Since 1986, the fate of fertilizer N (NH4NO3 or NaNO3) applied in field conditions on two main arable crops, winter wheat (Triticum aestivum) and sugar beet (Beta vulgaris), has been studied using N-15. UP to a rate of 200 kg ha(-1) of N, mean recovery of fertilizer by winter wheat was 70%, provided it had been split applied. Single application (with or without dicyandiamid) was less effective. For sugar beet, in 1990, 1991 and 1992, 40% of fertilizer N was found in the crop at harvest when NH,NO, had been broadcast at 100 to 160 kg N ha(-1) at sowing time. For the same N rate, recovery was 50% when row applied near the seeds and 60% for 80 kg N ha(-1). For the two experimental crops, residual fertilizer N in soil was exclusively organic. It ranged from 15 to 30% of applied N and was located in the 30 cm upper layer. Losses were generally lower with winter wheat (12%) than with sugar beet (20-40%) and could be ascribed to volatilization and denitrification. Soil derived N taken up by the plant was site and year dependent.
