CORPUS CHRISTI — The drought of 1998 was not kind to South Texas farmers, but it did show Texas A&M Universitiy agriculture researchers a thing or two about conservation tillage.
“Last year was one of the driest in the 19 years I’ve been doing this, 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.
Conservation tillage reduces the number of times farmers till their soil in a crop season, as well as altering other tillage factors, such as the depth to which soil is plowed. Matocha has been conducting experiments using different types of conservation tillage, including a no-till scenario and various minimum-tillage approaches.
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 his 1998 findings.
“With no-till, we yielded 621 pounds of lint per acre on our test plots last year, compared to 452 pounds for conventional tillage. That’s a 37 percent difference,” Matocha said. “For minimum tillage, we yielded 522 pounds an acre, or 15 percent more.”
“I’m still more in favor of minimum tillage than no tillage, but we’ve had herbicide improvements that allow us to look at no-till with more optimism,” Matocha added. “In looking at the long-term results, 10 or more years, cotton grown with conservation tillage outperformed that grown with conventional tillage and deep tillage.”
The 1998 yield differences primarily were due to increased soil moisture available because of conservation tillage, Matocha said.
“Water is the number one issue in crop production here, so anything we can do to increase water ‘harvesting’ and use efficiency will help the crops,” he said. “On a sunny, windy day, a field can lose up to three- or four-tenths of an inch of soil moisture to evaporation. The increased organic residue cover in conservation tillage decreases that loss.”
Normally, a farmer might till the soil between nine and 11 times in a cotton growing season, 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 3-inch depth, and formation of low-profile beds in the same operation. Knifing in fertilizer, planting and cultivating once involves a total of five 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 “narrow slit” knives.
“You need to consider several factors when looking at conservation tillage methods. First, you’ve got to have a pretty clean field to start with, relatively free of weeds,” Matocha said.
“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 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,” he added.
Occasional tillage is more important on fine sandy loams which tend to compact more than certain clay soils (termed montmorillionic) which have a swelling and shrinking characteristic, he said.
Matocha’s group has also added a minimum-till system that includes use of a deep-till (16-inch) “chisel” plow in previous years’ stubble rows. This replaces the post-harvest root plow (3-inch depth) operation and results in the same total of five tillage operations. Under 1998 drought conditions, that system did not yield enough lint increase to cover the cost of the deep tillage. The researchers will continue looking at 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 above 20 pounds per acre had no discernible effect in the conventional tillage system.
On a long-term average basis, minimum-till systems generally can save cotton producers between $35 and $40 an acre over conventional tillage under dryland conditions with the benefits fluctuating among seasons due to available rainfall, Matocha said.
These cost input comparisons did not include the reduced amount of equipment capital required for minimum tillage compared to conventional tillage, he added. There is also an additional benefit: protection of a valuable nonrenewable natural resource, the soil.
“Conservation tillage is definitely a way we can maintain our soil productivity and sustainability,” Matocha said.