Changes in N leaching and crop production as a result of measures to reduce N losses to water in a 6‐yr crop rotation

The effects of various measures introduced to increase nitrogen (N)-use efficiency and reduce N losses to water in a 6-yr crop rotation (winter wheat, spring barley, green manure, winter wheat, spring barley, spring oilseed rape) were examined with respect to N leaching, soil mineral N (SMN) accumulation and grain yield. An N-use efficient system (NUE) with delayed tillage until late autumn and spring, direct drilling of winter wheat, earlier sowing of winter and spring crops and use of a catch crop in winter wheat was compared with a conventional system (CON) in a field experiment with six separately tile-drained plots in south-western Sweden during the period 1999-2011 (two crop rotation cycles). Total leaching of NO3-N from the NUE system was significantly 46 and 33% lower than in the CON system during the first and second crop rotation cycle, respectively, with the most pronounced differences apparently related to management strategies for winter wheat. Differences in NO3-N leaching largely reflected differences in SMN during autumn and winter. There was a tendency for lower yields in the NUE system, probably due to problems with couch grass. Overall, the measures for conserving N, when frequently used within a crop rotation, effectively reduced NO3 concentrations in drainage water and NO3-N leaching losses, without severely affecting yield.