Managing corn crop nutrients
By David G. Hallauer
Meadowlark District Extension Agent
With a corn crop like many of you saw this year, any input cost reduction you can make for 2013 is likely on the table. Should your nutrient management plan change? Likely not.
According to Dave Mengel, Ph.D., KSU Soil Fertility specialist, the biggest nutrient "carryover" occurs with severely stunted plants--those 3- to 4-foot tall that didn't form any grain. If that's your situation, you may have retained a large portion of the applied nutrients.
In many cases, we were damaged, but we did form grain. On those fields (close to normal height but with poor grain yields due to heat/drought stress), the nutrient uptake will likely be near normal. Why? Most nutrients are first taken into the vegetation and used or stored, and then translocated to developing grain. Can we see higher residual nutrient levels? Sure, but not to the degree found in the more extreme drought situations.
Remember as well that the release of nutrients can be hard to predict. Nutrient release is based on the carbon to nitrogen ratio of decaying plants. Corn stalks are normally 60:1. Severely damaged stalks may be closer to 35:1 (we need organisms to reduce to 25:1 before N mineralization will occur). We're likely somewhere between, meaning little credit to our 2013 crop for N, P, and S.
How do you measure? Do a soil test. Potassium increases will likely be "captured" in surface soil tests pulled next spring. A profile sample (0" to 24") for nitrogen and sulfur in the spring or late winter will give a better feel for residual nutrients remaining. Phosphorous increases may or may not show up in a spring sampling program.