Using midday stem water potential for scheduling deficit irrigation in mid–late maturing peach trees under Mediterranean conditions

Irrigation techniques that reduce water applications are increasingly applied in areas with scarce water resources. In this study, the effect of two regulated deficit irrigation (RDI) strategies on peach [Prunus persica (L.) Batsch cv. “Catherine”] performance was studied over three growing seasons. The experimental site was located in Murcia (SE Spain), a Mediterranean region. Two RDI strategies (restricting water applications at stage II of fruit development and postharvest) based on stem water potential (Ψ_s) thresholds (?1.5 and ?1.8 MPa during fruit growth and ?1.5 and ?2.0 MPa during postharvest) were compared to a fully irrigated control. Soil water content (θ_v), Ψ_s, gas exchange parameters, vegetative growth, crop load, yield and fruit quality were determined. RDI treatments showed significantly lower values of θ_v and Ψ_s than control trees when irrigation water was restricted, causing reductions in stomatal conductance and photosynthesis rates. Vegetative growth was reduced by RDI, as lower shoot lengths and pruning weights were observed under those treatments when compared to control. However, fruit size and yield were unaffected, and fruit quality was slightly improved by RDI. Water savings from 43 to 65 % were achieved depending on the year and the RDI strategy, and no negative carryover effect was detected during the study period. In conclusion, RDI strategies using Ψ_s thresholds for scheduling irrigation in mid–late maturing peach trees under Mediterranean conditions are viable options to save water without compromising yield and even improving fruit quality.     

Effect of deficit irrigation on early-maturing peach tree performance

The effects of different deficit-irrigation strategies on plant-water status and yield were studied for 5 years in early-maturing peach trees (cv. Flordastar) growing under Mediterranean climatic conditions. The deficit-irrigation (DI) treatments were continuous, regulated (RDI), partial root-zone drying and a soil water content-based treatment. Peach fruit yield was more affected by post-harvest irrigation than by pre-harvest irrigation. Deficit irrigation for this cultivar produced significant water savings but caused a yield penalty, with the RDI treatment showing the clearest manifestation of this. Deficit irrigation in general affected the number of fruits per tree more than fruit size. Average stem water potential threshold values for summer (July–August–September) should be maintained above ?0.9 MPa if yields are not to decrease by more than 10 %. The marginal water use efficiency value of 0.07 for the irrigation range studied indicates that the maximum benefit, derived from a linear production function, will always occur at the limit of the water constraint prior to maximum yield values. Decision-makers should apply the minimal amount of irrigation water that allows maximum yields. Since DI treatments decrease yield due to smaller tree sizes, it is advisable that thinning practices be adapted when deficit irrigation is imposed.     

Regulated deficit irrigation improved fruit quality and water use efficiency of pear-jujube trees

Regulated deficit irrigation (RDI) was applied on field-grown pear-jujube trees in 2005 and 2006 and its effects on crop water-consumption, yield and fruit quality were investigated. Treatments included severe, moderate and low water deficit treatments at bud burst to leafing, flowering to fruit set, fruit growth and fruit maturation stages. Different deficit irrigation levels at different growth stages had significant effects on the fruit yield and quality. Moderate and severe water deficits at bud burst to leafing and fruit maturation stages increased fruit yield by 13.2-31.9% and 9.7-17.5%, respectively. Fruit yield under low water deficit at fruit growth and fruit maturation stages was similar to that of full irrigation (FI) treatment. All water deficit treatments reduced water consumption by 5-18% and saved irrigation water by 13-25% when compared to the FI treatment. During the bud burst to leafing stage, moderate and severe water deficits did not have effect on the fruit quality, but significantly saved irrigation water and increased fruit yield. Low water deficit during the fruit growth stage and low, moderate and severe water deficits during the fruit maturation stage had no significant effect on the fruit weight and fruit volume but reduced fruit water content slightly, which led to much reduced rotten fruit percentage during the post-harvest storage period. Such water deficit treatments also shortened the fruit maturation period by 10-15 d and raised the market price of the fruit. Fruit quality shown as fruit firmness, soluble solid content, sugar/acid ratio and vitamin C (V_C) content were all enhanced as a result of deficit irrigation. Our results suggest that RDI should be adopted as a beneficial agricultural practice in the production of pear-jujube fruit.     

Long-term evaluation of yield components of young olive trees during the onset of fruit production under different irrigation regimes

A four-year study was conducted on young Olea europaea L. trees to investigate the effect of deficit irrigation starting from the onset of fruit production. Subsurface drip irrigation was used to supply 100% (FI), 46–52% (DI), or 2–6% (SI) of tree water needs. Tree growth was reduced by deficit irrigation, whereas, return bloom was not. Per tree fruit yield of DI trees was 68% that of FI, but fruit yield efficiency based on tree size was similar between treatments. Fruit set and the number of fruits of FI trees were similar to those of DI trees and significantly higher than in SI trees. No significant differences in fruit fresh weight were found between FI and DI. The oil yield and oil yield efficiency of the DI treatment were 82 and 110% that of FI trees, respectively. A level of about 50% deficit proved sustainable to irrigate trees for oil production.     

Response of plum trees to deficit irrigation under two crop levels: tree growth, yield and fruit quality

The effects of regulated deficit irrigation (RDI) and crop load on Japanese plum were investigated. RDI applied during phase II of fruit growth and post-harvest was compared with irrigation to match full crop evapotranspiration. Each irrigation treatment was thinned to a commercial crop load (described as medium) and to approximately 40% less than the commercial practice (described as low). The RDI strategy allowed for 30% water savings, increasing tree water use efficiency, with minimal effect on crop yield and fruit growth providing that plant water stress during the fruit growth period was low (stem water potential > −1.5 MPa), trees could recover optimum water status well before harvest, and crop load was low. However, the economic return, calculated from fruit weight distribution by commercial categories, was more affected by RDI than yield. The combination of medium crop load and RDI shifted fruit mass distribution towards the low value categories. This lead to similar or even higher economic returns in the RDI treatment with low crop level than with the medium one. In addition, since both, low crop level and RDI, increased fruit total soluble solids (TSS) concentration, fruit under RDI and low crop levels had the highest values of TSS.     

Response of vegetative growth and fruit development to regulated deficit irrigation at different growth stages of pear-jujube tree

In order to investigate the response of vegetative growth, fruit development and water use efficiency to regulated deficit irrigation at different growth stages of pear-jujube tree (Zizyphus jujube Mill.), different water deficit at single-stage were treated on field grown 7-year old pear-jujube trees in 2005 and 2006. Treatments included severe (SD), moderate (MD) and low (LD) water deficit treatments at bud-burst to leafing (I), flowering to fruit set (II), fruit growth (III) and fruit maturation (IV) stages. Compared to the full irrigation (control), different water deficit treatments at different growth stages reduced photosynthesis rate (P_n) slightly and transpiration rate (T_r) significantly, thus it improved leaf water use efficiency (WUE_L, defined as the ratio of P_n to T_r) by 2.7-26.1%. After the re-watering, P_n had significant compensatory effect, but T_r was not enhanced significantly, thus WUE_L was improved by 31.4-42.2%. I-SD, I-MD, II-SD and II-MD decreased new shoot length, new shoot diameter and panicle length by 8-28%, 13-23% and 10-31%, respectively. Simultaneously, they reduced leaf area index (LAI) and pruning amount significantly. Flowering of pear-jujube tree advanced by 3-8 days in the water deficit treatments at stage I, Furthermore, SD and MD at stage I increased flowers per panicle and final fruit set by 18.9-40.5% and 15.5-36.6%, respectively. After a period of re-watering, different water deficit treatments at different growth stages improved the fruit growth rate by 15-30% without reduction of the final fruit volume. Compared to the control, I-MD, I-SD, I-LD, I-MD and I-SD treatments increased fruit yield by 13.2-31.9%, but reduced water consumption by 9.7-17.5%, therefore, they enhanced water use efficiency at yield level (WUE_Y, defined as ratio of fruit yield to total water use) by 17.3-41.4%. Therefore, suitable period and degree of water deficit can reduce irrigation water and restrain growth redundancy significantly, and it optimize the relationship between vegetative growth and reproductive growth of pear-jujube trees, which maintained or slightly increased the fruit yield, thus water use efficiency was significantly increased.     

温室梨枣树土壤水分和品质对调亏灌溉的响应

为探明调亏灌溉对温室梨枣树水分利用效率及梨枣品质的影响,以日光温室生长的9年生矮化密植成龄梨枣树为试材,试验设置充分供水处理(处理1(CK)),萌芽展叶期重度亏水处理(处理2),萌芽展叶期中度亏水处理(处理3)和果实膨大期中度亏水处理(处理4)。结果表明,亏水处理有利于提高梨枣树的根系吸水能力,促进根系向土壤深处生长,同时显著降低棵间蒸发;与CK相比,处理2和处理3对梨枣品质的所有指标都起到了提高和改善的作用,其中处理2最佳,处理3次之;综合考虑不同生育期调亏灌溉对梨枣树各项指标的影响,萌芽展叶期中度亏水能较好的改善果实品质,是实施调亏灌溉的最佳阶段。     

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

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.     

Deficit irrigation without reducing yield or nut splitting in pistachio (Pistacia vera cv Kerman on Pistacia terebinthus L.)

An irrigation experiment involving pistachio (Pistacia vera cv Kerman on Pistacia terebinthus L. rootstocks) was performed over a four-year period in central Spain to determine the effect of regulated deficit irrigation (RDI) on nut yield and quality. The growth season was divided into three phenological stages: stage I - from sprouting until the end of rapid nut growth; stage II - from maximum nut size until the beginning of kernel growth; and stage III - from the beginning of kernel growth until harvest. Control trees were irrigated to supply their full water needs throughout the growth season, except for the post-harvest period. Sustained deficit irrigation at 65% (DI₆₅) and 50% (DI₅₀) of control irrigation was provided to two other groups of trees. The RDI provided to a further group was designed to provide a stress period during stages I and II but no water stress during stage III; the aim was to reduce water use and increase the percentage of split nuts. A fifth group of trees was maintained under rain fed conditions. Water potential and leaf conductance were affected in the DI₆₅, DI₅₀ and rain fed treatments mainly during stages II and III, with midday water potentials below −2.0 MPa. The RDI trees were only significantly water stressed during stage II, showing midday water potentials of around −1.4 MPa. On most days, leaf conductance was not significantly affected in any of the irrigation treatments. The nuts of the DI₆₅ and DI₅₀ trees were smaller in diameter and their total yield was reduced compared to the controls. However, no significant differences in kernel dry weight were observed. The RDI trees showed a total yield and percentage of split nuts similar to those of the controls, even though they received around 20% less water. The split nut yield showed a linear relationship with crop evapotranspiration. However, since the percentage of split nuts was similar in all treatments this variation was likely related to the total yield. The RDI trees did not show the normal alternate bearing pattern (which was clearly maintained in the control trees). Early splitting, a process that decreases the quality of the yield, was not related to water status but to temperatures lower than 13 °C. The results suggest that P. terebinthus L. rootstocks confer P.vera scions a degree of drought-resistance, reducing the likelihood of water stress and, therefore, allowing more severe RDI scheduling.     

Financial analysis of wine grape production using regulated deficit irrigation and partial-root zone drying strategies

Cost-benefit analysis was performed to determine the profitability of producing wine grapes under different irrigation regimes. Vines irrigated by regulated deficit irrigation (RDI) and partial root-zone drying (PRD) were compared with vines grown under full irrigation in a typical vineyard in a semiarid environment with scarce water resources (south-eastern Spain) during three consecutive years. Five irrigation treatments were applied. The Control treatment irrigated at 60% of the ETc (Crop evapotranspiration) throughout the orchard cycle. PRD-1 and RDI-1 provided deficit irrigation from fruit set to harvest (irrigated 30% ETc) and post-harvest (45% ETc). PRD-2 and RDI-2 provided deficit irrigation from fruit set to harvest (irrigated 15% ETc) and post-harvest (45% ETc). From an economic point of view, only the Control, PRD-1 and RDI-1 treatments were economically viable since their profitability indicators were positive, although low, especially PRD-1. The more severe deficit irrigated treatments (PRD-2 and RDI-2) were unviable. The most profitable treatment was the Control which had a Net Margin/total cost ratio (NM/C) (representing the overall profitability of the vineyard) of 25.37% compared with the 1.90% of RDI-1 and 0.57% of PRD-1. The threshold price of water indicates that only the Control remains profitable with higher water prices of up to 0.46 € m⁻³. When the cost-benefit analysis took into account the extra quality achieved in PRD-2 and RDI-2, it indicated that these treatments, which were otherwise economically unviable, achieved high returns (17 and 16%, respectively) and were close to the Control treatment. Thus, a low or moderate bonus that encourages extra berry quality for premium wine production would make deficit irrigation practices profitable. Moreover, the financial indices estimated suggest that in the present situation, and with our soil and climatic conditions, PRD is less economically profitable (higher installation cost, lower NM/C, and threshold price of water) than RDI under the same conditions.     

调亏灌溉和灌溉方式对香梨树吸收根系重分布的影响

于2009—2010年开展了田间试验,研究了调亏灌溉对成龄库尔勒香梨树吸收根系重分布的影响。灌溉方式为地表滴灌与漫灌,滴灌试验包括轻度与重度水分胁迫处理(在新梢及果实生长缓慢期分别按蒸发量的60%与40%灌溉,在其他生育期按蒸发量的80%灌溉),对照处理为充分灌溉,在整个生育期按蒸发量的80%灌溉。每年4—8月份,漫灌每月灌溉1次,灌水定额为300 mm。所有处理在2009年之前均为漫灌。研究结果表明,成龄库尔勒香梨树的吸收根系主要分布于地表以下20~60 cm。梨树需要2 a时间调整吸收根系的分布以适应灌溉方式由漫灌转为滴灌。土壤水分胁迫减小了梨树吸收根系的根长,抑制了梨树的营养生长,其后恢复充分灌溉可促进根系的生长。梨树新梢及果实生长缓慢期的土壤水分胁迫对根系生长的抑制效果超过了对新梢生长的抑制;但吸收根系的生长与果实产量之间并无显著的相关性。     

Maximum diurnal trunk shrinkage is a sensitive indicator of plant water, stress in Diospyros kaki (Persimmon) trees

Persimmon tree (Diospyros kaki L.f.) is a deciduous fruit tree included in the so-called group of minor fruit tree species. Worldwide, it is not widely grown but, nowadays, Kaki culture is of some importance in the south-east of Spain because of the high fruit commercial value. Currently, neither it is known about Kaki trees water needs, nor crop responses to the irrigation regime. The objective of the present research was to assess the feasibility of using maximum diurnal trunk shrinkage (MDS) as a plant water stress indicator for Kaki trees. During two drought cycles, in trees under either full or deficit irrigation, the MDS obtained by means of LVDT sensors was compared with a reference indicator of fruit trees water status, the midday stem water potential (Ψ_stem). In addition, stomatal conductance and fruit diameter variations were also followed. As water restrictions began, there was an immediate increase in MDS, in correspondence with a decrease in Ψ_stem. Pooling data from both drought cycles and irrigation regimes, MDS and Ψ_stem were linearly correlated (r² = 0.77***). The magnitude of differences between well watered and deficit irrigated trees was much larger in the case of MDS than for Ψ_stem. However, the tree-to-tree variability of the MDS readings was three times higher than for Ψ_stem; average coefficient of variation of 14% and 38% for Ψ_stem and MDS, respectively. Overall, results reported indicated that MDS is a sensitive indicator of Kaki water status and it can be further used as an irrigation scheduling indicator for optimum irrigation management of this crop. However, the large MDS tree-to-tree variability should be taken into account when selecting the number of trees to monitor within an orchard.     

Response of Navel Lane Late citrus trees to regulated deficit irrigation: yield components and fruit composition

The effects of mid-summer regulated deficit irrigation (RDI) treatments were investigated on Navel Lane Late citrus trees over four seasons. Water restrictions applied from July until mid-September were compared with irrigation at full crop evapotranspiration (ETc). Two degrees of water restrictions were imposed: (1) RDI-1, irrigated at around 50% ETc and, (2) RDI-2, irrigated at 30–40% ETc. In addition, threshold values of midday stem water potential (Ψs) of ?1.3 to ?1.5 MPa for RDI-1 and of ?1.5 to ?1.7 MPa for RDI-2 were also taken into account. Results showed that Navel Lane Late is a citrus cultivar sensitive to water deficit since both RDI strategies reduced fruit size every year and water use efficiency in RDI trees was similar to control trees. However, the RDI-1 strategy allowed water savings up to 19% without reduction in yield when the water stress integral did not surpass 70 MPa day. RDI improved fruit quality, increasing total soluble solids and titratable acidity, while the fruit maturity was delayed. In conclusion, we suggest that RDI-1 strategy since it did not significantly impair the economic return can be applied in commercial orchards in case of water scarcity. Nevertheless, Navel Lane Late fruit is sensitive to water deficit and the fruit weight can be detrimentally affected.     

Production and oil quality in ‘Arbequina’ olive (Olea europaea, L.) trees under two deficit irrigation strategies

The effect of two deficit irrigation (DI) strategies on fruit and oil production and quality in a 12-year-old ‘Arbequina’ olive orchard with 238 trees ha^?1 was evaluated. The T1 treatment was a sustained DI regime (65% ETc, 2–3 irrigation events per week). The T2 treatment was a low-frequency DI (increasing stress/rewatering cycles, which consisted in withholding irrigation until fruit shrivelling and then applying a recovery irrigation providing the same amount of water that supplied in T1 for that period). As compared to full irrigation, both strategies reduced fruit production and increased the variability of fruit ripening, but favoured oil extraction. Free acidity, peroxide value, K₂₃₂, K₂₇₀ and sensory quality of oil were not affected by DI. Furthermore, carotenoid, chlorophyll, phenol, and oleic contents increased. The greatest phenol content and bitterness index were found in oil from T2 trees. Later harvesting caused sensory quality and tocopherol losses, although the oil synthesized in DI olives increased.     

Sustainability of regulated deficit irrigation in a mid-maturing peach cultivar

The level of irrigation restriction to apply in a deficit irrigation (DI) programme for sustainable peach (‘Baby gold 6’) production was investigated. The experiment involved four irrigation treatments over five consecutive seasons (2007–2011). They were full irrigation (control), reducing irrigation by 20 % during the first half of stage III (DI-80 %), withholding irrigation until reaching a light stress level (DI-L) and withholding irrigation until reaching a moderate stress level (DI-M). The withholding of irrigation in both DI-L and DI-M was applied only during stage II and postharvest periods and was based on midday stem water potential thresholds (Ψ _stem). For the DI-L treatment ?1.5 MPa was used in both periods, and for DI-M ?1.8 and ?2.0 MPa were used during stage II and postharvest, respectively. Average Ψ _stem values during DI periods were approximately ?1.4 and ?1.2 MPa for DI-M and DI-L, respectively. The pre-defined thresholds required to trigger irrigation were rarely reached. No significant differences between treatments were found in terms of yield in any experimental year. However, DI-M and to a lesser extent DI-L had lower final fruit fresh mass at harvest related to lower Ψ _stem after three consecutive years of the experiment (during 2010 and 2011). Therefore, in terms of fruit size, DI was not sustainable. Rather than lowering Ψ _stem thresholds, we recommend discontinuing DI after 3-year application.     

Interaction between water and nitrogen management in peaches for processing

A three-year field experiment (2006–2008) on clingstone peach cv. Andross was conducted in a commercial orchard under mechanical harvesting for the processing industry. Three irrigation strategies were evaluated: full irrigation throughout the growing season; restricted irrigation during stage-II (~70% restriction) and restricted irrigation during stage-III (~30% restriction), combined with three nitrogen fertilization treatments: 0, 60 and 120 kg N/ha. Trees were fertigated on a daily basis. Daily patterns of soil moisture were monitored with capacitance probes. Irrigation restriction strategies and nitrogen dose affected yield and fruit quality at commercial harvest. As well as the individual effects of applying irrigation strategies and N doses, interactions between the two factors were analyzed. In the second year, there was a nitrogen × irrigation interaction for fruit yield. A positive yield effect for N applied to fully irrigated trees occured, while the opposite was observed when the irrigation restrictions were applied during stage-III.     

Yield and fruit development in mango (Mangifera indica L. cv. Chok Anan) under different irrigation regimes

‘Chok Anan’ mangoes are mainly produced in the northern part of Thailand for the domestic fresh market and small scale processing. It is appreciated for its light to bright yellow color and its sweet taste. Most of the fruit development of on-season mango fruits takes place during the dry season and farmers have to irrigate mango trees to ensure high yields and good quality. Meanwhile, climate changes and expanding land use in horticulture have increased the pressure on water resources. Therefore research aims on the development of crop specific and water-saving irrigation techniques without detrimentally affecting crop productivity.The aim of this study was to assess the response of mango trees to varying amounts of available water. Influence of irrigation, rainfall, fruit set, retention rate and alternate bearing were considered as the fruit yield varies considerably during the growing seasons. Yield response and fruit size distribution were measured and WUE was determined for partial rootzone drying (PRD), regulated deficit irrigation (RDI) and irrigated control trees.One hundred ninety-six mango trees were organized in a randomized block design consisting of four repetitive blocks, subdivided into eight fields. Four irrigation treatments have been evaluated with respect to mango yield and fruit quality: (a) control (CO = 100% of ET_c), (b) (RDI = 50% of ET_c), (c) (PRD = 50% of ET_c, applied to alternating sides of the root system) and (d) no irrigation (NI).Over four years, the average yield in the different irrigation treatments was 83.35 kg/tree (CO), 80.16 kg/tree (RDI), 80.85 kg/tree (PRD) and 66.1 kg/tree (NI). Water use efficiency (WUE) calculated as yield per volume of irrigation water was always significantly higher in the deficit irrigation treatments as compared to the control. It turned out that in normal years the yields of the two deficit irrigation treatments (RDI and PRD) do not differ significantly, while in a dry year yield under PRD is higher than under RDI and in a year with early rainfall, RDI yields more than PRD. In all years PRD irrigated mangoes had a bigger average fruit size and a more favorable fruit size distribution.It was concluded that deficit irrigation strategies can save considerable amounts of water without affecting the yield to a large extend, possibly increasing the average fruit weight, apparently without negative long term effects.     

Pomegranate trees performance under sustained and regulated deficit irrigation

The effects of sustained and regulated deficit irrigation (SDI and RDI) on “Mollar de Elche” pomegranate tree performance were investigated in a field trial conducted over three consecutive seasons. In the RDI regimes, severe water restrictions were applied during one of three phases: flowering and fruit set, fruit growth, or the final phase of fruit growth and ripening. In another approach, SDI was applied by watering trees at 50 % of the estimated crop water needs (ET_c) during the entire season. Results showed that even after three consecutive seasons of water restrictions, similar yield levels were obtained in SDI and Control trees watered at 100 % ET_c. This was because a 22 % reduction in average fresh fruit weight recorded in the SDI treatment was compensated by an increase in 28 % in the quantity of fruit collected per tree. This was most likely due to a reduction in the fall of the reproductive organs. However, the SDI strategy led to a reduction in 28 % in the yield value when fruits are sold for fresh fruit markets. Water restrictions applied only during flowering and fruit set also resulted in an increase in the quantity of fruit collected per tree, with only a slight reduction in fruit weight and without affecting the yield value. On the other hand, severe water restrictions applied during the summer (i.e., mid-phase of fruit growth) led to 24 % water savings with only a 7 % reduction in fruit weight. Fruit cracking was very low in all treatments and seasons (2–6 % over the total quantity fruit collected per tree). Only the RDI regime with restrictions during the summer increased cracking in one out of the three seasons. It is concluded that RDI can be used as a measure to cope with water scarcity and high water prices. Among all the RDI explored, the one with restrictions applied early in the season (during flowering and fruit set) was the most convenient strategy.     

Response of Clementina de Nules citrus trees to summer deficit irrigation. Yield components and fruit composition

The effects of mid-summer regulated deficit irrigation (RDI) treatments were investigated on Clementina de Nules citrus trees over three seasons. Water restrictions applied from July, once the June physiological fruit drop had finished, until mid September were compared with a Control treatment irrigated during all the season to match full crop evapotranspiration (ET_c). Two degrees of water restrictions were imposed based on previous results also obtained in Clementina de Nules trees ( [Ginestar and Castel, 1996] and [González-Altozano and Castel, 1999]). During the RDI period, deficit irrigation was applied based on given reductions over the ET_c, but also taking into account threshold values of midday stem water potential (Ψ_s) of −1.3 to −1.5 MPa for RDI-1 and of −1.5 to −1.7 MPa for RDI-2. Results showed that water savings achieved in the RDI-2 treatment impaired yield by reducing fruit size. On the contrary, the RDI-1 strategy allowed for 20% water savings, with a reduction in tree growth but without any significant reduction in yield, fruit size nor in the economic return when irrigation was resumed to normal dose about three months before harvest. Water use efficiency (WUE) in the RDI trees was similar or even higher than in Control trees. RDI improved fruit quality increasing total soluble solids (TSS) and titratable acidity (TA). In conclusion, we suggest that the RDI-1 strategy here evaluated can be applied in commercial orchards not only in case of water scarcity, but also as a tool to control vegetative growth improving fruit composition and reducing costs associated with the crop management.     

Loquat as a crop model for successful deficit irrigation

During three consecutive seasons, two different deficit irrigation strategies were compared with control fully irrigated trees regarding their capacity to induce early bloom and harvest in “Algerie” loquat. The first strategy, a continuous deficit irrigation strategy, consisted in a uniform reduction of 20% water needs through the entire season; the second strategy, a regulated deficit irrigation approach, while accounting for the same global reduction of 20% loquat water needs, concentrated water shortages after harvest from mid-May through the end of August. Regulated deficit irrigation resulted more successful. Postharvest regulated deficit irrigation advanced full bloom 10–20 days depending on the season. Such enhancement led to more precocious and valuable yield, with an average increase of fruit value of 0.21 € kg⁻¹. The effects of continuous deficit irrigation were less noticeable and average fruit value was increased 0.08 € kg⁻¹. Yield and fruit quality were not affected for the different deficit irrigation strategies. Water savings established around 1450 m³ ha⁻¹ year⁻¹. Deficit irrigation rose water use efficiency up to more than a 40%.