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Conserving cropland for the future.

Conserving Cropland for the Future

Rich brown soil blankets the hilly farmland of eastern Washington's Palouse region. But during the long, cold winter, drizzling rains - lasting for weeks on end - sweep away that precious soil.

That topsoil has helped make the Palouse famous for its bountiful wheat harvests - and infamous for its severe erosion problems. An average of 10 to 12 tons of soil per acre wash away from Palouse farmland each year. Much moves to the bottom of the sloping fields, eventually working its sediment-clogging way into streams.

For every inch of topsoil lost, wheat yields drop by 2 to 3 bushels per acre.

Researchers and farmers know how to slow this erosion - by changing the way plowing and sowing are done. The practice known as conservation tillage uses tilling and planting implements that leave residues - wheat stubble, barley straw, or pea vines - from last season's crop on the soil surface. These residues cover and protect fields during the cold, rainy months and help retain the topsoil. And conservation tillage, also known as reduced or minimum tillage, typically involves fewer passes over the field with farm implements.

One major problem, however, has stalled widespread use of this tactic - weeds. With less tillage, weeds thrive. Crop residues left on the soil help keep the ground moist and give weed seedlings a better environment in which to emerge and grow. Deep tillage, on the other hand, helps kill weeds by burying their seeds and disrupting their roots.

But farmers may be able to save their soil and their money, as well as keeping weeds at bay, says Frank L. Young, a weed scientist at the ARS Weed Research Unit in Pullman, Washington. Young heads a comprehensive, large-scale integrated pest management project in the Palouse that is now in its sixth and final year.

The project involved seven ARS and five Washington State University and University of Idaho scientists from varied disciplines: soil and weed scientists, economists, engineers, entomologists, and plant pathologists.

They compared two different tillage systems (conventional and conservation), two different crop rotations (2 years of winter wheat followed by spring wheat; and winter wheat, spring barley, and spring peas), and three weed management levels ranging from minimum to maximum.

Each of the 12 different combinations was replicated on four different plots. The plots covered 80 acres and were farmed using field-scale tractors and equipment.

The best systems produced substantially higher profits per acre compared to the others. What's more, the same best-paying methods also meet federal requirements for soil-saving techniques that farmers need to stay in business. The key? Control weeds, plant different crops each year, and practice conservation tillage.

To achieve the same yields with conservation tillage, the researchers had to boost levels of herbicides for a period of time. Although such a tradeoff - substituting herbicides for tillage - was previously known, it had not been documented in the small grain-growing region of the Pacific Northwest.

In most test plots, especially those under conservation tillage, moderate or maximum herbicide levels were economically warranted, but that could change over the long-term, says project leader Young.

"Farmers will be able to reduce the chemical inputs once they get a handle on the existing weed populations with intense treatments for a few years," he says.

The researchers determined their weed treatment levels based on field surveys of the existing weeds, which varied from year to year. Generally, says Young, the moderate herbicide level was close to the standard recommendations from extension specialists, who advise growers on farming tactics.

The maximum rates used in the study never exceeded the recommended rates on herbicide labels. Moderate and minimum rates were usually equivalent to 80 and 60 percent, respectively, of the maximum level.

In addition to eventually allowing farmers to scale down chemical use, future studies will be on herbicides that don't persist in the environment and have low toxicity to birds and mammals, says study collaborator Alex G. Ogg. He is the research leader of the Weed Management Research Unit in Pullman.

Young's future work will also look at nonchemical methods of weed control. These include cultural practices, such as choosing more competitive varieties - a tall, sturdy wheat with an extensive root system, for instance - that can more effectively compete with weed species. Another method is to examine different crop-planting patterns, such as paired rows. Paired rows with banded fertilizer provide rapid plant growth, which shades weeds and slows their growth. However, weeds must be controlled in the open space between pairs of rows.

With the years of data gleaned from this study, Young, with economists and extension specialists, hopes to develop a computer model to predict the best weed management strategy for a farmer. As an example, he'll use a similar model developed for weed control in corn by ARS scientist Edward E. Schweizer at Fort Collins, Colorado. After fine-tuning the specific details of the model, using data from research plots, Young anticipates testing it on actual farms in 3 to 4 years.

"A farmer in the Palouse might one day be able to take a laptop computer out to the field, survey the weeds and input that information," says Young. "Then the computer would give the farmer the most economic strategy, based on the expected yield and price of the crop."

Rotating or alternating crops from year to year reduces soilborne pathogens, like the devastating fungus take-all that builds up when wheat is grown year after year. Rotation also helps control weeds naturally. Planting peas or barley in the spring breaks the growing cycle of winter annual grassy weeds such as downy brome and jointed goat grass.

Weeds are a particularly bad problem in peas, the worst culprits being wild oats, lambsquarters, mayweed chamomile, and mustards.

Yet some of the most encouraging results occurred in the pea plots. "We were able to grow peas with equal or greater yields in conservation tillage, compared to conventional tillage," says Young.

For farm profits, the top-ranked system was the wheat-barley-pea rotation using conservation tillage and optimum safe doses of herbicides. The least profitable was the wheat-only system grown under conventional tillage, according to Douglas L. Young, a Washington State University agricultural economist. He documented the financial aspects of the study.

The economic benefits could pay off even more in the long run. The 1985 Farm Bill requires farmers to have farming practices, such as conservation tillage, in place to save their soil by 1995. If farmers don't comply, they aren't eligible for certain government assistance programs and deficiency payments. These payments make up the difference between the target price set by Congress and the market price farmers receive.

While individual farms will require different practices to control erosion, USDA's Soil Conservation Service criteria for conservation tillage is a minimum of 30 percent residue cover after seeding. All the plots with conservation tillage met the requirements, while none of the conventionally tilled plots did, says agricultural engineer Donald K. McCool, who is with the ARS Land Management and Water Conservation Research Unit.

The principal difference between the two tillage systems was the type of tillage used after harvest. Conventional tillage uses a moldboard plow, which inverts the soil and buries about 90 percent of the residues, leaving a mere 10 percent to cover and protect the soil.

Conservation tillage is done with a chisel plow, which breaks up the soil without turning it over, leaving 50 to 60 percent of the residues on the surface. In some instances during the study, they also used a no-till drill, which leaves even more of the crop residues on the surface. That was feasible after the spring pea harvest, for example, since peas leave fewer residues than grains. Some no-till drills can't always penetrate a heavy residue cover of wheat stubble for a suitable crop stand, so some tillage is needed.

While standing on stepladders, McCool and his technicians took color slides of each field plot before and after each tillage operation. They projected the slides onto a screen with a grid, enabling them to determine the percentage of field that was residue-covered.

Conservation tillage helps save water as well as soil. And many studies have shown that more available water means higher crop yields, says hydrologist Keith E. Saxton, another project participant.

Saxton, who is also at the Land Management and Water Conservation Research Unit, found that the conventionally tilled plots had 1 to 3 inches less water available for crops compared to the minimum-till plots.

The reason, he says, is the lessened snow catch and increased evaporation and runoff from the plowed ground. Residues on the surface catch and trap more snowfall than the smooth, tilled surfaces. "Each inch of water not available to the crop translates to a loss of 7 to 8 bushels of wheat," says Saxton.

Residues might also help stave off insects, like the English grain aphid, a major pest of wheat and barley. WSU graduate student Erin Borden found higher numbers of the aphids on the conventionally tilled plots than on those under conservation tillage. That may be because the higher residue levels repel the aphids, says Borden. A related study in the Midwest showed that mulches seemed to keep aphids from landing on crops.

Borden is also looking at whether certain weed species tend to harbor different pests of beneficial insects. - By Julie Corliss, ARS.

PHOTO : This no-till drill can penetrate residues from previous crops to plant wheat and other small grains.

PHOTO : Palouse region of eastern Washington.

PHOTO : Winter wheat shown in photos on this page was grown in adjacent plots under conservation-tillage practices, but with maximum (above) and minimum (below) weed control methods.

PHOTO : On left, chisel-plowed area retains a layer of straw on the surface that conserves moisture and prevents erosion.

Frank L. Young and Alex G. Ogg are at the USDA-ARS Nonirrigated Agriculture Weed Science Research Unit, 215 Johnson Hall, Washington State University, Pullman, WA 99164-6414. Phone (509) 335-1551. Donald M. McCool and Keith E. Saxton are at the USDA-ARS Land Management and Water Conservation Research Unit, Smith Agricultural Engineering, Washington State University, Pullman, WA 99164-6120. Phone (509) 335-1347 (McCool), (509) 335-2724 (Saxton).
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Author:Corliss, Julie
Publication:Agricultural Research
Date:Jun 1, 1991
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