Application Of Deficit Irrigation Research Articles

Consideration of Water Productivity for Farm Water Management in Different Conditions of Water Availability for Dominant Summer Crops

ABSTRACT- Efficient use of irrigation water for summer crops should be considered seriously due to rare occurrence of precipitation in summer. This research was focused on the assessment of water use efficiency for dominant crops of summer cropping pattern in the study area (i.e., maize and rice) via considering water productivity (WP) with different water management scenarios at farm level at different climatic conditions. Results indicated that in most cases the maximum WP was not occurred at full irrigation scenario. With increasing irrigation application efficiency (Ea), WP increased and the maximum WP shifted toward higher water reduction fraction (WRF). For maize, in deficit irrigation scheduling (DIS) methods with full irrigation at flowering stage, more deficit irrigation application was economically acceptable. For rice, with increasing Ea and WRF, WP increased and deficit irrigation at different growth stages was economically acceptable. Considering the real cost of water, economic water productivity ratio (EWPR) decreased greatly and in surface irrigation system, Ea should be increased and high WRF should be avoided (WRF should be lower than 0.4). In solid-set sprinkler system, EWPR increased with increasing Ea and application of WRF higher than 0.2 (0.2-0.6 for maize) was acceptable. Tape irrigation of maize was acceptable only for WRF less than 0.2; also, 0.2-0.4 was acceptable for WRF by decreasing the Ea.

Quality attributes of pistachio nuts as affected by rootstock and deficit irrigation.

In this work, the influence of two regulated deficit irrigation (RDI) treatments and three different rootstocks on the quality of pistachios was evaluated by analyzing different parameters: morphological analysis, physicochemical analysis and sensory analysis. The results obtained in terms of the choice of rootstock revealed that Pistacia atlantica had increased production yields, nut weight, mineral content, higher intensities of characteristic sensory attributes and a higher degree of consumer satisfaction, than the other rootstocks studied. Moreover, the results established that the application of RDI on pistachio cultivation had no significant influence on production yield, weight, size, colour, water activity or mineral composition. Furthermore, T1 treatment (stem water potential < -1.3 MPa) resulted in higher intensities of characteristic sensory attributes and a greater level of satisfaction among international consumers. These results confirm that the application of deficit irrigation (T1) contributes to an increase in overall product quality. Furthermore, Pistacia atlantica rootstock provided better yield and quality than the other rootstocks studied.

Optimizing Reservoir Operation Policy Using Chance Constraint Nonlinear Programming for Koga Irrigation Dam, Ethiopia

One of typical problems in water resources system modeling is derivation of optimal operating policy for reservoir to ensure water is used more efficiently. This paper introduces optimization analysis to determine monthly reservoir operating policies for five scenarios of predetermined cropping patterns for Koga irrigation scheme, Ethiopia. The objective function of the model was set to minimize the sum of squared deviation (SSD) from the desired targeted supply. Reservoir operation under different water availability and thresholds of irrigation demands has been analyzed by running a chance constraint nonlinear programming model based on uncertain inflow data. The model was optimized using Microsoft Excel Solver. The lowest SSD and vulnerability, and the highest volumetric reliability were gained at irrigation deficit thresholds of 20 % under scenario I, 30 % under scenario II, III and V, and at 40 % under scenario IV when compensation release is permitted for downstream environment. These thresholds of deficits could be reduced by 10 % for all scenarios if compensation release is not permitted. In conclusion the reservoir water is not sufficient enough to meet 100 % irrigation demand for design command areas of 7,000 ha. The developed model could be used for real time reservoir operation decision making for similar reservoir irrigation systems. In this specific case study system, attempt should be made to evaluate the technical performance of the scheme and introduce a regulated deficit irrigation application.

Water shortage and quality of fleshy fruits--making the most of the unavoidable.

Extreme climatic events, including drought, are predicted to increase in intensity, frequency, and geographic extent as a consequence of global climate change. In general, to grow crops successfully in the future, growers will need to adapt to less available water and to take better advantage of the positive effects of drought. Fortunately, there are positive effects associated with drought. Drought stimulates the secondary metabolism, thereby potentially increasing plant defences and the concentrations of compounds involved in plant quality, particularly taste and health benefits. The role of drought on the production of secondary metabolites is of paramount importance for fruit crops. However, to manage crops effectively under conditions of limited water supply, for example by applying deficit irrigation, growers must consider not only the impact of drought on productivity but also on how plants manage the primary and secondary metabolisms. This question is obviously complex because during water deficit, trade-offs among productivity, defence, and quality depend upon the intensity, duration, and repetition of events of water deficit. The stage of plant development during the period of water deficit is also crucial, as are the effects of other stressors. In addition, growers must rely on relevant indicators of water status, i.e. parameters involved in the relevant metabolic processes, including those affecting quality. Although many reports on the effects of drought on plant function and crop productivity have been published, these issues have not been reviewed thus far. Here, we provide an up-to-date review of current knowledge of the effects of different forms of drought on fruit quality relative to the primary and secondary metabolisms and their interactions. We also review conventional and less conventional indicators of water status that could be used for monitoring purposes, such as volatile compounds. We focus on fruit crops owing to the importance of secondary metabolism in fruit quality and the importance of fruits in the human diet. The issue of defence is also briefly discussed.

A proposed method to determine yield response factors of different crops under deficit irrigation using inverse formulation approach

Yield response factors of a given crop can be determined following the FAO approach (Doorenbos and Kassam, 1979. Yield response to water. FAO Irrigation and Drainage Paper no. 33. Rome, Italy, pp. 1–40) either by applying deficit irrigation throughout the whole growing period, or at one stage of the crop growth while maintaining full irrigation at the other stages. In this study, an inverse formulation methodology is proposed to determine the stage wise yield response factors (modified kyi values) for eight crops in the Lower Indus Basin. The proposed inverse formulation was based on the multiplicative (Jensen, 1968. Water consumption by agricultural plants. Chapter 1. In: T.T. Kozlowski (Ed.) Water Deficits and Plant Growth Vol. II (pp 1–22). Academic Press, New York) and additive (Stewart et al., 1977. Determination and utilization of water production functions for principal California crops. W-67 California Contributory Project, University of California) approaches to determine yield response factors. To illustrate the applicability of the proposed inverse formulation, the widely used seasonal ky values of FAO Irrigation and Drainage Paper No 33 (Doorenbos and Kassam, 1979. Yield response to water. FAO Irrigation and Drainage Paper no. 33. Rome, Italy, pp. 1–40) were used to generate a data set of yields and evapotranspirations for the crops under study after applying theoretical levels of deficit irrigation at different growth stages using climatic and soil data of the Lower Indus Basin. This data set was then used to estimate the modified kyi values separately for the additive and the multiplicative approaches from the inverse formulations. Modified kyi values were found to be different for additive and multiplicative approaches but there was a good agreement between the relative yield reductions using modified kyi values and seasonal ky values. However, there was a complete mismatch between relative yield reductions using FAO 33 stage wise kyi values and using FAO 33 seasonal ky values. Modified kyi values, based on the proposed inverse formulation, may be more representative by taking into account the effects of deficit irrigation on crop production.

Adaptive strategies of on-farm water management under water supply constraints in south-eastern Spain

The study analyses the effect of irrigation water constraints on-farm management in the Campo de Cartagena Irrigation District (south-eastern Spain), which is characterised by a semi-arid climate with a marked structural water deficit. The methodology applied was the comparative assessment of management indicators during two periods with very differing water availability. A set of performance indicators was selected and calculated to assess the effects on on-farm water management and productivity.The results indicate low productivity sensitivity to water supply constraints since the farmers adopt a number of adaptive strategies, such as intensifying the extraction of brackish groundwater, reducing the irrigated surface area of short-cycle crops, applying deficit irrigation, and even desalinating brackish groundwater in the more sensible to salinity crops. As a consequence of managing water with a greater salinity the leachable fraction needed is increased, giving rise to greater irrigation requirements. Moreover, the greater salinity of the irrigation water causes lower yields in the majority of crops. Although these adaptive strategies let the farmers maintaining their activity under water scarcity periods, their effect in the groundwater and soil salinization as well as in the crop production costs and yields can be unsustainable in the mid-long term.

Performance of mungbean under deficit irrigation application in the semi-arid highlands of Ethiopia

Knowing the performance of short season crops under deficit irrigation has a paramount importance for arid and semi-arid regions with limited access to on-farm water harvesting or other irrigation infrastructure. In this research, the performance of mungbean, a newly introduced crop into the cropping systems in Ethiopia, to stage-wise and uniform deficit irrigation was tested at Sekota Dryland Agricultural Research Center, Northern Ethiopia. Eight treatments – four stage-wise deficit and four uniform deficit irrigation applications were evaluated during the 2010/2011 dry season. Plant phenological variables, grain yield and irrigation water use efficiency were used for performance evaluation. The results showed that a uniform water stress shortened the dates to 50% flowering and maturity, but with proportionate reduction in yield. The yield obtained varied between 1366kg/ha under 331mm optimal seasonal irrigation to 492kg/ha when one-fourth of ETc (102mm) was uniformly applied though out the growing season. The flowering/reproductive stage was noted as the most sensitive growth stage with a 24.9% yield reduction compared to the control treatment. In all other stages, yield is linearly associated (R2=0.93) with the amount of irrigation water applied, over the range tested. IWUE values ranged from 0.248 to 0.304kg/m3. It can therefore be concluded that provided stress at the midseason stage is avoided and depending on the volume of water available, different deficit irrigation arrangements using on-farm pond water is possible.

Involvement of berry hormonal content in the response to pre- and post-veraison water deficit in different grapevine (Vitis vinifera L.) cultivars

Background and Aims The application of deficit irrigation to grapevines modifies the hormonal status of berries, but little information about the influence of berry hormones on phenological sensitivity to water deficit is available. Therefore, the aim of this research was to assess the involvement of berry hormonal status in fruit composition in response to regulated deficit irrigation applied during different phenological stages in two grapevine cultivars. Methods and Results The study was carried out on fruiting cuttings of two cultivars of Vitis vinifera L., Tempranillo and Graciano. Treatments were: (i) early water deficit from fruitset to onset of veraison (early deficit); (ii) late water deficit from onset of veraison to harvest (late deficit); and (iii) plants regularly irrigated (Control). Both early water deficit and late water-deficit strategies modified evolution of indole-3-acetic acid, abscisic acid, salicylic acid and jasmonic acid, which was related to changes in berry size, increases in phenolic substances and accumulation of amines. Conclusions Differential sensitivity of Tempranillo and Graciano grapevines to seasonal water stress was mediated, at least in part, by alterations in hormonal status of berries at the time of water stress imposition. Significance of Study This study relates interspecific differences in the sensitivity of seasonal water-deficit irrigation to changes in the endogenous hormonal status of berries.

Application of AquaCrop model for yield and irrigation requirement estimation of sugar beet under climate change conditions in Serbia

Climate change impact on field production may play a great role in strategic planning on soil and water resources management. Therefore, the aim of this work was to find out the impact of climate change on sugar beet yield, irrigation depth variation and water saving practices. AquaCrop model v.4.0 was used for yield and irrigation requirement estimation. Input data for future climatic parameters were obtained from EBU-POM for four scenarios A1B, A2, A1B* and A* (*&gt;CO2), and periods of observation were first (2010-2039); second (2040-2069), and third (2070-2099). Undoubtedly, yield will not be reduced in the first period by any scenario, on the contrary, it might be increased. In the second period, yield reduction was observed in A1B and A2 scenarios, hence without the increment of CO2 in the Vojvodina region, whereas in Central Serbia, yield reduction might be expected even in scenarios of A1B and A2*. Irrigation could ensure yield increment in both regions, provided that an increase is more considerable in Central Serbia, due to lower soil water capacity. Application of optimal irrigation depth yield could be increased by up to 57-97% in Vojvodina and 77-285% in Central Serbia. Lower values are obtained in the first period and the highest in the third period. Applying deficit irrigation, water saving would reduce yield in scenario A2, otherwise to obtain high yield, irrigation depth of 300-500 mm should be ensured in Central Serbia. In the same scenario, 300-420 mm of water for irrigation is needed in Vojvodina, but its water savings could be 80-120 mm, or 20%. In scenario A1B, to obtain high yield, 80 mm could be saved in both regions.

The influence of regular deficit irrigation applications on water use, yield, and quality components of two corn (Zea mays L.) genotypes

The objective of the present study was to determine the mechanisms of tolerance of two corn (Zea mays L.) genotypes (Şafak and Ant-İ90) to water stress under five different irrigation treatments designated as full irrigation (I100) with no water stress and slight (I75), mild (I50), severe water stress (I25) and no irrigation (I0) treatments. The results showed that different irrigation levels applied has statistically significant effect on yield components such as anthesis–silking interval, plant height, ear diameter, ear length, kernel number and 1000 grain weight, except for ear number. In both of the genotypes, water deficit stress significantly (P≤0.01) increased glucose, fructose, and sucrose contents while it decreased protein content. The maximum grain yield was obtained from Şafak genotype under full irrigation, slight, mild, severe and full water deficit stress as much as 9.35tha−1, 8.34tha−1, 7.89tha−1, 5.56tha−1 and 3.63tha−1, respectively. The highest water use was observed in I100 treatment as 738.1mm for Şafak genotype, while the lowest was found in I0 treatment as 260.0mm for Ant-İ90 genotype. The highest water use efficiency was found in I50 as 15.7kgha−1mm−1 for Şafak genotype, and the lowest one was found in I0 as 5.5kgha−1mm−1 for Ant-İ90. It was concluded that Şafak was more tolerant genotype to water stress than that of Ant-İ90.

Cereal yield stabilization in Terai (Nepal) by water and soil fertility management modeling

Rice (Oryza sativa L.), maize (Zea mays L.) and wheat (Triticum aestivum L.) are the major cereals cultivated in the Terai region of Nepal. In the region, agriculture is mainly rainfed and fertilizer applications are low. In this study, water and soil fertility management was modeled with the FAO AquaCrop model. For the model calibration and validation, field trials were set up during two years in Rampur, a representative area of Terai at Chitwan. The statistical comparison between the simulated and observed yield of the validation fields resulted in an average RRMSE (relative root mean squared error), R2 (coefficient of determination) and EF (Nash–Sutcliffe efficiency) of 0.05, 0.94 and 0.90 for rice, 0.08, 0.90 and 0.87 for wheat and 0.08, 0.97 and 0.96 for maize, respectively. The validated model was subsequently used to simulate different scenarios with 30 years of historical climatic data to determine realistic soil fertility and water management strategies for increasing crop yields. For the monsoon crops (rice and maize) that benefit from abundant rainfall, only an improved fertility management could increase crop yields by up to 65% and 58%, for rice and maize, respectively. During the winter and spring, seasons with lesser rainfall, crops were severely under-watered in absence of irrigation. For winter wheat, application of deficit irrigation increased yield by up to 67–197% compared to the rainfed crop yield for different fertility levels. For spring maize, full irrigation with increased fertilizer application was recommended to increase the yield. However, by considering the water scarcity in the region, application of deficit irrigation resulted in good and stable yields under low to moderate fertility and always resulted in a better water productivity than fully irrigated crops. It was demonstrated that increasing soil fertility of the winter and spring crops without considering irrigation could sometimes result in crop failure, instead of a yield increase. For fertilizer applications above 50% of the national recommended fertilizer applications, full irrigations are recommended for best yield results for winter and spring crops.

RESPONSE OF POTATO YIELD AND WATER EFFICIENCY TO DEFICIT DRIP AND FURROW IRRIGATION

Potatoes is one of the main vegetable irrigated-crops in Yemen which uses large quantity of irrigation water, mainly because surface irrigation methods, characterized with low efficiency, are mostly used. This study aims to improve water use efficiency (WUE) for growing potatoes through applying deficit irrigation technique coupled with drip and furrow irrigation methods. The study was undertaken at the College of Agriculture farm having clayey loam soil. Drip irrigation system was compared with furrow irrigation system at three levels of deficit irrigation, namely :100%, 80% and 60 % of ET0. For the drip irrigation method, the potatoes yield was found 24.9 t/ha and 17.5 t/ha for irrigation levels of 100 and 60 % of ET0, respectively. While for furrow irrigation method, the yield was found 21.1 t/ha and 15.3 t/ha for irrigation levels of 100 and 60 % of ET0, respectively. The results showed linear increase in WUE with the decrease in irrigation levels. For drip irrigation method, the WUE increased from 6.2 kg/ m3 at full irrigation level to 7.3 kg/m3 for irrigation level 60 % of ET0. The WUE for furrow irrigation methods was lower and was 3.4 kg/ m3 and 4.1 kg/ m3 for irrigation levels of 100 and 60 % of ET0, respectively.

Sensory Quality and Consumer Acceptance of ‘Tardibelle’ Peach Are Improved by Deficit Irrigation Applied During Stage II of Fruit Development

Deficit irrigation (DI) applied during Stage II of fruit development has the potential of improving fruit quality in peach (Prunus persica). Existing information only covers instrumental assessment of quality. No report is available on how sensory attributes and consumer acceptance are affected. We applied DI at Stage II to ‘Tardibelle’ peach and evaluated fruit composition, sensory attributes, and consumer acceptance during the growing seasons of 2009 and 2010. Results were compared with those from trees that received conventional irrigation (CI). Stem water potential in DI trees was indicative of a moderate water stress during Stage II. In 2010, water stress persisted at the beginning of Stage III and average fruit weight was reduced in DI trees. A panel of trained judges decided that DI increased sweetness, juiciness, and the intensity of peach flavor but it reduced fruit firmness and crispness. A panel of consumers indicated increased preference for DI fruit. The higher appeal for DI fruit could have been partially the result of their more advanced maturity. Improvement of fruit quality could be an important incentive for the application of DI during Stage II because growers may expect to receive a premium price for their higher quality fruit.

Water and land productivities of wheat and food legumes with deficit supplemental irrigation in a Mediterranean environment

Selecting appropriate crops and applying deficit irrigation can help increase water productivity in water-limited regions such as the Mediterranean. The objective of this study was to develop water production functions of major cereal and legume crops under the same environmental and management conditions. Bread and durum wheat, faba bean, chickpea, and lentil were grown under full supplemental irrigation (FSI), two deficit irrigations levels of 2/3 of FSI (2/3SI) and 1/3 of FSI (1/3SI), and under rainfed conditions (no irrigation). In average, the actual evapotranspirations (ETs) under FSI were 549, 552, 365, 451 and 297mm, for bread wheat, durum wheat, faba bean, chickpea and lentil, respectively. For the same crops, they were 463, 458, 330, 393 and 277mm for the treatment 2/3SI and 357, 351, 265, 318 and 244mm for the treatment 1/3SI, respectively. In the case of the rainfed treatment, ETs for the mentioned crops were 250, 251, 227, 237 and 215mm, respectively. The experiment was conducted at the ICARDA experimental station at Tel Hadya, near Aleppo, Syria, over three growing seasons from 2007 to 2010.Results showed that, in general, the treatment with 1/3 of FSI gave the highest rate of increase in grain yield and water productivity. The mean grain yield from rainfed, 1/3SI, 2/3SI, and FSI were 1.36, 3.82, 5.18, and 5.70t/ha for bread wheat; 1.24, 3.80, 5.10, and 5.75t/ha for durum wheat; 1.57, 2.35, 2.86, and 3.54t/ha for faba bean, 1.36, 2.63, 3.36, and 3.74t/ha for chickpea, and 0.64, 1.16, 1.42, and 1.58t/ha for lentil respectively. Grain yield reductions due to the application of 2/3SI were around 10, 5, 15.6, and 10.2% of FSI on average for wheat, chickpea, faba bean, and lentils, respectively. Deficit irrigation at 2/3SI increased water productivity compared to rainfed treatments, by 200, 223, 126, 148 and 190% for bread wheat, durum wheat, faba bean, chickpea, and lentils, respectively. However, differences in total water productivity of crops grown under full irrigation compared to deficit irrigation were not significant. Irrigation water productivity ranged from 25kgha−1mm−1 in wheat with 1/3SI to 10kgha−1mm−1 for legumes under the FSI treatment. Unlike legumes, maximizing wheat grain yield caused a decline in water productivity.

The effect of different vigour olive clones on growth, dry matter partitioning and gas exchange under water deficit

In the last decade, high-density olive planting systems have been developed to facilitate less costly mechanical harvesting and pruning by using straddle harvesters. High-density orchards allow faster production since the first crop of fruit starts a few years after planting. In high-density orchards the control of tree size is essential. It is possible to control the vigour and size of the tree by selecting suitable cultivars, by choosing rootstocks capable of controlling scion vigour and, finally, by applying deficit irrigation to reduce plant vegetative growth. Knowledge of tree water requirements is needed for precise irrigation scheduling. In this study, the dwarfing capacity of two Leccino clones, Leccino Dwarf (LD) showing low vigour, and Leccino Minerva (LM) highly vigorous, was investigated under two water regimens, well-watered ( T 100) and water deficit ( T 50). We analysed growth rates, dry matter production, gas exchanges and water relations of one-year-old plants of Leccino Dwarf (LD) and Leccino Minerva (LM), grown in pots in open fields. The two genotypes showed significant differences in vigour, demonstrated by measuring the trunk diameter, shoot length and leaf area; values were significantly lower in clone LD. Stem water potential, photosynthesis and stomatal conductance were similar in both genotypes under a well-watered regime; they decreased when subjected to water deficit with values significantly lower in LM clone during the summer months, indicating physiological differences among clones and that LD adapts better to water deficit.

Postharvest deficit irrigation in ‘Conference’ pear: Effects on subsequent yield and fruit quality

Abstract The best time for applying deficit irrigation (DI) to pear is not yet known although it was the first fruit crop to be studied for regulated DI. We explored postharvest application. Over the growing seasons of 2007–2010, three irrigation treatments were applied to ‘Conference’ pear in an experimental orchard. They were full irrigation (control, C), withholding irrigation after harvest (DI-PH a+b ), and full irrigation for two weeks after harvest followed by withholding irrigation (DI-PH b ). According to our previous experience with ‘Conference’, the DI treatments were to be irrigated if midday stem water potential ( Ψ stem ) became lower than −1.5 MPa. But it never did. The average annual irrigation water applied to C was 590 mm. This was reduced by 15% for DI-PH b and by 27% for DI-PH a+b . Fruit yield in DI-PH a+b was similar to C for each of the three years following DI. But a carry-over effect was observed after the dry season of 2008. In 2009 fruit set and crop load were therefore reduced for DI-PH a+b but fruit size was increased. For all years DI-PH b was similar to C in terms of fruit set, crop load, fruit size, and yield. Fruit soluble solids concentration (SSC), titratable acidity, and flesh firmness were measured in 2009 and 2010. They were the same in C and DI fruit except for 2009 when SSC was higher in DI-PH a+b fruit. ‘Conference’ adapted to DI in such a way that Ψ stem could be maintained by higher water depletion at a greater soil depth as the experiment progressed. Postharvest DI is recommended for ‘Conference’ but to the extent that midday Ψ stem does not become lower than −1.2 MPa.

Effects of deficit irrigation on biomass, yield, water productivity and fruit quality of processing tomato under semi-arid Mediterranean climate conditions

Processing tomato is a high water demanding crop, thus requiring irrigation throughout growing season in arid and semiarid areas. The application of deficit irrigation (DI) strategies to this crop may greatly contribute to save irrigation water. A two-year study was carried out in order to assess the effects of DI upon water productivity, final biomass, fruit yield and some quality traits of open-field processing tomato cv. Brigade in a typical semi-arid Mediterranean environment of South Italy. Four irrigation treatments were studied: no irrigation following plant establishment (V0); 100% (V100) or 50% (V50) evapotranspiration (ETc) restoration up to fruit maturity, 100% ETc restoration up to flowering, then 50% ETc restoration (V100-50). Total dry biomass accumulation was significantly depressed by early soil water deficit in V0; irrigation at a reduced rate (50% ETc) from initial stages (V50) or from flowering onwards (V100-50) did not induce any losses in final dry biomass. The marketable yield did not significantly differ among plots irrigated, but an averaged irrigation water saving of 30.4% in V100-50 and 46.2% in V50 was allowed as compared to V100. Marketable yield was negatively affected by the early water shortage in V0, due to the high fruit losses (>44%). The effects of DI on fruit quality were generally the converse of those on fruit yield. DI improved total soluble solids content, titratable acidity and vitamin C content. Water use efficiency was positively affected by DI, suggesting that the crop does not benefits from the water when this last is supplied to fulfil total crop requirements for the whole season. Yield response factor, which indicates the level of tolerance of a crop to water stress, was 0.49 for total dry biomass ( Kss) and 0.76 for marketable yield ( Ky), indicating that in both cases the reduction in crop productivity is proportionally less than the relative ET deficit. In conclusion, the adoption of DI strategies where a 50% reduction of ETc restored is applied for the whole growing season or part of it could be suggested in processing tomato, to save water improving its use efficiency, minimizing fruit losses and maintaining high fruit quality levels. This aspect is quite important in semi-arid environments, where water scarcity is an increasing concern and water costs are continuously rising.

Yield and water use of eggplants (Solanum melongena L.) under full and deficit irrigation regimes

Abstract Field experiments were conducted in 2008 and 2009 to determine the effects of deficit irrigation on yield and water use of field grown eggplants. A total of 8 irrigation treatments (four each year), which received different amounts of irrigation water, were evaluated. In 2008, deficit irrigation was applied at full vegetative growth (WS-V), pre-flowering (WS-F) and fruit ripening (WS-R), while in 2009 deficit irrigation was applied during the whole growing season at 80 (WS-80), 60 (WS-60) and 40% (WS-40) of field capacity. Deficit-irrigated treatments were in both years compared to a well irrigated control. Regular readings of soil water content (SWC) in 2008 and 2009 showed that average soil water deficit (SWD) in the control was around 30% of total available water (TAW) while in deficit-irrigated treatments it varied between 50 and 75% of TAW. In 2008, deficit irrigation reduced fruit fresh yield by 35, 25 and 33% in WS-V, WS-F and WS-R treatments, respectively, when compared to the control (33.0 t ha−1). However, the reduction in fresh yield in response to deficit irrigation was compensated by an increase in fruit mean weight. Results obtained in 2009 showed that fruit fresh yield in the control was 33.7 t ha−1, while it was 12, 39 and 60% less in WS-80, WS-60 and WS-40 treatments, respectively. On the other hand, fruit dry matter content and water productivity were found to increase significantly in both years in deficit-irrigated treatments. Applying deficit irrigation for 2 weeks prior to flowering (WS-F) resulted in water saving of the same magnitude of the WS-80 treatment, with the least yield reduction, making more water available to irrigate other crops, and thereby considered optimal strategies for drip-irrigated eggplants in the semi-arid climate of the central Bekaa Valley of Lebanon.

Evapotranspiration and water use of full and deficit irrigated cotton in the Mediterranean environment in northern Syria

► Deficit irrigation has moderate impact on cotton water productivity. ► Rationalizing water application can contribute to natural resources conservation . ► Sufficient fertilization can contribute to natural resources conservation in water scarce areas. Cotton ( Gossypium hirsutum L.) is the most important industrial and summer cash crop in Syria and many other countries in the arid areas but there are concerns about future production levels, given the high water requirements and the decline in water availability. Most farmers in Syria aim to maximize yield per unit of land regardless of the quantity of water applied. Water losses can be reduced and water productivity (yield per unit of water consumed) improved by applying deficit irrigation, but this requires a better understanding of crop response to various levels of water stress. This paper presents results from a 3-year study (2004–2006) conducted in northern Syria to quantify cotton yield response to different levels of water and fertilizer. The experiment included four irrigation levels and three levels of nitrogen (N) fertilizer under drip irrigation. The overall mean cotton (lint plus seed, or lintseed) yield was 2502 kg ha −1 , ranging from 1520 kg ha −1 under 40% irrigation to 3460 kg ha −1 under 100% irrigation. Mean water productivity (WP ET ) was 0.36 kg lintseed per m 3 of crop actual evapotranspiration (ET c ), ranging from 0.32 kg m −3 under 40% irrigation to 0.39 kg m −3 under the 100% treatment. Results suggest that deficit irrigation does not improve biological water productivity of drip-irrigated cotton. Water and fertilizer levels (especially the former) have significant effects on yield, crop growth and WP ET . Water, but not N level, has a highly significant effect on crop ET c . The study provides production functions relating cotton yield to ET c as well as soil water content at planting. These functions are useful for irrigation optimization and for forecasting the impact of water rationing and drought on regional water budgets and agricultural economies. The WP ET values obtained in this study compare well with those reported from the southwestern USA, Argentina and other developed cotton producing regions. Most importantly, these WP ET values are double the current values in Syria, suggesting that improved irrigation water and system management can improve WP ET , and thus enhance conservation and sustainability in this water-scarce region.

WATER MANAGEMENT STRATEGIES UNDER DEFICIT IRRIGATION

Deficit irrigation (DI) is an optimization strategy whereby net returns are maximized by reducing the amount of irrigation water; crops are deliberated allowed to sustain some degree of water deficit and yield reduction. Although the DI strategy dates back to the 1970s, this technique is not usually adopted as a practical alternative to full irrigation by either academics or practitioners. Furthermore, there is a certain amount of confusion regarding its concept. In fact, a review of recent literature dealing with DI has shown that only a few papers use the concept of DI in its complete sense (e.g. both the agronomic and economic aspects). A number of papers only deal with the physiological and agronomical aspects of DI or concern techniques such as Regulated Deficit Irrigation (RDI) and Partial Root Drying (PRD). The paper includes two main parts: i) a review of the principal water management strategies under deficit conditions (e.g. conventional DI, RDI and PRD); and ii) a description of a recent experimental research conducted by the authors in Sicily (Italy) that integrates agronomic, engineering and economic aspects of DI at farm level. Most of the literature reviewed here showed, in general, quite positive effects from DI application, mostly evidenced when the economics of DI is included in the research approach. With regard to the agronomic effects, total fresh mass and total production is generally reduced under DI, whereas the effects on dry matter and product quality are positive, mainly in crops for which excessive soil water availability can cause significant reductions in fruit size, colour or composition (grapes, tomatoes, mangos, etc.). The experimental trial on a lettuce crop in Sicily, during 2005 and 2006, shows that the highest mean marketable yield of lettuce (55.3 t ha-1 in 2005 and 51.9 t ha-1 in 2006) was recorded in plots which received 100% of ET0-PM (reference evapotranspiration by the Penman- Monteith method) applied water. In the land-limiting case, the estimated optimal economic levels were quite similar to the optimal agronomic levels. In the waterlimiting case DI ranges, at least as profitable as full irrigation, were of 17-49% ET0-PM and of 71-90% ET0-PM in 2005 and 2006 respectively.