The organic matter content of soils

In the discussion that follows, the more important factors that determine the extent to which organic carbon commonly increases or decreases in soil are considered. The natural environmental factors, and also modifications brought about by man in his endeavor to produce abundant crops with the minimum expense for labor and materials, are discussed. 

ORGANIC MATTER DISTRIBUTION IN THE PROFILES OF VIRGIN SOILS 

A consideration of the organic matter distribution in the profiles of our main types of virgin soils is necessary in order to understand the conditions that now exist in our agricultural soils. Although many years removed from the virgin condition, cultivated 

The most typical podzols are usually those formed under coniferous forests less typical are the podzol-like soils formed chiefly under deciduous forests or in a warm climate. In many areas of the United States these two types of vegetation occur in mixture and the resulting soil shows characteristics that are intermediate between the two. In other cases, where man has interfered with nature, deciduous trees may follow coniferous ones, or the reverse. The podzol-like soils are commonly referred to as either gray-brown forest soils of the Temperate Zone or red and yellow podzolic soils of the warmer regions. 

In Finland, for example, where typical podzols are predominant, the forest soils have a humus layer of varying thickness with even larger amounts found in the upper portion of the mineral soil. Viro (1963) states that over 95% of the tree roots are found in the humus layer and the upper foot of mineral soil. In south Finland the humus layer of the 

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Toxaphene, lindane, chlordan, and heptachlor were adsorbed by soil particulate matter (158, 216, 255, 261, 268, 279, 291, 295, 299, 301, 302, 303, 304, 305) and volatilized from aqueous (292, 297) and soil (255, 264, 275, 280, 283, 293, 306) systems in a way analogous to that of aldrin, dieldrin, and endrin. Adsorption of the pesticides was most highly related to the organic matter content of soils and aquatic systems and probably occurred through weak physical intermolecular forces at lipophilic sites. Adsorbing and volatizing processes were involved in the fate of these compounds in aquatic and soil systems. Lindane was much more mobile in soil systems than the others (246, 255), probably because of its greater solubility (Table VI), and lindane and heptachlor volatilized much more readily from soils and aquatic systems (290, 292, 293, 296, 306). 

Dichlobenil is considerably less soluble in water and has a much lower vapor pressure than the other herbicides given in Table XI, but in aqueous and soils system it behaves similarly. It was relatively immobile in most soils but did leach considerably in sand (402, 403). Adsorption was related to the organic matter content of soils (404). Much dichlobenil was adsorbed from aqueous solutions by organic soil, lignin, and lanolin wax, but it was not significantly adsorbed by cellulose, sandy soil, sand, or soybean protein (403). 

The organic matter content of muck soil in Florida is about 80%.)... 

Sorption coefficients also have been expressed on an organic matter basis (Kom) by assuming that the organic matter content of a soil or sediment equals some factor, usually between 1.7 to 1.9, times its organic carbon content on a mass basis (Hamaker and Thompson, 1972 Lyman et al., 1982). Often 1.724 is used as this factor, implying that the carbon content of organic matter is 1 /1.724 or 60%. However, Koc is considered a more definite and less ambiguous measure than Kom (Hamaker and Thompson, 1972). 

Soil. Leaching behavior is inversely related to clay and organic matter content of soils. In soil column and soil layer studies, 97% was remaining in the top soil, with 0.1% in leachate... 

With the exception of soil 3, the sorption of all three herbicidal materials is well correlated to the organic matter content of these soils. 

An adsorptive is distributed between the adsorbed phase on a soil and the surrounding aqueous phase depending on soil adsorbent properties such as pH, organic matter content, amount and type of clay minerals, surface area and porosity, and on the other hand, on properties of the adsorbate such as ionization constant, solubility, polarity, size, shape and configuration [ 13 ]. Usually, the attachment of uncharged organics correlates well with the organic matter content of the soil adsorbent, whereas the influence of the... 

Cd) from nonpolluted soils has also been investigated thoroughly, and pH-DOC synergic effects have been identified for some elements under certain scenarios (Strobel et al., 2001). Stirred-flow cells have also been presented as a promising vehicle to assess the metal readsorption phenomenon in the various steps of SEPs, the extent of which was found to be influenced by the element itself, the organic matter content of the sample, the extracting flow rate, and the metal concentration level (Chomchoei et al., 2002). 

Fomesafen is weakly adsorbed by soils. Its adsorption coefficients (kj are in the range of 0.5 to 3.0 depending on the organic matter content of the soils. Under aerobic conditions fomesafen degrades slowly in soil, its half-life is generally greater than 6 months. 

The herbicidal properties of nitralin were first reported by Schieferstein and Hughes (1966). The volatility of the compound is relatively low thus it requires only shallow incorporation. It is remarkable that in spite of its very slight solubility in water (0.6 ppm), nitralin does not require moisture for the exertion of its action. E)epending on the organic matter content of the soil, it is used at rates of O.S-1.5 kg... 

The adsorption of terbacil is in close correlation with the organic matter content of the soil. According to the investigations of Kratky and Warren (1973), to achieve the same herbicidal effect, 24 times as much terbacil was needed in a soil with 24% organic matter content as in a soil with 0.3% organic content. 

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