A common mistake when farmers are determining their nutrient need for their upcoming crops is to forget to include nitrogen credits from previous years. 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 and yet not often done is adjust nitrogen rates accurately. Not only should a grower consider soil tests but also any other residual nitrogen sources should be accounted for when determining nitrogen applications.
Legumes are a great source for nitrogen. Alfalfa, clover, and soybeans are the 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 number of challenges using cover crops for even the most experienced cover crop users. Reliable establishment and species selection are often listed and the primary challenges most farmers face incorporating cover crops into their cropping systems. To help farmers address these challenges, an Interseeding Cover Crops Field Day is planned for Oct. 21, 2015, in St Joseph County at the Larry Walton Farm in Nottawa, Michigan. The program begins at 10 a.m. and continues until 2 p.m. with lunch provided. There is no cost for attending this field day.
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.
Farmers that farm near surface water or those within a high-risk watershed, such as the Western Lake Erie Basin or Saginaw Bay, need to be especially careful to not over apply nutrients. Michigan State University Extension educators and specialist have put together a website with information specifically for those in the Western Lake Erie Basin to assist them with water quality issues. The information on this page can be useful to all growers.
Source: Christina Curell, Michigan State University