Postharvest Deficit Irrigation Research Articles

Effects of postharvest deficit irrigation on sweet cherry (Prunus avium) in five Okanagan Valley, Canada, orchards: II. Phenology, cold hardiness, fruit yield, and quality

Irrigated agriculture in semi-arid regions is expected to increase in the future, which puts greater demands on scarce water resources. Sustainable irrigation strategies in semi-arid regions will support agricultural resilience to climatic change. The response of “Sweetheart”/Mazzard sweet cherry trees ( Prunus avium L.) to postharvest deficit irrigation (PDI), as a water conservation method, was studied over three seasons (2019–2022) in the semi-arid Okanagan Valley of British Columbia, at five commercial orchards. The following irrigation treatments were applied; ( i) a control of full irrigation, irrigated according to conventional growers’ practice at each orchard, ( ii) PDI-30: 27%–33% reduction in irrigation volume, after harvest (67%–73% of control), and ( iii) PDI-50: 47%–52% reduction in irrigation volume, after harvest (48–53% of control). Spring phenology (the timing of flower bud development, from side green to full bloom), flower bud moisture content and cold hardiness, and fruit yield and quality (before and after cold storage and shelf-life conditions) were assessed to determine if PDI altered fruit development over the subsequent growing season. Neither PDI-30 nor PDI-50 caused changes in the timing of flower bud phenology, cold hardiness or moisture content relative to the control. PDI treatments also had no effect on fruit yield or fruit quality at harvest or after storage and shelf-life conditions. These results suggest PDI could be used to reduce irrigation water use in semi-arid regions, like the Okanagan Valley, without affecting sweet cherry production or fruit quality.

Effects of postharvest deficit irrigation on sweet cherry (Prunus avium) in five Okanagan Valley, Canada, orchards: I. Tree water status, photosynthesis, and growth

The timing and availability of water supply are changing in the Okanagan Valley, and the availability of irrigation water in the late summers is a growing concern. Postharvest deficit irrigation (PDI) is a strategy that can be used to reduce water demands in sweet cherry orchards; previous studies in this region have reported no change in plant physiology or tree growth with irrigation volume reductions of up to 25%, postharvest. However, the effects of more severe postharvest reductions in irrigation volume remain unknown. We compared the effects of full irrigation (100% of conventional grower practice through the growing season) with 27%–33% reductions in irrigation postharvest (∼70% of conventional grower practice) and 47%–52% reductions in irrigation postharvest (∼50% of conventional grower practice) over a 3-year period (2019–2021) in five commercial sweet cherry orchards that ranged in elevation and latitude across the Okanagan Valley, BC, Canada. In the growing season following treatment application, PDI had no effect on stem water potential or photosynthesis in any year and at any site; there were also no effects of PDI treatment on tree growth. Findings from this study suggest that postharvest stem water potentials from −0.5 to −1.3 MPa, and one-time stem water potentials as low as −2.0 MPa, have no lasting effects on future plant water status, rates of photosynthesis, or plant growth. PDI shows potential as an effective water-saving measure in sweet cherry orchards in the Okanagan Valley.

Mulching improved soil fertility, plant growth and productivity, and postharvest deficit irrigation reduced water use in sweet cherry orchards in a semi-arid region

ABSTRACT In the Okanagan Valley, sweet cherry production has expanded to higher latitudes due to climate change, but the availability of irrigation water is limited in this semi-arid region. Postharvest deficit irrigation (PDI) and organic mulches can reduce water use in orchards, but their interactive effects on soil fertility, water relations, and crop performance in new orchard environments are unknown. In a randomized block split-plot design, full irrigation (100%) or PDI (72–76% of full irrigation) was applied to the main plots, and mulches (compost, woodchips, bare) were subplots at three sites. Compost increased soil organic matter, nutrients, pH, and electrical conductivity over three seasons at all sites. Woodchips increased tree growth and foliar P and Mn, while compost increased some fruit quality attributes, and foliar P compared to bare soil. Relative to full, PDI saved 24–28% irrigation water after harvest per season at each site without affecting soil moisture and chemical properties, stem water potential, or crop performance, or interacting with mulch effects. These results suggest that in this semi-arid cherry growing region mulches are a promising strategy to maintain soil moisture and improve soil fertility and crop performance, and PDI can reduce water use after harvest without affecting commercial production.

The Effects of Combined Pre and Postharvest Deficit Irrigation on Loquat Yield, Fruit Quality and Handling Aptitude

Loquat prices depend on fruit size and earliness. Earliness is improved by postharvest deficit irrigation (DI), without negative effects on fruit size. An optimization of postharvest DI strategies carried out by limiting the dry period led to greater harvest date advancement, but water savings were reduced. To further improve fruit earliness and quality and increase water savings, we combined pre and postharvest DI strategies. Treatments were T1: trees not irrigated during six weeks after harvest (no preharvest DI applied); T2: trees that, in addition to postharvest DI, were not watered from the rapid fruit growth phase to harvest (nine extra weeks of DI); T3: trees that, in addition to postharvest DI, were not watered from color break to harvest (six weeks of DI plus postharvest DI); and T4: trees that in addition to postharvest DI were not watered during rapid fruit growth, but were re-irrigated at color break (2–3 weeks of DI, depending on the season). Full-irrigated trees were grown for comparison. T1 saved 18% water with respect to full-irrigation, and advanced harvesting by 16 days. T2 saved more water, had an earlier harvest and produced a higher early yield. Shorter dry periods were beneficial to a lower extent. Fruit size was significantly diminished by T2, but not by T4. A major advantage of T3 and T4 was the better performance of fruit during handling and shelf life. T2 fruits were favored by panelists for their sweetness but criticized for their smaller size.

Yield and water productivity responses of olive trees (cv. Manzanilla) to post-harvest deficit irrigation in a non-Mediterranean climate

Olive trees are harvested in late summer or during the fall in the Mediterranean Basin with considerable rainfall often occurring after harvest, which largely eliminates the need to irrigate at that time. As olive cultivation has expanded to new regions, it has become necessary to develop new water management strategies to account for non-Mediterranean climate conditions. In northwestern Argentina, olive cultivars are harvested as early as mid-summer for green table olive processing, but rainfall is low and temperatures remain high after harvest. Thus, we evaluated the responses of yield determinants and components, crop water productivity, and vegetative growth of olive trees (cv. Manzanilla fina) to different post-harvest irrigation levels in three growing seasons. A fully irrigated control (100% crop evapotranspiration; ETc) and three regulated deficit irrigation treatments (RDI; T66 = 66% ETc, T33 = 33% ETc, T0 = 0% ETc) were applied for 75 days after harvest from mid-summer to mid-fall. The RDI treatments received irrigation equivalent to the control during the rest of the year. The return flowering in the spring after the first season of RDI tended to be greater in T0 than in the well-watered control and other RDI treatments. Despite some decrease in fruit set, this led to a significant increase in fruit number and yield in T0 compared to the control and the other RDI treatments. In contrast, flowering tended to be lower in T0 than in the irrigated control, T66, and T33 following the second season of RDI, but fruit number and yield were not different at harvest. Similarly, no differences in fruit number and yield were observed after the third RDI season. Cumulative total yield over the three seasons was not significantly affected by applying post-harvest RDI. Crop water productivity expressed as fruit yield per amount of annual irrigation plus effective rainfall was significantly higher in T0 than in the control after the first and second seasons of RDI. Shoot growth during the RDI period was very low, and only reduced significantly during the third RDI period. The results suggest that alternative irrigation strategies that adapt to regional climatic conditions should be further developed in non-Mediterranean climates. Water savings up to 20% per year appear feasible with post-harvest RDI in northwestern Argentina without significant losses in yield.

Long-term productivity of early season peach trees under different irrigation methods and postharvest deficit irrigation

Deficit irrigation can be used as a potential means of dealing with lack of irrigation water, however, the long-term impact of deficit irrigation on productivity is not fully understood. A 10-year long field study was carried out to compare effects of furrow, drip, and micro sprinkler irrigation under either full irrigation or postharvest deficit irrigation treatments on peach tree health and fruit yield and quality. In the first three years of the experiment, trees under full irrigation grew faster which led to larger trunks than trees under deficit irrigation. At the end of the study, tree canopy size showed no difference among different methods of irrigation or between full and deficit irrigation. Deficit irrigation of up to 40% water savings did not lead to significant yield losses for 8–9 years. Deficit irrigation also did not cause a significant reduction in fruit quality except for an increase in percentage of double fruits, but the worst year case was still less than 1.5%. Fruit color showed lower lightness in furrow full irrigation than in furrow deficit treatment, but no difference was found in deficit drip or micro sprinkler treatment. Also, no difference was found for fruit firmness, total soluble solids, pH, malic acid, or total phenolics between the respective full and deficit irrigation treatments. The study demonstrated the feasibility of applying continued postharvest deficit irrigation for up to10 years for peach production which resulted in significant water savings during the summer peak water use period.

Using Soil Moisture Sensors for Automated Irrigation Scheduling in a Plum Crop

The growing scarcity and competition for water resources requires the urgent implementation of measures to ensure their rational use. Farmers need affordable irrigation tools that allow them to take advantage of scientific know-how to improve water use efficiency in their common irrigation practices. The aim of this study is to test under field conditions, and adjust where required, an automated irrigation system that allows the establishment of regulated deficit irrigation (RDI) strategies in a stone fruit orchard. For this, an automated device with an algorithm which combines water-balance-based irrigation scheduling with a feedback adjustment mechanism using 15 capacitive sensors for continuous soil moisture measurement was used. The tests were carried out in 2016 and 2017 in Vegas Bajas del Guadiana (Extremadura, Spain) on an experimental plot of ‘Red Beaut’, an early-maturing Japanese plum cultivar. Three irrigation treatments were established: control, RDI and automatic. The control treatment was scheduled to cover crop water needs, a postharvest deficit irrigation (40% crop evapotranspiration (ETc)) strategy was applied in the RDI treatment, while the Automatic treatment simulated the RDI but without human intervention. After two years of testing, the automated system was able to “simulate” the irrigation scheduling programmed by a human expert without the need for human intervention.

Vegetative and reproductive response of ‘Prime Giant’ sweet cherry trees to regulated deficit irrigation

The agronomic response of sweet cherry (Prunus avium L.) ‘Prime Giant’ to a 4 year-long experiment involving deficit irrigation strategies in a Mediterranean climate was studied in a commercial orchard located in the southeast of Spain (Jumilla, Spain). Four drip irrigation treatments were imposed: (i) control treatment (CTL), irrigated without restrictions at 110% of seasonal crop evapotranspiration (ETc); (ii) sustained deficit irrigation (SDI) treatment irrigated at 85% ETc during pre-harvest and post-harvest periods and at 100% ETc during floral differentiation; (iii) regulated deficit irrigation (RDI) treatment irrigated at 100% ETc during pre-harvest and floral differentiation and at 55% ETc during post-harvest, and (iv) farmer treatment (FRM), irrigated according to the farmer’s normal practice. The crop’s response to the different irrigation treatments was analyzed in relation to tree water status. Soil water deficit reduced tree midday stem water potential (Ψstem), stomatal conductance (gs) and net photosynthesis (Pn). Branch maximum daily shrinkage (MDS) responded rapidly to irrigation changes during pre-harvest and post-harvest. The lowest Ψstem values were reached by SDI during pre-harvest and by RDI and FRM during post-harvest. RDI did not lead to Ψstem water potentials falling to below the threshold of −1.6 MPa in any season, although, FRM caused, Ψstem to fall below −1.8 MPa in 2017.RDI reduced vegetative growth and did not cause significant lower yields or fruit quality. However, with SDI there was a trend towards smaller fruits and a slightly higher soluble solid content. Post-harvest deficit irrigation increased water productivity without penalizing fruit yield or the quality parameters studied, and allowed water savings of 39% compared to CTL at a time when other fruit tree species require more water. Moreover, RDI and SDI led to significantly less cracking incidence and a lower cracking index, which could extend fruit shelf life.

Postharvest regulated deficit irrigation in early- and intermediate-maturing loquat trees

Postharvest deficit irrigation (DI) strategies have been proven to advance bloom, harvest dates and economic return in loquat ‘Algerie’ trees because an early harvest results in higher loquat fruit prices. This fact poses the question of whether postharvest DI strategies could have a similar effect on more precocious cultivars than cv. Algerie, providing thus a more profitable option to farmers. In this work, the response of an early- and intermediate-maturing loquat cultivars (cv. Cardona and Algerie, respectively) to a summer early (DIearly) and late (DIlate) DI strategy was assessed in two parallel studies during three consecutive years. The effects of the DIearly and DIlate strategies on bloom date, percentage of fruit picked at harvest per picking date and yield of both loquat varieties were studied. Moreover, fruit quality of cv. Cardona at harvest was also assessed. Plant water status was monitored by midday stem water potential (Ψstem) measurements. Results showed that DIearly and DIlate strategies advanced bloom in both cultivars although a higher effect was observed with the DIearly than with the DIlate treatment. Water restrictions did not increase the percentage of fruit picked at any of the picking dates and did not affect yield or fruit quality in the early-maturing cultivar. In ‘Algerie’ trees, a higher percentage of fruit was generally picked during the first picking dates in the DIearly and DIlate treatments than in the control although differences were only statistically significant during the last experimental season. Yield was significantly higher in ‘Algerie’ DIlate trees than in control or DIearly trees two out of the three experimental seasons. Overall, results showed that the DIearly and DIlate strategies tested here did advance bloom in the early-maturing cultivar but did not have an effect on the percentage of fruit picked per picking date at harvest. Nevertheless, the fact that substantial water savings (>30%) were obtained with no detrimental effect on yield presents the use of postharvest DI strategies as an interesting option to be followed in early-maturing cultivars for a more efficient crop production.

Influence of Irrigation Scheduling Using Thermometry on Peach Tree Water Status and Yield under Different Irrigation Systems

Remotely-sensed canopy temperature from infrared thermometer (IRT) sensors has long been shown to be effective for detecting plant water stress. A field study was conducted to investigate peach tree responses to deficit irrigation which was controlled using canopy to air temperature difference (ΔT) during the postharvest period at the USDA-ARS (U.S. Department of Agriculture, Agricultural Research Service) San Joaquin Valley Agricultural Sciences Center in Parlier, California, USA. The experimental site consisted of a 1.6 ha early maturing peach tree orchard. A total of 18 IRT sensors were used to control six irrigation treatments including furrow, micro-spray, and surface drip irrigation systems with and without postharvest deficit irrigation. During the postharvest period in the 2012–2013 and 2013–2014 growing seasons, ΔT threshold values at mid-day was tested to trigger irrigation in three irrigation systems. The results showed that mid-day stem water potentials (ψ) for well irrigated trees were maintained at a range of −0.5 to −1.2 MPa while ψ of deficit irrigated trees dropped to lower values. Soil water content in deficit surface drip irrigation treatment was higher compared to deficit furrow and micro-spray irrigation treatments in 2012. The number of fruits and fruit weight from peach trees under postharvest deficit irrigation treatment were less than those well-watered trees; however, no statistically significant (at the p < 0.05 level) reduction in fruit size or quality was found for trees irrigated by surface drip and micro-spray irrigation systems by deficit irrigation. Beside doubles, we found an increased number of fruits with deep sutures and dimples which may be a long-term (seven-year postharvest regulated deficit irrigation) impact of deficit irrigation on this peach tree variety. Overall, deployment of IRT sensors provided real-time measurement of canopy water status and the information is valuable for making irrigation management decisions.

Soil Microbial Community Composition in a Peach Orchard Under Different Irrigation Methods and Postharvest Deficit Irrigation

The San Joaquin Valley produces more than 250 unique crops and much of the U.S. fruits, vegetables, and nuts. One of the main limiting factors for production in this region is reduced availability of water. Deficit irrigation is a management practice where plants receive less than full irrigation but only at certain growth stages to minimize yield loss or long-term impacts to the crop. Given the multiple roles of soil microorganisms in the soil system, it is important to asses any impact of deficit irrigation on soil microbial communities. In the present study, full and deficit irrigation treatments were applied for 7 years using furrow, microsprinkler, and surface drip irrigation systems in a peach orchard. In the seventh year, soil samples were collected before and after implementation of deficit irrigation treatments to investigate effects on soil microbial community biomass and composition. Results showed that the proportion of Gram-positive bacteria and actinomycetes were significantly higher in furrow irrigation, whereas fungi and Gram-negative bacteria were lower in proportion under furrow irrigation as compared with microsprinkler and drip irrigation methods. Canonical variate analysis showed that soil microbial communities markedly differed after deficit treatment in furrow and microspray irrigation, but remained similar in surface drip irrigation in deficit and full irrigation. This may be due to frequent irrigation in surface drip where soil surface remained moist most of the time as compared with furrow and microsprinkler irrigation methods where irrigation was less frequent.

A review of optimal systems for organic production of blueberry and blackberry for fresh and processed markets in the northwestern United States

Various production systems have been evaluated in blackberry (Rubus L. subgenus Rubus Watson) and northern highbush blueberry (Vaccinium corymbosum L.) in certified organic research trials for 5 and 8 years, respectively, in Aurora, OR, USA (lat. 45°16′47″N, long. 122°45′23″W) and are reviewed here. Treatments included cultivar, weed management, and fertilizer source in both crops; planting system, use of municipal yard debris compost, and fertilizer rate in blueberry; and effectiveness of liquid sources of fertilizer through the drip irrigation system, training time, and impact of withholding irrigation after fruit harvest in blackberry. In blueberry, cumulative yield per plant (2008–2014) averaged 21% greater on raised beds than on flat ground. A black, woven polyethylene ground cover (weed mat) offered the most economical method of weed control, as compared to a mulch of municipal yard debris compost topped with sawdust or sawdust alone. Mulching with weed mat increased cumulative yield compared to the organic mulches, but there was little effect of mulch type on fruit quality. Plants grown with weed mat had a higher shoot-to-root ratio during establishment and required more irrigation water be applied. Addition of yard debris compost to the mulch increased soil and leaf potassium (K), but had little effect on plant nitrogen (N). However, when this compost was used as an amendment prior to planting, soil pH increased to levels above the recommended range for blueberry. Some cultivars were less adapted to the various fertilizer sources and production systems tested. Trailing blackberry plants grown with weed mat produced 25% and 100% higher yield than plants grown with hand-weeding and without weed control, respectively, making this the most economical weed management option. We found no effect of post-harvest deficit irrigation on yield over 2 years. There was little effect of fertilizer source on blackberry yield or fruit quality in processed or fresh production systems. Cultivar differences in adaptation to organic production systems and susceptibility to insect pests were noted. Organic sources of fertilizer contain high levels of nutrients other than N, particularly phosphorus, K, and calcium. The addition of these nutrients when using organic fertilizers, even when they are not required by the plants, must be considered in these production systems. The cost of organic fertilizers tested ranged from $US5.60 to $17.95 per kg of N and varied by method of application. Liquid sources of fish and grain blends were successfully fertigated during the study with little impact on emitter performance. Since our research began, weed mat has become very common in organic as well as conventional blueberry fields in the Pacific northwestern United States thus reducing costs of herbicides and hand weeding.

Water Use Dynamics of Peach Trees under Postharvest Deficit Irrigation

Postharvest deficit irrigation is a potential strategy for conserving valuable fresh water for production of early season tree fruit crops such as peaches. However, water use dynamics under deficit irrigation conditions that can be described as seasonal changes in crop evapotranspiration (ETc) and crop coefficient (Kc) are largely unknown. A three-year field study was carried out in a 1.6 ha peach orchard to determine seasonal ETc and Kc characteristics. The orchard was divided equally into 72 plots, in which 12 randomly selected plots received deficit irrigation and the remaining 60 plots received full irrigation. A Bowen ratio flux tower was installed in the orchard to make meteorological measurements for estimating an integrated ETc for the orchard. The study showed that from July to August 75-85% of the daily net radiation was used by latent heat or partitioned into ETc. The average monthly cumulative ETc was 151 mm in June, 162 mm in July, and 155 mm in August. Kc values under deficit irrigation conditions or termed as Deficit_Kc was computed as ratios of the ETc over potential evapotranspiration or ETo, and were compared with Kc derived from a lysimeter study under non-water stressed conditions or termed as Lysimeter_Kc. The maximum Deficit_Kc values were 0.90, 1.03, and 1.07 for the three field seasons but all were smaller than 1.20, the maximum Lysimeter_Kc. The study demonstrated that water stress under deficit irrigation can be characterized in Kc values. The approach may be used to detect if portions of an orchard or the entire orchard are under water stress. Conversely, the method may provide guidance on deploying deficit irrigation practices with pre-determined Deficit_Kc.

Effects of post-harvest deficit irrigation in ‘Red Beaut’ Japanese plum: Tree water status, vegetative growth, fruit yield, quality and economic return

In early maturing fruit crops, post-harvest is usually the preferred period to apply regulated deficit irrigation (RDI) because it offers the opportunity of reducing vegetative growth and saving water without interfering with fruit growth. There are few studies of RDI on Japanese plum, in comparison with the number available for other fruit crops. We examined the effect of RDI over the post-harvest seasons of 2009–2013 on tree water status, vegetative growth, yield, fruit quality and economic return in an adult orchard of early maturing ‘Red Beaut’ Japanese plum. All treatments received the same pre-harvest irrigation of 100% of crop evapotranspiration (ETc) and post-harvest irrigation treatments were: irrigated at 100% of ETc (Control); applying 60% of water in Control (RDI-60); and applying 30% of water in Control (RDI-30). The average annual irrigation water applied to Control was 639mm. Maximum annual water savings with respect to Control were 39% for RDI-60 and 70% for RDI-30. Intercepted photosynthetically active radiation at solar noon displayed a similar pattern throughout the years with no significant differences between irrigation treatments in any year. However, the RDI treatments were suitable for reducing total pruning weight. Fruit yield in RDI-30 was similar to Control for each of the five years following deficit irrigation. In the long-term (five seasons), the effect of post-harvest RDI had no negative cumulative effect on tree productivity. Therefore, for early maturing Japanese plum it can be concluded that allowing a progressive post-harvest water stress that limits the decline in Ψstem to values of −1.65MPa in early August, with a maximum decrease of 0.014MPaday−1, corresponding in this study to RDI-30, appears not only to be an effective way of saving water, but also acts as a useful tool to control vegetative growth (considered as total pruning), maintain fruit yield and quality and increase grower's final return.

Management of Postharvest Deficit Irrigation of Peach Trees Using Infrared Canopy Temperature

Remotely sensed canopy temperature from infrared thermometer (IRT) sensors is an effective tool for detecting plant water stress. Deficit irrigation, where the plants receive less than full irrigations and come under water stress at certain growth stages, can be used to help alleviate water shortage in the San Joaquin Valley of California. Thus, new irrigation scheduling procedures need to be developed. A field study was conducted from 2009 to 2011 to evaluate the performance of using midday infrared canopy to air temperature difference (ΔT) to manage postharvest deficit irrigation of early season peach trees. Threshold values of ΔT were selected, based on previous years' stem water potential and ΔT measurements, for four irrigation treatments: Furrow and surface drip irrigation with or without postharvest water stress. A wired network of 12 IRT sensors was installed above the orchard for canopy temperature measurement. Soil water content and stem water potential were also monitored weekly for each treatment. In both growing seasons (2009–2010 and 2010–2011), the measured ΔT values showed consistent differences among treatments, which correlated to both soil water content (R2 ≈ 0.47–0.53) and stem water potential readings (R2 ≈ 0.46–0.65). The relationship between fruit mass and postharvest irrigation amount indicated that up to 53% water savings could be achieved without impacting fruit size. The study demonstrated that infrared canopy temperature measured from above the tree top can potentially be used for managing deficit irrigation in peach and possibly other tree crops. Additional research is needed to further validate this approach.

Postharvest deficit irrigation in ‘Tatura 204’ peach: Subsequent productivity and water saving

Variable and unreliable water supply due to drought substantially reduced irrigation allocation to Australian peach growers from 2005 to 2009. Strategies to maintain productivity with less water were a high priority. Reduced irrigation allocation is likely to continue due to drought and diversion of water for environmental flows. The objective of this study was to investigate the effects of postharvest water deficits on subsequent yield and fruit quality. Treatments were imposed immediately after harvest in 2008 (Year 1, Y1), 2009 (Year 2, Y2) and 2010 (Year 3, Y3) in a commercial ‘Tatura 204’ peach (Prunus persica (L.) Batsch) orchard in the Goulburn Valley Region of Victoria, Australia. Irrigation treatments were 50%, 80%, 100%, 150% and 190% of grower postharvest irrigation practice. In all years the average postharvest midday leaf water potential (ψleaf) increased with irrigation application. After applying the treatments in Y1, in the subsequent season fruit number per lateral prior to thinning was substantially less and even after commercial thinning there was a significant difference (p<0.05) in fruit number per tree at harvest in the deficit treatments. The decrease in fruit number was attributed to flower number per lateral, the duration of flowering and fruit set. There were no differences in subsequent fruit number or yield following the application of the treatments in Y2 and Y3. There was no effect of the deficit irrigation treatments on the subsequent number of defective fruit (split stones, twins, deep sutures or abnormal) in all years. The results showed that 0.9–3.3MLha−1 of water savings can be made by the combination of cutting-back postharvest irrigation to 0.8–1.1MLha−1 and fruit thinning to a defined crop load in ‘Tatura 204’ peach orchards.

Optimal duration of irrigation withholding to promote early bloom and harvest in ‘Algerie’ loquat (Eriobotrya japonica Lindl.)

Postharvest deficit irrigation advances the following bloom and harvest in loquat (Eriobotrya japonica Lindl.), making the crop more profitable. This bloom advancement can be achieved by a combination of water shortages of different durations and intensities. Previous results have shown that completely suspending irrigation is more useful than deficit irrigation strategies in which watering is only partly restricted. In order to determine the optimal duration of irrigation withholding, ‘Algerie’ trees were subjected to different levels of water stress over two consecutive seasons, suspending watering for a short (3–5 weeks), medium (6–7 weeks), or long (8–9 weeks) period starting one month after harvest and ending when the trees reached prescribed midday stem water potentials (Ψs) of −1.4MPa, −1.8MPa, and −2.2MPa, respectively. The results show that a severe water stress (Ψs≈−2.2MPa) achieved by withholding watering for 8–9 weeks was more successful in advancing next bloom and harvest than milder stresses caused by the suspension of irrigation during shorter periods. The advancement of bloom was related to an earlier cease of new shoot growth, which led to earlier panicle development formed in the apical buds after summer rest release. Water use efficiency was improved the most by a moderate water stress (Ψs≈−1.8MPa) achieved by suppressing watering for 6–7 weeks, although on average, loquat profitability was even greater under severe water stress, because the improvement in fruit earliness was higher when water withholding lasted 8–9 weeks. On the contrary, a slight water stress (Ψs≈−1.4MPa) failed to substantially modify ‘Algerie’ loquat phenology. No detrimental effects on yield or fruit quality were attributable to regulated deficit irrigation.

Postharvest deficit irrigation in ‘Conference’ pear: Effects on subsequent yield and fruit quality

Abstract The best time for applying deficit irrigation (DI) to pear is not yet known although it was the first fruit crop to be studied for regulated DI. We explored postharvest application. Over the growing seasons of 2007–2010, three irrigation treatments were applied to ‘Conference’ pear in an experimental orchard. They were full irrigation (control, C), withholding irrigation after harvest (DI-PH a+b ), and full irrigation for two weeks after harvest followed by withholding irrigation (DI-PH b ). According to our previous experience with ‘Conference’, the DI treatments were to be irrigated if midday stem water potential ( Ψ stem ) became lower than −1.5 MPa. But it never did. The average annual irrigation water applied to C was 590 mm. This was reduced by 15% for DI-PH b and by 27% for DI-PH a+b . Fruit yield in DI-PH a+b was similar to C for each of the three years following DI. But a carry-over effect was observed after the dry season of 2008. In 2009 fruit set and crop load were therefore reduced for DI-PH a+b but fruit size was increased. For all years DI-PH b was similar to C in terms of fruit set, crop load, fruit size, and yield. Fruit soluble solids concentration (SSC), titratable acidity, and flesh firmness were measured in 2009 and 2010. They were the same in C and DI fruit except for 2009 when SSC was higher in DI-PH a+b fruit. ‘Conference’ adapted to DI in such a way that Ψ stem could be maintained by higher water depletion at a greater soil depth as the experiment progressed. Postharvest DI is recommended for ‘Conference’ but to the extent that midday Ψ stem does not become lower than −1.2 MPa.

Infrared canopy temperature of early-ripening peach trees under postharvest deficit irrigation

Abstract Canopy temperature measurements with infrared thermometry have been extensively studied as a means of assessing plant water status for field and row crops but not for fruit trees such as peaches. Like in many regions of the world, the lack of water is beginning to impact production of tree fruit such as peaches in the San Joaquin Valley of California. This is an area where irrigation is the only source of water for agricultural crops in the summer growing season. A two-year field study was conducted to assess plant water stress using infrared canopy temperature measurements and to examine its feasibility for managing postharvest deficit irrigation of peach trees. Twelve infrared temperature sensors were installed in a mature peach orchard which received four irrigation treatments: furrow and subsurface drip irrigation with or without postharvest water stress. During the two-year period, measured midday canopy to air temperature differences in the water-stressed postharvest deficit irrigation treatments were in the 5–7 °C range, which were consistently higher than the 1.4–2 °C range found in the non-water-stressed control treatments. A reasonable correlation (R2 = 0.67–0.70) was obtained between stem water potential and the canopy to air temperature difference, indicating the possibility of using the canopy temperature to trigger irrigation events. Crop water stress index (CWSI) was estimated and consistently higher CWSI values were found in the deficit irrigation than in the control treatments. Results of yield and fruit quality assessments were consistent with the literature when deficit irrigation was deployed.

Influence of post-harvest deficit irrigation and pre-harvest fruit thinning on sweet cherry (cv. New Star) fruit firmness and quality

SummaryThe effects of tree water stress on sweet cherry (‘New Star’) fruit quality during post-harvest and pre-harvest fruit thinning were evaluated in a 2-year field experiment (2005 – 2006). Four different treatments were applied: (i) fully irrigated (Control), in which irrigation was scheduled according to a water budget approach; (ii) RDI-80%, in which the crop received 0.8× Control irrigation during post-harvest and was irrigated like the Control during pre-harvest; (iii) RDI-50% in which the crop received 0.5× Control irrigation during post-harvest and was irrigated like the Control during pre-harvest; and (iv) RDI-80%-T in which irrigation management was the same as for RDI-80%, but fruits were only thinned 1 month prior to harvest in 2006. No significant effects on fruit load or yield were observed in 2006 as a consequence of the 2005 irrigation treatments. However, the RDI-50% treatment produced a noticeable advance in ripening, as evaluated from the percentage of fruit harvested at the first pick. Post-harvest water stress did not affect fruit quality at harvest, but slightly reduced fruit firmness (FF) and soluble solids content (SSC) after cold storage, with no significant variation in fruit flesh red colour (expressed as hue angle). Fruit-thinning reduced the fruit load by 38% compared to Control trees, and significantly increased fruit fresh weight (FW), FF, and SSC for cherries with similar flesh colour to the other treatments. Reducing irrigation by 50% during post-harvest advanced the harvest date (RDI-50% treatment), but did not provide any advantage in terms of fruit quality.