Two field experiments were conducted during 1981-1982 to determine the feasibility of using midday canopy temperatures, measured with an infrared radiation thermometer, for irrigation scheduling in ‘Oregon 1604’ and ‘Galamor’ snap beans (Phaseolus vulgaris L.) Treatments which allowed various levels of positive canopy minus air temperature differences [stress-degree-days (SDD)] to accumulate between irrigations were evaluated along with a treatment irrigated at 4 growth stages, a dry treatment, and a control treatment which was irrigated at -0.06 MPa soil water potential (SWP). Diurnal measurement of canopy and air temperatures indicated that the greatest differences between canopy and air temperature occurred near solar noon. In 1981, all treatments irrigated by an accumulation of positive SDD had reduced yields compared to the control SWP treatment. In 1982, under higher rainfall and lower air saturation vapor pressure deficits (VPD) than in 1981, yields of the SDD irrigated treatments were comparable to those obtained with the SWP treatment. Accumulation of positive SDD values to schedule irrigations was adequate when midday VPD values were low. However, when high VPD occurred, SDD values were always negative. A model is presented in which SDD values can be adjusted for environmental variability to more accurately schedule irrigations. Measurements of air temperatures within the canopy were made and compared to surface canopy temperatures measured with an infrared thermometer. Regression analysis showed that canopy temperature could be predicted using the air temperature within the canopy (R2 = 0.89). The sum of SDD values for the season was used to estimate canning maturity pod yield (R2 = 0.65).
Present address: Department of Horticultural Science, North Carolina State University, Raleigh, NC 27650.
Received for publication December 14, 1982. Oregon Agricultural Experiment Station Technical Paper No. 6650. Data reported herein are from a dissertation by the senior author in partial fulfillment of the requirements for the PhD degree. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.