Saturday, 15 July 2006
136-15

The Regularities of Changes in Soil Surface Properties Due to the Soil Formation and Field Agricultural Technogeneses.

V.F. Utkaeva, V.V.Dokuchaev Soil Science Institute, Pyzhevskii per., 7, Moscow, Russia

A comprehensive analysis has been made to study the profile changes taking place in such surface properties as the heat of wetting and parameters of soil specific surface in several subtypes of sod-podzolic soils, chernozems and soils of solonetzic complex, developed under different natural conditions and used in agriculture to be compared with the other soil properties. The obtained results testify to the profile specific in every soil type, being regularly changed under the effect of human activities. The effect of irrigation on the surface properties of soil were studied on the soils of solonetzic complex. In the virgin plot, all tree (above-solonetzic, solonetzic, and salic) horizons were clearly classified by the surface parameters in the profile of solonetz. The solonetzic horizon is distinguished by the highest heat of wetting, which is related to the higher content of colloidal particles. In lower horizons, the heat of wetting decreases down to 16 J/g. In the chestnut soil, two layers are classified by the heat of wetting: the first layer includes the horizons A1 and B down to the depth of 40 cm (it is characterized by the heat of wetting 20-21 J/g), and the second layer occurs deeper than 40 cm. The meadow-chestnut soil, being the richest in humus, is characterized by the highest values of heat of wetting and the larger specific surface. The heat of wetting of irrigated soils was found to be lower than that of virgin soils. The values of heat of wetting in the lower soil horizons of both complexes are similar and equal to 12 J/g which is inherent to soil-forming rock. The distribution of the values of heat of wetting through the profile changes under the effect of irrigation. The maximum heat of wetting is observed in the B1 horizons of all soils. The effect of drainage on the surface properties of soil was examined by the comparison between the properties of three soils (deep gley soddy-podzolic soils, gleyed soddy-podzolic soils, and gley soddy-podzolic soils) under drained and undrained conditions on a drainage system of 10-year maintenance. A decrease in total specific surface was noted under drying conditions because of decreasing soil dispersity. The nonaggregated material is removed first under drying conditions. Microaggregates of the 0.25-0.01-mm fraction are predominant (80%) in these soils. Similar changes were also observed for the heat of soil wetting. The decrease in specific surface of soils under drainage is more intensive than the decrease in heat of wetting. During drying, incompletely decomposed plant debris disappears, the amount of black nontransparent mulch organic matter decreases. The heat of wetting increases with enhancing hydromorphism symptoms both for drained and undrained soils. The study of surface parameters is of great interest for the evaluation of dispersion state of soil and its possible change as a result of chemical effects of fertilizers applied. The effects of organic and mineral fertilizers on the surface properties of soils were studied in 20-year experiments with chernozem. The contents of the I-0.25-mm fraction in the microaggregate composition of chernozem increased more than by two times under the structuring action of manure. The specific surface increased at the cost of enlarging both the external and internal surfaces because of finely dispersed humus structures formed at the solid phase surface. The heat of wetting of typical chernozem varies from 20 to 25 J/g. The maximal decrease in heat of wetting of typical chernozem is revealed for the resting fallow. The lowest hydrophilicity is observed for the manure treatments, which can be determined by the hydrophobicity of incompletely decomposed manure debris. The application of organic and mineral fertilizers on typical chernozem for more than 20 years increased the humus content, total specific surface, and heat of wetting. The durable continuous fallowing resulted in decreasing humus content and specific surface and increasing hydrophilicity. According to the data from analyzing the heat of wetting and the main hydrophysical characteristics the interaction between the adsorbed water and the soil solid phase reveals its stability. The moisture in the top of wetting film is shown to be close to that in soil, calculated by using the values of heat of wetting. Essential differences are identified between values of the maximum gygroscopic water and the moisture calculated by using the values of heat of wetting. Two categories are distinguished for the adsorbed water in the volume of the maximum gygroscopic one.

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