INFLUENCE OF WASTE ORGANIC-MATTER ON SOIL MICRO AND MACROSTRUCTURE

Changes in soil porosity and microstructure are discussed for a silty clay soil and a sandy loam soil following the surface application of livestock effluents and composts from sewage sludges and urban refuse. - Porosity measurements were carried out on large, thin-sections of undisturbed soil samples by means of scanning electron microscopy, light microscopy and electro-optical image analysis. The organic materials significantly increased the micro- and macroporosites of the two soils. Micromorphometric measurements showed that the increase in microporosity was mainly due to the elongated micropores associated with newly formed microaggregates. The increase in macroporosity was due to enlarged pores ranging from 50-500 mu m, which are considered the most important both in soil-water-plant relationships and in maintaining a good soil structure. The increase of porosity in the topsoil was accompanied by a reduction in the presence of surface crusts, thus indicating that such organic materials play an important role in improving soil structure.