Stickstoffverluste unter begülltem Grünland

Leaching of nitrogen from permanent grassland treated with cattle slurry The objective of this study was to determine the effect of cattle slurry and mineral nitrogen fertilization on nitrate contamination of the interflow soil water. Field experiments were conducted at grassland research station ‘Rengen’ in the Eifel area (475 m a.s.L., 7.5 °C mean temperature, 806 mm mean yearly precipitation). In the respective plots soil consisted of 40 cm loamy material over a compact, almost water impermeable soil layer. The 2 × 6 m sized individual plots were prepared 1985 in a way so that surrounding soil was removed down to the compact soil layer about 45 cm deep and the monolith beeing packed by polyethylene sheets, waterproofing the plots down to the water impermeable soil layer. At the open lower ends of the plots near the soil surface and at 45 cm depth respectively, metal sheets were inserted to drain the surface run‐off and interflow water into gutters and from there into collecting tanks. Nitrogen fertilization included two cattle slurry treatments (240 kg and 480 kg ha −1 a −1 total nitrogen), combination of mineral nitrogen with cattle slurry (200 kg + 160 kg ha −1 a −1 ) and mineral nitrogen treatments without slurry (200 kg ‐ ha −1 a −1 ). Control plots received neither mineral nor slurry nitrogen. The quantification of interflow water and its nitrogen concentration started in 1986. In this year relatively high nitrate concentrations up to 56 mg l −1 appeared in the interflow water. 1987 nitrogen concentrations dramatically decreased to mean values between 10 and 15 mg l −1 in all fertilization treatments. Similar levels of nitrate concentrations were observed in the following two years. Total amounts of nitrogen losses did nor exceed 5 kg ha −1 a −1 in any of the years from 1986 to 1988, nor were differences observed in nitrate concentration among the fertilization treatments.