FACTORS OF SOIL FORMATION - Midlands State University

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CHAPTER III TIME AS A <strong>SOIL</strong>-FORMING FACTOR The estimation of relative age or degree of maturity of soils is universally based on horizon differentiation. In practice, it is generally maintained that the larger the number of horizons and the greater their thickness and intensity the more mature is the soil. However, it should be kept in mind that no one has ever witnessed the formation of a mature soil. In other words, our ideas about soil genesis as revealed by profile criteria are inferences. They are theories, not facts. This accounts for the great diversity of opinion as to the degree of maturity of specific soil profiles. It is well known that certain eminent pedologists take objection to the general belief that chernozems are mature soils; others consider brown forest soils and gray-brownpodsolic soils merely as immature podsols. The list of controversial soil types is quite long. Whatever the correct interpretation may be, it is evident that the issues center around the factor time in soil formation. General Aspects of Time Functions.—If the fundamental equation of soil-forming factors s = f(cl, b, r, p, t, • • •) (4) is evaluated for time, we obtain an expression of soil-time functions as follows: s = f (time) cl, o, r, p, . . . (7) This equation states that the magnitude of any soil property (s type) is related to time. If we wish to ascertain accurately the nature of a time function, all remaining soil-forming factors must be kept constant. If they vary effectively, at one time or another, the trends of soil development are shifted, new processes are instigated, and we must start counting anew. The requirement of constancy of soilforming factors is easily accomplished with controlled laboratory or field experiments. Under natural conditions, especially in the absence of historic records, we must be satisfied with approximate solutions of Eq. (7). FIG. 15.—Hilger's experimental weathering series. Coarse particles of limestone are much more resistant than those of sandstone (var. Stuben).
Studies on Experimental Weathering.—Hilger (8) exposed uniform rock particles of from 10 to 20 mm. diameter to atmospheric influences for a period of 17 years. The percentage of original particles left at various time intervals and the amounts of fine earth FIG. 16.—Hilger's experimental weathering series. This figure shows the amount of fine earth formed, expressed in per cent of original rock material. (particles less than 0.5 mm. diameter) formed are shown in Figs. 15 and 16. The great variation in rates of physical weathering of different rock species is striking. Limestone was the most and sandstone the least resistant material. Nearly 90 per cent of the coarse fraction of the sandstone disappeared within less than two decades. At the end of the 17-year period, Bissinger (4) determined the chemical composition of Hilger's weathering series. The results of both the original and the weathered rocks are given in Table 4 in terms of ratios. Differential weathering is clearly indicated. Limestone suffered greater relative losses of potassium and sodium than sandstone. The same relationship exists for the relative leaching of silica. In all cases, the fine earth has a lower sa value than the original rock, which indicates relative enrichment of aluminum. These changes are probably due in part to chemical leaching and in part to selective physical disintegration of the rock constituents. It is of interest to note that in these specific cases the sandstone exceeded the limestone in physical weathering but lagged behind in chemical weathering. TABLE 4.—CHEMICAL DATA ON ROCK WEATHERING (17-YEAR PERIOD) Type of material K 2 O + Na 2 O SiO 2 ————— = ba 1 ——— = sa Al 2 O 3 i Al 2 O 5 Absolute Relative Absolute Relative Limestone Rock 5.00 1 17.08 1 Fine earth. 0.514 0.103 7.33 0.429 Mica schist Rock 0.418 1 5.88 1 Fine earth 0.288 0.690 4.87 0.829 Sandstone Rock 0.247 1 40.1 1 (Stuben) Fine earth 0.275 1.111 23.9 0.596 Further Estimates of Rates of Weathering.—Some 60 years ago, Geikie (5) made a survey of dated tombstones in Edinburgh churchyards. A marble stone with the inscription 1792 was partly crumbled into sand, whereas, in the case of a clay slate stone, the lettering was still sharp and showed scarcely any change. A sandstone of good quality indicated practically no effect of weathering during a period of 200 years. Goodchild (6), in 1890, published some notes on
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 and 24: Colloid chemists favor size-distrib
Page 25 and 26: These ratios afford a means of dete
Page 27: FIG. 14.—Illustration of soil var
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
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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
show all

FACTORS OF SOIL FORMATION - Midlands State University

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