( Pittenger et al. 2001 ) is mainly anecdotal because few studies have assessed the response of groundcovers to deficit irrigation ( Costello and Jones 2014 ; Garcia-Navarro et al. 2004 ; Nazemi Rafi et al. 2019 ; Pittenger et al. 2001 ). Moreover, the
Prunes trees are believed to be relatively tolerant of water stress, and because prune fruit are dried, a low fresh to dry weight ratio of the fruit will reduce energy requirements for fruit drying and will represent an economic benefit to the grower. In previous research, we found that, under some orchard conditions, irrigation deprivation was associated with a number of economically beneficial effects, including a lower fresh to dry weight ratio of the fruit, increased return bloom, and final saleable crop yield. Analysis of these results was complicated by the effects of irrigation on alternate bearing, and the fact that tree water stress could be substantially different under different soil conditions for the same level of irrigation deprivation. Taking these factors into account, however, indicated that economic yield in prune could be maintained or increased by managing trees at a moderate level of water stress. An experiment was established to determine whether midday stem water potential could be used to guide irrigation and achieve a target level of water stress during the growing season, and whether a moderate level of water stress would be economically beneficial to prune production. By managing prune trees at a moderate level of water stress (midday stem water potential reaching about –1.5 Mpa by the end of the season) over 3 years, an average savings of 40% in applied irrigation water was obtained. Modest increases in return bloom, and an improved fruit dry to fresh weight ratio, occurred in moderately water stressed trees, although overall yield was not changed. The substantial savings in water, without reducing yield, should represent a net economic benefit to growers, depending on the price they pay for water.
Reductions in the supply of high-quality irrigation water from underground aquifers is affecting production and irrigation management in the Winter Garden of southwestern Texas. This study was conducted to determine how growth, yield, and quality of watermelons [Citrullus lanatus (Thunb.) Matsum. & Nakai] grown with subsurface drip are affected by synchronizing irrigation with specific growth stages. In 1995 irrigation rates were: 1.0 evapotranspiration (ET) throughout the entire growth period (T1); 1.0ET until fruit set followed by 0.6ET until final harvest (T2); 1.0ET until fruit set followed by 0.6ET until first fruit maturity followed by 0.4ET until final harvest (T3); 1.0ET until fruit set followed by 0.6ET until first fruit maturity followed by 0.2ET until final harvest (T4). In 1996, two irrigation rates were constant 1.0ET (T1) and 0.5ET (T4), and two with varying ET rates throughout the entire growth period. Varying irrigation rates with specific growth stages had more influence on fruit set and early yield than on leaf and vine growth. Total marketable fruit yield ranged from 94.4 to 71.8 Mg·ha–1 when 569 mm (T1) and 371 mm (T4) of irrigation water, respectively, were applied in Spring 1995, and from 90.3 to 80.9 Mg·ha–1 when 881 mm (T1) and 577 mm (T4) of irrigation water, respectively, were applied in Spring 1996. However, plants irrigated with constant 0.5ET demonstrated greater water use efficiency than those with 1.0ET. Information on water use will assist farmers in designing management strategies that minimize risks due to uncertainties in weather and water supplies.
A 2-ac block of `Bing'/Colt, Mahaleb or GM61/1 was planted 8×15′, Feb 1991 so that 7 treatments were arranged in 6 blocks. We imposed water stress during 2 distinct periods, June or July in 1992. Once trees had stopped growing water was added (estimated @ 50% ETc) to maintain leaf turgor, but not to initiate further shoot growth. Well-watered (100% ETc) trees were summer pruned to check growth. Water stress was monitored by measuring water potential of basal bagged leaves with a pressure chamber at midday. Shoot growth was stopped by water stress. Shoot growth ceased at a trunk water potential of approximately -17 bars in both Colt and Mahaleb rootstocks although Colt rootstock went into stress more rapidly than Mahaleb. Colt may be more sensitive to water deprivation at this site than Mahaleb rootstock. Well-watered GM 61/1 trees had tree sizes much like those of water stressed Colt trees. A combination of early season stress and summer pruning (heading) may be the best combination used to control growth. Flower bud formation was noticed by season's end in these 2nd leaf trees. Water stress can be used to control tree growth, save water and encourage fruitfulness when integrated into an appropriate orchard system.
One-year-old `Gala'/M7 apple trees were potted into 30-L containers and approach-grafted about 45 cm above the graft union in late Spring 2003. Trees were grown with both tops for the remainder of the 2003 season in a greenhouse. In Apr. 2004, one of the tops was removed. Trees were fully watered by an overhead irrigation system until July 2004, when trees were subjected to one of four irrigation regimes: control received >100% of ETc applied evenly to the two pots; PRD100 received >100% ETc applied to one pot only; and two regimes received 50% ETc applied to either one (PRD50) or both pots (DI50). Both gravimetric (tripod) and volumetric (time-domain reflectometry) soil moisture measurements were taken daily prior to and after irrigations. In addition, heavy isotope H2O (18O) was applied to one of the two root compartments and analyzed in the leaves to further determine the validity of the model. Sap flow was monitored in six split-rooted trees using miniaturized heat-pulse probes inserted into the stem above the graft union and into each of the two root systems below the graft union. Under fully irrigated conditions, root sap flow was proportional to root trunk cross-sectional area, and was not a function of root system origin (i.e., roots of mother plant with original top remaining or roots of daughter plant with original top detached). Water uptake from a previously dried root zone was rapid when the irrigated side was switched, but much more gradual when the other side was maintained wet. Interactions between soil moisture and sap flow in relation to factors governing canopy demand will be presented.
treatments were applied in a completely randomized design with three plots (18 plants) per treatment: control (C), with soil matric potential (Ψ m ) at ≈ –30 kPa, and two deficit irrigation (T-1 and T-2), corresponding to ≈50% (Ψ m ≈ –60 kPa) and 30% (Ψ m
the second experiment, trees were exposed to floral-inductive water deficit at a constant floral-inductive temperature (12 ± 1 °C) for 40 d. After each treatment was over, trees were transferred back to the greenhouse and irrigation was restored to
-induced dormancy as a coping mechanism during extended periods of water deficit stress ( Zhang et al., 2019 ). Recovery and regrowth from drought-induced dormancy would be expected as rainfall or irrigation returned, as long as soil conditions did not restrict root