EFFECT OF DIFFERENT TYPES OF ORGANIC MATERIALS AND LIME ON SOIL AGGREGATION

Abstract

Studies were made of the effect of a single application of 12 different organic materials and lime at 1, 3, 6, and 12 months after application on aggregation of a Gilpin silty clay loam and a Holston clay loam soil maintained under laboratory conditions. Organic materials that decompose rapidly increase aggregation within a few days after they are incorporated with the soil, have their max. effect in about 20-30 days and then gradually lose their effectiveness with time. The materials that are slower to decompose require a longer time to exert their building effect but continue to be effective over a longer period of time. Materials that are relatively inert have little, if any effect upon aggregation. Lime when added with the different organic materials significantly decreased aggregation in the subsoil samples of the Gilpin silty clay loam and Holston clay loam soils and in a sample of the Holston clay loam surface soil. In the Gilpin surface soil, lime significantly increased aggregation when added with buckwheat, rye, broomsedge, oat straw, soybeans, or corn stover; decreased aggregation with peat moss, and did not cause a significant change in the other organic materials studied. The percolation rate of laboratory-packed samples appears to be affected both by the mechanical loosening of the soil and the aggregating effect of the organic material. In general, lime has decreased the percolation rate. The organic colloidal material was more highly dispersed in the presence of lime, which may have been a factor in decreasing the percolation rate. Aggregates formed in a short time from a single application of organic material were relatively stable under the condition of this experiment. The dynamic nature of aggregation in soils necessitates carefully controlled conditions if results are to be comparable between and within seasons. The relation of aggregate distribution to the dispersion ratio is negative and varies with different soils and with the type of organic material. Correlation coeffs. between different grouping of aggregates and the dispersion ratio are shown. In general, the addition of organic material to these soils has improved some of the physical characteristics which are recognized as affecting the susceptibility of a soil to erosion.