Regulated Deficit Irrigation Treatments Research Articles

Crop load regulation and irrigation strategies to accelerate the recovery of previously water-stressed Japanese plum trees

Regulated deficit irrigation (RDI) has been proven as a useful irrigation strategy in a wide range of fruit crops to deal with water scarcity. However, long-term RDI techniques in developing orchards can reduce tree growth resulting in a loss of tree yield capacity. Strategies that could be used to quickly recover trees from the possible carry-over effects of long-term deficit irrigation are then of physiological and commercial interest. Tree crop load is a determinant factor of the carbohydrates partitioning between fruit and vegetative sinks, being fruit sink strength higher than that of vegetative organs. The working hypothesis of this study was that tree crop load reduction could be employed to alleviate the detrimental effects that long lasting RDI strategies have on tree growth. The recovery of a young plum Japanese orchard (Prunus salicina, cv. ‘Black Gold’) after seven seasons under RDI was studied by testing combinations of two crop load levels (medium and low), two drip irrigation regimes [100 and 133% of crop evapotranspiration (ETc)] and two different number of emitters per tree (six and eight). Results showed that treatments applied led former RDI treatment trees to significantly reduce their differences in tree shaded area and particularly in trunk perimeter with respect to the control treatment trees. After two seasons of treatments, differences in yield, economic return and number of fruit per tree were exclusively due to the crop load levels imposed and not to a smaller size of former RDI treatment trees. Trees watered at 133% ETc and thinned at low crop load, which underwent a very severe RDI strategy previous to this experiment, were the trees that showed the greatest recovery in tree size. In this treatment, the lower competition between fruit and vegetative growth and the increase in the soil wetting area by using a higher number of emitters per tree, probably favored root growth significantly increasing tree growth with respect to the other treatments. Overall, this work shows that crop load regulation is a useful tool to quickly recover plum trees from the detrimental effects of long-term deficit irrigation.

Effects of irrigation and fruit position on size, colour, firmness and sugar contents of fruits in a mid-late maturing peach cultivar

Experiments were conducted on a mid-late maturing peach (Prunus persica) cv. ‘Catherine’ in 2008 in order to study the influences of irrigation and fruit location within the canopy, on fruit growth and several fruit-quality attributes, including sugar and acid contents. Trees were subjected to full irrigation (FI) and regulated deficit irrigation (RDI). Fruit height in the crown, exposure to sunlight and orientation were recorded. Fruit diameter, fresh weight, firmness, flesh and skin colour attributes, soluble solids content, pH and sugar and acid contents were determined for each fruit at harvest. Water stress had a high impact on most of the fruit-quality variables studied. Fruits from trees under RDI were firmer than those from FI trees but did not differ in weight and diameter, perhaps due to the low crop load supported by the studied trees. In contrast, fruits from RDI trees had more soluble solids, glucose, sorbitol, and malic, citric and tartaric acids. Height in the crown partially affected positively soluble solids content. Exposure to sunlight strongly influenced stone dry weight and soluble solid content. Finally, orientation did not have a significant influence on most of the fruit-quality attributes considered in this study. Our results suggested that leaving a low crop load on the tree maintaining fruits only in the most ideal parts of the canopy may improve fruit quality under water restriction conditions. In this way, the negative effects of water stress may be counteracted and fruit quality for this mid-late maturing peach cultivar would be improved.

Regulated deficit irrigation based on threshold values of trunk diameter fluctuation indicators in table olive trees

The aim of this study was to establish threshold TGR and MDS values which could be used in regulated deficit irrigation in future work. Three irrigation treatments were performed during three seasons in a 37 year-old table olive orchard in Seville (Spain). Control treatment was irrigated with 125% of the crop evapotranspiration. Regulated deficit irrigation (RDI) treatments were performed according to the phenological stage of the trees and different water stress levels. RDI trees were irrigated only when the threshold values of water stress level was reached. Water stress conditions were applied during the massive pit hardening period (phase II, RDI-2) or during this period and the shoot-flowering period (phase I, RDI-12). The water stress level was performed with the trunk growth rate (TGR) during phase I and recovery and maximum daily shrinkage signal (MDS signal) during phase II. Both parameters were calculated as relative values of the Control trees. TGR threshold values varied from equal to Control (RDI-2) or 0.25μm day−1 less than Control (RDI-12) during phase I. MDS signal (ratio between MDS in RDI vs MDS Control) threshold values varied from 0.5 (RDI-12) to 0.75 (RDI-2). In the recovery period, trees were irrigated when TGR values were lower than Control. This scheduled changed the amount of applied water between high and low fruit load seasons. The total amount of applied water in RDI trees oscillated from 38 to 160mm, depending on the season and the treatment. The yield was not significantly different between Control and deficit treatments. Fruit volume and number of fruits was affected for the irrigation. Limitations and management of TDF in irrigation scheduling is discussed.

Sensory Impact of Extended Maceration and Regulated Deficit Irrigation on Washington State Cabernet Sauvignon Wines

Irrigation practices such as regulated deficit irrigation (RDI) and winemaking practices such as extended maceration have been experimentally evaluated from a chemical perspective but their impacts on sensory composition and interactive effects merit scientific attention. This study evaluated the sensory impact of extended maceration applied to Cabernet Sauvignon grapes sourced from a vineyard subjected to four RDI treatments: replenishment of 100%, 70%, and 25% of full-vine crop evapotranspiration (ETc) from fruit set until veraison followed by 100% ETc until harvest (labeled 100% ETc, 70% ETc, and 25% ETc, respectively) and 25% ETc from fruit set to veraison followed by 100% ETc from veraison to harvest (labeled 25/100% ETc). Each RDI treatment was replicated four times (n = 4) and made into wine, with two replicates designated as controls (10 day skin contact) and two as extended maceration (30 day skin contact). Wines were evaluated by descriptive analysis with a trained panel (n = 15) and chemical and sensory data were correlated using canonical correlation analysis. Wine-perceived saturation and purple component ratings were highest in 25% ETc wines and were highly correlated with the concentration of flavonols, malvidin- and delphinidin-derivatives, and small polymeric pigments. Fruit-based aroma descriptors were highest in the 25/100% ETc and 70% ETc wines. Extended maceration increased perceived astringency and bitterness, which were in turn correlated with the concentration of flavan-3-ol and oligomeric proanthocyanidins. These results suggest that moderate RDI protocols such as 70% ETc and 25/100% ETc impact positively the fruity aroma component (black and red fruit), whereas extended maceration lowered fruity aromas, possibly due to the masking effect of the oxidized character perceived in these wines.

Soil Nutrients and Grain Yield Performance in Spring Wheat (<i>Triticum aestivum</i>) as Influenced by Regulated Deficit Irrigation

A field trial was conducted in 2007 and 2008 to investigate the difference in soil nutrients and grain yield of spring wheat (Triticum aestivum) as influenced by regulated deficit irrigation (RDI) in an arid area. Three RDI treatments and a no-water-deficit control (CK) were designed to subject wheat to various degrees of soil water deficit at different crop developmental stages. Significant differences (p<0.05) occurred in soil organic matter (SOM) and soil available potassium (SAK) contents in both growing seasons, but no difference (p>0.05) occurred among the RDI treatments. Meanwhile, no differences were found in soil total nitrogen (STN) and soil total phosphorus (STP) contents among the treatments and CK. SOM content was improved by 6.2% to 7.2% in RDI treatments than in the CK over the two growing seasons, while the STN, STP, and SAK contents were increased by 1.2% to 2.5%, 1.4% to 5.6%, and 9.0% to 11.2%, respectiely. The STP (t=10.900, p<0.001), soil available phosphorus (SAP, t=8.894, p<0.001), and SAK (t=11.706, p<0.001) contents in 0~40 cm soil layer at wheat harvest were significantly lower in 2008 than in 2007, while the SOM (t=-2.513, p<0.05) and STN (t=-9.950, p<0.001) contents were significantly higher in 2008. Soil organic C, STN, and SAP balance was greatly influenced by RDI in two growing seasons. Compared to the no-water-deficit control, grain yields over the two years were respectively improved by 16.5% to 24.9% in RDI plots.The relationship between grain yield and the soil nutrients was described as y=15843.4 +713.3SOM-20989.1STN+38.7SAN-15.0SAP-39.7SAK (R2=1, p<0.001).

Impact of Extended Maceration and Regulated Deficit Irrigation (RDI) in Cabernet Sauvignon Wines: Characterization of Proanthocyanidin Distribution, Anthocyanin Extraction, and Chromatic Properties

The impact of extended maceration (EM) was studied in Cabernet Sauvignon grapes sourced from a vineyard subjected to four regulated deficit irrigation (RDI) treatments: (I) 100% replenishment of crop evapotranspiration (100% ETc), (II) 70% ETc, (III) 25% ETc until véraison, followed by 100% ETc until harvest, and IV) 25% ETc. Each vineyard replicate was made into wine with two replicates designated as controls (10-day skin contact) and two as extended maceration (EM, 30-day skin contact). The mean degree of polymerization (mDP), size distribution, concentration, and composition of wine proanthocyanidins (PAs) and monomeric flavan-3-ols of 90 fractions were characterized by preparative and analytical HPLC techniques. The maceration length imparted a larger effect on most chemical parameters. The RDI treatment had no effect on the extraction patterns of anthocyanins, PAs, and/or on the origin of the PAs extracted into the wines. Conversely, EM led to anthocyanin losses and increased PA extraction during maceration, with ~73% of seed-derived PAs. Accordingly, the concentration of monomeric flavan-3-ols, oligomeric (2 ≤ mDP < 5) and polymeric PAs (mDP ≥ 5) was higher in EM wines. The size distribution of the wines' PAs revealed two major peaks as a function of concentration at mDP 2 (22-27% of total PAs mass) and at mDP 6-7 (12-17% of total PAs mass) and was found to follow a non-normal Rayleigh-type distribution.

Regulated deficit irrigation in persimmon trees (Diospyros kaki) cv. ‘Rojo Brillante’

The response of persimmon trees to deficit irrigation applied in three different phenological stages was evaluated during three consecutive seasons in a commercial orchard planted with the cv. ‘Rojo Brillante’, the most important cultivar in the Mediterranean basin. The experiment was performed in a drip-irrigated orchard located in Valencia, Spain, planted with eight-year-old trees at a spacing of 5.5m×4m and grafted on the rootstock Diospyrus lotus. Three regulated deficit irrigation (RDI) regimes were tested and compared to a Control treatment irrigated at full water requirements. In the RDI treatments, moderate water restrictions (50% of Control irrigation), were applied during one of three periods (i) RDIspring, where water restrictions were applied from late May to mid July; (ii) RDIsummer, deficit irrigated from mid July to late August and; (iii) RDIfall, in which water restrictions were applied from late August early September to mid November. Results showed that persimmon fruit growth was sensitive to water stress. RDI reduced final fruit weight being this reduction more marked in the most stressed treatment (RDIsummer). This decrease in fruit weight was also because spring and specially summer RDI treatments increased the number of fruit harvested. Thus, RDI techniques allowed water savings of up to 20% without any reduction in yield increasing significantly the water use efficiency. In spite of the similar yields obtained in RDI and control trees, the economic return was negatively affected by deficit irrigation, because the lower fruit weight resulted in a decrease in the fruit commercial value. In conclusion, fruit growth of persimmon cv. ‘Rojo Brillante’ was shown as highly sensitive to deficit irrigation. Based on the results obtained, RDI would need further research in order to define an RDI strategy that could increase water use efficiency without affecting the economic return.

Effect of deficit irrigation on crop growth, yield and quality of onion in subsurface drip irrigation

India has the largest area under onion (Allium cepa) crop but its average productivity (14.21 t ha -1 ) is considerably lower than the world’s average of 19.4 t ha -1 . Besides low productivity, irrigation efficiencies are also very low i.e. 30-35% in India. Managing onion crop with less than adequate irrigation water availability is a challenge in several parts of the country. Options of i) deficit irrigation (DI) i.e. 20% or 40% less water application at one of the growth stages of the crop and ii) controlled deficit of 20% or 40% on all growth stages i.e. regulated deficit irrigation (RDI) were explored for maximizing IWUE of onion under deficit water application through subsurface drip irrigation. A field experiment was conducted on onion (var. Agrifound light red) for three years from October to May in 2007-08, 2008-09 and 2009-10 to study the effect of DI and RDI on onion yield and its quality under subsurface drip irrigation. In DI treatments, the crop was provided the irrigation with 60% and 80% of ETc creating water stress of 40 and 20%, respectively at developmental (2 nd ), bulb formation (3 rd ) and bulb maturity (4 th ) crop growth stages. In case of RDI treatments, 20% and 40% water stress was created throughout the crop season by applying the irrigation water at 80% and 60% ETc. The maximum yield (44.7 t ha -1 ) was obtained in the full-irrigation treatment (T1). In RDI, 20 and 40% deficit water application saved 19.2 and 41.7% water and resulted in 20 and 32% reduction in yield, respectively. In DI, 20% water deficit in the growth stages of 2 nd , 3 rd and 4 th saved 2.1, 13.2 and 4.6% of water with 19.8, 18.3 and 11.2% reduction in yield, respectively in comparison to full irrigation water application. This suggests that RDI is better option of water saving than DI. Saving of water through RDI may be used to irrigate additional cropped area. Strategy suggested for productions of onion crop can be adopted in large scale to offset high cost of onion, which is cause of concern for all stake holders.

Thermographic measurement of canopy temperature is a useful tool for predicting water deficit effects on fruit weight in citrus trees

Alternative and more practical methods for plant water stress detection than stem water potential (ψs) and stomatal conductance (gs) are needed when regulated deficit irrigation (RDI) strategies are applied. The aim of this experiment was to compare sap flow and canopy temperature (Tc) measurements with more classical methods like ψs or gs to predict the effect of deficit irrigation on fresh fruit weight in citrus trees. The experiment was performed during the summer of 2011 in a “Clementina de Nules” orchard undergoing RDI. Sap flow was determined by means of the compensation heat pulse method in well-watered and RDI trees. Tc was measured continuously with infrared thermometers (IRTs) mounted over the canopies and also weekly with an infrared hand-operated thermographic camera taking frontal images of the sunlit side of tree crowns. Concurrently, ψs and gs were also measured on all trees. Results showed that the evolution of the relative transpiration obtained with the sap flow sensors was in agreement with the plant water stress experienced. The values of Tc obtained with the fixed IRTs, normalized by air temperature (Tc−Ta) were in general poorly related with ψs and gs. However, when Tc was obtained from thermal imaging, there was a good correlation with ψs in days of relatively high water stress (i.e. when ψs differences among treatments were >1.0MPa). The average fruit weight at harvest was significantly correlated with all the stress indicators, and the best correlation was that of thermographic Tc followed by ψs and gs. Overall, results showed that in citrus trees Tc measurement obtained from thermal imaging is a good tool to predict the effect of water deficit on fresh fruit weight.

Regulated Deficit Irrigation based upon optimum water status improves phenolic composition in Monastrell grapes and wines

The effects of three deficit irrigation strategies pre and post-véraison, on soil–plant water status and their influence on leaf area, cluster microclimate, fruit growth, yield and berry and wine quality were evaluated for three years (2009–2011) in field-grown Monastrell grapevines under semiarid conditions in South-Eastern (SE) Spain. Three treatments were applied: a Sustained Deficit Irrigated treatment (SDI) was irrigated at 40% of the Crop Evapotranspiration (ETc) throughout the orchard cycle, 211mmyear−1; a Regulated Deficit Irrigation treatment 1 (RDI-1threholds) received 30% ETc (2009 and 2010) or 20% ETc (2011) from budburst to fruit set. From fruit set to harvest the irrigation was established by maintaining an average mid-day stem water potential (Ψs) within the range −1.2>Ψs≥−1.3MPa and from véraison to harvest within the range −1.3>Ψs>−1.4MPa, 106mmyear−1); And a Regulated Deficit Irrigation treatment 2 (RDI-2cutoff-thresholds) received 20% ETc (2009 and 2010) or 10% ETc (2011) from budburst to fruit set and from fruit set to véraison an irrigation cut-off was applied. Then, from véraison to harvest, an irrigation recovery was applied based on maintaining mid-day Ψs within the range of Ψs proposed: −1.3>Ψs>−1.4MPa (similar to RDI-1), 76mmyear−1). A recovery of irrigation at 40% ETc was used in all treatments from harvest to leaf fall. The RDI-1thresholds strategy, which applied moderate water stress during pre and post-véraison, saved water, reduced vine vigor and vegetative development, controlled yield, improved cluster microclimate, maintained similar or even higher sugar content in the berries and improved the phenolic composition of Monastrell grapes and wines compared to the SDI and RDI-2 strategies. RDI-1thresholds vines increased color intensity, sugar and total anthocyanins in the berries, and color intensity, alcohol content, concentration of polyphenols and total anthocyanins and flavonols in the wines. In contrast, in the RDI-2cutoff-thresholds strategy, which had complete irrigation cut-off during the pre-véraison period (from fruit set to véraison) substantially decreased lateral shoot and berry growth at véraison, and also excessively reduced photosynthetic activity, water status pre-véraison and the resilience of photosynthesis during véraison- early ripening period, which was not beneficial from a physiological and agronomical point of view for Monastrell grapevines in SE Spain.

Legume Production and Irrigation Strategies in the Aral Sea Basin: Yield, Yield Components, Water Relations and Crop Development of Common Bean (Phaseolus vulgaris L.) and Mungbean (Vigna radiata (L.) Wilczek)

AbstractWith world population expected to reach 9.2 billion people by 2050, improved irrigation methods will be needed to increase the productivity of agricultural land and improve food supply worldwide. The objective of this work was to examine the effect of regulated deficit irrigation (RDI) and alternate furrow irrigation (AFI) on the yield and yield components of two legume species (common bean and mungbean) produced as a second crop following winter wheat in Uzbekistan, Central Asia. Water relations and crop development were also examined. The research was conducted during two successive growing seasons in the Fergana valley. Production of mungbean using the severe stress RDI treatment in combination with AFI resulted in the highest yields with the lowest quantity of applied water in 2004. In addition, yields of common bean in the moderate stress treatment were not different from the recommended schedule, although irrigation events were decreased from 4 to 2. AFI did not reduce yields, and it did not interact with RDI to reduce yields further. In general, mungbean yields were higher than those of common bean. The combination of AFI and RDI can allow legume production with reduced water inputs.

Effect of Regulated Deficit Irrigation on Productivity, Quality and Water Use in Olive cv “Manzanilla”

The objective of this experiment was to determine the effect of different regulated deficit irrigation (RDI) strategies on productivity, oil quality and water-use efficiency on olive grown in the Sonoran Desert. The experiments were carried out in 2009 and 2010, and in a ten years old traditional (10 × 5 m) “Manzanilla” olive orchard. The control treatment was irrigated at 100% ETc during the whole season while RDI treatments were applied at 75% ETc or 50% ETc. The two RDI were applied during two phenological stages: at postharvest to evaluate the effect on table olive or from pit hardening to harvest to evaluate the effect on oil olive. Our results indicated that RDI applying 50% ETc during postharvest period reduced significantly fruit set and table olive yield, while applied during pit hardening to harvest period, it decreased oil yield but increased oil content. The RDI applying an ETc of 75% during the postharvest period gave similar table olive yield to the control, and applied form of pit hardening to harvest also gave similar oil yield to the control. The RDI using an ETc of 75% resulted in the highest water-use efficiency for oil or table olive production.

Regulated deficit irrigation in different phenological stages of potted geranium plants: water consumption, water relations and ornamental quality

The irrigation water requirements and sensitivity to water deficits of ornamental plants is of great interest to horticultural producers for planning irrigation strategies. The effect of different deficit irrigation strategies on physiological and morphological parameters in geranium plants was studied in different growth phases to evaluate how such strategies can be safely used and to ascertain whether the flowering phase is sensitive to deficit irrigation. Pelargonium × hortorum L.H. Bailey plants, grown in a controlled growth chamber, were subjected to four irrigation treatments: control (100 % water field capacity throughout the experiment), sustainable deficit irrigation (75 % water field capacity throughout the experiment), and two regulated deficit irrigation treatments that included water stress during the vegetative growth phase or during the flowering development phase. Although the total amount of irrigation water was similar in the three deficit irrigation treatments (around 80 % of the control value), the lowest values for both height and flowering were found when deficit irrigation was applied during flowering. This indicates that plant quality does not only depend on the amount of water applied but also on the time when the reduction is applied, and that flowering is the most sensitive phase to water stress. Evapotranspiration was related to the formation of inflorescences and to increased plant height. When the irrigation strategy was changed, plants increased or decreased their water consumption and stomatal conductance to adjust to the new conditions by regulating stomatal opening, although, in general, the values of both parameters remained below those observed in the control plants.

Transient soil salinity under the combined effect of reclaimed water and regulated deficit drip irrigation of Mandarin trees

Regulated deficit irrigation (RDI) strategy using saline reclaimed water is becoming a frequent practice under semiarid Mediterranean climatic conditions in the southeastern region of Spain. There is a concern that the long-term use of this strategy will affect the production sustainability of the agricultural soils. This paper evaluates the field consequences of this strategy on the accumulation of salts within the plant root zone. Full and regulated deficit surface drip deficit irrigation was combined with fresh water (EC 1dSm−1) and saline (EC 3dSm−1) tertiary reclaimed water to irrigate adult mandarin trees over a 3-year period. The control treatment received 100% of the crop evapotranspiration “ETc” and the RDI treatment received 50% of ETc during the 2nd stage of fruit growth. Soil water content was monitored every other week within the soil wetted volume under the emitter. Gravimetric soil samples were collected from 3 depths and at 3 distances to the emitter, twice a year: at the end of irrigation season and at the conclusion of RDI period. Soluble salts, electrical conductivity and sodium adsorption ratio were determined in the saturated paste extract. The results show how the RDI strategy intensifies the development of salinity gradient away from the emitter even when using good quality water. The combination of RDI with saline reclaimed water produced transient saline-sodic conditions at the outer superficial limits of the wetted bulb under the emitter. The appearance of such adverse conditions is alarming and would threaten the sustainability of agricultural soils. Therefore soil water deficit should be avoided whenever saline reclaimed water is in use for irrigation.

Steps toward an improvement in process-based models of water use by fruit trees: A case study in olive

We applied two process-based models in a hedgerow olive orchard with the aim of understanding the limitations and mechanisms behind the control of transpiration in olive trees under drip irrigation. One model is based on the biophysics of water flow through the porous media of soil and xylem. The other is a hydromechanical model based on the observed dependence of stomatal aperture on whole-plant and epidermis water relations. The experiments were made in a hedgerow olive orchard (1667treesha−1) planted with 5-year-old ‘Arbequina’ trees. Measurements were made in control trees irrigated to replace 100% of the crop water needs, and in trees under regulated deficit irrigation (RDI) strategy, in which irrigation replaced ca. 30% of the control. Soil physical properties, root distribution, leaf area, sap flow, leaf osmotic pressure and key variables of leaf gas exchange and water status were measured and models were applied. Results show how in our orchard, with a shallow root distribution and very coarse soil, most of the limitation to transpiration was imposed by the hydraulics of the rhizosphere. The model shows how this limitation was related to the ratio of root to leaf area, and how this ratio can be managed by canopy pruning or by changing the number of drippers. Likewise, osmotic adjustment occurred similarly in both irrigation treatments, despite differences found on leaf water potential. Water stress largely affected plant hydraulic conductivity of RDI trees. A potential involvement of regulating signals, other than purely hydraulics, was evident in both treatments, although our data suggests that these signals were not regulated by the soil water status only.

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.

Impact of water stress on citrus yield

Water shortage is becoming a severe problem in arid and semi-arid regions worldwide, reducing the availability of agricultural land and water resources. Deficit irrigation strategies can improve water-use efficiency and the sustainability of agro-ecosystems, although it is important to model the effects on yield loss due to irrigation water restrictions. This work estimates the water production function in citrus trees, determining the relationship between plant water stress and yield depression, as well as establishing a mathematical model for each phenological stage considered (flowering, fruit growth and ripening), and for the entire productive process. For three consecutive years (2006–2008), four regulated deficit irrigation treatments plus a control (100% crop water evapotranspiration (ETC)) were implemented in 13-year-old citrus trees (Citrus sinensis L. Osb. cv. Navelina). Different water production functions were determined for each phenological stage, establishing the relationship between the irrigation water stress and crop yield. Our results show that the fruit growth and flowering stages were the most sensitive periods in relation to irrigation water deficit and yield loss. Water stress close to 50% of ETC during the flowering stage would impose a yield loss of up to 20%, whereas this same water stress level during the fruit growth or ripening stages would result in yield losses of nearly 10% and 6%, respectively. The adjustment with cross terms (r 2 = 0.87) estimated the yield loss with good accuracy, being very similar to data measured in each study season. Consequently, the combined effect of deficit irrigation in different stages would be an additive–multiplicative model, considering that the effect of water stress in previous periods determined the crop yield response. Our model indicated that the crop water production function under deficit irrigation programmes would have a quasi-linear relation for water deficits below to 40% ETC. The previous model functions did not enable us to establish an accurate relationship when the water stress was applied in different phenological stages. Thus, this new interpretation is valuable to improve our knowledge and predict the impact of regulated deficit irrigation and have potential application in precision water stress and sustainable irrigation scheduling for citrus.

Online-monitoring of tree water stress in a hedgerow olive orchard using the leaf patch clamp pressure probe

Abstract The need for sophisticated irrigation strategies in fruit tree orchards has led to an increasing interest in reliable and robust sensor technology that allows automatic and continuous recording of the water stress of trees under field conditions. In this work we have evaluated the potential of the leaf patch clamp pressure (LPCP) probe for monitoring water stress in a 4-year-old ‘Arbequina’ hedgerow olive orchard with 1667 trees ha−1. The leaf patch output pressure (Pp) measured by the LPCP probe is inversely correlated with the leaf turgor pressure (>50 kPa). Measurements of Pp were made over the entire irrigation season of 2010 (April to November) on control trees, irrigated up to 100% of the crop water needs (ETc), and on trees under two regulated deficit irrigation (RDI) strategies. The 60RDI trees received 59.2% of ETc and the 30RDI trees received 29.4% of ETc. In the case of the RDI trees the irrigation amounts were particularly low during July and August, when the trees are less sensitive to water stress. At severe water stress levels (values of stem water potential dropped below ca. −1.70 MPa; turgor pressure

Fruit physical characteristics responses of young apricot trees to different irrigation regimes and yield, quality, vegetative growth, and evapotranspiration relations

This study was carried out to investigate effects of different irrigation regimes on fruit pomological properties of drip-irrigated young apricot trees in 2005 and 2008. Six different irrigation treatments were used: five of which (S1, S2, S3, S4, and S5) were based on adjustment coefficients of Class A pan evaporation (0.50, 0.75, 1.00, 1.25, and 1.50). The other treatment (S6) was regulated deficit irrigation treatment that was irrigated by applying 100% of Class A pan evaporation until harvest, but not irrigated after harvest in all the years of study. The effect of different water application levels on fruit weight, fruit diameter, fruit height, seed weight, and flesh / seed ratio was found statistically insignificant. Regression analysis showed that there were significant relations among fruit yield, some quality characteristics, vegetative growth, and evapotranspiration in both 2005 and 2008. Also, the yield per tree and evapotranspiration were related with high R2 values of 0.97 and 0.76 in 2005 and 2008, respectively. The fruit yield values showed an increasing trend depending on an increase in the tree crown volume, and trunk cross-section area in the experimental years. Fruit quality relationships weredifferent according to the years and quality properties. In 2008, fruit weight reduced while fruit yield increased with fruit diameter and fruit height of more than about 47 and 38 mm, respectively. Thus, it was understood that yield increased, depending on the number of fruit rather than the weight of fruit. Key words: Apricot, class a pan, drip-irrigation, evapotranspiration, fruit yield and quality, regulated deficit irrigation, vegetative growth.

LONG-TERM EFFECT OF WATER DEFICIT IRRIGATION ON CHERRY VIGOR AND PRECOCITY

Different post-harvest regulated deficit irrigation treatments were established in a young and vigorous commercial ‘Bing’ cherry (Prunus avium L.) orchard planted in dry shallow soil with drip irrigation. The treatments given over a three-year period were as follows: T1= 100%, T2= 75% and T3= 50% of full ETc. The available water remaining percentage (%AWr) and midday stem water potential (SWP) were measured during the water-deficit period. During the three-year period average SWP was -0.68, -0.83 and -1.04 MPa while %AWr was 89.9, 71.7 and 41.4 for T1, T2 and T3 respectively. SWP was highly correlated with %AWr (r2= 0.89). After three years trunk growth decreased by 6% (T2) and 10% (T3). Shoot length for T3 was 27% lower, flower bud density and yield efficiency were 85% and 57% higher when compared to T1. Seasonal shoot length was highly correlated with flower bud density on productive branches (r2= -0.76). Average fruit weight was not affected while double fruits were not substantially affected by treatments. An accurately adjusted post-harvest water deficit can be used to control vigor and promote early production of cherries, while saving significant amounts of water.