Fall fertility issues: Answers for your questions
Soil characteristics should be a major determinant of application. A light, sandy soil should not get a fall application because it just won’t remain there until next spring. Heavier organic soils can hold it through the fall, winter and spring, so keep the soil type at the top of the list on issues to consider. Fernandez says ensure soil conditions are fit for the application, and the means not too dry or not too wet. Either will allow the liquid to volatilize and either escape between dry soil particles or up through the unsealed knife track.
Amount to apply
Your ultimate decision on the nitrogen available to the crop should be based on an optimal rate determined by the cost of the nitrogen and the price of corn, which is the Maximum Return to Nitrogen or MRTN. MRTN can easily be determined by the corn nitrogen rate calculator that is available for IA, IL, IN, MI, MN, OH, and WI soil conditions. The only entries needed are your state (and location), whether you have a C-C or C-S rotation, the type of nitrogen source you plan to use, its cost per ton, and the price of corn. Yes, it is simple. You will be provided with an optimal rate in pounds per acre, along with a profitability range, and the actual N cost per acre when applied at the MRTN rate.
Fernandez reminds you that you do not need to apply all of it in the fall, and should consider applying some in the spring. He says that is because, “Many fields will likely have high nitrate levels this fall because of the drought, and it is uncertain how much of that N will be present for the next crop. If a good portion is available, that should be all the plant needs to get started until sidedress time, which would reduce the need to supply additional N in the fall. If N is not present because of excessively wet conditions in the spring, chances are that a fall application of N could suffer similar losses.”
While many farmers will apply nitrogen in the fall to take advantage of the time availability, Fernandez says that is an expensive decision. “An ongoing study over three years showed that fall applications reduced yield 17% relative to preplant applications done within three weeks of planting. The difference in yield, averaged across N rates, was 23 bushels per acre less with fall than with preplant applications.” Based on 2013 harvest prices, that is a $150 per acre loss, with a fall application, compared to a spring application.
Source: FarmGate blog