Nitrogen Load Estimate Calculator (Excel)
The nitrate-N load estimate calculator is designed to calculate estimates based on cropping systems, land use, and nitrate reduction practice implementation. The user interface allows watershed coordinators and other conservation professionals to create load estimates at the watershed and field scale.
The Nitrogen Load Estimate Calculator is based on the data and inputs used to calculate the nitrate load estimates in the Science Assessment of the Iowa Nutrient Reduction Strategy. The user interface allows watershed coordinators and other conservation professionals to create load estimates at the watershed and field scale to support goal setting and scenario building with farmers and other stakeholders.
Nitrogen Load Estimate Calculator Guide
Getting Started
After downloading the calculator and opening it in Microsoft Excel, select the MLRA from the dropdown menu that corresponds with the location of the watershed or field being assessed. If unknown, a map is available in the right-hand margin of the calculator spreadsheet. The MLRA selection loads the soils, climate, and other landscape information to create a region-specific load estimate.
Watershed or Field Scale Land Use
Enter total acres for the watershed or field including the portion of land in agriculture and non-agricultural uses.
Nitrogen Management
Enter nitrogen application as an average per acre for fall, spring pre-plant, and/or sidedress timing for the corn/soybean, corn/corn and extended rotation acres in the watershed or field. The calculator does not have the ability to incorporate several different nitrogen application timing, methods, etc on the same acre so a representative average for the application method and rate will need to be estimated.
If an average application rate is not available, the second spreadsheet tab labeled “napptables” includes an average calculated nitrogen rate for each MLRA that is based on fertilizer sales and animal units.
Cover Crops
Cover crop acres are entered with the average nitrogen rate applied to those acres. The acres with cover crops applied will need to be taken out of the nitrogen application timing and method categories to avoid a miscalculation.
Edge of Field Practices
Enter edge of field practices as acres treated. The acres treated with edge of field practices can overlap with the in-field nutrient management or cover crop practices, however, any land taken out of production for a buffer or other edge of field practice needs to be deducted from the original row crop acres entered when comparing scenarios.
Drainage Water Management Practices
The acres treated with drainage water management practices such as bioreactors, saturated buffers or wetlands cannot exceed the total number of acres drained.