Résumé :
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Losses of nitrogen (N) and phosphorus (P) from perennial grass ley on a fine sand soil were studied with five treatments: no fertilizer (1), cow slurry applied in autumn (2), winter (3) or spring (4), and mineral fertilizer applied in spring (5). For N, the total amounts applied (1992-96) were 0, 772, 807, 805 and 510 kg ha(-1) and for P 0, 141, 119, 143 and 107 kg ha(-1), respectively. In the first year (establishment of the ley, 1992-93), N losses (drainage,ae + surface runoff) were slightly higher after application of slurry in autumn (with immediate ploughing, treatment 2) than in treatments 1, 4 and 5 (21 kg ha(-1) vs. 17 kg ha(-1)), but the respective P losses (0.7-0.9 kg ha(-1)) were not affected. During the Iey years (1993-96) the N and P losses were increased by surface application of fertilizers and by abundance of surface runoff (83-100% of the total runoff). Nutrient losses were extremely high after slurry application in autumn and winter, accounting for 11% and 33% of the applied N and 17% and 59% of the applied P, respectively. The N losses during the Iey years from treatments 1-5 were 13, 62, 191, 23 and 24 kg ha(-1), where the proportion of NH,-N was 21, 49, 56, 33 and 39%. The respective P losses were 0.73, 16, 54, 4.2 and 4.0 kg ha(-1), where the proportion of PO4-P was 52, 85, 77, 68 and 64%.
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