Mapping Crop Nutrient Use and Removal in the U.S

There is a need for a systematic examination of current nutrient use in the United States.  Knowing the status of nutrient use and crop removal provides a basis for identifying regions for improvements in management and potential areas for water and air quality improvement.  The “Nutrient GIS” (NuGIS) database creates county-level estimates of N, P, and K applied to the soil in fertilizer and livestock manure, and removed by harvested agricultural crops. Geospatial techniques are used to estimate balances for 8-digit hydrologic units using the county-level data. The current version makes estimates for five-year periods, coinciding with the USDA Census of Agriculture, from 1987–2007. A version that can be updated annually for non-Census years is under development. The following major conclusions are evident:  Crop nutrient removal in the United States is increasing faster than nutrient use.  Great variation exists across the country in major nutrient (N, P, K) balances.  The most positive P balances are found in the South Atlantic Gulf, New England, and California watershed regions.  Much of the Corn Belt has negative P balances and the entire western half of the country has highly negative K balances.  Removal to use ratios appear unsustainably high in some regions and unsustainably low in others calling for intensive monitoring of soil fertility and more intensive nutrient management.  Substantial uncertainty exists in such aggregate data and points to a need for farm-level measurement of nutrient balance and removal to use ratios as a basis for indicating progress in nutrient management.