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United States Department of Agriculture

Agricultural Research Service

Research Project: PRINCIPLES AND PRACTICES FOR IMPROVING ORGANIC FARMING IN THE MID-ATLANTIC REGION Title: Mineralizable soil nitrogen and labile soil organic matter in diverse long-term cropping systems

Authors
item Spargo, John
item Cavigelli, Michel
item Mirsky, Steven
item Maul, Jude
item Meisinger, John

Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 31, 2011
Publication Date: February 20, 2011
Citation: Spargo, J.T., Cavigelli, M.A., Mirsky, S.B., Maul, J.E., Meisinger, J.J. 2011. Mineralizable soil nitrogen and labile soil organic matter in diverse long-term cropping systems. Nutrient Cycling in Agroecosystems. 90:253-266.

Interpretive Summary: Sustainable agriculture depends on soil fertility strategies that build and maintain soil organic matter (SOM). Since SOM serves as a continuous-release nitrogen (N) source for plants, building up levels of SOM allows farmers to reduce external N inputs, providing economic benefit to farmers and improving environmental health. However, the impacts of diverse management practices on SOM pools are not well understood. To better understand these impacts, we conducted field and laboratory research on five diverse management systems at a long-term study in Maryland, the USDA-ARS Beltsville Farming Systems Project (FSP). The FSP is comprised of a conventional no till rotation (NT), a conventional chisel-till rotation (CT), a 2-yr organic rotation (Org2), a 3-yr organic rotation (Org3), and a 6-yr organic rotation (Org6). We found that particulate organic matter (POM) C and N , chemically-labile organic matter (CLOM), potentially mineralizable soil N, and corn yield and N uptake from unamended plots were greater in organic than conventional cropping systems. All these measures of soil N availability were generally similar between NT and CT. 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). Our results demonstrate that organic management practices increase soil N availability by increasing labile SOM compared to conventional systems. These results will help farmers better understand the impact of their management on building soil fertility and will provide scientists additional data upon which to develop improved nutrient management recommendations.

Technical 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 cycling 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-ARS Beltsville Farming Systems Project (FSP). The FSP is comprised of a conventional no till corn–soybean–wheat/ soybean rotation (NT), a conventional chisel-till corn–soybean–wheat/soybean rotation (CT), a 2-yr organic corn–soybean rotation (Org2), a 3-yr organic corn–soybean–wheat rotation (Org3), and a 6-yr organic corn–soybean–wheat–alfalfa rotation (Org6). We found that particulate organic matter (POM) C and N , chemically-labile organic matter (CLOM), potentially mineralizable soil N, and corn yield and N uptake from unamended plots were greater in organic than conventional cropping systems. All measures of N availability were generally similar between NT and CT. 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). Our results demonstrate that organic management practices increase soil N availability by increasing labile soil organic matter compared to conventional systems. Relatively high levels of mineralizable soil N must be considered when developing soil fertility management plans for these systems.

Last Modified: 11/21/2014