Irrigation Scheduling Using Predawn Leaf Water Potential Improves Water Productivity in Drip-Irrigated Cotton.

To address the effectiveness of predawn leaf water potential in plant-based irrigation scheduling, Gossypium hirsutum L. plants were grown under fully irrigated and dryland conditions and under three predawn water potential (Ψ_PD) thresholds (-0.5, -0.7, and -0.9 MPa). Measurements included Ψ_PD, plant height, mainstem node number, lint yield, water productivity, and continuous crop canopy temperature. We found that Ψ_PD produced similar yields to current practices, while decreasing overall water use from 7 to 31%, depending on rainfall levels and the treatment utilized. When considered across both years of the study (2013 and 2014), using a -0.5-MPa Ψ_PD irrigation threshold consistently resulted in less irrigation applied than the checkbook method and maximum water productivity and lint yield. Using a well-watered baseline developed in 2013 for canopy temperature versus vapor pressure deficit, we calculated a crop water stress index (CWSI) that exhibited a very strong, nonlinear relationship with season average Ψ_PD values between approximately -0.4 and -0.7 MPa (r² = 0.81). A strong, nonlinear relationship was also seen between CWSI and lint yield (r² = 0.81). Predawn water potential appears to be an effective means of determining the need for irrigation in cotton, and in the current study, yield and water productivity were maximized at a season-long average Ψ_PD threshold of -0.5 MPa. Furthermore, when calibrated using Ψ_PD--based irrigation triggers, canopy-temperature derived CWSI appears to be a promising tool for future automated plant-based irrigation scheduling in the southeastern United States. [ABSTRACT FROM AUTHOR]