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Fluid Journal : Fluid Journal 1996-1998
Winter 1997 is a resounding yes. A good rule of thumb to remember: the harder you work a soil, the better it becomes. Tillage. Some forms of tillage are more desirable than others for the production of organic matter. The old moldboard plow, used to break prairie soils, is one sure way of destroying organic matter. Two things happen when a moldboard plow is used. First, it exposes the deep soil to excessive aeration, which causes loss of organic matter. Second, residue that is turned under experiences what is called "anaerobic conditions" where there is a lack of air that prevents decaying of residue into organic matter. How many times have you plowed under crop residue and found it there a year or two later? The disk can create a good environment for digestion of residue into organic matter. But the disk also creates a compaction zone three to four inches deep, which can restrict root development. The disk also puts too much residue under the surface, losing two of the primary benefits of residue: erosion control and increased water infiltration rate. The chisel plow does an excellent job of fracturing the subsoil and incorporating some residue four to five inches under the surface. This is the area of greatest organic matter productivity because it is warm, moist, and well aerated. It satisfies all the conditions discussed earlier about mineralization, immobilization, and nitrification. Figure 3 compares the level of organic matter after ten years in the no-till field in Kentucky already cited and a conventional-till field. In the no-till plot, organic matter increased to 5 percent in the top two inches. However, the conventional-till field, using a moldboard plow, stayed at only 2.5 percent organic matter in the top two inches. The comparison demonstrates how the practice of reduced tillage, which leaves more residue on the surface, makes conditions more favorable for residue to be converted into organic matter. The payoff in the end is higher yields. ! Table 2. Nitrogen required to obtain different organic matter levels and corn yield levels while building tilth. Tons dry Possible addition to Additional N Yield residue organic matter reserve needed _________________________________________________________ bu/A (ears removed) % lbs/A 100 2.5 .12 50 150 3.8 .18 75 200 5.0 .24 100 250 6.3 .30 125 Figure 3. Soil organic matter distribution after 10 years in a Kentucky no-till field. Figure 2. The residue cycle.
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