Extension Ag Update
January/February 2004
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More about No-Till and Greenhouse Gas Emissions

Don Comis, USDA - ARS News Service, (301) 504-1625, comis@ars.usda.gov

The type of fertilizer used, and the manner in which it is applied, can make or break reduced tillage's ability to control greenhouse gases, Agricultural Research Service (ARS) scientists report.  No-till and reduced tillage are promoted as a way farmers can reduce greenhouse gas concentrations in the atmosphere by storing more carbon in soil.  But there has been limited information on how tillage or other farm practices affect soil emissions of greenhouse gases other than carbon dioxide.

A study conducted by ARS soil scientist Rod Venterea on the effects of long-term tillage techniques and fertilizer practices has shown that, if not done with care, reduced tillage practices can increase emissions of more powerful greenhouse gases, particularly nitrous oxide.  At 300 times the strength of carbon dioxide, nitrous oxide can easily offset the benefit of carbon dioxide reduction. Venterea works at the ARS Soil and Water Management Unit in St. Paul, Minn.

Farm fields are the biggest source of nitrous oxide emissions in the United States, with up to one-third of the agricultural emissions coming from farms in the north central region of the country.  Venterea and colleagues have shown that farmers using no-till should inject nitrogen fertilizer more than 4 inches below the soil surface, beneath the layer of soil that is most conducive to nitrous oxide production.

In field tests, Venterea and his colleagues compared the nitrous oxide emissions from three different tillage systems in combination with anhydrous ammonia, urea nitrogen fertilizer pellets, or liquid urea ammonium nitrate.  Anhydrous ammonia caused about double the losses of nitrous oxide than the other two fertilizers. But combining no-till with anhydrous ammonia injected 6 to 8 inches deep emitted the least nitrous oxide of the three tillage-anhydrous ammonia combinations tested.  In contrast, spreading urea nitrogen fertilizer pellets on a field's surface caused higher nitrous oxide emissions under no-till compared to more intense tillage.  Tillage had no effect on emissions when liquid urea ammonium nitrate was applied to the surface.

Research Determining Best Time to Subsoil

Candace Pollock, (614) 292-3799, pollock.58@osu.edu, Source: Randall Reeder, (614) 292-6648, reeder.1@osu.edu

To capitalize on the benefits of deep tillage, also known as subsoiling, when the technique is performed may be just as important as how and where it’s practiced.  The most common time of year to subsoil is in the fall immediately following harvest. But sometimes growers are forced to delay subsoiling until mid-winter.  Randall Reeder, an Ohio State University agricultural engineer, has launched research at the Ohio Agricultural Research and Development Center’s Northwest Agricultural Research Station near Hoytville, Ohio, to determine if winter subsoiling is just as beneficial as subsoiling in the fall.

“The best time to subsoil is in the fall, but sometimes because of late harvest, unsuitable weather or other circumstances, growers delay subsoiling until January,” said Reeder. “No research data exists on subsoiling in mid-winter in Ohio. We hope the weather cooperates and gives us an opportunity to conduct the research.”  Subsoiling with a low disturbance tillage tool is a conservation practice that breaks up soil 12-18 inches deep, allowing increased water movement, better aeration of the roots and access to additional minerals and nutrients for plant growth. The benefits associated with subsoiling are the alleviation of soil compaction and improved corn and soybean yields. By comparison, conventional tillage breaks up the soil 6-8 inches below the surface, and in areas compacted by heavy combines and grain carts, such a practice is not adequate.

Ten years of Ohio State research has shown that subsoiling works well on the silty clay loam soil commonly found in northwest Ohio.   Reeder said the soil type tends to “compact naturally,” creating drainage problems that are only compounded with additional compaction from heavy machinery.“ The culmination of Ohio State research has proven the benefits of subsoiling in November. Now we want to find out if January subsoiling can be just as effective,” said Reeder.

Subsoiling is best practiced in the fall because the freezing and thawing cycles associated with the onset of Ohio’s winters help to settle the soil prior to planting in the spring. One of the concerns of delayed subsoiling is running the risk of a loose soil structure that is not conducive to seed germination and root growth.  “The longer a grower waits to subsoil, say as late as March, the higher the risk of decreased yields,” said Reeder.   Like other production practices, subsoiling has its advantages and disadvantages. Low-disturbance subsoiling equipment is capable of breaking up deep soil while leaving surface residue virtually untouched, affording the farmer the benefits of both deep tillage and no-till. Residue from the previous crop remains on the surface and the following season’s crop is planted directly into it, minimizing soil erosion.

“A grower has three options with subsoiling: not to subsoil at all, subsoil every year, or subsoil occasionally,” said Reeder. “Our research has shown that subsoiling every two or three years produces the same benefits as subsoiling every year, which is good news for farmers because of the expense. Note that our research plots are farmed with relatively light equipment, so we are not recompacting the soil the way many farmers do.”   A disadvantage of subsoiling is the increased horsepower that is needed compared to no-till or chisel plowing, raising production costs for the farmer. But the benefits of subsoiling can outweigh the extra expense. Based on Ohio State research on Hoytville soil, subsoiling can increase yields anywhere from 5 to 10 percent. For 1,000 acres of corn, that can translate into a $15,000 to $30,000 savings for the grower, said Reeder.

Shiitake Mushrooms' Secret May Benefit Earth-Friendly Fuels

Marcia Wood, ARS News Service, USDA,  (301) 504-1662, MarciaWood@ars.usda.gov

Fallen logs on the forest floor make a perfect home for Shiitake mushrooms. These fungi--sold as a delicacy in the produce section of your local supermarket--thrive on the downed wood, turning it into sugars that they use for food.  Now, Agricultural Research Service scientists in California are looking at bringing the gourmet mushrooms' mostly unstudied talent indoors. And, as a first step towards doing that, they've found and copied a Shiitake gene that's key to the mushroom's ability to dissolve wood.

Called Xyn11A, the gene carries the instructions that the mushroom uses to make an enzyme known as xylanase. The researchers want to see if a ramped-up version of the gene could be put to work digesting rice hulls or other harvest leftovers.  If enzymes can do that quickly and efficiently in huge vats, or fermenters, at biorefineries, they could help make ethanol and other products a practical alternative to today's petroleum-based fuels, for example. That's according to Charles C. Lee, an ARS research chemist.

With colleagues, Lee isolated and tested the Xyn11A gene, the first of its kind to be discovered in Shiitake mushrooms, Lentinula edodes.  Lee did the work with research chemist Dominic W.S. Wong and chemical engineer George H. Robertson. The scientists are based at the ARS Western Regional Research Center in Albany, Calif.  In laboratory experiments, they transferred the Xyn11A gene into yeast. Equipped with the gene, the yeast was able to produce xylanase. In nature, the yeast normally can't do that.

Next, the scientists will work on engineering the mushroom gene so that it enables yeast or some other organism to produce greater amounts of the xylanase enzyme in less time. Gains in efficiency could help make biorefining of plant-based fuels and other products a practical alternative to petroleum refining.