FACTORS OF SOIL FORMATION - Midlands State University

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soluble salts and colloidal particles. Their minima and maxima are named with capital letters A, referring to minima, B, referring to maxima, and C, which applies to the horizontal branch of the curve. The interpretation of the horizons is as follows: Horizon A: Eluvial horizon, or leached horizon. Material has been removed from this zone. Horizon B: Illuvial horizon, or accumulation horizon, in which substances, presumably from A, have been deposited. FIG. 5.—Colloidal clay and CO 2 of carbonates as a function of depth of a clay-pan soil. The maxima of these two soil properties do not occur at the same depth. Horizon C: Parent material, from which the soil originated. Frosterus (2) designates the zone of maxima and minima (A + B) as solum. Variations within the horizons are indicated by subscripts, like A 1 and A 2, or, B 1 , B 2 , B 3 , etc. Organic-matter deposits on top of the mineral soil are often labeled as A 0 , F, H, etc. If it so happens that several soil characteristics have maxima and minima that coincide spatially, as in Fig. 4 (podsol profile), the ABC terminology affords an easy means of describing and classifying soil profiles. Not all soils possess such simple patterns. In the clay-pan soil shown in Fig. 5, the maximum for the carbon dioxide content (carbonates) occurs at greater depth than the peak of the colloid (clay particles). Assignment of the letters A and B is left to individual judgment. In the United <strong>State</strong>s, the accumulation horizon frequently, but not exclusively, refers to the zone of enrichment in clay particles, and some uncertainty in horizon designations still exists. The difficulty of horizon designation is accentuated in soils derived from anisotropic parent materials such as stratified sand and of fact, there exists great need for rigorous criteria of horizon identification, because all scientific clay deposits. As a matter systems of soil classification as well as the theories regarding soil development rest on horizon interpretations.
FIG. 6.—Illustration of a soil indicatrix. Colloidal Al 2O 3 of a podsol profile on level topography. FIG. 7.—Illustration of a soil indicatrix. Total nitrogen of a prairie soil profile on a slope of 26°34' or 50 per cent. The Soil Indicatrix.—On level land, soils derived from homogeneous, isotropic parent material are anisotropic only along the Z-axis. In the direction of right angles to it, the properties are isotropic. If the graph of Fig. 4 is rotated about the depth axis, a figure of revolution is obtained that indicates the spatial distribution of the properties of a soil. This figure might be designated as soil indicatrix. In the case of the distribution of colloidal alumina in Fig. 4, the indicatrix resembles a vase, as shown in Fig. 6. If the surface of the land deviates from horizontal, the shape of the indicatrix becomes asymmetrical (Fig. 7) and is no longer a simple figure of revolution. The concept of the soil indicatrix offers a convenient tool for purposes of clarification and refinement of soil-profile descriptions. Soil Defined as a System.—In this book, the soil is treated as a physical system. The word "physical" is inserted to distinguish it from purely logical systems, and the term corresponds with Joffe's statement that the soil is a natural body. The soil system is an open system; substances may be added to or removed from it. Every system is characterized by properties that we may designate by symbols, such as s 1 , s 2 , s 3 , s 4 , s 5 , etc. For example, s 1 may indicate nitrogen content, s 2 acidity, s 3 apparent density, s 4 amount of calcium, s 5 pressure of carbon dioxide, etc. Any system is defined when its properties are stated. We further assume that the foregoing properties possess not only qualitative but also quantitative character, i.e., we may express them with numerical figures. At present, not all soil properties have been sufficiently studied to permit quantitative expression, but there is reason to believe that the properties that can be given quantitative representation gradually will be increased in number as scientific research goes on. We shall now make the additional obvious but important assumption that the properties of the soil system are functionally interrelated. That is to say, they stand in certain relationships to each other. If one property changes, many others also change. For instance, if water is added to a soil, not only is the magnitude of the moisture content increased but other properties like density, heat capacity, salt
Page 1 and 2: FACTORS OF SOIL FORMATION A System
Page 3 and 4: To MY WIFE
Page 5 and 6: PREFACE The College of Agriculture
Page 7 and 8: FACTORS OF SOIL FORMATION CHAPTER I
Page 9: To a certain extent, many geologica
Page 13 and 14: FIG. 8.—The larger system. (After
Page 15 and 16: However, it remained for Hilgard in
Page 17 and 18: These terms are identical with the
Page 19 and 20: thus avoid lengthy excursions into
Page 21 and 22: CHAPTER II METHODS OF PRESENTATION
Page 23 and 24: Colloid chemists favor size-distrib
Page 25 and 26: These ratios afford a means of dete
Page 27 and 28: FIG. 14.—Illustration of soil var
Page 29 and 30: Studies on Experimental Weathering.
Page 31 and 32: een very rapid, an average thicknes
Page 33 and 34: FIG. 18.—This graph shows in a sk
Page 35 and 36: thickness of the eluvial horizon in
Page 37 and 38: material contained from 9 to 10 per
Page 39 and 40: FIG. 25.—Schematic illustration o
Page 41 and 42: Tujunga sand —> Hanford fine sand
Page 43 and 44: CHAPTER IV PARENT MATERIAL AS A SOI
Page 45 and 46: they would have to be considered as
Page 48 and 49: Physical and Chemical Rock Decay.
Page 50 and 51: FIG. 31.—Comparison of relative b
Page 52 and 53: environment should produce soils th
Page 54 and 55: TABLE 13.—RELATIVE PERCOLATION VE
Page 56 and 57: In certain parts of the world, espe
Page 58 and 59: minds of all students of loessial s
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that parent material is one of the
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Jersey, out of 48 soil types, 24, o
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Scherf claims that the climate of t
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13. KAY, G. F., and APPEL, E. T.: T
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FIG. 42.—Relationship between slo
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Specific examples of the relationsh
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FIG. 46.—Distribution of organic
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suffered salinization. Some of the
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from Marbut's standpoint; but, in t
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FIG. 50.—Distribution of mean ann
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main, they have not been very succe
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modifications in environment due to
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correlation exists between total so
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FIG. 59.—Soil nitrogen-depth func
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eliminates chance correlation. More
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TABLE 25.—CHEMICAL EVIDENCE OF TH
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(49), and thereby identify the soil
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FIG. 65.—Relationship between CaO
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published in the Soil Survey Report
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(usually pH 7) is known as the base
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In Table 30 are given corresponding
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particularly in the more humid regi
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The hydrogen ion concentration and
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Soil Color.—In humid regions of t
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Nitrogen and Organic Matter as a Fu
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area by soil scientists of the U. S
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TABLE 38.—DATA FOR THE PARENT MAT
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Crowther correlates clay compositio
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Podsols.—In vast areas of norther
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FIG. 85.—Diagrammatic section of
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FIG. 87.—Comparison of podsolizat
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ft. above sea level, the total nitr
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Generalized Soil-climate Functions.
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d. Under conditions of constant moi
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horizons. The decrease in the clay
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directly from the melting ice. Thic
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FIG. 97.—Climatic and vegetationa
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soil processes occur mainly during
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FIG. 98.—Chernozem soil near Khar
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FIG. 99.—Marbut's classification
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47. MARBUT, C. F.: A scheme for soi
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CHAPTER VII ORGANISMS AS A SOIL-FOR
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as a consequence of natural reinocu
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intensive leaching supports acidoph
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TABLE 51.—AREAS OF NATURAL VEGETA
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TABLE 53.—DRY WEIGHTS OF LIVING U
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TABLE 56.—RAINFALL AND PLANT PROD
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the yields of corn: that is to say,
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disappear and acid-tolerant species
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TABLE 60.—COMPARISON OF PRAIRIE A
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differences are found in the distri
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Here also the leaves of the deciduo
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indeterminate past. The land, after
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chapters, we must be content with a
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Duley (44) initiated the first scie
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matter acts as a binding agent betw
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areas in the San Joaquin Valley of
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independent variables. These latter
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Inherent Productive Capacity of Soi
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FIG. 121.—Showing the relation be
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FIG. 123.—Decline of soil nitroge
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FIG. 124.—This graph depicts the
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25. HOSKING, J. S.: The carbon-nitr
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CHAPTER VIII CONCLUSIONS In this ch
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the other correlates soils in terms
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knowledge of the physical, chemical
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