Regulated Deficit Irrigation Treatments Research Articles

Response of Pear Trees’ (Pyrus bretschneideri ‘Sinkiangensis’) Fine Roots to a Soil Water Regime of Regulated Deficit Irrigation

A field experiment was conducted to evaluate the effects of regulated deficit irrigation (RDI) on the fine root redistribution of mature pear trees in 2009 and 2010. The experiment consisted of four RDI treatments: MRDI-1 and SRDI-1, in which the trees received irrigation replacing 60% and 40% of pan evaporation (Ep) during Stage 1 (cell division stage), and MRDI-1+2 and SRDI-1+2, in which the trees received irrigation replacing 60% and 40% of Ep during Stage 1+2 (cell division and slow shoot growth stage). All the RDI-treated trees received irrigation replacing 80% of Ep (full irrigation) in other stages, and the control trees were fully irrigated during the whole growth season. The results showed that the fine root length density (RLD) of mature pear trees was reduced by water stress. The resumption of full irrigation boosted fine root growth. The RLD of the SRDI-1-treated trees in the irrigated zones recovered in early July, they maintained water and nutrient absorption during the fruit enlargement stage, and the final fruit yield was significantly improved. The RLD of trees in the irrigated zones with MRDI-1 and MRDI-1+2 recovered in July and September, respectively, but there were no significant differences in fruit yield between the MRDI-1, MRDI-1+2, and the control. This indicates that the fruit yield was not negatively or positively impacted by the redistribution of moderate water stress applied during either Stage 1 or Stage 1+2.

Physiological responses of almond trees under regulated deficit irrigation using saline and desalinated reclaimed water

Regulated deficit irrigation (RDI) strategy using reclaimed water (RW) is becoming a common procedure in some Mediterranean regions. Full and regulated deficit irrigation were combined with desalinated (ECw 1 dS m−1) and saline (ECw 3 dS m−1) reclaimed water to irrigate young potted almond trees over a 3-year period. The full irrigation treatments received 130% of the crop evapotranspiration (ETc) and the RDI treatments received 80% of ETc during the kernel filling. Trunk diameter decreased in both RDI treatments at the end of the experimental period, although this response was more marked in the trees irrigated with saline RW. There were negative relationships between shoot growth and leaf Na+ and Cl+ contents in the saline treated trees, in which the accumulation of salts in leaves was associated with osmotic adjustment, which was responsible for maintaining midday leaf turgor. Plant water status, measured by the leaf and water potential, decreased in almond exposed to water deficit or irrigated with saline RW, indicating a slight dehydration in these plants due to the difficulty in water uptake from the substrate. Trees subjected to both deficit irrigation treatments showed lower stomatal conductance values than full irrigated treatments during the RDI period. However, at the end of experimental period, the lowest Pn values were found in plants irrigated with saline RW, especially in trees irrigated with saline RW combined with RDI strategy, verifying the relevance of duration of exposure to the stress. Saline and desalinated RW can be successfully used for irrigating almond trees, which might be of great economic and competitive significance for agriculture, but further research focused on a longer term should be carried out since detrimental effects might appear. Deficit irrigation combined with saline RW in P. dulcis is not recommended since it intensifies the negative effects of water and salt stress applied individually.

The Effect of Deficit Irrigation Strategies on the Efficiency From Plant to Essential Oil Production in Peppermint (Mentha piperita L.)

The effect of deficit irrigation on water productivity in the water supply and utilization chain has been computed, employing a systematic and quantitative approach. By applying such an investigation, weaknesses and strengths of deficit irrigation strategies could be revealed, and actions and measures could be implemented to improve water productivity as much as possible. The peppermint plants were subjected to regulated deficit irrigation (RDI) and partial root-zone drying (PRD). Peppermint was cultivated under full irrigation (FI, control) and RDI treatments including RDI85, RDI70, RDI55, and RDI40, receiving 85, 70, 55, and 40% of FI treatment, respectively; PRD techniques including PRD70, PRD55, and PRD40, receiving 70, 55, and 40% of FI treatment in one side of the root-zone at each irrigation event, respectively during two cutting seasons. There was no significant improvement in leaves weight and dried yield step by applying deficit irrigation treatments. Leaves and aerial parts from the whole plant and dried yield as the main source of essential oil had the weakest function, which should be optimized to adjust and gain more efficiency. In the essential oil yield step, as a final procedure, the highest improvements were observed in PRD55 treatment with 90% improvement in efficiency compared to control treatment. According to the results and calculating water productivity, PRD55 treatment improved water productivity by 179% compared to the control treatment. Two-way ANOVA analysis, between deficit volume and the deficit applying method, showed that total water productivity was affected (increased) significantly by the deficit applying method. This implies the contribution of the PRD technique to enhance more signals than RDI-based signals, which resulted in more improvements in secondary metabolism production in peppermint.

Monitoring of Emerging Water Stress Situations by Thermal and Vegetation Indices in Different Almond Cultivars

In recent years, the area dedicated to modern irrigated almond plantations has increased significantly in Spain. However, the legal irrigation allocations are lower than the maximum water requirements of the crop in most cases. Therefore, almond growers are forced to implement regulated deficit irrigation strategies on their farms, applying water stress in certain resistant phenological periods and avoiding it in sensitive periods. Given the need to monitor the water status of the crop, especially in the most sensitive periods to water stress, the objective of this work was to evaluate the sensitivity of two UAV-based crop water status indicators to detect early water stress conditions in four almond cultivars. The field trial was conducted during 2020 in an experimental almond orchard, where two irrigation strategies were established: full irrigation (FI), which received 100% of irrigation requirements (IR), and regulated deficit irrigation (RDI), which received 70% of IR during the whole irrigation period except during the kernel-filling stage when received 40% IR. The UAV flights were performed on four selected dates of the irrigation season. The Crop Water Status Index (CWSI) and the Normalized Difference Vegetation Index (NDVI) were derived from thermal and multispectral images, respectively, and compared to classical water status indicators, i.e., stem water potential (Ψstem), stomatal conductance (gs), and photosynthetic rate (AN). Of the four flights performed, three corresponded to mild water stress conditions and a single flight was performed under moderate water stress conditions. Under mild water stress, CWSI was not able to capture the differences between FI and RDI trees that were observed with Ψstem. Under moderate stress conditions, CWSI was sensitive to the water deficit reached in the trees and showed significant differences among both irrigation treatments. No differences were observed in the CWSI and NVDI response to water stress among cultivars. Although NDVI and CWSI were sensitive to water stress, the low signal intensity observed in NDVI makes this index less robust than CWSI to monitor crop water stress. It can be concluded that UAV-based CWSI measurements are reliable to monitor almond water status, although for early (mild) levels of water stress, Ψstem seems to be the preferred option.

Scheduling Regulated Deficit Irrigation with Leaf Water Potential of Cherry Tomato in Greenhouse and its Effect on Fruit Quality

The tomato cultivated surface is one of the most important surfaces in the world. This crop needs a sufficient and continuous supply of water during vegetative growth. Therefore, production may be at risk in warm and water-scarce areas. Therefore, the implementation of irrigation alternatives such as regulated deficit irrigation (RDI) is of great importance to reduce the use of water and improve the production of the quality of tomatoes. The objective of this work was to evaluate the deficit irrigation scheduling using plant water status as a tool in deficit irrigation. Experimental design was a randomized design with four replications per treatment. Two irrigation treatments were applied: Control (125% of crop evapotranspiration (ETc)) and Regulated Deficit Irrigation (RDI). This latter treatment considered different threshold values of midday leaf water depending on crop phenological stage. No differences were observed in yield, with RDI treatment being more efficient in the use of irrigation water than the control. Besides, RDI tomatoes presented, in general, greater weight, size, Total soluble solids (TSS), sugars, antioxidant activity, lycopene, β-Carotene, and redder color with more intense tomatoes flavor. Finally, it might be said that RDI strategy helped to reduce 53% of irrigation water and to improve the nutritional, functional, and sensory quality of tomatoes.

Yield and chemical components from the constitutive parts of olive (cv. Genovesa) fruits are barely affected by spring deficit irrigation

An important concern for the expansion of olive production is related to the irrigation water availability. This study was driven on the hypothesis that regulated deficit irrigation (RDI) during spring - a period covering basically the fruit set, the seed development and the seed/pit hardening - does not affect significantly yield and chemical components from cv. Genovesa olive fruits. The objectives were twofold: a) to evaluate productive responses to RDI treatments, and b) to gain further information on the effect of irrigation on yield and chemical components from the constitutive parts of the olive fruit. To test the hypothesis, data of selected productive and quality parameters obtained from trees of three RDI treatments were tested and compared with those from full-irrigated trees. Results showed that over a 3-year period, water restriction had no effects on fruit pulp dry matter accumulation. Neither were significant effects on oil accumulation and fatty acid composition from both oil-bearing tissues (pulp and seed). Both tocopherols and total phenols (TP) from pulp were unchanged among RDI. Conversely, significant and opposite tendencies were noted for these parameters from the seeds: deficit irrigation caused lower amounts of α-tocopherol but higher TP than the full-irrigated treatment. Overall, results indicate that spring water restriction can save a significant amount of irrigation water with minor impact on important productive and quality parameters.

Effects of pre-harvest deficit irrigation during the oil accumulation period on fruit characteristics, oil yield extraction, and oil quality in olive cv. Genovesa in an arid region of Argentina

The effect of pre-harvest deficit irrigation was studied as a tool to reduce fruit moisture and evaluate its influence on fruit characteristics, oil yield extraction, and oil quality. Two regulated deficit irrigation treatments (RDI) were evaluated over two seasons in a cv. Genovesa olive orchard. This study included a Control treatment, irrigated at 100% crop evapotranspiration over the season, and two RDI treatments, irrigated at 50% (RDI1) and 30% (RDI2) of Control. These treatments were applied from the end of pit hardening (mid-January) until harvest (early- April), when oil is accumulated in fruits. Fruit moisture decreased as the deficit irrigation period advanced, being significantly lower in RDI2 and RDI1 than in the Control treatment. Fruits harvested from the RDI2 treatment had lower moisture, dry mass and oil deposition, and higher maturation and pulp flavonoid compounds concentration than in RDI1 and Control. Pooled data across seasons showed that a 1% reduction in fruit moisture produced an increase of 0.16% in oil yield extraction. Phenolic compounds increased consistently with fruit moisture decreasing from 60% to 50%. However, when fruit moisture was as low as 35%, phenolic compounds were the lowest. Additional fruit samples from RDI2 were processed with water addition after malaxation. Water addition led to a general pattern of increases in oil yield extraction, reduction of phenolic compounds, and no influence on acidity, UV indexes, or fatty acids profile.

Partial rootzone drying and regulated deficit irrigation can be used as water-saving strategies without compromising fruit yield and quality in tropically grown sweet orange

ABSTRACT We examined the effects of partial rootzone drying (PRD) and regulated deficit irrigation (RDI) on some physiological and agronomical traits in tropically grown sweet orange (Citrus sinensis (L.) Osbeck). Seven different irrigation strategies were applied over three consecutive years and compared regarding their effects on leaf gas exchange, vegetative growth, fruit yield and quality and gene expression of fruit quality-related genes. Stomatal conductance and leaf temperature were significantly affected by the different irrigation treatments and seasonal variations in the atmospheric vapour pressure deficit and air temperature. Both PRD treatments (with alternation of the irrigation side every 15 and 30 days) significantly increased the irrigation water use efficiency by 41–56% compared to the full irrigation treatment. RDI treatments induced a significant upregulation of genes related to the citrate metabolism and carotenoid biosynthesis. Trees exposed to PRD with alternation of the irrigation side at every 15 days, as well as to RDI at the fruit ripening stage, showed values of yield, productive efficiency, fruit mass, length and size, juice yield and ratio between soluble solids and titratable acidity similar to those of the full irrigation treatment. Therefore, PRD and RDI can be viable water saving irrigation strategies for sweet orange production in tropical conditions.

YIELD AND FRUIT QUALITY OF ALMOND, PEACH AND PLUM UNDER REGULATED DEFICIT IRRIGATION

<List><ListItem><ItemContent> • Regulated deficit irrigation was assessed in almond, peach and plum over 3 years. </ItemContent></ListItem><ListItem><ItemContent> • Fruit-growth slowdown stages are appropriate periods to apply deficit irrigation. </ItemContent></ListItem><ListItem><ItemContent> • Peach yields were unaffected under a regulated deficit irrigation of 75% ET_C. </ItemContent></ListItem><ListItem><ItemContent> • Regulated deficit irrigation of 50% ET_C maintained yields of almond and plum. </ItemContent></ListItem><ListItem><ItemContent> • Fruit quality improved under regulated deficit irrigation. </ItemContent></ListItem></List> The effects of regulated deficit irrigation (RDI) on the performance of almond cv. Tuono, peach cv. JH-Hall and plum cv. Stanley were assessed on the Saiss Plain (NW, Morocco) over three consecutive growing seasons (2011–2013). Irrigation treatments consisted of a control, irrigation applied to fully satisfy crop water requirements (100% ET_C), and two RDI treatments, irrigation applied to 75% ET_C (RDI-75) and 50% ET_C (RDI-50). These three treatments were applied during fruit-growth slowdown periods corresponding to Stages II and III in almond and Stage II in peach and plum. Yield and fruit quality traits were determined. The effect of RDI differed between species. Yield and fruit size were reduced significantly only in peach under RDI-50. Fruit quality improved in this species in the first year of the experiment, with an increase of sugar/acid ratio and polyphenol content. Plum quality also improved but the effects were significant only in the second and third years. Similar results were recorded in almond kernel, but their epidermal grooves were deeper under RDI-50, and this may have affected their commercial value. It is concluded that water can be saved during the fruit-growth slowdown period by up to 25% in peach and 50% in almond and plum with improvements in fruit quality without affecting total yield.

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.

ABA signaling plays a key role in regulated deficit irrigation-driven anthocyanins accumulation in ‘Cabernet Sauvignon’ grape berries

Regulated deficit irrigation (RDI) induces anthocyanins biosynthesis in grape berries; however, the mechanisms involved remain unclear. Here, we compared the change in endogenous hormones in grape berries under RDI treatment and analyzed the effect of nordihydroguaiaretic acid (NDGA), an abscisic acid (ABA) synthesis inhibitor, on anthocyanins biosynthesis in grape berries under RDI treatment. ABA showed the greatest change under RDI treatment; cluster analysis revealed the shortest distance with anthocyanins content. It is noteworthy that NDGA also inhibited the increase in anthocyanins content and the expression of synthesis-related genes in grape berries. ABA promoted anthocyanins accumulation by enhancing the expression of VvMYBPA1 and VvOMT in RDI-treated grape berries. In addition, RDI mainly promoted the synthesis and accumulation of monoglycosides anthocyanins, as well as the accumulation of malvidin-3-O-glucoside and its derivatives. These results indicated that ABA signaling plays key roles in RDI-induced anthocyanins accumulation in grape berries.

Regulated deficit irrigation strategies affect the terpene accumulation in Gewürztraminer (Vitis vinifera L.) grapes grown in the Okanagan Valley

Regulated deficit irrigation (RDI) is a viticultural practice known to improve grape phenolics and color in red grapes; however, the impact of this practice on grape aromas remains largely unknown. The effects of RDI treatments applied at various berry developmental stages on canopy, yield, and free and glycoside-bound terpenes of the berry were investigated for three consecutive seasons. All RDI treatments reduced leaf photosynthesis and yield, but not when applied after veraison. Berry total soluble solids at harvest were reduced by RDI applied after veraison or throughout the season. Despite reducing berry sugars, RDI applied after veraison increased the concentration at harvest of key free terpenes for Gewürztraminer grapes such as geraniol and citronellol. RDI treatments down-regulated some terpene genes, which indicates that the observed changes in terpene concentration were not transcriptionally regulated. This study suggests that RDI applied after version can potentially improve wine aroma in Gewürztraminer.

Effects of regulated deficit irrigation applied at different growth stages of greenhouse grown tomato on substrate moisture, yield, fruit quality, and physiological traits.

Given a critical water scarcity in arid and semi-arid Tunisian areas and aiming to reduce irrigation water request, it is crucial to identify and apply the best water-saving practices in these irrigated areas. Tomato is a high-water-requiring vegetable crop, thus increasing the pressure on water resources and environment. Its sustainable cultivation in such alarming conditions requires an adaptation of on-farm irrigation water-saving strategies preserving also the crop yield and leading to a fruit quality improvement. This study aimed to explore the effects of the regulated deficit irrigation (RDI) as an irrigation water-saving strategy, on yield, fruit quality, and physiological behavior of greenhouse grown potted tomato crop (Solanum lycopersicum L.) during three identified growth stages. The managed water regimes were (i) full irrigation (FI) ensuring 100% of the estimated water crop requirements, (ii) RDI1-25 and RDI1-50 ensuring respectively 75% and 50% of FI water supplies during the vegetative crop stage (stage I), (iii) RDI2-25 and RDI2-50 ensuring respectively 75% and 50% of FI water supplies from first truss blossom until first harvest (stage II), and (iv) RDI3-25 and RDI3-50 ensuring respectively 75% and 50% of FI supplies during the rest of the harvest period (stage III). The results showed that the substrate moisture vary significantly with the water deficit regime applied under different growth stages, thus providing different levels of substrate water content. Under RDI2, the tomato yield was the highest when compared with FI, RDI1, and RDI3 regimes. Indeed, saving the water by 20% under RDI2-50 reduced only 3% of tomato yield. Deficit irrigation under ripening fruit and flowering stages, mainly with 50% of water supplies shortage, resulted in higher fruit skin color, firmness, and refractometry index (°Brix) when compared to FI and RDI1. Physiological traits measurements indicated that FI exhibited the highest leaf stomatal conductance (gs) and chlorophyll index (CI) values while RDI3 exhibited the lowest gs and CI values among all the RDI treatments. Results are valuable in considering gs and CI as an efficient indicators of tomato plant water status. The results are also an important contribution to identify the second tomato growth stage as the best period that tomato plant tolerate water shortage without significant yield decrease, as well a rather fruit quality improvement. These results help to reach the challenge "more crop per drop" and can contribute to water scarcity remediation.

Stem water potential-based regulated deficit irrigation scheduling for olive table trees

Regulated deficit irrigation (RDI) involves water stress management in different phenological periods throughout the season. Research in olive trees (oil production) suggested RDI during pit hardening based in pre-dawn and midday stem water potential (SWP) thresholds. However, the previous thresholds may not be extrapolated to table olive because fruit size, a very important feature in the table olive yield quality, is very sensitive to water stress. RDI in table olive deserve further research to determine the optimal water potential thresholds and the duration of the RDI periods for the specificity of the crop (low crop load to promote high fruit size). The aim of this work was to study different RDI schedules during pit hardening, considering different levels and durations of water stress. The experiment was performed in the 2015, 2016 and 2017 seasons, in a commercial mature table olive orchard (cv. Manzanilla) in Dos Hermanas (Seville, Spain). Control treatments were based on midday SWP measurement in order to optimize the water status with values around −1.4 MPa. Two RDI treatments were applied during pit hardening, dated (according to the changes in longitudinal fruit growth) from mid-June to the last week of August) to maintain water potential values around −2 MPa (RDI-1) and −3.5 MPa (RDI-3). Another RDI treatment (RDI-2) received irrigation to maintain values around −3.5 MPa but the recovery was performed at early July in order to obtain different durations of water stress. Irrigation strategies were evaluated with water relations measurements (soil moisture, gas exchange), fruit and shoot growth and quality and quantity yield indicators. Yield was not significantly affected in any of the RDI treatments with an ANOVA analysis. However, fruit drop estimated as the percentage of fruit lost only in the period of water deficit was related with water stress parameters (SWP and stress integral, IS). In addition, the relationship between fruits size and these latter parameters were significant and change according to yield level. Irrigation treatments did not affect next season yield because shoot growth and number of inflorescence at the beginning of each season were not different. RDI effect changed according to yield level, mainly in relation with fruit size. Data suggest that yield levels up to 12 t ha−1 were possible to manage RDI without affecting fruit size or reducing commercial quality.

Potential of UAS-Based Remote Sensing for Estimating Tree Water Status and Yield in Sweet Cherry Trees

The present work aims to assess the usefulness of five vegetation indices (VI) derived from multispectral UAS imagery to capture the effects of deficit irrigation on the canopy structure of sweet cherry trees (Prunus avium L.) in southeastern Spain. Three irrigation treatments were assayed, a control treatment and two regulated deficit irrigation treatments. Four airborne flights were carried out during two consecutive seasons; to compare the results of the remote sensing VI, the conventional and continuous water status indicators commonly used to manage sweet cherry tree irrigation were measured, including midday stem water potential (Ψs) and maximum daily shrinkage (MDS). Simple regression between individual VIs and Ψs or MDS found stronger relationships in postharvest than in preharvest. Thus, the normalized difference vegetation index (NDVI), resulted in the strongest relationship with Ψs (r2 = 0.67) and MDS (r2 = 0.45), followed by the normalized difference red edge (NDRE). The sensitivity analysis identified the optimal soil adjusted vegetation index (OSAVI) as the VI with the highest coefficient of variation in postharvest and the difference vegetation index (DVI) in preharvest. A new index is proposed, the transformed red range vegetation index (TRRVI), which was the only VI able to statistically identify a slight water deficit applied in preharvest. The combination of the VIs studied was used in two machine learning models, decision tree and artificial neural networks, to estimate the extra labor needed for harvesting and the sweet cherry yield.

Spring deficit irrigation in olive (cv. Genovesa) growing under arid continental climate: Effects on vegetative growth and productive parameters

This study was aimed to evaluate the effect of regulated deficit irrigation (RDI), applied from mid-spring to early summer, on physiological parameters, vegetative growth and productivity in an intensive hedgerow olive orchard located in a non-traditional (marked winter-spring water-deficit) olive growing region. The experiments were carried out during three crop seasons by using four years old (7 m × 3.5 m) ‘Genovesa’ olive trees. Three RDI treatments (T25, T50 and T75) were applied as a percentage of crop evapotranspiration (25, 50 and 75% ETc, respectively) during the period from fruit set to pit hardening. Also, a control treatment was irrigated at 100% ETc during the whole crop season. Under the analyzed environmental conditions, stomatal conductance was less sensitive in young leaves than in mature leaves against changes in water availability. This fact should be considered when being used as benchmarks in olives trees submitted to water deprivation during periods with marked water constraint. Regarding vegetative parameters, significant reductions in apical vegetative shoot growth, trunk cross-sectional area and canopy volume were found in less irrigated treatments (T25 and T50) with respect to most irrigated ones (T75 and T100). Moreover, the strongest effects of deficit irrigation were observed when pruning was applied at the end of the second crop season evaluated. Both fruit and oil yields were barely affected by water availability. Although in the first crop season evaluated the fruit yield was greater in the full-irrigation treatment – which could be due to the age of the olive trees -, at the end of the whole experimental period (three crop years) the mean values from this yield component did not present significant differences among all irrigation treatments. Similarly, water availability did not affect oil yield (kg/ha); no significant differences were found among irrigation treatments in any of the crop seasons analyzed. The effects of water availability on productive parameters were more evident when analyzed as an estimated productive response; the total water productivity, calculated on both fruit weight and oil weight bases, gave the highest values in the most restrictive irrigation treatment. Overall, findings from this study could be of interest for olive cultivation in regions with dry spring period and for intensive hedgerow orchards suited to over-row harvesters. Imposing water restriction during this period could be suitable for achieving sustainable fruit and oil productivity while saving considerable amount of irrigation water.

Effect of Preveraison Water Deficits on the Yield Components of 15 Winegrape Cultivars

Accurate information regarding crop reproductive development and yield formation in response to water deficits is needed for informed vineyard irrigation management decisions, particularly when water supply is limiting. Fifteen red winegrape cultivars grown in the San Joaquin Valley of California were subjected to two regulated deficit irrigation (RDI) treatments for four years to determine yield component responses to water deficits (no applied water) preveraison (ED) and postveraison (LD). In the fifth year, the cultivars were kept well-watered to determine carryover effects. In the first four years, early water deficits (ED) consistently and significantly reduced yields compared to the control (sustained deficit, SD; applied water at 50% of estimated crop evapotranspiration (ETc) throughout the growing season) across all years and cultivars, but the late (postveraison) deficit (LD) treatment vines were not different from the control. The reduction in yield with ED was primarily due to a significant reduction in berry fresh weight (FW) and clusters per vine, with little change in berries per cluster. Neither flowers per cluster nor percent berry set were affected by the treatments, although flowers per cluster varied significantly among cultivars. Berries per cluster increased linearly with flowers per cluster until saturation at ~150 berries per cluster as percent berry set declined at ~250 flowers per cluster. In the fifth year, yields of the two RDI treatments recovered somewhat because of increases in berry FW and a small, but significant, increase in clusters per vine. These results show that berry size, because of a reduction in FW, is the most sensitive yield component to water deficits, followed by clusters per vine and berries per cluster, with sensitivity maximum preveraison and few differences among cultivars.

Influence of Regulated Deficit Irrigation and Environmental Conditions on Reproductive Response of Sweet Cherry Trees.

The reproductive response of fifteen year old sweet cherry trees (Prunus avium L.) combination ‘Prime Giant’/SL64 under Mediterranean climate to deficit irrigation was studied in a commercial orchard in south-eastern Spain for four seasons. Three irrigation treatments were assayed: (i) control treatment, irrigated without restrictions at 110% of seasonal crop evapotranspiration; (ii) sustained deficit irrigation treatment, irrigated at 85% ETc during pre-harvest and post-harvest periods, and at 100% ETc during floral differentiation, and (iii) regulated deficit irrigation treatment, irrigated at 100% ETc during pre-harvest and floral differentiation and at 55% ETc during post-harvest. The duration and intensity of the phenological phases of sweet cherry trees, including cold accumulation, flowering, fruit set or fruit and vegetative growth, were assessed to ascertain whether the different irrigation strategies imposed affect the trees’ reproductive response (fruit yield, fruit size, leaf area, fruit physiological disturbances, and starch and soluble carbohydrates stock) in the same season or have a negative effect in the next season. Deficit irrigation did not advance, enhance or penalize flowering, fruit set or fruit growth. Neither did it diminish carbohydrate concentration in roots or cause an increase in the number of double fruits, which was more linked to high temperatures after harvest. However, deficit irrigation decreased vegetative growth and consequently the leaf area/fruit ratio, which, when it fell below 180 cm2 fruit−1, affected cherry size.

Effect of regulated deficit irrigation on the content of soluble sugars, organic acids and endogenous hormones in Cabernet Sauvignon in the Ningxia region of China

The aim of this work, which was conducted in 2017 and 2018, was to gain insight into the effects of regulated deficit irrigation (RDI) treatments on the content of soluble sugars, organic acids and endogenous hormones in Cabernet Sauvignon. The RDI treatments slightly decreased the hundred-grain weight and total acid content before vintage but significantly increased the soluble solids content, juice pH and reducing sugar content. The glucose and fructose contents were increased by the RDI treatments, and the ratio of G:F was reduced. Most genes associated with sugar unloading were upregulated by RDI, especially in the RDI1 group. The tartaric acid, malic acid and citric acid contents were decreased by RDI. Under the RDI treatments, the ABA content increased from E-L 33 to 38, and the IAA, GA3, JA-Me and BR contents decreased from E-L 33 to 34. The results of this study ultimately benefit the promotion of RDI measures, and our data might be useful for the improvement of wine grape quality.

Does partial root-zone drying have advantages over regulated deficit irrigation in pear orchard under desert climates?

The impacts of partial root-zone drying (PRD) and regulated deficit irrigation (RDI) with the same irrigation volume on vegetative and fruit growth and leaf physiological parameters of pear trees planted under desert climate were evaluated. The experiment involved RDI and PRD treatment, irrigated with the 50 % replacement of pan evaporation (Ep) during the slow fruit growth stage, and 80 % replacement of Ep during rapid fruit enlargement stage. Control trees were irrigated with the 80 % replacement of Ep during the whole growing season. No significant differences in the soil and leaf water status between PRD and RDI were observed, which resulted in the similar vegetative growth, fruit yield and leaf gas exchange between PRD and RDI trees. In conclusion, the leaf gas exchange, the vegetative and fruit growth of pear trees planted under extreme drought condition were mainly controlled by the irrigation volume rather than the irrigation method. Therefore, application of the PRD technique was not recommended in the extremely arid region compared with the RDI strategy.