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Effectiveness of Irrigated Crop Management Practice in Reducing Groundwater Nitrate Concentrations


Our primary objective is to evaluate the effectiveness of long-term nutrient and water management in reducing groundwater nitrate concentrations. Groundwater nitrate data collected from 1988-2006 will be used in the evaluation. Statistical approaches including ArcGIS and cokriging and Bayesian Maximum Entropy will be used in the evaluation of irrigation and nutrient impacts on nitrate concentrations. <P>An evaluation of the effects of crop rotation and sprinkler irrigation will be completed. The sensitivity of the reduction of nitrate to these management alternatives will be assessed. The impact of natural variables on groundwater nitrate concentrations will be assessed. <P>Our analysis will determine practices that can optimize reduction in leaching and improve groundwater quality. We will also analyze the economic factors associated with the nitrate reduction in terms of cost per unit gain and identify the importance of outlier producer behaviors have on groundwater nitrate concentrations. <P>We will meet with selected outlier producers to encourage adoption of more appropriate practices and evaluate their acceptance after three tears of targeted education. results will be disseminated to stakeholders through outreach mechanisms.

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Non-Technical Summary: Groundwater in the irrigated corn-producing areas of the central Platte region of Nebraska is contaminated by commercial N-fertilizer leachates. The purpose of this investigation is to evaluate the effectiveness of improved water and nutrient management on reducing groundwater nitrate-N contamination. <P> Approach: The approach first assesses the physical situation in terms of the vertical and horizontal distribution of nitrate contamination in the investigated area and then applies spatial statistics to relationships between nitrate contamination and management practices. Screening intervals of irrigation wells in the Buffallo-Hall County Phase III management area will be assessed in order to determine relative aquifer contributions. Vertical nitrate distribution will be delineated in the investigated area via Geoprobe sampling. Simple groundwater models will be used to estimate irrigation well contaminant concentrations in the two aquifer system. Conversion dates for about 175 pivot systems will be obtained directly from the producers. Statistcal approaches include several cokriging methods which will be evaluated for goodness of fit with the assumptions of the management area data. Methods that will be evaluated include simple, ordinary, and universal cokrieging and Baysian Maximum Entropy (BME). BME has the added feature of being able to assimilate various forms of collateral data into the estimation procedure. The above methods however do not provide for measurements over time. SAS or ASREML programs will be used to incorporate time series aspects into the study. Associations between water table elevations and nitrate concentration will be evaluated using cross variogram techniques. The impact of sprinkler irrigation on groundwater nitrate concentration will be evaluated using paired treatment analysis. Analysis will include a lag effect so that observed values may be adjusted by the spatial covariance structure. For the analysis of crop rotation, each location is only one of several possible rotations. Thus, the analysis will evaluate rotation differences after the data are adjusted for spatial structure and year. Sensitivity analysis will determine the management practices with the greatest impact on reducing groundwater nitrate concentrations and will also be used to determine additive impacts. A spatial anlysis for each year (1988-2006) of data for each data set will be used to determine if groundwater nitrate concentrations from the statewide database and resources district's data are different. Analysis of nitrogen use, economic and productivity data will provide an assessment of the economic impact of improved nutrient and management practices. Producer behavior will be analyzed using primary and secondary data. Staistical efforts will focus on two townships in order to select outlier producers for outreach demonstrations and behavioral analysis. A set of management practices with the greatest potential impact on reducing groundwater nitrate concentrations produced from the research phase will be shared with producers and demonstrated at several area fields.

Spalding, Roy
University of Nebraska - Lincoln
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