Removing crop residue: How much is too much?
Crop residue is a funny thing. Most folks agree they’ve got too much. But start talking removal, and they get nervous about losing valuable nutrients.
Sterling farmer Dale Pfundstein falls into this category. He’s been baling cornstalks for bedding for the past 15 years. In the winter, he replaces lost nutrients with dry manure. Plus, he sidedresses 32% nitrogen.
“Everybody I talk to has a hard time taking off residue and not putting anything back,” he adds.
Still, planting an average of 35,000 plants per acre in 22-inch rows, he has a notion that he might be able to lose a little residue without noticing a dip in yields. Speaking of yields, his manure-replacement system has averaged 200 bushels over the years.
There are a lot of folks out there like Pfundstein. Pushing plant populations results in more residue, making planting conditions tougher in the spring. As groups push toward utilizing cellulosic material for energy, there are bound to be opportunities for residue removal. Still, there’s value in that dry matter, right?
Emerson Nafziger, agronomy professor with the University of Illinois, has been working on an experiment to answer farmers’ residue questions. Namely, he wants to know how much can be removed without hurting productivity.
For the past five years, Nafziger has experimented with residue removal in four Illinois locations. Plots receive one of three treatments: leave all the residue untouched, remove half or remove all. Within each of these, he does tillage and no-till, and applies different N rates.
To date, Nafziger’s main finding shows effects of residue removal vary with tillage, or rather, lack thereof. No-till fields with all the residue left on averaged 194 bushels per acre. No-till with half the residue produced 207 bushels, while removing all the residue pushed the average up to 212 bushels.
“The research seems to point to an advantage of removing residue on no-till fields,” he adds. “A lot of that probably has to do with increased soil temperatures and an earlier planting date as a result.”
Conventional tillage does not show the same advantage. Leaving the residue untouched yielded 215 bushels, half the residue produced 213 bushels, and none resulted in 217 bushels.
As for nutrient removal, Nafziger believes the experiment is too young for an accurate assessment.
“The question is, how much N, P and K are in dead stalk tissue,” he notes. “Some, but we know that amounts, especially of N and K, will vary considerably.”
Researchers can do a good job of analyzing crop residue for nutrient content. Based on published values, Nafziger estimates removing 2.5 tons per acre (about half the residue from a 200-bushel crop) takes about 75 pounds of nitrogen, 10 pounds of phosphorus and 100 pounds of potassium. Expect N and K values to be lower than this, by as much as half, if there’s been a lot of weather after harvest.
Most of the residue is made up of carbon-containing materials like cellulose and lignin. For carbon to become part of the soil organic matter, Nafziger says it must be broken down into stable products that resist further breakdown. While there’s no good way to know exactly what portion of a cornstalk becomes stable organic matter, estimates are that it is less than 1%. Most of the rest goes off as carbon dioxide as it’s broken down by soil microbes.
Some researchers have buried residue in a bag and then dug it up later to see what’s left. Nafziger says that helps establish an initial decomposition timeline, but can’t accurately predict how much will be added to soil organic matter.
“The guess is, though, that we can remove half the residue from high-yielding, continuous corn under no- or reduced-tillage conditions and not have soil organic matter levels drift downward over time,” he adds.
Nafziger’s fields have consistently yielded more than 200 bushels, without adding extra P or K.
With 200-bushel corn producing about 5 tons of dry matter per acre, Nafziger thinks farmers can stand to remove at least half of it, as long as the soil is kept in place. “And if we want to no-till, removing some of the residue can be beneficial in terms of yield and N fertilizer expense,” he concludes.
This article published in the June, 2010 edition of THE FARMER.