PERCOLATION STABILITY OF AGGREGATES FROM ARABLE TOPSOILS

Percolation stability (PS) measured in a simple laboratory test with air-dried 1 to 2-mm aggregates correlates closely with surface roughness, decay and erosion. The processes involved in this test and the influence of soil properties on PS were studied. Air entrapment was the major cause of aggregate disintegration. Shear forces of the percolating water (10(-1) Pa), however, scarcely contributed to aggregate breakdown, although they can be one order of magnitude larger than forces of sheet flow on the soil surface. Percolation stability is a superior stability indicator for erosion studies. It is simple, needs little labor, soil, or equipment, results are highly correlated with soil loss, and, most importantly, they can be interpreted physically. The PS of 113 arable topsoils was inversely related to pH/(organic matter) or linearly to (14-pH) x (organic matter) with r(2) = 0.72 in both cases. Both regressions indicate an increase in stability with increasing organic matter content and decreasing pH. The influence of pH increases with increasing organic matter content. The decrease in stability with pH argues against liming to reduce surface crusting. This result is also supported by findings of other authors.