| This study was undertaken to determine the effects of preconditioning water deficits on the internal water relations, agronomic properties, and water use of cotton, and to examine the feasibility of using deficit irrigation to improve water-use efficiency (WUE) and conserve irrigation water with minimal impact on yield and fiber quality.;For field experiments, treatments were factorial combinations of five SWPI levels (-0.25, -0.50, -1.00, -1.50, -2.00 MPa) before flowering with two SWPI levels (-0.25 and -0.50 MPa) during flowering in 1982 and three SWPI levels (-0.15, -0.40, and -1.50 MPa) before flowering and during flowering in 1983. Both seed cotton yield and WUE were decreased by -2.00 MPa preflower SWPI. However, delaying the preflower irrigation down to -1.50 MPa SWPI, which coincided with the initiation of flowering, significantly improved WUE. This improvement resulted from the conservation of water as yields were not affected by preflower SWPI down to -1.50 MPa. Delaying preflower irrigation also hastened earliness of maturity. Both yield and WUE were decreased by low SWPI levels during the flowering stage.;Deficit irrigation treatments of -0.40 and -1.50 MPa preflower SWPI induced osmotic adjustment by lowering leaf water potential at zero turgor and leaf osmotic potential at full turgor, increasing solute content and specific leaf weight, and decreasing turgid:dry weight ratio. Deficit irrigation did not affect the LWP-stomatal conductance, however.;The level of leaf water potential (LWP) necessary to produce the preconditioning response and the effects of preconditioning water stress on plant morphology, yield components, and physiological responses were determined in two greenhouse experiments. Factorial combinations of two levels of soil water potential at irrigation (SWPI) before flowering (-0.17 and -1.50 MPa) and during flowering (-0.17 and -0.45 MPa) were used as four treatments in experiment 1. Plants irrigated at -1.50 MPa SWPI before flowering used significantly less water than those irrigated at -0.17 MPa. However the -1.50 MPa SWPI before flowering did not reduce water use during the flowering stage. In the second experiment, plants prestressed to -3.00 MPa LWP had more negative leaf water potential at zero turgor and stomatal closure. |
