Potential Irrigation Water Research Articles

Water accounting of groundwater over exploited districts in Haryana and Punjab states to analyse impacts of water conservation measures on water availability

ABSTRACT Escalating water scarcity threatens to sustainable food production, necessitating enhanced water use efficiency through effective water management practices. The present study aims to conduct water accounting in the groundwater-depleted districts of Haryana and Punjab, India, analysing the potential irrigation water savings achievable through the implementation of efficient management techniques in these selected districts. The study area encompasses Kaithal and Karnal districts in Haryana and Patiala and Sangrur districts in Punjab with water availability assessment for 2015. Results showed that there is a mismatch between the annual groundwater pumped and replenishable groundwater recharge in all selected districts indicating a need for improved water management. Adjusting the timing of rice sowing to align with the onset of the rainy season can significantly save water and reduce groundwater extraction. For instance, delaying rice transplanting from May 21st to June 15th can reduce crop water demand by 10.89%. Similarly, transplanting rice on June 15th can reduce water demand by 9.03%, 6.23%, 4.31%, and 2.46% compared to transplanting on May 26th, May 31st, June 5th, and June 10th, respectively. Shifting of a rice-wheat cropping system to a maize-wheat system can substantially decrease crop water demand. Replacing rice with maize can result in a 54.66% reduction in crop water demand per hectare.

Evaluation of potential irrigation water savings by assessing the soil water balance in a vineyard in central Chile

AbstractThe main aim of this study was to evaluate the potential savings of irrigation water by assessing the soil water balance during the growing season in a wine vineyard in the Maule region, Chile. This study provides insights into the influences of different irrigation water applications on soil water status and its potential effects on grape yields, water use efficiency (WUE) and the cost of irrigation to help improve irrigation practices in the region and other similar Mediterranean regions. The field experiment compared three levels of irrigation water applied: current irrigation of the vineyard (T0) and two deficit irrigation treatments with reductions to 75% (T1) and 50% of the irrigated water (T2). The measurements included volumetric soil water content, shallow groundwater table, canopy cover and grape yield at harvest during the entire growing season (October 2017 to April 2018). We found a potential reduction of 25% or 50% in the current irrigation system while maintaining the grape yield, increasing the WUE and reducing the cost of irrigation. Consideration of the water stored in the soil by the accumulation of rainfall in the winter season and the potential for capillary rise of shallow groundwaters is crucial for adjusting irrigation to vine water requirements.

Landscape and Horticultural Fertigation Using Roof-Derived Storm Water: The Potential Multiple Benefits of Blue Green Roof Installations

A contribution to the sustainable management of storm water is the use of sustainable drainage (SuDS)-derived water as an unconventional source for irrigation. If storm-water runoff contains dissolved nutrients in excess of those found in conventional irrigation, reusing this water can contribute to the nutrient demands of horticulture or landscaping, which is known as “fertigation”. Green roofs are SuDS devices, and those with below-substrate water storage, blue green roofs, can be additional water sources. The nutrients released from a roof-substrate-growing medium could contribute to the growth of crop and landscape plants, but materials from blue green roofs must not release residues harmful to fertigated plants or receiving soils. This plant growth experiment examined the effects of water from a blue green roof on plant growth and health and the effects on soil and roof-harvested water when functioning as a nutrient-rich irrigation source. Tomatoes and ryegrass were used as examples of horticultural and landscaping plants, respectively. Blue green roof water was compared with potable water irrigation. The blue-green-roof-derived water provided a distinct growth advantage for tomatoes and lower sodium in fruits than tap water, at 285 mg/kg and 636 mg/kg, respectively. For ryegrass, the differences were minimal, but there was no disadvantage to using roof water for fertigation. Following three years of a blue green roof’s operational life, export of inorganic nutrients from the roof, local storage, and then application to plants were effective in contributing additional fertiliser.

Assessing the Microclimate Effects and Irrigation Water Requirements of Mesic, Oasis, and Xeric Landscapes

Urban irrigation is an essential process in land–atmosphere interactions. It is one of the uncertain parameters of urban hydrology due to various microclimates. This study investigated the microclimate effects and irrigation water requirements of three landscape types in an arid region of Phoenix, AZ. The microclimate effect encompassed surface temperature, air temperature, and wind speed. The simulations of the three landscapes were conducted using ENVI-met software for the hottest day of the year (23 June 2011). The simulated model was validated using ground data. Results show that the mesic landscape induced cooling effects, both in the daytime and nighttime, by reducing surface and air temperatures. However, the mesic landscape showed high-water consumption because of a high leaf area density. The oasis landscape showed 2 °C more daytime cooling than the mesic landscape, but the nighttime warming (surface temperature) was comparable to the xeric landscape. The potential irrigation water requirement was 1 mm/day lower than the mesic landscape. Moreover, microclimate conditions varied spatially in each neighborhood. The xeric landscape showed lower wind speeds and air temperatures between the buildings. The wind speed variations in the three landscapes were inconclusive due to differences in building orientations and discrepancies in trees’ heights. The findings can have implications for restricting the municipal irrigation budget. In addition, they can help water managers in choosing a landscape in urban areas. Urban scientists can adapt the methodology to quantify urban ET in arid regions.

Selecting High-Impact Landscape Irrigation Conservation Behaviors: Formative Research to Inform Behavior-Change Efforts

Background This work addresses the increasing prevalence of water scarcity. Droughts are projected to worsen as a result of climate change and urbanization, increasing the need for all sectors to reduce the amount of water used. Home landscape irrigation represents an important opportunity to reduce water use in the United States. Focus of the Article This formative research study used social marketing techniques to estimate potential impact of irrigation water conservation behaviors, weight and prioritize the behaviors to guide behavior selection in the context of residential irrigation conservation. Research Objective The objectives were to estimate (1) the potential impact of, (2) current adoption levels and likelihood of adoption of, and to (3) prioritize various landscape irrigation water conservation behaviors. Program Design/Approach When addressing any issue, including water scarcity, identifying target behaviors is the first, foundational step for a successful social marketing campaign. This research focuses on formative social marketing research to inform local interventions designed to reduce the amount of water applied to residential yards across the United States. Importance to the Social Marketing Field This study outlines a process to compare and prioritize water conservation behaviors with the goal of reducing residential landscape irrigation usage. We demonstrate a technique for obtaining this type of formative research, the lack of which can serve as a barrier to change agents promoting behaviors in any context. Methods We employed a two-pronged quantitative survey research approach to collect technical experts’ impact ranking and U.S. residents’ current adoption levels and likelihood of adopting potential irrigation water conservation behaviors. The 14-member expert panel was selected using purposive and snowball sampling techniques, and the residential sample ( N = 2601) was recruited using purposive sampling. Results Mean weights ranged from −46.55 to 61.13. Singly considering impact, current adoption levels, or likelihood of adoption would result in a different behavior receiving priority for a campaign (eliminating irrigated areas in landscapes, installing smart irrigation controllers, and following local watering restrictions, respectively). However, when these values were considered together, installing drought-tolerant plants in the yard had the greatest overall weight. Limitations A possible conceptual limitation of this case study was the national scope of our research. The findings provide valuable baseline data for behavior change practitioners working across the country, and it is advisable to replicate this process at a local scale corresponding to the targeted intervention. Recommendations for Research or Practice The findings underscore the importance of including technical experts and target audience members early in social marketing program planning and reveal the importance of systematically approaching behavior change selection to thoroughly consider different components of potential behaviors. Behavior change practitioners working on water issues can use the weights reported here to prioritize behaviors for targeted interventions, and those working in all areas can follow the process to prioritize behaviors at the local level. There are exciting opportunities to decompose likelihood into behavioral antecedents for both research and application.

Greywater irrigation can support climbing plant growth on building green façades

Green façades can help to cool cities and buildings best when they are irrigated to provide good canopy growth and transpiration cooling. Irrigating green façades with greywater can reduce potable water demand and make use of building greywater supplies, however, greywater may negatively impact climbing plant growth through salt accumulation. We evaluated the effects of greywater irrigation on substrate properties (pH and EC) and the growth of six climbing plant species in an 18-week glasshouse experiment. Three irrigation treatments were applied to climbing plants: (1) potable water, (2) greywater, and (3) greywater flushed with potable water once every three weeks. Substrate pH did not differ among treatments, but substrate EC was greatest when irrigated with greywater flushed with potable water. Greywater irrigation was not detrimental to climbing plant growth, demonstrating that domestic greywater could replace potable water irrigation of building green façades in urban environments.

Evaluating deficit irrigation scheduling strategies to improve yield and water productivity of maize in arid environment using simulation

Water scarcity and rising temperatures are creating serious concerns over the sustainability of agriculture systems in arid regions of the Middle East and North Africa. The aims were (i) to calibrate and evaluate the Decision Support System for Agrotechnology Transfer (DSSAT) model using detailed experimental datasets on maize (Zea mays L.) yield and water productivity in an arid Mediterranean environment and (ii) to determine the impacts of various irrigation scheduling strategies on maize yield and water productivity in arid sandy soils and produce irrigation scheduling recommendations that maximize the marginal benefit per unit water applied. The goodness-of-fit statistics comparing the observed and simulated crop phenology, grain yield, dry matter, evapotranspiration (ET), and soil water content indicate that the model simulates these crop and soil variables reasonably well for a medium-maturity maize hybrid (~ 110 days to physiological maturity) commonly grown in the study region. Long-term simulations (1984–2018) using the well-calibrated model were performed and included three irrigation scheduling strategies: (i) soil water-based irrigation scheduling, (ii) ET-based threshold irrigation scheduling, and (iii) growth-stage ET-based irrigation scheduling. In the soil water-based, four levels of maximum allowable depletion (MAD) of available soil water content (AWC) were tested using the auto-irrigation option of DSSAT. Results indicated that MAD 50% is recommended for scheduling irrigation in arid sandy soils for potential irrigation water saving without unacceptable yield loss. The ET-based threshold consisted of a combination of four cumulative net ET threshold (ETH) triggers of 14, 21, 28, and 35 mm and five ET replacement levels of 50%, 70%, 90%, 110%, and 130% ET using the DSSAT ET-based auto-irrigation option. Based on this irrigation strategy, it is more favorable to irrigate at the high frequency of ETH 14 or 21 mm than low frequency of ETH 35 mm, even when replacing 130% ET, as high drought-stress during the crop development and reproductive stages were observed for ETH 35 mm due to the omission of key irrigation events. In the growth-stage ET-based, two levels of irrigation of 100% ET and 60% ET estimated based on the crop coefficient approach were tested with different combinations of targets during the vegetative and reproductive growth stages. Results indicated that meeting crop ET requirements during the reproductive stage is more essential than during the vegetative stage for greater yield and enhanced WUE, particularly when available seasonal irrigation water is less than seasonal full crop ET requirements. In water limited environments, reasonable yield and enhanced WUE can be achieved by applying a deficit rate of 40% ET during the vegetative stage and 80% ET during the reproductive stage or scheduling irrigation based on soil water content to ensure AWC of 30% in the top 0–30 cm soil layer throughout the growing season. Concepts developed in the present study can be adapted to effectively manage irrigation scheduling for medium-maturity maize hybrids in arid sandy soils with low AWC and organic C content.

Reducing sugarcane irrigation demand through planting date adjustment in Alagoas State, Brazil

ABSTRACT Sugarcane is both an important crop for the Brazilian Northeast economy, which faces severe water scarcity, and a water-intensive crop. Thus, it is important to develop irrigation strategies to reduce irrigation water demand in the region. This study aims to determine the sugarcane planting date that results in the maximum rainwater availability to the crop in the growing cycle. The crop effective precipitation was estimated from a soil water balance performed during three planting cycles of sugarcane, cultivar ‘RB 92579’. The crop was planted under subsurface drip irrigation in five months: October, November, December, January, and February, corresponding to the dry season period of the region. The experiment was conducted at the Açúcar e Álcool Coruripe Mill, located in the Coruripe municipality, State of Alagoas, Brazil, during the years 2012 to 2016. For all planting dates and growing cycles studied, the average effective rainy precipitation was equal to 30% of the total rainfall under irrigated conditions and 54.5% without considering the irrigation component in the soil water balance. November was the planting date that resulted in the minimum irrigation depth for the sugarcane growing cycle, with the potential irrigation water saving ranging from 5 to 129 mm.

Assessment of hydro-geochemical properties of groundwater under the effect of desalination wastewater discharge in an arid area.

Desalination to increase irrigation water supply for agricultural production is becoming important in water-scarce regions. While desalination has positive effects on the potential irrigation water quantity and quality, the technique may also be a considered potential source of groundwater pollution. The present study investigated the effects of desalination wastewater discharge on groundwater quality in an arid area in southern Iran for the 2012-2017 period. The chemical composition of the groundwater samples was evaluated considering pH, EC, Na+, Ca2+, Mg2+, SO42+, Cl-, and HCO3-. The suitability of groundwater for drinking and irrigation purposes as well as spatial pattern of groundwater pollution was analyzed. The results showed that mean concentration of Na+, Ca2+, Mg2+, SO42-, and Cl- in all investigated wells increased from 148, 94, 46, 247, and 257 mg/L in 2012 to 282, 146, 71, 319, and 582 mg/L in 2017, respectively. Using Gibb's diagram, it was shown that the groundwater quality is slightly alkaline and primarily controlled by evaporation. Based on our findings, about 78% of the study aquifer displayed groundwater with good to excellent water quality that can be used for drinking and irrigation purposes. However, the eastern part of the aquifer was classified as unsuitable for use due to the disposal of desalination plant wastewater. The spatial distribution of WQI and other indices such as SAR, TDS, and TH showed that groundwater in the eastern part of the aquifer has deteriorated since the establishment of the desalination plants. To reverse this trend, it is important to implement regulations against wastewater discharge from desalination plants.

Effect of Different Reclaimed Water Irrigation Methods on Bacterial Community Diversity and Pathogen Abundance in the Soil-Pepper Ecosystem

Reclaimed water is considered to be a reasonable and sustainable alternative water resource to improve water resource layout and mitigate the shortage of traditional water resources. Its use in irrigation will cause changes in the microbial community structure and opportunistic pathogen abundance in soils and crops, but few studies have been conducted on this subject. Peppers were used as the research subjects, and the treatments were direct irrigation of reclaimed water, mixed irrigation with freshwater and reclaimed water, rotated irrigation with freshwater and reclaimed water, with potable water irrigation as the control. The effects of different irrigation methods of reclaimed water on the soil physicochemical properties were analyzed through a pot experiment. Furthermore, changes in bacterial community and opportunistic pathogen abundance in pepper fruit and the rhizosphere under reclaimed water irrigation conditions were investigated based on high-throughput sequencing technology and quantitative PCR methods. The results showed that direct irrigation with reclaimed water increased soil EC and decreased soil pH. 16S rDNA high-throughput sequencing showed that Proteobacteria, Bacteroides, Actinobacteria, and Firmicutes were present in both pepper fruit and the rhizosphere at phylum level, and the most dominant genera (Pantoea, Pseudomonas, Sphingomonas, Sphingopyxis, Luteimonas, and Mariniflexile) were greatly affected by reclaimed water irrigation methods. Quantitative PCR results indicated that the influence of reclaimed water irrigation on the distribution and abundance of pathogenic bacteria in the soil-pepper system was different, and the abundance of Legionella spp. in pepper fruit and Pseudomonas syringae in the rhizosphere increased with reclaimed water irrigation. Our results indicated that the reclaimed water was suitable for agricultural irrigation, but different reclaimed water irrigation methods may introduce different degrees of microbial contamination. In addition, attention must be given to some opportunistic pathogens and phytopathogens.

Incidence of fecal indicator and pathogenic bacteria in reclaimed and return flow waters in Arizona, USA

The quality of irrigation water used to cultivate produce that is consumed raw is an important issue with regard to food safety. In this study, the microbiological quality of potential irrigation water sources in Arizona was evaluated by testing for the presence of indicator and pathogenic bacteria. Reclaimed water samples were collected from two wastewater treatment plants and return flow samples were collected from two drainage canals and one return flow pond. Standard membrane filtration methods were used for detection of indicator bacteria. Water samples (n = 28) were filtered through cellulose ester membrane filters and bacterial populations were enumerated by placing the filters on selective agar. For detection of pathogens (Salmonella enterica, Listeria monocytogenes and Shiga toxin-producing E. coli (STEC)), water samples were filtered through Modified Moore swabs and enriched in Universal Pre-enrichment Broth, followed by selective enrichment broth for each pathogen. The enriched broth was streaked onto agar media selective for each pathogen. Presumptive colonies were confirmed by PCR/real-time PCR. Among the 14 reclaimed water samples from two sites, the ranges of recovered populations of E. coli, total coliforms, and enterococci were 0–1.3, 0.5–8.3 × 103, and 0–5.5 CFU/100 mL, respectively. No L. monocytogenes, Salmonella or STEC were found. In the 13 return flow water samples from 3 sites, the ranges of recovered populations of E. coli, total coliforms and enterococci were 1.9–5.3 × 102, 6.5 × 102−9.1 × 104, and 2.9–3.7× 103 CFU/100 mL, respectively. All samples were negative for L. monocytogenes. One (7.1%) of the return flow samples was positive for E. coli O145. Nine (64.3%) of the samples were positive for Salmonella. Both real-time PCR and culture-based methods were used for the detection of Salmonella and L. monocytogenes, and the results from the two methods were comparable. The findings of this study provide evidence that irrigation waters in Arizona, including reclaimed water and return flows, could be potential sources of bacterial contamination of produce. Additional work is needed to evaluate whether bacteria present in irrigation water sources transfer to the edible portion of irrigated plants and are capable of persisting through post-harvest activities.

Chemical profile and bioactive properties of the essential oil isolated from Clinopodium serpyllifolium (M.Bieb.) Kuntze growing in Palestine

Medicinal aromatic plants (MAPs) are cultivated for the production of specialty materials including essential oils (EO), and pharmaceuticals, but most are still wild collected. The need for renewable sources of intensive industrial products as well as the protection of plant biodiversity can be satisfied by cultivating MAPs as agro-industrial crops. Such crops require ample amounts of irrigation water to meet their potential for rigorous production. Shortage of fresh water in arid and semi-arid zones has necessitated the development of MAPs production systems based on irrigation with treated effluents. In the present study we have investigated the MAP Clinopodium serpyllifolium for its suitability to grow under irrigation with treated effluents, as a source of EO and pharmaceuticals. The results have demonstrated the suitability of the utilization of treated effluents for agro-industrial production of C. serpyllifolium, as a promising source of high quality EO, and biomass production, without compromising yield parameters and bioactivities, compared with potable water irrigation. The results indicate that C. serpyllifolium is a valuable natural source of antioxidants and cholinesterase inhibitors, with interesting inhibitory actions against the key enzymes involved in Alzheimer’s disease (AD) and could represent a starting point for the development of new AD management strategies using natural butyrylcholinesterase inhibitors, including its use as a food supplement. The study has demonstrated the ability of C. serpyllifolium extracts to exert health benefits by inhibiting pancreatic lipase, a target for obesity. Treated effluents is suitable for growth and quality production in C. serpyllifolium, and hence it forms the foundation for effluent-based industrial EO production.

Secondary treated effluent irrigation did not impact chemical composition, and enzyme inhibition activities of essential oils from Origanum syriacum var. syriacum

Environmental conditions, including irrigation water quality, are known to affect secondary metabolite production in plants and hence the composition and activity of essential oils of aromatic plants. The aim of this study is to evaluate the effect of irrigation with secondary-treated effluent, as compared with potable water irrigation, on the composition, biological activities and yield of essential oil (EO) from Origanum syriacum L. var. syriacum (OSS). The EO from OSS cultivated in Palestine under secondary treated municipal effluent compared with potable water irrigation were analyzed seasonally over a two-year period for oil quantity and composition, antioxidant activities 1,1- diphenyl-2-picrylhydrazyl (DPPH), 2,2 azino-bis (3-ethylbenzothiazloine-6-sulfonic acid) radical cation (ABTS), ferric reducing antioxidant power (FRAP), antimicrobial and inhibitory properties against acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and porcine pancreatic lipase (PPL). The quality of the irrigation water did not affect the essential oil yield quantity and quality demonstrating the potential of this marginal water source for agri-industrial production of OSS. Under both irrigation water qualities, the EO contained 35 constituents, of which thymol (40.4–46.7%), and carvacrol (35.1–41.8%) were the most abundant. EOs from plants of both irrigation water qualities exhibited a strong free radical scavenging ability and reducing power activity, and high AChE, BChE, and PPL inhibitory activities. The EOs also showed a moderate antibacterial activity against most test bacterial strains, with high antibacterial activity against Staphylococcus aureus with 117 percent inhibition compared with chloramphenicol (30μg/disc). The high inhibitory activity of the EOs on AChE, BChE, and PPL, and its high antioxidant and antibacterial activities may be due to high concentrations of monoterpenes, especially thymol and carvacrol. The data demonstrate that secondary-treated municipal effluents can be successfully utilized for irrigation of industrial crop production setups for essential oil production from OSS (as a source of natural antioxidants, anticholinesterase, antiobesity and antistaphylococcal agents) without compromising yield quantity and bioactivities compared with potable water irrigation.

Wastewater Reuse for Agriculture: Development of a Regional Water Reuse Decision-Support Model (RWRM) for Cost-Effective Irrigation Sources.

Water scarcity has become a critical problem in many semiarid and arid regions. The single largest water use in such regions is for crop irrigation, which typically relies on groundwater and surface water sources. With increasing stress on these traditional water sources, it is important to consider alternative irrigation sources for areas with limited freshwater resources. One potential irrigation water resource is treated wastewater for agricultural fields located near urban centers. In addition, treated wastewater can contribute an appreciable amount of necessary nutrients for plants. The suitability of reclaimed water for specific applications depends on water quality and usage requirements. The main factors that determine the suitability of recycled water for agricultural irrigation are salinity, heavy metals, and pathogens, which cause adverse effects on human, plants, and soils. In this paper, we develop a regional water reuse decision-support model (RWRM) using the general algebraic modeling system to analyze the cost-effectiveness of alternative treatment trains to generate irrigation water from reclaimed wastewater, with the irrigation water designed to meet crop requirements as well as California's wastewater reuse regulations (Title 22). Using a cost-minimization framework, least-cost solutions consisting of treatment processes and their intensities (blending ratios) are identified to produce alternative irrigation sources for citrus and turfgrass. Our analysis illustrates the benefits of employing an optimization framework and flexible treatment design to identify cost-effective blending opportunities that may produce high-quality irrigation water for a wide range of end uses.

Assessing the suitability of saline wastewaters for irrigation of Citrus spp.: Emphasis on boron and specific-ion interactions

Many ground waters and recycled municipal wastewaters contain elevated concentrations of boron (B) and salts but are nonetheless potential irrigation water sources for agricultural production. Unlike most agricultural crops, Citrus spp. is among the most sensitive to B and salinity. Here, an extensive review of the literature from 1928 to present on Citrus spp. tolerance to B and specific ions has been conducted. The overall suitability of such water supplies largely depends upon the salt and B concentration in the irrigation water, irrigation management, rainfall, soil and climatic conditions and orange rootstock. Since salinity and B stresses often occur together, the overall suitability may depend on interactive abiotic stresses as well. The combination and potential interaction of these constituents, combined with the soil and climatic conditions, can affect the overall suitability of B in irrigation water over the long-term. And there is evidence of internal tolerance mechanisms (i.e. B transport/compartmentation; B complexation) present allowing leaves to tolerate higher B concentrations than they would otherwise and that certain amendments can reduce uptake and transport from rootstock to scion. Regardless, new research does not provide any more information to suggest that the existing B tolerance guidelines for orange (0.50–0.75mg/L in the soil solution, Bss) should be adjusted upwards or downwards. The challenge comes in determining the maximum B concentration in the irrigation water (Bw) that would result in these Bss tolerance values. Two steady-state approaches that were used here suggest that the maximum Bw for the protection of orange falls between 0.3 and 0.5mg/L over the long term provided good water management, adequate leaching and no additional stresses are affecting the tree. For lemon, maximum Bw concentrations would be less. The presence of specific ions and ion interactions makes water quality assessment difficult.

A global water scarcity assessment under Shared Socio-economic Pathways – Part 1: Water use

Abstract. A novel global water scarcity assessment for the 21st century is presented in a two-part paper. In this first paper, water use scenarios are presented for the latest global hydrological models. The scenarios are compatible with the socio-economic scenarios of the Shared Socio-economic Pathways (SSPs), which are a part of the latest set of scenarios on global change developed by the integrated assessment, the IAV (climate change impact, adaptation, and vulnerability assessment), and the climate modeling community. The SSPs depict five global situations based on substantially different socio-economic conditions during the 21st century. Water use scenarios were developed to reflect not only quantitative socio-economic factors, such as population and electricity production, but also key qualitative concepts such as the degree of technological change and overall environmental consciousness. Each scenario consists of five factors: irrigated area, crop intensity, irrigation efficiency, and withdrawal-based potential industrial and municipal water demands. The first three factors are used to estimate the potential irrigation water demand. All factors were developed using simple models based on a literature review and analysis of historical records. The factors are grid-based at a spatial resolution of 0.5° × 0.5° and cover the whole 21st century in five-year intervals. Each factor shows wide variation among the different global situations depicted: the irrigated area in 2085 varies between 2.7 × 106 and 4.5 × 106 km2, withdrawal-based potential industrial water demand between 246 and 1714 km3 yr−1, and municipal water between 573 and 1280 km3 yr−1. The water use scenarios can be used for global water scarcity assessments that identify the regions vulnerable to water scarcity and analyze the timing and magnitude of scarcity conditions.

TREATED EFFLUENT AND SALINE WATER IRRIGATION INFLUENCES SOIL PROPERTIES, YIELD, WATER PRODUCTIVITY AND SODIUM CONTENT OF SNOW PEAS AND CELERY

To determine the effects of irrigation water quality, plants were irrigated with normal potable water [0.25 dS m−1 electrical conductivity (EC), 25 mg L−1 sodium (Na), 55 mg L−1 chloride (Cl)], treated effluent (0.94 dS m−1 EC, 122 mg L−1 Na, 143 mg L−1 Cl) and saline water with low salinity (1.24 dS m−1 EC, 144 mg L−1 Na and 358 mg L−1 Cl) and high salinity (2.19 dS m−1 EC, 264 mg L −1Na and 662 mg L−1 Cl) for snow peas, and high salinity (3.07 dS m−1 EC, 383 mg L−1 Na and 965 mg L−1 Cl) and very high salinity (5.83 dS m−1 EC, 741 mg L−1 Na and 1876 mg L−1 Cl) for celery. The greater salts build up in the soil and ion toxicity (Cl and Na) with saline water irrigation contributed to significantly greater reduction in root and shoot biomass, water use, yield and water productivity (yield kg kL−1 of water used) of snow peas and celery compared with treated effluent and potable water irrigation. There was 8%, 56% and 74% reduction in celery yield respectively with treated effluent, high salinity and very high salinity saline water irrigation compared with potable water irrigation. The Na concentration in snow peas shoots increased by 54%, 234% and 501% with treated effluent, low and high salinity saline water irrigation. Similarly, the increases in Na concentration in celery shoots were 19%, 35% and 82%. The treated effluent irrigation also resulted in a significant increase in soil EC, nitrogen (N) and phosphorus (P) content compared with potable water irrigation. The heavy metals besides salts build up appears to have contributed to yield reductions with treated effluent irrigation. The study reveals strong implications for the use of saline water and treated effluent for irrigation of snow peas and celery. The salt build up within the root zone and soil environment would be critical in the long-run with the use of saline water and treated effluent for irrigation of crops. To minimize the salinity level in rhizosphere, an alternate irrigation of potable water with treated effluent or low salinity level water may be better option.

Midday stem water potential as a useful tool for estimating irrigation requirements in olive trees

Irrigation scheduling of fruit trees according to the water balance showed significant differences between locations. In recent years, water status measurements such as leaf water potential have been suggested as irrigation tools in different fruit trees. The aim of this study was to adjust water potential threshold values previously studied and water application approaches that permit the estimation of irrigation requirements of olive trees based on midday stem water potential. The experiments were performed during three seasons (from 2005 to 2007) in two different locations (Badajoz and Ciudad Real) with different weather and cultural conditions. In both locations, the olive orchards were seven years old at the beginning of the experiment but had significantly different canopy development. In Ciudad Real the canopy shaded area at the beginning of the experiment was 15% and the first crop was harvested in 2003. On the other hand, the canopy shaded area of the olive orchard in the Badajoz experiment was 40% and the first crop was harvested in 2001. We therefore considered the Ciudad Real orchard as young and Badajoz as mature. Three different irrigation treatments were compared in both locations: Control treatment with traditional water balance as irrigation scheduling and two treatments in which midday stem water potential (SWP) provided the information about water management. In the midday stem water potential irrigation (WI) treatment the threshold value of SWP was −1.2MPa before the beginning of the massive pit hardening period and −1.4MPa after this date. Finally, in the deficit irrigation (DI) treatment the threshold value of SWP was −2.0MPa throughout the season. In the WI and DI treatments irrigation was applied when SWP reached the threshold value. No significant differences were found between Control and WI in any of the seasons or locations when SWP, leaf conductance, shoot and fruit growth and yield (fruit and oil) were considered. In both locations, the same SWP value in WI treatment resulted in similar water application as the Control treatment. In DI treatment, shoot growth was significantly reduced in both locations in all the seasons. The SWP in DI trees was clearly affected in both locations, while leaf conductance was only reduced in the Badajoz experiment. In the Ciudad Real experiment no significant differences between DI and the other treatments were found in fruit growth, whereas differences were found in Badajoz. However, in Ciudad Real yield in DI treatment was significantly reduced, but not in Badajoz. WI treatment was successful for non-water-stress conditions. On the other hand, DI treatment was a mild water stress treatment which reduced yield only in low covered orchards, but not in the orchards with almost maximum canopy shaded area.

The Quality and Health Implications of Urban Irrigation Water Used for Vegetable Production in the Accra Metropolis

The quality of irrigation water from different sources used by urban farmers in the Accra Metropolis was investigated. These were, tap water stored in dugout, surface water (from stream) and wastewater in drains. The samples were analysed for their bacteriological, physical and chemical qualities using standard methods. Analytical Profile Index (API) identification system was used to characterize and identify the bacterial species isolated in the samples. The results showed that heavy metal concentrations in the samples were within the FAO/WHO recommended limits for irrigation. The concentrations of highly toxic Lead and Cadmium were even below detection limit. Total and faecal coliform bacteria loads in all three potential irrigation water sources were above the WHO recommended limit for irrigation. Different bacteria species belonging to seven genera were identified in the three irrigation water sources. These included Citrobacter, Chryseomonas, Enterobacter, Klebseila, Proteus, Providencia, Pseudomonas. Generally, the most dominant bacterial species were Pseudomonas aeruginosa and Chryseomonas luteola. Some of these bacteria spp. can pose a health threat to farmers especially those who have challenges with their health and immune system. For example, infection with some of the bacteria species such as Pseudomonas aeruginosa in patients with cystic fibrosis is known to be deadly over periods of time.

Effect of different irrigation water salinities on some yield and quality components of two field-grown Cucurbit species

Using irrigation water with a salinity level of 0.8, 2, and 5 g L^{-1}, the impact of saline water irrigation on the yield and quality of 2 Chinese Cucurbit species, melon (Cucumis melo cv. Huanghe) and watermelon (Citrullus lanatus. convar megulaspemus) were studied in Minqin Oasis, northwestern China. Our results show that melon yields decreased as water salinity increased, just as concentrations of glutamic acid content rose, although the concentration of most amino acids did not differ significantly. In contrast, watermelon yields decreased significantly as water salinity rose, and fruit number, fruit firmness, fruit crude protein, and essential amino acid (EAA) levels of the watermelon showed a significant increase as water salinity rose. Salt stress on both Cucurbit species resulted in an increase in total soluble solids (TSS) and Na^+ concentrations, while Ca^{2+} and Cl^- concentrations were not affected significantly. In conclusion, our results showed that, although melon and watermelon yields were restrained by saline water irrigation, fruit quality was not influenced, such as for the fruit's amino acids. The fact that saline water irrigation is feasible for melon and watermelon species shows that saline water is a potential irrigation water resource in arid areas of northwest China.