FACTORS OF SOIL FORMATION - Midlands State University

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Fig. 23.—Time function for organic matter for Salisbury's dune series. The carbonate curve, being of an exponential nature, is very steep at the beginning and becomes flatter as the age of the dune progresses. The hydrogen ion concentration of the initially calcareous dunes is necessarily low, and it remains so for over a century, in spite of very rapid removal of lime. Subsequent to the 200-year period, it rises very rapidly. Salisbury also determined the organic-matter content of the dunes, or, more precisely, the loss on ignition, corrected for the carbonates. The curve shown in Fig. 23 runs somewhat parallel to the acidity curve. The organic-matter contents of some of the dunes appear erratic, on account of human interference, as Salisbury contends. The same dunes also show deviations in the calcium carbonate and acidity curves. Fig. 24.—Leaching of calcium carbonate as a function of time in Dutch polders. (Hissink.) Leaching of Dutch Polders.-—For centuries, the people of Holland have enlarged their agricultural area along the seacoast by building dams or dikes that prevent flooding of land during high tides. The muddy deposits thus wrested from the sea mark the initial phase of a process of soil development during which the salty and unproductive muds are transformed into fertile lands. In recent years, Hissink (11) has given an interesting account of the changes in soil properties that have taken place in the course of centuries. In Fig. 24 are plotted the percentages of calcium carbonate of the surface soil (from 0 to 8 or 10 in.) as a function of time. Originally the soil
material contained from 9 to 10 per cent calcium carbonate, which completely disappeared from the surface soil within 300 years. It is of interest to reflect on the shape of the curve, especially in comparison with the corresponding data of Salisbury. On the sand dunes, the highest rate of removal of calcium carbonate occurs during the initial years of soil development, whereas on the polders it is postponed for a century or two at least. The explanation of this profound difference must be sought in nature of the soil material. Salisbury's dunes are of sandy texture. Rain water readily percolates through the porous material and immediately produces leaching effects. The polders, on the other hand, contain from 60 to 80 per cent clay, which retards the movement of water. Moreover, the presence of sodium ions accentuates the unfavorable conditions of water penetration. It is only after prolonged periods of alternate drying and wetting that the muddy and structureless material becomes sufficiently organized to permit percolation of water and leaching of calcium carbonate. Theoretical Aspects of Soil-time Relationships.—Although the data on quantitative time functions are scanty, nevertheless the knowledge at hand lends itself to a fruitful examination of fundamental pedological concepts such as initial and final states of the soil system. When Does Parent Material Become Soil?—Let us suppose that a river deposits several feet of mud, that a violent dust storm covers a region with a thick blanket of silt, or that a volcano lays down a bed of ash. Are these deposits parent material or soil? Opinions are divided. A few soil scientists consider them soils, but the majority look upon them as parent material. The question immediately arises: If these deposits are not soils now, when do they become soils? Most of us will agree that 1,000 years hence, the aforementioned deposits will have developed into soils. They will, perhaps, not be mature but in all probability will have acquired profile features that will be distinct enough to be seen in the field. In contrast to field examination, chemical analysis is able to detect eluvial and illuvial soil layers at a much earlier date. Clearly, the more refined our methods of observation, the sooner we shall be able to ascertain the change from geological material to soil. At what time, then, does parent material become soil? The problem becomes more tangible on examination of specific soil-time functions such as those provided by Salisbury's dune series. The freshly formed dune unquestionably deserves the attribute parent material. The 280-year-old dune is distinctly a soil, because it has a solum and a C horizon. Focusing attention upon a specific soil characteristic, e.g., the carbonate content, we see from the curve in Fig. 22 that it diminishes continuously as time advances. There is no break in the curve or a conspicuous point that might suggest the start of soil genesis. At the soil-formation time "zero," soil and parent material merge into each other. Mathematically speaking, we should say that parent material becomes soil after an infinitely small time interval dt. This idea leads to a simple and precise definition of parent material: It is merely the state of the soil system at the soil-formation time zero. It is for this very reason that in Chap. I we have defined parent material as the initial state of the soil system. Time of soil formation is not necessarily identical with the "age of the country" or the "geological age of the land," as maintained in some publications. As soon as a rock, consolidated or unconsolidated, is brought into a new environment and acted upon by water, temperature, and organisms, it ceases to be parent material and becomes soil. Returning to the questions asked at the beginning of this section, we are forced to conclude that young riverbanks, fresh loess
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 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: thickness of the eluvial horizon in
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
Page 80 and 81: main, they have not been very succe
Page 82 and 83: modifications in environment due to
Page 84 and 85: 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
Page 94 and 95:
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
Page 180 and 181:
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
Page 190 and 191:
knowledge of the physical, chemical
show all

FACTORS OF SOIL FORMATION - Midlands State University

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