Nitrate leaching from cut grassland as affected by the substitution of slurry with nitrogen mineral fertilizer on two soil types

Abstract

AbstractA field experiment was conducted to find out whether there is any difference in risk of N leaching to groundwater when cattle slurry and/or mineral fertilizer‐N was applied to cut grassland. The experiment was carried out over two consecutive years on two sites (one with a relatively wet sandy soil and one with a relatively dry sandy soil). Treatments were mineral fertilizer‐N at annual rates of 0–510 kg N ha−1 year−1 and combinations of sod‐injected cattle slurry (85, 170, 250 and 335 kg N ha−1 year−1) and mineral fertilizer‐N (289, 238, 190 and 139 kg N ha−1 year−1). Yield responses indicated that in the short run, 0·44–0·88 (average 0·60) of the slurry‐N was as available as mineral fertilizer‐N. The total N input from mineral fertilizer and slurry was a worse predictor of nitrate leaching ( 0·11) than the N surplus (i.e. the difference between total N input and harvested N) ( 0·60). The effective N surplus, based on the difference between the summed inputs of the plant‐available N and harvested N, proved to be the best indicator of leaching ( 0·86). Annual N application rates of up to 340 kg plant‐available N ha−1 complied with the target nitrate concentration in groundwater of 11·3 mg N L−1 set by the European Union in both years on the wet sandy soil, whereas on the dry sandy soil none of the treatments did.