Water Productivity Efficiency Research Articles

Evaluating the Performance of a Solar Distillation Technology in the Desalination of Brackish Waters

Desalination is set to become a major source of drinking water in several Middle Eastern countries over the coming decades. Solar distillation is a simple power-independent method of water desalination, which can be carried out in active or passive modes. This study is among the first attempts to investigate the possibility of desalinating brackish groundwater resources under the threat of saltwater intrusion in the southern areas of Razavi Khorasan province in Iran. For this purpose, a pilot solar distillation unit was constructed to analyze the effects of the unit orientation, depth of the water pool, atmospheric conditions, input salinity, and flow continuity on the solar distillation performance. The results showed that the unit exhibited the highest efficiency when it had a 3 cm deep water pool. It was oriented facing southward while operating a continuous flow for at least 3 days under sunny weather conditions. It was found that among the studied parameters, the unit orientation and pool depth had the greatest impact on the water production performance for this type of water desalination system. Conversely, the water production efficiency was not very sensitive to the input salinity level. Overall, the solar distillation technology was able to reduce the salinity by 99.7% and the hardness by 94.7%.

Simulation of multi-period paleotectonic stress fields and distribution prediction of natural Ordovician fractures in the Huainan coalfield, Northern China

Fractures are effective seepage channels and storage spaces for oil, gas, and groundwater. Understanding the distribution characteristics of fractures can improve the efficiency of water production and the control of water-related geohazards in fractured aquifers. The development and distribution of natural fractures are usually controlled by paleotectonic stress fields. In this study, the data obtained from outcrop, cores, and thin sections were used to determine the development characteristics of such fractures. By doing an analysis of burial history, tectonic evolution, acoustic emission test, rock mechanics test, and conjugate joint analysis, two-dimensional (2D) heterogeneous geomechanical models were established by using a finite element method (FEM) stress analysis approach to simulate paleotectonic stress fields during the Indosinian, Early Yanshanian and Late Yanshanian periods. The effects of the variations of paleotectonic stress fields, hydrodynamic fields, structures, and rock mechanical parameters on the development of fractures could then be identified. A calculation model for the rock rupture rate was established to determine the quantitative development of fractures in different periods. Favorable areas for natural fracture development were determined by examining the relationship between the fracture linear density and pumping capacity of eleven wells. The simulation results indicate that the distributions of the maximum and minimum principal stresses and the maximum shear stress were nonuniform during the Indosinian, Early Yanshanian and Late Yanshanian periods, and high stress and/or low stress were mostly distributed in the fault and fold belts. During the Indosinian period, the tectonic and dissolution fractures were not developed. During the Early and Late Yanshanian periods, the tectonic and dissolution fractures were primarily developed around the fault and fold belts in the NNW-SSE and NWW-SEE directions. Those fault and fold belts are the locations with the greatest development of the natural fractures, which are also the main channels for the migration and accumulation of karst groundwater in the Ordovician formation in the Huainan coalfield. This study provides an important reference for the prevention and control of the Ordovician karst water damage in the study area, and proposes a new method for the prediction of fractured carbonate reservoirs.

Thermal design strategy for enhanced freshwater harvesting with interfacial evaporation

Solar driven interfacial evaporation is considered to be a low-carbon, environment-friendly technology for achieving efficient evaporation, but the solar still equipped with the interfacial evaporation structure is found to process low fresh water production rate and production efficiency. In this work, an optimization scheme for the interfacial evaporation structure of the solar still is proposed through the theoretical analysis of the heat and mass transfer process of the interfacial evaporation solar still. The theoretical results show that there are significant differences in the optimization design between the interfacial evaporation solar still and conventional solar stills. The fresh water production rate of interfacial evaporative solar still is less sensitive to the insulation performance of the solar still, while is greatly affected by the convective heat transfer process inside and outside the solar still. The solar still with interfacial evaporation structure can reduce the use of insulation materials to improve the illumination area and reduce the construction cost, without affecting the production efficiency of fresh water. Under the input energy intensity of 1 kW·m−2, when the convective heat transfer process inside the solar still is strengthened, the theoretical fresh water production rate of the interfacial evaporation solar still can be increased by 28 %, and the efficiency can reach 73 %. However, different from the optimization results of the traditional solar still, the enhancement of convective heat transfer process outside the glass cover will lead to the decline of the efficiency of the solar still. The experimental results show that in a monoclinic interfacial evaporation solar still with an evaporation surface area of 60 cm * 60 cm, a high system performance can be achieved by attaching a thin layer of insulation material to the inner wall and using a 2 W fan for forced convection of internal air. Under the outdoor environment with the maximum light intensity of 1 kW·m−2, the production efficiency of fresh water can be stabilized at 62.6 %. This work provides important guidelines for the design and optimization of solar still with interfacial evaporation structure.

Evaluation of Elaj Irrigation Project in Babil Governorate

Climate change causes water shortage (water scarcity) in addition to the dams built by neighboring countries, which caused a lack of Iraq's water share. Therefore, evaluating the irrigation system requires considering its suitability, adequacy, and efficiency. Irrigation is considered adequate when it maintains water availability within the root zone, and if the amount to be added is determined, irrigation efficiency becomes possible by avoiding water loss. Babil Governorate is considered one of the agricultural governorates in the country that depends on its irrigation from Shatt Al-Hilla. The study area is the Elaj project. Three fields were selected for the project (B1, B2, and B3). These fields are located at the project's beginning, middle and end. The evaluation was based on the field measurements of water contents before and after watering during the growing season. Also, the root zone of each plant during the growing season is measured to give more accurate calculations. Accordingly, application efficiency, conveyance efficiency, distribution efficiency, storage efficiency, water productivity efficiency, and water use efficiency were calculated in the project. The application efficiency for the selected fields ranged between (33 to 39) % in B1, (32 to 38) % in B2, and (32 to 39) % in B3. The application efficiency in all fields increased by about 6% during the third watering period between (22/3/2021 to 4/4/2021) due to the low water level in Shatt Al-Hilla during maintenance work that lasted more than a month. The efficiency of the scheme [ηs%] in the project is 32.3%. This value is low and reflects the reality of irrigation in the Babil. Therefore, improvements must be made to the irrigation system.

Improving Potato Yield, Water Productivity and Nitrogen Use Efficiency by Managing Irrigation Based on Potato Root Distribution

Potato is a typical shallow-root crop and a good understanding of its root distribution is critical in potato water management, which is especially important for potato production in areas such as Inner Mongolia where water resource is limited. We conducted field experiments to investigate the dynamic distribution of potato root in the soil, then used this as a basis to design a new irrigation method for potato production in the region; effects of the improved irrigation and conventional method were analyzed as well by measuring plant growth, yield, water productivity and nitrogen use efficiency. The results showed that large difference existed in root distribution of potato plants at different growth stages in Inner Mongolia, suggesting the present water management strategy of uniform irrigation during potato production is inefficient and has great potential for improvement. Adjusting irrigation amount so that the wet soil zone depth covered 80% of root distribution during potato growth significantly increased water productivity, decreased N leaching, improved N absorption, nitrogen use efficiency and plant growth, leading to increased tuber yield. Therefore, the improved water management method can be used extensively.

Experimental investigation of two novel arrangements of air gap membrane distillation module with heat recovery

Experimental investigations of an air gap membrane distillation (AGMD) unit were carried out to study the energy-saving by heat recovery. The spiral air gap membrane module in the water desalination unit was used. The unit was configured to operate in two novel arrangements and designed to minimize the loss of heat within the drains which maximize the unit productivity as well as the thermal efficiency. Water of salt concentrations 10,000 ppm and 20,000 ppm were used. Measurements of the heat source in the form of inlet and outlet temperatures, water productivity, and thermal efficiency are conducted for different flow rates of coolant and water feeds. The new arrangements are found to save much of the supplied heat, minimize the heat loss, and maximize the unit performance. An enhancement of 38.62% in the water productivity was achieved compared to the conventional AGMD unit. The considered heat recovery system showed water productivity of 155.92 m3/year for the proposed fresh potable water system with a cost of $12.85 per m3.

Theoretical evaluation on performance of a novel bubbling humidification–dehumidification desalination system directly heated by concentrating sunlight

This work aims to analyze the heat and mass exchange of complex bubbling. First, an empirical correlation for estimating bubbling heat transfer coefficient in different superficial air velocities is obtained based on previous works. Then, a modified theoretical model is set up and used to discuss the performance of the bubbling HDH system. Results show that higher input power enhances water productivity and thermal efficiency, but a maximum exists. When input power is constant, the influence of air flow rate on water productivity is remarkable when air velocity is not large. More importantly, the system has optimal cooling water flow rate and temperature. The optimal cooling water flow rate increases with input power, whereas the optimal cooling water temperature decreases with input power. When input power is 1000 W, the optimal cooling water flow rate and temperature are 60 L/h and 59 ℃, respectively. In addition, ambient temperature variations show a very small effect on system productivity and thermal efficiency. The results of this paper can provide theoretical reference for the design of a bubbling HDH desalination system.

Economic analysis of tomato cultivation with drip irrigation system

The water crisis is going to be a major problem in all sectors including agriculture in the very future. In agriculture, to tackle this deficit of water availability, to make sure food security for the rising population with the scarce water resource, to increase water productivity and water use efficiency the environment-friendly drip irrigation technology is being adopted. It is widely utilized for the high-value horticultural, plantation, sugarcane and more specifically row spaced crops. According to India’s Agricultural Ministry annual report, vegetables are an important crop in India’s horticulture sector. In the production of horticultural crops, the state of Tamilnadu is being one of the key producers in the country. A multistage sampling technique is being used for the selection of the study area with a sample of 50 respondent farmers cultivating tomato with the adoption of the Drip Irrigation System in the study area. The objectives of the present study are i) To work out the cost of construction of a Drip Irrigation System ii) To calculate the cost of cultivation of Tomato with a Drip Irrigation System iii) To find the economic viability of the investment made in Drip Irrigation System.

Interaction effects of irrigation and nitrogen on the coordination between crop water productivity and nitrogen use efficiency in wheat production on the North China Plain

Improving nitrogen use efficiency-yield (NUEYield) and crop water productivity (CWP) simultaneously has been a focus for sustainable wheat production, especially for the North China Plain, which faces challenges with limited water resources and low fertilizer use efficiency. With three-year wheat field experiments with two irrigation levels (rainfed, and irrigated at jointing and anthesis) and three N rates (0, 180, and 270 kg ha−1), we systematically investigated the effect of irrigation and nitrogen management on wheat water consumption at different growth stages, and further determined on the relationship between CWP and NUEYield simultaneously under different irrigation and nitrogen interactions. The results showed that N application and irrigation increased the total crop water consumption (1.2%−3.6% and 42.4%−44.4%, respectively). Increasing the N rate improved the soil water use (7.5%−10.3%) and reduced crop dependence on irrigation and precipitation, whereas irrigation reduced soil water utilization (54.4%−57.8%). Both irrigation and N application significantly increased the amount, percentage, and intensity of water consumption, especially during the grain filling period. There was a significant positive synergistic relationship between CWP and NUEYield under different irrigation and nitrogen treatments. For every 1 kg m−3 increase in CWP, NUEYield increased by 2.71–11.37 kg kg−1, depending on the N rate and water conditions. Increasing the N rate reduced the positive response of NUEYield to increasing CWP, while irrigation increased the positive response of NUEYield to increasing CWP. After decomposing NUEYield into nitrogen uptake efficiency (NuptE) and nitrogen utilization efficiency for yield (NutEYield), we found that the positive synergistic relationship between CWP and NUEYield was mainly due to the positive response of NuptE but not NutEYield to CWP. Irrigation increased the grain nitrogen accumulation efficiency by simultaneously increasing both pre-anthesis N translocation (GNAT) and post-anthesis N assimilation (GNAA) but increased GNAT more significantly than GNAA. Our results provide a theoretical basis for the efficient management of water and fertilizer in wheat production on the North China Plain and offer critical insights for improving the modeling of water-nitrogen relationships in wheat.

Co-implementation of precision nutrient management in long-term conservation agriculture-based systems: A step towards sustainable energy-water-food nexus

The conventionally managed cereal-based cropping systems in the Indo-Gangetic Plains (IGP) of South Asia are energy intensive that overwhelm the farm profits and the environmental footprint. This research addresses a complex nexus between yield-energy-water-GHG footprints-economics of conservation agriculture (CA)-based intensified maize-wheat-mungbean rotation. This study evaluated the effect of long-term CA (2012–2020) with optimum nutrient management (2017–20) on energy budgeting, productivity, water and C-footprints, Water productivity (WP), and economics of the CA-based maize-wheat-mungbean system. CA-based permanent bed- and zero tillage flatbed with preceding crop residue retention were compared with the conventional till with preceding crop residue incorporation. These treatments were factored over three-nutrient management alternatives, i.e., GreenSeeker®-guided-N, site-specific nutrient management (SSNM), and recommended fertilizers' dose (Ad-hoc), were compared with farmers' fertilizers practices (FFP). Permanent bed and zero tillage treatments registered higher systems' productivity (18.2 and 12.0%), net returns (44.7 and 34.7%) and water productivity (35.6% and 22.1%), and C-sequestration (54.8 and 62.3%), respectively, over conventional till. Permanent bed- and zero tillage treatments increased the systems' net energy (NE), energy use efficiency (EUE), energy productivity (EP), and energy intensity (EI) by 22.6 and 14.0; 10.1 and 5.6; 9.7 and 5.4; 28.3 and 24.0%, respectively, over conventional till. Conventional till recorded higher net CO2-eq emission (26.5 and 27.2%), C-footprint (20.8 and 14.5%), and water footprint (27.3 and 18.0%) than permanent bed- and zero tillage treatments. SSNM increased the system's productivity, water productivity, and energy use efficiency, while reducing the system's water- and C-footprints and net CO2-eq emission. Thus, adopting permanent beds as a crop establishment method with SSNM could be a feasible alternative to attain higher productivity, profitability, and resource use efficiency in the maize-wheat-mungbean system in northwest India.

Emergy evaluation of positive and negative benefits of agricultural water use based on energy analysis of water cycle

The current assessment of the positive and negative benefits of agricultural water use lacks a depiction of the overall internal energy flow, which lead to the identification and analysis of agricultural water use benefits are not comprehensive enough. Based on the “water supply - water use and consumption - drainage - pollutant carrying” link in the ecological economic system of agricultural water resources, the energy conversion relationship of each link were analyzed, and the main connotation and composition of the positive and negative benefits of agricultural water use were raised, then a set of emergy quantitative method system of the positive and negative benefits of agricultural water use was built. Taking Zhengzhou city as an example, the positive and negative benefits of agricultural water use in 2017 were calculated. The research results show that the negative benefits of agricultural water resources eco-economic system production account for 37.93% of the positive benefits. The main reason for the negative benefits is non-point source pollution caused by TN, TP and COD.Consequently, developing production and social policies to limit the amount of non-point source pollution caused by pollutants in agricultural production is an effective way to increase the efficiency of agricultural water production while reducing the negative benefits generated.

Membrane Distillation Technology Using for Desalination of Associated Oil Water Production and Study Efficiency of Feed Water Operation Parameter on Air Gap Membrane Distillation Process Production

In this study; membrane distillation technology using to associated oil water production desalination by air gap membrane distillation unit to removed salt from the water after separating oil product, via PTEF commercial hydrophobic membrane distillation with 0.22 µm porous and 0.011 m contact surface area, evaluated the desalination system and operation parameter for feed water effected on process production by employment the distillation under boiling point temperature that getting commercial increments and study the energy gain by calculating the GOR of the desalination process.
 The study focusing on the air gap membrane distillation desalination process by a range of temperature after primary simple sedimentation and filtration it's obtained salt rejection up to 98.9% that proves process separation efficiency. Evaluated the mean operation parameters of feed water affected on permeate water production when selected the feed temperature and flow rate with fixed coolant temperature, coolant flow rate, and air gap width to get an optimum range for feed water operation parameter to obtain optimum value to permeate water production and saving energy.

Large-scale preparation of SCLNCM of lithium-ion batteries with an improved continuous spray pyrolysis method

Single-crystal precursor of hybrid oxides NiO–MnCo2O4–Ni6MnO8 (SCNCM) is synthesized via an improved continuous two-step spray pyrolysis system (CTSP). This kind of mixed oxide is to be regarded as an ideal precursor for the single-crystal Ni-rich Li[Ni[Formula: see text]Co[Formula: see text]Mn[Formula: see text]]O2 cathode materials (SCLNCM). The new pilot plant (30 t/a), method, and chlorate in this work could extremely improve the lengthy process, reducing segregation of metal element, excessive sintering temperature, high water consumption, non-polluting, and production efficiency of the SCLNCM. The resulting SCLNCM powders have a type of fine particle size and porous structure with a typical [Formula: see text]-NaFeO2 lamellar structure. It also has a type of better cyclic stability, safety, rate capability, crystallinity, and surface area than polycrystalline cathode materials. It delivers an initial discharge capacity of 184 mAh/g at 0.1 C (18 mA/g) with a capacity retention of 91% after 100 cycles in the voltage window of 2.8–4.3 V.

Modeling and assessing water and nitrogen use and crop growth of peanut in semi-arid areas of Northeast China

Water shortage and poor soil fertility are the main factors restricting the sustainable development of peanut production in semi-arid areas of Northeast China. It is thus essential to have a deep understanding of the soil water-nitrogen dynamics and crop water/nitrogen use for developing water and nutrient strategies. Three levels of irrigation treatment (W65, 65% of field capacity; W55, 55% of field capacity; W45, 45% of field capacity) and a rain-fed treatment (CK) were implemented in field experiments conducted for peanut during the growing seasons of 2016 and 2017 in Liaoning, Northeast China. The AHC (Agro-Hydrological & chemical and Crop systems simulator) model was calibrated and validated, and then applied to assess peanut yield, water productivity (WP) and nitrogen use efficiency (NUE) for the present situation and future irrigation scenarios. The results indicated that the AHC model was capable of simulating soil water and nitrogen status and peanut growth. Simulations of soil water/nitrogen contents and crop growth indicators (Leaf area index, aboveground biomass, plant height and yield) fitted well with field observations. Simulated dynamics showed that 9–21% of the total water input and 14–27% of the total N input were leached out the root zone (0–60 cm). Rainfall was the main cause of water percolation and nitrogen leaching. The highest average yield (5701 kg ha–1) and NUE (26.77 kg kg–1) were obtained in the W55 treatment. The WP was not obviously decreased under the W55 treatment, and was only 4.1% lower than that of the CK treatment, in which the WP was highest. Based on scenario analysis with the consideration of crop yield, WP and NUE, the optimal irrigation amount of 80–97 mm is recommended for peanut cultivation in this region. We demonstrated that the AHC model could be used to develop water management strategies for peanuts in Northeast China to conserve water while sustaining agriculture.

Estimation of Actual Evapotranspiration, Water productivity, and Irrigation Efficiency of Wheat Fields in Surface and Sprinkler Irrigation Systems Using Remote Sensing

Estimation of Actual Evapotranspiration, Water productivity, and Irrigation Efficiency of Wheat Fields in Surface and Sprinkler Irrigation Systems Using Remote Sensing

Scale-up of membrane distillation systems using bench-scale data

A procedure to design full-scale air gap membrane distillation (AGMD) processes is presented. A mathematical model was then developed for both direct contact membrane distillation (DCMD) and AGMD. The model is centered on solving local mass and energy balances using a finite difference approach. The full-scale model was calibrated by utilizing the membrane distillation coefficient (MDC) determined by DCMD bench-scale experiments, as the sole adjustable parameter. The MDC was then used to model the water production and energy efficiency of a spiral-wound AGMD full-scale element. The model yields accurate representation of full-scale AGMD elements using polytetrafluoroethylene (PTFE) and polyethylene (PE) membranes. Full-scale experimental results obtained over a wide range of feed flow rates (2 to 4.5 L/min), temperatures (40 to 80 °C), and salinities (0 to 200 g/L NaCl) confirmed that the developed procedure can be applied to model and design large-scale AGMD elements. Furthermore, the model guides the selection of specific temperature and flow conditions at a given salinity and element geometry to maximize water production and energy efficiency. This methodology is suitable for rapid evaluation of novel MD membranes performance in field AGMD applications.

Simulation of the responses of spring wheat yield to the rates and depths of nitrogen application in dryland based on APSIM model

Nitrogen limitation is an important factor for the improvement of crop water production potential in rain-fed areas of the Loess Plateau. The reasonable deep application of nitrogen fertilizer is a promising method to increase yield of rain-fed crop. Based on APSIM model, this study simulated spring wheat yield under different nitrogen application rates and depths, by using meteorological observation data from 1990 to 2020 in the semiarid areas of central Gansu Province, aiming to provide theoretical reference for optimizing wheat fertilization strategy. The results showed that the determination coefficient of simulated spring wheat yield, biomass and soil water content in 0-200 cm soil profile was greater than 0.80, the normalized root mean square error was less than 0.2, and the model validity index was greater than 0.5. These results indicated that the model had good fitting and adaptability in the test area. Across all the levels within the experimental design, increasing nitrogen application rates could significantly increase the yield of spring wheat in different precipitation years, and increasing nitrogen application depth could significantly increase spring wheat yield in wet and normal years, but had no effect in dry years. The rate and depth of nitrogen application had significant interaction effects on spring wheat yield in wet and normal years, but not in dry years. According to the binary quadratic regression fitting equation, when the potential maximum yield reached 2749 kg·hm-2 in wet year, nitrogen application depth was 22.7 cm, and nitrogen application rate was 245 kg·hm-2. When the maximum potential yield reached 2596 kg·hm-2 in normal year, nitrogen application depth was 20.6 cm, and nitrogen application rate was 235 kg·hm-2. Integrating the effects of nitrogen application rate and depth on yield, biomass and agronomic efficiency of nitrogen fertilizer, and farmer's fertilizer application habits, the recommended nitrogen application depth was 20-23 cm, and nitrogen application amount was 120-150 kg·hm-2, which could further improve water productivity and nitrogen use efficiency of spring wheat in arid areas of central Gansu Province.

Production Efficiency, Water Productivity and Monetary Efficiency of Okra Under Organic Manure and Biofertilzers Application

Field experiment was conducted during the kharif seasons of 2017 at Sri Karan Narendra Agriculture University, Jobner (Jaipur) to assess the effect of biofertilizers and organic manures on production efficiency, water productivity and monetary efficiency of okra. The study had four organic manures and four biofertilizer treatments that were replicated thrice in factorial randomized block design. Vermicompost application @ 6 t ha-1 resulted into the maximum production efficiency (201 kg ha-1day-1) and water productivity (54 kg ha-1mm-1) whereas poultry manure (@ 8 t ha-1) reported greatest monetary efficiency (Rs. 3013 ha-1day-1). Among the biofertilizers, dual seed treatment with both Azosprillum + PSB recorded 39%, 40% and 55% higher production efficiency, water productivity and monetary efficiency than control. Fourth picking yielded the greatest tonnes of fruit and yield declines after it. Application of organic manures and biofertilizer enhanced okra yield up to 5.9 and 3.8 t ha-1, respectively. Therefore, poultry manure and double inoculation with biofertilizer is advisable for okra production under poorly fertile soils.

Impact of Combining Long-Term Subsoiling and Organic Fertilizer on Soil Microbial Biomass Carbon and Nitrogen, Soil Enzyme Activity, and Water Use of Winter Wheat.

Reductions in soil productivity and soil water retention capacity, and water scarcity during crop growth, may occur due to long-term suboptimal tillage and fertilization practices. Therefore, the application of appropriate tillage (subsoiling) and fertilization (organic fertilizer) practices is important for improving soil structure, water conservation and soil productivity. We hypothesize that subsoiling tillage combined with organic fertilizer has a better effect than subsoiling or organic fertilizer alone. A field experiment in Henan, China, has been conducted since 2011 to explore the effects of subsoiling and organic fertilizer, in combination, on winter wheat (Triticum aestivum L.) farming. We studied the effects of conventional tillage (CT), subsoiling (S), organic fertilizer (OF), and organic fertilizer combined with subsoiling (S+OF) treatments on dry matter accumulation (DM), water consumption (ET), water use efficiency (WUE) at different growth stages, yield, and water production efficiency (WPE) of winter wheat over 3 years (2016–2017, 2017–2018, 2018–2019). We also analyzed the soil structure, soil organic carbon, soil microbial biomass carbon and nitrogen, and soil enzymes in 2019. The results indicate that compared with CT, the S, OF and S+OF treatments increased the proportion of >0.25 mm aggregates, and S+OF especially led to increased soil organic carbon, soil microbial biomass carbon and nitrogen, soil enzyme activity (sucrase, cellulose, and urease). S+OF treatment was most effective in reducing ET, and increasing DM and WUE during the entire growth period of wheat. S+OF treatment also increased the total dry matter accumulation (Total DM) and total water use efficiency (total WUE) by 18.6–32.0% and 36.6–42.7%, respectively, during these 3 years. Wheat yield and WPE under S+OF treatment increased by 11.6–28.6% and 26.8–43.6%, respectively, in these 3 years. Therefore, S+OF in combination was found to be superior to S or OF alone, which in turn yielded better results than the CT.

Water productivity in cultivating the cowpea under different production systems

The increase in irrigated areas and the water crisis in numerous regions have encouraged the use of irrigation systems and management that afford greater efficiency in the use of water. Wastewater is one option for maximising this efficiency. The aim of this study was to evaluate the indicators of water productivity in the cultivation of irrigated cowpea under different production systems. The study was carried out in the experimental area of the Sewage Treatment Station (ETE) located in Tianguá, Ceará. The experiment consisted of six production systems (treatments) in subdivided plots distributed in a completely randomised design (CRD) with fifteen replications in a (2 x 3) factorial scheme, i.e. two sources of water and energy: drinking water + electricity from the electrical grid (conventional system) and wastewater + solar photovoltaic energy (alternative system), and the different sources of fertiliser (mineral and organic), in addition to the control treatments. The water productivity indicator that expresses the relationship between the yield of the crop and the volume of water applied was determined, and the index in economic terms between crop yield and the volume of water applied. The system using wastewater and organic fertiliser showed better water productivity, 0.422 kg m-3, while the system that used drinking water with no fertiliser showed less efficiency, 0.188 kg m-3. Water use efficiency in the systems that used wastewater was higher in relation to the systems that used drinking water. Irrigation with treated domestic effluent increases water productivity and water use efficiency, in addition to being a strategy for agricultural exploitation under conditions of water scarcity