYSIS  •  (% OF ORIGINAL SAMPLE ON AN OVEN DRY WEIGHT BASIS) SIZE RANGE  111  Sit. DI Woo)  >4.76mm<1.00mm  7.90  DRAINED  >2.00mm<4.76mrn >1.16mm<2.00mm  R2 I  R3  R4^I R5  R6  R7  R8  MM  R10  MEAN  S.D.  Var.  • rt MP10  71.95 17.49  42.50 23.38  60.64 21.13  22.33 4.63  460.70 18.411  ft 0  3.32 7.42 23.38  4.44 6.48  8.61 66.37  23.63  3.06 7.14 23.13  I^R9  63.11 19.21  68.89 17.66  66.21 18.68  16.82 29.91  44.84  17.30  64.11 22.31  27.53  59.02 17.86  8.40 27.70 38.70  2.44 4.05 7.09  1.20  2.63  1.79 14.69  4.04 6.87  2.67 3.19  6.27 3.43  4.47 8.43  10.77 0.035  9.25  43.57  76.92  12.31  2.23 4.69 3.64  37.20  55.02  30.01  70.31  35.13  64.14  72.83  63.84  61.71  16.39  20.91  22.14  12.23  25.05  12.06  18.96  27.42  20.40  >1.111mnto:200nn  1.96  5.78  5.32  4.32  2.91  4.40  0.42  14.13  10.39  6.75  5.43  2.53 4.70  4.02  15.10  4.91 10.01  6.26 1.00  >.2111mm<1.111mm  2.22 6.70  17.34 2.51  37.44 24.95  50.30  22.70 7.70  >.219mm (d1ffrorenco)  17.30  14.25  32.73  5.40  50.26  17.70  8.94  0.73  0.00  1.51  14.31  4.63 16.02  Site UI 91..)  >4.76fiont<1.00mm  42.02  14.20  27.17  41.13  3E96  20.39  11.14  16.70  28.14  301.96 44.09  2.80  7.90  7.11  4.08  4.69  20.64 4.79  7.00  4.51  3286 6.56  19.37 23.56  64.95  14.72 6.24  9.67 15.46  27.03  22.44 3.40  25.96  UNDRAINED  43.34 15.40 0.60  40.59  >200mm<4.76nwe >1.111mnt000mm  0.80 9.84  5.55  6.55  16.87  11.22  12.09  12.61  9.22  222 4.67  19.63  25.57  47.97  22.19  59.98  36.54  6.61 7.66  7.28  23.02  12.62 42.10  18.76  29.36  16.39  261.30  53.77 21.75  4520 24.60  38.71  59.45  46.40  27.06  56.23  79.10  58.15  .66.52  63.06  14.62  192.46  24.87  13.80  23.61  18.03  20.20  26.86  19.10  21.41  3.34  13.30  3.29 6.47 11.72  %3.20 6.50 20.50  21.74 4.19 8.77  2.52 4.40  9.20 22.69  3.31 6.76  2.36 6.93  4.95 31.63  17.44  1.51 3.67 0.00  2.76 5.67  8.86  5.23 3.41 17.01  2.22 4.09  26.59  1.11 1.8.4 37.95  8.68  5.05  16.76  10.06  106.14  0.332 0.380  0.329 --  0.322 0.361  0.333 0.368  0.317 0.351  0.300 0.337  0.316 0.364  0.0162 0.246  0.0020 0.0006  0.309  0.285  0.0237  0.0006  >.219mm<1.13mm >.219mm (dliforono0  Site DI Weproesions9 DRAINED  >4.76mm<11.00mm >2.00mm<4.75innt  >.219mm<1.lSmm >.219mm (d11111woneo)  Site UI WoOrmiena0  >4.76mm<1.00mm >2.00mm<4.76mm  UNDRAINED  >1.111mm000mm >.219rnm<1.111mm >.219mm (difforonera  7.30  -  -  433.66  227.33 24.86 3.24 11.86 231.01  4.43  Correlation  DI riso  fravimoirle  0297  0.314  0.287  Di dopressional  molaturo coniont  0.343  0.361  0.311  UI Hs*  of oomph,  0.268  0.296  0.298  0.327  0.263  0.251  0.273  U1 dowssolonal  kg vist.d kg soil  0.327  0.372  0.305 0.326  0.328 0.332 0.290  0.316  0.271  0.294  0.321  0.345  0.338  0.327  0.324  0.0274  0.0007  3.60 5.07  4.124  1.364 0.979  1.649 0.862  0.374  4.104  3.70  3.130  1.296  1.611  4.97  4.210  0.873  0.690  0-206 0.465  Di rise DI dopresslonal U1 Moo U1 &pre ssiona I  11)  Moan .  1.46  4.91  4.70  4.54  5.25  4.35  2.82  5.59 2.68  3.92  3.37  5.06 5.14  221  Wolght  3.42  4.21  4.61  5.37  Diameter  5.21  3.44  3.67  1.62  3.02  1.27  2.25  2.30  (mm)  4.25  3.81  3.33  4.70  3.45  2.83  4.30  5.77  4.82 4.68  C" 111141•nt MWD vs Moisture Contont  0.196  98 agreement with the differences in mean water content, since a lower O m would result in more complete aggregate breakdown via slaking. The soil O m , however, shows only a weak negative correlation (r 2 =0.073) with the proportion of sample less than 212 Am when all forty samples are pooled. This indicates that factors other than O m account for most of the variations in the MWD results. It may be that some of the aggregates found in the low ponded areas are denser and more stable because they have been formed by the mechanical breakdown of larger compact clods. The likelihood that tillage or other field operations are carried out when the soil is not trafficable is greatest in the wetter depressions, and therefore so is the formation of compact soil clods. If present, these denser and more stable aggregates would tend to counter-balance the effects of unstable aggregates in calculating MWD values. The wet-sieving measurements show that land drainage and the higher earthworm populations on Farm D have produced no significant increase in the water-stability of soil aggregates. The early laboratory research which indicated that earthworms contribute to water-stable aggregate formation has not been born out in the fields studied on Westham Island. It is not clear what effects, if any, the technique used had on the water-stable aggregate results. Further research into the wet-sieving procedure as a method of evaluation the structural stability of field soils seems necessary. The aim should be to increase the meaningfulness and reproducibility  99 of results.  13. Penetration Resistance and Compaction The cone penetrometer is a widely used tool in soil compaction research, despite the fact that the theory behind it is not well understood. Frietag (1971) presents data showing near linear relationships between cone index and soil water content in the 0.25-0.35 kg H 20/kg soil range. The hypothesis being tested was that better drained and hence drier soil undergoes less compaction during normal tillage. The penetrometer measurements shown in Figure 27 (raw data are in Appendix 3) were made in the low areas at sites Ul, U2, Dl, and D2. It was felt that any differences in the degree of compaction would be most apparent there since water management practices contrasted most sharply in low areas. It should be noted, however, that ill-timed vehicle traffic on soil can cause severe compaction even under the best water management regime. The mean penetration resistance (30 replicates) for site Ul is significantly higher (5% level) than the drained site nearby, site D1, at the 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30 m depths. Site U2 had mean penetration resistance values that were significantly higher (5% level) from those at near by site D2 only at the 0.20 and 0.25 m depths. It is interesting that below 0.35 m the penetration resistance profiles are similar, and that they lie below the depth range strongly  100 Figure 27: Penetration resistance profiles. Each data point is the mean of 30 replicates.  101 influenced^by^ordinary^tillage. The^highest mean penetration resistance at each site was measured at depth of 0.25 m. This corresponds to the ploughpan depth qualitatively identified in the field, although, as the profiles in Figure 27 illustrate, the ploughpan is actually a zone of more compact soil generally between 0.15 and 0.30 m below the surface. The profiles for Farm D, though not identical, closely follow each other and the same can be said for those from Farm U. The penetration resistance profiles agree with the hypothesis that the better drained sites of Farm D have less compacted ploughpan zones. A precise interpretation of these results is hampered however, by differences in water content at the time of measurement and lack of knowledge about the relationship between penetration resistance and water content.  14. Effects of Moling, Subsoiling, and Subsurface Drainage on the Water Regime of Depressional Areas Moling If mole drainage channels are properly created and then persist for some time they may aggravate excess water conditions even on gently undulating land by directing subsurface water into depressions from surrounding higher areas. Since mole drains are installed at a fixed depth relative to the surface on which the tractor rides, water is always directed into and never out of low areas as shown in  102 Figure 28. One strategically located low spot may significantly reduce or halt flow in a "properly" installed mole drain. This would be much less of a problem in drained land where subsurface pipes would remove any water so delivered to a low spot or where mole drain collapse prevents water from flowing. No mole drains were encountered in all the digging that was done in farm U, nor were any seen transferring water into the ditch. The soil texture, along with these observations, indicates that mole drains are quite shortlived in this soil and are therefore an ineffective means of dealing with excess water. Where they do persist, mole drains would cause the problems mentioned above.  Subsoilina Without subsoiling there might be lateral flow of water into low areas on top of the ploughpan. With subsoiling there may be flow along the bottom of subsoiler slits into low areas similar to the case with mole drains. Subsoiling may also result in increased infiltration and vertical water movements and hence less flow from high to low areas.  Subsurface Drainage Plastic subsurface drainpipes are laid with laser-guided machines to give a slight grade from the most distant part of the field to the ditch. The drain-pipe depth is not constant but is inevitably at its shallowest relative to the surface in low areas. As a consequence of this, low areas receive the  103 Figure 28: Effect of mole draining at a constant depth below the soil surface. Arrows indicate the direction of water flow in the mole channel.  104 least direct benefit from subsurface drainage. Indirect benefits may derive from improvements in higher areas due to drainage which lead to decreases in runoff and through-flow. Low areas tend to be more poorly drained than surrounding higher areas partially as a result of the above. Even if other factors are not operating, where there is a "flat" water table it will be closest to the surface in low areas.  15. Surface Ditching to Remove Ponded Water Observations in the field indicated that surface ditches are generally not an efficient means of channeling away ponded water to deep ditches. The gently undulating topography in the sites, and in Delta area in general, make it difficult to construct a surface ditch with an adequate grade for water removal as shown in Figure 29. The surface ditch illustrated in Figure 29 was constructed using a mouldboard plough; other implements designed specifically for the purpose produce similar results. Trenching equipment is sometimes used and is more successful because of better depth control. Surface ditches suffer from two main problems even when an adequate grade can be obtained: (1) the soil thrown up on either side of the ditch often prevents ponded water from entering laterally; depending on where the surface ditch begins only part of the ponded water may be removed, and (2) inadequate water removal on a regional scale results in high water levels in deep ditches often to the point that water  105 Figure 29: A surface ditch installed in an attempt to remove ponded water was unsuccessful due to an inability to establish an adequate gradient.  106 flows into the fields rather than outward. Surface ditches, as a remedial measure to deal with the ccumulation of ponded water, would be most successful if they emptied into deep ditches whose water level is adequately controlled for agricultural requirements. A more effective alternative may be to construct a sump and use a portable gasoline pump to remove ponded water. It is recommended that pumping be tested in the field.  107 Chapter 4  SUMMARY AND CONCLUSIONS  The effectiveness of contrasting soil and water management practiced on adjacent farms with the same soil type was evaluated. The study involved measurement of soil physical and biological properties in the field and laboratory. Land drainage, through a system of subsurface perforated tubes that empty into a ditch whose water level was controlled by pumping, was found to be superior to the use of mole-drains, subsoiling and surface drainage used in combination. Land drainage was also more efficient in lowering the water table after rainfall, and thereby providing aerated conditions in the surface layer which benefits survival of crops and soil fauna, especially earthworms. Drainage reduced the depth and duration of ponding and resulted in more trafficable and opportunity days. There were no full opportunity days during the period of measurements in the undrained farm due to persistant high water table levels in depressions while there were six to twelve full opportunity days in the drained farm during the same period. There was a more severe ploughpan in the undrained farm and this was thought to reflect wetter conditions there for comparable plowing dates. There was no evidence that the ploughpan impeded vertical water movement in either farm. Measurements of the hydraulic conductivity of the ploughpan and the lower profile  108 indicated that their K, was too high to significantly retard water movement under saturated conditions. There was no measured difference in water-stable aggregates between the two farms. Greater water-stable aggregation in depressions was thought to be due to the physical break-up of compact clods. Further research into the wet-sieving method was recommended. The presence of ponded water in depressions was found to be a major problem. It was shown that flooding can occur due to the water table rising above the soil surface. In most cases, ponding was due to the presence of a slowly permeable surface crust. In high areas the crust reduced infiltration rates and resulted in runoff into depressions where ponded water accumulated. In the worst instance the crust K, was measured to be 0.002 m/day. This meant that on sunny days removal of ponded water was roughly equally partitioned between drainage and evaporation. The presence of high water tables and wet conditions in depressions created conditions favorable to crust formation. In the undrained farm growth of a cover crop reduced the severity of crusting and hence of ponding. In the drained farm ponding was less severe even without a cover crop. This was a result of the extensive perforation of the surface crust by earthworms which were abundant due to the more favorable aerated conditions there. Earthworms were scarce in the undrained farm. Earthworm burrows provided preferred pathways for water to bypass the crust thereby reducing runoff and ponding.  109 Surface runoff was also reduced in both farms by cracking which breached the crust as the soil dried. Surface cracking was influenced by surface geometry, as was earthworm survival during ponding. Further research into the nature of these influences was recommended. It was suggested that subsoiling and mole drainage may aggravate wet conditions in depressions when their channels are installed at a constant depth relative to the soil surface. Subsoiling to break up the ploughpan had no benefit with respect to ponding where a crust subsequently formed on the soil surface. The spacing of subsoiler blades in Farm U was found to be too great. Subsoiling in the absence of measures to control crusting and water table levels should be discouraged as it is relatively ineffective when applied in isolation. Surface ditches were found to be ineffective in removal of ponded water due to poor installation techniques and topographic constraints. Even where they are well installed they may channel water into fields where the adjacent regional water management is poor. Land drainage is recommended as the most effective system for managing soil water in poorly drained soils. However, even a well designed drainage system will not be fully successful if there is not an ongoing program to manage the system, including the soil, to maintain and promote optimum efficiency levels. Land leveling was suggested as a means of improving the efficiency of a drainage system. Good regional water management is required before a  110  drainage system can provide all its potential benefits.  111  BIBLIOGRAPHY Abbaspour, K. 1988. Hydrologic Responsiveness of a Lower Fraser Valley Lowland Soil. Unpublished M.Sc. Thesis. Department of Soil Science, University of British Columbia. Vancouver. Armstrong, A.C. 1987. The effect of drainage treatments on cereal yields: results from experiments on clay lands. J. Agricultural Science, Cambridge. 91:229-235. Atmospheric Environment Service. 1981. UBC Climate Station, Monthly Meteorological Summary. Environment Canada, Vancouver. Atmospheric Environment Service. 1984. Canadian Climatic Normals, 1951-1980. Environment Canada, Canadian Climate Program, Ottawa. Blake, G.R. 1965. Bulk Density. In Black, C.A. (ed.) Methods of Soil Analysis. American Society of Agronomy, Inc. Madison, Wisconsin. Boersma, L.^1965.^Field measurement of hydraulic conductivity below a water table. In Black, C.A. (ed.) Methods of Soil Analysis. American Society of Agronomy, Inc. Madison, Wisconsin. Bonsu, M. 1984. Hydrologic Behavior of Some Structurally Degraded Organic Soils. Unpublished Ph.D. Thesis. Department of Soil Science, University of British Columbia. Vancouver. Bouma, J. 1978. The drainability of some Dutch knick soils. Agr. Water Mngt. 1:1-9. Bouma, J. 1981. Soil morphology and preferential flow along macropores. Agr. Water Manage. 3:235-250. Bouma, J., Jongerius, A.,Boersma, 0., Jager, A. and Schoonderbeek, D. 1977. The function of different types of macropores during saturated flow through four swelling soil horizons. Soil Sci. Soc. Am. J., 41:945- 950. Bouwer, H. 1965. Drainage for Efficient Crop Production Conf., Amer. Soc. Agr. Eng., Pro. p.62-65. Bouwer, H. 1974. Developing drainage design criteria. In Van Schilfgaarde, J. (ed.) Drainage for Agriculture. 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Climate Station Evaporation (EV) and Bright Sunshine (BSS)Data February to April, Date  EV^BSS^EV mm^hrs^Date^mm  Feb.1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 25 26 27 28  0.4 0.6 0.4 0.4 0.4 0.6 0.0 0.2 2.4 1.3 1.2 0.1 1.8 0.0 0.2 1.0 0.4 1.2 1.2 1.2 0.1 1.0 0.8 0.2 0.6 2.5 1.9  TOTAL MEAN  0.3 5.3 7.5 7.5 8.4 6.5 0.0 7.7 6.7 8.7 0.1 0.0 0.0 1.1 0.0 3.0 0.0 0.0 2.1 0.0 0.1 3.8 0.8 0.0 0.7 9.3 8.7  22.9 88.3 0.8 3.2  Mar.1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 25 26 27 28 29 30 31  0.7 1.2 0.8 1.8 1.4 2.4 0.2 1.2 2.6 2.0 1.8 1.6 3.6 0.9 0.4 2.4 2.4 5.0 3.6 4.0 3.0 3.2 2.2 2.8 2.4 2.2 0.8 0.2 1.0 1.8  1981 BSS hrs^Date 7.1 5.8 0.0 8.5 7.6 6.4 0.0 8.3 9.5 8.8 7.7 9.0 8.1 2.1 0.0 9.0 9.7 10.0 9.8 8.9 6.4 7.6 4.9 8.5 10.3 0.3 0.0 0.0 0.0 3.8  63.0 179.4 2.0 5.8  Apr.1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 25 26 27 28 29 30  EV mm 3.4 2.0 2.9 0.3 2.8 2.8 2.8 1.0 2.2 1.9 0.8 0.8 2.4 2.8 2.4 4.3 8.2 4.3 4.7 0.7 0.4 0.4 1.6 3.9 3.0 1.2 0.8 2.0 2.0  BSS hrs 7.1 1.0 10.3 0.0 5.8 7.9 4.9 3.3 4.6 0.0 3.7 5.8 7.2 12.2 0.4 10.7 11.7 12.5 12.4 0.0 0.0 0.0 0.8 11.3 12.2 0.0 0.0 0.4 4.1  67.8 161.2 5.4 2.3  ^  117 APPENDIX 2 WESTHAM ISLAND RAINFALL DATA Rainfall (mm)  Date (1981)^RG1^RG2^RG3^RG4^Mean Feb. 13^13.3^13.3^----^----^13.3 14^10.3^9.9^11.2^10.1^10.4 15^11.7^11.9^8.0^8.4^10.0 16^14.6^----^18.6^22.1^18.4 17^5.7^4.4^2.2^2.7^3.7 18^19.8^18.8^16.4^19.9^18.7 19^19.6^14.5^16.4^20.4^17.7 21^7.4^6.6^7.1^7.1^11.5 25^16.8^17.9^15.5^15.9^16.5 27^2.8^3.0^4.0^3.8^3.4 Mar. 3^18.1^17.9^18.1^17.3^17.9 7^0.9^----^1.8^1.8^1.5 15^4.2^4.0^4.0^4.2^4.1 16^6.6^6.2^7.1^6.8^6.7 25^14.2^14.2^15.0^14.6^14.5 29^28.8^32.9^28.3^27.4^29.4 30^9.4^9.7^8.9^9.3^9.3 31^8.9^9.0^9.3^8.9^9.0 Apr. 3^4.3^5.0^4.4^5.3^4.7 4^6.0^5.8^6.6^6.2^6.2 5^11.5^11.9^15.0^13.3^12.9 8^4.9^----^5.3^5.0^5.1 10^ 0.9^0.9^0.9 13^----^----^8.8^8.0^8.4 16^----^----^0.9^0.9^0.9  

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