Mineralizable soil nitrogen and labile soil organic matter in diverse long-term cropping systems |
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Authors: | John T Spargo Michel A Cavigelli Steven B Mirsky Jude E Maul John J Meisinger |
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Affiliation: | (1) Sustainable Agricultural Systems Laboratory, Animal and Natural Resources Institute, United States Department of Agriculture-Agricultural Research Services (USDA-ARS), 10300 Baltimore Ave., Beltsville, MD 20705, USA;(2) Environmental Management and By-Product Utilization Laboratory, Animal and Natural Resources Institute, United States Department of Agriculture-Agricultural Research Services (USDA-ARS), 10300 Baltimore Ave., Beltsville, MD 20705, USA |
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Abstract: | Sustainable soil fertility management depends on long-term integrated strategies that build and maintain soil organic matter
and mineralizable soil N levels. These strategies increase the portion of crop N needs met by soil N and reduce dependence
on external N inputs required for crop production. To better understand the impact of management on soil N dynamics, we conducted
field and laboratory research on five diverse management systems at a long-term study in Maryland, the USDA- Agricultural
Research Service Beltsville Farming Systems Project (FSP). The FSP is comprised of a conventional no-till corn (Zea mays L.)–soybean (Glycine max L.)–wheat (Triticum aestivum L.)/double-crop soybean rotation (NT), a conventional chisel-till corn–soybean–wheat/soybean rotation (CT), a 2 year organic
corn–soybean rotation (Org2), a 3 year organic corn–soybean–wheat rotation (Org3), and a 6 year organic corn–soybean–wheat–alfalfa
(Medicago sativa L.) (3 years) rotation (Org6). We found that total potentially mineralizable N in organic systems (average 315 kg N ha−1) was significantly greater than the conventional systems (average 235 kg N ha−1). Particulate organic matter (POM)–C and –N also tended to be greater in organic than conventional cropping systems. Average
corn yield and N uptake from unamended (minus N) field microplots were 40 and 48%, respectively, greater in organic than conventional
grain cropping systems. Among the three organic systems, all measures of N availability tended to increase with increasing
frequency of manure application and crop rotation length (Org2 < Org3 ≤ Org6) while most measures were similar between NT
and CT. Our results demonstrate that organic soil fertility management increases soil N availability by increasing labile
soil organic matter. Relatively high levels of mineralizable soil N must be considered when developing soil fertility management
plans for organic systems. |
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