Nitrogen leaching from 15N labelled cow urine and dung applied to grassland on a sandy soil

Nitrogen ( N) leaching under grazed pastures can be very high directly under urine spots. The amount of N which is returned by one excretion of urine or dung can locally exceed 1000 kg ha(-1) a(-1) which is far more than the uptake by surrounding plants during one grazing period. We therefore quantified the contribution of N deriving from urine and dung to the total N leaching under urine and dung patches. Dung N and urine N was separately sampled from a cow feed with N-15 labelled grassilage, and were amended on lysimeters in October 2000 and October 2001. Lysimeters ( 350 mm diameter and 800 mm length) were filled with sand, and an intact grass sod from a pasture, 4 lysimeter each were amended with the N-15 labelled dung and urine; 4 lysimeters without an application of dung or urine served as control. During 11 months after dung and urine amendment the amount of leachate was monitored and leachate was analysed for nitrate, ammonium and total N. N-15 in these fractions was measured. Dung and urine applications of 1052 and 1030 kg N ha(-1) in autumn increased N leaching. Leaching loss of nitrate and dissolved organic N deriving from dung was only 37 kg N ha(-1) in both years, whereas under urine patches 447 kg nitrate-N ha(-1), 108 kg N ha(-1) ammonia-N and 53 kg ha(-1) dissolved organic N leached on average of both experimental years. N not deriving from dung and urine exceeded the leached N under the control by about 36 and 136 kg ha(-1) on average of both years, suggesting the contribution of different priming processes.