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A comparative study of some chemical and physical properties of Pineview, Vanderhoof and Nulki clay associations Farstad, Laurence 1947

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A COMPARATIVE STUDY OF S0M3 CHEMICAL AMD PHYSICAL PROPERTIES OF PINKVTEW, VANDEHHDOF AND NULKI CLAY ASSOCIATIONS by Laurence Farstad A Thesis Submitted in Partial Fulfilment of The Requirements for the Degree of Master of Science in Agriculture in the Department of Agronomy (Soils) -ooo-The University of British Columbia ^Jps i f 1-May, 1947 - i J j A ^ A ACKNOWLEDGED NT The author wishes to express grateful acknowledgment to Dr. D. G. Laird and Dr. C. A. Bowles of the Department of Agronomy, 'i'he University of British Columbia, for their assistance, guidance and helpful criticism during the oourse of this study. TABLE OF CONTENTS Page Introduction 1 Review of Literature 2 Podsolization 2 Physical Properties of Soils . . . . 7 lexture 7 Structure . . . . . . . . . . . . 7 Methods of Specifying Soil Structure . . 7 Porosity as a Measure of Soil Structure . 8 Factors Affecting Soil Porosity . . . . . 11 Plant Responses to Aeration 12 Soil Consistency 14 Soils Subjected to Study 16 Description of Soils . 17 Experimental 21 Methods of Analysis 21 Chemical Studies • 25 Physical Studies 31 Particle Size Distribution 31 Pore Size Distribution . 34 Plasticity Constants 4S Discussion and Summary 47 Conclusions * 9 Bibliography • 5 0 TABLES Table Page I Chemical Composition of Profile Samples . . . . 26 II Chemical Composition of Extracted Colloids . . . . 27 III Derived Data of Extracted Colloids . . . . . . . 29 17 Particle Size Distribution Data for Horizons of Pineview, Vanderhoof and Nulki Clay in Per Cent (dry Basis) 33 V A Distribution of Pores According to Donat (1937) . . . . 35 VI Volume Relationships of S o i l , Non-Capillary and Capillary Porosity In Profiles of Pineview, Vanderhoof, and Nulki Associations (at hydroscopic coefficient) 38 VII Lower Plastic Limit, Liquid Limit, and Plasticity Index Values for Average Profiles of Pineview, Vanderhoof, and Nulki Associations 45 FIGURES Figure Number 1 Apparatus for Determining Pore Size Distribu-tion eurves*hav!ng*Undisturbed Structure 23 2 Moisture Desorption Curves for the Various Horizons of Vanderhoof, Nulki, and Pineview Associations 36 3 Volume Relationships of Soil to Capillary and Non-Capillary Pores for the Profiles of Pineview, Nulki, and Vanderhoof Clays • . 41 4 Plasticity Relationships of Pineview, Vanderhoof and Nulki Profiles 46 ABSTRACT A study of the chemical and physical properties of Pineview, Vanderhoof and Nulki s o i l associations in the Central Interior of British Columbia was related to f i e l d observations. The results of the chemical data on the whole s o i l as well as the colloid fraction (.002) show varying degrees of podsolic development due to variations in parent material. Pore-size distribution and particle-size d i s t r i -bution studies point out that the unfavourable physical pro-perties associated with Vanderhoof soils are primarily the result of particle-size distribution and low organic matter content; aad the tight, impervious B horizon of Pineview clay is part i a l l y an inherited characteristic and partially developed. A simple modification of M.B. Russell's pore-size distributjbawapparatus is presented. INTRODUCTION Soil represents a three phase system, solid, liquid and gas, and, as such, is extremely complex. Bearing In mind the influence, on this system, of climate and biological features assoolated with different parent materials, one can appreciate the diversity of distinct s o i l types which are already recognized and obviously there are many more s t i l l to be differentiated. A study of the many problems assoolated with these types Involves detailed work by the chemist, physicist and biologist* Major attention in the past has been focused on chemical studies but more recently physical properties and biologloal characters are being cor-related with chemical data* Soil structure as related to drainage, aeration, erosion and favorable t i l t h has recently gained wide recogni-tion. As new methods of measurement and evaluation become available It Is expected that the many apparent limitations now existing w i l l be overcome. In the Central Interior of British Columbia certain s o i l areas have been mapped as Pineview, Vanderhoof and Nulki Clay Associations. Zt was observed during the process of the survey that these soils demon-strated certain peculiarities in relation to moisture and showed undesirable physical properties under cultivation* These observations prompted the study whieh is being reported at this time. The Investigations presented and discussed herewith consist of a number of phases, each concerned with an observed peculiarity. The conclusions drawn from the study are based en observations made in the f ie ld, and from physical and chemical laboratory data. This study should not only enhance one's knowledge respecting the fundamental nature of the soils themselves hut also clarify certain problems attendant In their agricultural utilization and contribute to the evolving of a more affec-tive s o i l management practice* REVIEW OF LTJERATURE The soils of the Central Interior of British Columbia a l l possess certain podsolic characteristics due to the olimatio and the biological conditions under which fray have developed* Thus in order to provide a background for discussion ,1 r the process of podsollza-tion and physical properties associated thereto are briefly reviewed* Podsolizatlon Podsol soils are usually in evidence In forested areas and the most prominent characteristic of these soils is that beneath the moist organic ground oover there develops a gray leached horizon (Ag) under which one or two aeeumulation horizons occur (B^ and Bg), Below the illuviated horizon Is the origional parent material or C horizon* There are few, i f any, s o i l types for which more chemical data exists than for the Podsol Soils of the Temperate Regions. A review of the literature, Dokuchaev (1879), Williams (192?), Glinka (1927, 1928), Mattson (1930), Marbut (1935), Thorpe (1935), and Joffe (1936), on the mechanism of podsolizatlon reveals many views as to the mechanism of their development* A possible explanation for the diversity of explanations i s PHHKEy ' ,^  • J the wide range of conditions under which these soils develop* Among the outstanding contributions those of Bamann (1911) in particular throw considerable light on the chemical processes involved in podsolio soi l development* His data show clearly that the apparent increase in SlOg In the leached or Ag horizon i s due to the removal of other constituents, particularly Iron, aluminum and humus, and their accumulation in the B* Glinka (1988), representing the Bussian view, considered podsollzation nothing more than the removal of mobile humus sols from the surface horizon resulting from the leaching of calcium. With the gradual removal of calcium the s o i l becomas acid and less stable, followed by partial decomposition of the colloidal complex* These aoid sols together with the highly dispersed colloidal fraction (mainly hydrates of Fe* and Al.) are carried lower down In the profile by the percolating waters and precipitated. Accordingly, iron is precipitated f i r s t , often in a fairly narrow range, with alumina and s i l i o a next, and praoipitated over a much wider range. She characteristic bleached appearance of the Ag Glinka attributes to finely powdered quartz which remains exposed following the removal of the hydrates of Iron and aluminum from the oolloidal complex* The work c f Anderson and Byers (1930) ,on the colloid material from podsols, has shown that in the podsol process a fractionation of the colloid takes place* Whether In the future this process w i l l be accepted as a characteristic of this group is not known* Gedroiz (1929), interpreting podsollzation in the light of base exchange reactions, suggests that the inorganic exchange complex undergoes gradual decomposition into i ts constituent oxides as the replacement of bases by hydrogen becomes excessive. In the opinion of Battson (1930) podsolizatlon is closely related to conditions of acid hydrolysis which exists In the humid temperate regions* Acid percolating waters, he explains, hydrolize the clay minerals in the surface horizons, resulting in the release of bases - and their replacement by hydrogen* Thus the iron and aluminum silicate complexes saturated with hydrogen ions become colloidally dispersed and move downward with the percolating waters* At the same time under certain conditions some SiOg may be replaced by humates and other anions giving rise to complex silieates of iron and aluminum which have a definite isolectric point of precipitation. These new formations, which originate* In the surface horizons, on moving downward, reach a point where a large portion precipitates, due to higher pH environment, and thereby impart to this layer a characteristic oompactness typical of B horizons* Such removal and aeeumulation of materials during podsoliza-tlon finds f u l l expression in well drained upland positions. This results i n the development of typical profile characters such as described by Be Sigmond (1938) for a forest s o i l developed on granite* The profile Is divided into horizons Aq, &1» Ag, *1» Bg, &3, and C* Of these, As is the gray or true podsol horizon, Bj. the horizon of iron accumulation and Bg and 0 the weathering horizons of granite out of which the s o i l profile was formed* The number of horizons and other details of a profile are today known to vary considerably depending on the climate, parent material, type of vegetation, slope, porosity of s o i l and ground water level , as well as the length of time the processes Involved have bean active* Under oertain conditions the regional profile character1stice do not find typical expression* Such a condition, according to Joffe (1936), may develop In soils having a high fluctuating water table. The movement of the ground waters determine the activity and movement of the sesquioxides* Anaerobic conditions which aoeompany the rise of the water table cause reducing conditions which are conducive to carrying away iron In soluble forms* Such a process is known as glei-formatioa. Accordingly, In low-lying areas or heavy wet soils podsollzation, glei-foxmation, or both processes may proceed. Several methods of expressing the process Involved and degree of development have been evolved. The use of molecular volumes and ratios is perhaps the most expressive. Jenny (1941) Is the foremost exponent In the use of ratios and advocates the following quotients and symbols! SlOg . siliea-sesqnloxide ratio AlaPg / FegOg SlOg • sa value AI2P3 8 1 0 a - sf value FegOg KgO / HagO /• gaO . Ba value AI2O3 i GaO 4 MflO s Bai 1 value Al2©3 These ratios serve as a means of detecting the relative move-mant of tme elements concerned. It i s frequently observed that the surface s o i l contains less s i l i c a (calculated on a percentage basis) than the parent material. This apparent loss may be due to the addition of organie matter to the s o i l which automatically lowers the relative percen-tage of SiOg* If one assumes that AlgOjj is the least mobile element, due to i ts insolubility at neutrality, then ratios involving aluminum repres-ent relative gains and losses in the various horizons. An inspection, therefore, of silica-alumina ratios is l ikely to reveal any previous faulty conclusions. By way of summary, the process of podsolizatlon Is dominant in areas of high humidity and forest vegetation* The process comprises two phases* The f irst Is the aeeumulation of a peaty mat of organie matter and the second the removal of colloids and sesquiozides from the A horizon to the B beneath* The translocated materials are generally partially segregated, and the different ingredients are often deposited in different horizons of the profile. Suspended organic material, as well as soma iron and aluminum compounds, are deposited Immediately below the bleached or Ag horizon* Iron compounds, slightly more mobile, are deposited next and often serve as cementing agents. The suspended inorganic matter Is deposited s t i l l lower by the percolating waters. In so far as chemical relations are concerned, podsolizatlon Is considered as essentially one of progressive hydrolysis of the soil minerals with subsequent translocation of the products in true solution, eolloidal suspension, or both. Physical Properties of Soils In studying the physical behavior of the soils under discus-sion in this paper the three main properties considered were texture, structure and consistence. Texture Texture refers to the size distribution of inorganic s o i l particles and is quantitatively expressed by such terms as clay, clay loam, loam, e t c Various procedures are used for the determination of the particle size distribution but they a l l include similar sample preparation, destruction of organic matter, dispersion and evaluation using Stokes* Law. Structure Soil structure refers to a condition of the s o i l material in which the primary particles like sand, s i l t , and clay are arranged into aggregates. The aggregates differ widely in size, shape, stability and in adhesion to one another. As such these structural units are difficult to give exact quantitative expression as is done in the ease of soi l texture. Methods of Specifying Soil Structure The methods of specifying soil structure have been reviewed in some detail by Baver (1940). He divided the methods into three groups, macroscopic and microscopic methods, aggregate analysis, and porosity or pore-space determinations. The macroscopic and microscopic methods as yet have not been - 8 -sufficiently perfected to provide a complete picture but definite progress has been made. The technique most commonly used is photographing the non-capillary pore-space that can be f i l l e d with some fixing solution. Harper and Volk (1956) as well as Kubiena (1938) used this method and photographed both structure and pore-space. Aggregate analysis, which is a direct determination, aims to measure the percentage of stable secondary particles. Three commonly employed techniques are used. They are: wet and dry solving, elutria-tlon and sedimentation. The details of procedure and value of these methods have been reviewed in considerable detail by Barer (1940). Porosity determinations are regarded by many workers to afford a reliable means of specifying soil structure (Bradfield and Jamison (1938), Chllds (1940), Haines (1930), Learner and Lutz (1940), Nelson and Baver (1940)). These determinations, in addition to a summation of the entire pore-space, show the size distribution of the voids in the assemblage of particles. From the standpoint of the plant such data would appear to be of prime Importance. Porosity as a Measure of Soil Structure The porosity or pore-space is of great importance in the proper understanding of the part played by structure of the s o i l as i t is related to f e r t i l i t y . The measurements required are simple in theory for i t is only necessary to measure the apparent specifio volume and the moisture content of the soi l when in equilibrium with water under dif-ferent suction tensions. These specifications may be given as the dif-ferent volumes of air and volume of water per unit volume of soil or, at different pF's as suggested by Sehofield (1935). Methods most commonly used, however, are those of Ramanrt (1838), Kopecky (1914), Burger (1922) and Dojaranko (1924)* These methods consist of dividing the pore-space into two divisions - capillary and non-capillary pore-space* The method commonly employed is to allow the soi l sample to reach capillary saturation, at which point i t is assumed a l l capillary pores are f i l l e d , then calculate total capillary and non-capillary porosity from volume, weight, moisture content and density of particles. In this method i t is assumed that capillary porosity is equal to the per cent moisture per unit volume, and non-capillary porosity is the difference between the total and capillary porosity. While numerous objections to the foregoing methods for determin-ing soil porosity have been registered they have nonetheless proven to be of great value in characterizing air and water relationships in the s o i l . The most serious objection, in addition to the rough approximation of the designations, is that no means of expressing the pore size and continuity has been provided. Recant developments have led to the measurement of the soi l moisture content at varying tensions, thus obtaining a picture of the various pore sizes as well as their distribution throughout the s o i l . |n so far as many important soi l phenomena, such as aeration and move-ment and storage of water are determined by the number, size distribution and configuration of the soi l pores i t would appear that s o i l structure can best be evaluated by measuring structural moments that can be inter-preted in terms of pore-size distribution. - 10 -Childs (1940) used the Haines Bflehner funnel method (Haines 1930) effectively in a study of t i l t h and s o i l stability. The use of "moisture characteristic curves" in this way depends on the fact that these characteristics may be interpreted as showing the pore size distribution within the s o i l . Thus, he writes, "they play an analogous and complementary part to mechanical analysis: they give the same kind of information about the pores as that given by mechanical analysis about the particles.* In a study on the movement of water through soils in relation to the nature of the pores, Nelson and Baver (1940) used a method based on the capillary forces in the s o i l system. It depended on the removal of water by the application of a reduced pressure on one side with atmospheric pressure on the other. By this method a theoretical pressure differential of 1 atmosphere should be possible. Actually, however, an equivalent to 563 cm. of water, was the highest they obtained. The apparatus was so designed that the system could be adjusted to the desired tension and held constant. Similar apparatus was constructed by Bradfield and Jamison (1938) and Learner and Lutz (1940). Russell (1941) designed a simple apparatus for the determina-tion of moisture desorption curves on soi l samples having undisturbed structure. This apparatus consisted of a 60 mm. sintered glass funnel attached to one end of a 80 em. length of 8 mm. glass tubing which is mounted Inside a reservoir tube. Donat (1937) also used the moisture tension curve method to calculate the size distribution of pores in the s o i l . His curves are similar to those of Russell (1941), Ohilds (1940) and others using the same technique. In as much as a modification of - 11 this method was used in the present investigation farther reference to i t w i l l be made later in the discussion. Factors Affeeting Soil Porosity Soil porosity varies with the size of particles and the extent of aggregation. Baver (1940) presents data showing clearly the relation of porosity to soi l texture. Sands and mucks, he points out, contain many large pores and therefore have high non-capillary porosity while clays, unless well aggregated, have relatively few large pores. Dojaranko (1924) and his co-workers have investigated the relationship of various soil properties to non-capillary porosity. They noted that accompanying a decrease in the size of s o i l granules due to compression or structural deterioration there was also a decrease in porosity. The significant change, they noted, was mainly in reducing the number of large pores. Baver (1938) in considering the significance of compaction on s o i l porosity compressed a s o i l so teiat i t contained 13 per oent more s o i l per unit volume. The effect of this compression caused a decrease of 58 per cent In the amount of the non-capillary pores while the capillary porosity was reduced by only 8 per cent. Everyone is aware of the deterioration in soi l structure following the plowing of virgin land. Humorous examples are to be found in s o i l literature showing astonishing decreases in organic matter, nitrogen and state of aggregation. In estimating the s o i l f e r t i l i t y losses in Missouri Jenny (1933) estimated that after 60 years of cultiva-tion Putnam s i l t loam had lost 38 per cent of its original organic matter, 33 per oent of the available bases with a corresponding decrease in aggregation. \ - 12 -The extent of aggregation and hence porosity In different zonal soils varies considerably. Bayer (1940) attempted to correlate aggre-gate formation with soil-forming climatic factors. Although his data are insufficient to formulate mathematical relationships the results show definite tendencies. For example, the proportion of aggregates in podsol, dark humid-prairie, chernozem-like, chestnut-colored and desert soils is approximately 10, 40, 40, 25 and 10 per cent respectively. Movement of water through a s o i l takes place through the various horizons. The porosity and permeability thus varies greatly. Jbffe (1941) in studying the root penetrations of forest species and apple trees on podsol and podsolio soils in New Hamshire concluded that whenever the B horizon is compact the roots of trees do not penetrate but flatten out, Mechanical and chemical treatment of this Impervious layer increased the quantity of roots and their penetration. He sug-gests that the failure of the roots to penetrate is not' due merely to the presence of toxic substances but also to laok of aeration. Toxic substances, he continues, are probably due to poor aeration. It is to be concluded, therefore, that i f an impermeable layer exists in the subsoil, water or air movement of any consequence through such a horizon can take place only through cracks and fissures or root channels. Plant Responses to Aeration In spite of the faet that much has been said about the effects of poor aeration on the growth of many plants, there is a decided laok of information on the exact air requirements of various plants. Eopeeky (192?) has proposed the following a i r capacity ranges for optimum growth of several cultivated crops. Sudan grass 6 - 1 0 per cent; wheat and 13 -oats 10 - 15 per cent; barley and sugar beets 15 - 20 per cent. It is fairly well established from practical experience that these crops are arranged in the correct order as far as relative needs for aeration are concerned. At East Lansing, Michigan, Smith and Cook (1947) studied the effects of soil aeration on the growth and yield of sugar beets. The data, unfortunately, does not include porosity determination but defin-itely confirms the high requirements of sugar beets. An example of their results is given, in part, as follows. Yield of Sugar Beet Roots Smith and Cook (1947) Physical treatment Mean dry weight for of Soil sugar beat roots*  1. Normal 15.45 2. Aeration 17*68 3. Compaction 1*43 4. Aeration and Compaction 5.19 * Series average in grams. Mean of 4 replicates. In studying the failure of com to respond to fertil izers in Ohio, Bradfield (1936) reports a s o i l which, having a porosity of 60.3 per cent in the surface foot, gave a yield of 80 bushels per acre* The field across the road, having a total porosity of 50.5 per cent, yielded only 80 bushels per acre. This great difference in yield he suggests is due the decrease in porosity. Hoffer (1945) attributes the failure of corn to respond to ferti l izers, on certain Indiana soils, as primarily due to lack of adequate aeration. McOeorge and Breazeale (1938) found that sead do not germinate in puddled soils unless looated at the surface or near a crack where air could he obtained. Further studies revealed that the availability and absorption of nutrients by plants was materially reduced. This was true of elements already present in the soil as well as those added as commercial ferti l izers. As previously mentioned exact data on the air requirements of various plants is lacking. However there seems to be ample justification that the non-capillary pore-space of the seed bed is a very important factor in successful crop production. Soil Consistency In the Report of the Committee on Soil Consistency (1928) Russell defined "consistency" as the manifestation of the physical forces of cohesion and adhesion acting within the s o i l at various moisture contents. These manifestations include: (1) the behavior towards gravity, pressure, thrust and p u l l , (2) the tendency of the s o i l mass to adhere to foreign bodies or substances, and (3) the sensations which are evidenced as feel by the fingers of the observer. Atterberg (1911) was the f irst to attach much significance to soi l consistency and recognized (1912) six consistency forms. Baver (1940) condensed them to four relating each to soil moisture content as follows: - 15 -Soli Consistency Variation with Moisture Barer (1940) Dry Moist Wet Hard Soft, Tough, Viscous, Consistency friable plastic, sticky Forms sticky Clods form Optimum Soil Soil runs here conditions puddles together for here here working Various Indirect methods have been used to determine s o i l plasticity but as yet few of them are sufficiently accurate* Atterberg (1911, 1912) studying plasticity, from the point of view of the soi l moisture range, suggested three constituents of particular significance to the classification of soils. These are the Lower Plastic Limit, Upper Plastic Limit, and the Plasticity Number. The lower plastic limit represents the moisture content at which the change from friable to plastic consistency occurs and signifies a point where sufficient water has been added to provide a film around each particle. Cohesion at this point reaches a maximum* The upper plastic limit is the moisture content at which the water film becomes so thick that the s o i l mass w i l l flow under a small applied force. The plasticity number (the difference between the upper and lower plastic limits) is an indirect measure of the foroe required to mold the s o i l . Russel (1928) found the above constants to be a satisfactory index of the degree of clay accumulation In the s o i l profile. Among the 49 samples reported on, the 5 micron day varied from 24*9 to 54*4 per cent; hence one might expect fairly close correlations. Smith and Bhoades (1942) used plasticity indices as a measure of 2 micron clay in the A and B horizons of eertain Planosol series in 16 -Nebraska. They stats that "plasticity index is primarily affected by clay content **; they however did not elaborate farther on this relationship. SOILS SUBJECTED TO STUDY As already recorded in the Introduction the soils used for the study and reported upon at this time are the Pineview, Vanderhoof and Nulki Associations. The f irst s o i l survey report of the Soils of the Central Interior of British Columbia was the Report of the Prince George Area by Eelley and Farstad (1946). The main agricultural soi l in the area was then mapped and classified as Pinsview Clay Association. In the Vanderhoof distr ict , some eighty miles west of Prince George, Farstad and Laird (1945) mapped a number of soils developed on similar geological deposits but differing markedly in physical and chemical properties. The two main agricultural soils mapped were called Vanderhoof and Nulki Clay Association? The three above mentioned associations, while similar in respect to origin, differ markedly in profile development, chemical and physical properties, as well as agricultural adaptation. While the authors brought together a l l the available information regarding soils, processes of soi l development involved, climate, vegetation, slope, stoniness, etc., the groupings were necessarily generalized because of the lack of detailed information as well as limitations of scale of mapping. Although the soi l associations as shown have many uses, the authors stressed the preliminary nature of the study and indicated the - 17 -urgent necessity for detailed information respecting soils and the problems associated therewith. Haggart (1944) in his investigations on the constitution of the Pineview and Vanderhoof colloids used molecular ratios as a means of detecting the translocation of elements involved in the soil forming processes. He concluded that the segregation of the colloidal fraction resulted mainly in the eluviation of iron compounds* Pineview d a y , he stated, points strongly to a podsol-glei type of development while Vanderhoof has developed more along the lines of a typical podsol* Description of Soils The soils used in this study are the dominant members of the Pineview, Vanderhoof and Nulki Associations. A detailed description of the s o i l profiles used is as follows: Pineview Clay: Level to undulating topography, dense mature stands of forest dominate the landscape of Pineview clay. The pit was dug on a S per cent slope which faced east. The surface was undisturbed and covered with a heavy growth of pine and spruce forest. Approximately . 300,000 acres of this type occur; in the Prince George area. Pine view Clay Soil Profile Horizon Depth Description inches AQ 4 i n . Dark brown partially decomposed leaves, needles, twigs, etc. 0 - 1 Dark gray to black colored usually of somewhat platy-granular structure which easily crushes to loose powdery structure of clay texture. Ag 1 - 5 Light gray colored plastic clay, coarse granular in structure, readily permeable to roots and water. Very hard when dry. Plastic and sticky when wet. A§ 5 - 8 Light gray clay, jointed fragmental struc-ture, somewhat heavier than Ag. Bx 8 -16 Brown heavy, plastic sticky clay, mettled with yellowish or bluish gray,, and of a massive to blocky structure. Impervious to roots and water, extremely tough. Exists as a continuous sheet resembling day pan. Bg 16-22 Light gray broken laminations alternating with brown ones. Less compact than above horizon. C 22 / Heavy varved clay, quite plastic and sticky when wet. Vanderhoof Silty Clay: Vanderhoof si l ty clay was chosen to represent the large area of podsolic soils occupying the clay plain in the Vanderhoof distriot. Approximately 275,000 acres of this type have been mapped. Level to undulating relief features characterize the landscape. With the exception of scattered clearings the area is domlnantly forested. The profile was sampled in an apparently undisturbed site covered with mature stands of spruce. Vanderhoof Silty Clay  Soli Profile Horizon Depth Description ________ inches ____________»_ AQ 2 in* Organic remains of needles, twigs, leaves, mosses, etc. Partially decomposed. Ai 0 - 2 Dark grey silty clay, weak platy structure• Ag 2 - 8 Light gray to ashy gray s i l ty clay. Compact and harsh consistency. Massive, run-together structure, which breaks down to irregular lumps. Low in organic matter, has strong tendency to pack and form crusts as i t dries. A3 8 - 9 Light gray si l ty clay, large angular nut structure. B_ 9 -15 Brown heavy si l ty clay, very plastic and sticky when wet, hard when dry. Strong angular irregular nutty structure. Imper-vious to roots or water except along cracks* Contains small concretionary forms. B 2 15-20 Gray and dark gray alternating bands of heavy si l ty clay* Water tight consistency. Angular fragmental structure. Somewhat more compact than B_ above* B 3 20-25 Very like B 2 , more laminated. C 25 / Gray and gray brown alternating bands of clay and s i l t . Quite compact and impervious to water penetration. Few small irregular shaped lime concretions* Nulki Clay: The Nulki soils are located in the Vanderhoof clay plain and have developed on essentially the same parent material as the Vanderhoof si l ty clay. This association was set up as belonging to the Degraded Black Soil Zone (Farstad and Laird (1945)}. It differs markedly from the other associations in having originally developed under grass vegetation. - 20 -The landscape is that of park land* consisting of small open grassy areas Interspersed with timbered lands* The surface condition of the profile was undisturbed and covered with a variety of grass species. Approximately 6,000 acres of this type were classified. Nulki Clay  Soil Profile Horizon *1 Depth Inches 0 - 6 *2 As 6 - 8 8 - 9 9 -15 B 2 15-20 20-25 25 / Description Dark gray to black clay. Upper 2 inches black friable and granular in structure. Lower 4 inches are dark gray and granular with a tendency to platiness in the lower depths. The whole Is interwoven with a mass of grass roots forming a firm sod. Gray to light gray plastic clay nutty structure with tendency to platiness in upper portion. Numerous small concretion-ary forms scattered throughout. Transition similar to Ag above but having somewhat larger and more sharply angular nutty structure. Brown gray compact plastic clay with occas-ional red-yellow mottlings. Weakly devel-oped oolumnar-like structure which breaks readily into sharply angular nutty frag-ments - few concretions. Gray to brown gray compact clay - consist-ing of laminated clay broken by vertical cracks and fissures thus producing a strong angular nutty to blooky type of structure* No effervescence. Transition. Moderately compact, partially weathered parent material. Strongly laminated clay of gray eolor. Lime speckled throughout. Very compact and impervious. Samples were collected in the f a l l of 1946 when the soi l was approximately at a moisture content of field eapacity. Samples were taken in virgin areas using the soil-sampling tube of Bradfield, as described by Baver (1940), placed in pint sized ice-cream containers and stored in a moist condition. EXPERIMENTAL Methods of Analysis The method of Isolating the colloidal material for the Vander-hoof and Pineview clays described above was as follows. A suspension containing the colloidal matter was obtained by shaking the soi l with water, in the proportion of 1 to 5, in the Bouyoucos mechanical st irrer. No dispersing agent was used. This suspension was then added to 14 l i ters of water in a carboy, the whole agitated and allowed to stand. After settling 24 hours the upper 20 em. of the suspension was siphoned off. The colloidal material held in the suspension was concentrated to the consistency of jelly by sucking off the water through a Chamberlain t?ftt f i l t e r , and the excess water then evaporated off. Prepared in this manner the colloid contained practically no contamination from soluble salts and no particles larger than 0.002 mm. in diameter. Total chemical analysis for s i l i c a , iron, aluminum, caloium and magnesium followed the procedures adapted by the TJ. S. Bureau of Soils (1939). Phosphorus was determined by the method of Truog (1936) and the total potassium content was determined by using Browning's eerio sulphate method as modified by Allaway and Pierre (1939). Particle size distribution determinations were made according to the U. S. standard pipette method of Olmstead, Alexander and - 22 -Middleton (1930). Soil pH was measured with a Bookman glass electrode potentiometer in a 1:1 suspension of soil and water which had been allow-ed to stand for 30 minutes before readings were taken. Nitrogen content was determined by the Kjeldahl method as outlined in o.A.O.C. (1945). For a l l samples the upper plastic limit was determined by method B423-S9, the "hand method", of the American Society for Testing Materials (1944). For lower plastic l i m i t , the "hammer method" described by Russel and Wehr (1928) was essentially the procedure employed. For the majority of the samples, due to the high clay content, i t was Impossible to obtain uniform mixing without puddling. These soils were, therefore, wetted to a point within the plastic range and kept thoroughly mixed by manipulation with a hammer until the sample could no longer be maintained as a cube and prevented from crumbling. This end point was found to be definite as well as reproduoable. The pore size distribution measurements were determined by the procedure desoribed by Russell (1941). The apparatus, somewhat modified, consisted of a 90 mm. Jena sintered glass funnel, attached to one arm of a U-tube, 80 em. long, consisting of 10 mm. bore glass tubing. This apparatus (Fig. 1) mounted on a 4 inch x 30 inch piece of ply wood was attached to a suitable scale to facilitate reading the various mercury levels• The soi l samples, after having been thoroughly evacuated, were allowed to soak unti l complete saturation was reached. Usually 48 hours was sufficient. The sample was then transferred to the sintered dise and exoess water removed. - S3 SOIL CORE SINTERED GLASS FUNNEL Figure 1. - Apparatus for Determining Pore Size Distribution Curves on Soils having Undisturbed Structure - 84 -TO put the apparatus In operation the funnel tube and sintered dise were f i l l e d with recently boiled dist i l led water and attached to the U-tube, previously f i l l e d with mercury, without allowing air to enter the funnel tube. In carrying out the measurements the procedure is somewhat similar to the method of Bussell (1941). Suction is applied by allowing mercury to flow out of the U-tube into the leveling bottle. As soon as a constant mercury-water interface reading is obtained the water holding soil pores are considered to have reached equilibrium with the pressure deficiency applied. The volume of water removed is then recorded as a function of the tension. The next increment of pressure is applied by allowing more mercury to pass into the leveling bottle. It is important that the sintered glass.disc supporting the soil sample through which the water must be drawn contain no pores larger than the smallest pores to be measured i n the s o i l . The maximum tension at which air-water interface wil l exist when the water is under tension is taken from the capillary rise equation (Bussell 1941). r m 2 T where r » radius of the tube ¥31 T m surface tension of the liquid d « density of l iquid g • acceleration of gravity The above described method is perhaps not as refined as that of Bradfield and Jamison (1938) or Nelson and Baver (1940), nor Is i t applic-able to as wide a range of tensions but It does have the advantage of greater simplicity. In the method of Bussell (1941) low tension values oannot be measured when mercury Is used as the heavy l iquid. This method does not have that disadvantage. Chemical Studies The results of the fusion analysis of the soils already des-cribed are presented in Table I. In a l l cases the samples were carefully collected by horizons and represent virgin soils. The podsolic oharaoter of Vanderhoof and Nulki profiles, as contrasted with Plneview, is brought out by the high content of s i l i c a , low alumina and iron, and loss on ignition in the horizons. The oontent of a l l constituents in the C horizons for both soils is essent-ially the same, indicating the similarity of the parent materials from which they have developed. Generally speaking, the Vanderhoof and Nulki soi l horizons oontain an average of 7 to 8 per cent more s i l i c a than those of Plneview while the iron, alumina and the alkaline earth contents are slightly higher in Plneview than in Vanderhoof and Nulki. Such differences, however, are expected and commonly occur in transported materials. Plneview clay, having developed on heavy lake-laid materials, shows very l i t t l e evidence of podsollzation; in fact, the reverse appears to be the case in that with the exoeption of s i l i c a the mineral elements have accumulated in the surface horizons. This upward movement of salts suggests a glei or elay-pan condition which is evident, too, in the morphological features and has affected the A and B horizons. TABLE It Chemical Composition ef Profile Samples PINBVIEW CLAY Hori- Depth SlOg AlgOg Fe £ 0 3 CaO MgO KgO Na20 p2°5 Ignition Nitro- pH zon i n . Loss gen Al 0 - 1 54.95 25.46 12,91 5.05 3.20 2.45 2.36 0.41 34.40 0.63 4.61 *2 1 - 5 56.71 24.00 13.28 4.08 3.20 2.27 1.68 0.32 11.83 0.31 5,10 *1 8 -16 58.98 23.66 10.76 2.96 2.99 2.06 0.76 0.16 6.54 0.13 5.19 B g 16-20 61.21 22.84 9.89 2.37 3.80 2.01 0.85 0.21 3.79 0.04 7.25 C 20 - 59.94 23.07 10.26 2.15 3.88 2.20 0.85 0.20 3.89 0.04 7.56 VANDERHOOF SILTY CLAY Al 0 - 2 70.01 16.88 4.26 1.82 1.47 1.97 3.03 0.30 7.00 0.16 5.14 Ag 2 - 8 70.41 15.94 4.52 1.84 1*38 1.85 3.34 0.19 2.20 0.04 6.42 Bl 9 -15 66.46 17.93 5.82 1.89 1.91 1.82 2.76 0.15 3.05 0.04 6.44 Bg 15-20 64.94 18.58 6.03 2.02 2.38 1.88 2.44 0.22 3.23 0.04 7.20 0 25 - 65.06 18.10 6.34 2.04 2.52 1.63 2.48 0.24 2.85 0.04 8.21 NULKI CLAY Al 0 - 6 68.20 16.95 4.92 1.96 1.55 2.30 3.04 0.25 9.26 0.36 5.59 Ag 6 - 8 69.35 16.45 4.34 1*71 1.44 2.10 3.20 0.08 2.46 0.06 6.19 B l 9 -15 65.64 18.72 5.86 1.73 2.01 1.94 3.00 0.10 3.70 0.06 6.66 Bg 15-20 65.24 18.24 6.00 2.13 2.18 2.05 2.96 0.18 2.74 0.04 8.47. C 25 - 64.76 16.89 5.67 3.11 2.09 1.98 2.65 0.24 1*92 0.03 8.84 Analyses calculated to a mineral basis TABLE II: Chemical Composition of Extracted Colloids * PINEVIEW CLAY  Hori- Depth SiO s Alg0 3 Fe 2 0 3 CaO HgO K 20 PgOg Ignition zon in* Loss A i 0 - 1 56.00 26,40 9.71 0,82 2,56 1,90 0,31 11.06 Ag 1 - 5 57,00 26.56 7.82 1.04 3,22 1.93 0.15 9.92 B i 8 -16 55,50 23.06 13.30 0.98 3.25 1,80 0.06 8.84 B 2 16-20 53.80 25.60 10,90 1.23 2.94 1.85 0.11 8.76 C 20 - 53.00 25.09 11.50 2.24 4*77 1,90 0.21 7.72 VANDERHOOF SILTY CLAY  A l 0 - 2 55.00 26.01 11.29 1.63 2.67 1.82 0.92 13.35 Ag 2 - 8 55,50 27.21 8.40 1,08 3,00 1.65 0.35 8.66 Bi 9 -15 53.45 27,44 12.25 1.08 4,07 1,76 0,29 8,78 Bg 15-20 53,45 25.10 11.98 1.05 4.50 1.76 0.20 8.72 C 25 - 54,70 24.80 11.61 1.34 4*82 1,89 0,32 6.66 Analysis calculated to a mineral basis The heavy clayey deposits on which Pineview has developed w i l l naturally exert a strong influence on the degree of soi l development and as such do not reflect regional profile features (Jenny (1941))* Following the separation of the colloidal fraction a fusion analysis of these extracted colloids was made* An examination of the data, fable II, reveals marked uniformity in composition of a l l horizons of both soils. This uniformity applies as well to both parent materials and i s of such an order as might be expected in an analysis of different samples of the same profile. The percentage of s i l i c a ranges from 57 to 53, that of aluminum oxide between 27.44 and 23*06, and iron from 7*8 to 13.3. The ranges of alkalies and alkaline earths are also narrow. There i s , however, a slight accumulation of CaO and HgO in the parent material. The findings as presented are In agreement with Robinson and Holmes (1924) who suggest that under similar processes of soi l develop-ment the colloids or clay minerals gravitate towards a common mean. Harrassowitz (1926) and Marbut (1935) suggested that various molecular ratios of soils provided an effective means of determining the extent of movement of elements from horizon to horizon. In his Soil Atlas Marbut (1935) chooses the relative accumulation of sesquioxldes as a primary criterion of podsolizatlon. Thus soils having a high silioa-sesquioxide ratio in the A and a lower value In the B he considers correspondingly podsolized. Jenny (1941) agrees with this concept in so far as classical podsols are concerned, but for his own work he applies the various molecular ratios to the colloidal fraction* The molecular ratios of the colloidal fraction have been c --- 29 -calculated for Pineview and Vanderhoof and are presented in Table III* TABLE III;, f Derived Data of Extracted Colloids  • PINEVIEW CLAY Molecular Ratio Horizon Depth inches S i 0 2 R 2 0 3 S i 0 2 AI2O3 8102 F e 2 0 3 F e 2 0 3 AI2O3 .CaO / MgO A 1 2 0 3 h 0 - 1 2*92 3.60 15.40 0.25 0.30 *2 1 - 5 3.03 4.02 19.40 0.19 , 0.38 H 8 -16 2.99 4.10 11.10 0.36 0.44 B 2 16-20 2.62 3.56 13.10 0.27 0.56 C 20 - 2.78 3.60 12.25 0.29 0.65 VANDERHOOF SILTY CLAY 0 - 2 2.83 3.59 12.99 0.28 0.38 2 - 8 2.88 3.48 17.58 0.20 0.35 Bl 9 -15 2.54 • 3.20 11.60 0.29 0.42 B 2 15-20 2.76 3.61 11.85 0.31 0.53 C 25 - 2.89 3.75 12.51 0.30 0.58 While the above ratios showed variations of l i t t l e signifi -cance there are., however,indications of translocation in the s l l i e a -sesquioxide ratio as evidenced by the slightly higher value in the Ag. The silica-iron and ir.on-alutaiiB ratios show the movement to be largely that of iron. The succession of values in the A i , Ag a n d upper B of Pineview are 15.4, 19.2 and 11.1, as compared to 12.99, 17.58 and 11.6 of Vanderhoof. This would suggest that, in the process of podsoliza-tlon, removal of elements is confined largely to iron oxide. Both ao l i s , however, have sufficiently well developed morphologic-al features to justify their being classed as members of the Podsolic Soil Group. The OaO 4 Mgt>/Al203 ratio ( B n value of Jenny (1941)), while of l i t t l e value in the interpretation of relative translocations and accumulations of materials, is of importance in expressing the amount of leaching that has taken place. Both soils (Table III) show a slight but gradual increase with depth in the amount of diavalent cations. The above data therefore further substantiates the theory that, in addition to a general downward movement of unfractionated colloids, podsollzation in these heavy soils is confined to the leaching out of the more soluble constituents. The work of Byers and Anderson (1932) on the s o i l colloids and soil classification has shown that in the process of podsollzation a fractionation of the colloid takes place. In view of the preceding discussion i t is evident that i f any segregation of the colloidal matter in the Plneview and Vanderhoof soils has taken place i t has resulted mainly in the removal of iron. That considerable eluviation has taken place in both soils is clearly indicated by the higher colloid oontent in the B than in the A. To what extent this colloid deficiency in the A^ is due to erosion (horizontal elutriation) is not known but i t must be recognized a considerable portion moves In this manner. Their level topography suggest as much. In this regard the work of Tamm (1920) i s of considerable Interest. He suggests that, in North Temperate Regions, the colloidal fraction has been only slightly hydrolysed, since glacial times. The - 31 -resulting material, therefore, has a relatively high silica-alumina ratio. This supposition appears to he in harmony with the results obtained. Physio el Studies Podsollzation, as discussed in the preceding section, has been dealt with mainly in the light of chemical considerations. The prinoipal physical action in the process is the downward movement of the clay fraction from out of the upper part of the s o i l , and i ts deposition In a lower horizon. After prolonged movement in this fashion, especially in humid regions, the A horizon becomes lighter in color, coarser in texture, while the B becomes heavier due to an increased percentage of clay and oolloidal material. Normally, therefore, the B horizon would be characterized by a marked reduction in the size and amount of pore-space, increased capillarity, higher water holding capacity and greater resistance to percolation. Particle Size Distribution The important role of the distribution of particles in the soil i s obvious since texture is related to practically a l l the funda-mental physical and chemical properties. On the size of the particle depends the diameter of the pores in the s o i l , the surface area of particles, and to a considerable degree the cohesion of the s o i l . Of special interest, too, are the colloidal particles whioh, owing to their small size and degree of hydration, strongly affect the water relations as well as mechanical behavior. Although the profile samples selected were from areas class-ified as day their textures vary somewhat. The Vanderhoof samples - 32 -(Tabla 17) have the lightest texture and the Pineview heaviest. Their laoustrlne origin is reflected in the large amount of clay they contain. A l l profile samples consist of 88 to 99 per cent of s i l t and clay which serves to illustrate that heaviness is an inherited charac-teristic. Considerable evidence, however, of a developed textural B is furnished by the higher content of day and colloidal matter in that horizon. The coarse fractions, as designated by sand, are concentrated in the Ai and Ag horizons. Examination of a number of these forms revealed them to be mainly dense metallic mater i d , presumably iron deposits, surrounding soi l material. It is significant to note the high s i l t content of Vanderhoof and Nulki soils, particularly so In the Vanderhoof Ag horizon* This horizon, which constitutes nine-tenths of the cultivated layer, shows a total s i l t content of 82*35 per cent, oonsistlng domlnantly of very fine particles having effective diameters of 0*005 to 0*002 mm. In the opinion of Bussell (1932) such a particle size distribution results in "close packing" and the development of unfavor-able physled properties which cannot be mitigated against by the usual methods of amelioration. While Russell's theory appears quite applicable to Vanderhoof i t does not apply so aptly to N d k i . The reason Is associated with the high and intimately associated organic matter content of the latter. - 33 TABLE IV: Particle Size Distribution data for Horizons of Pineview, Vanderhoof and Nulki Clay in Per Cent (Dry Basis) 8 8 S o S ° « , t "So S8 8 8 &° 2 S 5 A «§d gc> d v 5 PINEVIEW Al 11.95 13.84 21.90 52.50 39.89 As 11.45 14.15 21.50 52.90 39.76 V 5.77 10.00 21.17 63.25 40.45 1.96 6.90 16.50 74.70 48.07 C 0*70 10.85 29.70 58.80 34.06 VANDEBHOOF A l 4.25 23.85 48.43 23.32 16.75 Afi 8.35 27.75 54.60 20.95 6.27 B l 3.99 22.50 47.25 86.26 18.40 B 2 2.61 20.60 44.60 30.30 21.47 C 0.96 5.44 50.83 42.67 20.31 NULKI A l 5.06 10.45 54.20 30.25 - . Ag 4.17 11.10 57.45 27.45 , B l 1.17 8.40 55.50 35.00 -B 2 2.02 10.32 53.20 34.31 -34 Pore Size Distribution To determine the size distribution of the pores in the soi l profiles under investigation the following experiment was carried out. Undisturbed samples of soil horizons were collected in brass s o i l -sampling tubes. After the samples had reached saturation capacity desorption curves were then determined as previously described. Results reported are the average of three replicates and i t is therefore believed that differences in the pore size distribution between the various hori-zons of each profile and the several soils is significant. The data presented in Fig. 2,calculated from data using the capillary tube formula mentioned earlier(indicates at once the apparent similarity and unfavourable distribution between large and small pores In the C horizons of a l l the soils. This would suggest that any unsatis-factory distribution of pores in the solum i s , in part, inherent. The curves presented in Fig. 2 for Plneview, show the presence of a group of large pores in the A^ and Ag horizons. This is evidenced by the fact that 18.44 and 26*25 per cent moisture IS withdrawn from the respective horizons at a tension of less than 40 cm. of water. The significant point here is that 21.8 to 42.5 per oent of the total porosity consists of pores having a diameter greater than 0.20 mm. (Table V). The sub-surface horizons, B^, B 2 , and C are characterized by steep slopes throughout their moisture-tension curves. The total porosity as shown in Table Y i s 57.3, 58.6 and 61.3 per eent respectively for the above mentioned horizons. The distribution of pores i s , however, some-what unfavourable in that 87.6 to 94.3 per cent of the total porosity is confined to pores having an effective diameter of less than 0.05 mm. The significant change from surface to sub-surface is not the decrease in total porosity but the abrupt decrease in the percentage of the s o i l volume occupied by air* TABLE V: A Distribution of Pores According to Donat (1937) Pore Size Group I 11 III Tf Total Equiv. Diameter poroeity of the Pores in per oent mm* 0.02 0.02-0.05 0.05-0.10 0.10-0.20 0.20 Suction Tension cm. 150 150-60 60-30 30-15 15 in Al *78.8 21.8 61.0 o A2 *57.5 42.5 69.0 H Bl *87.2 1*4 2.7 8.7 57.3 | B 2 *92.7 0.4 1.1 5.8 56.8 Ai C •87.6 3.5 8.9 61.3 h 48.0 jj Ag 86*3 2*5 1.6 2.6 7.0 45.0 to _ A3 89.1 4.0 0.5 1.8 3.8 41.8 I B l 87.1 3.4 2.3 4.0 3.2 46.0 I B 2 *81.S 6.2 5.8 7.3 49.7 C 85.8 8.1 5.2 2.5 5.0 48.6 Al *91.4 8.6 66.3 I % *63.3 19.0 17.7 48.0 § B l *91.2 3.4 5.4 51.0 I B 2 *88.5 11.5 44.7 C *88.7 3.0 4.2 4.1 43.2 * Meniseus broken at tension indicated. Values a summation of undetermined groups. a 37 -The moisture-tension Ipore size distribution) curves for the Vanderhoof profile samples are shown in Fig. 2. It is significant to note that Ag and Bj follow identical courses above the 60 cm* tension point, while the Bg and C horizons, somewhat higher on the moisture scale, have similar slopes. The gradual decrease in the moisture content accompanied by the rapid increase in tension reveals the preponderance of small pores in whioh water is held. The total loss in water, in a l l horizons, was less than 3.5 per cent. This is quite revealing when one recalls that tensions exceeded 120 em. of water. The similarity and steepness of the slopes indicate a uniform distribution of the pores and the tenacity with which water is held indicates the majority are of very small diameter. This fact is brought out clearly i n Fig. 8. The total percentage pore space varies from 41.8 in the A to 49*7 in the Bg. Columns 1 and 2 in Table VI show that a minimum of 81.3 per cent is confined to pores having an effective diameter of less than 0.05 mm. This, as pointed out in regard to Plneview, is an unfavourable relationship and prohibits free movement of air and water. The total pore-space, as well as distribution of the various size groups, is clearly brought out. This uniformity of distribution Is unfavourable for plant growth in as much as oxygen content and nitrate formation are closely linked with root development and plant growth in general. TABLE VI: Volume Relationships of S o i l , Non-Capillary and Capillary - - I Porosity in Profiles of Plneview, Vanderhoof, and Nulki Associations (at hydroscopic coefficient) Soil Horizon Soil Volume Hon-capillary Porosity % Capillary Porosity $ Plneview Al H Bl B 2 C 39.0 31.0 42.7 43.2 38.7 24.5 23.0 3.9 3.6 7.7 36.5 46.0 53.4 53.2 53.6 Vanderhoof Ax H A3 Bl B 2 C 52.0 55.0 58.2 54.0 50.3 51.3 10.0 4.6 2.2 3.9 3.7 2.6 38.0 40.4 39.6 42.1 46.0 46.0 Nulki *2 Bl B 2 C 33.7 42.0 . 49.0 43.0 56.8 13.0 5.1 4.5 11.30 4.6 53.3 42.9 46.5 33.4 38.6 Average of 3 samples Nulki curves, Fig. 2, with the exception of the C horizon, show gradual slopes up a tension of 40 cm* of water. Beyond this point the curves show a tendency to rise more steeply indicating that water is being withdrawn from the finer pores. The curves further bring out that this soil has a uniform distribution of pores of diameter greater than 40 microns (Groups III, IV & V, Table VI). This is demonstrated clearly by the fact that i an average of 10.8 per cent of the total water content is withdrawn at tensions of less than 40 cm. The Bg horizon, having 11*5 per cent of i ts total porosity occupied by pores of effective diameter greater than 0*20 mm., probably owes this favourable relationship to the numerous cracks and fissures found concentrated there* Compared to Vanderhoof these curves show distinet variations in moisture holding capacity with depth, due to the distribution of organie matter as well as a greater concentration of large or non-capillary pores in the surface s o i l . Table VI, while incomplete, nonetheless, brings out the more favourable air-water relationships. As has been previously stressed the large pores are particul-arly significant in regard to infiltration, permeability, drainage and aeration. For this reason i t was felt that particular attention should be given to these larger pores. Following the system of Baver (1940), i t was found convenient to classify them as non-capillary and capillary. This is a purely arbitrary system but according to Baver toe non-capillary porosity has the significance of being "The sum of the volumes of the will not large pores, which/hold water tightly by capillarity*', and capillary porosity "The sum of the volumes of the small pores that hold water by capillarity. They are responsible for the water capacity of soi ls ." - 40 -In estimating the percentages of large pores i t was assumed the amount of water withdrawn from zero tension to that of the flex point on the moisture-tension curve to be a measure of the larger or non-capil-lary pores. This tension varied with horizons, i ts value ranging from 20 to 40 cm. of water (Fig. 2). The data presented in Fig. 2 makes possible the calculation of the volume relationships of s o i l , water and a i r . These percentages are tabulated in Table VI and presented graphically in Fig. 3. Sinoe the downward movement of water in soils must take place through the different horizons infiltration rate, porosity and permeability therefore may be greatly different. Wollny (1885) has demonstrated this fact very satisfactorily by a 1 cm. layer of loam placed in a 50 cm. column of sand. Permeability of water, he found, was reduced approximately 50 times. A rather simple analogy of this phenomena may be obtained i f one visualizes this semi-impermeable layer to a constriction in a funnel. A clear picture of the s o i l porosity i s given by the profiles in figure 3. Marshall s i l t loam showing ideal relationships of soil* water and air throughout its profile (Baver (1940)) serves as a control. The trend of the non-eaplllary porosity, in Plneview, shows a typical funnel-like arrangement. The maximum constriction occurs in the B± and Bg horizons and corresponds to non-capillary porosity values of 3.9 and 3.6 per cent respectively. This constriction coincides also with the zone of maximum llluviation (Table V). ^ 1 P E R C E N T Of T O T A L V O L U M E PINEVIEW C L A Y ASSOCIATION P E R C E N T OF T O T A L V O L U M E VANDERHOOF SILTY CLAY ASSOCIATION P E R C E N T OP T O T A L V O L U M E NULKI CLAY ASSOCIATION sf qp_ i P E R C E N T O f T O T A L V O L U N M A R S H A L L S I L T L O A M FIG. J V O L U M E R E L A T I O N S H I P S OF SOIL TO C A P I L L A R Y AND N O N - C A P I L L A R Y P O R E S FOR THE PROFILES OF PINEVIEW, NULKI.AND VANDERHOOF C L A Y S . AVERAGE OF 3 S A M P L E S - 42 -The trends In the pereentages of porosity in Vanderhoof profile follow the tendencies shown in Fig. 3. Throughout the entire profile, excepting the shallow A_, the percentages are very small ranging from 2.6 in the 0 horizon to 4*6 in the Ag. In the ease of Nulki soils a reasonably good relationship exists in the A_.< When i t is recalled that this horizon averages'six inches in thickness, contains a high organie matter content, this relation-ship, though far from ideal, is far superior to that of Vanderhoof. An abrupt constriction, however, occurs at the 10 to 18 inch depth, which corresponds to the zone of maximum accumulation. The distinct buldge in the Bg, while difficult to explain satisfactorily, is undoubtedly related to the numerous cracks and fissures which characterize this horizon. It might be concluded from the above data water intake, water movement, air-carbon dioxide exchange, while only moderately satis-factory in a l l surface horizons, is far from satisfactory in the sub-solis. These conclusions fully support field observations. Plasticity Constants The lower plastic l imit, liquid l imit, and plasticity index have been determined. The lower plastic limit represents the moisture content at the ohange from friable to plastic consistency. It, therefore, represents the minimum moisture content at which a s o i l w i l l puddle. The liquid limit is the moisture content at which the various surface phen-omena associated with water films permit the soi l mass to flow under an applied force. The plasticity index (the difference between the upper plastic limit and the lower plastic limit) is a measure of the applied force required to mold a s o i l . Table VII shows the plastic indices and plastic number together with that of the 2 micron clay fraction of the several soils. Except for the A± and Ag horizons of the s o i l profiles the lower plastic limit shows l i t t l e variation, the range being from 22.3 to 27.0. The higher values for the Ax undoubtedly are due to the higher organic matter content. The Ag horizons, in addition to having the lowest clay and organic matter contents,have also the lowest lower plastic limits. The effect of clay content (2 micron) on the liquid limit and hence the plasticity index is distinct in the B and Ag horizons* Within the Nulki and Vanderhoof profiles there is a definite trend of these indices. With the exception of the Ag which is quite low, there is a grad-ual increase with depth. The Plneview profile shows Intermediate values for the Ax, B, and 0 horizons, a low Ag, and exceptionally high value in the Bg. Bussel (1928) reported profile data showing a correlation relationship between plasticity numbers and 5 micron clay that was prac-tically linear. Baver (1940) also reports a similar relationship and points out that plasticity is not exhibited by soils having less than 20 per oent micron clay. In this study, while a good correlation between plasticity index and 2 micron clay is obvious, no attempt to elaborate on i t will be attempted since i t is felt an insufficient number of samples were analysed. The cultivated depth of Plneview and Vanderhoof clay (average Ax and Ag) have lower plastic limits of 37.1 and 31*7, upper plastic or "liquid" limits of 54.2 and 35.5 respectively. These soils should not be 44 worked until the moisture content has fallen below that indicated by their plastic limits when the soil is entering the friable state. The addition of organic matter, as evidenced by Nulki (lower plastic limit 40.7 per cent) w i l l significantly raise the percentage of water at which i t is advisable to cultivate them. 45 -TABLE VII: Lower Plastic Limit, Liquid Limit, and Plasticity Index Values for Average Profiles of Plneview, Vanderhoof, and Nulki Associations  Clay Horizon Pineview Vanderhoof Nulki 0,002 an.  Lower Plastic Limit (per cent) Al 39.2 34.4 40.5 52.50 Ag 34.0 26.1 26.6 52.90 »1 27.0 23.6 23.0 63.25 B 2 26.1 22.6 22.3 74,70 C 27.1 22,9 23.1 58.80 Liquid Limit (Per cent) Al 60.6 39.2 61.7 23.32 Ag 47.9 31.7 34.6 20.95 B l 53.4 33.6 46.1 26.26 Bg 72.7 37.8 49.0 30.30 C 49.5 43.6 51.2 42.67 Plasticity Index (per cent) A l 21.4 4.6 21.2 50.25 Ag 13.9 3.6 8.0 27.45 B l 26.4 10.0 23.0 35.00 Bg 46.6 15.2 26.7 34.31 - 46 VANDERHOOF CLAY A, B , B * C I B , C A , B , C Z 1 EZ2 I N N W N Ml INI l l l l PINEVIEW CLAY L e z z z z z a ii 11111"i11111• iii NULKI CLAY c ZZZZ2 " " ' ' I I I I II I I I I I I K W W N II i i i i i i i i n K W W W W W W N II I 11111 " " I I I I H K X X X X X X X X V X I : c r V7zn II M I N I IN i o n : 10 2 0 3 0 4 0 5 0 P E R C E N T 6 0 7 0 M O I S T U R E 10 2 0 3 0 4 0 P L A S T I C I T Y R A N G E P L A S T I C I T Y N U M B E R Figure 4. - Plasticity Relationships of Pineview, Vanderhoof and Nulki Profiles. - 47 DISCUSSION AND SUMMARY Fleld observations together with the supporting laboratory tests conducted have given much valuable information on the physical problems attendant the Pineview. Vanderhoof and Nulki Associations* Pineview clay, under undisturbed field conditions, was observed to have an extremely tight, plastic and heavy subsoil through which roots and moisture rarely penetrate* The surface, while also of heavy texture, was open, loose and readily permeable to roots and water. The downward movement of colloids, as disclosed by the chemical analysis and the data derived therefrom (Tables I, II and III), supports the field observations. The character of this tight B horizon is clearly brought out by the pore size distribution data as presented in Table V and graphically shown in Fig. 2. These data fully support the field observations and i t may therefore be assumed that the "clay-pan" layer owes its origin to the downward movement of clay and colloids and their deposition In the Interstitial voids in the subsoil. The net result of this impervious layer to agriculture is that the surface horizons are saturated in spring and f a l l thus characteriz-ing i t as slow, wet soi l that is difficult to maintain in proper t i l t h . The significance of such a layer in a soi l has been well demonstrated by the work of Wollny (1883) as previously stated. Remedial measures, therefore, must center around methods and practices which wil l tend to increase permeability, aeration, drainage, and conditions which in general favour plant growth. - 48 -Vanderhoof Association, as disclosed by the particle size distribution data, is a soil consisting mainly of fine s i l t particles having an effective diameter range of 0.005 to 0.002 mm. This extreme uniformity of fine particles, when associated with the crit ical ly low humus content, produces a condition not unlike that of quicksand. The commonly observed running together, settling, crusting, and low permeability are obviously associated with the above condition. The laboratory data presenting particle size and pore size distribution, as shown on Table IV and Fig. 2, verify the observed behavior. This assumption la also fully supported by the work of Bussell (1932). SO I IB containing over 15 to 25 per cent fine s i l t (English standards) he found to be diffioult to drain and work. The phenomena, he explained, Is due to the "close packing" of the soil particles, and not a colloidal property. Such soils, in his opinion, are extremely difficult to maintain in proper t i l t h . The unfavourable particle size distribution and the low organic matter content, as demonstrated, have resulted in a weakly aggregated structure, readily destroyed by cultivation. Obviously immediate remedial measures are needed to improve this unfavourable condition. While this paper i s not concerned with remedial or f e r t i l i t y aspects i t may, however, be stated that the solution to the problem depends on co-operation between agronomists, engineers, chemists, soil physicists and faimers. - 49 -Nulki soils, which have developed on similar parent materials to Vanderhoof, show very different physical properties* Particle size distribution as presented in Table IV is very similar to Vanderhoof but organic matter, pore space and pore continuity, as well as the plasticity indices, are considerably higher. Field observations indicate this soi l to be superior in every aspect to either Pineview or Vanderhoof* The reason for which, obviously l ies in the amount, kind and distribution of organic matter* CONCLUSIONS 1* On the basis of total chemical analyses of the soils, colloids, and the data derived therefrom i t i s shown that Pineview, Vanderhoof and Nulki Associations are a l l members of the Podsolic Group of Soils. 2. In the case of Pineview parent material exerts a very pronounced influence on soil development. S. The two soils, Vanderhoof and Nulki, have developed on essent-ial ly similar parent material. 4. Field observations supported by ohemlcal and physical data point out that: (a) the unfavourable physical properties associated with Vanderhoof soils are primarily the result of particle size distribution and low organic matter content, and (b) the tight, impervious B horizon of Pineview clay is partially an inherited characteristic and in part developed. 5. A modification of Russell's (1941) pore size distribution apparatus is presented* - 50 -BIBLIOGRAPHY Allaway, H . , and Pierre, W. H. (1939) Availability, fixation and liberation of potassium in high lime soils. Jour. Amer. Soc. Agron., 31: 940 - 953. American Society for Testing Materials (1944) Procedures for testing soils. Publ. Amer. Soc. for Testing Mater., 260 S. Broad St*, Philadelphia 2, Pa. Anderson, M. S. , and Byere, H. G. (1930) Character of the colloidal materials in the profiles of certain major soi l groups. U. S. Dept. Tech. Bui. 228 ASsoo. of Office Agric. Chemists. Methods of analysis. 5th Ed. Washington, D. C. Atterberg, A. (1911) Die Plastialtat der tone. Int. Mitt, fflr Bodenk., 1:10-43 (1912) Die konsistenz und die bindigkeit der b8den. Int. Mitt, fur Bodenk., 2:149-189. Baver, L. D, (1938) Soil permeability in relation to non-capillary porosity. Soil Sci . Soc. Amer. Proo., 3:52-56. Baver, L. D. (1940) Soil physics. Published by John Wiley and Sons, New York City. Bradfield, R. (1936) The value and limitations of calcium in soil structure. Amer. Soil Sur. Assn. Bui. 27:31-32. Bradfield, R., and Jamison, V. C. (1938) Soil structure - attempts at its quantitative characterization. Soil Sci. Soc. Proc. 3:70-76. (1926) Burger, H. Die physikalische Bodenuntersuchung inbesonde re die methoden zur bestimmung der luftkapazitat. Proo. 4th Int. Conf. Soil Sci . (Rome), 2:150-163. Byers, H. G. and Anderson, M. S. (1932) The composition of soi l oolloids in relation to s o i l classification. Jour. Phys. Chem. 36:348-366. Childs, E . C. (1940) The use of soil moisture characteristics in soil Studies. Soil S o i . , 50:239-252. De Sigmond, A. A. J . , (1938) The principles of soil science. Thomas Murphy and Co. London. - 51 -Dojarenko, A. J . (1924). Sci . Agron. No.7 - 8:451-74 Dokuchaev, T. V. (1879). Abridged historical account and c r i t i c a l examination of the principal soi l classifications existing. (Russian) Trans. St. Petersburg Soc. Nat. 10:64-67. Donat, J , (1937) Das gafuge des bodens und dessen kennzeichung. Trans. 6th Com. Int. Soc. Soil Sci . (Zurich), Vol„B:423-39 Farstad, L. and Laird, D. 0. (1945). Soil surrey of the Vanderhoof Smithere area (unpublished). Qedrolz, K, K. (1929). On the absorbing properties of soils. State publishing house, "Novaya Derevnya" Moscow* Glinka, K. D. (1927). Pochvovedenie, Pedology, Moscow. — (1928). The great soil groups of the world and their development. Translated from the German by C. F. Marbut. Haggart, D. A. (1944). A chemical study of the Fine-view and Vander-hoof clays. (Graduate essay, unpublished). Haines, W. B. (1930). On the existence of two equilibrium series in soil capillary phenomena. Second Intn'l . Cong. Soil S c i . , 1:8-14. Harper, H. J . and Volk, G. W. (1936). A method for the microscopic examination of natural structure and pore space in soils. Soil Sci . Soc. Amer. Proc. 1:39-42. Harrassowitz, H. (1926). Laterit, Fortscar. Geolog. und Paleent, Vols 4:253-566. Hoffer, G. N. (1945). Fertilized corn plants require well aerated s o i l . Better Crops with Plant Foods 29:(1). Jenny, H. H. (1941). Factors of soi l formation. McGraw-Hill Book Co. Inc., N. York and London. Joffe, J . S. (1936). Pedology. -Rutgers University Press. New Brunswick, New Jersey. — — (1941). Pedology in the service of soil science. Soil Sci. Soc. Amer. Proc. 6:68-77. Kelley, C. C. and Farstad, L. (1946). Soil survey of the Prince George area, B 0 C. Report No.2 of British Columbia Soil Survey, Kelewna, B. C. 58 -Kopscky, J . (1914). Die physikalisehen eiganschaftan des bodens. Int. Mitt. Bodenk., 4:138^198. (1927). Investigations of the relations of water to s o i l . Proo. First Int. Cong. Soil S c i . , 1:495-503. Kubiena, W. L. (1938). Mieropedology. Collegiate Press, Ames, Iowa. Lawton, K. (1945). Soil Aeration affects ferti l izer needs. Better Crops with Plant Foods. 30:(8). Marbut, C. F. (1935). Soils of the United States. Atlas of American Agriculture Part 3. U. S. Govt. Printing Office, Wash. D.C. Mattson, S. (1930). The laws of colloidal behavior IV Isoelectric precipitates, Soil So. 31:57-78. Method and procedure of s o i l analysis (1939). U.S.D.A. c irc. 139. McGfeorge, W. T . , and Breazeale, 7. F. (1938). Studies on soil struc-ture: Effect of puddled soils on plant growth. Tech. Bui. 72, Univ. of Ariz. Nelson, W. H . , and Baver, L. D. (1940). Movement of water through soils in relation to the nature of the pore. Soil Sci. Soc. P r o c , 5:69-76. Olmstead, 1. B . , Alexander, L. T . , and Middleton, H. E . (1930). A pipette method of mechanical analysis of soils based on improved dispersion procedure. U.S.D.A. Tech. Bui. No. 170. Bamann, E. (1911). Bodenkunde. J . Springer, Berlin. Bobinson, W. 0 . , and Holmes, B. S. (1924). The chemical composition Of soil colloids. U.S.D.A. Bul l . 1311. Rus8el, J . C. (1928). Report of committee on soil consistency. Amer. Soil Sur. Ass'n. Bui. 9:100-112. Russel, J . C , and Wehr, F. M. (1928). The Atterberg consistency constants. Jour. Amer. Soc. Agron. 20:354-372. Russell, E . J . (1932). Soil conditions and plant growth. 6th Ed. Longmans, Green and Co., London. Russell, M. B. (1941). Soil pore distribution as a measure of soil structure. Soil Sci . Soc. of Amer. P r o c , 6:108-112.v Schofield, R. K. (1935). The pF of the water in s o i l . Trans. 3rd. Int. Soil Cong. 8:37-48. - 53 -Smith, F. W., and Cook, B. L. (1947)• Better Crops with Plant Food. 31:(3). Smith, H. W., and Bhoades, H. F. (1942). Physical and chemical prop-erties of soil profiles of the Scott, Fillmore, Butler, Crete, and Hastings Series* Has. Bui. 126, Lincoln, Neb. Tamm, 0. (1920). Soil studies in the needle forest region of northern Sweden. Meddel. Statens. Skogarforsoksanst (Sweden) 17:49-300 (Reported by Marbut). Thorp, J . (1935). Soil profile Studies as an aid to understanding recent geology. Bui. Qeol. Soc. China, 14:359-392. Truog, E . (1935). Private communication. Williams, V. R. (1927). General agronomy and the fundamentals of pedology. Moscow. Wollny, E. (1885). Untersuchungen fiber die kapillare leitung des wassers in boden. Forisoh. Geb. Agr.-Phys., 7:269-308. 

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