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Fluid Journal : Fluid Journal 1993-1995
4 Fluid Journal Fall 1993 8-leaf stage) and a second application during early flowering. Economics If the growing season provides 2,100 to 2,300 heat units, which is what can be expected, dryland yields should average better than 400 pounds per acre and irrigated yields better than 800 pounds per acre---nearly 70 to 80 per-cent more than current averages. The only additional cost (approximately $10 per acre more) to produce these kinds of yields is 30 to 50 pounds more nitrogen per acre. The key management strategy is timing of inputs relative to growth stage of the plant and not an "after-it's-too-late" approach. An increase of 150 to 200 pounds of lint per acre, under dryland conditions represents an additional $75 to $100 income per acre. The 250- to 400-pound per acre yield increase under irrigated conditions represents an additional income of $125 to $200 per acre. Current yield levels represent "break even" levels. Cotton provides the only crop that can be grown on a large scale with real profit potential. The additional yield realized through better management strategies represents the primary approach to realizing that potential. Cotton reigns Cotton is king in Texas. Over five million acres of fiber crop are usually planted across the state. Texas represents nearly 40 percent of the total U.S. acreage. The southern High Plains region (within a 75-mile radius of Lubbock, TX) plants about 3.5 million acres annually and is commonly referred to as the "world's largest cotton patch." Annual precipitation averages 18 to 20 inches. Precipitation to evapotranspiration (P:ET) ratio is 0.25 or less. Over 65 percent of the annual precipitation occurs during the growing season from late April through mid- September. Only about 50 percent of the cotton acreage in the High Plains area has supplemental irrigation capabilities, with the application volume equal to less than 50 percent of potential evapotranspiration or about 0.15 to 0.20 inches per day per acre. Lack of an adequate water supply to meet transpirational demand represents the single greatest limitation to crop production. When water supplies can be properly managed through irrigation or when timely rains occur during the growing season, soil fertility becomes the limiting factor to crop yields (N in particular) and growing season length is measured in heat unit accumulation rather than calendar days. Average yields for the area (Figure 2) reflect rainfall patterns to a large extent, but also are strongly influenced by growing season length. Potential yields, given precipitation and normal heat unit patterns, are approximately twice the average yields. Dryland yields should average close to I bale per acre (500 pounds per acre) and irrigated yields should average close to 2 bales per acre (1,000 pounds per acre). Dr. Krieg is professor of crop physiology in the Department of Agronomy at Texas Tech University in Lubbock, Texas. Acknowledgments: Funding for this research has been provided in part through a grant from the Fluid Fertilizer Foundation and from the Texas State Support Committee Cotton, Inc.
Fluid Journal 1996-1998