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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)  -oooThe University of British Columbia May, 1947  - iJjA^  ^Jps  Ai f 1-  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 lexture Structure . . . . . . . . . . . .  . . . .  7 7 7  Methods of Specifying Soil Structure . . 7 Porosity as a Measure of Soil Structure . 8 Factors Affecting S o i l Porosity . . . . . 11 Plant Responses to Aeration 12 Soil Consistency  14  Soils Subjected to Study  16  Description of Soils  .  Experimental  17 21  Methods of Analysis Chemical Studies • Physical Studies  21 25 31  Particle Size Distribution Pore Size Distribution Plasticity Constants  .  31 34 4S  Discussion and Summary  47  Conclusions  *  Bibliography  •  9  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 i n 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 Distribution eurves*hav!ng*Undisturbed Structure  23  2  Moisture Desorption Curves for the Various Horizons of Vanderhoof, Nulki, and Pineview Associations  36  Volume Relationships of S o i l to Capillary and Non-Capillary Pores for the Profiles of Pineview, Nulki, and Vanderhoof Clays • .  41  3  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 i n the Central Interior of B r i t i s h Columbia was related to f i e l d observations.  The r e s u l t s of the chemical data on the whole  s o i l as well as the c o l l o i d f r a c t i o n (.002) show varying degrees of podsolic development due to variations i n parent material. Pore-size d i s t r i b u t i o n and p a r t i c l e - s i z e  distri-  bution studies point out that the unfavourable physical properties associated with Vanderhoof s o i l s are p r i m a r i l y the result of p a r t i c l e - s i z e d i s t r i b u t i o n and low organic matter content; aad the t i g h t , impervious B horizon of Pineview clay i s p a r t i a l l y an inherited c h a r a c t e r i s t i c and p a r t i a l l y developed. A simple modification of M.B. Russell's poresize distributjbawapparatus  i s presented.  INTRODUCTION S o i l represents a three phase system, s o l i d , liquid and gas, and, as such, i s 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 correlated with chemical data*  S o i l structure as related to drainage,  aeration, erosion and favorable t i l t h has recently gained wide recognition.  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 demonstrated certain peculiarities in relation to moisture and showed undesirable physical properties under cultivation*  These observations  prompted the study whieh i s 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 i e l d , 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 affective 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* to provide a background for discussion ,1  r  Thus in order  the process of podsollza-  tion and physical properties associated thereto are briefly reviewed* Podsolizatlon Podsol soils are usually i n evidence In forested areas and the most prominent characteristic of these soils i s 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 s o i 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 i s precipitated  f i r s t , often in a f a i r l y 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 i s not known* Gedroiz (1929), interpreting podsollzation i n the light of base exchange reactions, suggests that the inorganic exchange complex undergoes gradual decomposition into i t s constituent oxides as the  replacement of bases by hydrogen becomes excessive. In the opinion of Battson (1930) podsolizatlon i s closely related to conditions of acid hydrolysis which exists In the humid temperate regions*  Acid percolating waters, he explains, hydrolize the  clay minerals i n 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 podsolizatlon finds f u l l expression i n 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* Is divided into horizons Aq, &1» Ag, *1» Bg, &3, and C*  The profile  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 l e v e l , as well as the length of time the processes Involved have bean active*  Under oertain conditions the regional profile do not find typical expression*  character1stice  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 i s known as glei-formatioa.  Accordingly, In low-lying areas or heavy wet soils podsollzation, g l e i 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 i s perhaps the most expressive.  Jenny (1941) Is the foremost  exponent In the use of ratios and advocates the following quotients and symbols! SlOg AlaPg / FegOg  .  siliea-sesqnloxide ratio  SlOg  •  sa value  a FegOg  -  sf value  KgO / HagO /• gaO .  Ba value  AI2P3 8 1 0  AI2O3 i  GaO 4 MflO  s  Bai 1 value  Al ©3 2  These ratios serve as a means of detecting the relative movemant 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 percentage of SiOg*  If one assumes that AlgOjj is the least mobile element, due  to i t s insolubility at neutrality, then ratios involving aluminum represent relative gains and losses in the various horizons.  An inspection,  therefore, of silica-alumina ratios is l i k e l y to reveal any previous faulty conclusions. By way of summary, the process of podsolizatlon Is dominant in areas of high humidity and forest vegetation* two phases*  The process comprises  The f i r s t 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 s o i l minerals with subsequent translocation of the products i n true solution, eolloidal suspension, or both.  Physical Properties of Soils In studying the physical behavior of the soils under discussion 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 i s 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 S o i l 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 i s done in the ease of s o i l texture. Methods of Specifying S o i l Structure The methods of specifying s o i l 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 i s 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 i s a direct determination, aims to measure the percentage of stable secondary particles. employed techniques are used. tlon and sedimentation.  They are:  Three commonly  wet and dry solving, e l u t r i a -  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 s o i l 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 S o i l Structure The porosity or pore-space i s 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 i s only necessary to measure the apparent specifio volume and the moisture content of the s o i l when in equilibrium with water under different suction tensions.  These specifications may be given as the d i f -  ferent volumes of a i r and volume of water per unit volume of s o i l 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  s o i l sample to reach capillary saturation, at which point i t i s assumed a l l capillary pores are f i l l e d , then calculate total capillary and noncapillary porosity from volume, weight, moisture content and density of particles.  In this method i t is assumed that capillary porosity i s equal  to the per cent moisture per unit volume, and non-capillary porosity i s the difference between the total and capillary porosity. While numerous objections to the foregoing methods for determining s o i l porosity have been registered they have nonetheless proven to be of great value in characterizing a i r and water relationships in the soil.  The most serious objection, in addition to the rough approximation  of the designations, i s that no means of expressing the pore size and continuity has been provided. Recant developments have led to the measurement of the s o i 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 s o i l phenomena, such as aeration and movement and storage of water are determined by the number, size distribution and configuration of the s o i l pores i t would appear that s o i l structure can best be evaluated by measuring structural moments that can be interpreted 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 determination of moisture desorption curves on s o i 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 soil.  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 S o i l 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 s o i 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 s o i l 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) i n 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 i s aware of the deterioration in s o i 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 cultivation Putnam s i l t loam had lost 38 per cent of i t s 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  gate formation with soil-forming climatic factors.  aggre-  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. substances, he continues, are probably due to poor aeration.  Toxic It is to  be concluded, therefore, that i f an impermeable layer exists in the subsoil, water or a i r 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 a i r 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  f a i r l y 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 s o i l aeration on the growth and yield of sugar beets.  The  data, unfortunately, does not include porosity determination but definitely confirms the high requirements of sugar beets.  An example of  their results is given, in part, as follows. Yield of Sugar Beet Roots Physical treatment  Smith and Cook (1947)  Mean dry weight for  of S o i l  sugar beat roots*  1.  Normal  2.  Aeration  3.  Compaction  1*43  4.  Aeration and Compaction  5.19  *  15.45 17*68  Series average in grams.  Mean of 4 replicates.  In studying the failure of com to respond to f e r t i l i z e r s 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  f i e l d 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 i s  due the decrease in porosity.  Hoffer (1945) attributes the failure of  corn to respond to f e r t i l i z e r s , on certain Indiana s o i l s , 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 a i r 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 s o i l as well as those added as commercial f e r t i l i z e r s . As previously mentioned exact data on the a i r requirements of various plants is lacking.  However there seems to be ample justification  that the non-capillary pore-space of the seed bed i s a very important factor i n successful crop production. S o i l Consistency In the Report of the Committee on S o i l 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 i r s t to attach much significance to s o i l consistency and recognized (1912) six consistency forms.  Baver  (1940) condensed them to four relating each to s o i l moisture content as follows:  - 15 S o l i Consistency Variation with Moisture Dry  Moist  Hard  Soft, friable  Clods form here  Optimum conditions for working  Consistency Forms  Barer (1940) Wet Tough, plastic, sticky Soil puddles here  Viscous, sticky S o i l runs together here  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 s o i l moisture range, suggested three constituents of particular significance to the classification of s o i l s .  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 i s 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) i s 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 d a y  varied from 24*9 to 54*4 per cent; hence one might expect f a i r l y 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  affected by clay content  is primarily  **; 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 i r s t s o i l survey report of the Soils of the Central Interior of B r i t i s h Columbia was the Report of the Prince George Area by Eelley and Farstad (1946).  The main agricultural s o i l in the area  was then mapped and classified as Pinsview Clay Association. In the Vanderhoof d i s t r i c t , 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 i n profile development, chemical and physical properties, as well as agricultural adaptation.  While the  authors brought together a l l the available information regarding s o i l s , processes of s o i 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 s o i 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 s o i l 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 i s as follows: Pineview Clay:  Level to undulating topography, dense mature stands of  forest dominate the landscape of Pineview clay. S per cent slope which faced east.  The p i t was dug on a  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.  Pineview Clay Soil Profile Horizon AQ  Depth inches  Description  4 in.  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 structure, somewhat heavier than Ag.  Bx  8 -16  Bg  16-22  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 d a y pan. Light gray broken laminations alternating with brown ones. Less compact than above horizon.  C  22 /  Vanderhoof S i l t y Clay:  Heavy varved clay, quite plastic and sticky when wet. Vanderhoof s i l t y clay was chosen to represent  the large area of podsolic soils occupying the clay plain in the Vanderhoof d i s t r i o t .  Approximately 275,000 acres of this type have  been mapped. Level to undulating r e l i e f features characterize the landscape. With the exception of scattered clearings the area i s domlnantly forested.  The profile was sampled in an apparently undisturbed site  covered with mature stands of spruce.  Vanderhoof S i l t y Clay Soli Profile Horizon ________  Depth inches  Description ____________»_  AQ  2 in*  Organic remains of needles, twigs, leaves, mosses, etc. Partially decomposed.  Ai  0-2  Dark grey s i l t y clay, weak platy structure•  Ag  2-8  Light gray to ashy gray s i l t y clay. Compact and harsh consistency. Massive, runtogether 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 s i l t y clay, large angular nut structure.  B_  9 -15  Brown heavy s i l t y clay, very plastic and sticky when wet, hard when dry. Strong angular irregular nutty structure. Impervious to roots or water except along cracks* Contains small concretionary forms.  B  2  15-20  Gray and dark gray alternating bands of heavy s i l t y clay* Water tight consistency. Angular fragmental structure. Somewhat more compact than B_ above*  B  3  20-25  Very like B , more laminated.  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*  C  Nulki Clay:  2  The Nulki soils are located in the Vanderhoof clay plain  and have developed on essentially the same parent material as the Vanderhoof s i l t y 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  Depth Inches  Description  *1  0-6  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.  *2  6-8  Gray to light gray plastic clay nutty structure with tendency to platiness in upper portion. Numerous small concretionary forms scattered throughout.  As  8-9  Transition similar to Ag above but having somewhat larger and more sharply angular nutty structure.  9 -15  Brown gray compact plastic clay with occasional red-yellow mottlings. Weakly developed oolumnar-like structure which breaks readily into sharply angular nutty fragments - few concretions.  15-20  Gray to brown gray compact clay - consisting of laminated clay broken by vertical cracks and fissures thus producing a strong angular nutty to blooky type of structure* No effervescence.  20-25  Transition. Moderately compact, partially weathered parent material.  25 /  Strongly laminated clay of gray eolor. Lime speckled throughout. Very compact and impervious.  B  2  Samples were collected i n the f a l l of 1946 when the s o i 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 Vanderhoof and Pineview clays described above was as follows.  A suspension  containing the colloidal matter was obtained by shaking the s o i l with water, in the proportion of 1 to 5, in the Bouyoucos mechanical s t i r r e r . No dispersing agent was used.  This suspension was then added to 14  l i t e r s 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).  S o i l 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 u n t i l 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 s o i l samples, after having been thoroughly evacuated, were allowed to soak u n t i l complete saturation was reached. was sufficient.  Usually 48 hours  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 d i s t i l l e d water and attached to the U-tube, previously f i l l e d with mercury, without allowing a i r to enter the funnel tube. In carrying out the measurements the procedure i s somewhat similar to the method of Bussell (1941).  Suction i s applied by allowing  mercury to flow out of the U-tube into the leveling bottle.  As soon as  a constant mercury-water interface reading i s obtained the water holding s o i l 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 i s applied by  allowing more mercury to pass into the leveling bottle. It is important that the sintered glass.disc supporting the s o i l 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 w i l l exist when the water i s under tension i s taken from the capillary rise equation (Bussell 1941). r m 2 T ¥31  where r » radius of the tube T m surface tension of the liquid d « density of liquid 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 applicable 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 i q u i d .  This method  does not have that disadvantage. Chemical Studies The results of the fusion analysis of the soils already described are presented in Table I.  In a l l cases the samples were carefully  collected by horizons and represent virgin s o i l s . The podsolic oharaoter of Vanderhoof and Nulki profiles, as contrasted with Plneview, i s 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 i s essenti a l l y the same, indicating the similarity of the parent materials from which they have developed. Generally speaking, the Vanderhoof and Nulki s o i 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  Depth in.  Al  0-1  54.95  25.46  12,91  5.05  3.20  2.45  *2  1-5  56.71  24.00  13.28  4.08  3.20  *1  8 -16  58.98  23.66  10.76  2.96  g  16-20  61.21  22.84  9.89  20 -  59.94  23.07  10.26  C  Fe 0  PINBVIEW CLAY KgO Na 0 MgO  Horizon  B  AlgOg  CaO  SlOg  £  3  2°5  Ignition Loss  Nitrogen  pH  2.36  0.41  34.40  0.63  4.61  2.27  1.68  0.32  11.83  0.31  5,10  2.99  2.06  0.76  0.16  6.54  0.13  5.19  2.37  3.80  2.01  0.85  0.21  3.79  0.04  7.25  2.15  3.88  2.20  0.85  0.20  3.89  0.04  7.56  0.30  7.00  0.16  5.14  2  p  Al  0-2  70.01  16.88  4.26  VANDERHOOF SILTY CLAY 1.82 1.97 1.47 3.03  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  0.25  9.26  0.36  5.59  Al  0-6  68.20  16.95  4.92  1.96  NULKI CLAY 2.30 1.55 3.04  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  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  B  Analyses calculated to a mineral basis  TABLE II:  Chemical Composition of Extracted Colloids * PINEVIEW CLAY  Horizon  Depth in*  SiO  3  Fe 0  Ai  0- 1  56.00  26,40  Ag  1 - 5  57,00  Bi  8 -16  B  2  C  CaO  HgO  K0 2  PgOg  Ignition Loss  9.71  0,82  2,56  1,90  0,31  11.06  26.56  7.82  1.04  3,22  1.93  0.15  9.92  55,50  23.06  13.30  0.98  3.25  1,80  0.06  8.84  16-20  53.80  25.60  10,90  1.23  2.94  1.85  0.11  8.76  20 -  53.00  25.09  11.50  2.24  4*77  1,90  0.21  7.72  s  Alg0  2  3  VANDERHOOF SILTY CLAY Al  0- 2  55.00  26.01  Ag  2- 8  55,50  27.21  Bi  9 -15  53.45  Bg  15-20  C  25 -  11.29  1.63  2.67  1.82  0.92  13.35  8.40  1,08  3,00  1.65  0.35  8.66  27,44  12.25  1.08  4,07  1,76  0,29  8,78  53,45  25.10  11.98  1.05  4.50  1.76  0.20  8.72  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 s o i 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 i n 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 s o i l development 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. Atlas  In his Soil  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  Si0  2  Si0  R 0  3  AI2O3  8102 Fe 0  2  2  2  Fe 0 2  3  3  .CaO / MgO  AI2O3  A1 0 2  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  16-20  2.62  3.56  13.10  0.27  0.56  20 -  2.78  3.60  12.25  0.29  0.65  2  C  3  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  15-20  2.76  3.61  11.85  0.31  0.53  25 -  2.89  3.75  12.51  0.30  0.58  C  2  While the above ratios showed variations of l i t t l e s i g n i f i cance there are., however,indications of translocation in the s l l i e a sesquioxide ratio as evidenced by the slightly higher value i n the Ag. The s i l i c a - i r o n and ir.on-alutaiiB ratios show the movement to be largely that of iron.  The succession of values in the A i , Ag  Pineview are 15.4, 19.2 and 11.1, of Vanderhoof.  a n  d upper B of  as compared to 12.99, 17.58 and 11.6  This would suggest that, in the process of podsoliza-  tlon, removal of elements i s 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>/Al 0 2  3  ratio ( B  n  value of Jenny (1941)), while  of l i t t l e value i n the interpretation of relative translocations and accumulations of materials, i s 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 i s 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 s o i l classification has shown that in the process of podsollzation a fractionation of the colloid takes place.  In view of the preceding  discussion i t i s 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 i s clearly indicated by the higher colloid oontent in the B than in the A.  To what extent this colloid deficiency in the A^  i s due to erosion (horizontal elutriation) i s 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 i s the downward movement of the clay fraction from out of the upper part of the s o i l , and i t s deposition In a lower horizon.  After prolonged movement i n 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 porespace, increased capillarity, higher water holding capacity and greater resistance to percolation. Particle Size Distribution The important role of the distribution of particles in the s o i l i s obvious since texture i s related to practically a l l the fundamental 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 classified as day their textures vary somewhat.  The Vanderhoof samples  - 32 (Tabla 17) have the lightest texture and the Pineview heaviest.  Their  laoustrlne origin i s 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 i s an inherited characteristic.  Considerable evidence, however, of a developed textural B is  furnished by the higher content of d a y and colloidal matter in that horizon. The coarse fractions, as designated by sand, are concentrated in the A i and Ag horizons.  Examination of a number of these forms  revealed them to be mainly dense metallic mater i d , presumably iron deposits, surrounding s o i l material. It is significant to note the high s i l t content of Vanderhoof and Nulki s o i l s , 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 unfavorable 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  t S  "So 5A  So  S°  S8 «§d  88 gc>  « ,  d  &°  2 5  v  PINEVIEW Al  11.95  13.84  21.90  52.50  39.89  As  11.45  14.15  21.50  52.90  39.76  5.77  10.00  21.17  63.25  40.45  1.96  6.90  16.50  74.70  48.07  10.85  29.70  58.80  34.06  V  C  0*70  VANDEBHOOF Al  4.25  23.85  48.43  23.32  16.75  Afi  8.35  27.75  54.60  20.95  6.27  Bl  3.99  22.50  47.25  86.26  18.40  2  2.61  20.60  44.60  30.30  21.47  C  0.96  5.44  50.83  42.67  20.31  - .  B  NULKI Al  5.06  10.45  54.20  30.25  Ag  4.17  11.10  57.45  27.45  Bl  1.17  8.40  55.50  35.00  -  B  2.02  10.32  53.20  34.31  -  2  ,  34 Pore Size Distribution To determine the size distribution of the pores in the s o i l profiles under investigation the following experiment was carried out. Undisturbed samples of s o i l 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 i s therefore believed that differences in the pore size distribution between the various h o r i zons of each profile and the several soils i s significant. The data presented in F i g . 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 i s 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 i s 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 , and C are characterized by 2  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 i s 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)  in  o  H  |  Ai  jjj  to _  I I I  § I  11  III  Tf  0.02  0.02-0.05  0.05-0.10  0.10-0.20  150  150-60  60-30  30-15  I  Pore Size Group Equiv. Diameter of the Pores in mm* Suction Tension cm.  0.20  Total poroeity per oent  15  Al  *78.8  21.8  61.0  A2  *57.5  42.5  69.0  Bl  *87.2  1*4  2.7  8.7  57.3  B  *92.7  0.4  1.1  5.8  56.8  •87.6  3.5  8.9  61.3  2  C  48.0  h Ag  86*3  2*5  1.6  2.6  7.0  45.0  A3  89.1  4.0  0.5  1.8  3.8  41.8  B  l  87.1  3.4  2.3  4.0  3.2  46.0  B  2  *81.S  6.2  5.8  7.3  49.7  8.1  5.2  2.5  5.0  48.6  *91.4  8.6  66.3  C  85.8  Al  %  *63.3  19.0  17.7  48.0  l  *91.2  3.4  5.4  51.0  *88.5  11.5  44.7  4.2  4.1  43.2  B  B  2  *88.7  C *  3.0  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 i n F i g . 2.  It i s 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 i s held.  The total loss i n 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 i s 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 i s confined to pores having an effective diameter of less than 0.05 mm. This, as pointed out in regard to Plneview, i s an unfavourable relationship and prohibits free movement of a i r and water.  The total  pore-space, as well as distribution of the various size groups, i s 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 Soil Volume  Soil Horizon Plneview  Vanderhoof  coefficient)  Hon-capillary Porosity %  Capillary Porosity $  Al  39.0  24.5  36.5  H  31.0  23.0  46.0  Bl  42.7  3.9  53.4  B  43.2  3.6  53.2  C  38.7  7.7  53.6  Ax  52.0  10.0  38.0  H  55.0  4.6  40.4  A3  58.2  2.2  39.6  Bl  54.0  3.9  42.1  B  50.3  3.7  46.0  51.3  2.6  46.0  33.7  13.0  53.3  *2  42.0  5.1  42.9  Bl  . 49.0  4.5  46.5  43.0  11.30  33.4  56.8  4.6  38.6  2  2  C Nulki  B C  2  Average of 3 samples  Nulki curves, F i g . 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 i s being withdrawn from the finer pores.  The curves further bring out that  this s o i l 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 i s withdrawn at tensions of less than 40 cm. The Bg horizon, having 11*5 per cent of i t s 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 particularly significant in regard to i n f i l t r a t i o n , 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 i s 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 s o i l s . "  - 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-capillary pores.  This tension varied with horizons, i t s value ranging from  20 to 40 cm. of water (Fig. 2). The data presented in F i g . 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 F i g . 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. 50 times.  Permeability of water, he found, was reduced approximately  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 a i r throughout i t s 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 qp_  sf  PERCENT  Of  PINEVIEW  TOTAL  CLAY  PERCENT  VOLUME  OF  TOTAL  VANDERHOOF SILTY  ASSOCIATION  FIG.  J  CLAY  VOLUME  RELATIONSHIPS  AVERAGE  OF  3  P E R C E N T OP  VOLUME  SAMPLES  NULKI  ASSOCIATION  OF  SOIL  TO  CAPILLARY  AND  TOTAL  CLAY  NON-CAPILLARY  VOLUME  ASSOCIATION  PORES  i  PERCENT  MARSHALL  Of  TOTAL  SILT  VOL UN  LOAM  FOR THE PROFILES OF PINEVIEW, NULKI.AND VANDERHOOF C L A Y S .  - 42 The trends In the pereentages of porosity in Vanderhoof profile follow the tendencies shown in F i g . 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 relationship, though far from ideal, i s 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, i s 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 satisfactory 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 i m i t , liquid l i m i t , 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 i s the moisture content at which the various surface phenomena associated with water films permit the s o i l mass to flow under an applied force.  The plasticity index (the difference between the upper  plastic limit and the lower plastic limit) i s 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 s o i l s . 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 i s distinct in the B and Ag horizons* Within the Nulki and Vanderhoof profiles there i s a definite trend of these indices.  With the exception of the Ag which i s quite low, there i s 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 pract i c a l l y linear.  Baver (1940) also reports a similar relationship and  points out that plasticity i s 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 i s obvious, no attempt to elaborate on i t w i l l 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 u n t i l the moisture content has fallen below that indicated by their plastic limits when the s o i l 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  Horizon  Pineview  Vanderhoof  Nulki  Clay 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  26.1  22.6  22.3  74,70  27.1  22,9  23.1  58.80  B  2  C  Liquid Limit (Per cent) Al  60.6  39.2  61.7  23.32  Ag  47.9  31.7  34.6  20.95  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  B  Plasticity Index (per cent) Al  21.4  4.6  21.2  50.25  Ag  13.9  3.6  8.0  27.45  Bl  26.4  10.0  23.0  35.00  Bg  46.6  15.2  26.7  34.31  - 46  VANDERHOOF A,  CLAY  CZ1  EZ2 B,  INNWN  B*  Ml INI l l l l  KWWN II  iiii ii ii n  C  PINEVIEW  CLAY  L ezzzzza  I  K W W W W W W N  B,  ii 11111"i11111• i i i  II I 11111 " " I I I I H KXXXXXXXXVXI  C  NULKI CLAY : c ZZZZ2  A, B,  r  V7zn  " " ' ' I I I I II I I I I I I  10  20  30  c  40  50  PERCENT PLASTICITY  RANGE  II M I N I I N i o n :  60  70  10  20  30  40  MOISTURE  PLASTICITY  Figure 4. - Plasticity Relationships of Pineview, Vanderhoof and Nulki Profiles.  NUMBER  - 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 f i e l d 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 i s clearly brought out by the pore size distribution data as presented in Table V and graphically shown in F i g . 2. These data fully support the f i e l d 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 characterizing i t as slow, wet s o i l that is difficult to maintain in proper t i l t h . The significance of such a layer in a s o i l has been well demonstrated by the work of Wollny (1883) as previously stated. Remedial measures, therefore, must center around methods and practices which w i l 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, i s a s o i l 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 c r i t i c a l l y 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 F i g . 2, verify the observed behavior.  This assumption la also fully supported by the work of  Bussell (1932).  SOIIB  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 s o i l particles, and not a colloidal property.  Such s o i l s , 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, s o i l physicists and faimers.  - 49 Nulki s o i l s , which have developed on similar parent materials to Vanderhoof, show very different physical properties*  Particle size  distribution as presented in Table IV i s 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 s o i l to be superior i n every aspect to either Pineview or Vanderhoof*  The reason for which, obviously  l i e s in the amount, kind and distribution of organic matter*  CONCLUSIONS 1*  On the basis of total chemical analyses of the s o i l s , 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 s o i l development. S.  The two s o i l s , Vanderhoof and Nulki, have developed on essent-  i a l l y 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 i s partially an inherited characteristic and in part developed.  5. A modification of Russell's (1941) pore size distribution apparatus i s presented*  - 50 BIBLIOGRAPHY Allaway, H . , and Pierre, W. H. (1939) Availability, fixation and liberation of potassium i n high lime s o i l s . Jour. Amer. Soc. Agron., 31: 940 - 953. American Society for Testing Materials (1944) Procedures for testing s o i l s . 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 s o i l groups. U. S. Dept. Tech. Bui. 228 ASsoo. of Office Agric. Chemists. Washington, D. C. Atterberg, A. (1911) 1:10-43  Methods of analysis.  Die Plastialtat der tone.  5th Ed.  Int. Mitt, fflr Bodenk.,  (1912) Die konsistenz und die bindigkeit der b8den. Mitt, fur Bodenk., 2:149-189.  Int.  Baver, L. D, (1938) S o i l permeability in relation to non-capillary porosity. Soil S c i . Soc. Amer. Proo., 3:52-56. Baver, L . D. (1940) S o i l physics. New York City.  Published by John Wiley and Sons,  Bradfield, R. (1936) The value and limitations of calcium in s o i l structure. Amer. S o i l Sur. Assn. Bui. 27:31-32. Bradfield, R., and Jamison, V. C. (1938) S o i l structure - attempts at i t s quantitative characterization. S o i l S c i . Soc. Proc. 3:70-76. (1926) Burger, H. Die physikalische Bodenuntersuchung inbesonde re die methoden zur bestimmung der luftkapazitat. Proo. 4th Int. Conf. Soil S c i . (Rome), 2:150-163. Byers, H. G. and Anderson, M. S. (1932) The composition of s o i l oolloids in relation to s o i l classification. Jour. Phys. Chem. 36:348-366. Childs, E . C. (1940) The use of s o i l moisture characteristics in s o i l Studies. Soil S o i . , 50:239-252. De Sigmond, A. A. J . , (1938) The principles of s o i l science. Murphy and Co. London.  Thomas  - 51 Dojarenko, A. J .  (1924).  S c i . 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 s o i 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. S o i l S c i . (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 s o i l s . publishing house, "Novaya Derevnya" Moscow* Glinka, K. D.  (1927).  State  Pochvovedenie, Pedology, Moscow.  — (1928). The great s o i l 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 Vanderhoof clays. (Graduate essay, unpublished). Haines, W. B. (1930). On the existence of two equilibrium series in s o i l capillary phenomena. Second I n t n ' l . Cong. S o i l 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 s o i l s . Soil S c i . 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 s o i l formation. Co. Inc., N. York and London.  McGraw-Hill Book  Joffe, J . S. (1936). Pedology. -Rutgers University Press. Brunswick, New Jersey. —  —  New  (1941). Pedology in the service of s o i l science. S o i l S c i . Soc. Amer. Proc. 6:68-77.  Kelley, C. C. and Farstad, L. (1946). S o i l survey of the Prince George area, B C. Report No.2 of British Columbia Soil Survey, Kelewna, B. C. 0  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. F i r s t Int. Cong. Soil S c i . , 1:495-503. Kubiena, W. L. Lawton, K.  (1938).  Mieropedology.  Collegiate Press, Ames, Iowa.  (1945). S o i l Aeration affects f e r t i l i z e r needs. Crops with Plant Foods. 30:(8).  Better  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 precipitates, S o i l So. 31:57-78.  Method and procedure of s o i l analysis  (1939).  Isoelectric  U.S.D.A. c i r c . 139.  McGfeorge, W. T . , and Breazeale, 7. F. (1938). Studies on s o i l structure: 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. S o i l S c i . 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 s o i l colloids. U.S.D.A. B u l l . 1311. Rus8el, J . C. (1928). Report of committee on s o i l 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). S o i l conditions and plant growth. Longmans, Green and Co., London.  6th Ed.  Russell, M. B. (1941). Soil pore distribution as a measure of s o i l structure. S o i l S c i . 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 . Int. Soil Cong. 8:37-48.  Trans. 3rd.  - 53 Smith, F. W., and Cook, B. L . 31:(3).  (1947)•  Better Crops with Plant Food.  Smith, H. W., and Bhoades, H. F. (1942). Physical and chemical properties of s o i l 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). S o i l 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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