Nitrogenfrigjøring og ettervirkning ved bruk av grønngjødsel på utvalgte jordtyper på Østlandet: N frigjøring og ettervirkning av grønngjødsel

摘要

A study of green manure yields, nitrogen mineralization, and after-year effects was carried out on five soils in Southeast Norway. When used as a whole-season green manure, a mixture of red clover and grass gave a larger yield (8310 kg DM ha~(-1)) than from field beans (6775 kg DM ha~(-1)) and a mixture of common vetch, Italian ryegrass and Persian clover (6612 kg DM ha~(-1)). In the late autumn the leaching potential after green manure crops was not very much higher (42 kg N_(min) ha~(-1)) than that after grain cultivation (38 kg Nmin ha~(-1)), but leaching was affected by the type of species in the green manure mixture and the time of ploughing. A mixture of red clover gave the largest after-year effect (+875 kg grain ha~(-1)) compared with trials without green manuring. The root mass rather than the above-ground mass of the green manure crops seemed to play the most important role in after-year effect. A study of undersown green manure crops was also carried out. The study showed that white clover did not reduce the yield of grain in the undersown year. Red clover and mixtures of clover and Italian rye grass gave a 6-12% reduction in yield in the undersown year. Undersown white clover gave an 18% increase in yield the following year, while the other undersown crops gave an 0-10% increase compared with trials without undersown green manure. In trials with undersown green manure there was a reduction in leaching potential (14.7 kg N-min ha~(-1)) compared with trials without undersown green manure (17.9 kg Nmin ha~(-1)).