“Of course, this is just an estimate,” he said. “This calculation will tend to over-estimate stover quantity in high-yield fields (more than 180 bushels per acre) and tend to underestimate stover quantity in low-yield fields (less than 100 bushels per acre).

Determine amount of stover being removed

The most reliable method of determining the total amount of stover is to directly measure the weight and water content of the residue being removed. Doing this would eliminate the first step and give the most accurate information. Since this approach is not always feasible, approximate removal amounts need to be determined in relation to the harvest method.

Data from Iowa State University showed that with shredding and raking stover, 80 percent of the total will be removed; raking alone will remove 65 percent, and collecting stover from the combine windrow will remove 50 percent. To estimate the total amount of stover removed, multiply the estimated total stover produced (step 1) by the percent removed by the method of harvest used.
Calculate stover’s nutrient content

The third step in calculating how much nutrient is removed in stover is to determine the stover's nutrient content. The best approach is to analyze the nutrient content of a sample from the bale.

If that’s not possible, use ballpark values (7 pounds of phosphate and 30 pounds of potash per ton). Keep in mind that the actual amount of nutrients present in the stover can vary significantly depending on growing season conditions, hybrid, and general fertility of the soil. In addition, nutrients are also affected by the time elapsed and the amount and frequency of precipitation since the crop reached maturity, and the time the stover was removed from the field.

Estimate the value of stover

Finally, to calculate the estimated stover value, multiply the amount of nutrients removed in stover (step 3) by the current price of the corresponding nutrient. The impact of increased removal of these nutrients and organic carbon through removing stover is not as obvious in the short-term as for phosphorus and potassium, but it will definitely carry consequences. While calcium, magnesium, sulfur, and micronutrients are not typically provided through fertilization in Illinois, greater stover removal can accelerate depletion of these nutrients in the soil.

jshike@illinois.edu