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Drought underscores value of con-till

Recent droughts of 1998 and 2001 were not kind to south Texas farmers, but they did show Texas A&M agriculture program researchers a thing or two about conservation tillage.

“The 1998 and 2001 seasons were among the driest in the 22 years I've been doing conservation tillage research, but we had some of our best yield gain percentages with conservation tillage,” said Dr. John Matocha, a soil scientist at Texas A&M's Agricultural Research and Extension Center in Corpus Christi.

Through use of conservation tillage, the researcher reduces the number of tillage trips substantially during a crop season, as well as altering other tillage factors, such as the depth to which the soil is plowed. Matocha has been conducting experiments for 22 years using different types of conservation tillage, including a complete no-till scenario and various minimum-tillage scenarios on a sandy clay loam and on a clay soil.

Unlike some other programs in the United States., Matocha's no-till system involves zero tillage year round (no post-emergence cultivation).

In addition to improving water-use efficiency, the point of conservation tillage is to improve soil quality by building up organic matter and microbial activity in the soil. Theoretically, such tillage can both improve yields and decrease production costs, but even Matocha was slightly surprised by results in the extremely dry 1998 season.

“With no-till and only 25 percent of long-term average rainfall during the growing season, we yielded 621 pounds of lint per acre in our test plots in 1998, compared to 452 pounds for conventional tillage,” Matocha said. “That's a 37 percent difference.

“For minimum tillage, we yielded 522 pounds an acre, or 15 percent more.”

In 2001 (65 percent of average rainfall), no-till cofton produced 702 pounds of lint per acre compared to 515 for conventional tillage. In this season with about three inches more rainfall than 1998, the minimum till cofton approximated yields of those from no-till (665 pounds). In relative terms, the no-till cofton produced 36 percent more than conventional tillage while minimum till cofton showed a 29 percent advantage over the conventional.

Among other major crops that Matocha has been studying under various tillage schemes is corn. In the dry 2001 season, dryland corn produced 4,227 pounds of grain per acre under zero tillage and only 3802 pounds with CT tillage at 80 pounds of nitrogen per acre

At a higher rate than soil test recommended N rate (120 lb N/Ac), yields under no-till increased some 300 pounds per acre compared to a decrease of 675 pounds due to the higher N rate under the conventional system. With no-till, corn at 120 pounds of nitrogen per acre produced 45 percent more grain than with the conventional system at equivalent nitrogen fertilization.

At the same time, grain yields on a droughty Orelia soil were only about 58 percent of yields on the Victoria soil and reflected the substantial difference in soil profile water storage between the two soils. Yields on the Orelia soil averaged 2,440 pounds per acre with no-till and 1,052 pounds under conventional tillage.

Use of no-till with this droughty soil showed a dramatic 132 percent increase in grain yields.

“My original feelings in the 1980s favored more strongly minimum or reduced till over no-till, but very favorable yield outputs from complete no-till in recent years have modified my outlook,” Matocha said. “Improvements in herbicide technology and herbicide tolerant crops allow us to look at no-till with more optimism I'm looking at the long term results, 10 or more years, cofton grown with conservation tillage outperformed that grown with conventional tillage and deep tillage.

“At this point it appears that a complete no-till system with multiple years of no-tillage performs better on the finer textured clay soil than on sandy loam types.”

The 1998 and 2001 yield differences were due primarily to increased soil moisture availability to crops because of the tillage technique used, Matocha said.

“Water availability is the No. 1 issue in dryland crop production here, so anything we can do to increase water'harvesting' and use-efficiency will help the crops,” he said. “On a sunny and warm windy day, losses of up to three- or four-tenths of an inch of soil moisture water due to evaporation alone can occur.

“The increased organic residue cover in conservation tillage systems decreases that loss.”

During 1999, with near normal rainfall during the growing season, cofton yields were approximately 60 percent higher than in the droughty 1998 season. Cotton grown under conservation tillage produced in excess of two bales per acre, or slightly more than that grown under conventional tillage.

Lint yields with minimum tillage were slightly under no-till yields and comparable to yields with the conventional system.

Farmers using conventional tillage might till the soil between seven and nine times per year, depending on rainfall. A team led by Matocha compared that tillage system with a minimum-till program that included a post-harvest shredding and light disking, root plowing at a three-inch depth, and formation of low-profile beds in the same operation. Knifing in fertilizer, planting, and cultivating once involves a total of three to four tillage operations per year.

A combination of pre- and post-emergence herbicides was also used to control weeds and other unwanted growth.

An alternate no-till system had stalks shredded after harvest and regrowth sprayed with herbicide. Before planting, fertilizer was injected into the soil using thin knife openers or coulters.

“You need to consider several factors when looking at conservation tillage methods especially complete no-till,” Matocha said. “First, you've got to have a fairly clean field to start with, relatively free of weeds.

“The cost of each system — whether conventional, minimum or no-till — is dependent on the type of soils, precipitation, and herbicides, as well as other factors. You can do several years more of low-till or no-till on finer textured soils, such as clay loams and clays, without adverse effects on crop yields due to compaction than you can on sandy loam soils,” he added.

Occasional tillage is more important on fine sandy loams, which tend to compact more than montmorillionic clay type soils that have a swelling and shrinking characteristic, giving them vertical mulching properties.

The research group has also added a minimum-till system that includes use of a deep-till (16-inch) “chisel” plow.” This replaces the post-harvest root plow (three-inch depth) operation and results in the same total of tillage operations.

Under 1998 and 2001 drought conditions, that system did not yield enough lint increase to cover the cost of the deep tillage. The researchers will continue evaluating that system in future crop years.

They are also experimenting with different nitrogen fertilizer rates in the various tillage systems to determine the economically optimum rate. Improved soil water relations in minimum tillage and no-till situations in 1998 allowed greater lint increases and profitability at rates up to 60 pounds of nitrogen per acre, whereas amounts of nitrogen below 20 pounds per acre had no discernible effect in the conventional tillage system.

On a long-term average basis, minimum-till and no-till systems generally can improve net income to producers between $35.00 and $45.00 an acre over conventional tillage under dryland conditions, with the benefits fluctuation among seasons due to available rainfall, Matocha said.

Diesel fuel prices on farms have essentially doubled in the last five years. This should give greater impetus to producers to convert at least part of their farming to conservation tillage systems.

These cost input comparisons did not include economic benefits from the reduced amount of equipment capital required for minimum and no-till systems compared to conventional tillage, he added. There are also additional benefits protection of soil, a valuable nonrenewable natural resource, and cleaner air due to greater carbon sequestration in no-till soil releasing less CO2 into the air.

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