TRANSFER OF GRAIN LEGUME NITROGEN WITHIN A CROP-ROTATION CONTAINING WINTER-WHEAT AND WINTER BARLEY

In a crop rotation trial, conducted from 1985 to 1988 at TU-Munich's r esearch station in Roggenstein, the transfer of grain legume nitrogen was evaluated in crop rotations containing fababeans and dry peas as w ell as oars (reference crop) and winter wheat and winter barley as fol lowing crops. The results obtained can be summarized as follows: Dinit rogen fixation by fababeans ranged from 165 to 240 kg N ha(-1), wherea s N-2-fixation by peas amounted from 215 to 246 kg N ha(-1). In all se asons the calculated N-balance where only grain was removed was positi ve, with a net gain being on average 106 (peas) and 84 (fababeans) kg N ha(-1). After the harvest of peas 202 kg N ha(-1) remained on the fi eld on average over seasons (158 kg N ha(-1) in the above ground bioma ss and 44 kg N ha(-1) as NO3-N in 0-90 cm depth). As compared to peas, fababeans left 41 kg N ha(-1) less due to smaller amounts of nitrogen in the straw. After oats very small amounts of residual nitrogen (33 kg N ha(-1)) were detected. After the harvest of grain legumes always a very high nitrogen mineralization was observed during autumn especia lly after peas due to a close C/N relationship and higher amounts of n itrogen in the straw as compared to fababeans. In comparison with faba beans, N-mineralization after the cultivation of oats remained lower b y more than 50%. During winter, seepage water regularly led to a consi derable decrease of soil NO3-N content. The N-leaching losses were esp ecially high after cultivation of peas (80 kg N ha(-1)) and considerab ly lower after fababeans (50 kg N ha(-1)) and oats (20 kg N ha(-1)). A s compared to oats, a higher NO3-N content in soil was determined at t he beginning of the growing period after preceding grain legumes. Ther efore, winter wheat yielded highest after preceding peas (68 dt ha(-1) ) and fababeans (60 dt ha(-1)) and lowest after preceding oats (42 dt ha(-1)). The cultivation of grain legumes had no measurable effect on yield formation of the third crop winter barley in either of the growi ng seasons.