Keep soil pH up. “Soil pH is necessary,” says Tracy. “Corn has an optimum pH of about 6.2. If pH falls below 5.5, you're wasting fertilizer and sacrificing yield because nutrients are less efficient at low pH levels. This is Basic Agronomy 101.”

Borrow from what you have You can credit corn following soybeans with the atmospheric N the beans fixed. And if you've kept phosphorus (P) and potassium (K) at optimum levels, you can ride out a lean year without losing much yield, if any.

“Even if you're growing corn after corn, your soil may have quite a bit of residual nitrogen, especially deeper in the soil profile,” says Wayne Crook, University of Missouri Extension agronomist. “Sample soil at 18 in. to 2 ft. deep to see how much N is still available. With deep-down nitrogen at a decent level, 160 lbs. of applied N may give you the most profitable corn crop.”

Comparison-shop nutrients “Nitromax,” a Web-based program designed to help growers apply the most profitable rate of N on crops, automatically compares prices of different forms of N fertilizer (anhydrous, ammonium nitrate, urea, etc.). You simply plug in your cost per ton of each N form and the program converts it to price per pound.

Nitromax also computes the most profitable rate of N, and can be used to evaluate corn, grain sorghum, cotton or rice. The program is designed for Missouri's climate and growing conditions. Extension services in several other states have similar programs.

Nitromax can be used as a Web-based version or downloaded to computers with Microsoft Excel systems. To access Nitromax, go to http://agebb.missouri.edu/commag/crops/fert/nitro.

Don't overapply. Monte Burch, a corn-soybean grower in Marion County, MO, samples soils in several areas of each field and applies fertilizer in variable rates to supply only what's needed in each area of the field.

Keep in mind the form of N you're using, too. Urea has replaced ammonium nitrate in many areas, and urea is more volatile. “Especially if you are no-till or minimum-till, you may want to use a coated or slow-release form of urea to cut down on the loss to the atmosphere,” says Crook.

Litter heals cuts. Livestock manure and poultry litter can save fertilizer dollars for crop growers within range. But these are fairly low-analysis forms of nutrients, which limits the hauling distance.