Evaluating cotton plant population effects on irrigation management and yield stability

The rising cost of crop inputs has driven farmers to reduce costs. One area they have focused on is the seeding rate in an effort to minimize seed cost. Numerous studies have been completed every few years to evaluate optimum seeding rates across the U.S. cotton belt. However, few of these have focused on plant population effects on irrigation requirements and water use. To bridge this research gap, a two-year research trial was conducted at the University of Georgia’s Stripling Irrigation Research Park near Camilla, Georgia. This trial was implemented using a variable-rate overhead lateral irrigation system to irrigate nine treatments independently. The cotton cultivar Deltapine 2038 B3XF was planted and hand-thinned to represent Georgia's high, moderate, and low plant populations. Each population had a corresponding plot that was irrigated based on the UGA SmartIrrigation Cropfit app, another irrigated using a 45 kPa weighted average soil water tension (SWT) threshold, and a rainfed check in a factorial arrangement. Each treatment was replicated three times and had custom-built probes with Watermark tensiometers integrated at 8, 16, and 24 in. (Irrometer Co. Riverside, CA) attached to Realm5 telemetry (Realm, Lincoln, NE) installed randomly into two of the three replicates. SWT was logged hourly for all treatments and used for daily irrigation scheduling of appropriate plots. As populations increased, sensor-based irrigation requirements were reduced for the highest population density in both years by at least one 18 mm irrigation event compared to lower plant densities. There were no statistical correlations between crop density and yield, IWUE, or profitability, but rather irrigation treatments in 2023. Because reductions in seed input cost estimates were offset by increased irrigation input cost, which allowed for no significant benefit to reduced plant density in cotton grown in the southeastern U.S. Therefore a practical application of these findings suggest targeting a final population of 50,000 plants ha −1 as a middle ground compromise both scientifically documented yield stability and increased irrigation requirements