Development of a Drought-Stress Quantifying Index in Cotton Variety Trials.

Although the large number of dryland cotton (Gossypium hirsutum, L.) variety trials conducted each year allow producers to examine the yield response of varieties in similar growing conditions to their own, local trials may not fully express all varietal characteristics, specifically those of drought stress. The ability to characterize the drought stress of these trials would allow for a larger extrapolation of varietal yield response. The main objective of this initiative was to develop a crop/soil sensor-based index to accurately characterize location drought-stress. Trials at each location tested the response of drought-stress monitoring sensors to differences in variety and replication. Monitored data included standard meteorological parameters and either canopy temperature, soil moisture, or both at the plot scale. Soil moisture data was collected by PureSense Inc. (Fresno, CA).  Drought stress was characterized by an available soil moisture stress index, which was a function of total available water (TAW) adjusted for rooting depth. Canopy temperature data was collected and analyzed by Smartfield Inc. (Lubbock, TX). Strongest relationships between the accumulated available H₂O drought stress index units and seedcotton yield were found when the upper and lower limits of TAW were determined from in-season sensor readings. Preliminary results suggest a limited number of sensors under a standard variety could be used to characterize location drought stress, therefore increasing the utility of dryland variety trials. Still, further research is needed to more accurately define the response of the index to variety and spatial variability and to include and test a crop susceptibility factor.