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Fluid Journal : Fluid Journal 1996-1998
2 Fluid Journal Winter 1998 of water supplies from rainfed conditions to those replacing ETa. Our objective in this project (1994- 96) was to determine what effect the relationship between plant population and water supply has on lint yield and components of yield, namely fruit number and size. From this relationship, seeding rate guidelines, based upon available water supply, could be developed to minimize risk of yield losses or fiber quality reductions caused by excessive plant water stress. Search for right match Field experiments have been conducted for a period of years at two sites reflecting soil texture differences. One has clay loam texture about 4 feet deep, which is typical of the northern half of the southern High Plains cotton growing region. The other has a loamy fine sand about 6 feet deep, which is typical of the southern half of the production area. The two sites are separated by 60 miles, so that the weather components (other than rainfall) are very similar on a day-to- day basis. At each location, sprinkler irrigation capabilities exist such that water supply can be varied from rainfed only to 100 percent replacement of actual crop water use (ETa) at various frequencies. A range of water supplies from dryland to 50, 75, and 100 percent ETa replacement at -weekly frequencies has been the most common water supply variable studied during the course of this experiment. Several commercial cotton varieties differing in degree of indeterminancy have been used in all experiments. Row spacing and seeding rate have been the major experimental variables used to develop the relationship between water supply and plant density. Row spacing ranged from ultra-narrow (15-inch) to narrow (30- inch) to wide (40-inch) to skip row patterns (2 planted, 1 skip). The dryland system evaluated 30- and 40-inch row spacings planted either solid or in a 2 by I skip row pattern. Seeding rates within the row were also variable and usually consisted of approximately 2, 4, and 6 seeds/foot of plant row, providing a wide range in resultant plant densities. Final harvestable lint yield was evaluated in terms of yield components, including plant density (plants/A), fruit per acre and per plant, and fruit size (lint and seed weights per fruit). Multiple regression analyses were used to determine the relative contribution of each component to final lint yield/A. Bolls/A were the major yield component accounting for over 80 percent of the yield variation (Table 1) across all treatment variables. Boll size (lint per boll) contributed less than 10 percent to the yield variation, although boll size does differ among varieties, and due to temperature and nutritional variations. Boll number consists of two Figure 1. Plant population effects on fruit per plant within varios water supplies, Krieg, Texas Tech University, 1994-1996. Table 2. Correlation analyses of lint yield components of yield as a function of water supply during different parts of the growing season. Water supply Yield/A Bolls/A Bolls/plant Lint/boll Seasonal 0.27 0.33 0.31 -0.01 Planting to SI -0.53 -0.38 -0.32 -0.56 SI-FF 0.74 0.63 0.54 0.61 FF-PB 0.41 0.61 0.32 0.15 PB - Maturity -0.35 -0.38 0.11 -0.48 SI = square initiation, FF = first flower, PB = peak bloom
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