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, G. hirsutum plants were grown under fully irrigated and dryland conditions and under three predawn water potential (ΨPD) thresholds (-0.5, -0.7, and -0.9 MPa). Measurements included ΨPD, growth characteristics, lint yield, yield components, HVI fiber quality, and continuous crop canopy temperature. We found that ΨPD produced similar yields to current practices, while decreasing overall water use from 7-31 %, depending upon rainfall levels and treatment utilized. When the cotton crop was exposed to drought (2014), using a -0.5 MPa ΨPD produced the highest water productivity (40.7 kg ha^-1 cm^-1), produced the highest yields (1995.2 kg ha^-1), and did not negatively impact fiber quality relative to traditional practices. In addition, decreased fiber yield in drought-stressed treatments was primarily due to decreased bolls m^-2 (as much as a 43 % decline in severely stressed treatments). Using a well-watered baseline developed in 2013, we calculated a crop water stress index (CWSI) that exhibited a very strong, non-linear relationship with ΨPD values between ~-0.4 and -0.7 MPa (r² = 0.81). A strong, non-linear relationship was seen between CWSI and lint yield (r² = 0.81). ΨPD 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 ΨPD threshold of -0.5 MPa.