Nitrate leaching and apparent recovery of urine-N in grassland on sandy soils in the Netherlands

Urine patches are an important nitrogen input source in managed pasture systems. The objective of this study was to quantify the effect of artificial urine application at different dates on nitrate leaching in a well drained sandy soil. In three subsequent years, we measured nitrate leaching and apparent urine-nitrogen recovery (ANR) in a field experiment and in two lysimeter experiments over a period of 1 year post urine application. Artificial urine patches with 400 kg ha-1of urine-N were applied at different times of the grazing seasons. For the field experiment, we compared nitrate leaching measurements with NURP model calculations. In the field experiment, greatest ANR was measured for spring and summer applications (averaging 31% of applied urine-N), and significantly declined to 0% for October applications. Nitrate leaching increased under urine patches, with a significant effect of application date. This effect was not, however, consistent over the three years. Total recovery of N in grass and of mineral N in leachate and soil was generally less than the amount of urine-N applied, with a balance deficit of 60-80% (field) or 10-70% (lysimeters). For the field experiment, the total increase in nitrate leaching corresponded reasonably well with NURP model calculations. However, the effect of application date on nitrate leaching was much smaller in the field experiment. Our results suggest that restrictions to grazing in autumn probably will be effective in decreasing the annual amount of nitrate leached, although this decrease remains hard toquantify