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Fluid Journal : Fluid Journal 1993-1995
1 Fluid Journal Fall 1993 J.S. Kern and Dr. G. Johnson Conversion to Conservation-till will Help Reduce Atmospheric Carbon Levels Study projects conversion to year 2020 and accompanying reductions in soil organic carbon and fossil fuel emissions. Summary: Changes in tillage practices that minimize trips across the field have produced many benefits for producers and the environment. It is well established that reduced or conservation tillage increases soil organic matter. Coupled with reductions in fuel use, increases in soil organic matter may offer help in reducing greenhouse gases. Our study shows that increasing use of conservation tillage may offset U.S. fossil fuel emissions by as much as 1. 1 percent and global changes may reduce up to 16 percent of the annual global fossil fuel emissions. One potential method for increasing the amount of carbon held in agricultural soil is the conversion of conventional tillage practices to conservation tillage practices. It is well known that soils hold organic matter, which may have a large influence on the long-term sustainability of soil. Conservation and reduced tillage retain more crop residue. Conservation and enhancement of soil organic matter are essential for plant nutrition, soil structure and compactibility, and water holding capacity. But soil can also function as either a source of, or a sink for, atmospheric carbon. This is significant when one considers that soil organic matter is the largest terrestrial global carbon pool and affects the atmospheric content of C02, CH4, and other greenhouse gases. Thus, soil may have an added important role in holding carbon from the atmosphere, thereby helping to decrease the buildup of greenhouse gases and aid in reducing the possibility of global climate change. The purpose of this study is to estimate the amount of carbon that can be held in the soil and also conserved by reduced fossil fuel usage by the year 2020 as a result of projected changes in U.S. tillage practices for crop production. Attractive option Conservation tillage is an attractive option to farmers because it has the potential to reduce production costs. It does, however, require a higher level of farmer skill and farmer assistance for conservation tillage to succeed. Conservation tillage systems, as defined by the Conservation Technology Information Center (West Lafayette, IN), maintain more than 30 percent residue cover on the soil surface. No-till management consists of no tillage from after harvest to planting time. Ridge-till systems use no tillage from after harvest to planting, but crops are planted into tilled ridges and crop residues are left between the ridges. Mulch-till disturbs the entire soil surface while retaining more than 30 percent crop residue on the ground. In this study, the term minimum tillage is used for mulch-till and ridge-till Increasing carbon Levels Soil organic carbon tends to increase with conservation tillage because less organic matter is lost to oxidation from mixing of the soil. Soil temperatures also tend to be lower, which slows decomposition. Amount and kind of crop residues have an effect on soil organic carbon levels. The stability of carbon held in the soil is illustrated by data obtained from long-term tillage sites. These experiments show that soil had elevated levels of soil organic matter 100 years after manure additions were stopped. Conservation tillage may increase the amount of soil organic carbon by providing an environment where fungal decomposition is greater than bacterial decomposition. Fungal decomposition results in decomposition products that are more difficult to break into smaller parts than does bacterial decomposition. Less fossil fuel emissions In the U.S., fossil fuels used in agriculture emit approximately 84 million tons of carbon each year, excluding emissions from fertilizer and herbicide manufacturing. Fertilizer manufacturing, primarily N, releases about the same amount of carbon. Conventional tillage systems are the most energy intensive and no-till systems the least. Researchers have estimated that conventional tillage requires the energy equivalent of 7.5 gallons of diesel fuel per acre per year. No-till systems require slightly more than 4 gallons of diesel fuel per acre per year. Unlike conventionally tilled systems, no-till systems depend more on chemical weed control than on mechanical control. Therefore, a larger percentage of the energy budget for no- till systems is directed to manufacturing herbicides than for conventional tillage systems. Of the diesel fuel equivalent required for no-till, about 70 percent is needed for manufacturing herbicides. In the conventional till-age system, about 23 percent of the energy requirement is allocated to herbicide manufacturing. However, even though herbicide requirements are larger, no-till/
Fluid Journal 1996-1998