Tuesday, 11 July 2006

Development and Adoption of No-Tillage Soybean and Cotton Systems from Long-term Experiments.

Donald D. Tyler, University of Tennessee, 605 Airways Boulevard, Jackson, TN 38301

No-tillage cropping systems for soybeans, corn, and cotton are now commonly used by producers in state of Tennessee. More than half of the total hectares of each of these crops is now planted using no-tillage. Many research efforts contributed to this wide acceptance of this system. Two of these efforts, one involving soybeans and the other cotton are discussed in this paper. The soybean tillage experiment was begun in 1979. Initially, it compared no-tilled soybeans to five shallow and deep tillage treatments. After the first four years two of the tillage treatments were changed to no-tillage treatments. This was a consequence of no significant differences in the tilled treatments, all of which were equal to or less in yield than the no-tillage, and a severe increase in soybean cyst nematodes, a major pest problem in the Southeast, USA. This increase occurred in the fourth year, and only in the tilled treatments with the no-tillage treatment showing much lower nematode levels and no yield reduction as compared to the tilled treatments. Two tillage treatments were changed to no-till systems to attempt to determine the cause of this effect. Since then, the tilled and no-tilled treatments in this experiment have been unchanged. Various disease interactions have been documented and studied in this experiment. Changes in soil physical properties have been measured including bulk density, penetrometer resistance, aggregate stability, and trafficability. Measurements indicate less compaction in the no-tillage treatments but a higher ability of these treatments to support heavy equipment, trafficability, when the soil is wet. In the 2002 season, all treatments were split with one-half of each replication being changed from no-tilled to tilled and vice versa. Each of these new treatments is being monitored for carbon, nematode, and bacterial community changes. With adequate plant population and weed control, no-tillage soybean production has been shown to be as good as or better than the previous tilled systems. A tilled and no-tilled cotton system experiment was begun in 1981. It consists of main plots of four nitrogen rates, sub-plots of winter annual covers of wheat, crimson clover, hairy vetch, previous crop residue, and sub-sub plot of tilled and no-tilled. The initial objectives were to develop systems for no-tillage cotton production and determine the nitrogen contribution from nitrogen fixing winter annual legumes. No-tillage cotton was not being used when this and other cotton research began. Initial problems included poor plant populations, cool soil temperatures, and at times poor weed control. These were generally solved in the first five years of study and the University of Tennessee formally recommended the no-tillage cotton system in 1985. Adoption was relatively slow but began to increase in the late 1980's. An economic analysis after the first ten years, indicated that winter annual legume cover crops could supply all nitrogen for the following cotton crop with profitability depending on seed establishment costs and nitrogen fertilizer costs. The combinations of annually applied nitrogen fertilizer, combined with nitrogen fixing legumes produced very large consistent differences in soil acidity levels. This created an ideal experiment to reevaluate the University of Tennessee lime application recommendations. From this research, recommendations are now being modified. With the advent of glyphosate- resistant cotton varieties, control of certain problem weeds such as pigweed became possible in long-term continuous no-tilled cotton. We now have more than 50% of cotton planted with no-tillage. These no-tillage cropping system increases have had a dramatic effect on soil erosion losses from water erosion. In western TN, the loess derived soils were historically known to suffer some of the highest soil erosion rates in the USA. With no-tillage cropping, and residue management these losses are in some situations 100 fold lower than when soils were tilled.

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