Nitrate leaching is not controlled by the slurry application technique in productive grassland on organic–sandy soil

International audienceThe return of slurry is the most important means of fertilization in grassland dairy farming. Broadcast application of slurry induces air pollution by ammonia. Alternatives to broadcast application like sliding shoe or injection have therefore been introduced. These alternatives might, however, cause higher N losses by nitrate leaching because N prevented from volatilization may not completely be utilized for dry matter production. Information on the interactive effects of amount of N input and slurry application technique on nitrate leaching from productive organic–sandy soils are still scarce. Therefore, we tested the hypothesis that slurry application by sliding shoe or injection leads to larger NO3-N losses via leaching than broadcast application. In a 4-year experiment on cut grassland, we applied N at 0, 160, 240, and 320 kg ha−1 year−1 using four application techniques: in the form of a chemical-synthetic N fertilizer or as cattle slurry applied broadcast, by sliding shoe or shallow injection. We assessed nitrate leaching during winter using suction cups. Additionally, we determined herbage dry matter yields, N offtake, and soil mineral N content to compile N balances for the individual treatments based on these data. Our results show that nitrate leaching during winter did not differ significantly among treatments of N application technique. Nitrate leaching increased significantly with increasing amount of N input, but was on average lower than 16.5 kg N ha−1 for application rates of up to 320 kg N ha−1. Soil mineral N content in autumn was a reasonably good predictor for nitrate leaching, with R2 of 0.65. The proportion of nitrate leaching of positive N surpluses increased in the order broadcast, sliding shoe, injection, and chemical-synthetic N application. Our findings demonstrate that the amount of N input but not the technique of application results in a significant effect on nitrate leaching