Transfer of Grain Legume Nitrogen within a Crop Rotation Containing Winter Wheat and Winter Barley

Abstract

AbstractIn a crop rotation trial, conducted from 1985 to 1988 at TU‐Munich's research station in Roggenstein, the transfer of grain legume nitrogen was evaluated in crop rotations containing fababeans and dry peas as well as oats (reference crop) and winter wheat and winter barley as following crops. The results obtained can be summarized as follows:Dinitrogen fixation by fababeans ranged from 165 to 240 kg N ha1, whereas N2‐fixation by peas amounted from 215 to 246 kg N ha−1. In all seasons the calculated N‐balance where only grain was removed was positive, 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 field on average over seasons (158 kg N ha−1 in the above ground biomass 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 especially after peas due to a close C/N‐relationship and higher amounts of nitrogen in the straw as compared to fababeans. In comparison with fababeans, N‐mineralization after the cultivation of oats remained lower by more than 50%.During winter, seepage water regularly led to a considerable decrease of soil NO3‐N content. The N‐leaching losses were especially high after cultivation of peas (80 kg N ha −1) and considerably lower after fababeans (50 kg N ha−1) and oats (20 kg N ha−1).As compared to oats, a higher NO3‐N content in soil was determined at the beginning of the growing period after preceding grain legumes. Therefore, 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 growing seasons.