With current grain prices, a yield that might have been 10 bushels more per acre would generate considerable additional revenue; and slight fertility adjustments could make that happen. What does your latest soil test show, and by the way, how old is it? This is the time to take a new soil test, and you have many bushels of reasons to do it.

Your combine yield monitor might have been showing higher numbers, if your fertility had been at optimum levels for Phosphorous and Potassium, as well as Nitrogen. While your expense sheet might wince at varying prices for achieving top fertility levels, your income sheet would have benefited, say Iowa State agronomists Antonio Mallarino and John Sawyer. With the recent changes in crop and fertilizer prices, the agronomists urge farmers to examine the relationship between the two.

Among their recommendations in a recent newsletter are higher soil-test K levels for all crops, and update default yield levels for calculating P and K rates needed to maintain desirable soil test levels. Among their concerns are the increasing corn and soybean yields are removing P and K faster than many farmers are replacing it, if farmers are using standard recommendations for fertility levels. After speaking with farmers, the Iowa State agronomists are finding that to be true, and most producers are not paying attention to potential soybean response to P and K, if the nutrients are only being applied prior to a corn crop. They say there is no difference between annual or bi-annual application of fertilizer, as long as the appropriate amount is being applied. Their research shows that P and K application for the optimum soil test indicates higher maintenance rates than were common 5-6 years ago.

If farming a particular tract next year is uncertain, or your bank account cannot afford a large fertility expense, the Iowa State agronomists offer an alternative. “Due to a low proven probability of crop response in soils testing "Optimum," a reduced fertilizer rate (even as low as a starter rate) might be appropriate for a tenant with uncertain land tenure or a producer having a cash flow issue. On the other hand, producers with certain land tenure for two or more years into the future can minimize yield and economic losses by applying recommended maintenance rates.” At the same time, variable rate application can help improve yield, if there are significant differences in soil tests within a single field. The concept is parallel to the more recent push by Cornbelt agronomists to apply nitrogen at levels that pay back with a “return to nitrogen.”

Speaking of nitrogen, if your harvest ended early and there is daylight to spare, some farmers may be pushing the soil temperature envelope to apply nitrogen early and head to the shed before the end of October. University of Illinois agronomist Fabian Fernandez says nitrogen is one of your more expensive inputs, as well as one that can pose environmental problems. He urges judicious management of nitrogen with both of those issues in mind.

In a recent newsletter article about fall nitrogen application, Fernandez says it is critical to wait until the soil temperature at the 4 inch levels is below 50 degrees, and can be maintained below that level. If nitrogen must be applied at a higher temperature, that temperature must not exceed 60 degrees and the nitrogen must be applied with a nitrification inhibitor. That should not be news to anyone, but is offered as a reminder.

As a refresher, ammonium is a stable form of nitrogen that is readily absorbed into the soil. Above 50 degrees, ammonium converts to nitrate, which can be lost through denitrification and leaching that allows it to be picked up by the flow of groundwater and field tiles. So your first consideration should be the form of nitrogen you apply as determined by the temperature of the soil. If the choice is either ammonium nitrate or urea ammonium nitrate (UAN) the nitrate molecule is already in a form that can be lost through denitrification and leaching. So neither would be appropriate forms of nitrogen above 50 degrees.

Anhydrous ammonia quickly locks into the soil moisture and is converted to ammonium for stability. Urea converts first to ammonia, then to ammonium, and can be used in the fall, but there is a greater risk of conversion to a nitrate and being lost before it is used by a crop.

If the nitrogen is being applied above 60 degrees, a nitrification inhibitor needs to be applied, which interferes with the activity of the bacteria that are catalysts in nitrification process, consequently the nitrogen will be available for a longer period of time.

Summary:
Following harvest, 2008 fertility concerns may be one of your priorities. Nitrogen application should wait for cooler soil temperatures or it will convert to a nitrate that is lost for use by spring crops but will create water quality problems. Consider the various forms of nitrogen that are available and select one that will not be hampered by soil temperatures. On the issues of phosphorus and potassium, ensure that your crops are receiving an optimum amount for both corn and soybeans, since the latter has not always been the case in recent years. With high value crops, optimum fertility levels can mean the addition of revenue.