Tensiometer-based irrigation scheduling in perennial strawberry cultivation

Tensiometers are ideal for soil moisture monitoring in strawberry cultivation because they operate effectively at less than −1,000 hPa soil water tension, which includes the soil moisture range for strawberries. For this study, four different drip irrigation thresholds, at −150, −300, −600 hPa, and, depending on the development stage of the plants, −300 or −600 hPa, were applied in a trial carried out in southwest Finland in 2001–2003 with June-bearing cultivar ‘Bounty’. Higher soil moisture increased yield and fruit soluble solids content, but decreased fruit firmness. In healthy plants, no remarkable soil moisture effects on plant growth were observed, but in the years 2002–2003 it was observed that increased soil moisture in the previous growing season and the subsequent winter injuries decreased the following year’s growth. Water consumption of plants varied considerably depending on growth stage, yield potential and environmental factors. The volumes of irrigation water ranged from 5 to 22 l/plant per growing season.     

Long term responses of olive trees to salinity

Water demand for irrigation is increasing in olive orchards due to enhanced yields and profits. Because olive trees are considered moderately tolerant to salinity, irrigation water with salt concentrations that can be harmful for many of fruit tree crops is often used without considering the possible negative effects on olive tree growth and yield. We studied salt effects in mature olive trees in a long term field experiment (1998-2006). Eighteen-year-old olive trees (Olea europaea L.) cv. Picual were cultivated under drip irrigation with saline water composed of a mixture of NaCl and CaCl₂. Three irrigation regimes (i. no irrigation; ii. water application considering soil water reserves, short irrigation; iii. water application without considering soil water reserves and adding a 20% more as a leaching fraction, long irrigation) and three salt concentrations (0.5, 5 or 10 dS m⁻¹) were applied. Treatments were the result of the combination of three salt concentrations with two irrigation regimes, plus the non-irrigated treatment. Growth parameters, leaf and fruit nutrition, yield, oil content and fruit characteristics were annually studied. Annual leaf nutrient analyses indicate that all nutrients were within the adequate levels. After 8 years of treatment, salinity did not affect any growth measurement and leaf Na⁺ and Cl⁻ concentration were always below the toxicity threshold of 0.2 and 0.5%, respectively. Annual and accumulated yield, fruit size and pulp:stone ratio were also not affected by salts. However, oil content increased linearly with salinity, in most of the years studied. Soil salinity measurements showed that there was no accumulation of salts in the upper 30 cm of the soil (where most of the roots are present) because of leaching by rainfall at the end of the irrigation period. Results suggest that a proper management of saline water, supplying Ca²⁺ to the irrigation water, using drip irrigation until winter rest and seasonal rainfall typical of the Mediterranean climate leach the salts from the first 0-60 cm depth, and growing a tolerant cultivar, can allow using high saline irrigation water (up to 10 dS m⁻¹) for a long time without affecting growth and yield in olive trees.     

Long-term growth and yield responses of olive trees to different irrigation regimes

The aim of this work was to evaluate long-term effects of different irrigation regimes on mature olive trees growing under field conditions. A 9-year experiment was carried out. Three irrigation treatments were applied: no irrigation, water application considering soil water content (short irrigation), or irrigation without considering soil water reserves and applying a 20% of extra water as a leaching fraction (long irrigation). Leaf water content, leaf area, vegetative growth, yield and fruit characteristics (fruit size, pulp:stone ratio and oil content) were determined yearly. Results showed that growth parameters did not show significant differences as a consequence of applied water. Yield was increased in irrigated trees compared to non-irrigated ones, but little differences between short and long irrigation were observed, only when accumulated yield from 1998 to 2006 was considered. Irrigation did not cause significant differences in fruit size or pulp:stone ratio either. Irrigation regimes similar to those applied in this experiment, under environmental conditions with relatively high mean annual precipitation, does not increase growth, yield or fruit characteristics when compared to rain-fed treatment, and consequently, the installation of a irrigation system could be not financially profitable.     

Response of sweet orange cv ‘Lane late’ to deficit-irrigation strategy in two rootstocks. II: Flowering, fruit growth, yield and fruit quality

We evaluated the effects of a deficit-irrigation (DI) strategy in mature ‘Lane late’ sweet orange (Citrus sinensis (L.) Osb.) trees grafted on two different drought-tolerant rootstocks, ‘Cleopatra’ mandarin (Citrus reshni Hort. ex Tanaka) and ‘Carrizo’ citrange (Citrus sinensis (L.) Osbeck x Poncirus trifoliata L.). Two treatments were applied: a control treatment, irrigated at 100% of crop evapotranspiration (ETc) during the entire season, and a DI treatment, irrigated at 100% ETc, except during phases I (initial fruit-growth period,) and phase III (final fruit-growth period, ripening, harvest), when no irrigation was applied. Flowering, fruit abscission and fruit growth of trees on ‘Carrizo’ were more affected by DI than on ‘Cleopatra’. Deficit irrigation reduced yield in both rootstocks due mainly to a decrease in the number of fruits. The phase most sensitive to drought stress was phase I. Moreover, DI altered fruit quality depending on the period when drought stress was applied. Fruit quality was modified by DI: total soluble sugars and titratable acidity increased when a severe drought stress occurred only in phase III but only increased the peel/pulp ratio if it occurred only in phase I. The quality of fruits from trees on ‘Carrizo’ under DI was affected more than that of fruits from trees on ‘Cleopatra’. Under DI in semi-arid regions ‘Cleopatra’ mandarin can mitigate more the negative effects of drought stress on yield and fruit quality than ‘Carrizo’ citrange.     

Evaluating water stress in irrigated olives: correlation of soil water status,tree water status,and thermal imagery

Irrigation of olive orchards is challenged to optimize both yields and oil quality. Best management practices for olive irrigation will likely depend on the ability to maintain mild to moderate levels of water stress during at least some parts of the growing season. We examined a number of soil, plant and remote sensing parameters for evaluating water stress in bearing olive (var. Barnea) trees in Israel. The trees were irrigated with five water application treatments (30, 50, 75, 100 and 125% of potential evapotranspiration) and the measurements of soil water content and potential, mid-day stem water potential, and stomatal resistance were taken. Remote thermal images of individual trees were used to alternatively measure average canopy temperature and to calculate the tree’s crop water stress index (CWSI), testing empirical and analytical approaches. A strong non-linear response showing similar trends and behavior was evident in soil and plant water status measurements as well as in the CWSI, with decreasing rates of change at the higher irrigation application levels. No statistically significant difference was found between the analytical and the empirical CWSI, suggesting that the relative simplicity of the analytical method would make it preferable in practical applications.     

Response of sweet orange cv ‘Lane late’ to deficit irrigation in two rootstocks. I: water relations,leaf gas exchange and vegetative growth

The influence of a deficit-irrigation (DI) strategy on soil–plant water relations and gas exchange activity was analysed during a 3-year period in mature ‘Lane late’ (Citrus sinensis (L.) Osb.) citrus trees grafted on two different rootstocks, ‘Cleopatra’ mandarin (Citrus reshni Hort. ex Tanaka ) and ‘Carrizo’ citrange (C. sinensis L., Osbeck × Poncirus trifoliata L.). Two treatments were applied for each rootstock: a control treatment, irrigated at 100% ETc (crop evapotranspiration) during the entire season, and a DI treatment, irrigated at 100% ETc, except during Phase I (cell division) and Phase III (ripening and harvest) of fruit growth, when complete irrigation cut-off was applied. Under soil water deficit, the seasonal variations of soil water content suggested that ‘Cleopatra’ mandarin had a better root efficiency for soil water extraction than ‘Carrizo’ citrange. Moreover, in all years, trees on ‘Cleopatra’ reached a lower water-stress level (midday xylem water potential values (Ψ_md) > −2 MPa), maintaining a better plant water status during the water-stress periods than trees on ‘Carrizo’ (Ψ_md < −2 MPa). Similarly, net CO₂ assimilation rate (A) was higher in trees on ‘Cleopatra’ during the water-stress periods. In addition, the better plant water status in trees on ‘Cleopatra’ under DI conditions stimulated a greater vegetative growth compared to trees on ‘Carrizo’. From a physiological point of view, ‘Cleopatra’ mandarin was more tolerant of severe water stress (applied in Phases I and III of fruit growth) than ‘Carrizo’ citrange.     

Plant growth and yield responses in olive (Olea europaea) to different irrigation levels in an arid region of Argentina

Over the last two decades, a significant increase in intensively managed olive orchards has occurred in the northwest of Argentina where climatic conditions differ greatly from the Mediterranean Basin. Annual amounts of applied irrigation are generally high due to low rainfall, access to deep ground water, and little information about water use by the crop in the region. The objectives of this study were to: (1) assess the responses of plant growth, yield components, and several physiological parameters to five different irrigation levels and (2) determine an optimum crop coefficient (Kc) for the entire growing season considering both fruit yield and vegetative growth. Five irrigation treatments (Kc = 0.50, 0.70, 0.85, 1.0, 1.15) were employed from late winter to the fall over 2 years in a 6-year-old cv. ‘Manzanilla fina’ olive orchard. Tree canopy volume was approximately 15 m³ with a leaf area of about 40 m² at the beginning of the experiment. During much of each year, the volumetric soil water content was lower in the Kc = 0.50 treatment than in the other irrigation levels evaluated (Kc = 0.85 and 1.15). Although differences in midday stem water potential (Ψ_s) were not always apparent between treatments during the first year, there were lower Ψ_s values in Kc = 0.50 and 0.70 relative to the higher irrigation levels during the second year. Shoot elongation in Kc = 0.50 was about 50% of that in Kc = 1.0 and 1.15 during both years leading to significant differences in the increase of tree canopy volume by the end of the first year. Fruit yield was similar among irrigation levels the first year, but yield reached a maximum value the second year between Kc = 0.70 and 0.85 above which no increase was apparent. The somewhat lower fruit yield values in Kc = 0.50 and 0.70 were associated with decreased fruit number rather than reductions in individual fruit weight. The water productivity on a yield basis (fruit yield per mm of applied irrigation) decreased as irrigation increased in the second year, while similar calculations based on trunk cross-sectional area growth indicated that vegetative growth was proportional to the amount of irrigation. This suggests that the warm climate of northwest Argentina (28° S) can induce excessive vegetative growth when very high irrigation levels are applied. A Kc value of approximately 0.70 over the course of the growing season should be sufficient to maintain both fruit yield and vegetative growth at adequate levels. An evaluation of regulated deficit irrigation strategies for table olives in this region could be beneficial to further reduce irrigation.     

Yield and quality of two tomato (Solanum lycopersicum L.) cultivars as influenced by drip and furrow irrigation using waters having high residual sodium carbonate

Performance of tomato when irrigated with sodic waters particularly under drip irrigation is not well known. A field experiment was conducted for 3 years to study the response of tomato crop to sodic water irrigation on a sandy loam soil. Irrigation waters having 0, 5 and 10 mmol_c L⁻¹ residual sodium carbonate (RSC) were applied through drip and furrow irrigation to two tomato cultivars, Edkawi (a salt tolerant cultivar) and Punjab Chhuhara (PC). High RSC of irrigation water significantly increased soil pH, ECe and exchangeable sodium percentage progressively; the increases were higher in furrow compared to drip irrigation. Effect of high RSC on increasing bulk density and decreasing infiltration rate of soil was also pronounced in furrow-irrigated plots. Higher soil moisture and lower salinity near the plant was maintained under drip irrigation than under furrow irrigation. Performance of the two cultivars was significantly different; pooled over 2002–03 and 2003–04 seasons, PC yielded 38.8 and 30.0 Mg ha⁻¹ and Edkawi yielded 31.8 and 22.9 Mg ha⁻¹ under drip and furrow irrigation, respectively. At RSC10, cultivar PC produced 38 and 46% higher fruit yield than cultivar Edkawi under drip and furrow irrigation, respectively. Reduction in fruit yield at higher RSC was due to lower fruit weight under drip irrigation and due to reduced fruit number as well as fruit weight under furrow irrigation. Decrease in fruit weight was more pronounced in cultivar Edkawi than in cultivar PC. Increase in RSC lowered quality of the fruits except the ascorbic acid content. High RSC under drip irrigation, in general, had lesser deteriorating effect on the fruit quality particularly for cultivar PC than under furrow irrigation. For obtaining high tomato yield and better-quality fruits using high RSC sodic waters, drip irrigation should be preferred over furrow irrigation. Better performance of local cultivar PC compared to Edkawi at medium and high RSC suggests that cultivars categorized as tolerant to salinity should be evaluated in the sodic environment particularly when irrigated with high RSC sodic waters.     

Effects of different irrigation regimes on a super-high-density olive grove cv. “Arbequina”: vegetative growth,productivity and polyphenol content of the oil

The effects of multiple irrigation regimes on the relationships among tree water status, vegetative growth and productivity within a super-high-density (SHD) “Arbequina” olive grove (1950 tree/ha) were studied for three seasons (2008–2010). Five different irrigation levels calculated as percentage of crop irrigation requirement using FAO procedures (Allen et al. in Crop evapotranspiration. Guidelines for computing crop water requirements. Irrigation and drainage paper 56. FAO, Rome, 1998) were imposed during the growing season. Periodically during the growing season, daytime stem water potential (Ψ _STEM), inflorescences per branch, fruits per inflorescence and shoot absolute growth rate were measured. Crop yield, fruit average fresh weight and oil polyphenol content were measured after harvest. The midday Ψ _STEM ranged from ?7 to ?1.5 MPa and correlated well enough with yield efficiency, crop density and fruit fresh weight to demonstrate its utility as a precise method for determining water status in SHD olive orchards. The relationships between midday Ψ _STEM and the horticultural parameters suggest maintaining Ψ _STEM values between ?3.5 and ?2.5 MPa is optimal for moderate annual yields of good quality oil. Values below ?3.5 MPa reduced current season productivity, while values over ?2.5 MPa were less effective in increasing productivity, reduced oil quality and produced excessive crop set that strongly affected vegetative growth and fruit production the following season. On the basis of the result given here, irrigation scheduling in the new SHD orchards should be planned on a 2-year basis and corrected annually based on crop load. Collectively, these results suggest that deficit irrigation management is a viable strategy for SHD olive orchards.     

Water tension thresholds for processing tomatoes under drip irrigation in Central Brazil

Drip irrigation has the potential to save water and mitigate foliar diseases for processing tomato production in Central Brazil. Four experiments were carried out at Embrapa Vegetables, Brasília, Brazil, to establish irrigation management strategies during vegetative, fruit development, and maturation growth stages of drip-irrigated processing tomato. Soil water tension (SWT) threshold values ranging from 5 to 120 kPa were evaluated. Plants growing under higher water deficit during the vegetative stage showed root systems up to 10 cm deeper than those irrigated more frequently. Maximum fruit yield was reached when irrigations were performed at SWT thresholds of 35, 12, and 15 kPa during vegetative, fruit development, and maturation growth stages, respectively. Total soluble solids content was not affected by irrigation treatments during vegetative and fruit development stages, but increased as SWT increased during fruit maturation growth stage.

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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.     

Responses of ‘Petopride’ processing tomato to partial rootzone drying at different phenological stages

Partial rootzone drying (PRD) is a water-saving irrigation practice which involves watering only part of the rhizosphere at each irrigation with the complement left to dry to a pre-determined level. The effect of PRD, applied at different phenological stages, on yield, fruit growth, and quality of the processing tomato cv. ‘Petopride’ was studied in this experiment. The treatments were: daily full irrigation (FI) on both sides of the root system considered as the control, and PRD treatments applied at three phenological stages. These were: during the vegetative stage until the first truss was observed (PRD_VS–FT), from the first truss to fruit set (PRD_FT–FS), and from fruit set to harvest (PRD_FS–H). In some occasions, leaf xylem water potential was lower in each PRD period than in FI. Number of fruits, total fresh and dry weight of fruit per plant, harvest index, and fruit growth were lower in PRD_FT–FS and PRD_FS–H plants than in FI and PRD_VS–FT plants. However, irrigation water use efficiency, on a dry weight basis, was the same among the treatments. For PRD_FT–FS and PRD_FS–H treatments, mean fresh weight of fruit and fruit water content were reduced and dry matter concentration of cortex and total soluble solids concentration of fruit increased compared with FI and PRD_VS–FT treatments. Incidence of blossom-end rot was the same among PRD_VS–FT, PRD_FS–FH, and FI fruit, but it was higher in PRD_FT–FS fruit. Fruit skin colour was the same among treatments. Total dry weight of fruit per plant decreased by 23% for PRD_FT–FS and by 20% for PRD_FS–H relative to FI. Fruit quality improvement in PRD_FS–H could compensate for the reduction in total dry weight of fruit where water is expensive for tomato production. But an economical analysis would be needed to substantiate this. PRD from the first truss to fruit set is not recommended because of the high incidence of blossom-end rot. An erratum to this article can be found at     

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.     

Combined effects of water stress and fruit thinning on fruit and vegetative growth of a very early-maturing peach cultivar: assessment by means of a fruit tree model, QualiTree

Regulated deficit irrigation strategies are common practices in areas with low water availability. Thus, water stress, which can limit fruit growth, is imposed to the trees. Fruit thinning can be used to relieve this water stress in peach. In this paper, the ability of an existing fruit tree model (QualiTree) for describing the effects of water stress and fruit thinning on peach fruit and vegetative growth was assessed. The model was parameterized and calibrated for a very early-maturing peach cultivar (“Flordastar”). Important parameters were those expressing the effect of distance between organs on carbon exchange within the tree, the potential dry masses, and the relative growth rates of fruits and leafy shoots. Then, the model was tested in a wide range of water stress situations and three fruit thinning intensities: no thinning, commercial thinning, and heavy thinning. Fruit and vegetative growth simulations were consistent with observed data derived from 2006 field experiments. The variability over time of fruit and vegetative growth was well predicted. The model reproduced reductions in fruit growth observed in field experiments. It also reacted to simulated scenarios that combined water stress and thinning. Increasing thinning intensity reduced total fruit yield but increased fruit size at harvest, compensating the negative effects of water stress on fruit growth. These simulations broadened the predictive capabilities of the model and showed that it might be a useful tool in the design of innovative horticultural practices.     

Water-use patterns of tall fescue and hybrid bluegrass cultivars subjected to ET-based irrigation scheduling

In turf industry, the ability of a cultivar to use less water is an important consideration, especially where rainfall and irrigation water are insufficient. Knowledge of turf grass water-use patterns is therefore important for developing efficient water management practices and also for selection of drought-resistant cultivars. We evaluated the soil water‐use patterns of tall fescue and hybrid bluegrasses cultivars irrigated at different rates. Field experiments were conducted at the Turfgrass Research Facility, Auburn University, AL, in 2005 and 2006. Two tall fescue (Festuca arundinacea Schreb.) cultivars (‘Kentucky 31’ and ‘Green Keeper’) and four hybrid bluegrass (Poa pratensis L. × Poa arachnifera Torr.) cultivars, viz., HB 129 [‘Thermal Blue’], HB 130 (Experimental line), HB 328 (Experimental line) and HB 329 [‘Dura Blue’] were included in this study. Plots were irrigated based on the potential evapotranspiration, viz., 100% ET, 80% ET and 60% ET replacements. Tensiometers were installed at 0.075, 0.15 and 0.30 m depths, and their readings used to calculate the matric head, water content and water-use values. Turf color quality was determined from turf canopy digital images. Analysis of variance (ANOVA) for a random complete block design (RCBD) was conducted for available water, water-use and turf color quality values. Hybrid bluegrasses revealed significantly (P = 0.05) higher turf color indices compared to the tall fescue cultivars, but there was no indication of differential responses to irrigation among cultivars. Based on water-use data, hybrid bluegrass cultivars revealed significantly (P = 0.05) lower water-use compared to tall fescue cultivars.     

Effect of irrigation methods,management and salinity of irrigation water on tomato yield,soil moisture and salinity distribution

The increasing demand for irrigation water to secure food for growing populations with limited water supply suggests re-thinking the use of non-conventional water resources. The latter includes saline drainage water, brackish groundwater and treated waste water. The effects of using saline drainage water (electrical conductivity of 4.2–4.8 dS m⁻¹) to irrigate field-grown tomato (Lycopersicon esculentum Mill cv Floradade) using drip and furrow irrigation systems were evaluated, together with the distribution of soil moisture and salt. The saline water was either diluted to different salinity levels using fresh water (blended) or used cyclically with fresh water. The results of two seasons of study (2001 and 2002) showed that increasing salinity resulted in decreased leaf area index, plant dry weight, fruit total yield and individual fruit weight. In all cases, the growth parameters and yield as well as the water use efficiency were greater for drip irrigated tomato plants than furrow-irrigated plants. However, furrow irrigation produced higher individual fruit weight. The electrical conductivity of the soil solution (extracted 48 h after irrigation) showed greater fluctuations when cyclic water management was used compared to those plots irrigated with blended water. In both drip and furrow irrigation, measurements of soil moisture one day after irrigation, showed that soil moisture was higher at the top 20 cm layer and at the location of the irrigation water source; soil moisture was at a minimum in the root zone (20–40 cm layer), but showed a gradual increase at 40–60 and 60–90 cm and was stable at 90–120 cm depth. Soil water content decreased gradually as the distance from the irrigation water source increased. In addition, a few days after irrigation, the soil moisture content decreased, but the deficit was most pronounced in the surface layer. Soil salinity at the irrigation source was lower at a depth of 15 cm (surface layer) than that at 30 and 60 cm, and was minimal in deeper layers (i.e. 90 cm). Salinity increased as the distance from the irrigation source increased particularly in the surface layer. The results indicated that the salinity followed the water front. We concluded that the careful and efficient management of irrigation with saline water can leave the groundwater salinity levels unaffected and recommended the use of drip irrigation as the fruit yield per unit of water used was on average one-third higher than when using furrow irrigation.     

Yield and olive oil characteristics of a low-density orchard (cv. Cordovil) subjected to different irrigation regimes

The impact of different irrigation scheduling regimes on the quantity and quality of olive oil from a low-density olive grove in southern Portugal was assessed during the irrigation seasons of 2006 and 2007. Olive trees were subjected to one of the following treatments: A—full irrigation; B—sustained deficit irrigation (SDI) with 60% of ETc water applied with irrigation; C—regulated deficit irrigation (RDI) with irrigation water applied at three critical phases: before flowering, at the beginning of pit hardening and before crop harvesting and D—rain-fed treatment. Olive oil yield was significantly higher than rain-fed conditions in 2006, an “on year” of significant rainfall during summer. No significant yield differences were observed in the following “off year”. Among the irrigated treatments, olive oil production of treatment B was 32.5% and 40.1% higher in 2006 and 2007, respectively than the fully irrigated treatment A, despite receiving 49% less irrigation water. Such strategy could allow for an efficient use of water in the region, of very limited available resources, and for modest but important oil yield increase. Nonetheless, on the “on year” of 2006 treatment C used 13.9% of the water applied to treatment B and produced only 23.9% less olive fruits which could also make it illegible as the next possible strategy to use for irrigating olive trees in the region, provided that water is secured latter in the summer, a period of vital importance for oil accumulation and very sensitive to water stress as the poor results of 2007 revealed. The different treatment water regimes did not impact on the chemical characteristics of olive oils that were within the set threshold limits. Similarly, the sensory characteristics of the olive oils as well as bitterness and pungency were negligible for all treatments allowing them to be assessed as of “superior quality”.Overall, irrigation treatments had no influence on the commercial value of produced oils, being all classified as “extra virgin”. Such funding may be of vital importance to farmers willing to further their irrigation area, save water and still retain the protected designation of origin (PDO) seal of quality for their oil.     

调亏灌溉对大棚滴灌甜瓜生长发育的影响

在大棚滴灌条件下对厚皮甜瓜伊丽莎白不同生育期进行不同程度的亏缺灌溉,研究调亏灌溉对其植株生长、产量、品质及水分利用效率的影响.以土壤相对含水量为标准,在营养生长期和生殖生长期分别设置不同的土壤水分灌溉下限处理,分别是T1(75%~75%),T2(75%~55%),T3(65%~65%),T4(55%~75%),T5(55%~55%)5个试验处理.结果表明:在营养生长期,随着水分亏缺程度的加大,株高、茎粗、叶面积均呈减小趋势.在果实发育阶段,营养生长期及生殖生长期的水分亏缺对果实的生长、产量都有影响,均随亏缺程度的加大而降低,产量以处理T1和T2的最高,T5的最低,T3的大于T4的,各处理间差异具有统计学意义.水分利用效率为处理T2的最高,T1和T4的较低,T2与T4相比,在灌水基本相同的条件下,产量增加了26.2%,水分利用效率提高了27.7%.品质方面,水分亏缺提高了TSS含量;在营养生长期充分灌溉、生殖生长期亏水灌溉可以提高可溶性蛋白、游离氨基酸、维生素C的含量;而营养生长期亏水灌溉、生殖生长期充分灌溉有利于可滴定酸的合成.经综合分析,认为处理T2的灌溉下限设置可以作为武汉地区大棚滴灌条件下的甜瓜灌溉制度.     

Irrigation influences on growth, yield, and water use of persimmon trees

A 3-year irrigation trial provided basic information on the response of persimmon (Diospyros kaki cv. Triumph) water use and development to irrigation levels. Constant experimental factors applied to recommended “baseline” crop factors resulted in ratios of irrigation (I) to FAO56 reference crop evapotranspiration (ET₀) ranging from 0.35 to 1.14. Vegetative and reproductive growth, sap flow, stem water potential (SWP), and local climate were monitored. An overall increase in yield and vegetative growth in response to irrigation was found, which suggests a potential yield increase for higher irrigation levels (40 tons/ha for annual irrigation of 1,000 mm). At high irrigation, the yield response curve levelled off and the marginal contribution of additional water declined. The up to threefold increase in number of fruits with irrigation, with no influence on natural abscission, suggests that differences in fruit quantities stem from response to irrigation at the earlier growth stages. Mean fruit size and fruit quality, as indicated by the ratio of rejected fruit, increased with irrigation up to I/ET₀ of ~0.8. Relative yield increased linearly with relative transpiration. However, post-harvest quality was not influenced. SWP, sap flow, and non-transpirable water fractions indicated that the seasonal irrigation tables were not well tuned. Initial adjustments were made during the final season of the experiment and a new table was developed based on our results. The new table should be a basis for further trials.     

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.