Effects of taking away residue
Crop residue removal — what effect does it have on corn yield and soil quality? That’s a question Mahdi Al-Kaisi gets asked quite often these days.
The Iowa State University Extension agronomist and soil management specialist notes that more crop residue is left on the soil surface as no-till and conservation-tillage systems are being used on more acres. Also, more acres of continuous corn are being grown, which leads to a greater amount of crop residue on fields compared to a corn-soybean rotation. These higher levels of crop residue bring more challenges for farmers to deal with.
Increased use of no-till and other conservation systems helps sustain the soil quality and improve environmental quality by reducing soil erosion, which is good. However, in the near future corn residue could be removed from fields and used for cellulosic ethanol production. Also, we may see more crop residue being removed for animal uses.
“There is a high possibility that continuous corn production can lead to an increase in the use of conventional tillage,” says Al-Kaisi. “The increase in conventional tillage coupled with higher application rates of nitrogen fertilizer in continuous corn will present a significant soil and water quality challenge.” The trend to more continuous corn, more crop residue removal, higher rates of nitrogen applied and potentially more tillage “will present economic and environmental challenges that we need to consider,” he adds.
• What else do you remove when you harvest corn crop residue from a field?
• A significant amount of carbon, nitrogen, phosphorus and potassium is removed.
• Using no-till and higher N application rates can minimize organic matter loss.
The use of corn stover for cellulosic ethanol production or any other use should be weighed against the potential impact on soil productivity, environmental consequences and food availability. That’s why researchers are looking at the potential for crops like miscanthus and switchgrass for making cellulosic ethanol.
“It is imperative that alternative perennial biomass sources for cellulosic ethanol production should be researched and explored in combination with corn grain ethanol to strike a balance between environmental sustainability and economic viability,” says Al-Kaisi.
How much residue to harvest?
The main crop Iowa grows is corn, and the crop residue corn produces each year is the most readily available feedstock for making cellulosic ethanol. But that residue plays a very important role that must be kept in mind when deciding how much corn stover to harvest and how much to leave on a field.
“Leaving crop residue on the soil surface will improve the cycling of nutrients and ultimately soil quality, both of which increase and sustain soil productivity,” says Al-Kaisi. “Residue left on the field after harvest is a critical source of soil organic matter, and it provides protection for the soil against water and wind erosion, and it improves soil and water quality.”
Alternative uses of corn crop residue for various purposes, such as baling the residue for livestock use or for cellulosic ethanol production, needs to be approached carefully. Removing too much crop residue potentially can have adverse effects on soil and water quality.
How much corn residue can be safely removed from a field? Al-Kaisi says sustainable stover removal rates depend on several factors such as soil erodibility, surface slope, cultural practices and climate conditions. Recent studies suggest only 20% to 30% of the total stover production could be safely removed for biofuel, based on ground cover requirements to control soil erosion. However, other studies suggest that residue removal should be lower than 20%, especially with conventional tillage, to maintain soil quality and nutrient cycling for long-term soil productivity.
Consider long-term effects
“The impact of crop residue removal on soil productivity and environmental quality is not a short-term outcome, particularly in the Midwest, where high organic matter, high soil productivity and good agriculture production conditions minimize the effect of residue removal in the short term,” notes Al-Kaisi.
Possible short-term impacts of corn stover removal may include an increase in nitrogen, phosphorus, potassium, calcium and magnesium that needs to be applied to replace these nutrients due to crop residue removal and potential deficiencies of nutrients and decline of organic matter in the soil in the long term.
It’s estimated the nutrient replacement cost due to crop residue removal is approximately $20 per ton of harvested crop residue. That’s primarily for N-P-K removed. These nutrients will be permanently lost from the soil system’s nutrient pool due to lack of replenishment from crop residue, and they have to be added to maintain soil productivity.
Summing up: “Keep in mind that when you harvest corn crop residue from a field, a significant amount of carbon, nitrogen, phosphorus and potassium is removed with the stover,” says Al-Kaisi.
Using no-till and increased application rates of nitrogen fertilizer can minimize soil organic matter loss due to crop residue removal. But regardless of the tillage system you use, only 10% to 20% of the crop residue can be removed if you want to maintain soil organic matter and soil quality in the long run.
This article published in the March, 2012 edition of WALLACES FARMER.