Application Of Deficit Irrigation Research Articles

How does water stress affect the low molecular weight phenolics of hydroSOStainable almonds?

Water scarcity is a threat for food production because, water, is more and more limited and force farmers to use new deficit irrigation (DI) strategies without affecting fruit yield and quality. No information exists on almond polyphenols and proanthocyanidins (PAs) produced under DI. The present work studied the effect of 2 regulated DI (RDI) and one sustained (SDI) on the low molecular weight phenolics together with the antioxidant activity (AA) in almonds. Fifteen phenolic compounds were identified (13 flavonoids and 2 non-flavonoids) and 10 PAs. Kaempferol-3-O-galactoside was the predominant compound in almond skin and whole kernel but it was not found in deskinned kernels. The use of moderate RDI significantly increased the total phenolic content in skin (∼9.8%), PAs, and the AA. Consequently, after one season the application of DI positively affected the almond cv. Vairo phenols, however, several seasons must be evaluated in order to corroborate the present results.

Performance Evaluation of Sesame under Regulated Deficit Irrigation Application in the Low Land of Western Gondar, Ethiopia

Sesame (Sesamum indicum L.) is the leading oil seed crop produced in Ethiopia. It is the second most important agricultural commodity for export market in the country. It is well suited as an alternative crop production system, and it has low crop water requirement with moderate resistance to soil moisture deficit. The low land of North Western Ethiopia is the major sesame producer in the country, and the entire production is from rainfed. The rainfall distribution in North Western Ethiopia is significantly varied. This significant rainfall variability hampers the productivity of sesame. Irrigation agriculture has the potential to stabilize crop production and mitigate the negative impacts of variable rainfall. This study was proposed to identify critical growth stages during which sesame is most vulnerable to soil moisture deficit and to evaluate the crop water productivity of sesame under deficit irrigation. The performance of sesame to stage-wise and uniform deficit irrigation scheduling technique was tested at Gondar Agricultural Research Center (Metema Station), Northern Western Ethiopia. Eight treatments, four stage-wise deficit, two uniform deficit, one above optimal, and one optimal irrigation applications, were evaluated during the 2017 irrigation season. The experiment was designed as a randomized complete block design with three replications. Plant phenological variables, grain yield and crop water productivity, were used for performance evaluation. The result showed that deficit irrigation can be applied both throughout and at selected growth stages except the midseason stage. Imposing deficit during the midseason gave the lowest yield indicating the severe effect of water deficit during flowering and capsule initiation stages. When deficit irrigation is induced throughout, a 25% uniform deficit irrigation can give the highest crop water productivity with no or little yield reduction as compared with optimal irrigation. Implementing deficit irrigation scheduling technique will be beneficial for sesame production. Imposing 75% deficit at the initial, development, late season growth stages or 25% deficit irrigation throughout whole seasons will improve sesame crop water productivity.

Is new olive farming sustainable? A spatial comparison of productive and environmental performances between traditional and new olive orchards with the model OliveCan

Olive (Olea europaea L.) is a widely spread tree species in the Mediterranean. In the last decades, olive farming has known major management changes with high economic and environmental impacts. The fast track expansion of this modern olive farming in these recent years casts doubts on the sustainability of such important tree plantation across the Mediterranean. In this work, we performed a spatial modelling analysis to investigate the implications of climate variability and farming management on the productivity and environmental performances of olive orchards around the Mediterranean. Implementation of this research is based on the use of OliveCan; a process-based model able to illustrate responses of water and carbon balances to weather variables, soil characteristics and management techniques enabling the comprehension of olive orchard dynamics under heterogeneous conditions of climate and agricultural practices. Four main intensification levels were adopted to reflect the main olive grove types from traditional to new intensive plantations: low density LD (100 trees ha−1), medium density MD (200 trees ha−1), high density HD (400 trees ha−1) and super high density SHD (1650 trees ha−1). Managements tested were intensification, water supply (rainfed, deficit and full irrigated) and the fate of pruning residues (exported or left on the soil). Two cases studies in two of the main Mediterranean olive-growing regions with contrasting environmental conditions, Tuscany and Jaen regions, focused on mitigation alternative managements for carbon sequestration. Results showed that olive orchards responses in terms of yield and Net Ecosystem Productivity (NEP) vary along with climatic conditions. Water supply was the main driver with a production function that varies for different atmospheric demands. Application of deficit irrigation proved to boost water use efficiency. Besides, intensification from LD to SHD, presented the greatest improvements, 28–73% for yield and 50–100% for NEP. The C sequestration potential of olive orchards was confirmed. In fact, soil organic carbon (SOC) increased continuously over 400 years of simulation, reaching a state of equilibrium. Moreover, intensification and irrigation improved total carbon sequestration. Management of incorporating pruning residues in the soil increased SOC of 10.5 t C ha−1 for Tuscany and 10.8 t C ha−1 for Jaen. Findings of this research enabled the identification of the main drivers influencing the productive and environmental performance of olive groves in the different Mediterranean sub-climates. Impacts of management innovations on olive farming sustainability were also quantified which may help improve production systems for a more sustainable olive cultivation.

Physiological characteristics and irrigation water productivity of quinoa (Chenopodium quinoa Willd.) in response to deficit irrigation imposed at different growing stages—A field study from Southern Iran

AbstractIran has been faced to drought during last decades, and one way to overcome this phenomenon is to improve the water productivity by introducing new crops tolerant to water stresses such as quinoa. Two‐year field experiment was performed to find out the response of quinoa (cv. Titicaca) to deficit irrigation imposed at different growing stages. Hence, the effect of full irrigation (100% irrigation water requirement) and deficit irrigation (50% full irrigation) on physiological parameters, yield, irrigation water productivity and root density of quinoa was investigated during 2016 and 2017 growing seasons. The result showed that there was a significant difference between all variables in two years. Higher average air temperature in 2017 (2.0°C) resulted in a reduction of seed yield and water productivity (55% and 40% of that obtained in 2016, respectively). Application of deficit irrigation during different growing stages reduced crop height, stomatal conductance and seed yield, while it increased the root length density in both years. In conclusion, flowering stage of quinoa was very sensitive to deficit irrigation, and irrigation at grain filling stage would not help to recover the seed yield. Furthermore, the seed yield was lower than that obtained in other studies performed in other countries using same quinoa cultivar, which could be due to higher amount of applied irrigation water and different phenology under different climatic conditions. A decision on cultivating this crop under semi‐arid conditions has to be made considering limited water resources.

Responses of water accumulation and solute metabolism in tomato fruit to water scarcity and implications for main fruit quality variables.

Fruit is important for human health, and applying deficit irrigation in fruit production is a strategy to regulate fruit quality and support environmental sustainability. Responses of different fruit quality variables to deficit irrigation have been widely documented, and much progress has been made in understanding the mechanisms of these responses. We review the effects of water shortage on fruit water accumulation considering water transport from the parent plant into the fruit determined by hydraulic properties of the pathway (including xylem water transport and transmembrane water transport regulated by aquaporins) and the driving force for water movement. We discuss water relations and solute metabolism that affect the main fruit quality variables (e.g. size, flavour, nutrition, and firmness) at the cellular level under water shortage. We also summarize the most recent advances in the understanding of responses of the main fruit quality variables to water shortage, considering the effects of variety, the severity of water deficit imposed, and the developmental stage of the fruit. We finally identify knowledge gaps and suggest avenues for future research. This review provides new insights into the stress physiology of fleshy fruit, which will be beneficial for the sustainable production of high-quality fruit under deficit irrigation.

Physiological and Biochemical Responses of Orange Trees to Different Deficit Irrigation Regimes.

The article presents the results of research consisting of the application of deficit irrigation (DI) criteria, combined with the adoption of micro-irrigation methods, on orange orchards (Citrus sinensis (L.) Osbeck) in Sicily (Italy) during the irrigation season of 2015. Regulated deficit irrigation (RDI, T3) and partial root-zone drying (PRD, T4) strategies were compared with full irrigation (T1) and sustained deficit irrigation (SDI, T2) treatments in terms of physiological, biochemical, and productive crop response. A geophysical survey (electrical resistivity tomography, ERT) was carried out to identify a link between the percentages of drying soil volume in T4 with leaves abscisic acid (ABA) signal. Results highlight that the orange trees physiological response to water stress conditions did not show particular differences among the different irrigation treatments, not inducing detrimental effects on crop production features. ABA levels in leaves were rather constant in all the treatments, except in T4 during late irrigation season. ERT technique identified that prolonged drying cycles during alternate PRD exposed more roots to severe soil drying, thus increasing leaf ABA accumulation.

Application of deficit irrigation in Phillyrea angustifolia for landscaping purposes

Phillyrea angustifolia is an evergreen shrub of interest for urban landscape design, as well as for use in revegetation projects in Mediterranean areas, which are characterized by an acute scarcity of water. The effect of different levels of water deficit on several physiological, ornamental and morphological parameters of Phillyrea angustifolia plants was studied to evaluate their adaptability to xerogarden and/or landscape conditions. Nursery grown plants were subjected to three irrigation treatments: a control (watered to container capacity) and two deficit irrigation treatments of 60 and 40% of the amount of water supplied in the control treatment (moderate and severe deficit irrigation). After 23 months, plant height was significantly inhibited by both water deficit treatments, although plant compactness (foliar area in relation to plant height) was not affected. Plants under severe deficit irrigation increased their root to shoot ratio and water use efficiency, which are positive aspects for hardening. Plants exposed to both deficit irrigation treatments exhibited slight dehydration throughout the experiment, especially in spring, as indicated by the lower leaf water potential and relative water content. The tolerance of P. angustifolia to drought was mainly related to adjust osmotic and regulated stomatal closure. It is concluded that both deficit irrigation treatments can be used successfully in P. angustifolia plant production to reduce water consumption while maintaining good overall quality. Moderate deficit irrigation is specially recommended for gardening purposes, since this treatment produced plants with of visual quality. Severe deficit irrigation is more suitable for landscaping purposes, as an effective nursery technique to produce plants better adapted to environmental stress during transplanting.

Modeling Deficit Irrigation of Maize with the DayCent Model

Core Ideas A new version of the DayCent model was capable of simulating the responses in maize‐dominated agroecosystems under water‐deficit conditions. The accuracy of DayCent‐simulated GLAI, biomass, SWC, and yield was similar to that observed with more complex models. There was no significant difference in the major output variables when the stress coefficient, Ks, was calculated by the FAO method or the original DayCent method. A promising solution to help close the gap between water demand and supply in semiarid regions is deficit irrigation strategies that use less water but aim to increase crop yield per unit of water applied. Dynamic models can be used to assess the impacts of deficit irrigation and to support decision‐making. In this study, we evaluated the capability of a new version of the DayCent agroecosystem model to model crop growth, yield, and water use in response to water‐deficit conditions resulting from different deficit irrigation strategies employed in three field experiments with maize (Zea mays L.) in eastern Colorado. Overall, the DayCent model with improved algorithms for plant canopy development provided accurate estimates of green leaf area index (GLAI) for full and deficit irrigation treatments, though the method tended to overpredict the GLAI during the late vegetative growth period in the deficit irrigation treatments. Simulated soil water content (SWC), biomass, and grain yields compared well with the field measurements. We tested the drought stress coefficient (Ks) method in the FAO Irrigation and Drainage Paper No. 56 as an alternative to the original DayCent method for estimating drought stress. There were only marginal differences between the two Ks methods in predicting the major output variables in DayCent, but the FAO method is simpler and easier to parameterize. Overall, the DayCent model can simulate the responses in agroecosystems with maize under water deficit conditions and could be used as a guide for applying deficit irrigation strategies for water savings.

Simulation of regional irrigation requirement with SWAT in different agro-climatic zones driven by observed climate and two reanalysis datasets

Irrigation water is one of the most substantial water uses worldwide. Thus, global simulation studies about water availability and demand typically include irrigation. Nowadays, regional scale is of major interest for water resources management but irrigation lacks attention in many catchment modelling studies. This study evaluated the performance of the agro-hydrological model SWAT (Soil and Water Assessment Tool) for simulating streamflow, evapotranspiration and irrigation in four catchments of different agro-climatic zones at meso-scale (Baitarani/India: Subtropical monsoon; Ilmenau/Germany: Humid; Itata/Chile: Mediterranean; Thubon/Vietnam: Tropical). The models were calibrated well with Kling-Gupta Efficiency (KGE) varying from 0.74–0.89 and percentage bias (PBIAS) from 5.66–6.43%. The simulated irrigation is higher when irrigation is triggered by soil-water deficit compared to plant-water stress. The simulated irrigation scheduling scenarios showed that a significant amount of water can be saved by applying deficit irrigation (25–48%) with a small reduction in annual average crop yield (0–3.3%) in all climatic zones.Many catchments with a high share of irrigated agriculture are located in developing countries with a low availability of input data. For that reason, the application of uncorrected and bias-corrected National Centers for Environmental Prediction (NCEP) and ERA-interim (ERA) reanalysis data was evaluated for all model scenarios. The simulated streamflow under bias-corrected climate variables is close to the observed streamflow with ERA performing better than NCEP. However, the deviation in simulated irrigation between observed and reanalysis climate varies from −25.5–45.3%, whereas the relative irrigation water savings by deficit irrigation could be shown by all climate input data. The overall variability in simulated irrigation requirement depends mainly on the climate input data. Studies about irrigation requirement in data scarce areas must address this in particular when using reanalysis data.

Effects of deficit irrigation on essential oil composition and yield of fennel (Foeniculum vulgare Mill) in a high-altitude environment

ABSTRACTSuccessful fennel (Foeniculum vulgare Mill) production in semi-arid environments depends largely on irrigation applications. Deficit irrigation studies on fennel are lacking or very limited, particularly in high-altitude environments. This study was conducted to determine the effects of deficit irrigation levels on the essential oil content, essential oil yield, and chemical composition of fennel. The experiment was carried out in 2014 and included four deficit irrigation levels: 100% (I1), 80% (I2), 60% (I3), and 40% (I4) of Class A pan evaporation. All parameters were significantly affected by deficit irrigation applications. Essential oil content tended to increase under increased water deficit conditions with the range of 2.21% to 2.42%. Anethole (90.71–91.62%) was the major compound in the fennel fruit oil, followed by estragole (3.60–4.02%), limonene (2.19–3.24%), and fenchone (0.96–1.55%), respectively. Essential oil yield showed an increase with increased irrigation amounts.

DEFICIT DRIP IRRIGATION MANAGEMENT FOR SUNFLOWER CROP UNDER CLAY SOIL CONDITIONS

Egypt faces a very challenging situation regarding decreasing water availability and the area of arable land specified for crop production. Uneven water distribution, misuse of water resources and inefficient irrigation techniques are some of the major factors playing havoc with water security in the country, so maximizing water productivity is one of the most important strategies. Therefore, the aim of this study was to investigate the drip irrigation management for sunflower grown under clay soil conditions to encourage farmers to use drip irrigation systems in their clay soil fields. Such management should be a tool for maximizing crop yield, increasing water productivity (Water Use Efficiency, WUE) and saving water to irrigate new areas. A field experiment was conducted to study the effect of deficit irrigation and drip irrigation laterals arrangements on yield and water productivity of sunflower crop (seed and oil). Deficit irrigation treatments were (FI100), (DI80), (DI60) and (DI100-60) (Full crop evapotranspiration 100% ETc, 80% ETc, 60%ETc and (100 – 60 % ETc respectively). The DI100-60 treatment was applied as 100 % ETc up to seed formation then reduced to 60%ETc before crop harvesting. ) The drip irrigation lateral arrangements were (R1L1-2) and (R2L1-4) (single and double planting rows per one drip irrigation lateral line, with 2 l/h and 4 l/h drippers, respectively), this was to ensure similar water application rate per row for both lateral arrangements. Results revealed that using higher dripper discharge (4l/h) under clay soil conditions resulted in wide horizontal distribution of moisture patterns more than the vertical distribution. Salt accumulation slightly increased with deficit irrigation. Applying deficit irrigation by either DI80 or DI100-60 produced almost the same or more yield of sunflower seeds and oil than that obtained from full irrigation FI100, besides saving about 20% of irrigation water. These two deficit irrigation treatments maximized water productivity WUE. The highest seed yields were 1895 kg/fed and 1822 kg/fed obtained from R1L1-2 and R2L1-4 under DI100-60 respectively. The oil yield values were taken the same trend as seed yield. Accordingly, it could be recommended that irrigating row crops such as sunflower under clay soil conditions could be done by using one lateral line of 4l/h drippers per two planting rows and applying DI80 or DI100-60 deficit irrigation strategy, taking many advantages such as increasing seed and oil yield, maximizing WUE, reducing the cost of drip lateral lines by 50% and saving water by about 20%).

Optimizing yield and water use efficiency of furrow-irrigated potato under different depth of irrigation water levels

Development of optimum irrigation water management is important for water productivity and food security enhancement. Hence, introducing the knowledge of crop-specific irrigation water requirement is crucial. This study aims at investigating crop water requirement, water use efficiency, and yield of potato at different water regimes for better potato productivity. This study was conducted in Emba Alaje district, southern zone of Tigray regional state, Ethiopia. The crop water requirement of potato was estimated using CROPWAT 8 software and determined as 604 mm for the whole growing period. Potato crop was grown under seven treatments of irrigation water application in complete randomized blocks design with three replications each. Potato yield and water use efficiency (WUE) were significantly (p < 0.05) affected by depth of water application. The highest yield and WUE was obtained from 100% of ETc (25864 kg/ha) and 55% of ETc (6.08 kg/m3) respectively. Irrigation water application with 70% of ETc produces yield and WUE of (22639 kg/ha) and (5.4 kg/m3), respectively, and this has no significant difference with 100% ETc. Application of 423 mm irrigation water (70% of gross irrigation) is an optimum amount to improve both yield and WUE. These results encouraged application of deficit irrigation up to 30% of ETc can save significant amount of irrigation water without substantial yield reduction. The authors of this study would like to recommend farmers and irrigation experts to apply 70% of ETc as deficit irrigation to enhance irrigation water productivity in areas where water is a limiting factor.

Effect of Irrigation Schemes on Forage Yield, Water Use Efficiency, and Nutrients in Artificial Grassland under Arid Conditions

Artificial grasslands are effective solutions to problems with grassland degradation. Water scarcity is an important limitation for grassland production in arid regions. In this study, we carried out comparison experiments to assess the impacts of irrigation schemes on forage yield, water use efficiency, and nutrients in the single and mixed sowing ways of Medicago sativa L. and Agropyron cristatum in different stages in artificial grassland. Results indicated that deficit irrigation can increase forage yields of M. sativa and A. cristatum in most growth stages and sowing treatments. Heavy deficit irrigation or even no irrigation had the greatest potential to increase forage yields of both species in the squaring stage and instantaneous water-use efficiency (WUEI) in all growth stages. They can also significantly increase the nutritional level of M. sativa using a mixed sowing method. In June and September, only irrigating to near field capacity (T1) can increase the long-term water-use efficiency (WUEL) of both species. We suggest irrigating with water to near field capacity in June, and applying deficit irrigation in July and August. Deficit irrigation is an effective water management technique to both save water and increase forage quality in arid areas.

Deficit irrigation and planting patterns strategies to improve maize yield and water productivity at different plant densities in semi-arid regions

Field research was done in two consecutive years to optimize deficit irrigation under different crop densities (low, medium, and high) using the ridge and furrow rainfall harvesting (RFRH) system. We demonstrate that applying deficit irrigation (375 m3 ha−1) at the flowering stage of maize grown at medium density (M: 75000 plant ha−1) under the RFRH system (MIF) can improve soil water storage (0–200 cm) at the bell, filling and flowering stages. MIF increased biomass by 10% and grain yield by 21%, thereby achieving a 17% increase in water use efficiency (WUE) and a 22% increase in precipitation use efficiency (PUE) compared with conventional flat planting (CKM). MIF also improved irrigation water use efficiency (IWUE) (9%) and irrigation water productivity (IWP) (46%) compared with no-irrigation under the RFRH system (MI0). We observed that applying deficit irrigation (750 m3 ha−1) at the bell and flowering stage (IBF) had positive effects on dry matter, leaf area, and evapotranspiration, but there were no significant increases in IWUE, IWP, WUE, biomass and grain yield compared with maize grown under IF at low, medium and high plant densities. The average net profit over the two years was 34% higher for MIF compared with the CKM treatment.

Dry-season deficit irrigation increases agricultural water use efficiency at the expense of yield and agronomic nutrient use efficiency of Sacha Inchi plants in a tropical humid monsoon area

Application of deficit irrigation (DI) will be problematic in tropical humid monsoon areas, since high relative air humidity during growth there leads to stomata malfunctioning. A field split-plot experiment was used to evaluate the physiological features, growth and seed and oil yield of Sacha Inchi (Plukenetia volubilis Linneo) plants, a tropical promising woody oilseed crop, responded to DI and fertilization in southwest China. The field experiment consisted of a factorial combination of five irrigation levels applied in the dry season [rainfed; DI20, DI50, DI100 (i.e., with irrigation amount of 20, 50 and 100% crop evapotranspiration, respectively); and full irrigation (irrigation of water saturated soil)] combined with two levels of compound fertilizer (0 and 200kgha−1) over two growing seasons, in a randomized complete block design with three replicates.Results showed the growth and root to stem mass ratio had lower sensitivity responded to DI, probably owing to their extremely low root mass fraction and seasonal short-term effect of DI on leaf photosynthetic traits. Irrigation affected the seasonal variations in seed size, seed oil concentration and seed yield, depending on the harvest date; whereas, with constant mean seed size and mean seed oil concentration across irrigation and fertilization treatments, the total seed and seed oil yield over the growing seasons were largely determined by the seed numbers per unit area. The soluble sugar and nitrogen storages as the active process, are related to effective flower formation, fruit (seed) development and enhance productivity of Sacha Inchi plants, which was indicated by the positive relationships between total seed yield and total nitrogen pool in the vegetative tissues or sugar pool in stems across all treatments. Fertilization increased total seed and seed oil yield, but no interaction between irrigation and fertilization was found. Compared with DI100, DI50 and DI20 had significant lower total seed yield, especially under the fertilized condition, although having higher agronomic water use efficiency (WUEagr, yield divided by irrigated water applied) but lower agronomic nutrient use efficiency (NUEagr, increased yield divided by fertilization rate). As a water-demanding crop species, Sacha Inchi plants under DI100 with the similar values to full irrigation had the highest total seed yield and NUEagr, but at the expense of water use efficiency. The maximum seed yield and maximum WUEagr, or maximum WUEagr and maximum NUEagr of Sacha Inchi plants are not compatible because the negative relationships existed between each of them. The polynomial regression relationships between total seed or seed oil yield and relative evapotranspiration could help to develop appropriate water-saving techniques for Sacha Inchi plantation in the tropical humid monsoon region.

Modelling of Response of the Growth and Yield of Soybean to Full and Deficit Irrigation by Using Aquacrop

The use of crop yield models is important in simulating and predicting yield of crops and in making decisions under changing climate conditions, in order to optimize production. In this study the AquaCrop model was calibrated and validated to predict canopy cover, dry above-ground biomass, yield, evapotranspiration, soil moisture content and water productivity of soybeans. The study was conducted in Ile-Ife, Nigeria, for two seasons. Treatments were full irrigation and different deficit irrigation applications during the growth stages: flowering, pod initiation, pod filling and maturity. Calibration and validation were done by using the 2013 and 2013/2014 data sets respectively. The coefficient of determination, root mean square error, normalized root mean square error, Nash–Sutcliffe model efficiency coefficient and degree of agreement were used to test the performance of the model. AquaCrop overestimated biomass under deficit irrigation conditions, but performed better in simulating soil moisture under full irrigation conditions. Considering the overall performance of AquaCrop with respect to these aspects, we conclude that the model can be used for accurate prediction of yield, soil moisture and hence to optimize water productivity of soybeans at farm level and basin scale. Copyright © 2017 John Wiley & Sons, Ltd.

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.

Using the SWAT model to assess the impacts of changing irrigation from surface to pressurized systems on water productivity and water saving in the Zarrineh Rud catchment

Considering global water scarcity, especially in the agricultural sector, many attempts are being made to improve water productivity and save more water. Changing irrigation systems from surface to pressurized has been one of the considerable actions in this regard. However, any attempts to do so must be evaluated in an integrated perspective at the basin level by means of relevant agro-hydrological models before making them operational. This paper aims to address this issue by using the soil and water assessment tool (SWAT). Zarrineh Rud River, the main feeding river of northwest Iran’s Lake Urmia, is selected as the case study for exploring this methodology. This lake has been shrinking since 1995, and to save water and increase the basin’s water productivity, improvement of pressurized systems is considered as a solution. SWAT cannot directly simulate changing the irrigation system from surface to pressurized. In this study, we use the innovative approach of applying the model to simulate different irrigation systems considering real irrigation management variables such as depth and date of each irrigation event. Also, in order to improve its performance in simulation of such systems, a comprehensive calibration procedure was used based on a wide range of data for hydrological and agricultural variables. The results showed that changing the current irrigation to a pressurized system can increase water productivity up to 15% due to increases in crop yield, better water distribution and greater actual evapotranspiration. However, pressurized irrigation results in no significant change in total inflow to the lake. Notably, these systems can intensify drawdown of the basin’s water table up to 20%. So, any significant “real water saving” program in the basin must be associated with reduction of evapotranspiration by adopting measures like reducing cultivated areas, changing cropping patterns to less water consuming plants, or applying deficit irrigation. The applied methodology of this paper as well as the comprehensive calibration and setup of the SWAT model with the readily available hydrological and agricultural variables can be a good sample for similar works. However, further work is still needed to more broadly test this approach in areas with intensive irrigation systems.

Modelling hydrological processes, crop yields and NPS pollution in a small sub-tropical catchment in South Africa using ACRU-NPS

The Agricultural Catchment Research Unit—Nitrates, Phosphorous and Sediments (ACRU-NPS) model, which simulates runoff, sediment and nutrient (NO3 and P) production in agricultural catchments, is used to evaluate the impact of farming practices and land-use changes on crop yields, water discharge, sediment and nutrient loads in the 41-km2 Mkabela catchment in the KwaZulu-Natal midlands, South Africa. The ACRU-NPS model was modified with the following objectives: (a) to develop and incorporate algorithms to simulate crop growth and NPS pollution dynamics in process zones and control features; (b) simulate sediment and nutrient production from land segments for various land uses; (c) model crop yield where crop growth is influenced by water and nitrogen stress; and (d) simulate sediment and nutrient fate at controls and buffers in the stream network. Five management practice scenarios were simulated and run with a series of fertilizer management applications. The resulting crop yields, water discharge, sediment and nutrient loadings were analysed. On average, doubling fertilizer application from base rates resulted in the highest sugarcane yield increase of 5 t/ha, zero fertilizer application resulted in the highest sugarcane yield reduction of 11 t/ha, while applying deficit irrigation, with base fertilizer application rates retained, resulted in 16 t/ha sugarcane yield increase. Flood attenuation and retention capacities for the total non-point source (NPS) pollutants for the period 2006–2012 were also investigated in the study area.

Application of deficit irrigation to container-grown hardy ornamental nursery stock via overhead irrigation, compared to drip irrigation

Growth control of container-grown hardy nursery stock generally requires substantial labour investment. Therefore the possibility of alternative growth control using deficit irrigation is appealing. Increasing water costs and limited availability of abstraction licences have added further incentives for nursery stock producers to use deficit irrigation. There are still, however, concerns that inherent non-uniformity of water uptake under commonly used overhead irrigation, and differing irrigation requirements of diverse crops and substrates, may limit the commercial relevance of a protocol developed for single crops growing in 100% peat and irrigated with a high precision drip system. The aim of this research was to determine whether growth control of hardy nursery stock is possible using deficit irrigation applied with conventional overhead irrigation. Over two years, crop growth under an overhead irrigation system was compared under full irrigation and two severities of deficit irrigation. Initially, two crops of contrasting canopy structure i.e. Cornus alba and Lonicera periclymenum were grown. In a subsequent experiment one crop (Forsythia×intermedia) was grown in two substrates with contrasting quantities of peat (60 and 100%). Deficit irrigation was found to be highly effective in controlling vegetative growth when applied using overhead irrigation—with similar results as when drip irrigation was used. This comparable response suggests that deficit irrigation can be applied without precision drip irrigation. Scheduling two very different crops with respect to their water use and uptake potential, however, highlighted challenges with respect to application of appropriate deficits for very different crops under one system; responses to deficit irrigation will be more consistent where nursery management allows for scheduling of crops with very different architecture and water use under different regimes. The effectiveness of deficit irrigation in controlling the growth of Forsythia was similar when a reduced peat based substrate was compared with pure peat; additionally, flowering was enhanced.