Tuesday, November 6, 2007
224-7
Historic and Present Nitrate Loss in a Long Term Farming Systems Trial.
Barbara Fricks1, Jason Kaye1, Rita Seidel2, and Paul Hepperly3. (1) Crop and Soils, Penn State University, 115 ASI, University Park, PA 16802, (2) The Rodale Institute, 611 Siegfriedale Road, Kutztown, PA 19530, (3) Rodale Inst., The Rodale Institute, 611 Siegfriedale Road, Kutztown, PA 19530
Agricultural systems have been the main focus of a variety of environmental concerns. For example agricultural systems are one of the leading non-point sources for nitrate pollution. Different management practices can affect nitrate loss. Conventional agricultural systems use chemical fertilizers which have the potential for increased nitrate loss when broadcast, but reduced when banded. Organic agricultural systems rely on internal cycling of organic matter for plant nutrients. In organic systems nitrogen (N) cycling and subsequent nitrate loss are dependent primarily on weather and plant uses.
Our study examined N cycling over the course of a growing season in three agroecosystems at the Rodale Institute: 1) organically managed with composted manure, 2) organically managed with legumes and 3) conventionally managed. We used in-situ cores in the field to measure N-mineralization rates, buried resin bags to measure plant available N, and potential N-mineralization in lab incubations. Our goals were to examine differences between whole systems, rather than focusing on different management options. We found organic systems have comparable nitrate levels to conventional systems during the growing season, but both organic systems have greater potential to mineralize nitrate than the conventional system. We also analyzed nitrate loss from 1991-2006. Historically the conventional system had greater nitrate losses until management practice was changed in 1996; since then there has been no significant difference in rate of nitrate loss among the systems. Future studies examining management influence on N dynamics in the organic systems are needed to better understand and subsequently reduce nitrate loss from these systems.
Our study examined N cycling over the course of a growing season in three agroecosystems at the Rodale Institute: 1) organically managed with composted manure, 2) organically managed with legumes and 3) conventionally managed. We used in-situ cores in the field to measure N-mineralization rates, buried resin bags to measure plant available N, and potential N-mineralization in lab incubations. Our goals were to examine differences between whole systems, rather than focusing on different management options. We found organic systems have comparable nitrate levels to conventional systems during the growing season, but both organic systems have greater potential to mineralize nitrate than the conventional system. We also analyzed nitrate loss from 1991-2006. Historically the conventional system had greater nitrate losses until management practice was changed in 1996; since then there has been no significant difference in rate of nitrate loss among the systems. Future studies examining management influence on N dynamics in the organic systems are needed to better understand and subsequently reduce nitrate loss from these systems.