Thu May 20, 2010 07:35 AM CDT
Carbon Connections - 1 05/20 07:33 Tillage Practices, Fertilizer Use at Heart of Reducing Greenhouse Gases Most of the research on farming's ability to sequester carbon and reduce greenhouse gases has been driven by the hope of a carbon payment scheme. Meanwhile, that research also reveals the more esoteric, but yield-increasing, benefits to better soil and fertility management. By Greg D. Horstmeier DTN Production Editor COLUMBIA, Mo. (DTN) -- To most growers, organic matter was one number among many that showed up on their soil test report. While they recognized it indicated soil quality and tilth, they also considered it in much the same way as their ability to drain 30-foot jump shots in basketball. Some folks were naturally blessed, others weren't. If they farmed soils with strong organic matter levels, good for them. If not, there was little sense pining about it. Along came climate change and concerns about too much carbon dioxide and other greenhouse gases in the atmosphere. By weight, soil organic matter is 57 percent carbon. Increase organic matter in fields and you pull carbon from the air and safely sequester it in the soil. Suddenly, building organic matter wasn't just for the soil tilth fanatics. Carbon credit markets, and the debate over "cap-and-trade" legislation, offered the promise of a paycheck for sequestering carbon in the soil. Once again, the world quickly divided into "haves" and "have-nots." The basic distinction was no-tillers sequester carbon, tillers release it. Growers in regions where no-till hasn't worked saw the idea of carbon credits as just an extra support payment for those lucky no-tillers. Most participants in carbon credit contracts traded by the Chicago Climate Exchange are using no-till practices. At the time, no-tilling was the most-sure bet that a farmer was reliably sequestering carbon. A new report, on greenhouse gas and carbon sequestration, created under the auspices of the Soil Science Society of America, may help bring more farmers into the sequestration fold. Due in June, the report looks at the science of assessing farming's ability to lower atmospheric greenhouse gases and offers more definitive ways to measure that ability. BASED ON AVERAGES "For growers now involved in carbon trading contracts, those value indexes are essentially based on averages. If you farm in a certain area, and use certain practices, this is the sequestration rate you get," said Charles Rice, Kansas State University soil microbiologist and a member of the panel that reviewed the upcoming SSSA report. Regional averages are low-cost and reliable, but conservative, Rice said. They can substantially underestimate the carbon sequestered, eliminating some practices from consideration. Rice, who also is director of the Consortium for Agricultural Soils Mitigation of Greenhouse Gases, said the other extreme is to take actual carbon measurements in every field. "Here again, it's standard soil science to take measurements of bulk density, which can be converted to accurate carbon estimates." The problem with such accuracy, Rice said, is it's doubtful a carbon credit market, or a government payment, would be enough to warrant the cost of those field-by-field measurements. Rice said the report points to a hybrid of those extremes. It discusses establishing a series of "benchmark sites" throughout a region, GPS-located, that would be resampled every three to five years to re-evaluate carbon sequestration. Growers would use values from those sites, then add their production inputs, tillage, yields, climate and other variables, which would feed greenhouse gas models to give a more accurate picture of their farms' influence on climate. On-farm numbers could be generated from a farmer's yield maps, or from remote sensing to gather vegetative data, Rice said. More accurate greenhouse gas estimations would tell a truer story of how much effect various practices have on carbon and other gases. It could broaden the kinds of farm practices that would benefit from greenhouse mitigation payments, should they become reality. "You may be tilling, but if you're using cover crops, or have an intensive crop rotation that sequesters carbon, you would get credit for that." NONCASH BENEFITS In the meantime, soil scientists like Jerry Hatfield use the buzz around sequestering carbon to remind growers about their organic matter levels: higher is better. "The benefits to higher organic matter, which is what we're talking about in sequestering carbon, go way beyond some potential payment," said Hatfield, supervisory plant physiologist at the National Laboratory for Agriculture and the Environment in Ames, Iowa. Improving soil structure and tilth by increasing organic matter improves water-holding capacity and reduces potential for soil erosion, he said. Higher organic matter soils are better at releasing nutrients throughout the growing season. Hatfield, like Rice, stressed that creating better soils is not just for no-tillers. He notes the up-tick in tillage the past few seasons, due to higher crop residues from better yields, the need to fix field ruts from wet harvests, and the need to control some Roundup-resistant weeds. "You can do those things and still minimize the carbon lost," said Hatfield, who also is familiar with the upcoming SSSA report. Vertical tillage, being careful not to disturb soil below the two-inch depth, lessens the impact. Tilling in cooler temperatures oxides less soil carbon than tilling on a summer day. "It's really more about, if you need tillage, that you have a game plan on when and where to do it, realizing the impact you're having on the soil," Hatfield said. Tilling heavy weed populations into the soil adds organic matter, just as plowing in a clover crop once did, he said. FERTILIZER PART OF EQUATION Fertilizer plans also enter into the greenhouse gas equation, he said. Nitrogen fertilizer in the soil, under the right conditions, can produce nitrous oxide (N20), which is 296 times more potent than carbon dioxide as a greenhouse gas. According to a 2007 study compiled by the International Plant Nutrition Institute, agriculture contributes 78 percent of the N20 emissions in the U.S. Those emissions can be reduced, Hatfield said, by applying the right amount of nitrogen for the crop, and using nitrogen tests and sidedressing when the crop needs more N. Using nitrogen inhibitors also can help, and the benefits of new nitrogen management schemes are not yet included in typical greenhouse gas models. Recent Colorado research studied various tillage and fertility programs for N20 emissions. In no-till continuous corn plots, researchers found untreated urea produced the most N20 emissions. Using urea coated with ESN reduced emissions an average of 33 percent over two seasons. UAN nitrogen treated with AgroTainPlus likewise reduced N20 levels by 35 percent, versus untreated UAN. Greg D. Horstmeier can be reached at Copyright 2010 DTN/The Progressive Farmer, A Telvent Brand. All rights reserved.