Leaf Stomatal Conductance, Transpiration and Leaf Area Growth Patterns of Four Cotton Varieties Under Different Irrigation Regimes in Southern Texas

We studied four cotton varieties under irrigated conditions in southwest Texas with the objective of characterizing ecophysiological traits related to water use and yield. Four cotton varieties, ‘PHY499 WRF’, ‘DP1044 B2RF’, ‘FM1944 GLB2’ and ‘DP0935 B2RF’, were planted in a center pivot field under three levels of irrigation (100%, 75% and 50% of crop evapotranspiration) in a split plot design. Both variety and irrigation level were replicated twice. Planting date was April 18, 2014 and harvest date was September 18, 2014. Total irrigation applied during the growing season (100% ETc) was 9.27 in. and total rainfall was 11.75 in. Two heavy rains caused flooding to one of the plots at 75% irrigation. As a result data analysis was done only to the plots with 100% and 50% irrigation. Results show a significant effect of irrigation on cotton yield (p=0.001), while variety effect was not significant (p=0.3). At 50% and 100% irrigation levels, the yield of seed cotton increased in the following order: FM1944 (2149 and 2750 lbs/acre, respectively), PHY499 (2242 and 2817 lbs/acre), DP0935 (2268 and 2878 lbs/acre) and DP1044 (2533 and 2966 lbs/acre). Leaf gas exchange, leaf area index and sap flow rate were measured during the experiment. Leaf area index reached highest values for all varieties a week following peak flower, with DP1044 maintaining low values from mid- to late growing season. At peak flower (July 17) the highest and lowest values of stomatal conductance were measured in DP1044 and PHY499, respectively. However, stem sap flow measurements during August indicated an opposite trend. From August 4 to 10, the average daily sap flow rate under 50% irrigation was 2.1 and 1.27 kg/day/m² (leaf area), respectively, for PHY499 and DP1044. Preliminary data from this study suggest that DP1044 and PHY499 have a greater potential for saving water while maintaining yield.