Cotton (Gossypium hirsutum L.) grown under drip irrigation was evaluated over a two year period for physiological and morphological responses. Three water levels representing, 103, 93 and 87% of estimated consumptive use (63.6 ha-cm) were used in Marana, AZ. in 1983. In 1984, cotton was grown under eight drip irrigation treatments corresponding to 120, 100, 80 and 60% of the estimated consumptive use (79.5 ha-cm) in Stanfield, AZ. These volumes of water were applied as small daily amounts and larger weekly amounts for a total of eight irrigation treatments. The experimental design was a randomized complete block with four replications. Mean leaf area ratio (LAR), leaf area index (LAI), mean net assimilation rate (NAR), mean relative growth rate (RGR), mean crop growth rate (CGR), plant height and the number of mainstem nodes were determined using the growth analysis method. Transpiration, diffusive resistance, leaf and ambient temperatures were measured with a steady state porometer. Apparent photosynthesis (APS) was determined in 1983 with an infrared gas analyzer which measured CO(,2) concentrations. In 1983, the cotton plants from the 103% irrigation treatment had greater transpiration, lower diffusive resistance and lower APS than the 93% treatment plants. In 1984, no significant differences were observed between the seasonal transpiration rates from the eight irrigation treatments. Cotton plants grown under the 120% treatment showed superior diffusive resistance responses than those from the 60% treatment. Temperature differentials were higher in the 120% treatments than in the 60% treatments. No significant differences were found between LAR, NAR, RGR and CGR during 1983 and 1984. Even though there were no differences between the total number of flowers produced in the three treatments in 1983, the 93 and 87% treatment plants produced more seed cotton than the 103% treatment plants. In 1984, the seed cotton yield from the 60% daily treatment was significantly the lowest. Due to the problems related to the late initiation of treatments and excessive rainfall, the physiological and morphological responses of cotton were inconsistent across the various water levels in 1983. Regression analysis confirmed the erratic responses of cotton plants from the weekly treatments across the wide range of environmental conditions in 1984.

Studies were conducted on commercial farms in 1982 and 1983 to study the effects of above surface drip irrigation, below surface drip irrigation, and furrow irrigation on flowering, boll set, yield, and growth of cotton (Gossypium hirsutum L.). Two varieties were used in 1982, 'Deltapine 62' and 'Deltapine 90', using both above and below ground drip irrigation and Deltapine 90 was grown under furrow irrigation. In 1983 the study was conducted at a different location with above ground drip irrigation and furrow irrigation using the cotton variety 'Deltapine 41'. The irrigation water was monitored to deliver 100% of consumptive use (CU), 85% of CU, 70% of CU, 100% of CU every other day and CU which was the grower's estimate of consumptive use. All open flowers were tagged using Kwik-Lok labels dated with the day the flower opened. Tagging of flowers started from first open flower and continued for 17 weeks in 1982 and 15 weeks in 1983. Plants were sampled twice in 1982 and three times in 1983 for LAI and partitioning studies. All open bolls were harvested on a weekly basis for a total of 12 harvests. In the 1982 experiments no statistical analyses were made because the five treatments were grown in different fields and could not be randomized together. A general comparison showed that Treatment 1, Deltapine 62 above ground drip system produced the highest number of flowers but it had the lowest percent of boll set. Treatment 5, Deltapine 90, furrow system, produced the lowest number of flowers but it had the highest percent of boll set. Treatment 3, Deltapine 62 below ground drip system, had the highest boll set and Treatment 5 retained the least number of bolls. Treatment 2, Deltapine 90 above ground dry system, had the highest seed cotton yield and Treatment 5 had the lowest yield. In the 1983 experiment, there were no significant differences in flowering, boll set, or yield among the five irrigated treatments. The furrow treatment could not be compared statistically with validity with the drip treatment because it was grown in a different field but a general comparison showed that it produced the lowest number of flowers and seed cotton yield although it had the highest percent of boll set.

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