Effect of cattle excreta on leaching losses under a grass sward

Urine and dung of dairy cattle have been applied for two years at two periods of the year and in single or double quantity on a grass sward to assess nutrients losses by leaching. The total nitrogen losses varied from 18 to 226 kg/ha/year. Treatments without excreta or with dung applications led to N losses under 50 kg/ha/year, while losses exceeded clearly 100 kg/ha/year in the treatments with 2 urine applications in autumn. The total phosphorus losses were negligible, always under 1 kg/ha/year. For potassium, the apparent balance (input – export by the eight annual harvests) varied very much depending on the treatment, but K losses were hardly influenced by cattle excreta. K losses were very often close to 30 kg/ha/year and reached 49 kg/ha/year in the treatment with the largest K surplus (+716 kg/ha/year with 4 urine applications per year). The total magnesium losses averaged 70 kg/ha/year. They exceeded always the apparent balance and were little influenced by cattle excreta. To limit the risk of leaching losses during grazing, particularly of nitrogen, an even distribution of cattle excreta should be promoted by a adequate design and number of paddocks, a short length of stay per paddock and a regular pace throughout the grazing season. In autumn, full grazing should be avoided.