FACTORS OF SOIL FORMATION - Midlands State University

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FIG. 12.—Triangular presentation of the composition of the Cecil fine sandy loam profile given in Table 2. Note the accumulation of clay in the B horizon. For the purpose of interpretation of chemical data, it is advisable to construct a table of molecular values by dividing the customary percentage data by the molecular weights. If a soil contains 55.90 per cent SiO 2 , the molecular value is 55.90/60 = 0.932. Chemists are determining atomic weights more and more accurately, and this necessitates endless recalculations of molecular values. Since these changes are beyond the accuracy of soil and rock analyses, it appears expedient to use the rounded figures of H. S. Washington that Niggli (7) advocates for international use. SiO 2 = 60 TiO 2 =80 S = 32 Al 2 O 3 = 102 P 2 O 5 = 142 Cr 2 O 3 = 152 Fe 2 O 3 = 160 MnO = 71 NiO = 75 FeO = 72 ZrO 2 = 123 CoO = 75 MgO = 40 CO 2 = 44 BaO = 153.5 CaO = 56 SO 3 = 80 SrO = 103.5 Na 2 O = 62 Cl 2 = 71 Li 2 O = 30 K 2 O =94 F 2 = 38 Molecular values offer many advantages. In the first place, we are not so much interested in the weight changes of the soil constituents as in changes in their atomic and molecular proportions. Stoichiometric relationships are more clearly brought out by molecular data than by weight figures. In the second place, chemistry has shown that chemical laws assume the simplest form when expressed in molecular relationships. In order to reduce the number of items in a table of analyses, two or more values may be combined into ratios. The following quotients and symbols are often encountered in soil literature:
These ratios afford a means of detecting relative translocations of elements. If one assumes, for example, that Al 2 O 3 is the most stable of the aforementioned compounds—because of its insolubility at neutral reaction—the ratios involving aluminum represent numerical indexes of relative accumulations and depletions in various horizons. The ratios may also serve as checks against faulty conclusions regarding actual losses of substances. It is frequently found that surface soils contain less silica (on a percentage basis) than the parent material, and one might conclude that silica has been leached out. This loss may be only fictitious, caused by addition of organic matter to the soil, which automatically lowers the percentage composition of SiO 2 . An inspection of the SiO 2 –Al 2 O3 ratio values is likely to reveal the fallacy at once, because the quotient is not affected by the mere addition or subtraction of a third component. The author (3) has suggested a leaching factor β that consists of the ratio In this instance, six analytical values are combined into one figure. The smaller β the greater is the relative leaching of K 2 O and Na 2 O with respect to Al 2 O 3 . If no relative loss of monovalent cations occurs, β equals unity. Data on the weathering of limestone may serve to illustrate the calculation of β (Table 3). TABLE 3.—CALCULATION <strong>OF</strong> LEACHING VALUE β Constituent Rock Soil Per cent Molecular Per cent Molecular Value value Al 2 O 3 0.15 0.00147 7.59 0.0745 K 2 O 0.20 0.00213 1.38 0.0147 Na 2 O 0.06 0.00098 0.55 0.0089 ba 1 — 2.11 — 0.32 β — — — 0.152 Owing to pronounced leaching of CaCO 3 , the values for Al 2 O 3 , K 2 O, and Na 2 O are higher in the soil than in the original rock. Nevertheless, with respect to Al, the cations K and Na also have been drastically reduced. Niggli (7) has suggested a system of symbols that is more comprehensive than the collection of ratios given above and yet not too cumbersome to handle. It differs from all other systems in that silica is treated independently.
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 and 10: To a certain extent, many geologica
Page 11 and 12: FIG. 6.—Illustration of a soil in
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: Colloid chemists favor size-distrib
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
Page 60 and 61: that parent material is one of the
Page 62 and 63: Jersey, out of 48 soil types, 24, o
Page 64 and 65: Scherf claims that the climate of t
Page 66 and 67: 13. KAY, G. F., and APPEL, E. T.: T
Page 68 and 69: FIG. 42.—Relationship between slo
Page 70 and 71: Specific examples of the relationsh
Page 72 and 73: FIG. 46.—Distribution of organic
Page 74 and 75:
suffered salinization. Some of the
Page 76 and 77:
from Marbut's standpoint; but, in t
Page 78 and 79:
FIG. 50.—Distribution of mean ann
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main, they have not been very succe
Page 82 and 83:
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
Page 106 and 107:
Soil Color.—In humid regions of t
Page 108 and 109:
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
Page 118 and 119:
FIG. 85.—Diagrammatic section of
Page 120 and 121:
FIG. 87.—Comparison of podsolizat
Page 122 and 123:
ft. above sea level, the total nitr
Page 124 and 125:
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
Page 168 and 169:
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
Page 176 and 177:
Inherent Productive Capacity of Soi
Page 178 and 179:
FIG. 121.—Showing the relation be
Page 180 and 181:
FIG. 123.—Decline of soil nitroge
Page 182 and 183:
FIG. 124.—This graph depicts the
Page 184 and 185:
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
Page 190 and 191:
knowledge of the physical, chemical
show all

FACTORS OF SOIL FORMATION - Midlands State University

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