Crop stover is used for livestock feed, bedding, and cellulosic ethanol production. When stover is removed from the field, nutrients, in addition to what is removed with grain harvest, are removed and not recycled back to the soil for future use by crops. Crop stover removal amounts are also complicated by when the stover is baled. Plant potassium (K) is highly soluble and will leach from stover during rainfall events. Stover baled prior to rainfall may have higher K levels, leaving less recycled to the soil, while stover baled after rainfall, may have leached K from the stover back to the soil.
Corn Nutrient Removal
First, let’s distinguish between nutrient removal amounts for phosphorus as P205 and potassium as K20 for corn grain, corn silage, and corn stover. The primary difference between silage and stover is that silage contains nearly the entire plant, including the ear, husks, cobs and stalks, while stover contains all those things minus the grain, but does not remove as much material from the field. The ISU publication PM 1688 provides a table of nutrient concentrations for P205 and K20 to calculate removal rates for grain, silage and stover. See Table 1 below.
Here is an example of P205 and K20 nutrient removal for corn grain harvest and stover removal from a field that yielded 230 bushels per acre.
Corn grain P205 removal:
230 bushels/acre x 0.32 lbs/bushel of P205 removed = 73.6 lbs of P205 removed per acre.
Corn stover P205 removal:
2 cornstalk bales per acre at 1,500 lbs per bale (10% moisture) x 4.8 lbs/ton of P205 removed =
3,000 lbs/2000 lbs/ton x 4.8 lbs/ton =7.2 lbs of P205 removed per acre.
Total P205 Removed: 73.6 + 7.2 = 80.8 lbs of P205 removed per acre from this field.
Corn grain K20 removal
230 bushels/acre x 0.22 lbs/bushel of K20 removed = 50.6 lbs of K20 removed per acre.
Corn stover K20 removal:
2 cornstalk bales per acre at 1,500 lbs per bale (10% moisture) x 18 lbs/ton of K20 removed =
3,000 lbs/2000 lbs x 18 lbs/ton = 27 lbs of K20 removed per acre.
Total K20 Removed: 50.6 + 27 lbs = 77.6 lbs of K20 removed per acre from this field.
If soil tests are in PM1688’s optimum range, these nutrient need to be replaced to maintain the optimum soil test category for crop production. If soil tests are low or very low, not only do the nutrients removed with this year’s harvest need to be replaced, but you will also want to increase the application rate beyond the removal rate to build the soil test level back to the optimum category.
Table 1. Adapted from A General Guide for Crop Nutrient and Limestone Recommendations in Iowa (Table 2.) Nutrient concentrations to calculate removal amounts of P205 and K20 in the optimum soil test category.
Soybean Nutrient Removal
Due to short forage and bedding supplies, we are seeing soybean stover being baled this year. While this is not uncommon, it is important to remember the same principles apply when baling soybean stover, nutrients need to be replaced to optimize crop production the following year if soil test levels are in the optimum, low, or very low soil test categories. This is particularly true for potassium as soybean is a heavy user of potassium.
It is also important to recognize that stover harvest also removes carbon (C), nitrogen, (N), calcium (Ca), magnesium (Mg) and sulfur (S). Crop removal of these nutrients is difficult to plan for because it depends on many factors, including hybrid and varieties. ISU publication PM 3052C “Nutrient Considerations with Corn Stover Harvest”, discusses the implications of removal of these nutrients. https://store.extension.iastate.edu/product/14052
Herbicide rotation restrictions
Some pesticides have pre-harvest interval restrictions that will impact crop stover harvest plans. These restrictions require so many days between pesticide application and harvest of the crop, including stover. Consult your pesticide labels to determine if you can legally harvest stover if it will be used for feed/bedding.