Released September 4, 2009
AMES, Iowa -- The fall season is a common time for making crop nutrient applications. Soil sampling, and applications of phosphorus and potassium, nitrogen, and manure are a few things to consider as you plan fall fertilization activities.
Manure Application
Manure is a good nutrient source but can be tough to manage because of handling issues and multiple N, P, and K nutrient content. It also must be analyzed and efforts made for uniform distribution at field application. The relative nutrient content ratio and differential crop nutrient availability often means that one application rate will not be optimal for one or more nutrients, and what may be good management for P or K may not be the best for N. Since N is a critical nutrient for corn, is expensive, and is subject to N loss when converted to nitrate, care should be taken to ensure greatest possible N efficiency.
It is important to pay attention to the P and K amount applied when soil tests are deficient (with total needs meet with inorganic fertilizer if manure P or K is short) or monitoring the P and K amount applied if in excess of crop needs. Giving priority to manure N also means that manure sources that have high inorganic ammonium content, like liquid swine manure, should be applied in late fall after soils cool (see guidance in the N application section). Such late fall application will not affect P or K crop availability.
For manure that has considerable bedding, high organic N and low inorganic N content, or composted, then fall application can give a longer time-period for microbial mineralization to inorganic N. This can enhance crop available N supply and/or avoid low crop availability with spring application and when spring temperatures are cold. Manure N can be subject to volatile loss, so injection or immediate incorporation will reduce potential losses associated with surface application.
As with P fertilizers, manure P application should be managed in a way to reduce risk of P loss with runoff. Injection or incorporation into the soil (most importantly for fields with high risk of erosion and runoff), avoiding application to soils with a very high P-Index rating, avoiding application in winter to frozen/sloping soils, and managing soil residue cover will help with reducing P loss in runoff. These practices will also reduce N loss.
Extension resources
PMR 1003 - Using Manure Nutrients for Crop Production, http://www.extension.iastate.edu/Publications/PMR1003.pdf
PM 1558 - How to sample manure for nutrient analysis, http://www.extension.iastate.edu/Publications/PM1558.pdf
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This is a portion of the original article. See http://www.extension.iastate.edu/CropNews/2009/0904sawyermallarino.htm
Sources: John Sawyer, jsawyer@iastate.edu, (515) 294-7078
Antonio Mallarino, apmallar@iastate.edu, (515) 294-6200
