Abstract: | Fate of 15N after one single application of labelled N fertilizer in the long-term experiment Eternal Rye Cropping Halle To elucidate the fate of N in the long-term field experiment with continuous rye cropping in Halle, Germany (Haplic Phaeozem derived from sandy loess; mean annual precipitation: 466 mm) micro plots (9 m2) were established within the NPK main plot in 1993 and 1994 and the routine N dose (60 kg N ha—1 a—1) was once applied as 15N labelled fertilizer. In the subsequent four years each micro plot was analyzed for the 15N withdrawn with grain and straw and that remaining in the soil after harvest. Parallel to this, micro plots on the unfertilized main plot received a single dose of 5 kg ha—1 of high-label 15N in order to achieve labelling of the annual N input from the air (˜40 kg ha—1 a—1) and to follow its fate. — In the NPK treatment about one third of the labelled fertilizer N applied (= *N) was taken up by the rye in the first year, while nearly half of it remained in the soil (0—100 cm), and 10—15% was not recovered (most likely lost via leaching). During the following three years the amount of *N remaining in the soil decreased from 32.7 kg ha—1 to 21.5 kg ha—1. However, less than half of the remobilized *N had been taken up by the crop. On the unfertilized plot the uptake of *N was lower at the end of the experiment compared to the NPK plot, while the loss exceeded the comparative figure correspondingly. |