Test of the Stress‐Degree‐Day Concept Using Multiple Planting Dates of Red Kidney Beans

Abstract

Canopy temperature measurements indicate crop water stress and should be related to crop yield. In this study, several planting dates and soil moisture levels were used to evaluate the stress‐degree‐day (SDD) concept as an indicator of crop yield. Red kidney beans (Phaseolus vulgaris L.) were planted on four dates, equally spaced, during a 9 week period from mid‐May to mid‐July, 1978. Beans were hand‐planted in 20 ✕ 5 m field plots on a silt loam with 76 cm row spacing at 165,000 ha‐2 Five irrigation treatments within each planting date provided a wide range of soil moisture conditions. The driest treatment in each planting didn't receive additional water after germination, while the wettest was continually well supplied with water. Moisture extraction in all treatments was measured to 180 cm three times weekly with the neutron scattering technique. Canopy temperatures were measured with an infrared thermometer each day throughout the growing season about 1 hour after solar noon. Stress‐degree‐days were calculated for each treatment by using air temperature recorded next to the plot area. Linear regression demonstrated that seed yields were strongly dependent on the accumulation of stress degree days from flowering to maturity (r² = 0.82), indicating the importance of the post‐vegetative stage to final yield. Inclusion of the SDD summation from emergence to flowering as a second independent variable did not significantly improve the regression (R² = 0.83). Individual regression lines for each planting were not significantly different (P = 0.05), demonstrating that the yield‐stress degree day relationship was stable over a wide range of planting dates. Total water use was negatively correlated with stress‐degree‐days summed from flowering to maturity (r = −0.83), verifying the potential for using the SDD concept in water management. The data also confirm that the SDD concept is a valid representation of the effect of moisture stress on yield, and point to the potential for using remotely determined canopy temperatures in estimating yields over large areas.