Assessing Your Nitrogen Management – Derek Porter

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Assessing Your Nitrogen Management – Derek Porter

The corn crop in central Illinois is well past pollination with kernel fill now taking place. I love the period from tassel time to grain fill because the corn crop is telling us quite a bit about how well our fertility program is working, particularly as it pertains to nitrogen. Nitrogen management should almost always be at the forefront of everyone’s mind when growing corn because it’s usually the most costly and volatile nutrient that we apply. An excellent way to assess how well your nitrogen program is working for you is to go out in your field at pollination to 2-weeks after pollination and count the number of nitrogen deficient leaves. Nitrogen deficient leaves will start at the bottom of the plant and form a v-shape starting at the tip of the leaf and move down the mid rib. For every leaf that shows a nitrogen deficiency you can figure your about 10 units of nitrogen short. So, for example if your corn plants are showing an average of 3 leaves with a nitrogen deficiency, that equates to about 30 lbs of nitrogen short in the soil. The question then becomes did we apply enough nitrogen, or did we suffer a loss of nitrogen from leaching or denitrification? Unless we pull some nitrate and ammonia analysis from the field, this is a tough question to answer.

I will make note that the growers that split apply nitrogen seem to be showing less nitrogen deficiency post pollination than the growers that applied all their nitrogen up front regardless if a stabilizer was used or not. A good rule of thumb to follow when figuring how much nitrogen to apply at one time is for every unit of CEC, the soil will hold 10 lbs of nitrogen. If your soil has a CEC of 15, it should be able to hold 150 lbs of nitrogen at any one time. When assessing corn on corn, the amount of residue needs to be considered. High amounts of corn residue that’s high in carbon can cause nitrogen to be tied up in the soil by the microbes that are breaking down the corn stalk residue. One grower that I spoke with 2 weeks ago has a continuous corn on corn field that is exhibiting severe nitrogen deficiency particularly where the previous years corn residue is the heaviest. This grower uses minimal tillage, so he is leaving quite a bit of crop residue on the surface after harvest. In cases like this, I’m a big believer in broadcasting nitrogen such stabilized urea or UAN to help offset the amount of nitrogen that’s being tied up by the residues. This grower applied anhydrous ammonia as his main form of nitrogen which put most of his nitrogen below ground. Some of this nitrogen needed to be placed towards the surface to help feed the biology and it would have benefited to have some sulfur, sugar, biologicals, and some soluble calcium to further aid in the residue breakdown and help stabilize the nitrogen. At Soil Service we have our Nutrient Recycling Program (NRP) that has shown to work awesome in the fall and early spring to help manage crop residue. Our NRP program used in conjunction with some surface applied nitrogen also works well for managing cover crop residues.

For more information and ways to help manage your nitrogen program, give us a call and we will be more than happy to help.



       High Amount of corn residue can tie up nitrogen making it unavailable to the plant

Derek Porter CCA

Sales Manager Central Illinois