Browsing by Author "Rodrigue, P. B."
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Item Determining the Transpiration Rate of Peach Trees Under Two Trickle Irrigation Regimes(Texas Water Resources Institute, 1980-12) Reeder, E. L.; Van Bavel, C. H. M.; Rodrigue, P. B.; Newton, R. J.; Brown, K. W.; Reddell, D. L.; McFarland, M. J.; Howell, T. A.The scientific design and management of a modern irrigation system requires that the designer or manager have knowledge of site and plant criteria such as infiltration, drainage, soil fertility, plant water needs, and plant production under varying conditions. With modern trickle systems water control is very precise and thus precise information on irrigation needs of a crop allow for the optimal use of water supplies. Work has been conducted on the effects of trickle irrigation on peach trees in North Central Texas. Initial data relating trickle irrigation amounts to total production, peach size, and plant growth have indicated that trickle irrigation may provide benefits that would offset costs of the irrigation system and water. Previous work however has related these benefits only to the amount of water applied through irrigation and did not consider the total water use of the tree. Research was undertaken to determine the transpiration rate of peach trees under two trickle irrigation regimes. To determine the transpiration rate a volume of soil around the test trees was instrumented with neutron access tubes. Soil moisture depletion was measured weekly. A soil water balance was conducted equating evapotranspiration to the sum of the change in the soil moisture content (a decrease being positive) plus irrigation applied, plus any rainfall that occurred in the period. For this work runoff and flux across the measurement zone boundaries was assumed zero. Estimates of evaporation from the soil surface were made using a two-stage evaporation process along with values of potential evapotranspiration made with the Penman (1956) equation. The estimates of evaporation from the soil surface were subtracted from total evapotranspiration to give estimates of the transpiration of the peach trees. Estimates of transpiration were not consistent from one measurement period to the next. Errors in the estimation of evaporation from the soil surface directly affect the estimate of transpiration. During latter stages of a rain-free period an estimate of transpiration was made which should not have been influences by the low values of evaporation from the soil surface that existed. This method of estimating transpiration has many errors and can be much improved upon by using a method such as a lysimeter to estimate transpiration more accurately.Item Management of Trickle Irrigated Orchards for Increased Water Use Efficiency(Texas Water Resources Institute, 1982-08) Worthington, J. W.; Rodrigue, P. B.; Punthakey, J. F.; McFarland, M. J.Trickle irrigation is the most efficient method of irrigating peach orchards in Texas. With a trickle irrigation system, a producer may make full use of a limited or low-volume water supply to apply precise amounts of water to the root zones of individual trees. Improved irrigation scheduling methods offer the potential for further savings in water and energy to pressurize the water since peach trees require less than a fully-watered state for production. This report describes research to determine the crop coefficients for peach trees that would result in an optimum irrigation schedule. One major effort evaluated the physiological response of the peach tree to varying irrigation regimes. This thrust indicated that a crop coefficient as low as 0.53 produced similar physiological responses (leaf water potential, leaf resistance, and transpiration rate) as a crop coefficient of 0.7. The critical period for initiation of stress was during the period before harvest. A large twin weighing lysimeter facility was designed and installed. Preliminary results for mature peach trees showed water use rates at the maximum evapotranspiration rate approached a crop coefficient of 1.0. The research indicates that the peach tree is a luxury consumer of water; improved irrigation scheduling is achievable.Item Plant Responses of Drip Irrigated Trees to Climate and Water Stress(Texas Water Resources Institute, 1982-08) Worthington, J. W.; Rodrigue, P. B.; McFarland, M. J.; Punthakey, J. F.Past irrigation research has shown that peach (prunus persica) trees vary in their field response to water stress, and the degree of stress is a function of the plants' environment. Water deficits reduce plant growth and crop yields, therefore, measurements of plant water stress are fundamental in understanding how the environment affects plant performance. This in turn will facilitate the irrigator to have very precise water control and to determine optimum irrigation quantities. This research examined the effect of environmental variables on leaf water potential, leaf resistance, canopy resistance and transpiration rate; and evaluated their ultimate effect on yield, water use efficiency and pruning weights for trees under four drip irrigation regimes at Stephenville, Texas. Treatments selected were instrumented with 1-, 2-, 3- and 4-emitters per tree, and single trees from each treatment were instrumented with ground covers. Plant responses were measured hourly on sunlit and shaded leaves of each treatment. Leaf water potentials and leaf resistances were higher in shaded leaves, resulting in reduced transpiration. An increase in early morning leaf water potentials indicated irrigation had decreased stress. Lower leaf water potentials and higher leaf resistance indicated the tress were being severely stressed prior to harvest. Leaf water potentials decreased linearly, whereas leaf resistance decreased exponentially, with increasing solar radiation. In stressed trees critical leaf water potentials were lower suggesting some degree of adaptation to stress. Leaf water potentials decreased linearly with increasing transpiration. Total resistance (sum of plant and soil resistance) increased with increasing severity of stress. The 3-emitter tree was recommended, since yield and water use efficiency are relatively high. Proper irrigation increased total yields and also the number of fruit within a marketable size range, while maintaining high water use efficiency, resulting in economic benefits to the farmer.