Abstract
No-tillage (NT) and addition of organic matter can improve soil aggregation and affect soil organic matter (SOM) levels. The effects of short-term (3 years, 1993–1996) conventional tillage (CT), NT, and cattle manure applications on SOM quality and water-stable aggregates (WSA) were investigated on a Melfort silty clay loam (Orthic Black Chernozem) at Melfort (Saskatchewan, Canada). Four methods for managing manure (dry weight basis) within CT and NT were established: fresh manure (FM) was applied at the beginning of the experiment at 23.0 Mg ha −1 and annually at 4.5 Mg ha −1, whereas stockpiled manure (SM) with equal N concentration to FM was applied at the beginning of the study at 23.0 Mg ha −1 and annually at 4.5 Mg ha −1. The control treatment consisted in annual application of 81.0 kg N ha −1 as ammonium nitrate and 9.3 kg P ha −1 as monoammonium phosphate, according to soil test recommendations. Soil samples (0–15 cm) were collected at the end of the 3-year period and lipids were extracted with diethyl ether (DEE) and chloroform (CHCl 3) to assess SOM quality. Water-stable aggregates were measured with and without ethanol pretreatment and before and after extraction of unbound lipids. The amounts of C and N was not affected by the treatments. Between NT and CT, the changes in SOM were expressed by an increase of 21% of the amounts of total extractable lipids (TEL) in the CT soils, whereas in the NT soils, the DEE/CHCl 3 ratio used to assess the degree of biodegradability of OM increased by 40%. Following the application of FM, the stability of soil aggregates against the dissolution and dispersive actions of water decreased by 13 and 16% in CT and NT soils, respectively; however, this effect was compensated by an equivalent increase in resistance to slaking forces. In contrast, the incorporation of SM did not affect the stability of soil aggregates against the dissolution and dispersive actions of water, but increased by 7% the resistance of aggregates to slaking forces.
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