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.     

Postharvest regulated deficit irrigation in ‘Summit’ sweet cherry: fruit yield and quality in the following season

We examined, over the postharvest seasons of 2005–2007, regulated deficit irrigation (RDI) for its potential of saving water and maintaining fruit yield and quality in ‘Summit’ sweet cherry. The postharvest irrigation treatments were: full irrigation (Control), receiving 80% of water in Control (RDI-80%), and receiving 50% of water in Control (RDI-50%). Midday stem water potential (Ψ_stem) was used for assessing plant water status. In 2006, trees produced a large crop and commercial fruit thinning had to be applied, whereas 2007 was a low crop year. The RDI treatment, first applied in 2005, reduced fruit set in 2006 and also reduced root winter starch concentration. In 2006, fruit set was lower in RDI-50% than in Control. But fruit thinning had still to be done with the final yield being the same among treatments. In 2007, RDI-50% produced more fruit and higher yields than Control. Relationship between postharvest Ψ_stem and crop load in the following season varied according to the year. They were negatively correlated in 2006 and positively correlated in 2007. Fruit firmness did not vary with irrigation treatments in any of the years. Fruit soluble solid concentration (SSC) and fruit relative dry matter (RDM) for RDI-50% was the highest in 2006 when RDI-50% trees had the lowest fruit set. In 2007, SSC and RDM for RDI-50% were the lowest with the trees having the highest fruit set and crop load at harvest. This study indicates that RDI-50% firstly applied in an “off” year, after crop has been harvested, can maintain fruit yield at similar levels to fully irrigated trees while saving water by 45%. Correction of biennial bearing and partial saving of thinning costs are additional advantages of this treatment.     

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.     

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.     

The effects of crop load and irrigation rate in the oil accumulation stage on oil yield and water relations of ‘Koroneiki’ olives

The interactions between irrigation rates applied during the oil accumulation stage and crop load were studied in a six-year-old very-high-density Koroneiki (Olea europaea L.) orchard. Five irrigation rates, determined as thresholds of midday stem water potential, were applied from July 1st until harvest in 2008 and 2009 and from July 1st to the end of September in 2010. Oil yield increased with increasing crop load in all the irrigation treatments. Oil yield did not respond to increasing irrigation at very low crop load and the higher the crop load the higher the response to irrigation. There was no response to irrigation at the lowest crop loads, but the higher the irrigation rate the higher the oil yield at high crop loads. The predicted commercial oil yield at common fruit counts increased from 1.99 t/ha at the lowest irrigation rate to 3.06 t/ha at the highest irrigation rate. Stomatal conductance decreased with decreasing stem water potential but leveled off at 30–60 mmol m^?2 s^?1 at stem water potential values lower than ?4.0 MPa. High crop load increased stomatal conductance and decreased stem water potential relative to low crop load at low and medium irrigation rates. The effect of crop load on water relations became evident by the end of August and was well pronounced at the beginning of October. Physiological and irrigation water management implications related to the interactions between tree water status and crop load are discussed.     

Response of apricot trees to deficit irrigation strategies

During four growing seasons, 10-year-old apricot trees (Prunus armeniaca L., cv. ‘Búlida’) were submitted to three different drip irrigation regimes: (1) a control treatment, irrigated at 100% of seasonal crop evapotranspiration (ETc), (2) a continuous deficit irrigation (DI) treatment, irrigated at 50% of the control treatment, and (3) a regulated deficit irrigation (RDI) treatment, irrigated at 100% of ETc during the critical periods, which correspond to stage III of fruit growth and 2 months after harvest (early postharvest), and at 25% of ETc during the rest of the non-critical periods in the first two growing seasons and at 40% of ETc in the third and fourth. Soil–plant–water relation parameters were sensitive to the water deficits applied, which caused reductions in leaf and soil water potentials. The longer and severer deficits of the RDI treatment decreased fruit yield in the first two seasons. The RDI treatment pointed to two threshold values that defined the level at which both plant growth and yield were negatively affected with respect to the control treatment: (1) a predawn leaf water potential of around −0.5 MPa during the critical periods, and (2) a 22% drop in irrigation water. The total yield obtained in the DI treatment was significantly reduced in all the years studied due to the lower number of fruits per tree. No changes in the physical characteristics of fruits were observed at harvest. RDI can be considered a useful strategy in semiarid areas with limited water resources.     

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.     

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.     

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.     

Ten consecutive years of regulated deficit irrigation probe the sustainability and profitability of this water saving strategy in loquat

The successful application of postharvest regulated deficit irrigation (RDI) over ten consecutive years (from season 1999/2000 to season 2007/2008) confirms the sustainability of this strategy for producing ‘Algerie’ loquat. Postharvest RDI consisting in a reduction of watering (between 45 and 80% depending on the season) from early June until the end of August, improved loquat profitability by increasing fruit value and by reducing water consumption with respect to fully irrigated trees (control). The increase in fruit value in RDI trees was due to a consistent improvement in harvest earliness as a result of an earlier blooming. Water savings of around 20% did not diminish yield nor fruit quality. Water use efficiency in RDI trees rose by over 30%. Water productivity reached 9.5 € m⁻³ of water applied in RDI trees versus 6.6 € m⁻³ in control trees. The most noticeable effect of RDI on vegetative growth was a significant and progressive decline in trunk growth. The canopy volume seems to be strongly influenced by pruning and no significant effects were detected in this parameter. Our results confirm the suitability of RDI in loquat and the economic benefits of saving water during the summer.     

Quantifying reductions in consumptive water use under regulated deficit irrigation in pistachio (Pistacia vera L.)

The reduction in agricultural water use in areas of scarce supplies can release significant amounts of water for other uses. As improvements in irrigation systems and management have been widely adopted by fruit tree growers already, there is a need to explore the potential for reducing irrigation requirements via deficit irrigation (DI). It is also important to quantify to what extent the reduction in applied water through DI is translated into net water savings via tree evapotranspiration (ET) reduction. An experiment was conducted in a commercial pistachio orchard in Madera, CA, where a regulated deficit irrigation (RDI) program was applied to a 32.3-ha block, while another block of the same size was fully irrigated (FI). Four trees were instrumented with six neutron probe access tubes each, in the two treatments and the soil water balance method was used to determine tree ET. Seasonal irrigation water in FI, applied through a full-coverage microsprinkler system, amounted to 842 mm, while only 669 mm were applied in RDI. Seasonal ET in FI was 1024 mm, of which 308 mm were computed as evaporation from soil (E_s). In RDI, seasonal ET was reduced to 784 mm with 288 mm as Es. The reduction in applied water during the deficit period amounted to 147 mm. The ET of RDI during the deficit period was also reduced relative to that of FI by 133 mm, which represented 33% of the ET of FI during the deficit irrigation period. There was an additional ET reduction in RDI of about 100 mm that occurred in the post-deficit period.     

Regulated deficit irrigation effects on growth, yield, grape quality and individual anthocyanin composition in Vitis vinifera L. cv. ‘Tempranillo’

Regulated Deficit Irrigation (RDI) is an irrigation scheduling technique, originally developed for fruit orchards, that has been successfully adapted for winegrape production. The aim of this work is to evaluate the effect of RDI in vegetative growth, yield and harvest quality in ‘Tempranillo’ vineyards grown under semiarid conditions typical in Mediterranean areas. Two RDI strategies were compared with conventional irrigation practices (CI). CI that consisted in a progressive increase in water deficit as summer progressed, whereas RDI strategies (RDI1 and RDI2) had in common a deficit period just after fruit set and, in RDI2, vines were subjected to an additional stress period shortly after veraison. The experiment was carried out in four consecutive seasons in a commercial vineyard.Water stress at the beginning of berry development resulted in an important reduction of both vegetative growth and berry weight in RDI strategies. No differences in sugar concentration were found between treatments, and RDI berries tended to have lower acidity. The most relevant effect of RDI strategies on grape quality was an increase in anthocyanin and phenolics concentration. In RDI1 berries, this increase was mainly an indirect consequence of smaller berry size. However, in the RDI2 treatment the higher berry anthocyanin concentration reported was not exclusively due to a reduction in berry size. Since harvest quality has been clearly improved by any of the RDI strategies in both years, it can be concluded that RDI constitutes an interesting technique to be applied in ‘Tempranillo’ vineyards grown in semiarid areas aiming to obtain high quality grape.     

Regulated deficit irrigation in almonds: effects of variations in applied water and stress timing on yield and yield components

The impacts of three different water stress-timing patterns for three levels of seasonal applied water on production were evaluated in mature almond trees [Prunus dulcis (Mill.) Webb cv. Nonpareil] grown under high-evaporative demand conditions in the southern San Joaquin Valley of California. The stress timing patterns involved biasing water deficits to the pre-harvest or post-harvest periods in addition to uniform deficit irrigation for the entire season, referred to as A–C patterns. The three levels of water availability were 55, 70, and 85% of potential seasonal evapotranspiration (ET_c) equivalent to 580, 720, and 860 mm of applied water per season, respectively. Treatments were imposed over four seasons. Predawn leaf water potential was used as the stress indicator and approached −4.0 MPa with the A pattern at the lowest applied water level and −3.5 MPa with the B pattern at the same irrigation level. For every level of applied water, kernel weight at harvest was significantly reduced in the A pattern relative to the B and C patterns. At harvest, the most severe reduction in kernel dry weight relative to the control (17%) occurred in 580A, while there were 11% reductions in 580B and 580C. At the 860 mm level, only the A pattern dry kernel weight was less than the control. Moreover, the A patterns for all irrigation levels had lower kernel percentages than for the B and C patterns, indicating the greater sensitivity of kernel growth relative to shell growth in the regulated deficit irrigation (RDI) scenarios that biased the stress toward pre-harvest. The B stress patterns had a strong negative impact on fruit load relative to the A patterns at the 580 and 720 mm levels of applied water. No differences in crop load relative to the control were observed among the A and C regimes for all three levels of applied water. Nut load tended to increase during the experiment with 580A and 720A while it decreased with time with the B patterns for the same irrigation levels. We believe that the lower fruit loads involve stress during flower bud differentiation, which occurs mid-August–September in this cultivar and location, quite late in the season relative to other fruit and nut crops. The most successful stress timing pattern in terms of yield (the integrator of fruit size and load) was C, which avoided the large swings in tree stress observed with A and B. The onset of hull splitting was delayed by the severe pre-harvest stress in 580A while being accelerated by the milder stress of 720A. Spider mite levels were unaffected by the RDI. Canopy size was reduced with the A patterns at all irrigation levels. This occurred without any concomitant reduction in fruit load, resulting in higher fruiting densities (305 and 283 nuts/m² of orchard floor shaded area in 580A and 720A, respectively, vs. 214 nuts/m² in the control). Coupling the higher fruiting densities and smaller canopy sizes with higher tree planting densities offers growers the possibility of increasing yields while consuming less water. Maintaining more compact canopies with RDI rather than pruning would also lessen the amount of wood requiring disposal, thereby moderating air quality degradation resulting from burning. It must be emphasized that the scenario we outline—increasing kernel yields while using less water due to stress-related higher fruiting densities—requires that the smaller canopies be maintained by RDI, not pruning.     

The influence of bearing cycles on olive oil production response to irrigation

Water requirements for olive oil production and the effects of deficit irrigation were determined while considering the relative fruit loads on trees occurring as a result of biennial bearing cycles. Two Israeli olive (Olea europaea) varieties (Barnea and Souri) were evaluated for growth and yield parameters in a 4-year field study where five relative irrigation rates were applied. Increasing irrigation increased stem water potential, vegetative growth, and olive fruit yield with the increases tapering off at application rates reaching 75–100% of potential crop evapotranspiration. Tree water status, growth, and fruit characteristic parameters were highly affected by both fruit load and by irrigation level. Oil yield increases as a function of increased irrigation were initiated for each cultivar only following an ‘off’ season when the treatments lead to higher vegetative growth. The increased oil yields as a function of increased irrigation were primarily explained by higher tree-scale capacity for carrying fruit, especially as irrigation alleviated measureable water stress. For the Barnea cultivar in ‘on’ years, a secondary effect due to increased oil per fruit as irrigation increased was evident, particularly at the higher application rates.     

The effects of contrasted deficit irrigation strategies on the fruit growth and kernel quality of mature almond trees

The aim of this study was to quantify and compare the effects of two different deficit irrigation (DI) strategies (regulated deficit irrigation, or RDI, and partial rootzone drying, PRD) on almond (Prunus dulcis (Mill.) D.A. Webb) fruit growth and quality. Five irrigation treatments, ranging from moderate to severe water restriction, were applied: (i) full irrigation (FI), irrigated to satisfy the maximum crop water requirements (ET_c); (ii) regulated deficit irrigation (RDI), receiving 50% of ET_c during the kernel-filling stage and at 100% ET_c throughout the remaining periods; and three PRD treatments – PRD₇₀, PRD₅₀ and PRD₃₀ – irrigated at 70%, 50% and 30% ET_c, respectively, during the whole growth season. The DI treatments did not affect the overall fruit growth pattern compared to the FI treatment, but they had a negative impact on the final kernel dry weight for the most stressed treatments. The allocation of water to the different components of the fruit, characterized by the fresh weight ratio of kernel to fruit, appeared to be the process most clearly affected by DI. Attributes of the kernel chemical composition (lipid, protein, sugar and organic acid contents) were not negatively affected by the intensity of water deprivation. Overall, our results indicated that PRD did not present a clear advantage (or disadvantage) over RDI with regard to almond fruit growth and quality.     

Interactive responses to water deficits and crop load in olive (Olea europaea L., cv. Morisca). II: Water use, fruit and oil yield

To understand the relations between water use and yield in response to crop load, two experiments were conducted in olive (cv. Morisca), during six consecutive years (2002-2007) in an experimental orchard located in Badajoz, Southwest Spain. Experiment 1, assessed the responses during the early years of the orchard (2002-2004) using four irrigation treatments that applied fractions of the estimated crop evapotranspiration (ET_c) (125%, 100%, 75% and 0%) and three crop load levels (100%, 50% and 0% of fruit removal, termed Off, Medium and On treatments). Experiment 2 assessed the response of more mature trees (2005-2007) to three irrigation treatments (115%, 100%, and 60% of ET_c) and the natural crop load which were Off, On, and Medium in 2005, 2006 and 2007, respectively. Yield was reduced by water deficits and so did the estimated tree transpiration which was linearly related to yield (y = 1.2302x − 21.15, R² = 0.8864), showing the high sensitivity of cultivar Morisca to water deficits. The relations between fruit number and fruit weight showed that high crop loads had lower fruit weights and oil yield, a decrease that was more pronounced as water deficits increased. The yield response to water supply in the control and excess treatments, and the observations on the water relations of these two treatments suggest that the calculations made using the FAO method (Doorenbos and Pruit, 1974) with the crop coefficient proposed by Pastor et al. (1998) and the reduction coefficient (Fereres et al., 1982) to apply 100% of ET_c in the control treatment, underestimated the ET_c of the orchard. The results indicate that, although the absence of fruits lead to reduced water use as compared to situations of medium and high crop loads, canopy size was much more determinant of orchard water requirements than crop load.     

Regulated deficit irrigation during the kernel-filling period and optimal irrigation rates in almond

The use of Regulated deficit irrigation (RDI) in almond, applied during the kernel-filling phase, was evaluated over four consecutive years. To determine the reference optimal irrigation rate, three treatments were applied: T-100, which was irrigated by replacing crop evapotranspiration; T-130, which was irrigated by applying 30% more water than in T-100 and T-70, which received 30% less water than T-100. The RDI treatment received the same irrigation rate as T-100, but during the kernel-filling period irrigation was reduced to 20% of T-100. The optimum yield response was observed in treatment T-100, while T-130 trees never improved on T-100 kernel production over the 4 years of the study. During the first two experimental years, kernel dry matter accumulation did not decrease with drought in the RDI treatment. However, both cropping and kernel growth were reduced during the third and fourth years of the experiment. A possible explanation for this decrease could be found in a hypothetical depletion of the carbohydrate reservoir in RDI trees and also to the negative soil water balance that was evident in the T-70 and RDI treatments during winter and spring of the last 2 years. Although yield reductions for RDI trees were significant (20% with respect to T-100), the water savings obtained (about 60% of that applied with respect to T-100), may help to promote the adoption of RDI in areas, where water availability has been reduced. Bearing in mind the water conservation aspect in almond, RDI, as applied in this case, seemed more interesting than a seasonal sustained deficit irrigation strategy like T-70.     

Interactive responses to water deficits and crop load in olive (olea europaea L., cv. Morisca) I. - Growth and water relations

To characterize the interactions between variable water supply and crop load on vegetative growth and water relations of an olive orchard (cv. Morisca) planted in 1998 at 417 trees ha⁻¹, two different experiments were conducted over a six-year period (2002-2007) in Badajoz, Southwest of Spain. Experiment 1, assessed the responses during the early years of the orchard (2002-2004) using four irrigation treatments that applied fractions of the estimated crop evapotranspiration (ET_c) (125%, 100%, 75% and 0%) and three crop load levels (100%, 50% and 0% of fruit removal, termed off, medium and on treatments). Experiment 2, assessed the response of more mature trees (2005-2007) to three irrigation treatments (115%, 100%, and 60% of ET_c) and the natural crop load which were off, on, and medium in 2005, 2006 and 2007, respectively. Although vegetative growth was mainly affected by the level of water supply, crop load also influenced vegetative parameters, especially the interaction between high loads and water deficit. Trunk growth was more sensitive to water deficits than ground cover, and at the branch scale, water deficits reduced branch length and node numbers but only reduced internode length in on trees. Water relations were more affected by the level of water supply than by crop load. Nevertheless, the presence of fruits affected olive tree water status and, particularly, increased the stomatal conductance of on trees during late summer and early fall under all levels of water supply. Interactions between water stress and crop load levels were not very strong, and were more evident in mature than in young olive trees.     

Effects of soil water deficit on yield and quality of processing tomato under a Mediterranean climate

In order to assess the effect of soil water deficit (SWD) during fruit development and ripening, on yield and quality of processing tomato under deficit irrigation in the Mediterranean climate, an open-field experiment was carried out in two sites differing from soil and climatic characteristics, in Sicily, South Italy. Six irrigation treatments were studied: no irrigation following plant establishment (NI); 100% (F = full) or 50% (D = deficit) ET_c restoration with long-season irrigation (L) or short-season irrigation up to 1st fruit set (S); and long-season irrigation with 100% ET_c restoration up to beginning of flowering, then 50% ET_c restoration (LFD). The greatest effect of increasing SWD was the rise in fruit firmness, total solids and soluble solids (SS). A negative trend in response to increasing SWD was observed for fruit yield and size. Tough yield and SS were negatively correlated, the final SS yield under the LD regime was close to that of LF, and 47% water was saved. However, SS seems to be more environmental sensitive than SWD, since it varied more between sites than within site. The variations between sites in fruit quality response to deficit irrigation demonstrate that not only SWD but also soil and climatic characteristics influence the quality traits of the crop.     

Response of Vitis vinifera cv. ‘Tempranillo’ to partial rootzone drying in the field: Water relations, growth, yield and fruit and wine quality

This paper reports the effects of irrigation amount and partial rootzone drying (PRD) on water relations, growth, yield and wine quality of Vitis vinifera cv. ‘Tempranillo’ during two consecutive years in a commercial vineyard with a deep, light-clay soil located in Requena, Valencia, Spain. Partial rootzone drying applied at two amounts (100% and 50% of the estimated crop evapotranspiration), was compared to conventional drip irrigation, and also to rainfed vines. Results showed that the effects of irrigation amount on yield and wine quality were different between years. In 2003 with low yield values (around 6.3 t ha⁻¹) irrigation did neither affect grape production nor wine quality. However, in the following year, with much higher general yield (17 t ha⁻¹), the high irrigation dose increased yield by 30% compared to rainfed vines and it also increased must total soluble solids and wine alcohol content. In both seasons, PRD did not significantly affect physiological parameters, nor growth, yield or fruit and wine quality, when compared to the same amount of water applied by conventional drip irrigation. Overall these results suggest that, under our experimental conditions, it was the irrigation amount rather than the system of application what affected vine performance, indicating the difficulties of successfully employing the PRD type of irrigation with a drip system in heavy and deep soils.