Evaluation of Nutrient Use Efficiency Using County and Hydrologic Unit Nutrient Budgets for U.S. Cropland and Soil Test Summaries, 1987-2007.

Several critical contemporary agricultural issues have the potential to impact nutrient budgets for U.S. cropland. Production of bioenergy can alter nutrient removal due to changes in crop species and plant parts harvested, and can alter nutrient additions due to production of bioash and changes in manure composition induced by feeding distillers grain. Climate change may cause changes in crop yields, cropping patterns, and soil processes. Accelerated genetic changes have been promised that could alter crop yields and nutrient use efficiency. Recent major changes in fertilizer costs and crop prices have altered farm fertilizer use decisions. And, government policy can cause shifts in all of the above. Considering the potential future impact of these issues, it is critical to understand the current status of nutrient budgets, temporal trends of those budgets, and relevant inferences about nutrient use efficiency. This project integrates multiple data layers to create county-level estimates of nutrient removal by crops, fertilizer applied, and excreted and recoverable manure nutrients. Data sources include USDA-National Agricultural Statistics Service, Association of American Plant Food Control Officials, USDA Agricultural Census, and the International Plant Nutrition Institute. Nutrient budgets and recovery efficiencies by the balance method were estimated for the five Census years from 1987 through 2007. Geospatial techniques were used to migrate the county data to eight-digit hydrologic units for watershed evaluation. The analysis reveals areas of both highly positive and highly negative nutrient budgets as well as correctable weaknesses in existing data for conducting such analyses.