Deficit Irrigation Practices Research Articles

GIS‐Based Surface Irrigation Potential Assessment for Ethiopian River Basin

AbstractThe suitability of the Dirma River Basin in Ethiopia for surface irrigation potential development and identification of potentially irrigable sites were the subject of the present study. The river basin area suitability was evaluated based on slope, soil and surface water resource availability using ArcGIS 10.1. Potentially suitable sites for surface irrigation development were evaluated for potato and tomato crops. The reference crop evapotranspiration, effective rainfall, net irrigation and gross irrigation water requirement were estimated using CROPWAT software. The results of the suitability model developed indicated that about 68.3% of the total river basin area falls in marginally to highly suitable categories for surface irrigation development. The water resource availability reveals that due to very high intra‐annual variability in river flows, only 6% of the mean annual flow is available for the period from January to May, and with this up to 30% of land that is suitable for surface irrigation can be irrigated. However, with suitable water storage infrastructure and deficit irrigation practices, utilization of land and water resources of the Dirma River Basin can be increased significantly. Therefore, this study will help decision makers, investors, planners and policymakers at the local, regional and national levels in better identification of profitable and sustainable irrigation investment opportunities in the region. © 2019 John Wiley & Sons, Ltd.

Soil salinization in very high-density olive orchards grown in southern Portugal: Current risks and possible trends

Deficit irrigation practices carried out in very high-density olive orchards grown in the Alentejo region of southern Portugal can bring important economic benefits in terms of water savings, yields, and oils. They can also result in serious salinization/sodification problems without proper management of soil and water resources. The main objective of this study was to evaluate the long-term (30 years) impact of those irrigation practices on local soil resources using a multicomponent transport modeling approach embedded in the HYDRUS-1D model. Soil salinization and sodification risks were quantified for 160 soil profiles by considering eight different scenarios: current monitored irrigation practices (S1), using waters of variable quality (S2-S6), planting maize as an alternative crop (S7), and using climate change projections for the region (S8). Despite the large observed variability, simulations that considered current irrigation practices (S1) produced average values of the electrical conductivity of the soil solution (ECsw) at the end of the leaching seasons always below the threshold limit for crops moderately tolerant to soil salinity. In this scenario, the average values of the sodium adsorption ratio (SAR) were also kept within the same magnitude of those determined at the beginning of the simulation period (initial conditions). Irrigations with worse quality waters (S2-S6) led to higher ECsw and SAR values. Although annual rainfall amounts influenced the salinity build-up, the SAR evolution depended mainly on water quality. In maize soil profiles (S7), the simulated ECsw and SAR values were lower than in olive soil profiles, with irrigation practices contributing to salt removal during the seasons. Conversely, the climate change scenario (S8) resulted in slightly higher ECsw and SAR values than those simulated for current conditions, indicating a potentially greater risk of soil degradation in the near future. Although current irrigation practices seem to present relatively low soil salinization/sodification risks, the variability of results and the uncertainty associated with model predictions indicate that close monitoring to prevent further degradation of soil and water resources in the region should be recommended.

Impact of different irrigation regimes under varied planting density on growth, yield and economic return of cashew (Anacardium occidentale L.)

To assess the effect of planting density and irrigation in cashew (Anacardium occidentale L.) during its critical growth stages such as flowering and fruit set on, growth, yield, water-use efficiency and farm income, a field experiment was initiated in a split-plot design in 2011 at Puttur, Karnataka, India. The main plot consisted of three planting densities namely, 5 × 4 m, 6 × 4 m and 10 × 5 m. The irrigation treatments were imposed in subplots as, irrigation at 60% cumulative pan evaporation (CPE), at 40% CPE, at 20% CPE, irrigation once in 15 days, soil and water conservation technique, and control (without any irrigation or soil water conservation technique). The results indicated that the growth, raw cashew nut yield and net income during 5th and 6th year of plantation of cashew increased with increase in planting density per unit area. The average increase in nut yield under high density planting ranged from 75 to 81% compared to normal density planting. Irrigation using drip system from December to March at 20% CPE and 40% CPE was beneficial to increase the nut yield by 53.5% and 34.1% compared to control. The yield increase under soil and water conservation practice was 12.9%, and 59.7% under irrigation once in 15 days. The increased planting density was beneficial to increase the net income and benefit–cost ratio. The deficit irrigation practices were useful to increase the water-use efficiency in cashew. Widely spaced trees showed increased water-use efficiency compared to high-density planting. Overall, the study demonstrated the usefulness of increased planting density and appropriate irrigation practices to increase yield and net income from cashew orchards.

Effectiveness of Trichoderma harzianum in soil and yield conservation of tomato crops under saline irrigation

Protected horticultural crops in the Mediterranean region are typically under deficit irrigation and intensive cultivation practices and must cope with poor irrigation and soil quality due to salinization. The effects of variable irrigation water quality and use of the beneficial fungus Trichoderma harzianum on the evolution of soil salinization and yield during a single cropping season are examined at a small-scale Solanum lycopersicum L. cv Elpida greenhouse experiment. The experiment simulates typical coastal Mediterranean greenhouse cultivation conditions of the RECARE Project soil salinization Case Study in Greece (Timpaki basin in Crete). Local NaCl-free but highly calcareous planting soil as well as local cultivation practices were used to replicate prevailing conditions at the Case Study. Tomato plants were drip irrigated with NaCl solutions of low (L) (ECw = 1.1 dS m−1) and high (H) (ECw = 3.5 dS m−1) concentration to emulate a typical “good quality” and “marginal quality” irrigation water, respectively. T. harzianum (T) was selectively applied resulting in a total of 2 treatments colonized with the fungus (LT, HT) and two not (N) colonized (LN, HN). For high salinity irrigation treatments HN and HT, sodium adsorption ratio (SAR) values settled at 22.2 and 13.4, respectively, showing that T. harzianum reduced the effect salinity significantly. Monitoring of soil nutrients showed a significant decrease of P-Olsen in non-T. harzianum treatments versus no change in P-Olsen in T. harzianum treatments. Final total and marketable tomato yield for treatment HN were reduced compared to LN by 28% and 42%, respectively, with in T. harzianum treatments having no significant effect. Fruit quality characteristics were overall less sensitive to higher irrigation salinity than to timing of harvest. We conclude that, under high salinity irrigation, an early harvest and termination of the cultivation has no significant impact on tomato yield while obviating pressure on soil resources and conserving agricultural input.

Fostering sustainable water use in almond (Prunus dulcis Mill.) orchards in a semiarid Mediterranean environment

ABSTRACTThis work examines the long-term effects of deficit-irrigation (DI) practices in almond crop (Prunus dulcis Mill.) in agronomical and physiological terms. The trial was conducted during four-year monitoring period (2014–2017), in an experimental orchard (SW Spain), subjected to three irrigation regimes; i) a full-irrigation treatment (FI), which received 100% of crop evapotranspiration (ETC); ii) a regulated-deficit irrigation (RDI50), which received 50% of ETC during the kernel-filling period; and iii) a low-frequency deficit irrigation (LFDI), that was subjected to continuous periods of irrigation-restriction defined in terms of threshold values of leaf-water potential (Ψleaf) during the kernel-filling period. During the water stress period, there were monitored Ψleaf, stomatal conductance (gs) and canopy temperature (TC). Significant improvements in terms of water-use efficiency were found, as no differences in terms of yield between FI and LFDI were found, leading to the conclusion that significant water savings (between 27 and 40%) can be achieved without compromising the yield. Moreover, threshold values of Ψleaf and thermal indicators were defined which will allow establishing future irrigation scheduling without compromising almond yield, especially when DI strategies are being applied.

Optimizing irrigation water levels to improve yield and water use efficiency of vegetables: case study of tomato

Optimizing irrigation water requirement is necessary to improve productivity of irrigated agriculture. Hence, adapting the knowledge of irrigation scheduling for specific crop and location is important. Field experiment was then conducted in Raya Alamata district of Tigray, Ethiopia to investigate the impact of different irrigation water levels on yield and irrigation water use efficiency (IWUE) of tomato. Eight treatments (50, 35, 25% above estimated crop water requirement (CWR), estimated CWR, 25, 35, 50% below the estimated CWR and farmers practice) were arranged in randomized complete block design under three replications. Tomato water requirement was estimated using CROPWAT 8 software and it was estimated to be 500 mm throughout the base period. The result indicates significant difference between marketable yield (MY), total yield (TY) and IWUE of tomato by the level of irrigation. The application of estimated CWR of tomato gave higher MY (36.37 ton/ha) and TY (38.58 ton/ha). Unmarketable fruit yield of tomato was unaffected by level of irrigation. Farmers’ practice gave considerable MY (36.32 ton/ha). But, the depth of water applied by farmers throughout the growing season was 561 mm which was 12.2% above the estimated CWR. The yield obtained per unit of applied water (IWUE) ranges from 0.357 to 0.876 kg/m3 for the different irrigation water levels. This shows that IWUE increases with decreasing depth of water application. In conclusion, deficit irrigation practice could be successful in saving irrigation water up to 35% of tomato CWR without significant reduction in fruit yield of tomato in regions where water is a limiting factor for vegetable production.

Crop production with limited irrigation: A review

When water supplies are restricted, so that full evapotranspiration demands cannot be met, limited irrigation is practised. Management strategy of limited irrigation is to optimise production per unit of applied water rather than to maximise yield per unit of land. Principles that help to facilitate limited irrigation strategies can be broadly grouped into three: agricultural water management, crop considerations and agronomic options. When anticipating low water year, choose crops which maximise production with limited water. In decreasing order of efficiency, short season indeterminate and long season indeterminate crops should be chosen judiciously. Deficit irrigation practices, localised irrigation methods, reducing water losses,conjunctive use of water resources etc can help minimise yield losses due to soil moisture stress. Additional agronomic management options that can maximise production include conservation tillage, advancing or delaying planting dates in order to coincide the crop’s critical period with water availability, decreasing plant competition byreducing seeding density and controlling weeds. Available options to address the challenge of limited irrigation have been briefly presented.

Effects of different irrigation practices using treated wastewater on tomato yields, quality, water productivity, and soil and fruit mineral contents

Wastewater use in agricultural irrigation is becoming a common practice in order to meet the rising water demands in arid and semi-arid regions. The study was conducted to determine the effects of the full (FI), deficit (DI), and partial root-zone drying (PRD) irrigation practices using treated municipal wastewater (TWW) and freshwater (FW) on tomato yield, water use, fruit quality, and soil and fruit heavy metal concentrations. The TWW significantly increased marketable yield compared to the FW, as well as decreased water consumption. Therefore, water use efficiency (WUE) in the TWW was significantly higher than in the FW. Although the DI and the PRD practices caused less yields, these practices significantly increased WUE values due to less irrigation water applied. The water-yield linear relationships were statistically significant. TWW significantly increased titratable acidity and vitamin C contents. Reduced irrigation provided significantly lower titratable acidity, vitamin C, and lycopene contents. TWW increased the surface soil and fruit mineral contents in response to FW. Greater increases were observed under FI, and mineral contents declined with reduction in irrigation water. Heavy metal accumulation in soils was within safe limits. However, Cd and Pb contents in fruits exceeded standard limits given by FAO/WHO. Higher metal pollution index values determined for fruits also indicated that TWW application, especially under FI, might cause health risks in long term.

Sustainability Implications of Deficit Irrigation in a Mature Water Economy: A Case Study in Southern Spain

Deficit irrigation (DI) is an agricultural practice in which the volume of irrigation water applied during the crop cycle is below the irrigation requirements for maximum production, the aim of which is to increase irrigation water productivity. Most research on this technique has focused on agronomic strategies while the economic and environmental consequences have received little attention. This study aims to shed some light on this matter and presents preliminary results regarding the implications of DI with respect to the sustainable use of water resources. The analysis is based on the DPSIR analytical framework (Driving force/Pressure/State/Impact/Response) and the microeconomics of DI. The case study focuses on intensive olive groves in the Guadalquivir river basin in Southern Spain (where olive cultivation accounts for 50% of the total irrigated area). The analysis shows that the widespread use of DI practices, which is the farmers’ response to a decreasing net water supply and falling farm incomes (driving force) in the context of a mature water economy, may help to break the DPSIR chain of causality, provided that there are restrictions on any expansion in irrigated area. They can, thus, play a role in achieving sustainable water use. Conversely, demand and supply (regulator) responses involving raising the price of water would lead to higher pressures on the resource and represent a negative driving force in our DPSIR model.

Evaluating Water Exclusion using Plastic Ground Cover in Maize at Two Population Densities

Core Ideas Evaluating drought‐tolerant maize hybrids is a challenge in the eastern U.S. Corn Belt. Treatments with black plastic had lower soil moisture with minor increases in soil temperature. Water exclusion using plastic ground cover reduced soil moisture and grain yield compared to the rain‐fed plus irrigation control. Evaluating maize (Zea mays L.) hybrids under drought conditions in rain‐fed environments can be difficult using deficit irrigation practices, and installation of permanent rain‐exclusion structures can be cost prohibitive. Covering the soil surface to reduce infiltration has been successful in other crops, but limited evaluation has been conducted in maize systems of the U.S. Corn Belt. The objective of this study was to determine if black plastic ground cover could exclude water from maize under varying agronomic conditions to generate dry soil conditions. A field study was conducted in South Charleston, OH, in 2013 and 2014 in maize using two hybrids with varying drought tolerance at two plant populations (74,000 and 124,000 plants ha−1). Black plastic ground cover was installed at canopy closure (V6) as a water exclusion practice, and a rain‐fed plus irrigation treatment was also installed at V6 for comparison. Water exclusion reduced soil moisture at R2, R5, and R6 by 0.02 to 0.09 m3 water m−3 soil and reduced yield by 2.11 Mg ha−1 compared to the rain‐fed plus irrigation treatment. While water stress symptoms during the season were not observed, volumetric water content decreased below the permanent wilting point at R5 in the top 30 cm in 2013 and at R2, R5, and R6 in the top 20 cm in 2014. These results suggest that surface‐applied black plastic can be an effective water exclusion method in maize, but should be evaluated further to optimize installation timing and its utility in suboptimal growing seasons.

Water productivity in fruit trees orchards under water scarcity

With growing water shortages, agriculture faces the challenge of increasing water productivity (WP). In this work, WP of two main crops, peach and olive, is evaluated for different cultivars and deficit irrigation practices. WP in peach was estimated over 4-7 years for three cultivars (early, mid-season and late-maturing), two rootstocks and two deficit irrigation strategies. In terms of yield/total water supply, the late maturing cultivar subjected to mild deficit irrigation, gave the highest WP (4.1 kg m-3), compared to the mid-season (3.0 kg m-3) and early cultivar (1.9 kg m-3). Full irrigation reduced slightly the performance of the most productive cultivar (3.7 kg m-3). Performances of early and mid-season cultivars were affected by rootstock. Interaction between mild deficit irrigation and vigorous rootstock induced better WP. Experimental work in olives targeted WP under contrasted environments. In northern Tunisia (450 mm annual rainfall), average yield for three cultivars ('Picholine', 'Chetoui' and 'Mansanille') planted at 6×6 m spacing on a clay soil, varied between 3.9-4.7 and 4.7-6.1 t ha-1, respectively when irrigation was increased from 100 to 200 mm. Under these restrictive conditions, the highest WP values were obtained for 'Picholine', respectively 0.77 and 0.86 kg m-3. However, in southern Tunisia (200 mm rainfall), the 'Chemlali' cultivar, conducted under intensive planting (4×4 m) on sandy soils, showed a drastic increase in production. With irrigation water supply of 200-400 mm, average yield reached 10-12 t ha-1, and WP 2.1 kg m-3. Adaptation to water scarcity is discussed on the basis of the obtained results.

Optimal irrigation water management for adaptation to climate change

In this paper, an optimisation model is developed to determine the optimal crop pattern and allocation of irrigation water under full and deficit irrigation conditions for adaptation to climate change. Climate change is considered as a global challenge with significant impacts on different aspects of social activity and on the natural environment. For this purpose, the optimisation model is applied for two study periods. The one period refer to historical data (1977–1997) and the other one refer to climate change during 2030–2050. Two climate change scenarios were used (SRES scenarios B1 and A2) – which were taken from the general circulation models (GCMs), CGCM3.1/T63. The optimisation approach is performed using a simulated annealing (SA) algorithm combined with a stochastic gradient descent technique. Given the continuous decrease of water resources availability due to climate change, the results of the optimisation model reinforce the necessity of adequate deficit irrigation practices.

Modeling Soil Salinity in Greenhouse Cultivations Under a Changing Climate With SALTMED

Soil salinity is a major soil degradation threat especially for arid coastal environments where it hinders agricultural production, thus imposing a desertification risk. In the prospect of a changing climate, soil salinity caused by brackish water irrigation introduces additional uncertainties regarding the viability of deficit irrigation and intensive cultivation practices such as greenhouse cropping. Here, we propose a modification of the SALTMED leaching requirement model to account for greenhouse cultivation conditions. The model is applied in the RECARE Project Case Study of Timpaki, a semiarid region in south-central Crete, Greece, where greenhouse horticulture is an important land use. Excessive groundwater abstractions toward irrigation have resulted in a drop of the groundwater level in the coastal part of the aquifer, thus leading to seawater intrusion and in turn to soil salinization. Crop yield and soil profile electrical conductivity (EC) sensitivity to initial soil EC (up to 2 dS m−1) and irrigation water EC (up to 3 dS m−1) are modeled for the locally popular horticultural crops of Solanum lycopersicum, Solanum melongena, and Capsicum annuum. Climate model data obtained from nine general circulation models for the “worst case” representative concentration pathway of 8.5 W m−2 of the fifth phase of the Coupled Model Intercomparison Project are corrected for bias against historical observations with the Multisegment Statistical Bias Correction method and used to estimate crop yield and soil profile EC sensitivity in a warmer future. Results show that the effects of climate change on S. lycopersicum greenhouse cultivations of Timpaki will be detrimental, whereas S. melongena and C. annuum cultivations may show greater resilience.

Improving berry and wine quality attributes and vineyard economic efficiency by long-term deficit irrigation practices under semiarid conditions

Sustained deficit irrigation (SDI), Regulated deficit irrigation (RDI) and partial root zone irrigation (PRI) were compared for seven years (2006–2012), in field-grown Monastrell grapevines grafted onto 1103P, in South Eastern Spain. The aim was to distinguish the effects of deficit irrigation per se (irrigation volume) from specific PRI effects (placement of water) on long-term yield-WUE response and berry and wine quality. In addition, we compare several financial indices using cost-benefit analysis to determine economic efficiency and the long-term profitability of producing Monastrell wine grapes under SDI, RDI and PRI in semiarid conditions of SE Spain. Five treatments were applied: SDI irrigated at 60–40% ETc (crop evapotranspiration) for the whole season (308-211mmyear−1); a moderate RDI strategy (110–191mmyear−1) under conventional drip irrigation (RDI-1) and under PRI (PRI-1); and a more-severe RDI strategy (90–144mmyear−1) under conventional drip irrigation (RDI-2) and under PRI (PRI-2). In general, the SDI strategy, involving more irrigation, improved technological berry quality and financial efficiency, to the detriment of WUEyield, berry and wine polyphenolic content. By contrast, long-term deficit irrigation strategies (PRI and RDI) increased WUEyield, berry polyphenolic content and wine quality, but at the expense of lower financial efficiency compared to SDI. PRI-2 and RDI-2 (the most-severely water-stressed vines) showed greater carryover effects of water stress, yield reduction and lower overall berry and wine quality (including technological and phenolic composition) than the moderately-water-stressed vines (RDI-1 and PRI-1). Among the DI treatments, the PRI-1 strategy was the one which most improved the long-term yield-quality-WUE response, water productivity and berry anthocyanin content and was also the most economically profitable. In contrast, long-term PRI-2, although it improved some technological quality attributes and phenolic characteristics and enhanced nutraceutical properties in Monastrell berries and wines (flavonols, malvidins, acylated anthocyanins and amino acids) compared to RDI-2, did not have a positive effect on WUEyield and yield (yield, cluster and berry weight decreased in some years) and its implementation in the current market conditions, was economically unviable. The significant interaction between irrigation volume (high vs. low) and irrigation system (PRI vs. RDI) indicate that the response to PRI also depended on the volume of water applied in the wet root zone and the soil total water availability. We identified an optimum irrigation water volume range (134–200mmyear−1) and an optimum range of yield (8000–12000kgha−1) in order to develop long-term, efficient and economically-profitable deficit irrigation strategies in Monastrell vineyards under semiarid conditions.

Yield and water use efficiency of furrow irrigated potato under regulated deficit irrigation, Atsibi-Wemberta, North Ethiopia

The pressure on availability of water in Tigray regional state is likely to increase as the requirement for food production in couple with rapidly growing of the population is at increasing rate. Hence, improving water productivity using regulated deficit irrigation is important to reduce the water consumption while minimizing adverse effects on the crop yield. This study was conducted in the eastern zone of Tigray regional state, Atsibi Womberta district. The aim of this study was to determine the yield and water use efficiency of potato under deficit irrigation practice in the 2012 growing period. The effect of water deficit or water stress on crop yield and water use efficiencies were evaluated. Guasa variety potato was grown under eight (T1–T8) irrigation treatments. The treatments were replicated three times under completely randomized blocks experimental design. Water was applied to every furrow using watering can with fixed interval and variable depth irrigation scheduling technique was selected. Yield of potato was significantly (p<0.05) affected by water stress (deficit irrigation). The highest yield was found in T1 (18770kg/ha) which was not subjected to water stress (full water requirement) whereas minimum yield of potato was obtained under the fully stressed treatment T8 (7037kg/ha). There was no significant different between the yield of T1 (18770kg/ha) and T6 (14440kg/ha) which was 25% deficit throughout the growing season. According to the result obtained, stressed at the middle stage was affected more the yield of potato as compared to other treatments. This showed that stressing the crop at flowering/middle stage is sensitive to deficit irrigation. Giving 65% of crop water requirement throughout the growing season is better than stressing the crop only at the middle stage. The second sensitive period for water stress is the late crop stage. Crop water use efficiency was not statistically significant. Though it was not significantly different, T6 (2.86kg/m3) and T4 (1.60kg/m3) had the highest and the lowest water use efficiency respectively. This elaborated that applying 75% of crop water requirement has better water use efficiency than optimal or “no stress” irrigation. It can be conclude that using deficit irrigation is a good water management technique to save irrigation water without reducing the yield of potato. For dry land areas like The Tigray regional state of Ethiopia and other similar agro-ecology elsewhere in the world with scarce water and agricultural water management is very poor. The authors of this study would like to recommend farmers, water managers, water use associations and decision makers to use water efficiently using deficit irrigation and increase their agricultural production by expanding irrigable land with the same amount of water in a given irrigation scheme

Effect of Deficit Irrigation on Water Productivity of Onion (Allium cepal.)under Drip Irrigation

Deficit irrigation (DI) improves water productivity and irrigation management practices resulting in water saving by maintaining soil moisture content below optimum level throughout growth season. Field study was carried out on clay loam soil at Melkassa Agricultural Research Center, Ethiopia with the objectives to estimate water productivity of onion and evaluate the effect of water deficit on onion yield and quality using drip irrigation. The experiment contained five DI treatments of 90%, 80%, 70%, 60%, and 50% Crop water use (ETc) and the control (100% ETc) laid out in RCBD design with three replications. Irrigation water was applied at allowable soil moisture depletion (p=0.25) of the total available soil moisture throughout the crops growth stage. Statistical analysis revealed that plant height was not affected by the level of DI while, leaf number, bulb diameter, marketable bulb yield and total bulb yield had shown a highly significant (P<0.01) differences among DI treatments. The highest bulb diameter was observed from a control treatment that was significantly different to all other treatments. The highest total bulb yield of 15,690 kg/ha was observed from a control treatment which was not significantly different with treatment receiving 90% ETc. Highest water productivity of onion bulb yield was observed from treatment receiving 70% ETc and better onion bulb diameter was observed from treatment receiving 100% ETc to 70% ETc. The yield response factor ranged between 0.8 and 1.7. Thus, DI practices should be avoided for Ky values that are less than unity. Considering yield response factors (Ky) is limiting factor, 80% ETc application was a marginal and beyond that yield losses are intolerable. Thus, the practice of DI application up to 20% saved 45 to 108 mm depth of water from the gross onion irrigation water requirement.

Greenhouse Soil Moisture Deficit under Saline Irrigation and Climate Change

The sustainability of protected horticultural crops in the Mediterranean region, typically under deficit irrigation and intensive cultivation practices, is facing increasing risks due to soil salinization. Climate change may augment this threat to ecosystem services. In this study, the SALTMED leaching requirements model was calibrated using soil moisture measurements from time domain reflectometry (TDR) sensors. Measurements are performed on a small-scale Solanum lycopersicum (tomato) greenhouse experiment that simulates semi-arid conditions in the RECARE Project Case Study in Greece (Timpaki basin in Crete). The use of local planting soil with initial Electrical Conductivity (ECe) 1.8 dS m-1 and local cultivation practices aim to replicate prevailing conditions at the Case Study. Plants are drip irrigated with two NaCl treatments: slightly (S) saline (ECw= 1.1 dS m-1) and moderately (M) saline water (ECw= 3.5 dS m-1), resulting to very high and excessively high ECe, respectively. Based on these approaches, the calibrated SALTMED model was used for simulating groundwater degradation by seawater intrusion. In order to estimate crop yield in a warmer future, climate model data obtained from 9 GCMs for the “worst case” Representative Concentration Pathway of 8.5W m−2 of the 5th phase of the Coupled Model Intercomparison Project are corrected for bias against historical observations with the Multisegment Statistical Bias Correction method. Preliminary results predict that to sustain greenhouse productivity at current levels in the future, a substantial increase of water demand will be required.

Water Use Dynamics of Peach Trees under Postharvest Deficit Irrigation

Postharvest deficit irrigation is a potential strategy for conserving valuable fresh water for production of early season tree fruit crops such as peaches. However, water use dynamics under deficit irrigation conditions that can be described as seasonal changes in crop evapotranspiration (ETc) and crop coefficient (Kc) are largely unknown. A three-year field study was carried out in a 1.6 ha peach orchard to determine seasonal ETc and Kc characteristics. The orchard was divided equally into 72 plots, in which 12 randomly selected plots received deficit irrigation and the remaining 60 plots received full irrigation. A Bowen ratio flux tower was installed in the orchard to make meteorological measurements for estimating an integrated ETc for the orchard. The study showed that from July to August 75-85% of the daily net radiation was used by latent heat or partitioned into ETc. The average monthly cumulative ETc was 151 mm in June, 162 mm in July, and 155 mm in August. Kc values under deficit irrigation conditions or termed as Deficit_Kc was computed as ratios of the ETc over potential evapotranspiration or ETo, and were compared with Kc derived from a lysimeter study under non-water stressed conditions or termed as Lysimeter_Kc. The maximum Deficit_Kc values were 0.90, 1.03, and 1.07 for the three field seasons but all were smaller than 1.20, the maximum Lysimeter_Kc. The study demonstrated that water stress under deficit irrigation can be characterized in Kc values. The approach may be used to detect if portions of an orchard or the entire orchard are under water stress. Conversely, the method may provide guidance on deploying deficit irrigation practices with pre-determined Deficit_Kc.

Crop water productivity and economic evaluation of drip-irrigated soybeans (Glyxine max L. Merr.)

Effective management of water under irrigated agriculture is crucial to ensure food security. One crop that has high irrigation economic potential at local and international scales is soybean. This article presents the outcome of field experiments conducted in the dry seasons of 2013 and 2014 in Nigeria on the effects of deficit irrigation (DI) practices on reproductive stages of soybean. The experimental factor was the timing of irrigation. The five treatments were full irrigation (FI); skipping of irrigation every other week during flowering; pod initiation; seed filling and maturity stages.The crop was planted in a randomized complete block design with three replicates and inline drip irrigation was used to apply water. Leaf area index, dry above-ground biomass and seed yield were measured and the soil water balance approach was used to determine seasonal crop water use. Seasonal crop water use for the treatment in which deficit irrigation was imposed at seed filling stage was 364 mm while for the control treatment with full irrigation, seasonal crop water use was 532 mm. The seed yield reduced by 18.8 and 21.9% when DI was imposed during flowering and pod initiation, respectively. Similarly, the seed yield reduced by 24.4 and 47.9% when DI was imposed during maturity and seed filling. Water productivity (WP) reduced by 6.8 and 12.4% when DI was used during flowering and pod initiation, respectively. However, WP reduced by 20 and 35% during maturity and seed filling. DI during reproductive stages reduced economic water productivity by 6.7–35% while revenue was reduced by 18.5–47.7%. Full irrigation should be practiced to maximize water productivity. Weekly skipping of irrigation during seed filling will substantially reduce the seed yield and water productivity while skipping during flowering may be a viable option when water is scarce and land is not limiting. Economic evaluation will guide policy makers at basin scales for formulating improved and efficient water management plans under all varying weather conditions. DI can be used to optimise water productivity. The results will be beneficial in adopting deficit irrigation in a manner that will improve economic water productivity.

A decision tool for sustainable agricultural policies: the case of water saving scenarios for Apulia Region (Southern Italy)

The economy of Apulia Region largely depends on agriculture but the scarce water resources are the main factor threatening the sustainable production of this sector. This paper describes a geographical information system (GIS) based water balance tool that integrates maps of crops, climate and soil parameters with various scenarios of cropping pattern and farming practice changes. The aim is to assess the implication of these scenarios on the spatial and volumetric water needs of the region's irrigated agriculture. The total net volumetric irrigation needs, under current land use and full irrigation practices, were estimated on an average year to be 973 million m3. The deficit irrigation practices currently used in Capitanata water districts can save a volume of 302 million m3 if they are extrapolated over the entire region. Based on the Common Agricultural Policy (CAP), a replacement of 30% of the actual tomato areas in Foggia Province with sunflowers (energy crop) or durum wheat (rainfed crop) has potential water saving of 9 million m3 and 67 million m3, respectively. An additional 103 million m3 of water saving may be obtained through modernisation of the vineyards' growing practices. Findings of this paper could be used to address the agricultural policies towards a sustainable use of the scarce fresh water.