Abstract
The yield and quality response of sweet corn (Zea mays L.) to variable water supply was evaluated in 1984 and 1985. Irrigation depths were established with sprinklers at five intervals from 0% to 100%, with the 100% treatment intended to refill the root zone to field capacity. The other treatments were considered as deficit irrigation. Irrigations were scheduled when 47–57% of the available water was depleted in the root zone of the 100% treatment level plots. Yields were similar when irrigation depths were 50% or greater in 1984 and 1985, although water application depths varied between years. Water balance measurements indicated very little deep percolation. Deficit irrigations of about 50% and 70% saved water and maintained yield. Yield, ear weight, and kernel weight decreased in the nonirrigated treatments or when water application depths were about 25%. Nonirrigated sweet corn tended to be more mature at harvest then irrigated corn.
Previous research indicated that bedding plants can be maintained in landscape soils allowed to dry to substantially less than field capacity before irrigation; however, canopy size and aesthetic quality were compromised. Continuing this research, Solenostemon scutellarioides (coleus) were grown in drainage lysimeters in an open-sided clear polyethylene-covered shelter to assess growth characteristics and landscape quality when irrigated at various managed allowable deficits. Using tensiometers, plants were irrigated back to field capacity when 30%, 40%, or 50% of plant available water within a soil was depleted. Deficits were evaluated against a control treatment of 1.25 cm daily irrigation. Additional plants were grown in a companion open field plot. Growth indices, biomass, irrigation volumes, and landscape quality ratings were recorded. No differences in final height, growth index, shoot or root dry weights, total biomass, or shoot-to-root ratios were found among treatments for either lysimeter or companion field plots. Landscape quality was comparable among treatments. However, total irrigation volume applied was significantly greater for the control treatments than deficit irrigation treatments. On average, irrigation volumes were 4.75-fold greater for daily irrigation in comparison to other treatments.
Three-year-old `Braeburn' apple trees (Malus domestica Borkh.) on MM106 rootstock were studied in a glasshouse to assess the effects of deficit irrigation on fruit growth, water relations, composition, and the vegetative growth of the trees. Trees were assigned to one of three treatments. The control (C) was fully watered. The first deficit treatment (D1) was deficit-irrigated from 55 days after full bloom (DAFB) until final harvest at 183 DAFB. The second deficit treatment (D2) was deficit-irrigated from 105 to 183 DAFB. Compared to C, the D1 and D2 trees developed a lower photosynthetic rate, leaf water potential (Ψl), and stomatal conductance (gs) during the stress period. Trunk-circumference growth was reduced in both D1 and D2 trees, but leaf area and shoot length were reduced in D1 only. Total soluble solids increased in both D1 and D2 fruit. Fructose, sorbitol, and total soluble sugar concentrations were higher in D1 fruit than in C and D2. Titratable acidity and K+ levels were higher in D1 fruit than C and D2. For D1, lowering of fruit water potential (Ψw) was accompanied by a decrease in osmotic potential (Ψs), and therefore turgor potential (Ψp) was maintained throughout the sampling period. Regardless of fruit turgor maintenance, the weight of D1 fruit was reduced from 135 DAFB. Weight, sugar concentration, and water relations of D2 fruit were not affected by deficit irrigation. This indicates that fruit water relations and sugar concentration are modified if water deficit is imposed from early in the season. However, if water deficit is imposed later in the season it has less impact on the composition and water relations of the fruit.
A two-year experiment was conducted to determine yield, water use efficiency, and leaf quality responses to deficit irrigation and plant population of spinach (Spinacia oleracea L.). Three irrigation regimes were imposed with a center pivot system, 100%, 75%, and 50% crop evapotranspiration rates (ETc). Spinach seeds were planted on 11 Nov. 2003 at three plant populations: 494 (P-1), 618 (P-2), and 741 (P-3) thousand seeds/ha on cvs. DMC 16 and ASR 157, and on 15 Oct. 2004 at four plant populations: 655, 815, 988, and 1149 thousand seeds/ha on cv. DMC 16. Harvests were done on 3 Mar. 2004 and 26 Jan. 2005. In the first season, marketable yield was not reduced by deficit irrigation, but water use efficiency was significantly higher for 50% ETc compared to 100% ETc. The cv. DMC 16 had a significantly lower percentage of stem weight than ASR 157 (8.3 vs. 16.4%). The cv. ASR 157 had an excess of stem weight at 100% and 75% ETc compared to 50% ETc at P-1, but similar at P-2 and P-3. The cv. DMC 16 had a trend of reduced stem weight for P3 at 50% ETc. In the second season, marketable yield was reduced by deficit irrigation. However, water use efficiency was significantly higher for 50% ETc compared to 100% ETc, but similar to 75% ETc. Deficit irrigation also decreased the percentage of stem weight. Despite a slight increase in the percentage of of yellow leaves, but not in percentage of of stem weight, marketable yield and water use efficiency were significantly higher at 1149 thousand seeds/ha. This study showed that deficit irrigation in combination with increased plant population has the potential to increase yield and water savings, without adversely affecting leaf quality.
The influence of deficit irrigation on predawn leaf water potential (Ψpd) and leaf gas-exchange parameters was analyzed in almond [Prunus dulcis (Mill.) D.A. Webb] and compared to hazelnut (Corylus avellana L.). Both species were planted in adjacent plots in which four irrigation treatments were applied: T-100%, T-130%, and T-70%, which were irrigated at full crop evapotranspiration (ETc), 1.3 × ETc, and 0.7 × ETc, respectively, and a regulated deficit irrigation (RDI) treatment, which consisted of full irrigation for the full season, except from middle June to late August when 0.2 × ETc was applied. Under nonstressful conditions, hazelnut had a lower net CO2 assimilation rate (A) (12.2 μmol·m-2·s-1) than almond (15.5 μmol·m-2·s-1). Reductions in net CO2 assimilation rate (A) induced by decreases in Ψpd were higher in hazelnut than in almond. Gas-exchange activity from early morning to midday decreased in hazelnut for all irrigation treatments, but in almond increased in the well-watered treatments and decreased slightly or remained constant in the RDI. Hazelnut had a higher A sensitivity to variations in stomatal conductance (gs) than almond, especially at low gs values. The Ψpd values in almond and hazelnut of the T-100% and T-130% treatments were affected by decreasing values in midsummer, but in hazelnut Ψpd was probably also affected by sink kernel filling. These facts indicate that hazelnut RDI management could be more problematic than in almond.
This experiment was conducted to determine the effects of deficit irrigation and growing season on fruit quality, carotenoid content and yield of red-, orange-, and yellow-fleshed diploid and triploid watermelon. Irrigation rates were 1.0 evapotranspiration (ET) and 0.5 ET. Diploid cultivars were Summer Flavor 710 (red), Tendersweet (orange), and Summer Gold (yellow). Triploid cultivars were Summer Sweet 5244 (red), Sunshine (orange), and Amarillo (yellow). Four-week old containerized transplants were planted in the field at TAES-Uvalde on 27 Mar. and 21 May 2003. Deficit irrigation imposed after plants were fully established reduced the individual fruit weight and size in the early planting. Soluble solids content (SSC) and firmness was not affected by irrigation rate in both plantings. SSC varied across cultivars and increased with maturity, particularly for the triploid cultivar Amarillo. In general, triploids were firmer than diploid cultivars. Total carotenoid content was not affected by irrigation during early planting. Diploid and triploid red-fleshed watermelon cultivars had significantly higher carotenoid content than orange- and yellow-fleshed cultivars. The major carotenoid was lycopene (more than 65%), followed by prolycopene (20%) and B-carotene (7%).
Abstract
After initially withholding irrigation (WI) to dry out the root zone of pear trees, regulated deficit irrigation (RDI) applied to replace 23% and 46% of evaporation over the planting square (Eps) was compared with 69% and 92% Eps applied during the WI and RDI periods, respectively (full irrigation). Irrigation was increased to 120% Eps on all treatments after rapid fruit growth commenced. Leaf water potential (ψ1) measured at dawn and midday became less negative during RDI than during WI but in both periods was more negative than the control (69%/92% Eps). On the other hand, ψ1 of treatments receiving WI and RDI became less negative than the control when all irrigation treatments were increased to 120% Eps. Withholding irrigation followed by RDI reduced vegetative growth by 52%. In contrast, however, WI did not inhibit fruit growth, while, during RDI following WI fruit, growth was stimulated. A similar but greater stimulation of fruit growth (consistent with relatively less negative ψ1) was measured on WI/RDI plants when all treatments received 120% Eps. This stimulation of fruit growth increased yields by about 20%. The results indicate fruit osmoregulate to maintain and/or increase growth at the expense of inhibited vegetative growth when WI and or RDI reduce ψ1 in spring to values approaching −0.5 MPa at dawn.
Productive and vegetative tree responses were analyzed during 3 consecutive years in peach [Prunus persica (L.) Batsch cv. Sudanell] plots subjected to three regulated deficit irrigation (RDI) strategies plus a control irrigation treatment. A postharvest RDI treatment (RDI-P) was irrigated at 0.35 of control after harvest. A Stage II RDI treatment (RDI-SII) was irrigated at 0.5 of control during the lag phase of the fruit growth curve. The third treatment (RDI-SII-P) applied RDI during Stage II at 0.5 of control and postharvest at 0.35 of control. The control treatment, like RDI-P and RDI-SII-P when not receiving RDI, was irrigated at 100% of a water budget irrigation scheduling in 1994 and 1996, full crop years, and 80% of the budget in 1995, an off year with a very small crop. A carry-over effect of deficit irrigation was highly significant in all parameters measured during the third year of the experiment. The general effect of water stress during Stage II did not affect return bloom and fruit set, whereas water stress during postharvest apparently reduced both parameters. As a consequence, fruit counts and fruit load manifested marked differences between treatments, which were also correlated to changes in fruit size. The RDI-II, which had the highest fruit yield, also had the smallest fruit size, whereas RDI-P manifested the lowest yield and largest fruit size. Vegetative growth (shoot elongation and trunk cross sectional area) was significantly reduced during the first 2 years of the experiment in accordance with the amount of the irrigation reduction. However, in 1996 growth was strongly governed by fruit load. The use of RDI-SII-P represented an intermediate cropping effect between the opposite bearing behavior of RDI-SII and RDI-P, while not expecting distinctive fruit yield or size reductions and offering remarkable water savings of 22% of the control applied water.
Water conservation strategies are being investigated for watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] production in the Winter Garden region of southwest Texas. Our objective was to determine how yield and fruit quality of a triploid (cv. Summer Sweet 5244) and hybrid (cv. Summer Flavor 710) watermelon were affected by irrigation based on evapotranspiration (ET) rates and timing of application during spring. Irrigation treatments included constant 1.0 and 0.5 ET, three with varying ET before or after fruit set, and one with cycles of 1.0 and 0.5 ET. Fruit quality characteristics were measured at the unripe, ripe, and overripe maturity stages. Water deficit before or after fruit set decreased yield and fruit number. Flesh color was not affected by irrigation at any maturity stage. Soluble solid content at the ripe stage increased only in triploids irrigated with constant 0.5 ET or with 0.5 ET applied after fruit set. Triploid plants exposed to frequent cycles of water deficit set more and smaller fruit than hybrids. These data suggest that triploid watermelon types may have a different acclimation response to drought stress than diploid hybrids.
In glasshouse-grown tomatoes (Lycopersicon esculentum Mill. `Virosa'), deficit irrigation (DI), in which plant water potential was allowed to decrease from –0.5 to –1.2 MPa, reduced plant growth and fruit yield, size and count, and caused blossom-end rot. Deficit-irrigated fruit had higher color intensity, lower water content, and higher concentration of sucrose, glucose, and fructose than well-watered (control) fruit. Fruit concentrations of Ca, Mg, and K were the same for both treatments on a dry weight basis, but they were higher in DI fruit than in control fruit on a fresh weight basis. Fruit gas exchange was measured for two 30-day-apart harvests. For both harvests, DI fruit produced higher quantities of CO2 and ethylene than control fruit. Ethylene and CO2 production peaks coincided for the first harvest in both treatments. In the second harvest, the CO2 production peak preceded that of ethylene. Despite yield reduction, DI enhanced fruit desirability in terms of higher concentration of soluble sugars and higher color intensity.