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Fluid Journal : Fluid Journal 2002-2004
Fall 2004 Fluid Journal 2 in developing countries. If yields and food output do not keep pace with population growth on the good arable land now in production, it will be impossible to protect the remnant natural ecosystems from being turned into farmland, and much of this expansion will occur on marginal lands not suited for continuous cropping. Sustaining increases in crop yields will require improved crop cultivars and hybrids, as well as improved pest protection, crop nutrition, and maintenance of soil fertility. Potential supply of organic nutrients is simply not large enough to be a significant factor in raising crop yields and maintaining soil fertility. Therefore, environmentalists concerned with protecting natural ecosystems and biodiversity must eventually come to recognize the need for increasing crop yields on existing cultivated land through appropriate use of fertilizer nutrients. Data worldwide shows that maintaining an adequate supply of food crops to meet global demand will depend on maintaining an annual rate increase in yield on existing farmland of about 1.4 percent in major producing countries. An even higher rate of growth in yield will be required if these crops are increasingly used for bio- energy and bio-based feedstocks for industry. Thus, to protect biodiversity and natural ecosystems, it is much preferable to increase yields on existing farmland. I suspect that the environmental movement will soon come to embrace intensification of agriculture in order to avoid agricultural expansion into native grasslands, wetlands, and rain forests---especially in Argentina and Brazil. Water quality. The greatest threats to water quality are soil erosion, leaching, and runoff of N and phosphorus (P) from agricultural systems. Both can be greatly reduced via conservation tillage methods and use of improved nutrient management practices that have been widely adopted in the U.S. in the past 25 years. For example, N fertilizer use on USA corn reached a peak in 1980 and has remained constant since then although corn yields have increased steadily by 1.7 bu/A/yr (Figure 1). Taken together, these trends have contributed to a 35 percent increase in N-use efficiency (NUE)---from about 0.76 bu/A of corn produced per pound of N applied in 1980 to 1.03 bu/A per pound applied in 2000. Despite this progress, however, average N fertilizer uptake efficiency by corn and the other major cereals averages 30 to 50 percent of applied N, which means that 50 to 70 percent of applied N is at risk of being lost to the environment via leaching, volatilization, and denitrification. The potential scope for improvement in NUE is best illustrated by recent studies from a productionscale field study conducted by the University of Nebraska Carbon Sequestration Program, which have demonstrated the potential to achieve a substantial increase in both crop yields and NUE (Table 1). Several aspects of crop management used in this study were derived from our Ecological Intensification program funded in part by the Fluid Fertilizer Foundation. The potential to sequester carbon in soil organic matter, which contributes to improved soil quality and a reduction in carbon dioxide emissions, is being measured in both studies. Our working hypothesis is that progressive crop and soil management practices make it possible to achieve substantial Table 1. Corn yield and NUE obtained in three cropping systems in which progressive crop and soil management practices* were employed in quarter section fields (approximately 160 acres), 2001. System Yield N Fertilizer NUE bu/A lbs N/A bu/lb of N IrrigatedCorn/soybean 217 137 1.59 Continuous corn 209 175 1.20 Rain-fedCorn/soybean 142 114 1.25 USA Corn Avg. 135 140 1.03 * Progressive management practices include no-till, soil-test-based N fertilizer recommendations, split N applications and pivot fertigations, ETbased irrigation scheduling, Bt corn hybrid. Table 2. Life-cycle energy balance* (in diesel fuel equivalents) in high-yield irrigated continuous corn used to produce ethanol, U of Nebraska. System Energy Output Energy Input Net Energy Gain (output/input ratio) Irrigated 981 767 215 (1.3 to 1) Rain-fed 686 470 166 (1.4 to 1) USA Corn Avg. 135 140 1.03 * Energy balance includes all energy inputs used in corn production (fertilizer, irrigation, field operations, etc.), transport from the field to the ethanol plant, and ethanol production. Energy outputs include energy content of the ethanol produced and the wet distillers grain.
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