United States Salinity Laboratory Research Articles

Spatial assessment of groundwater quality using water quality index and hydrochemical indices in the Kodavanar sub-basin, Tamil Nadu, India

The purpose of this study was to assess the drinking and irrigation groundwater quality in Kodavanar sub-basin, Dindigul and Karur region, Tamil Nadu, India. Water samples were measured according to the geological and hydrogeological aspects. Geographically, the study area is situated in 10°11′37″–10°27′30″N and 77°37′46″–78°01′10″E with an entire area of 2255 km2. Overall, 82 groundwater samples were taken from bore wells and various physicochemical parameters and major ion chemistry like pH, electrical conductivity, total dissolved solids, calcium, magnesium, sodium, potassium, bicarbonate, chloride, sulfate, nitrate, and phosphate were analyzed. According to the groundwater quality, Gibbs, United States Salinity Laboratory and Wilcox’s diagrams were plotted; and groundwater quality has been illustrated for domestic and agricultural purposes. Gibbs plot results showed that 87% of the sample falls under the rock dominance. Sodium absorption ratio 100%, sodium percentage 85%, and Kelly’s ratio 51% recommends that majority of the sample falls under the acceptable border of irrigation and drinking utility. Using geospatial analysis, the water-quality index was calculated. The result shows that most of the area comes under excellent (402 km2) and good (1297 km2) groundwater categories. Based on the studies, the quality of groundwater is safe for drinking purposes, but in a limited sample, which exceed the limit, due to anthropogenic activities.

Analysis of groundwater quality for irrigation purposes in shallow aquifers: A case study from West Aceh, Indonesia

The aim of this study is to evaluate the groundwater quality in shallow aquifers from West Aceh, Sumatra, for irrigation uses. Groundwater samples have been collected from 32 stations for pH, electrical conductivity (EC), sodium adsorption ratio (SAR), total dissolved solids (TDS), sodium percentage (per cent Na) and residual sodium carbonate (RSC) analysis. Evaluation of water quality for irrigation using the United States Salinity Laboratory classifications suggests that the majority of the groundwater samples are good for irrigation. The crop tolerance of irrigation water salinity, as based on EC value, showed that paddy (rice), soybeans and sweet tomatoes are suitable for agricultural cultivation, but that corn and field beans are not suitable. Results indicate that, if used for agricultural irrigation, the groundwater quality ranges from excellent to good, except for a few locations (e.g. Meureubo sub‐district) which indicate signs of deterioration.

Managed aquifer recharge by a check dam to improve the quality of fluoride-rich groundwater: a case study from southern India.

In many regions around the globe, including India, degradation in the quality of groundwater is of great concern. The objective of this investigation is to determine the effect of recharge from a check dam on quality of groundwater in a region of Krishnagiri District of Tamil Nadu State, India. For this study, water samples from 15 wells were periodically obtained and analysed for major ions and fluoride concentrations. The amount of major ions present in groundwater was compared with the drinking water guideline values of the Bureau of Indian Standards. With respect to the sodium and fluoride concentrations, 38% of groundwater samples collected was not suitable for direct use as drinking water. Suitability of water for agricultural use was determined considering the electrical conductivity, sodium adsorption ratio, sodium percentage, permeability index, Wilcox and United States Salinity Laboratory diagrams. The influence of freshwater recharge from the dam is evident as the groundwater in wells nearer to the check dam was suitable for both irrigation and domestic purposes. However, the groundwater away from the dam had a high ionic composition. This study demonstrated that in other fluoride-affected areas, the concentration can be reduced by dilution with the construction of check dams as a measure of managed aquifer recharge.

Evaluation of water quality and hydrogeochemistry of surface and groundwater, Tiruvallur District, Tamil Nadu, India

Water quality of Tiruvallur Taluk of Tiruvallur district, Tamil Nadu, India has been analysed to assess its suitability in relation to domestic and agricultural uses. Thirty water samples, including 8 surface water (S), 22 groundwater samples [15 shallow ground waters (SW) and 7 deep ground waters (DW)], were collected to assess the various physico-chemical parameters such as Temperature, pH, Electrical conductivity (EC), Total dissolved solids (TDS), cations (Ca, Mg, Na, K), anions (CO3, HCO3, Cl, SO4, NO3, PO4) and trace elements (Fe, Mn, Zn). Various irrigation water quality diagrams and parameters such as United states salinity laboratory (USSL), Wilcox, sodium absorption ratio (SAR), sodium percentage (Na %), Residual sodium carbonate (RSC), Residual Sodium Bicarbonate (RSBC) and Kelley’s ratio revealed that most of the water samples are suitable for irrigation. Langelier Saturation Index (LSI) values suggest that the water is slightly corrosive and non-scale forming in nature. Gibbs plot suggests that the study area is dominated by evaporation and rock–water dominance process. Piper plot indicates the chemical composition of water, chiefly controlled by dissolution and mixing of irrigation return flow.

Efficiency of Two Models for Prediction of Exchangeable Sodium Percentage from Sodium Adsorption Ratio on Saline and Non Saline Soil

The relationships between soil physical and chemical properties play a key role in facilitating the measurement of soil properties, particularly Exchangeable Sodium percentage (ESP) measurement, which is often using laborious and time-consuming laboratory tests. The aim of this study is to investigate the efficiency of the United States Salinity Laboratory (USSL) model and the ESP-SAR model for prediction of exchangeable Sodium percentage (ESP) from Sodium Adsorption Ratio (SAR) on saline and non-saline soil samples. For this purpose, 23 soil samples were collected from the field of experiment, Jabal Awliya, south of Khartoum state, Sudan. Exchangeable Sodium Percentage (ESP) was estimated as a function of soil SAR in order to compare the predicted results with measured ESP using laboratory tests. The results show that on saline soil samples, the Standard Error of Mean (SEM) of predicted ESP obtained by USSL model and ESP-SAR model was (1.084) and (1.463) respectively. On non- saline soil samples, the Standard Error of Mean (SEM) of predicted ESP acquired by USSL model was (0.7034) and (0.6070) for ESP-SAR model. The statistical results indicated that USSL model has a good prediction on saline soil samples compared with ESP-SAR model. On non-saline soil samples, USSL model showed less prediction performance than ESP-SAR model. It can be concluded that the United States Salinity Laboratory model can be recommended on saline soil samples and ESP-SAR model is more reliable on non-saline soil samples.

Assessment of water quality in drainage canals of Çarşamba Plain, Turkey, through water quality indexes and graphical methods

<p>In this study, the seasonal variation on drainage water quality of Çarşamba Plain, Turkey has been evaluated from June 2012 to January 2013 and determined the suitability of water for irrigation purpose. Water samples collected from 21 drainage canals during July and January were analysed for 12 water quality parameters including physico-chemical analyses<strong>. </strong>Piper diagram and United States Salinity Laboratory (USSL) diagram were prepared to investigate water quality. Sodium Adsorption Ratio (SAR), Percent Sodium (Na%), Residual Sodium Carbonate (RSC), Kelly Index (KI), Magnesium Ratio (MR), Langelier Saturation Index (LSI), Permeability Index (PI) and Potential Salinity (PS) were also used to assess suitability of waters for irrigation.</p> <p>In July 2012, EC values varied between 0.45-4.23 dS/m. Waters of 7 drainage canals were found to be unsuitable for irrigation with regard to KI, 3 canals with regard to RSC and 13 canals with regard to MR. According to USSL diagram, 24% of drainage waters were classified in C<sub>2</sub>S<sub>1</sub>, 62% in C<sub>3</sub>S<sub>1</sub>, 4% in C<sub>4</sub>S<sub>2</sub> and 10% in C<sub>4</sub>S<sub>4</sub> class. In January 2013, EC values varied between 0.16-1.44 dS/m. Waters of one canal was found to be unsuitable for irrigation with regard to KI and 8 canals with regard to MR values.</p> <div> <p>The result obtained from paired sample <em>t</em>-test revealed that the drainage canal water quality varies significantly between June 2012 and January 2013 except for Ca, Mg and SO<sub>4</sub>.  According to analysed parameters, some of  the drainage canals were considered unsuitable for irrigation in june 2012. The water properties of all canals were observed as unsuitable to be used for drip irrigation in accordance to the LSI index. Classification of drainage water by USSL diagrams indicates a low sodium and high salinity hazard. </p> </div> <p> </p>

Environmental Study on a Coastal River of Bangladesh with Reference to Irrigation Water Quality Assessment: A Case Study on Shailmari River, Khulna

Water quality is the critical environmental determinant that influences the agricultural production and therefore, the economy that solely depends on its agricultural productions. Batiaghata Upazilla is one of the major crop productive areas of Khulna region and the agricultural production here largely depends on the natural water of the Shailmari River system around it. The present study was conducted to assess the suitability of this coastal river water for irrigational use. 66 water samples were collected during this study in three consecutive agricultural seasons, viz., pre-monsoon (22), monsoon (22) and post-monsoon (22) from 11 sampling stations within the river system considering the high (11) and ebb (11) tides for each station. Standard methods were followed throughout the study period for the collection of the samples and analysis of major physicochemical parameters (pH, EC, TDS, salinity, Na, K, Ca, Mg, Cl, HCO3, SO4, NO3 and PO4). Hydrocehmical characterization using Piper trilinear diagram shows that the water of the river system is Na-Cl dominated saline water type in pre-monsoon, whilst most of the samples of the river and the connected channel are characterized as fresh water of Ca-Mg-Na-HCO3 and Ca-Na-Mg-HCO3 types in monsoon and post-monsoon respectively. The calculated values of chemical indices like SAR, %Na, KI, PI and MH using the results of the analysed parameters indicate that the river water is chemically unsuitable for use in irrigation during pre-monsoon, while in the monsoon and post-monsoon the river water is within good to permissible limit for the use in the agricultural fields. However, high %Na, KI and MH values with high salinity of the channel water limit its use in agricultural applications in monsoon and post-monsoon. The USSL (United States Salinity Laboratory) diagram depicts that the river water is C4-S4 type with very high salinity and sodium content in pre-monsoon, while in other seasons the water is mostly C1-S1, C2-S1 or C2-S2 types (low to moderate salinity and sodium) in the river. Wilcox diagram shows that the river water is “suitable” for irrigation during monsoon and post-monsoon as the most of the samples range within “Excellent to Good” and “Good to permissible” categories, while it is “unsuitable” for crop irrigation during pre-monsoon when SAR (Sodium Adsorption Ratio) and EC (Electrical Conductivity) values of the water reach to their peaks.

Chemistry and quality of groundwater in a coastal region of Andhra Pradesh, India

The chemistry of groundwater in the coastal region between Chirala and Ongole of Andhra Pradesh, India shows pollution to varying extent. The relative contribution of ions in six zones divided based on TDS indicates unsuitability of groundwater here for drinking, irrigation and industrial use. The water is brackish except in first zone and further alkaline. TDS is less than 1,000 mg/L in first zone, while it is more in other zones. This classification of groundwater into zones is also investigated by hydrogeochemical facies, genetic classification, mechanisms of groundwater chemistry and geochemical signatures. Hydrogeochemical facies of Na+>Mg2+>Ca2+: {text{HCO}}_{3}^{ - } > Cl− > SO _{4}^{2 - } is observed from zone I, while that of Na+>Mg2+>Ca2+:Cl− > HCO _{3}^{ - } > SO _{4}^{2 - } from second to sixth zones. The genetic classification of groundwater in first and second zones is HCO _{3}^{ - } type and supported by good drainage conditions, while zones III to VI belong to Cl− category evident from poor drainage scenario. The location of six zones on mechanisms of groundwater chemistry supports sluggish drainage conditions of second to six zones, while predominate rock-water interaction in first zone. The geochemical signatures (HCO _{3}^{ - } :Cl− > 1 and Na+:Cl− < 1) also endorse the pollution. The quantities of chemical species (Mg2+, Na+, K+, HCO _{3}^{ - } , Cl ^{ - } , SO _{4}^{2 - } , NO _{3}^{ - } and F ^{ - } ) and TDS in all zones are far greater than the stipulated limits for drinking. The United States Salinity Laboratory plots discriminated the suitability of groundwater in second to sixth zones for irrigation after only special soil treatment. Higher concentrations of TDS, HCO _{3}^{ - } , Cl− and SO _{4}^{2 - } in all zones render it unsuitable for industry too. This information is crucial for public and civic authorities for taking up strategic management plan for preventing further deterioration of hydrogeochemical environmental conditions of this part of the coastal region.

Hydro-environmental assessment of a regional ground water aquifer: Hirakud command area (India)

A hydro-environmental assessment has been performed for Hirakud command area (India) in terms of quantity and physicochemical quality analysis of groundwater. Quantity analysis has been performed in terms of water level variation and groundwater potential zone identification. Groundwater table fluctuation analysis reveals that water level is declining rapidly due to insufficient recharge owing to frequent recession of monsoon and excessive pumping of groundwater. Inefficient distribution of canal water especially in the tail end of the Hirakud command is accentuating the high dependency on ground water. The groundwater potential zone index map is generated using analytic hierarchy process along with different influencing features, e.g., land use/cover, soil type, geology. Three zones have been identified for Hirakud command area (poor: 21.15 %, moderate: 46.32 %, and good: 32.53 %). Physical and chemical parameters of groundwater, e.g., electrical conductivity, pH, total dissolved solids, total hardness, nitrate, iron, sodium, potassium, calcium, magnesium, chlorine, bicarbonate and fluoride are analyzed for the study area. Piper analysis is used to identify dominant hydrochemical facies. United States Salinity Laboratory and Wilcox Diagram are used to determine the irrigation water quality. Principal component analysis is utilized to find out key groundwater quality parameters. The chemical analysis shows that values of all parameters are within permissible limit. However, nitrate, iron and fluoride are found above permissible limit in some areas. The assessment reveals the state of the aquifer in terms of quantity and quality.

Ground water quality classification by decision tree method in Ardebil region, Iran

A decision tree-based approach is proposed to predict ground water quality based on the United States Salinity Laboratory (USSL) diagram using the data from aquifers in agricultural lands of Ardebil province, northwest of Iran. Several combinations of hydro chemical parameters of groundwater and monthly precipitation with different lag time were considered to find an accurate and economical alternative for groundwater quality classification. The performance evaluation was based on the number of correctly classified instances (CCI) and kappa statistics. The results suggested the suitability of decision tree-based classification approach for the used data sets. The overall average of CCI and kappa statistic for the prediction of groundwater quality classes based on the USSL diagram was 0.88 and 0.83 %, respectively. Principal component analysis (PCA) was also used to determine the important parameters for groundwater quality classification. The results showed that groundwater quality classification by decision tree is more precise and efficient in comparison with PCA. The best alternative could evaluate groundwater quality class with only two parameters: electrical conductivity and cumulative precipitation of 11 months earlier. The developed model is able to predict water quality class by only two variables and this lead to a reduction in the number of variables analyzed on a routine basis, resulting in a significant reduction in laboratory costs and latency times between the sampling moment and the outcome of the laboratory analyses.

Sources of contaminants and groundwater quality in the coastal part of a river delta

Assessment of possible sources that control the groundwater quality was carried out in the Cauvery deltaic region, India, since domestic and agricultural water requirements are largely met by groundwater abstraction. Major ion and bromide contents are high in groundwater in the coastal wells. Spatial and vertical distributions of ions reveal that the shallow wells and wells in coastal parts have high chloride, nitrate, ammonium and phosphate. Groundwater quality assessment was carried out using the prescribed limits of World Health Organization and Bureau of Indian Standards which indicates that 55 % of samples are not fit for drinking. Integrated suitability map for drinking was created based on the concept that if the water sample exceeds any one of the standards by World Health Organization or Bureau of Indian Standards, the well is not fit for drinking. Groundwater quality for agricultural activities was assessed using electrical conductivity, sodium adsorption ratio, residual sodium carbonate, United States salinity laboratory diagram and Food and Agricultural Organization methods. According to Food and Agricultural Organization, 84 % of samples are classified as low sodium water and are suitable for all crops and soils. It was found that the water quality in this area is affected by improper disposal of waste, sewage/drainage canals near the wells, irrigation return flow, application of agrochemicals and saline water intrusion in the coastal region. Further, integrated suitability map produced in this study will be useful for future groundwater development and planning in this area. The suitability map needs to be updated periodically for proper management plan to preserve the groundwater resource in this region.

A Fuzzy Logic Approach for Irrigation Water Quality Assessment: A Case Study of Karunya Watershed, India

A Fuzzy Logic Approach for Irrigation Water Quality Assessment: A Case Study of Karunya Watershed, India The water used for irrigation purposes remains unnoticed in a quality perspective. The ground water is a major source for irrigation in many arid and semi arid regions of India. The widely accepted standard for irrigation water is the United States Salinity Laboratory (USSL) classification system, which is based on Sodium Absorption Ratio (SAR) and Electrical Conductivity (EC). In the present study, a Fuzzy Inference System (FIS) has been developed to classify ground water for irrigation purposes.

Seasonal variation of groundwater quality in a part of Vadodara District for irrigation, Gujarat, India

The area in Vadodara district, Gujarat, India, is selected to discuss the impact of seasonal variation of groundwater quality on irrigation, where the agriculture is the main livelihood of rural people and the groundwater is the main source for irrigation and drinking. Groundwater samples collected seasonally, pre and post-monsoons, during three years from Twenty five wells in the area were analyzed for pH, EC, TDS, TH, Ca 2+ , Mg 2+ , Na + , K + , CO3 2− , HCO3 − , Cl − , SO4 2− , NO3 − and F − .Various tools such as Electrical conductivity (EC), Sodium Absorption Ratio (SAR), United States Salinity Laboratory (USSL) were used to evaluate the quality of water and its suitability for irrigation purposes. Results of SAR shows that many of the wells during premonsoon illustrate high values indicating the unsuitable nature of groundwater for irrigation but during post monsoon, SAR values found to be decreased due to the dilution effect of precipitation by monsoon.

Assessment of water quality in the Messolonghi–Etoliko and Neochorio region (West Greece) using hydrochemical and statistical analysis methods

Assessment of the water quality can enhance understanding of the hydrochemical system and effective management of water resources. To this end, an assessment of water quality was conducted in the Messolonghi-Etoliko and Neochorio region. Surface water and groundwater samples have been collected, treated, and subjected to chemical analysis for the following parameters: Br⁻, Cl⁻, F⁻, NO₂⁻, NO₃⁻, PO₄³⁻, SO₄²⁻, Li⁺, Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺, HCO₃⁻, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn. A characterization has been carried out using the Piper trilinear diagram, the United States Salinity Laboratory diagram, and the Wilcox diagram. Assessment of water samples by comparing the recorded values of the water quality parameters with the parametric values established by European Community indicated that the 50% of the surface water samples and 67% of the groundwater samples in the study area are chemically suitable for drinking use. Assessment of water samples from calculation of chemical indexes like sodium adsorption ratio, sodium percentage, residual sodium carbonate, and by comparing the values of the water quality parameters with the water quality limits established by Canadian Council of Minister of the Environment indicated that 75% of the surface water and that all the groundwater samples are chemically suitable for irrigation use.

Hydro-geochemical appraisal of groundwater quality from weathered basement aquifers in Northern Malawi

The obligation to ensure adequate potable water supply to everyone, has necessitated the development of groundwater resources for reliable rural water supply in most developing countries. An understanding of spatial variation and processes affecting water quality is essential in sustaining usable water supplies under changing climate and local environmental pressures. In this study, an assessment of quality and dominant hydro-geochemical processes affecting the quality of groundwater from weathered basement aquifers in Mzimba district, Northern Malawi, has been conducted. Groundwater samples were collected from 172 hand-pumped boreholes, drilled for domestic rural water supply and analysed for major and minor ions, pH and total dissolved solids (TDS). In general, groundwater is of low mineralisation (TDS range: 29–1896mgL−1 for the dry season), with hydro-geochemical facies dominated by Ca–HCO3, which evolves to Ca–Cl water type. Multivariate statistical analysis (HCA and PCA) and geochemical interpretation showed that the Ca–HCO3 groundwater type result from hydrolysis of silicate minerals, which causes the solution to reach equilibrium with kaolinite. The processes of cation exchange of Na+ and K+ in the groundwater for Ca2+ and Mg2+ on clay minerals, carbonate precipitation and evaporation, are shown to modify the chemical composition from Ca–HCO3 types to Ca–Cl types. Groundwater is generally of good quality in both rainy and dry seasons, with little seasonal changes. The United States Salinity Laboratory Staff and Wilcox diagrams showed that most samples were also suitable for irrigation except for 4% (eight samples) of the groundwater samples (with EC>2000μScm−1). These are located in alluviums and colluviums localised near river banks and in inter hill valleys.

Irrigation water quality evaluation using adaptive network-based fuzzy inference system

Water quality diagrams are comprised of quality classes defined by crisp sets, and as a consequence the boundaries between classes have an inherent imprecision. In this study, the concentration values of electrical conductivity (EC) and sodium adsorption ratio (SAR) in United States Salinity Laboratory diagram (USSL) are combined together through an adaptive network-based fuzzy inference system (ANFIS) to generate a new method that can be used instead of the USSL-diagram. The results showed that water quality classification based on the proposed method is more precise in comparison with the USSL-diagram classification, and it is a promising alternative to traditional approach. It has been observed that the ANFIS model with 96% accuracy has much better predicting capability than the Mamdani fuzzy inference system (MFIS). The results indicated that the ANFIS modeling decreases error effects in hydro-chemical experiments and it also significantly decreases computation time for the irrigation water quality evaluation.

Water quality analysis of groundwater in crystalline basement rocks, Northern Ghana

Hydrochemical data are presented for groundwater samples, collected from fractured aquifers in parts of northern Ghana. The data was collected to assess the groundwater suitability for domestic and agricultural use. Results of the study reveal that the pH of the groundwater in the area is slightly acidic to slightly alkaline. The electrical conductivity values, total dissolved solids (TDS) values and calcium, magnesium and sodium concentrations in the groundwater are generally below the limit set by the WHO for potable water supply. On the basis of activity diagrams, groundwater from the fractured aquifers appears to be stable within the montmorillonite field, suggesting weathering of silicate minerals. An inverse distance weighting interpolator with a power of 2 was applied to the data points to produce prediction maps for nitrate and fluoride. The distribution maps show the presence of high nitrate concentrations (50–194 mg/l) in some of the boreholes in the western part of the study area indicating anthropogenic impact on the groundwater. Elevated fluoride level (1.5–4 mg/l), higher than the WHO allowable fluoride concentration of 1.5, is recorded in the groundwater underlying the northeastern part of the study area, more specifically Bongo and its surrounding communities of the Upper East region. Results of this study suggest that groundwater from the fractured aquifers in the area exhibit low sodicity–low salinity (S1–C1), low sodicity–medium salinity (S1–C2) characteristics [United States Salinity Laboratory (USSL) classification scheme]. All data points from this study plot within the ‘Excellent to good’ category on a Wilcox diagram. Groundwater in this area thus appears to provide irrigation water of excellent quality. The hydrochemical results indicate that, although nitrate and fluoride concentrations in some boreholes are high, the groundwater in the study area, based on the parameters analyzed, is chemically potable and suitable for domestic and agricultural purposes.

Geospatial Methods for Monitoring a Vegetative Treatment Area Receiving Beef Feedlot Runoff

A vegetative treatment area (VTA) offers alternative solutions to traditional feedlot runoff holding ponds, but the distribution of nutrients is not easily defined. Methods for monitoring salt accumulations in soils have been demonstrated at the United States Salinity Laboratory, Riverside, CA. This study was conducted to determine if methods developed to inventory saline soils can be used to inventory a VTA designed to control feedlot runoff. A soil conductivity map was generated at a VTA site using electromagnetic induction equipment (Dualem-1S) and global positioning satellite. The ESAP software package, developed by the United States Salinity Laboratory at Riverside, CA, was used to determine a representative set of (n = 20) soil sampling locations for estimating the chloride distribution in the VTA (Cl(-): selected as an indicator ion to track feedlot runoff). An additional set of (n = 20) stratified random sampling (SRS) locations were selected for comparison. The ESAP-generated, prediction-based sampling plan exhibited better design optimality criteria than the SRS plan. Statistical validation tests confirmed that the regression model estimated from the ESAP-generated sample data was capable of producing accurate and unbiased predictions of the natural log (Cl(-)) levels at the independently chosen SRS sites. The combination of geo-referenced soil conductivity, directed soil sample data, and regression modeling provides a cost-effective tool to observe and manage liquid flow patterns in a VTA.

Effect of ionic strength and clay mineralogy on Na–Ca exchange and the SAR–ESP relationship

SummaryThe relationship between sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) for all soils has traditionally been assumed to be similar to that developed by the United States Salinity Laboratory (USSL) in 1954. However, under certain conditions, this relationship has been shown not to be constant, but to vary with both ionic strength and clay mineralogy. We conducted a detailed experiment to determine the effect of ionic strength on the Na+–Ca2+ exchange of four clay minerals (kaolinite, illite, pyrophyllite, and montmorillonite), with results related to the diffuse double‐layer (DDL) model. Clays in which external exchange sites dominated (kaolinite and pyrophyllite) tended to show an overall preference for Na+, with the magnitude of this preference increasing with decreasing ESP. For these external surfaces, increases in ionic strength were found to increase preference for Na+. Although illite (2:1 non‐expanding mineral) was expected to be dominated by external surfaces, this clay displayed an overall preference for Ca2+, possibly indicating the opening of quasicrystals and the formation of internal exchange surfaces. For the expanding 2:1 clay, montmorillonite, Na+–Ca2+ exchange varied due to the formation of quasicrystals (and internal exchange surfaces) from individual clay platelets. At small ionic strength and large ESP, the clay platelets dispersed and were dominated by external exchange surfaces (displaying preference for Na+). However, as ionic strength increased and ESP decreased, quasicrystals (and internal exchange surfaces) formed, and preference for Ca2+ increased. Therefore, the relationship between SAR and ESP is not constant and should be determined directly for the soil of interest.

Grain yields from spring-sown Canadian wheats grown in saline rooting media

Farmers seek information about the salt tolerances of wheat. Two greenhouse tests conducted at the Swift Current Salt Tolerance Testing Laboratory determined the response of four spring-sown Canadian wheat cultivars (Katepwa, Biggar, Fielder and Kyle) to increasingly saline rooting media. The first test followed the United States Salinity Laboratory procedure of increasing root-zone salinity gradually after plant emergence, and the second provided full complements of salts before seeding. The plants were grown in sand tanks irrigated four times daily with hydroponic solutions containing salt concentrations of up to 14 dS m−1 equivalent electrical conductivity for saturated soil paste extracts (ECe) Grain yield and plant height began to decline within all cultivars at equivalent ECe-values ranging between 0.5 and 2.5 dS m−1. At 4 dS m−1, grain production dropped to 80% or less of that produced in non-saline rooting media. Kyle and Fielder plants showed slightly more salt tolerance than those of Katepwa or Biggar (i.e., moderately sensitive rather than sensitive). Gradually adding the salts after plant emergence resulted in a tendency for greater salt-tolerance estimates than obtained by subjecting the plants to the full complement of salts at seeding. At the concentrations tested, the salinity affected the number of fertile spikes per plant more than it affected the number of plants reaching harvest. Key words: Salt tolerance, salt resistance, salinity, crop growth modelling, crop response