Nutrient management after a failed corn crop
Potassium and chloride exist in plant cells as free ions. When the plant dies and those cells rupture, the K and Cl rapidly leach from the crop residues and return to the soil to be “recycled” in the next crop. These two nutrients will likely be available quickly for the 2012 crop and can be measured by soil tests later this winter and next spring. If the crop was taken off for silage or forage, these nutrients will have been removed.
Wheat planted this fall into these residues will not benefit nearly as much from the N, P, and S present in the corn vegetation as will next summer’s corn or sorghum crops. With wheat, there is not as much time for soil organisms to break down the residues and mineralize these nutrients.
Measuring nutrient levels on fields of failed corn
For those planting wheat this fall in these failed crop fields, a profile soil test for N, S, and Cl is a must. P and K applications should also be made based on a surface soil sample. For those planting corn or sorghum next spring, it would be best to wait until late winter or early spring to take the profile sample to get a better feel for the amount of the residual N which will be remaining in the soil. Mobile N can be moved below the root zone, especially in sandy soils if we get a wet winter.
Another potentially valuable tool to consider is the use of a crop sensor to help estimate the amount of the N being mineralized from the 2011 crop residues. Kansas has good recommendation systems for both wheat and sorghum to help interpret sensor data. The rate of mineralization will depend greatly on soil moisture and soil temperatures during March through June. A sensor-based N management system can help take some of the risk out trying to take credit for mineralized N.
A significant amount of residual nutrients will be present in many fields where this year’s crops failed. In severe situations, only a fraction of the nutrients applied were actually taken up by this year’s crop. Many of the nutrients remain in the soil and can be measured using soil tests. This is especially true for the mobile nutrients such as N, S, and Cl. But to get a good estimate of the amounts present, a profile soil test to a depth of 24 inches will be required.
Many of the nutrients taken up by this year’s crop will also be available, especially the K and Cl, which are not incorporated into organic compounds. However the N, P, and S must be mineralized as the vegetation decays. This process will be likely be faster than normal, and will increase the availability of these nutrients. But the exact rate of mineralization will depend on the weather, and is difficult to estimate. Crop sensors can help take some of the risk out of crediting these mineralized nutrients.