The Use of Plant Water Status As an Irrigation Scheduling Method.

In an effort to evaluate the utility of plant water status as an irrigation scheduling tool, G. hirsutum plants were grown under fully irrigated and dryland conditions as well as under three irrigation treatments using predawn water potential (Ψ_PD) thresholds (-0.5, -0.7, and -0.9 MPa). Plant responses such as growth, lint yield, yield components, as well as continuous crop canopy temperature were monitored. We found that Ψ_PD offers the potential to produce similar yields to current irrigation practices, while decreasing overall water use from 7-31 %.  In addition, we found that decreased fiber yield is primarily due to decreased bolls m^-2 (as much as 43 % decline) relative to dryland treatments.  Using a well-watered baseline developed in 2013 (a year with unusually high rainfall), we derived a crop water stress index (CWSI) that exhibited a very strong, non-linear relationship for Ψ_PD values between ~-0.4 and -0.7 MPa (r² = 0.79).  This CWSI also showed a strong, non-linear relationship was seen between CWSI and lint yield (r² = 0.81).  Ψ_PD 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.