Applications of manure, biosolids, and other organic sources that contain nitrogen can be applied to meet crop nutrient needs. Depending on the nitrogen content of the organic source and factors that might limit the total rate of the organic source applied, additional nitrogen might be needed. Commercial fertilizer should be used as a supplement in these situations. Care should be given to ensure that excessive amounts of nitrogen are not applied. Credits for applied organic nitrogen should be used to reduce commercial fertilizer rates and to match the total nitrogen needs of the crop. The highest measured nitrogen losses in water are seen where full rates of commercial fertilizer nitrogen are applied in combination with manure. Observed losses of 90 lbs of nitrogen per acre have been measured.
Recommended Nitrogen Strategies
- Use a maximum return-to-nitrogen-rate as a starting point to determine the nitrogen need for corn. For wheat, use the yield goal rate from the Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat and Alfalfa as a starting point. Use appropriate recommendations for other crops.
- Use a presidedress nitrogen soil test (PSNT) to evaluate organic available nitrogen release, and reduce sidedress nitrogen application rates appropriately.
- Use a nitrogen potential test to predict the soil nitrogen that will become available to the crop, and adjust the rates appropriately.
- Use remote sensing technology to evaluate the plant-nitrogen status and adjust the rates based on the plant needs.
- Apply manure to nitrogen-requiring crops to take advantage of the nitrogen available to meet the crop needs while balancing phosphorus appropriately to meet the 2- to 3-year crop rotation phosphorus need.
- Apply manure close to when plant uptake of nitrogen occurs to best utilize manure-available nitrogen. Systems to sidedress corn or topdress wheat with manure sources are becoming common.
- Use placement strategies that maximize nitrogen availability by reducing volatilization losses after manure application.