SOIL AMENDMENTS AND WATER-STABLE AGGREGATION OF A DESURFACED DARK BROWN CHERNOZEM

Aggregate stability, which influences soil resistance to wind and wate r erosion, can be improved by the application of organic amendments. I n spring 1992, a desurfaced Dark Brown Chernozem in southern Alberta w as amended with six animal manures, four crop residues and two rates o f phosphate fertilizer, to determine their efficacy in restoring soil productivity. Eroded check (no amendment) and topsoil check (no desurf acing) treatments were left for comparison. One year later, wet aggreg ate stability at five levels of aggregate pre-wetting was determined. Aggregate stabilities of crop residue-amended soils were significantly higher (P < 0.01) than those of soils treated with animal manures or fertilizer/checks at all wetness levels. Significant (P < 0.01) quadra tic response and plateau relationships between aggregate stability and soil water content showed that there was a threshold moisture content for maximum stability. With the onset of rainfall, aggregates on the crop residue-amended treatments would reach maximum stability sooner t han those on the fertilizer/check treatments, thereby decreasing the p otential for water erosion. Stability of air-dry aggregates showed wea k positive relationships with organic and inorganic C. Amendment of er oded soils with crop residues is likely more effective in limiting ero sion than amendment with animal manures or chemical fertilizers, at le ast in the first year after incorporation.