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Fluid Journal : Fluid Journal 1999-2001
1 Fluid Journal Spring 1999 FFF Review Residues: A Problem or an Opportunity Recent studies show why residues are the key to maximizing soil productivity (MSP). Years ago, after harvest, there was barely enough residue left on the surface for erosion control. Residue from a 100-bu/A corn crop amounted only to about 2 tons of tops and 1.2 tons of roots, hardly enough to control erosion and certainly not enough to incorporate into the soil for possible soil quality improvement. For the past 40 years, however, U.S. corn yields have been steadily rising. Concomitant with this steady rise has also been the production of more and more residue. Though such heavier accumulations of residue can and have caused tillage and weed control problems, properly handled, these residues can be a great asset to growers. Today, with a 200-bu/A crop, which is commonplace, 4.7 tons of residue gives enough tops and roots for both erosion control and soil quality improvement. The higher the yield, the greater the opportunity to increase yield even more. Proper residue management can produce a soil with: • higher organic matter • lower bulk density • higher water holding capacity • higher water infiltration rate • erosion control But that's not all. As we shall see from a recent study, residues can increase nitrogen and phosphorus availability many years into the future. Managing residue Unfortunately, many farmers are not aware of the high value of corn residue. Many bale it for bedding or feed or even burn it, when they should be building soil quality with it. Why is the residue so valuable? Residue consists of leaves, husks, and stems on the surface, and roots in the ground. Such residue contains about 45 percent carbon. Organic matter contains 58 percent carbon and 5.3 percent nitrogen (N). It also contains 1.7 percent phosphorus (P2O5) and 0.7 percent sulfur (S). The carbon can be sequestered into organic matter in the soil under certain environmental conditions. This organic matter, which is eventually distributed deeply into the soil profile, can improve soil quality ---essential for high yields. As yields increase, residues (roots and tops) increase. As residues increase yields increase. It's like a snowball rolling downhill! It amounts to proper management of corn residues, making it possible to obtain yields significantly higher than the national average. Documentation A recent study by Power, et al., in Nebraska shows that residue contributes more to soil properties than just organic matter. In these trials, residue was returned to the soil in variable amounts. Some plots were clean (0% residue), while others FIGURE 1. Residual effect of corn residue applied from 1978 to '85 on corn yield in trials run from 1988 to '95, Power, et al., University of Nebraska. 80 70 60 50 40 30 20 10 '88 --'89 '90 --'91 '92 -- '93 '94 --'95 Year (2-Year Average) Yield -- bu/A 0% Residue 150% Residue TABLE 1. Effect of corn residue on soil properties after applying 150% vs. 0% residue, J.F. Power, et al., 1997. • Yields up 16% for ten years after application • Estimated N availability up 13% • BraysoilPup21% • Soil density down 22% • Increased organic matter contained 50, 100, and 150 percent of the previous corn yield. The study continued for eight years (1978-1985). The second part of the trial began in 1986. Continuous corn was grown on these plots and something amazing happened. For 10 years the plots with residue outyielded the plots with residue removed! In fact, yields (150% vs. 0% residue) were 16 percent better throughout the 10 years (Figure 1)! As reported in the study: "Results show that use of increased residues for 8
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