Soil microaggregation as influenced by uncharged organic conditioners

Abstract

To assess the interaction of water soluble stabilizing agents with soil particles, soil microaggregation was studied after treatments with two uncharged organic conditioners, Polyvinyl alcohols (PVAs) and Dextrans, of different molecular weight. The size distribution of microaggregates (diameter <250 pm) was determined on two soils of low organic matter contents with differing texture by means of a laser light technique. PVAs and Dextrans modified the microaggregate size distribution, increasing the proportion of >75 μm aggregates. The extent of this modification increased with the molecular weight of the conditioners and, for the same molecular weight, decreased with increasing amount of conditioner used. The aggregating effect of PVAs was stronger on particles smaller then 5 μm, which formed microaggregates in the range 10–100 μm which were not broken down even by ultrasonication. S.E.M. micrographs of soil aggregates confirmed the results reported above. PVAs and Dextrans appeared to produce a more porus structure with more aggregates of about 100 μm size, both in the clay soil and, to a lesser extent, in the sandy soil.