?url_ver=Z39.88-2004&rft_id=doi%3A10.2136%2Fsssaj2012.0147&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.relation=https%3A%2F%2Forgprints.org%2Fid%2Feprint%2F22015%2F&rft.title=Sources+of+nitrogen+for+winter+wheat+in+organic+cropping+systems&rft.creator=Petersen%2C+S%C3%B8ren+O.&rft.creator=Schj%C3%B8nning%2C+P.&rft.creator=Olesen%2C+J%C3%B8rgen+E.&rft.creator=Christensen%2C+S.&rft.creator=Christensen%2C+B.T.&rft.subject=+Crop+combinations+and+interactions&rft.subject=+Soil+biology&rft.subject=+Nutrient+turnover&rft.subject=Farm+nutrient+management&rft.description=In+organic+cropping+systems%2C+legumes%2C+cover+crops%2C+residue+incorporation%2C+and+manure+application+are+used+to+maintain+soil+fertility%2C+but+the+contributions+of+these+management+practices+to+soil+nitrogen+(N)+supply+remain+obscure.+We+examined+potential+sources+of+N+for+winter+wheat+(Triticum+aestivum+L.)+in+four+experimental+cropping+systems+established+in+1997+on+three+soil+types.+Three+of+the+four+systems+were+under+organic+management.+Topsoil+N%2C+depth+of+the+A+horizon%2C+and+cumulated+inputs+of+N+since+1997+were+determined+at+plot+level.+Labile+soil+N+pools+(mineral+N%2C+potentially+mineralizable+N+%5BPMN%5D%2C+microbial+biomass+N+%5BMBN%5D)+were+monitored+during+two+growth+periods%3B+at+one+site%2C+biomass+C%2FN+ratios+were+also+determined.+Soil+for+labile+N+analysis+was+shielded+from+N+inputs+during+spring+application+to+isolate+cumulated+system+effects.+PMN+and+MBN+were+correlated+across+all+sites+and+rotations+(r2%3D0.72).+The+MBN+corresponded+to+46-85%2C+85-145+and+74-172+kg+N+ha-1+at+the+three+sites+and+differed+significantly+between+cropping+systems%2C+but+MBN+could+not+explain+differences+in+wheat+grain+N+yields.+Instead%2C+a+multiple+linear+regression+model+explained+76+and+82%25+of+the+variation+in+grain+N+yields+in+organic+cropping+systems+in+2007+and+2008%2C+showing+significant+effects+of%2C+respectively%2C+topsoil+N%2C+depth+of+A+horizon%2C+cumulated+inputs+of+N%2C+and+N+applied+to+winter+wheat+in+manure.+Thus%2C+soil+properties%2C+and+past+and+current+management+all+contributed+to+winter+wheat+N+supply.&rft.date=2013-02&rft.type=Journal+paper&rft.type=NonPeerReviewed&rft.format=application%2Fpdf&rft.language=en&rft.identifier=%2Fid%2Feprint%2F22015%2F1%2FPetersen%252C%2520Schj%25C3%25B8nning%252C%2520Olesen%252C%2520Christensen%2520and%2520Christensen%2520SSSAJ%25202013.pdf&rft.identifier=+++Petersen%2C+S%C3%B8ren+O.%3B+Schj%C3%B8nning%2C+P.%3B+Olesen%2C+J%C3%B8rgen+E.%3B+Christensen%2C+S.+and+Christensen%2C+B.T.+++(2013)+Sources+of+nitrogen+for+winter+wheat+in+organic+cropping+systems.+++Soil+Science+Society+of+America+Journal%2C+77+(2)%2C+pp.+696-697.++++++++&rft.relation=doi%3A10.2136%2Fsssaj2012.0147&rft.identifier=doi%3A10.2136%2Fsssaj2012.0147