What is the next step this season in N management?
For more information on the corn stalk nitrate-N test, check out http://www.extension.iastate.edu/Publications/PM1584.pdf.
Are there other ways to evaluate my nitrogen program? A simple one is to count the number of nitrogen deficient leaves from the ground to the corn ear. The number of N deficient leafs is related to nitrogen sufficiency. A nitrogen deficiency in a corn leaf starts with yellowing along the midrib. As the deficiency progresses, the yellowing will move out towards the edges of the leaf. Finally the yellow area on the leaf will turn brown and die. Since nitrogen is mobile in the plant, this process of leaf yellowing starts with the bottom leaf first and progresses up the plant. The further up the plant the deficient leaves are, the more nitrogen deficient a plant is. In a perfect world, there should be some N deficient leaves at black layer. If all the leaves are green, then there was too much for the corn plant. Also you do not want all the leaves up to the ear to be nitrogen deficient. In this case, there was not enough N for the plant. While this system is very simple, it may be as effective as the stalk nitrate test without the hassle of sampling stalks. Remember, this is also not a predictive test!
As a crop consultant and grower, these tests can be a good evaluation tool for a good established nitrogen management plan. The important words are a good established nitrogen management plan. Without a good plan, the tools are worthless. The first thing to do is get the management plan figured out, implement it, and adjust to your local conditions. The important ingredient is to use reasonable research based N nutrient guidelines and follow the research based Nitrogen Best Management Practices.
In Minnesota, the starting place of this information is:
http://www.extension.umn.edu/nutrient-management/Docs/corn-fertilization-2006.pdf and http://www.extension.umn.edu/nutrient-management/nitrogen-best-management-practices/ .