Alternative nitrogen sources
Remember to take nitrogen credits when you use other nitrogen sources.
There are simple management practices that farms can implement to optimize nitrogen applications as well as protect groundwater from nitrogen leaching. One of the easiest but not often done is adjust nitrogen rates accurately. When determining nitrogen applications, a grower should consider soil tests as well as any other residual nitrogen sources should be accounted for.
Legumes are a great source for nitrogen. Alfalfa, clover and soybeans are the most common legumes grown. More growers are using legume cover crops to assist in nitrogen production. Hairy vetch is a common cover crop that has the potential to produce a great amount of nitrogen.
Adjusting nitrogen application in correlation to adding manure is another management practice that could have great benefit to the farm both economically and environmentally. To determine the nitrogen value of manure the best method is to have a sample analyzed. There are book values that can give the approximate nutrient value for manure but every farm is different so the best strategy is to get a sample from your farm.
Cover crop usage is growing exponentially. Many farms are looking at cover crops as another fertilizer source. The challenge for using cover crops as a nutrient source is in the amount of credit to take as well timing of the nitrogen release. Nitrogen availability may not correlate with when the crop needs it. If a farm wants to use cover crops as a nutrient source, cover crops should be considered during the planning process.
There are some book values that can be found on how much nitrogen credit can be calculated but the best practice is still to use soil samples followed by Pre-Sidedress Nitrogen Tests (PSNT) when applicable. Later in the growing season a petiole sample or a stalk nitrate sample should be taken to further determine if the farm has an efficient and effective nitrogen plan. Michigan State University Extension educators can assist you in planning for nitrogen management.