Electromagnetic induction methodology for mapping sodium adsorption ratio (SAR) and ionic composition in salt-affected soils for developing soil database and reclamation planning

The traditional method of determining electrical conductivity (ECe) and sodium adsorption ratio (SAR) from saturated paste is destructive and time consuming. The electromagnetic induction (EMI) method determines apparent electrical conductivity (ECa) and offers an alternative to traditional wet chemistry methods. This study evaluated the effects of 2 yr of subsurface‐drip and sprinkler irrigation with saline water on soil salinity and sodicity using both EMI technique and wet chemistry methods. Site specific calibration equations used to estimate ECe and SAR from ECa values were derived using a multiple linear regression (MLR) model included in the ECe sampling assessment and prediction model developed by the U.S. Salinity Laboratory. The ECe and SAR values were strongly correlated with ECa, with R2 ranging from 0.82 to 0.98. Both wet chemistry methods and EMI data indicated that salinity and sodicity values were greater in turf irrigated with saline water from a subsurface drip system compared to a sprinkler system. Salinity in the top 30 cm ranged from <1 dS m–1 in plots irrigated with potable water from both irrigation systems to 6.5 dS m–1 in plots irrigated with saline water from a subsurface drip system. Similarly, SAR ranged from <1 mmol1/2 L–1/2 in root zones irrigated with potable water regardless of the irrigation system, to >7 mmol1/2 L–1/2 when saline water was applied from the drip system. Study results indicated that the EMI technique provides accurate predictions of the spatial distribution of both salinity and sodicity in turf soils watered from differing irrigation systems and water qualities.

In order to manage soil salinity effectively, it is necessary to understand the origin and the spatial distribution of salinity. There are about 120 salt dome outcrops in southern Iran and little is known about their contribution as the potential sources of salts and the spatial pattern of salts around them. Six machine learning algorithms were applied to model topsoil electrical conductivity (EC) and sodium adsorption ratio (SAR) in the Darab Plain (surrounded by six salt domes), Fars Province. Decision trees (DT), k‐nearest neighbours (kNN), support vector machines (SVM), Cubist, random forests (RF) and extreme gradient boosting (XGBoost) were used as primary models and the Granger–Ramanathan (GR) method was used to combine the predictions of these models. The results showed that remotely sensed data contributed more to predict EC and SAR than terrain‐based data. In terms of root mean square errors (RMSE), Cubist followed by the RF model, tended to give the best estimates of EC, whereas for SAR, RF performed best and was followed closely by SVM and Cubist. Compared to the primary models, the GR method on average resulted in a decrease of 6.1% and 3.9% in RMSE and an increase of 10% and 10.9% in R2 for EC and SAR, respectively. The spatial pattern of SAR and EC suggested that the contribution of salt domes in soil salinization varied significantly according to their hydraulic behaviour in relation to adjacent aquifers and their activity. In general, the model averaging approach showed the potential to improve the estimates of EC and SAR.

Currently used soil salinity models do not contain a mechanism for including exchangeable sodium effects on soil pH. A method is needed that allows pH calculation from the sodium adsorption ratio (SAR) or exchangeable sodium percentage (ESP) and electrical conductivity (EC) data. This study developed a simple method for calculating saturated soil paste and aqueous solution pH from SAR (or ESP) and EC data and compared the results with measured values from a number of soils and subsurface waters. The equation pH =A+{B*(SAR)1/2/(1+C*EC)} estimated soil pH from EC and SAR or ESP values. When rewritten as: SAR or ESP={(pH-A)(1 + C*EC)/B)2, the SAR or ESP was estimated from pH and EC data. By using shallow bore (well) water and soil extract data from the Murray Basin, values were determined for the scalar terms A, B and C. These values differed among subsurface water and soil types, however, the range of each scalar was reasonably small. It was found that a range of at least 2.5 pH units in the calibration data was necessary to obtain reliable regression between predicted and measured pH and SAR or ESP values. When these conditions were met, the predicted results were satisfactory. These relationships provide a method for pH calculation in soil salinity models which takes into account soil EC and sodium effects. They also provide a rapid field method to estimate SAR or ESP from easily obtainable EC and pH data. Further research is needed to define the factors that determine the values of A, B and C.

Nutrient constraints in salt-affected soils are one of the limiting factors for crop production. We investigated phosphorus (P) availability to wheat crop and its correlations with different fractions of P in salt-affected soils in response to various phosphatic fertilizer’s application. Three different types of soils having electrical conductivity of soil extract (ECe) < 4 dS m−1 and sodium adsorption ratio (SAR) < 13.2 (mmol L−1)1/2, ECe 8 dS m−1 SAR 20 (mmol L−1)1/2 and ECe 12 dS m−1 and SAR 30 (mmol L−1)1/2 were used for this experiment. Different P fertilizers viz. control, diammonium phosphate (DAP), single super phosphate (SSP) and nitrophos (NP) were applied on these soils. The doses of nitrogen, phosphorus and potassium were remained same for all the treatments. The P fractions, agronomic parameters and P-availability to plants were determined. Results indicated increase in shoot dry weight (61%) and photosynthetic rate (9%) in SSP treated soil at EC 8 dS m−1 and SAR 20 (mmol L)1/2. The total P (7.6%) in soil and respiration rate (1.9%) in plant was recorded maximum in DAP treated soil at EC 8 dS m−1 and SAR 20 (mmol L)1/2, and membrane stability index (44%) in plant shoot, extractable P (23%) in soil and P concentration (22%) in shoot were recorded maximum in SSP treated soil at EC 12 dS m−1 and SAR 30 (mmol L)1/2. It was concluded that SSP fertilizer perform better in salt-affected soil for growth and yield of wheat compared to other phosphatic fertilizers.

Salinity is a major problem affecting the sustainability of agriculture and environment in the Rio Grande river basin in Texas, USA. An accurate data on the spatial distribution of salinity is necessary for developing effective salinity management practices. However, at present information is lacking on the amount and distribution of salts within the Rio Grande river basin. Manual methods of salinity assessment at high spatial resolution are labor intensive, time consuming and involve expensive laboratory analysis. Electromagnetic induction technique (EMI) can be a relatively low cost, non-invasive and rapid alternative for measuring and mapping soil salinity. This project evaluated utility, accuracy and factors affecting the accuracy of EMI technique to delineate salt affected areas within the Rio Grande river basin in the Far West Texas, USA. Results of this project indicated that the EMI technique provided accurate data on spatial distribution of salinity within a geographical location. Furthermore, accuracy of EMI data was influenced by factors such as amount of clay and soil moisture content at the time of EMI survey. Results also indicated that the EMI technique is rapid, cheaper, and provides accurate spatial data at a much higher resolution than the conventional manual method.

Evaluating machine learning performance in predicting sodium adsorption ratio for sustainable soil-water management in the eastern Mediterranean

Use of either pumice or willow-based biochar amendments to decrease soil salinity under arid conditions

The spatio-temporal distribution of soil salinity and sodicity is the key to understand the law of water and salt transport in porous media and put forward the amendment measures of saline soil. A total of 56 soil sample sites were selected from four agricultural reclamation regions and an adjoining coastal wetland. Descriptive statistical and geostatistical analyses were performed to describe the spatio-temporal variability of soluble salt ions, soil salinity and sodicity indicators. The results showed that the average concentration of soil soluble salt (SSC), pH, sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) decreased by 97.1%, 2.9%, 95.1% and 94.9% during the whole reclamation period. Meanwhile, soil salinity and sodicity indicators showed a significant positive correlation with soluble salt ions and declined significantly with increasing years of reclamation except HCO3 −. The spatial distribution of concentration of SSC, pH, SAR and ESP was similar to that of soluble salt ions except HCO3 −, which showed a higher concentration in areas reclaimed for 5 and 30 years, and lower concentration in areas reclaimed for 38 and 61 years. Additionally, the area of saline and alkaline soils above moderate levels accounted for 54.5% and 62.7% of the total area.

Numerous methods have been used in the spatial prediction of soil salinity. However, the most suitable method is still unknown in arid irrigation regions. In this paper, 78 locations were sampled in salt-affected land caused by irrigation in an arid area in northern China. The geostatistical characteristics of the soil pH, Sodium Adsorption Ratio (SAR), Total Salt Content (TSC), and Soil Organic Matter (SOM) of the surface (0–20 cm) and subsurface (20–40 cm) layers were analyzed. The abilities of the Inverse Distance Weighting (IDW), Ordinary Kriging (OK), and CoKriging (CK) interpolation methods were compared, and the Root Mean Square Error (RMSE) was used to justify the results of the methods. The results showed that the spatial distributions of the soil properties obtained using the different interpolation methods were similar. However, the surface layer exhibits more spatial heterogeneity than the subsurface layer. Based on the RSME, the nugget/sill value and range significantly affected which method was the most suitable. Lower nugget/sill values and lower ranges can be fitted using the IDW method, but higher nugget/sill values and higher ranges can be fitted using the OK method. These results provide a valuable reference for the prediction of soil salinity.

Background: Irrigation water quality is a fundamental determinant of soil health, crop productivity, and the synthesis of health-promoting bioactive compounds in functional foods. This study evaluates the hydrochemical status of the Berqaber (Joghas) Reservoir and its inflowing rivers (Aghstev and Joghas) in the Tavush region of Armenia, a strategic water resource for regional agriculture, to assess their suitability for sustainable functional crop production. Objective: This study aims to evaluate the hydrochemical status of the Berqaber Reservoir and its inflowing rivers (Aghstev and Joghas) in northern Armenia, assess their suitability for irrigation using established water quality indices, and examine the implications of irrigation water quality for the safety, nutritional content, and bioactive compound accumulation in functional crops. Methods: Water samples were collected in April and July 2024. Analyses included physicochemical parameters, such as pH, total dissolved solids (TDS), and major ions: calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), bicarbonate (HCO₃⁻), and chloride (Cl⁻). Heavy metals analyzed included lead (Pb), copper (Cu), zinc (Zn), manganese (Mn), and nickel (Ni). Irrigation suitability indices were calculated: Sodium Adsorption Ratio (SAR), Magnesium Hazard (MH), and Stabler’s coefficient (k). To validate irrigation safety, nitrate ion (NO₃⁻) concentrations, heavy metal accumulation, and nutritional indicators (vitamin C and starch) were assessed in irrigated potatoes, tomatoes, and eggplants. Results: The irrigation waters exhibited a slightly alkaline reaction (pH 7.4–7.5) with low salinity (TDS 480–570 mg/L). The ionic composition was dominated by Ca²⁺, Mg²⁺, Na⁺, HCO₃⁻, and Cl⁻. SAR values (2.22–2.26) and Stabler’s coefficients (≈10) classified the water as satisfactory for irrigation with low sodicity risk (United States Salinity Laboratory (USSL C2–S1 category). MH values (48.78–49.46%) approached the 50% threshold associated with potential soil structural sensitivity. NO₃⁻ concentrations (12.4–13.0 mg/L) exceeded the Armenian regulatory limit of 10 mg/L (Class 3, Moderate Quality), yet nitrate and heavy metal concentrations in edible crop tissues remained well below Maximum Permissible Concentrations (MPC), and nutritional parameters were unaffected. Conclusion: The Berqaber Reservoir system provides irrigation water with low sodicity risk; however, borderline MH and elevated nitrate levels indicate moderate anthropogenic pressure. Despite this, nitrate and heavy metal concentrations in crops remain within permissible limits, ensuring their safety and functional quality. Effective institutional oversight and compliance with water quality regulations are essential to maintain long-term, sustainable, functional crop production. Novelty of the Study: This study is the first to integrate hydrochemical assessment of irrigation water with empirical validation of functional crop safety in the Tavush agroecosystem of northern Armenia. By linking irrigation water chemistry with crop nitrate accumulation, heavy metal transfer, and nutritional quality indicators, the research establishes a comprehensive “water-to-table” evaluation framework for sustainable functional food production in mountainous agricultural systems. Keywords: irrigation water, water quality, heavy metals, sodium adsorption ratio, nitrates, magnesium hazard, Berqaber Reservoir, functional foods, water regulation

SummaryA field survey was conducted to determine the effect of salinity in irrigation water on the yield of orange trees (Citrus sinensis). The part of the survey reported here included 104 sampling sites containing the three variety-rootstock combinations Shamouti orange on sweet lime (Sh × SL), Shamouti on sour orange (Sh × SO) and Valencia orange on sour orange (V × SO). The multiple regression technique was used for the statistical analysis of the data.The analysis yielded multiple regression equations of yield (Y) on salt content of the irrigation water (Cw), soil moisture saturation percentage (SP), the product of the two (interaction term), and qualitative variables (region, tree age, and tree age × Cw interaction). Cw was expressed in terms of chloride (Clw), sodium (Naw) or sodium adsorption ratio (SARW). There was a highly significant correlation between Clw, Naw and SARW, and therefore it was impossible to isolate the effect of each component of salinity. The discussion is given terms of Clw.The regression equation for Sh × SL explained 78% of the variation in Y, in terms of squared deviations from the mean; 20% was due to regional and tree age effects and the rest was due to Clw and SP. Only 42% and 54% of the variability in Y was explained by the regression equations for Sh × SO and V × SO, respectively. Nevertheless, all regression equations had significant R2 values.In all cases the effect of soil texture as expressed by SP and the interaction of SP on Cw was highly significant. The higher the SP value was, the lower was the effect of salinity. For the mean SP value for Sh × SL, there was a yield decrease of 2.31 ton/ha (4.3%) per meq/l increase in Clw. For V×SO, the corresponding yield decrease was 3.25 ton/ha (5.5%) and for Sh×SO there was essentially no effect (actually a slight yield increase).

In arid regions, the soil degradation from salinization, low organic matter content, and compaction severely limits agricultural productivity. Leguminous perennials such as alfalfa (Medicago sativa L.) have the potential to restore soil quality, but their long-term effects remain underexplored in North African drylands. This study aimed to evaluate the impacts of long-term (7–8 years) alfalfa cultivation on soil fertility and salinity in the Ziban region of Algeria. Ninety topsoil samples (0–30 cm) from cultivated and adjacent uncultivated plots were collected and analyzed, determining organic matter (OM), soil organic carbon (SOC), soil nitrogen stock (SNS), electrical conductivity (EC), sodium adsorption ratio (SAR), pH, major cations (Ca2+, Mg2+, Na+), sulfate (SO42−), bulk density (BD), and texture. Compared with uncultivated soils, alfalfa cultivation increased OM by 82.26%, SOC by 78.38%, and SNS by 102.99%, while reducing EC by 40.36%, SAR by 28.94% and BD by 6.16% (p &lt; 0.05), indicating significant improvements in fertility, structure and reductions in sodicity. PCA revealed distinct gradients separating fertility–salinity parameters from compaction–sodicity in cultivated and uncultivated soils. These results confirm that alfalfa systems enhance nutrient cycling, reduce salt stress, and improve structural stability in arid agroecosystems through reduced bulk density and increased organic matter in arid agroecosystems. Integrating alfalfa into land management strategies could promote sustainable restoration of degraded soils in drylands. Further research should optimize irrigation and organic inputs to maximize these benefits under climate-stress conditions.

The objectives of this study were to investigate the degree of spatial variability and variance structure of salinization parameters using classical and geostatistical method in Songnen Plain of China, which is one of largest saline-sodic areas in the World, and to analyze the relationship between salinization parameters, including soil salinity content (SC), electrical conductivity (EC), sodium adsorption ratio (SAR), and pH, and seven environmental factors by Pearson and stepwise regression analysis. The environmental factors were ground elevation, surface ponding time, surface ponding depth, and soil moistures at four layers (0–10 cm, 10–30 cm, 30–60 cm, and 60–100 cm). The results indicated that SC, EC, and SAR showed great variations, whereas pH exhibited low variations. Four salinization parameters showed strongly spatial autocorrelation resulting from the compound impact of structural factors. The empirical semivariograms in the four parameters could be simulated by spherical and exponential models. The spatial distributions of SC, EC, SAR and pH showed similar patterns, with the coexistence of high salinity and sodicity in the areas with high ground elevation. By Pearson analysis, the soil salinization parameters showed a significant positive relationship with ground elevation, but a negative correlation with surface ponding time, surface ponding depth, and soil moistures. Both correlation and stepwise regression analysis showed that ground elevation is the most important environmental factor for spatial variation of soil sanilization. The results from this research can provide some useful information for explaining mechanism of salinization process and utilization of saline-sodic soils in the Western Songnen Plain.

Problem statement: Groundwater is an important source of freshwater for agricultural, drinking and domestic uses in many regions of the world including Bangladesh. Demand of groundwater has been increasing day by day for irrigation by bringing more area under cultivation. As a drinking water the bottled water market currently has an average annual growth rate of 7.4% between 2002 and 2007, which is parallel to the growth of this industry all over the world. Obviously, the feed water should be free of particles and colloidal material and as low as possible in soluble organic matter. Series of water quality problems have been identified and addressed since the 1950s. These include point and non-point source pollutants such as nutrients, hydrocarbons, pesticides and heavy metals. In this regard, some studies to assessment the quality of water had been conducted in world wide. Where as, a Chiribandar a selected southern part of Bangladesh has great importance in agriculture and industrial perspective, no study has been done yet to asses the ground water quality for agricultural, drinking and industrial uses. Approach: A research was conducted to assess the degree of ionic toxicity of groundwater sources as irrigation, drinking and industrial purposes. Twenty eight groundwater samples were analyzed for different elements of dominant cations and anions such as Ca, Mg, Na, K, Fe, HCO3 and other minor ions P, B, As, N03-N, S04-S and Cl. In addition, to classify water quality as excellent, good suitable, Sodium Adsorption Ratio (SAR), Soluble Sodium Percentage (SSP) and Residual Sodium Carbonate (RSC) were calculated following standard equations. The quality of water is generally judged by its total salts concentrations, relative proportion of cations or Sodium Absorption Ratio (SAR) and the contents of HCO3. Results: According to the concentration of cation and anion constitutes of groundwater, water quality of study area were suitable for irrigation, drinking and industrial purposes. Except for a few cases there was neither chloride toxicity nor sulphate acidity in the area. The content for NO-3 and P was negligible and water samples were 'good' to 'excellent' with respect to boron and SSP. Range of EC (361-802 μS cm-1) and that of SAR (0.23-0.54) indicated that all samples were in 'medium-salinity low-alkali' hazard class. In respect of TDS and RSC values, all samples were of fresh water and suitable class. Among SSP and SAR, TDS and EC were highly correlated. An Arsanic range was far below than recommended upper limit. Conclusion/Recommendations: In respect of all evaluating criteria, groundwater of all the 28 locations can be safely used for long-term irrigation and drinking purposes. All samples were found suitable for drinking and industrial purpose in consideration of Fe concentration. However, none of the water samples was suitable for industrial use, because of higher TDS and pH values exceeding recommendation.

A long term field experiment was conducted for 8 years during 1994–2001 to evaluate the effect of N, P, K and Zn fertilizer use alone and in combination with gypsum, farmyard manure (FYM) and pressmud on changes in soil properties and yields of rice and wheat under continuous use of sodic irrigation water (residual sodium carbonate (RSC) 8.5 meq l−1, and sodium adsorption ratio (SAR) 8.8 (m mol/l)1/2 at Bhaini Majra experimental farm of Central Soil Salinity Research Institute, Karnal, India. Continuous use of fertilizer N alone (120 kg ha−1) or in combination with P and K significantly improved rice and wheat yields over control (no fertilizer). Phosphorus applied at the rate of 26 kg P ha−1 each to rice and wheat significantly improved the yields and led to a considerable build up in available soil P. When N alone was applied, available soil P and K declined from the initial level of 14.8 and 275 kg ha−1 to 8.5 and 250 kg ha−1 respectively. Potassium applied at a rate of 42 kg K ha−1 to both crops had no effect on yields. Response of rice to Zinc application occurred since 1997 when DTPA extractable Zn declined to 1.48 kg ha−1 from the initial level of 1.99 kg ha−1. Farmyard manure 10 Mg ha−1, gypsum 5 Mg ha−1 and pressmud 10 Mg ha−1 along with NPK fertilizer use significantly enhanced yields over NPK treatment alone. Continuous cropping with sodic water and inorganic fertilizer use for 8 years slightly decreased the soil pHe and SAR from the initial value of 8.6 and 29.0 to 8.50 and 18.7 respectively. However, treatments involving the use of gypsum, FYM and pressmud significantly decreased the soil pH and SAR over inorganic fertilizer treatments and control. Nitrogen, phosphorus and zinc uptake were far less than additions made by fertilizer. The actual soil N balance was much lower than the expected balance thereby indicating large losses of N from the soil. There was a negative potassium balance due to greater removal by the crops when compared to K additions. The results suggest that either gypsum or FYM/pressmud along with recommended dose of fertilizers must be used to sustain the productivity of rice – wheat system in areas having sodic ground water for irrigation.