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CROP RESIDUE MANAGEMENT STRATEGIES TO REDUCE N-LOSSES—INTERACTION WITH CROP N SUPPLY

Management of the crop residues may provide a means to preserve nitrogen (N) in the agro-ecosystem. In a field study, we examined the effects of barley (Hordeum vulgare L.) residue particle size combined with shallow (10 cm) or deep (20 cm) incorporation on soil N immobilization-mineralization, microbial biomass N dynamics, and plant N uptake. Deep incorporation of ground (<3 mm) residues in the autumn gave an immobilization of 415 mg Nm−2 over 18 days which was 30 % higher than with cut (25 mm) residue, and about twice as much as for shallow incorporation of the same amounts of residue. In the spring, deep incorporation of ground residue mineralized 756 mg N m−2over a 53-day period, comparable to residue-free soil. Ground residue incorporated to 10 cm gave 72 % less mineralization than the residue-free control soil. Microbial biomass N increased during autumn and winter in response to residue applications suggesting that residue carbon remained available for microbial growth, probably because decomposition was N-limited. High N mineralization with deep incorporation of ground residue in the spring was accompanied by a reduction in microbial biomass N, indicating that the mineralized N was derived from microbial N turnover. Growth of winter barley (cv Ermo) was limited 25 % by deep incorporated ground residue, but not significantly by the other treatments. In contrast, spring barley (cv Alexis) was not limited by deep incorporation of ground residue. The sequestration of N for the barley crops constituted less than 4 % of the residue N, and was 45 % to 63 % lower with shallow than with deep residue incorporation. Growth of winter oilseed rape (Brassica napus L. cv Bristol) after the barley crops was generally not influenced by the residue treatment. Overall, the study shows that by management of crop residues it may be possible to regulate soil N mineralization-immobilization and match the N release synchronously with the crop requirement.