Three Soil Water Potential Strategies to Schedule Irrigation Events using S3DI in Cotton

Scheduling irrigation events in the humid Southeast can be challenging due to unreliable rainfall patterns. The objective of this study was to evaluate three water potential strategies for scheduling irrigation events in cotton (Gossypium hirsutum L.) using shallow subsurface drip irrigation (S3DI) with respect to lint yield and quality, irrigation water-use efficiency (IWUE), and value water-use efficiency (VWUE). Research was conducted in 2012 through 2016 in southwest Georgia, U.S. using an S3DI system. Water potential sensors were installed at 25- and 50-cm soil depth. Irrigation treatments and events occurred when the average water potential values were: -40 kPa (treatment I1), -70 kPa (treatment I2), -70/-40/-60 kPa (treatment I3) (emergence to 1st square/1st square to 1st cracked boll/1st cracked boll to defoliation) and a dryland control. All irrigated treatments had higher yield (1975 kg ha-1) than dryland (987 kg ha-1) except during 2013 (wet year). When 2013 data was deleted, there was no lint yield difference across years (p = 0.07) or across irrigation treatments (p = 0.06). Irrigation treatments I2 and I3 applied 170 mm less irrigation water compared to I1. There were differences in lint quality by irrigation treatment and year, but quality values were within acceptable ranges little or no price deductions. Dry year IWUE for treatments I2 and I3 averaged 3.1 kg lint mm-1 compared with I1 at 2.2 kg lint mm-1. For VWUE, both I2 and I3 had 44% greater value per unit of irrigation applied compared with I1. Either I2 or I3 can be used for scheduling irrigation events efficiently and economically.