Nutrient Management Practices: The fertilizer rate, timing, placement and the form of nutrients applied are managed to maximize the nutrients that are taken up by the crop while minimizing the loss of nutrients to surface water, groundwater or to the atmosphere. The nutrients of greatest interest in Iowa are nitrogen and phosphorus.
While there are many different approaches to nutrient management, a high level overview is presented here. Keys to nutrient management include good planning, good data and a mindset of continuous improvement towards maximizing crop uptake while minimizing losses.
Nitrogen (N) management practices highlighted in the Iowa Nutrient Reduction Strategy (INRS) include:
- Adjustments in timing of N applications (fall vs. spring; spring preplant vs. sidedress)
- Reducing the total N rate applied to the Iowa State University’s Maximum Return To Nitrogen (MRTN) rate
- Use of the nitrification inhibitor nitrapyrin for fall anhydrous ammonia
- Use of swine manure as a source of N in place of spring applied fertilizer N
Other types of enhanced efficiency fertilizers, such as urease inhibitors, other nitrification inhibitors and slow release (coated) fertilizers, may reduce losses of applied N, but specific average values have not been incorporated into the science assessment of the INRS.
Phosphorus (P) management practices highlighted in the INRS include:
- Applying a rate of P based on crop removal
- Applying a rate of P based on soil test
- Use of manure as source of P compared to commercial fertilizer
- Placement of P to reduce the potential for loss through runoff (incorporation through tillage or knifed in)
- Extensive summary of best practices and standards
- Corn nitrogen calculator from Iowa State University
- Iowa phosphorus index (How phosphorus loss is assessed.)
- The Fertilizer Institute
- The fertilizer industry endorses a best management practice concept known as 4R nutrient stewardship – focused on the right fertilizer source, at the right rate, at the right time, with the right placement.