Monday, September 26, 2011
Fall Nitrogen: Combining Profitability With Responsibility
About as fast as the last loaded truck leaves a harvested field, anhydrous ammonia tanks are being parked at the entrance to many fields in preparation for fall nitrogen application. While those operators have already made their decisions and placed their orders, many others may be in a quandary about what to apply and how much to apply after a difficult weather year and unpredictable prices for the 2012 crop. If you have questions, we have answers.
While fall nitrogen application may be common throughout the Cornbelt, it may not be the best for every farm, or may not be the best for every field on a farm. Different soils, different weather conditions, and other variables almost require nitrogen to be customized for every field. University of Illinois fertility specialist Fabian Fernandez addresses numerous issues which will help with both profitability and environmental responsibility.
To begin, he only recommends anhydrous ammonia or ammonium sulfate for fall application, because ammonia quickly transforms to ammonium and ammonium sulfate is already in that form, which attaches to soil particles and is protected from leaching. Fernandez says the nitrate forms of nitrogen, such as ammonium nitrate and urea ammonium nitrate, should not be used because they do not attach to soil and easily move through the soil to tile lines. Urea converts to ammonia, then to ammonium, but Fernandez says it has a greater risk of loss than anhydrous ammonia and should not be used in the fall. He says polymer coatings on urea can also deteriorate and allow it to leach through the soil before corn plants are ready to use it the following year.
Anhydrous ammonia will temporarily kill nitrifying bacteria in the soil which would otherwise allow it to convert to a nitrate and be lost through leaching. Instead it combines with water to form ammonium. With the use of a nitrification inhibitor, the re-population of the bacteria is delayed, and the ammonium is protected until soil temperatures are low enough to prevent a resurgence of the bacterial populations. Inhibitors, such as N-serve, may be expensive, but they keep the nitrogen in a form and place that the following crop of corn can use it.
However, Fernandez says the inhibitor will not always pay for itself, “From the standpoint of production profit, in times when nitrogen prices were low, it was cheaper to buy additional nitrogen rather than the nitrification inhibitor. As nitrogen prices increase and the cost of nitrification inhibitors remains relatively constant, using an inhibitor is becoming more profitable. Still, while an inhibitor represents an added cost, it is important to realize that a reduction in nitrogen efficiency due to losses plus the environmental degradation linked to nitrogen loss also represent added costs. Farmers must carefully consider all these factors when deciding to apply nitrogen in the fall.”
Fernandez says ammonium sulfate is a good source of nitrogen for no-till fields where it can be broadcast. But he says it needs to be applied while rain can dissolve it and carry it into the soil before the ground freezes. And he says be sure to watch the soil pH because of the acidity of the nitrogen. Five pounds of lime is needed per pound of ammonium sulfate and two pounds of lime are needed per pound of anhydrous ammonia.
The timing of the fall application is important because the early harvest, like 2010, allows early fertilizer application, which may come while soil temperatures allow active bacterial action. Such action can be detrimental to the nitrogen by converting it to nitrates that leach away and are not available as needed nutrients for the following corn crop. Fifty degrees is the threshold level for using a nitrification inhibitor. If the soil temperature is under 50ºF as the maximum temperature at the 4-inch soil level, then nitrogen can be applied without an inhibitor. One of your best investments may be in a soil thermometer, since its minimal cost may save the loss of thousands of dollars you have spent for anhydrous ammonia.
Soil types will determine where fall application of nitrogen is a good or poor investment. Fernandez says, “Soils with high potential for nitrate leaching in the fall or early spring (sandy soils or those with excessive drainage) should not receive fall nitrogen applications. Also, regardless of location in the state, do not apply nitrogen in the fall to soils with high potential for nitrate leaching or soils that are very poorly drained. Given the length of time between application and utilization by the crop, application of manure and other organic nitrogen sources should be done as far as possible from environmentally sensitive areas, such as on steep slopes and near bodies of water. If the application cannot be accomplished in late fall, do not apply on frozen soils in the winter; it is better to wait until spring.”
So how much do you apply? The old rule of thumb used to be 1.2 pounds of nitrogen per bushel of corn. But that was when corn prices were $2.50 per bushel. Because the relationship between corn prices and nitrogen prices is constantly changing, Fernandez recommends the use of the Iowa State University web-based calculator, http://extension.agron.iastate.edu/soilfertility/nrate.aspx which helps you identify a nitrogen rate that will provide a financial return to your investment in nitrogen. After accounting for nitrogen left in the soil from a prior crop such as soybeans, Fernandez says the remaining amount does not have to be applied at once. He suggests a partial application for early use by the corn, and a second application for later use by the corn. Some research has indicated that several small applications have provided significant yield boosts through the “spoon-feeding” process.
Summary:
Nitrogen application in the fall can help save time in the spring, and is more likely to occur in dry soil than in wet spring soil that might become compacted. However, nitrogen sitting in the soil in warm temperatures will quickly be lost to leaching if nitrifying bacteria are allowed to have their way with it. The application of anhydrous ammonia is best left to cooler soil conditions or along with a nitrifying inhibitor. The amount applied should also be a concern because of cost, and the need for it to become a profitable input.
Posted by Stu Ellis on 09/26 at 05:34 AM | Permalink