The severe drought in the Midwest has caused complete crop failure in some areas; in others, yields are reduced to the point that it is not economical to harvest the grain.

Producers who are considering baling or chopping for silage have asked University of Illinois assistant professor Fabián Fernández how much nutrient would be removed if the stunted corn crop is taken out of the field.

“The condition of the drought-affected corn crop is so varied it would be difficult to establish a removal rate that represents every condition,” he said.

To determine total nutrient removal, the amount of biomass and nutrient concentrations must first be determined. Fernández notes that doing so is difficult because some crops died while they were still at vegetative stages, others are dying with barren ears, and others are hanging on trying to fill the kernels

“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.

The most widely used dry weight ratio is one-to-one residue to grain. Using this ratio to calculate the pounds of dry residue, the grain yield in bushels per acre is multiplied by 47.3 (a 56-pound bushel of corn at 15.5 percent moisture contains 8.7 pounds of water). The value is divided by 2,000 to obtain the number of dry tons produced.

This approach will not work well this year.

“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,” Fernández explained. “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.”

The amount of biomass removed also depends on the cutting height: the higher the cutting height, the less stover is removed. Thus, the best way to determine total amount produced would be by weight of bales or silage loads adjusted for moisture content.

Nutrient concentration is the other piece of information needed to determine nutrient removal amounts.

In a normal growing season, phosphorus and potassium levels in biomass can vary considerably. Typical values for stover after grain harvest range from 5 to 8 pounds of P2O5/ton and from 5 to 40 pounds of K2O/ton, with 20 to 30 pounds K2O/ton being the normal range.

Low potassium levels are usually due to rain leaching it out of the plant after the crop starts dying — obviously not a problem this season.