Saline Drainage Water Research Articles

Long-term Cyclic Irrigation in Subsurface Drained Lands: Simulation Studies with SWAP

SWAP (Soil-Water-Atmosphere-Plant) version 2.0 was evaluated for its capability to simulate the crop growth and salinity profile for cyclic irrigation of saline waters at Sampla (India) having shallow water table provided with a subsurface drainage system. Cyclic mode with canal water (EC=0.4 dS m -1 ) and saline drainage water (EC=12.5-15.5 dS m -1 ) were used to calibrate and validate the model for the years 1989-91. Canal water was used for pre-sowing irrigation and thereafter, canal and saline drainage waters were used as per pre-decided irrigation modes like all CW, CW:DW, 2CW:2DW, DW:CW, and 1CW:3DW. Absolute deviations and standard error between the SWAP simulated and observed relative yields during calibration ranged from 1.3 to 1.8% and 1.7 to 2.2% respectively. A close agreement was observed between the measured and simulated soil salinity profile. It established the validity of SWAP model under the experimental conditions prevalent at the site. It could also be concluded that the crops could be grown very well under subsurface drainage conditions; but, in dry rainfall years, salinity build-up might occur. To achieve a yield potential exceeding 80%, it could be suggested that cyclic use of saline waters such as 1CW:1DW and 2CW:2DW could be used in such years. A pre-sowing irrigation with canal water could be helpful to overcome the build-up of salts and salt amount washing depends upon the rainfall. Thus, there seems to be no fear of use of cyclic irrigation under drained conditions. The same fact was established through the use of model SWAP.

RESPONSE OF TOMATO TO IRRIGATION WITH SALINE WATER APPLIED BY DIFFERENT IRRIGATION METHODS AND WATER MANAGEMENT STRATEGIES

In a field experiment the effects of irrigation with saline drainage water (seasonal average of 4.5 dS/m) and non-saline water (0.55 dS/m) applied by two different water management strategies (cyclic or blended saline water with non-saline water in different ratios) and two different irrigation methods (drip or furrow) were studied on growth and productivity of tomato (Lycopersicon esculentum Mill cv Floradade), salinity distribution in root zone and water use efficiency. The results indicated that salinity (at 3 dS/m and above) significantly reduced leaf area, height and dry weight of plant as well as fruit weight and number and hence total yield, but increased fruit T.S.S. content. Water use efficiency (WUE) was increased by using water with low and moderate salinity levels (2 and 3 dS/m) as compared to those obtained with non-saline water (0.55 dS/m) or the highest salinity level (4.5 dS/m). Salinity increased Na, Cl and Mg contents as well as dry matter percentage, but decreased N, P, K and Ca contents in leaves of plants. Drip irrigation enhanced tomato growth, yield and WUE under both saline and non-saline conditions, but showed more advantages under saline conditions as compared with furrow irrigation. Drip irrigation method did not allow salt accumulation in root zone (wetted area beneath the emitters and the plants). However, more salt accumulated in root zone (30 cm apart from irrigation source) of furrow irrigated plants. Mixing saline with non saline waters (blending) produced better results in terms of more vigorous vegetative growth and highest yield, than that produced by alternate saline with non saline water (cyclic). Using saline water up to 3 dS/m produced yield that was not significantly differ than that produced by non saline water if applied by drip irrigation and blended water management.

Apparent steady state conditions in high resolution weighing-drainage lysimeters containing date palms grown under different salinities

This study presents a novel investigation of long-term apparent steady state conditions under a prescribed leaching fraction criterion. The research was carried out during a 7-year investigation of date palm (Phoenix dactylifera L., cv. Medjool) trees exposed to elevated levels of irrigation water salinity. High resolution weighing lysimeters were designed and constructed to generate an accuracy of ±0.0075mm. The lysimeters were equipped with precision flux data acquisition that measured the oscillations of their daily water storage difference (ΔW) and evapotranspiration. The leaching fraction was kept constant throughout the study.The results generally confirmed that the assumption of apparent steady state conditions under the preprogrammed irrigation procedure was correct, even though inter- and intra-seasonal climate variations were observed. Measured ΔW oscillated slightly around zero even under high evapotranspiration demands. Drainage water electrical conductivity and leaching fraction were also found to stay fairly constant. The evapotranspiration of the date trees was found to be a function of the potential evapotranspiration, and rather insensitive to changes in the soil water storage (ΔW). Our analysis also indicates that for most practical purposes of monitoring and sustaining apparent steady state conditions, simple low-cost lysimeters, without weighing capability, can serve to monitor and sustain apparent steady state conditions, as long as there is water outflow from the lysimeters.However, the high resolution (high cost) weighing lysimeters proved to be an efficient system for accurate data acquisition, which is necessary for accurate modeling. An annual numerical crop yield model, modified for a date palm field study, was successfully calibrated using data from a 2 month period, and subsequently validated against measured data from the following 8 months. The modified model closely predicted the daily oscillations of drainage water salinity and actual leaching fraction throughout the eight-month period.

Evapotranspiration potential of forages irrigated with saline-sodic drainage water

Abstract In the western San Joaquin Valley (SJV) of California, re-use of saline-sodic drainage water (DW) for the irrigation of salt tolerant forages and field crops is an important strategy for drainage water reduction and to extend irrigation water supplies. Drainage reuse designs require estimates of crop water use under saline conditions, so this study employed two methods to estimate the actual evapotranspiration (ET a ) of saline-irrigated forages. Using sand-filled drainage lysimeters, ET was measured for ‘Jose’ tall wheatgrass (TWG; Thinopyrum ponticum var. ‘Jose’) creeping wildrye (CWR; Leymus triticoides , var. ‘Rio’) and Paspalum ( Paspalum vaginatum , var. ‘SeaIsle’) irrigated with saline DW with an electrical conductivity (EC) averaging 13.2 dS m −1 . Annual ET in 2005 (20 January to 28 December) was 1470 mm for TWG, 1376 mm for CWR, and 1275 mm for Paspalum. Comparing to standardized reference evapotranspiration (ET o ), the annual (ET a /ET o ) lys ratios in 2005 were 0.98 for TWG, 0.92 for CWR, and 0.85 for Paspalum. Forage ET was also estimated by a surface renewal (SR) method in large pastures of TWG and CWR irrigated with saline DW. For TWG, the seasonal (ET a /ET o ) SR in 2005 was 0.94, slightly lower than the ratio of 0.98 determined by lysimetry. For CWR, the seasonal (ET a /ET o ) SR was only 0.73 in 2005; however, in 2006 it was 1.03 which was closer to the ratio of 0.92 determined by lysimetry in 2005. Conditions were less uniform in the CWR pasture as compared to the TWG pasture which may have caused the greater variability in (ET a /ET o ) SR for this forage. These findings, along with earlier work, demonstrate that tall wheatgrass, creeping wildrye and Paspalum are suitable candidates for DW re-use systems for the western SJV due to their high ET under saline irrigation and adequate dry matter production and forage quality.

Grazing as an alternative for utilization of saline-sodic soils in the San Joaquin Valley: Selenium accretion and performance of beef heifers

Two experiments were conducted to evaluate Se accumulation and health of non-pregnant, non-breeding beef cattle grazing on forages with a high Se content due to irrigation with saline drainage water. Heifers grazed experimental pastures of “Jose” tall wheatgrass (TWG; Thinopyrum ponticum var. “Jose”) and creeping wildrye (CWR; Leymus triticoides var. “Rio”) for190days in Experiment 1 (2007) and for 165days in Experiment 2 (2008). In experiment 1, mean Se concentrations were similar in TWG and CWR herbage (4.0 versus 3.7±0.26mg/kg dry weight; p=0.34) as was crude protein (113 versus 114±7.9g/kg dry weight; p=0.94). Concentrations of Se in blood increased by 300% during the grazing period, and were similar for heifers grazing the TWG or CWR pastures (0.94 versus 0.87±0.03mg/kg; p=0.89). Heifers grazing on TWG gained more body weight than did heifers grazing on CWR (0.59 versus 0.27±0.07kg/days; p<0.01). In experiment 2, concentration of Se (4.0 versus 2.8mg/kg±0.19mg/kg dry weight; p<0.01) and crude protein (79 versus 90±5.6g/kg dry weight; p<0.01) differed, for TWG and CWR, respectively. Within 20days, Se concentrations in blood had increased by 300% and by nearly 200% in heifers grazing on TWG or CWR. All data cited are least square means±standard error of the mean. Data from our two grazing seasons are consistent in demonstrating the safety of grazing beef cattle for a period of up to 6months on TWG and CWR forages having high levels of Se due to irrigation with saline drainage water. This suggests that forage production using saline drainage water is a viable alternative for saline soils with limited potential for producing high value, salt-sensitive, crops.

Synthesis of hydrotalcite by neutralization of bauxite residue mud leachate with acidic saline drainage water

Bauxite residue (‘red mud’) storage areas discharge alkaline, saline leachate which is collected and presents a challenge for management well after closure of residue deposit areas. The alkaline and saline (sodic) nature of leachate limits opportunities for treatment or reuse. Mixing alkaline, saline bauxite residue leachate with acidic, saline drainage waters from deep drains installed in the Western Australian Wheatbelt harnesses the unfavorable pH and salinity of these waters to achieve neutralization and decrease salinity through precipitation of hydrotalcite-like minerals. A mixing ratio of 1:5 bauxite residue leachate:acidic saline drainage was required to achieve circumneutral pH (8.5); and though the electrical conductivity of the mixed solution was still high (81.5 mS/cm), it was significantly lower (α = 0.05) than predicted in the case of simple mixing, indicating that mineral precipitation lowers solution salinity.

Field-evaluation of DRAINMOD-S for predicting soil and drainage water salinity under semi-arid conditions in Turkey

The aim of this study was to determine the reliability of DRAINMOD-S for simulating water management in irrigated land and to simulate drainage system design criteria to ensure high crop yields for the western part of the Central Kızılırmak Basin in Turkey. The model was tested under arid conditions using field data for winter wheat and corn. Daily water-table depth, drain outflows and drainage water salinity were monitored throughout the growing season. Soil salinities were measured to a depth of 1.00 m from the soil surface. The reliability of the model was evaluated by comparing measured and predicted values of the daily ground water table depth, drain outflows, drainage water and soil salinity during each season, and relative crop yield. Good agreement was found between the measured and predicted values. Absolute deviation was 5.68 cm for water table depth, 10.13 mm for drain outflows, 0.66 dS m–1 for drainage water salinity, and ranged from 0.51 to 0.96 dS m–1 for soil salinity. The corresponding coefficients of efficiency (E) were between 0.48 and 0.95. The results also showed that Drainmod -S can be recommended as a useful tool for design and evaluation of irrigation and drainage systems in salt-affected soils under arid and semi-arid climates.

Application of some combined adsorbents to remove salinity parameters from drainage water

Due to high expenses of energy, desalination of saline waters by low-cost methods is important. To investigate the ability of combinations of five adsorbents (peat, activated carbon, zeolite, anionic resin, and cationic resin) to remove salinity ions from aqueous solutions, ten treatments were prepared for a batch experiment, using saline drainage water with total dissolved solids of 3.24gL−1. At first, a pre-test was conducted to analyze the behavior of these adsorbents in adsorption of chromium (from an industrial wastewater containing 15.1mgL−1 Cr(III) and 45.1mgL−1 Cr(VI)). Then, the same combinations of the adsorbents were used to remove salinity ions from the drainage water. The results showed that except cationic resin+zeolite, other treatments tended to adsorb Cr(III) and Cr(VI) completely. Cationic resin+peat, anionic resin+peat, and cationic resin+activated carbon have satisfactory results in desalination process as compared to anionic resin+cationic resin. Almost in all treatments, adsorption of anions was 2.3 to 2.9 times more than cations. Adsorption rates of Ca, Mg, HCO3 and SO4 by adsorbents was satisfactory as compared to adsorptions of Cr(VI) and Cr(III). This study confirmed that cationic resin had higher ability in desalination of the drainage water as compared to anionic resin, and application of cationic resin with peat was the best choice.

Soil salinity related to physical soil characteristics and irrigation management in four Mediterranean irrigation districts

Abstract Irrigated agriculture is threatened by soil salinity in numerous arid and semiarid areas of the Mediterranean basin. The objective of this work was to quantify soil salinity through electromagnetic induction (EMI) techniques and relate it to the physical characteristics and irrigation management of four Mediterranean irrigation districts located in Morocco, Spain, Tunisia and Turkey. The volume and salinity of the main water inputs (irrigation and precipitation) and outputs (crop evapotranspiration and drainage) were measured or estimated in each district. Soil salinity (ECe) maps were obtained through electromagnetic induction surveys (ECa readings) and district-specific ECa–ECe calibrations. Gravimetric soil water content (WC) and soil saturation percentage (SP) were also measured in the soil calibration samples. The ECa–ECe calibration equations were highly significant (P 0.1) with WC, and was only significantly correlated (P Morocco (2.2 dS m−1) > Spain (1.4 dS m−1) > Turkey (0.45 dS m−1). Soil salinity was mainly affected by irrigation water salinity and irrigation efficiency. Drainage water salinity at the exit of each district was mostly affected by soil salinity and irrigation efficiency, with values very high in Tunisia (9.0 dS m−1), high in Spain (4.6 dS m−1), moderate in Morocco (estimated at 2.6 dS m−1), and low in Turkey (1.4 dS m−1). Salt loads in drainage waters, calculated from their salinity (ECdw) and volume (Q), were highest in Tunisia (very high Q and very high ECdw), intermediate in Turkey (extremely high Q and low ECdw) and lowest in Spain (very low Q and high ECdw) (there were no Q data for Morocco). Reduction of these high drainage volumes through sound irrigation management would be the most efficient way to control the off-site salt-pollution caused by these Mediterranean irrigation districts.

Alfalfa production using saline drainage water

AbstractA three‐year study investigated the use of saline (EC &lt; 6 dS m−1) drainage water for irrigation of salt‐tolerant alfalfa in the presence of shallow saline groundwater. The irrigation treatments included: (1) irrigating twice between cuttings with nonsaline water, (2) irrigating twice with moderately saline water between cuttings, and(3) once between cuttings with moderately saline water. Yield data demonstrated an approximately 30% reduction in total yield over 3 years as a result of using the saline water for irrigation compared to irrigating with the nonsaline water. The overall alfalfa quality improved when irrigated with saline water compared to the non‐saline water. However, both boron and chloride progressively accumulated in alfalfa plant tissue during each growing season when irrigated with saline water. The plant tissue boron and chloride values returned to previously low levels by the start of the next growing season due to the influence of winter rainfall and irrigating with low‐salinity water at the break of dormancy. There was measurable accumulation of salt in the soil profile and in the shallow groundwater as a result of using saline drainage water for irrigation. A gradual decrease in depth to the shallow groundwater was observed as result of the lack of drainage capability. Electromagnetic induction proved adequate for characterizing root zone salinity with time. Published in 2010 John Wiley &amp; Sons, Ltd.

Simulating root water uptake from a shallow saline groundwater resource

Disposal of saline drainage water is a significant problem for irrigated agriculture. One proposal to deal with this problem is sequential biological concentration (SBC), which is the process of recycling drainage water on increasingly more salt tolerant crops until the volume of drainage water has been reduced sufficiently to enable its final disposal by evaporation in a small area. For maximum effectiveness this concept will require crop water reuse from shallow groundwater. To evaluate the concept of sequential biological concentration, a column lysimeter study was used to determine the potential crop water use from shallow groundwater by alfalfa as a function of ground water quality and depth to ground water. However, lysimeter studies are not practical for characterizing all the possible scenarios for crop water use related to ground water quality and depth. Models are suited to do this type of characterization if they can be validated. To this end, we used the HYDRUS-1D water flow and solute transport simulation model to simulate our experimental results. Considering the precision of the experimental boundary and initial conditions, numerical simulations matched the experimental results very well. The modeling results indicate that it is possible to reduce the dependence on experimental research by extrapolating experimental results obtained in this study to other specific sites where shallow saline groundwater is of concern.

Pre‐ and Post‐Irrigation Mapping of Soil Salinity with Electromagnetic Induction Techniques and Relationships with Drainage Water Salinity

Irrigated agriculture may impair negative “on‐site” (i.e., soil salinization) and “off‐site” (i.e., salts exported in irrigation return flows) effects. The aim of this study was to assess these effects, and the relationships between soil‐ and drainage‐water salinity in a basin before and after the development of irrigation. Soil salinity (ECe) was estimated through electromagnetic induction (EMI) techniques (ECa) and the corresponding calibration equations, and drainage water salinity (ECdw) was measured in the outlets of 22 watersheds delineated within a 505‐ha study area before (Year 2006) and after (Year 2008) irrigation development. Apparent soil EC was about 50% higher in 2008 than in 2006 due to increasing soil water contents, but estimated ECe was about 15% lower in 2008 than in 2006 due to salt leaching induced by irrigation. Drainage water EC increased by one order of magnitude from the upper (ECdw = 0.4 dS m−1) to the lower (ECdw = 4.5 dS m−1) reaches of the drainage network. The mean ECdw of the 22 watershed drainage outlets increased from pre‐irrigation 2006 (2.4 dS m−1) to post‐irrigation 2007 (3.1 dS m−1) and 2008 (2.7 dS m−1) years. Drainage water EC significantly depended (P &lt; 0.001) on surface‐weighted EC (ECe*) of each watershed, but the linear regressions were different in 2006 and 2008. The transformation from dryland to irrigation led to the leaching of salts and its export in the irrigation return flows. A compromise needs to be attained in the study area to achieve the beneficial “on‐site” leaching of salts while minimizing the detrimental “off‐site” export of salts.

Effect of Magnetic Conditioning of Saline Water Characteristics on corn plants growth (Zea mays L.) and up take of Nitrogen, Phosphorus and Potassium

A biological Pots experiment was conducted in lath house of soil and water sci.Dept. using silty clay loam Typic Torrifluvent soil collected form Agriculture College fields. The soil was fertilized by 240 kg N.ha-1 as Urea fertilizer ,75 kg P.ha-1 as super phosphate and 120 kg K.ha-1 as Potassium sulphate fertilize. Corn seeds were planted in spring 2007 irrigated by tap water with electrical conductivity of 0.4 dS.m-1 and drainage saline water 7.4 ds.m-1 with and without magnetic . 10 Weeks after planting , plants were harvested, hights and dry weight of shoots were measured also total uptake of N,P and K nutrients were measured . The results of this experiment showed that Corn Plants hight ,dry weights ,total uptake of N,P and K nutrients were significantly decreased when drainage saline water used as campared with tap water with decreament 10.8 ,28.9 ,17.7 ,22.7 ,17.8 % of these characters respectively. On other hand magnetic water significantly increased all studied characters as compared with non-magnetic. The increase were 17.7 ,34.6 ,23.8 ,28.4 ,21.9 % for plant hight , dry matter weight ,total uptake of N ,P and K nutrients respectively. The results also indicated that there was a significant interaction between water quality and magnetic water , The highst values were obtined with magnetic tap water treatment with no significant differences between magnetic saline drainage water and non-magnetic tap water.

Long-term Use of Saline Drainage Waters for Irrigation in Subsurface Drained Lands: Simulation Modelling with SWAP

SWAP (Soil-Water-Atmosphere-Plant) version 2.0 was evaluated for its capability to simulate crop growth and salinity profiles for a saline water irrigated area (Sampla, District Rohtak, Haryana) having shallow water table provided with a subsurface drainage system. Canal water (0.7 dS.m-1) was used for pre-sowing irrigation in all the treatments and thereafter, canal (0.7 dS.m-1), mixed canal and saline drainage water of varying salinity (6, 9, 12 dS.m-1) and drainage water alone varying in salinity from 12 to 27 dS.m-1 were used for irrigation. Absolute deviations and standard error between the SWAP simulated and the observed relative yields during calibration ranged from 2.6 to 7.2% and 3.1 to 9.7%, respectively, and established the validity of SWAP model under the experimental conditions. The scenario building simulations carried out with the validated SWAP revealed that yield at a higher level could be sustained with subsurface drainage than without it. Optimum yields in most years could be obtained with irrigation water of EC dS.m-1. It was established that notwithstanding the seasonal build-up of salts due to saline water use, there would be no long-term build-up of salts as leaching during the monsoon season would render the soil profile salt free at the time of sowing of rabi crops. SWAP was found to be a useful tool to assess the performance of subsurface drainage systems with reuse of saline drainage water for crop production.

Bacterial diversity in cucumber ( Cucumis sativus) rhizosphere in response to salinity, soil pH, and boron

Soil salinity is a major factor relating microbial communities to environmental stress in the microbial selection process as stress can reduce bacterial diversity. In the San Joaquin Valley (SJV) of California, the problem of increasing salinity and consequently, decreasing crop productivity, due to reuse of saline drainage water are major concerns. An experiment was conducted in a closed, recirculating volumetric lysimeter system (VLS) consisting of 24 experimental plant growth units to determine the interactive effects of salinity, boron and pH on rhizosphere and non-rhizosphere microbial composition of cucumber ( Cucumis sativus L. cv. Seminis Turbo hybrid). Plants in the VLS were irrigated from individual reservoirs containing a modified half-strength Hoagland's nutrient solution combined with salinity, boron (B), and pH treatments. The results indicated that salinity and pH were the most influential factors affecting the growth of plants and the effect of boron on the plant was more severe under slightly acidic conditions. Total bacterial DNA was extracted from rhizosphere and non-rhizosphere samples, and a 236-bp DNA fragment in the V3 region of the small subunit ribosomal RNA genes of eubacteria was amplified. The 16S rRNA and the products were subjected to denaturing gradient gel electrophoresis (DGGE) and sequencing. Analyses of bacterial diversity showed that the effects of salinity, boron, and pH were more severe on the rhizosphere bacterial population during the first week of growing cucumber, with decreasing impacts with plant growth. However, there was no salinity–B–pH interaction effects on plant biomass, but the effects were seen in the number of heterotrophic bacteria in the rhizosphere and on species richness and diversity during week seven of the study. These suggest that the effects of salinity–B–pH interactions may influence microorganisms first before plants and may pose long term effects on soil quality.

Organic Substrates in Bioremediation of Acidic Saline Drainage Waters by Sulfate-Reducing Bacteria

Deep drains used to manage shallow saline water tables in the Western Australian agricultural region discharge acidic, saline drainage water with high concentrations of metals. The activity of sulfate-reducing bacteria can treat these waters by generating alkalinity in the form of bicarbonate and by generating sulfide, which removes metals from solution as sulfide precipitates. Bacterial sulfate reduction was strongly influenced by the organic carbon substrate provided for bacterial consumption. Mixtures of lupin compost, wheat chaff, oil mallee distillate wastes, straw, ethanol, and sheep manure were compared to determine which substrate was most effective in promoting the activity of sulfate-reducing bacteria and the contribution of this to bioremediation of acidic saline drainage. Mesocosm treatment systems containing reactive mixtures and acidic saline drainage were operated for a 50-day establishment period and subsequent 27-day “batch flow” period. Effluent from the treatment systems was analyzed for pH, sulfate, metals, and nutrients over the period of operation. Effluents from all reactive mixtures showed increased pH (to 5.1–5.9) and decreased sulfate and metal concentrations compared with untreated drainage water. Straw with ethanol appeared to be the most effective substrate for treatment of low pH and high metal concentrations, followed equally by both lupin compost and wheat chaff. The latter are likely to be more suitable for use in a field scale low-maintenance bioreactor or composting wetland.

In situ use of groundwater by alfalfa

Disposal of saline drainage water is a significant problem for irrigated agriculture. One proposal is to recycle drainage water to irrigate salt tolerant crops until the volume has been reduced sufficiently to enable final disposal by evaporation. Part of this concept requires in situ crop water reuse from shallow groundwater; and data is needed to quantify the potential use of groundwater by alternative crops. A column lysimeter study was initiated to determine the potential crop water use from shallow groundwater by alfalfa as a function of groundwater quality and depth to groundwater. The results demonstrated that up to 50% of the crop water use could be met from shallow groundwater (<1.2 m) with an electrical conductivity less than 4 dS/m, and that the potential crop water use from deeper groundwater (2 m) increased over the years. The columns with high salinity (>4 dS/m) in the shallow groundwater experienced increased salinity in the soil profile with time, which resulted in reduced crop water use from shallow groundwater. Yields decreased with time as the groundwater salinity increased and periodic leaching will be required for in situ use to be a sustainable practice. Statistical analysis of crop yield demonstrated that there was significant use of groundwater with an EC of 6 dS/m for a few years.

Treatment of saline, acidic, metal-contaminated groundwater from the Western Australian Wheatbelt

Managing acidic, metal-containing saline ground and drainage waters in the Wheatbelt of Western Australia is an environmental and economic challenge. Sulfate-reducing fluidised bed bioreactors are shown to be technically capable of treating high salt, low pH, metal containing waters from the town of Narembeen in the Wheatbelt so as to reduce acidity and to remove most of the undesirable metal contaminants. The hydraulic residence time (HRT) limit for a stable process with groundwater from the region of Narembeen was >16 hours. The maximal rate of sulfate reduction in the laboratory system treating Narembeen groundwater was similar to rates observed in comparable applications of the process at other sites, ca. 3 g sulfate (L-reactor)(-1) day(-1). Salts that are relatively free of metal contaminants can be produced from water that has been treated by the sulfate-reducing fluidised bed bioreactor. It is unlikely that metal precipitates, captured from Wheatbelt waters by the process, would be of economic value. If sulfate-reducing fluidised bed reactors were considered technologically appropriate at larger scale, the decision to use them would be based on the necessity to take action, the comparative effectiveness of competing technologies, and the relative costs of competing technologies.

Mobile and georeferenced electromagnetic sensors and applications for salinity assessment

Soil salinity is a major threat in irrigated agriculture because of its negative on-site (decreased productivity) and off-site (salinization of irrigation return flows) effects. The delineation of the spatial variability of soil salinity is best suited using non-invasive geophysical measurements of the apparent soil electrical conductivity (ECa) using mobile GPS-based systems. Two simple and cost-effective Mobile Georeferenced Electromagnetic Sensors (MGES) developed in Aragón and Navarra (Spain) are described. These devices involve electromagnetic instruments towed by all terrain vehicles and combined with GPS units and data acquisition systems that collect both ECa readings and GPS coordinates. Two applications of the MGES aimed at delineating ECa maps for (1) selecting the most suitable crops in a 43-ha saline site (Hondo de Espartosa) and (2) correlating ECa with drainage water salinity to ascertain the salinity-source areas in a new 715 ha irrigated basin (Barranco de Lerma) were examined. These examples demonstrate the MGES surveying capacities for management of salt-affected agricultural areas.

Productivity enhancement of salt‐affected environments through crop diversification

AbstractRecent trends and future demographic projections suggest that the need to produce more food and fibre will necessitate effective utilization of salt‐affected land and saline water resources. Currently at least 20 per cent of the world's irrigated land is salt affected and/or irrigated with waters containing elevated levels of salts. Several major irrigation schemes have suffered from the problems of salinity and sodicity, reducing their agricultural productivity and sustainability. Productivity enhancement of salt‐affected land and saline water resources through crop‐based management has the potential to transform them from environmental burdens into economic opportunities. Research efforts have led to the identification of a number of field crops, forage grasses and shrubs, aromatic and medicinal species, bio‐fuel crops, and fruit tree and agroforestry systems, which are profitable and suit a variety of salt‐affected environments. Several of these species have agricultural significance in terms of their local utilization on the farm. Therefore, crop diversification systems based on salt‐tolerant plant species are likely to be the key to future agricultural and economic growth in regions where salt‐affected soils exist, saline drainage waters are generated, and/or saline aquifers are pumped for irrigation. However, such systems will need to consider three issues: improving the productivity per unit of salt‐affected land and saline water resources, protecting the environment and involving farmers in the most suitable and sustainable crop diversifying systems to mitigate any perceived risks. This review covers different aspects of salt‐affected land and saline water resources, synthesizes research knowledge on salinity/sodicity tolerances in different plant species, and highlights promising examples of crop diversification and management to improve and maximize benefits from these resources. Copyright © 2008 John Wiley &amp; Sons, Ltd.