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 barle y (Hordeum vulgare L.) residue particle size combined with shallow (10 cm) or deep (20 cm) incorporation on soil N immobilization-mineralization, micr obial biomass N dynamics, and plant N uptake. Deep incorporation of ground (< 3 mm) residues in the autumn gave an immobilization of 415 mg N m(-2) ov er 18 days which was 30 % higher than with cut (25 mm) residue, and about t wice as much as for shallow incorporation of the same amounts of residue. I n the spring, deep incorporation of over a 53-day period, ground residue mi neralized 756 inc, N m(-2) comparable to residue-free soil. Ground residue incorporated to 10 cm gave 72 % less mineralization than the residue-free c ontrol soil. Microbial biomass N increased during autumn and winter in resp onse to residue applications suggesting that residue carbon remained availa ble for microbial growth, probably because decomposition was N-limited. Hig h 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 barle y (ev Ermo) was limited 25 % by deep incorporated ground residue, but not s ignificantly by the other treatments. In contrast, spring barley (cv Alexis ) was not limited by deep incorporation of ground residue. The sequestratio n of N for the barley crop., constituted less than 4 % of the residue N, an d was 45 % to 63 % lower with shallow than with deep residue incorporation. Growth of winter oilseed rape (Brassica napus L. ev Bristol) after the bar ley crops was generally not influenced by the residue treatment. Overall, t he study shows that by management of crop residues it may be possible to re gulate soil N mineralization-immobilization and match the N release synchro nously with the crop requirement.