Graduate Thesis Or Dissertation
 

Effects of irrigation scheduling, using remotely sensed canopy-air temperature differentials, on water relations, yield, and quality of snap beans (Phaseolus vulgaris L.)

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/sx61dp48s

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  • Field experiments were conducted in 1981 and 1982 to develop a method for using remotely measured leaf canopy-air temperature differences (stress-degree-days (SDD)) to schedule irrigations and to evaluate the effects of differential irrigation on snap bean cultivars, 'Oregon 1604' and 'Galamor'. Effects on soil water potential (SWP), leaf water potential (Ψ), leaf osmotic potential (fir ), leaf turgor potential (Ψp), leaf transpiration, leaf diffusive resistance, plant growth and development, yield components, and pod quality factors were measured. To schedule irrigations, various levels of positive SDD's, measured daily at midday, were allowed to accumulate between irrigations. When air vapor pressure deficits (VPD) were small, water stressed plants had positive. SDD's and well watered plants had negative SDD's. When VPD's were large, SDD's were always negative (i.e., canopy temperatures were cooler than air temperature). At these high VPD's, temperature differences between leaves of well watered and stressed plants were as much as 5-7 C. A model is presented in which SDD's can be adjusted based on the expected SDD of well watered plants at a given VPD. With this modification, irrigations can be adequately scheduled using only canopy temperatures, air temperatures, and relative humidity measurements. In both seasons, yield was strongly related to average SWP at 0-45 cm depth. In 1981, evaporative demand on the crop was much higher than in 1982. As a result, yields in 1982 were at least 5 t/ha greater at a given SWP than in 1981. Under water stress, total leaf area per plant was reduced more by a decrease in area per leaf than by a reduction in leaf number. Leaf water potential was not consistent with level of plant water stress. Although some osmotic adjustment occurred in stressed plants, Ψp was still generally lower than in well watered plants throughout the day. As Ψ decreased from early morning through midday, transpiration rates increased due to increasing evaporative demand. Leaf diffusive resistance also increased with decreasing V, but a "threshold value" for stomatal closure was not demonstrated.
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