Quantifying nitrogen flux after application of N-15-labelled pig slurry on triticale in the late autumn.

Predicting nitrate leaching after spreading slurry in autumn is difficult because plant uptake, mineralization, immobilization, volatilization and denitrification occur and modify the nitrate pool available for leaching. To estimate these fluxes, pig slurry was labelled with ((NH4)-N-15)(2)SO4 and spread in December (110 kg NH4-N.ha(-1)) on triticale. Soil microbial immobilization, crop uptake and soil inorganic nitrogen were measured at seven dates between day 2 and 63 after application. NH4-N in the slurry follows three ways of transformation: volatilization (38 kg N.ha(-1) in 16 days), immobilization (29 kg N.ha(-1) at day 30) and nitrification (42 kg N.ha(-1)). This last one was achieved 48 days after spreading, despite the cold mean temperatures measured during the experiment. Gross mineralization of soil and slurry organic nitrogen was large (35 kg N.ha(-1) for the 0-10 cm soil layer). The real utilization coefficient of N-15- labelled N was low, smaller than 4% at day 63. The leaching of nitrate was small because there was no rainfall after day 48. Thus, from the balance of N-15-labelled N, it is suggested that 22 kg NO3 N.ha(-1) has been lost by denitrification.