Organic matter quality and structural stability of a Black Chernozemic soil under different manure and tillage practices

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 (CHCl3) 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 CT 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/CHCl3 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 Sh I 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. (C) 1999 Elsevier Science B.V. All rights reserved.