CARBONDALE, Ill. — One of the few positives to take away from this year’s drought throughout much of the Midwest is that less fertilizer likely will be needed for next season’s crops.

According to Fabian Fernandez, an assistant professor of crop sciences at the University of Illinois, growers who leave a fair amount of residue from scorched corn and soybean crops in their fields this year will probably need fewer nutrients for crops that are planted next spring.

How much of the crop this year to leave, though, depends on the part of the state, the amount of rain received and soil conditions overall. “Normally, the first step in determining total nutrient removal in stover is to use a harvest index, also known as residue-to-corn grain ratio, to estimate how much stover has been produced,” he explained.

Most years, Fernandez said, that ratio is 1:1 residue to grain, but not this year. Cornstalks this year are smaller than usual.

“One could expect to remove up to about 1 ton of dry biomass per foot of corn height per acre if the stalk diameters are small,” Fernandez said. “If the stalks have a more typical diameter, I would estimate as much as 1.2 to 1.3 tons of dry biomass per acre per foot of corn height.”

Growers also must gauge how much phosphorous and potassium remains in the stalks and leaves. Values for stover after a typical harvest ranged from 5-8 pounds of phosphorous per ton, and 5-40 pounds of potassium. What is left during this year’s unique conditions can vary depending on the part of the state, Fernandez said.

“Severe drought conditions reduce the crop’s capacity to take up nutrients. So, if the nutrient removal rate is very small, which it likely will be for many, they can substantially save in terms of application for next year’s crops,” he explained.

He also said the best way for growers to determine the level of nutrients left after removal of the crops is to send a sample to a commercial lab.

“It is important to perform nutrient analysis on drought-stressed corn to determine nitrate concentrations if it is going to be used for livestock feeding,” he said. “Asking for phosphorus and potassium analysis at the same time does not add much to the cost.”

That’s what cow-calf producers David Mool and Enid Schilpf did on part of their cornfield, and the test results showed nitrate levels safe enough for their 50 head. They set them loose to graze on about three acres earlier this month, and plan to chop up the rest of their fields for silage as fall turns into winter.

Effects of the drought also have led to lower fertilizer estimates as part of the projected 2013 corn and soybean costs for Illinois growers, released by the University of Illinois. This is based on data collected from 5,500 statewide farmers belonging to local Farm Business Farm Management associations.

The estimates show that overall fertilizer costs are projected to drop by about 3-7 percent per acre for the 2013 growing season; the percentages vary based on the different regions in the state.

In southern Illinois, for instance, estimated fertilizer cost for corn per acre for the 2013 season is pegged at $134. This year’s total is projected to be $144, according to the study.

For soybeans, the cost for 2013 is estimated at $43 per acre in southern Illinois, down from this year’s projection of $48.