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Fluid Journal : Fluid Journal 1996-1998
1 Fluid Journal Winter 1998 Summary: Our cotton physiology research program has been addressing the interaction between plant density and water supply on yield performance for several years. Under irrigated conditions, where water supply can be managed to minimize plant stress, narrow row spacings with 3 to 4 plants/foot of planted row resulted in highest yields. Under dryland conditions, where water stress is frequent and often severe, narrow rows still out produce wider rows (40-inch or skip row), but population responses were dependent on stored water at planting and rainfall patterns during the growing season. No consistent pattern was observed, since considerable year to year variation existed in water supply components. Determination of water supply required to produce 5 to 6 mature fruit per plant indicated that a population density of 3,000 plants/A/inch of available water was maximum. Optimum plant densities can be determined at planting by knowing volume of stored water and potential rainfall (and irrigation water) that can be expected in the next 90 days. In the Texas High Plains, the question of ideal cotton plant population for maximum yield of highest quality fiber and seed has been debated for many decades. Planting period (late April to mid May) is fairly turbulent due to rapidly changing temperatures and frequent rain and wind storms that damage young seedlings. Low, non-uniform populations produce large, stemmy plants that create harvesting and fiber quality problems from excess stems in the lint and a high percentage of immature fruit resulting from prolonged flowering. Excessive populations delay fruiting onset and increase the risk of intense water stress through varying periods of the growing season. Due to indeterminate growth habit and woody perennial characteristics of cotton, vegetative growth is dominant over reproductive growth under both excessive water and by D.R. Krieg Interaction Between Plant Density And Water Supply Affects Cotton Yield Texas scientist concludes only way to reduce risk of excessive stress is to match population with expected water supply. nutrient supplies, as well as deficit conditions of each. Therefore, under water stress conditions, the plant will stop initiating fruiting sites and/or abort existing young fruit, either of which drastically reduces yield potential. Production conditions on the Texas High Plains range from complete dryland to fully irrigated. About half the planted 3.5 million acres is grown under rainfed conditions where water supply is the single greatest limiting factor. Average annual precipitation is 18.5 inches with about 65 percent occurring during the summer growing season. However, evaporative demand averages between 0.30 to 0.35 inches/ day during this period, resulting in a precipitation/evapotranspiration ratio of 0.25 or less. Excessive demand relative to water supply results in considerable plant stress, reducing yield of lint and seed. The remaining half of the production area has supplemental irrigation. Water supply is highly variable and ranges from 50 to 100 percent replacement capabilities of actual crop water use (ETa). When water supply meets evaporative demand, growing season length becomes the limiting factor. Anything that delays fruiting onset, reduces retention, or prolongs the fruiting period, results in low yields of poor quality fiber and seed. Therefore, ideal or optimum population must be defined for ranges Table 1. Multiple regression analyses of lint yield and relative contribution of each component across 6 site years (n=120). Source Component Parameter estimate Partial R2 Lint yield Intercept 0.00 --- Bolls/A 16.77 0.854 Lint/boll 38.42 0.097 Total R2 0.951 Boll/A Intercept 0.00 --- Bolls/plant 6.43 0.374 Plants/A 1.51 0.374 Total R2 0.748
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