Crop residue: Take it or leave it?
Growing markets for biomass, biofuels and alternative feeds have created a demand for materials formerly burned or sold for animal bedding or compost. Today these byproducts can be harvested to add value to farm and forest operations.
Generations of farmers have known, though, that crop residues provide valuable fertilizer and contribute to soil health when left in the field.
So, take it or leave it? What’s the best deal for a producer’s bottom line? Oregon State University soil scientist Don Wysocki has an answer.
“It depends,” Wysocki says. “Think about the things that residue does for you in the field. How much of that are you willing to trade away by exporting it off the farm, and at what price?”
Each farmer will come up with a different answer, depending on how much straw a farm produces and the tillage and rotation practices involved. To help with the calculations, Wysocki has developed an Excel spreadsheet. He takes wheat, the crop he works with at the Columbia Basin Agricultural Research Center in Pendleton, Ore., as an example.
Wheat stubble in the field provides nutrients, water and temperature buffers, erosion protection, carbon sequestration and soil organic matter. It can also add to tillage costs, interfere with equipment and alter crop performance.
• Crop residue is in demand for fuel and feed.
• Residue is also a valuable fertilizer, contributing to soil health.
• Scientist develops a spreadsheet to help calculate residue value.
Doing the numbers
“The nutrient costs are pretty easy to come up with,” Wysocki says. “People know what they’re paying for nitrogen, phosphorus and sulfur.”
Wheat straw runs about 0.3% to 0.5% nitrogen, 0.1% phosphorus and 0.04% sulfur. One bushel of wheat leaves behind about 100 pounds of straw.
Numbers for insulation value, soil carbon and erosion protection are less tangible. Wysocki makes some guesses, figuring the insulation value of winter straw at $21 to $42 per acre, carbon at $2 per acre, and erosion protection at anywhere from zero to $75 per acre, depending on the site. With those numbers, he comes up with a bottom line.
“If you are producing 50 bushels or less of wheat per acre, you don’t have any straw to spare. That’s in a wheat-fallow situation, with wind and water erosion. If you are getting 70 bushels in a higher-rainfall area, you might want to harvest residue off the field once every other crop rotation,” Wysocki says.
He suggests working residue removal into a multiyear crop rotation rather than removing only a certain amount each year. “The take-home message is: Don’t look at straw as simply low-value material you want to get rid of,” he says.
For a spreadsheet copy, call 541-278-4396 or e-mail [email protected]
Farren writes from Ukiah, Ore.
This article published in the January, 2010 edition of WESTERN FARMER-STOCKMAN.