Nitrogen leaching from winter cereals grown as part of a 5-year ley–arable rotation

Abstract

Ceramic suction cups were used to measure nitrogen (N) leaching over three consecutive winter periods from a long established ley–arable rotation experiment. We examined four treatments: 3-year all-arable, grass–clover ley and grass ley each followed by two seasons of arable test crops and an 8-year grass ley that remained as grass throughout our study. Four rates of fertilizer N were applied to sub-plots of the test crops. Our primary objective was to compare the effect that the rotations had on N leaching from the arable test crops. Cultivation of the 3-year grass and grass/clover leys and the sowing of winter wheat did not create a major flush of net N mineralization because of the unusually dry autumn weather. In the first winter following sward destruction, although the concentration of N in drainage following the grass/clover was low, it was significantly greater than that following the grass, which was greater than that from the continuous grass treatment. In contrast, the concentration and quantity of N in drainage from the all-arable treatment was at least five times greater than any other treatment. This was due to earlier and more rapid N release from the residue of the preceding arable crop. In the winters after harvest of the cereal test crops (i.e. the second and third season of measurements), the peak drainage N concentrations were similar in all treatments (20 μg NO 3-N ml −1). The amount of N leached was not related to fertilizer addition. Over the full 5-year rotation, we found that the rotations that included a ley were better at conserving N; the estimated annual N leaching losses from the all-arable, grass, grass/clover and continuous grass were 29, 17, 17 and 2 kg N ha −1 year −1, respectively. On all treatments, but especially the grass–clover ley, the greatest rate of fertilizer addition caused a yield reduction. The N-balance indicates a considerable net immobilization during this study under the sub-plots of the arable test-crops that received N fertilizer. This corresponds to similar results of N-balance studies on other long-term experiments.