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Data from 25 years presented: No-till proves best in long-term study

Like a good wine, a no-till crop production system improves with age.

Success of continuous no-till comes through a slow but steady increase in soil organic matter, improved soil structure and better availability of soil nutrients, says Texas A&M University professor and research soil chemist John Matocha.

Matocha, who works out of the Texas A&M Research and Extension Center at Corpus Christi, presented findings from a 25-year study at the annual National Conference on Conservation Tillage held earlier this year in Houston.

Matocha says the intensity of soil tillage affects the physical properties of soil and that biochemical changes can influence rainfall utilization, plant nutrient availability and crop yields.

“Zero tillage had positive effects on the degree of soil aggregation and stability of the soil aggregates in the surface layers of both an Orelia sandy loam and Victoria clay soils,” he says. “This influenced root proliferation and water infiltration.”

He reports an apparent “substantial decrease in percent of clay in surface layers, which could have a negative effect on plant nutrient retention,” but says an increase in soil organic matter and an improvement in cation exchange capacity and the net effect on nutrient availability and retention offsets the loss.

Soil organic matter (SOM) may by a key to no-till success, Matocha says. “Organic matter contributes significantly to soil quality and subsequently to crop productivity. Data from the long-term study showed relatively small changes in soil organic matter among three conventional tillage systems. Moldboard plowing produced the largest reduction in soil organic matter, a 14 percent decrease.”

A 12-inch chisel plow system and a 6-inch bedding and rebedding system also decreased soil organic matter levels.

Minimum tillage (three tillage operations at 3-inch depth per year) increased soil organic matter by 12 percent.

Greatest increase

“By far the greatest increase in soil organic matter came from zero tillage in which the soil contained 2.64 percent (SOM) and was 58 percent and 39 percent higher than moldboard plow and conventional tillage systems, respectively,” Matocha says.

Less tillage also made certain plant nutrients more available, according to the research results. Soil phosphorus increased substantially in surface layers in plots with zero tillage. “We measured a 50 percent increase in unfertilized, no-till soil and approximately a 100 percent gain in extractable soil phosphorus when we used soil test recommended rates of nitrogen and phosphorus, compared with conventional tillage.

“We found substantially more potassium in surface layers of no-till soils. At least part of the positive influence on extractable soil phosphorus from reduced tillage comes from the associated decrease in soil pH. On highly calcareous soils, decreasing soil pH generally increases plant availability of certain nutrients, including phosphorus.”

Worms also like no-till systems. Matocha says earthworm activity increases significantly in zero-tillage systems. “Soil in the no-till plots showed 200 percent to 300 percent higher concentration of earthworms, compared to conventional tillage, and 400 percent to 500 percent higher compared to moldboard plow.

Earthworm benefits

“Also, soil compacted from wheel traffic had substantially higher worm activity, which served as a large benefit to the no-till system.”

Matocha says earthworms play a significant role in improving soils and refers to them as “underground farm aid.” Earthworms break down organic matter and convert it to nutrients for crop use and help turn organic matter into more soluble forms of phosphorus, potassium and other essential nutrients.

“Also, the earthworms burrow through the soil to bury organic matter, create tunnels for water infiltration, improve soil structure and reduce runoff and soil erosion. Improved soil aggregation is partly a result of increased earthworm activity.”

The soil improvements may be interesting but the proof in the process comes from crop production. Matocha says earlier yield comparisons of corn and cotton between the conservation tillage and conventional tillage systems with both the Orelia and Victoria soils “provided less encouraging results compared to yields 10, 15, and 20 years following the start of the experiments.

“(Now) yields of both crops grown under the two conservation tillage systems have compared extremely well with conventional tillage yields with yields on the clay soil being stronger in favor of no till than on the sandy loam soil,” he says.

“Results (from five seasons) on the clay soils show that no-till cotton produced higher yields than minimum till or deep plowed cotton in an extremely dry season (1989) and substantially more (83 pounds per acre) in a very wet season (2003). In the best season (2003) no-till cotton yields approached three bales (2.93 bales, dryland) per acre while lint yields from deep chiseled plots measured 2.76 bales per acre.

“Ripping the soil to 16 inches produced only a slight increase in yield, 39 pounds per acre, over the minimum till plot with tillage depth maintained at 3 inches over the past 18 years.”

Improve with time

Matocha says yield comparisons between conservation tillage and conventional and/or deep tillage appear to get stronger in favor of no-till and minimum till systems with longevity of the study.

“Results of this long-term project indicate that conservation tillage systems are viable alternatives to conventional and deep tillage systems on finer textured soils such as Victoria clay. In addition to crop productivity other benefits include improved soils quality and anticipated reduced production costs.”

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