The effect of crop residue incorporation date on soil inorganic nitrogen, nitrate leaching and nitrogen mineralization

Delaying cultivation and incorporation of arable crop residues may delay th e release of NO, and hence reduce leaching. The objective of this study was to investigate the effect of timing of cultivation on the mineralization a nd leaching of NO3- from an arable crop residue. Overwinter N leaching and periodic measurements of soil inorganic N were combined to estimate net N m ineralized after ploughing a crop residue into a free-draining loamy sand s oil in central England on six dates from June 1994 to January 1995. The cro p residue-was whole green barley with approximately 2% N. N leaching in the two following winters was increased by the addition of crop residues. Earl y residue application also tended to increase N leached in the first winter , largely as a consequence of relatively large losses early in the drainage period. Thus, early incorporation ration:of crop residues presents a great er leaching risk. The amount of N leached in the second (drier) winter was similar for all dates of incorporation. At the end of the first winter, ino rganic N derived from the crop residue was greatest for earlier additions: June (40% N applied) > September (30% N applied) > August (20% N applied) > October (19% N applied) > November (11% N applied) > January (3% N applied ). However, at the end of the experiment, there was no evidence that the re sidues which had mineralized least by the end of the first winter had, to a ny significant degree, caught up, and this was confirmed by the parameters of the equation for first-order decomposition in thermal time. These result s indicate that the effect of temperature, particularly in the early stages of residue mineralization, is complex and interacts with other soil proces ses in terms of the fate of the N mineralized.