Effect of freezing and thawing on the stability of soil aggregates treated with organic wastes

Abstract

The susceptibility of three highly aggregated, texturally contrasting, agricultural soils (in north-central Italy) to frost action and the role of organic matter in moderating the adverse effect of cyclic freezing and thawing on soil aggregate stability were investigated in the laboratory using soils from Lamporecchio (Sandy Loam), Cremona (Sandy Clay Loam) and Vicarello (Clay Loam) and five rates of organic matter (OM): 0, 18, 36, 54 and 90 t/ha. Results indicated that in the samples that were not treated with OM (controls) aggregate stability as evaluated by the mean-weight diameter of water-stable aggregates (MWD) technique differed significantly among the soils, showing an increase with increasing OM level, clay and iron contents and decreasing silica/alumina ratio. This order was Vicarello > Cremona > Lamporecchio. However, the susceptibility of these soils to frost action, defined in terms of a frost-susceptibility factor, showed an order of Lamporecchio ⩽ Cremona < Vicarello, reflecting decreasing clay contents. In the sandy Lamporecchio and Cremona soils, the rate of 36 t/ha OM prior to cyclic freezing and thawing maintained MWD at levels similar to the control pre-freeze stage. With the clayey Vicarello soil, no OM rate was able to maintain the MWD of the frost-treated samples at the pre-freeze levels.