Nutrient management after a failed corn crop
The plants fell into three basic groups. The corn from Edwards and Reno counties was the most severely stressed of those sampled, with only 1,200 to 4,500 pounds of dry matter present. The plants from Franklin and Cherokee counties had more normal vegetative growth, but little or no grain yield due to poor pollination. The remaining sites from Riley, Shawnee, and Republic counties had varying levels of growth and yield, but took up normal or slightly reduced levels of nutrients.
The severely damaged samples from Reno and Edwards counties had high nutrient concentrations but very low total nutrient uptake per acre because of the low level of dry matter produced. In those fields a large portion of the applied nutrients are likely still present in the soil, and potentially available for the 2012 crop. The fields in the other areas had varying levels of dry matter and grain yield, and in many cases near-normal nutrient uptake per acre. In this situation, residual nutrients in the soil would likely be elevated, but not to the degree found in the extreme drought areas in south central and southwest Kansas.
The majority of the nitrogen, phosphorus, and sulfur in plant material is present as protein and other organic compounds. For these nutrients to become available to plants, these compounds must be broken down and the N and P mineralized. This process will normally take three or more years to run to completion, with the C:N ratio being the primary factor controlling the rate of release. Corn stalks are normally a very high C:N material, with a C:N ratio around 60:1. In high C:N materials, very little net N mineralization will occur until the organisms utilizing this material as a food stuff reduce the carbon content of the residue to a C:N ratio of roughly 25:1.
In the drought-damaged crops, especially the severely damaged ones with reduced vegetative growth, the N content is much higher than normal, since there is little or no grain present. The C:N ratio in many of these severely damaged crops is less than 35:1. As a result, net mineralization will occur much more quickly -- a matter of months rather than years. In very severely damaged corn where N content is around 2% or more, such as at the Edwards and Reno county sites, roughly half of this N, P, and S is likely to be available for a summer crop planted next spring. In the fields with more normal vegetation but little or no grain yield (Cherokee and Franklin counties), the N will remain in the vegetation and enhance decomposition -- but likely not as quickly as where vegetative growth was more severely damaged by drought.