Nitrogen uptake by Italian ryegrass after destruction of non-fertilized set-aside covers at different times in autumn and winter

The introduction of the European set-aside into the rotation can modify the nitrogen availability for subsequent crops. With a view to evaluating this effect, three non-fertilized covers were sown in May 1995. These covers we re ploughed in at three different times: October 1995, December 1995 and Ma rch 1996. The ploughed-in nitrogen quantities did not vary greatly with des truction time. The greatest quantities were incorporated into red clover pl ots and the smallest quantities into perennial ryegrass plots. The C/N of p erennial ryegrass was on average 24 and that of red clover 14. The soil cover by clover just before ploughing is significantly related to the ploughed-in nitrogen quantities. An Italian ryegrass was sown as the subsequent crop to the set-aside. Overa ll, during the whole year 1996 and 1996-1997, there was no difference betwe en the yields for different destruction times except for the first cut of 1 996. The highest production was obtained after red clover and the lowest after p erennial ryegrass. The relationship between the nitrogen amount or C/N of t he ploughed-in material and the nitrogen export for the annual harvest of I talian ryegrass showed highly significant correlations in 1996 as well as f or the 2-year harvest. Two multiple regressions were calculated in order to take into consideration the characteristics of the ploughed-in material of the set-aside. The measured percentage of soil cover by clover before ploughing and the an nual nitrogen export of Italian ryegrass were also significantly related in 1996 and for both years.