At present and more so in the future, irrigated agriculture will take place under water scarcity. Insufficient water supply for irrigation will be the norm rather than the exception, and irrigation management will shift from emphasizing production per unit area towards maximizing the production per unit of water consumed, the water productivity. To cope with scarce supplies, deficit irrigation, defined as the application of water below full crop-water requirements (evapotranspiration), is an important tool to achieve the goal of reducing irrigation water use. While deficit irrigation is widely practised over millions of hectares for a number of reasons–from inadequate network design to excessive irrigation expansion relative to catchment supplies–it has not received sufficient attention in research. Its use in reducing water consumption for biomass production, and for irrigation of annual and perennial crops is reviewed here. There is potential for improving water productivity in many field crops and there is sufficient information for defining the best deficit irrigation strategy for many situations. One conclusion is that the level of irrigation supply under deficit irrigation should be relatively high in most cases, one that permits achieving 60–100% of full evapotranspiration. Several cases on the successful use of regulated deficit irrigation (RDI) in fruit trees and vines are reviewed, showing that RDI not only increases water productivity, but also farmers' profits. Research linking the physiological basis of these responses to the design of RDI strategies is likely to have a significant impact in increasing its adoption in water-limited areas.
Deficit irrigation (DI) has been widely investigated as a valuable and sustainable production strategy in dry regions. By limiting water applications to drought-sensitive growth stages, this practice aims to maximize water productivity and to stabilize – rather than maximize – yields. We review selected research from around the world and we summarize the advantages and disadvantages of deficit irrigation. Research results confirm that DI is successful in increasing water productivity for various crops without causing severe yield reductions. Nevertheless, a certain minimum amount of seasonal moisture must be guaranteed. DI requires precise knowledge of crop response to drought stress, as drought tolerance varies considerably by genotype and phenological stage. In developing and optimizing DI strategies, field research should therefore be combined with crop water productivity modeling.
Increased water demands and drought have resulted in a need to determine the impact of deficit water management in irrigated sugarbeet (Beta vulgaris L.) production. This study was conducted over 3 yr at USDA-ARS in Kimberly, ID, on a Portneuf silt loam soil. Eight irrigation treatments consisted of crop evapotranspiration (ETc) rates combined with application timing. Treatments were: W1 Even: approximately (approximate to) 100% ETc evenly throughout the growing season; W2 Even: approximate to 65% crop evapotranspiration; W2 Early: approximate to 100% ETc early in season, approximate to 55% ETc the remainder of the season; W2 Late: rain-fed from emergence to end of July, approximate to 100% ETc the remainder of the season; W3 Even: approximate to 40% ETc; W3 Early: approximate to 100% ETc early in season, approximate to 25% the remainder of the season; W3 Late: rain-fed through mid-August, approximate to 100% ETc the remainder of the season, and rain-fed: no post emergence irrigation. Results showed that within deficit irrigation treatments, higher yields were obtained when water was applied evenly throughout the season (Even) or approximate to 100% of ETc was applied early with deficit irrigation later in the season (Early). Thus, the W2 Even and W2 Early treatments had 31.6, 32.9, and 28.2% greater estimated recoverable sucrose (ERS) yields compared to the W2 Late treatment in 2011, 2012, and 2016, respectively. Across all years, ERS yields increased at rates ranging from 17.3 to 22.0 kg ha(-1) mm(-1) actual crop water evapotranspiration (ETa). Generally, sugarbeet with greater water stress early in the season followed by approximate to 100% ETc later had lower yields and sucrose content (late treatments).
Reservoirs play a strategic role in the rapid monetary growth of the world by providing numerous benefits. However, the reduction in appropriate sites along with environmental and social apprehensions has resulted in curtailment of new reservoirs around the world in twenty-first century. There is a potential of benefits available from existing reservoirs which can be best capitalized through their optimized operation. Reservoirs Operation Optimization considering Sediment Evacuation (RESOOSE), recently developed model which combines multiple reservoirs operation and sediment evacuation with Genetic Algorithm based optimization module, has been used in the study. The objective of the study was to optimize the irrigation deficit through cascade reservoirs with consideration to hydropower, sediment evacuation and flood damages reduction benefits. The RESOOSE model was applied to optimize the irrigation deficits of Tarbela and Diamer Basha Reservoirs in Pakistan using developed objective function. The article computed and compared the benefits of optimized and existing rule curves. The hydropower benefits of 36.92 Billion Kw, sediment evacuation benefits of 21.534 Million m3 and flood damages of 616.19 Million US$ due to existing rule curves were considered as minimum benefits for achieving the optimized rule curves to minimize irrigation deficits. The developed optimized rule curves reduced the irrigation shortages of case study reservoirs from 6.9 to 5.8 Billion m3 (16% enhancement) annually as compared to existing rule curves. The optimized rule curves minimized the irrigation deficits by maintaining the existing benefits and without lowering the minimum operating levels of case study reservoirs. The study suggests change in existing rule curves of Tarbela and Diamer Basha Reservoirs due to less irrigation shortages. The RESOOSE model can be applied to other cascade reservoirs for optimizing the rule curves.
Straightforward guidelines for deficit irrigation (DI) can help in increasing crop water productivity in agriculture. To elaborate such guidelines, crop models assist in assessing the conjunctive effect of different environmental stresses on crop yield. We use the AquaCrop model to simulate crop development for long series of historical climate data. Subsequently we carry out a frequency analysis on the simulated intermediate biomass levels at the start of the critical growth stage, during which irrigation will be applied. From the start of the critical growth stage onwards, we simulate dry weather conditions and derive optimal frequencies (time interval of a fixed net application depth) of irrigation to avoid drought stress during the sensitive growth stages and to guarantee maximum water productivity. By summarizing these results in easy readable charts, they become appropriate for policy, extension and farmer level use. We illustrate the procedure to derive DI schedules with an example of quinoa in Bolivia. If applied to other crops and regions, the presented methodology can be an illustrative decision support tool for sustainable agriculture based on DI.
The effect of controlled deficit irrigation (CDI) on the accumulation of carotenoids, polyphenols and -ascorbic acid was studied in conventional and high lycopene tomato cultivars. Plants were initially irrigated to cover 100%ET and after the fruit set phase, the dose was reduced to 75% or 50% of ET . CDI had no significant effect on the accumulation of carotenoids, while it increased the levels of the hydroxycinnamic acids chlorogenic and ferulic acids, the flavonoid rutin and -ascorbic acid. Nevertheless, there were important interactions and this effect was highly dependent on the year and site of cultivation. Certain growing areas would be more favorable to supply high quality markets, and, fortunately, CDI would maximize polyphenol (100–75%ET ) and -ascorbic acid (100–50%ET ) in these areas. A combination of the best genotype and growing area with CDI would offer high quality products, preserving a scarce resource: water.
Orange tree cultivation is widespread throughout the world, and the Mediterranean Basin is an important producer. The Mediterranean climate is characterised by scarce water resources that limit crop sustainability. In this study, controlled deficit irrigation is evaluated as a water conservation strategy with the aim of improving crop sustainability. To accomplish this objective, a trial is conducted in southern Spain for nine months with four treatments (five repetitions each): normal irrigation (the control variable), deficit irrigation and two treatments of controlled deficit irrigation. In relation to the crop, physiological parameters, production and fruit quality were analysed, all with respect to water usage. Finally, an efficiency curve was established for water usage, which determined the optimum water usage to be between 700 and 800 mm. It has been experimentally determined that controlled deficit irrigation reduces water used by 5% compared with constant deficit irrigation and improves productivity by 4%. The primary conclusion is that controlled deficit irrigation strategies present certain advantages to crop management and are an alternative to reducing water inputs with minimal effects on production and fruit quality, thus contributing to crop sustainability.
In North America, almond [Prunus dulcis (Mill.) D. A. Webb] trees are grown almost exclusively in the Central Valley of California. Research on deficit irrigation is needed to improve water productivity. Real-time technology assessing soil water potential to manage irrigation initiation has led to significant improvements in water productivity in other crops. The objective of this study was to examine the possibility of using realtime tensiometry for irrigation to trigger irrigation events and to generate water savings without affecting crop yield. The yield responses and water consumption of mature almond trees were quantified from 2012 to 2015 for four different irrigation strategies in a commercial orchard located in the San Joaquin Valley in California. Three of the treatments were based on soil water potential threshold (SWPT) measurements and the fourth on the grower's current management practices, which used estimated crop evapotranspiration (ETc). The SWPT treatments were based on three different stress levels: wet (-35 kPa), medium (-45 kPa), and dry (-55 kPa). There was no significant difference in marketable yield between the grower irrigation strategy and the medium treatment, although the latter used 139 mm less water as a yearly average. In the dry treatment, there was 10% less water applied relative to the medium treatments and 30% less than the grower treatment but a 10% yield reduction compared with the medium and grower treatments. These results indicate that irrigation management for almond could be optimized by initiating irrigation at -45 kPa.
AbstractDeficit irrigation, or the deliberate underirrigation of a crop, is a way to save farm water and allocate it to uses such as municipal, industrial, or agricultural expansion. Research on this practice has focused on profitability, but with conflicting results. The feasibility of deficit irrigation involves more than economic concerns, and agronomic and legal aspects are also important in improving farm operations. The feasibility of deficit irrigation depends to a large extent on context, and a case involving the water law system of the State of Colorado in the western United States was examined to provide a real-world instance to study the institutional and technical challenges of implementing it. Colorado has experienced extensive transfers from agriculture to urban areas and is interested in employing deficit irrigation to free more irrigation water for use in the future. Based on the results, the paper suggests practical methods for implementation of deficit irrigation in Colorado, with possible implications for similar regions with irrigated agriculture.