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Enhancing Farmland Water Quality and Availability Through Soil-Building Crop Rotations and Organic Practices


<ol> <LI>Design integrated, multi-functional organic crop rotations that include legume and grass crops for improved water retention and water quality enhancement, based on stakeholder input in focus groups prior to the establishment of research sites;<LI> Establish experimental systems at University and on-farm sites, including extensive instrumentation to monitor water quantity and water quality; <LI> Develop recommendations for methods to improve water quality based on results derived from agronomic and soil data, tile drain water flux and water quality, and simulation models: a. Develop nitrogen budget and water balance estimates; b. Develop relationships between individual/integrative indicators of soil quality and water balance/environmental/productivity endpoints; c. Calibrate and validate the Root Zone Water Quality Model (RZWQM) for organic grain cropping systems;<LI>Enhance economic performance of farms that develop Best Management Practices (BMPs) for managing water resources; <LI>Develop and offer educational projects through specific class modules taught at Iowa State University, and technology transfer techniques with farmer networks, that enhance understanding of water quality and organic farming connections for undergraduate/graduate students, farmers, Extension, and policymakers. </ol>Expected outputs from Objectives 1, 2, and 3 of this project include the development of a new site for tile drainage water quality research in certified organic systems at the ISU Agronomy Research Farm. Once the infrastructure for tile drain water monitoring has been installed, the site will provide the opportunity for long-term studies to accurately assess water quality for the extended cropping rotations typically used in organic agriculture. <P>The project will provide unique data, including model calibration and validation of the RZWQM for organic systems, that quantifies the impact of extended organic cropping rotations and pasture systems on subsurface tile drain water quantity and quality. Possible limitations include similar potential limitations for any water quality study: difficulty in calibrating drainage flow from each plot or failure of some plots to drain adequately due to differences in soil type at the site. <P>Expected outcomes from Objectives 4 and 5 include a better understanding of water quality parameters and BMPs by local communities resulting from the demonstrations and educational modules; more efficient organic crop and animal production systems; and more vibrant local communities resulting from additional economic activities associated with diversified farming and marketing systems.

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Non-Technical Summary: U.S. agriculture is facing worldwide competition for petroleum and increased costs for fertility inputs, leaving producers to compete within the larger system or re-align their farming practices to allow participation in alternative markets, such as organic agriculture, to garner greater economic returns. Non-point source contamination from leaching of nitrates in synthetic fertilizers is a major water quality concern in the upper Midwest, where extensive subsurface tiling drains the highly productive soils. Surface-water nitrate concentrations routinely have been reported in excess of the 10 mg L-1 drinking water standard. This multi-disciplinary, multi-agency project, with over 50 years combined experience in water quality and organic agriculture research, aims to assist producers in developing systems that would facilitate access to the growing organic market while improving water quality on their farms. This is a long-term, integrated project encompassing research, extension and education, targeted at meeting Program Goals to improve water quality on organic and conventional farms through the development of science-based management practices identified as a result of state-of-the art water quantity and quality monitoring in replicated organic and conventional research station and on-farm sites. The hypothesis is that the use of integrated organic crop rotations with legume and grass crops will result in improved water retention and water quality by enhancing nutrient and water cycling in the soil-plant system. Our objectives include the development of nitrogen budget and water balance estimates from research sites and the identification of relationships between individual/integrative indicators of soil quality and water balance/environmental/productivity endpoints. Additionally, research results will be used to calibrate and validate the Root Zone Water Quality Model (RZWQM) for organic grain cropping systems. Results will be presented in classroom and Extension programs and publications to facilitate producer involvement in self-development of water quality enhancement techniques. National environmental benefits include the reduction of crop nutrient losses, soil erosion, and pesticide transport; and improved security and quality of the food system. <P> Approach: Research will be conducted at a field site located on the Iowa State University Research Farm near Boone, IA. The field was transitioned to organic management in 2006 and will remain in oats/alfalfa through 2010. Thirty field plots (30.5 m by 32 m) will be established in spring 2010. The plots will be arranged in three tiers along the long axis of the field. Each tier will be separated by a 12.2 m grass alleyway. Installation of the tile drainage tubes and water-monitoring infrastructure will occur in August 2010 after stakeholder input and extensive site analysis to isolate the near subsurface drainage in order to obtain tile water flow (water quantity) and tile water nutrient concentrations (quality) from each plot. A 20.3-cm diameter drainage pipe will be installed to a depth of 1.2 m around the entire perimeter of the field to isolate the site drainage from surrounding field drainage. A perforated, 10.2-cm diameter corrugated drainage pipe will be installed 1.2 m below the surface lengthwise down the center of each plot. Drainage from each plot will be conducted by solid plastic pipe to one of five sump pits. Within each sump pit, drainage from six plots will be collected into dedicated sumps for measurement of flow volume and flow-weighted sampling for nitrate analysis. A hydrologic barrier will be buried to a depth of 1.2 m on the east and west border of each plot to prevent subsurface lateral flow of water between the plots. To prevent subsurface lateral flow between the plots at the north and south plot border, a 10.2-cm drainage pipe will be installed within the grass alleyways to a depth of 1.2 m. Water from the perimeter tile and the horizontal tiles will be diverted to a county tile located close to the field site. Ultimately, after the tile water is sampled under each plot, the excess water will be also diverted to the county tile. Tile drainage from each plot will be collected in dedicated sumps with a pump that empties the sump whenever the water level exceeds a preset level. Only the center drainage line will be monitored for drainage volume and NO3-N concentration. Flow from each pump will be monitored through a combination electrical and mechanical totalizing flow meter with flow volume versus time recorded with a data logger. Flow proportional water samples are composited over approximately weekly intervals via a capillary tube connected to each sump pump outlet. Water samples will be taken to the laboratory, refrigerated, and analyzed for (NO3+NO2)-N using a colorimetric method and flow injection technology. Nitrate-N loads will be calculated by multiplying the NO3-N concentration for the composite sample by the total volume of drainage during the compositing. Water and nutrient balances will be calculated from this system, along with agronomic parameters, including crop growth and yield.

Delate, Kathleen
Iowa State University
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