' ql{ winkleman, G' E' 1996' Nitrogen bclefits from four green-manure legumes in dryland cropping systems. can. i. punt Partial replacement of fallow with legume green manures has the p"ll"ti""i to improve i.ia ptJu"tt-"r.14 agricultural sustainability in the northern Great Plains' This is possible if N gains by annual legumes and enhan.eirrrent of soil N aiailability are optimized. The objectives of the study were to (i) determine the N distributionln different vegetative components of four annual legumes; (ii) estimate their ability to accumulate N through fixation; and (iii) compare the N uptate of ihe cereal crop that follows tegume green manure with that of cereal grown on fallow or of cereal ieceiving N fertilizer. Blac k lentii-(Lens culinaris Medik.), Tangier flatpea (Lathyrus tingitanus L'), chickling vetch (Lathyrus sativus L)l and feedpea (Pisum satiwm L.) were grown in rotation with spring wheat (Triticum aestivum L.). Nitrogen concentration in iegume nodulei was several times greater than in any other plant part' However, N concentration in legume shoots was, on average, 27o/o greiter than in legume rJots. Total legume N content (% x mass) ranged from 4l to 126 kg hrl in years of low weedinJss. fn tt ose yeari, Uetow-"grounA
Galculations and Statistical AnalysesSoil bulk densities determined at the same experimental site in a previous study (Dyck et al. 1977) were used together with depth increments to convert nutrient concentrations to nutrienfcontents. Plant and grain N yields were calculated as the product of nutrient concentrations and crop yields' The difference in plant N uptake between each legume at firll bloom and the N taken up by spring wheat from the continuous-wheat control treaunent when sampled the same day as the legumes was used to estimate total N fxed by the green--atture crop. For the wheat refefence crop, it was issumed, on the baiis of earlier experiments at the same site, that the below-ground N uptake was 20Yo of the total plant uptake and that the recovery of fertilizerN was 50% of the amonnt applied Campbell and Paul 1978
CANADIAN JOURNAL OF PLANT SCIENCE