Field nitrogen budgets and post-harvest soil nitrate as indicators of N leaching to groundwater in a Pacific Northwest dairy grass field

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• 作者：Barbara M. Carey ; Charles F. Pitz ; Joseph H. Harrison
• 关键词：Nitrate ; Leaching ; Groundwater ; Mass balance ; Soil nitrate ; Spreadsheet model
• 刊名：Nutrient Cycling in Agroecosystems
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：107
• 期：1
• 页码：107-123
• 全文大小：
• 刊物类别：Earth and Environmental Science
• 刊物主题：Agriculture;
• 出版者：Springer Netherlands
• ISSN：1573-0867
• 卷排序：107

文摘

Dairy farms in the U.S. are expected to use farm-field nitrogen (N) budgeting techniques to determine appropriate agronomic manure application rates for crops. As part of nutrient management, post-harvest soil nitrate sampling is often relied upon to indicate the amount of N not used for crop growth during the growing season. A 4–1/2-year study was conducted that quantified the major N inputs, outputs, and residuals (soil and groundwater) at a commercial dairy field overlying a shallow unconfined aquifer in the Pacific Northwest. The purpose of the study was to evaluate the relationships between two indicators, (1) N mass residuals estimated by farm-field N budget and (2) post-harvest soil nitrate residuals, against measured groundwater nitrate-N concentrations following high seasonal recharge. A mass balance mixing-box spreadsheet model that accounts for the hydrogeologic characteristics of the site was used to quantitatively predict the impact of excess farm-field N on underlying shallow groundwater nitrate-N concentrations. Despite intensive sampling of N balance components and post-harvest soil nitrate conditions, the N-budget-predicted groundwater nitrate-N was 37% of the average field-measured early winter groundwater concentration. The post-harvest soil nitrate-predicted groundwater nitrate-N concentration was 140% of that measured in the field. Neither indicator provided a reliable prediction of the groundwater quality response to land application of nutrients using the spreadsheet model in this poorly drained/high water table setting. The mixing-box model provides a basic tool for testing hypothetical nutrient management scenarios in a variety of conditions. However, groundwater nitrate monitoring data are needed to determine actual outcomes.