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Sources of Nitrogen for Winter Wheat in Organic Cropping Systems
Author(s) -
Petersen Søren O.,
Schjønning Per,
Olesen Jørgen E.,
Christensen Søren,
Christensen Bent T.
Publication year - 2013
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2012.0147
Subject(s) - topsoil , agronomy , subsoil , cropping system , plough , nitrogen , environmental science , cropping , soil fertility , green manure , manure , cover crop , biomass (ecology) , winter wheat , soil water , chemistry , crop , soil science , biology , agriculture , ecology , organic chemistry
In organic cropping systems, legumes, cover crops (CC), residue incorporation, and manure application are used to maintain soil fertility, 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, depth of the A horizon, and cumulated inputs of N since 1997 were determined at plot level. Labile soil N pools [mineral N, potentially mineralizable N (PMN), microbial biomass N (MBN)] were monitored during two growth periods; at one site, biomass C/N ratios were also determined. Soil for labile N analysis was shielded from N inputs during spring application to isolate cumulated system effects. Potentially mineralizable N and MBN were correlated across all sites and rotations ( r 2 = 0.72). The MBN corresponded to 46 to 85, 85 to 145, and 74 to 172 kg N ha −1 at the three sites and differed significantly between cropping systems, but MBN could not explain differences in wheat grain N yields. Instead, a multiple linear regression model explained 76 and 82% of the variation in grain N yields in organic cropping systems in 2007 and 2008, showing significant effects of, respectively, topsoil N, depth of A horizon, cumulated inputs of N, and N applied to winter wheat in manure. Thus, soil properties and past and current management all contributed to winter wheat N supply.