Exchangeable Sodium Percentage Levels Research Articles

Ameliorating saline‐sodic soils: A global meta‐analysis of field studies on the influence of exogenous amendments on crop yield

AbstractAs the demand for food continues to rise, soil salinization and sodification pose an increasingly pressing challenge. Currently, there is a knowledge gap regarding how to effectively improve saline‐sodic soils to support sustainable agricultural production, especially the lack of systematic analysis on the effects of different amendments at a global scale. To address this gap, this study aims to explore the feasibility of using exogenous amendments to ameliorate saline‐sodic soils, conducting a global‐scale meta‐analysis based on 685 data pairs from 70 published studies. Our results showed that applying amendments to saline‐sodic soils significantly reduced electrical conductivity of saturated paste extract (ECe) by 33.0% and exchangeable sodium percentage (ESP) by 44.6%, while simultaneously increasing crop yield by 50.7%. Heterogeneity analysis further unveiled significant variations (p < 0.05) in the overall effect size, driven by factors such as initial soil properties (salinity and ESP levels), amendment type, climate and practical management conditions (application dose and experimental duration). The categorical variable analysis showed that, compared to soils with other salinization levels, the application of amendments in severe salinization soils was most effective in reducing soil ECe and enhancing crop yield. Considering the goals of mitigating soil salinity, sodicity, and increasing crop yield, the study suggests the application of mixed‐type amendments in practical settings. It is noteworthy that while extremely high doses (greater than 40 t ha−1) effectively increased crop yield, they also posed a risk of salt accumulation. In conclusion, this research offers critical insights for sustainable agriculture, guiding future work on soil health and food security in the context of global environmental challenges.

Evaluation of Physiological and Biochemical Traits in Relation to Sodicity Tolerance in Selected Rice Genotypes under Different Sodicity Levels

Background: Soil sodicity is becoming a serious problem which is increasing every year has a negative impact the physical and nutritional qualities of the soil and plant which has an immense adverse effect on crop growth. Sodicity tolerance includes the manifestation of biochemical and physiological variations. Understanding these physiological and biochemical mechanism in rice is one of the biological solution for increasing the yield of crops through increased tolerance mechanism. Methods: A field experiment was conducted at Anbil Dharmalingam Agricultural College and Research Institute, Tiruchirappalli, Tamil Nadu to evaluate the performance of different rice varieties i.e., TRY 1, CO 43, TRY 2, CSR 27, TRY 3, white ponni (WP) with particular reference to Exchangeable Sodium Percentage (ESP) at various levels viz., ESP 8, 16, 24, 32, 40 and 48 and its impact on physiological and biochemical components. Plant samples were collected at flowering stage was analyzed for chlorophyll, sugars and proline content. Grain and straw yield of the crop was recorded. Result: The Chlorophyll and non-reducing sugars showed decreasing trend with increasing ESP levels but proline, reducing sugar and total sugar showed an increasing trend with increasing sodicity levels. The variation in biochemical and physiological components had significantly affected the growth and yield of rice crop. Among different rice varieties TRY 3 was found to be superior at increasing sodicity levels..

Effect of Different Levels of Sodicity on Soil Enzymes, Soil Microbial Biomass Carbon and Activity of Antioxidant Enzymes in Different Rice Varieties under Semi-arid Conditions

Background: Soil sodicity is a major abiotic stress for crop production in many parts of the world. Soil enzymes have been proposed as potential indicators of soil quality due to their connection to soil biology, ease of measurement and quick responsiveness to changes in soil management. Concerning that how different levels of sodicity affects the activity of soil enzymes, soil MBC and antioxidant enzymes in different rice varieties will promote us to understand the mechanism behind the tolerant varieties and to find out the ways to improve the tolerance mechanism. Methods: A field experiment was conducted at Anbil Dharmalingam Agricultural College and Research Institute, Tiruchirappalli, Tamil Nadu during late samba season. Different rice varieties viz., TRY 1, CO 43, TRY 2, CSR 27, TRY 3 and white ponni (WP) were grown at different levels of Exchangeable Sodium Percentage (ESP) ie., 8, 16, 24, 32, 40 and 48 under field condition. The soil samples were collected at flowering stage and analyzed for urease, alkaline phosphatase (APH), dehydrogenase (DHG) and soil microbial biomass carbon (MBC). The plant samples collected at flowering stage were examined for activity of antioxidant enzymes like catalase (CAT), peroxidase (POX) and superoxide dismutase (SOD). Result: The growth and yield decreases with increasing sodicity levels. The soil enzyme and microbial biomass carbon found to be decreased with increasing ESP levels. The antioxidant enzyme increases with increase in sodicity levels in tolerant varieties and decreases at high ESP levels in susceptible varieties. Overall TRY 3 outperformed under increasing sodicity levels compared to other varieties.

Foliar-Applied Potassium Silicate Coupled with Plant Growth-Promoting Rhizobacteria Improves Growth, Physiology, Nutrient Uptake and Productivity of Faba Bean (Vicia faba L.) Irrigated with Saline Water in Salt-Affected Soil.

The continuity of traditional planting systems in the last few decades has encountered its most significant challenge in the harsh changes in the global climate, leading to frustration in the plant growth and productivity, especially in the arid and semi-arid regions cultivated with moderate or sensitive crops to abiotic stresses. Faba bean, like most legume crops, is considered a moderately sensitive crop to saline soil and/or saline water. In this connection, a field experiment was conducted during the successive winter seasons 2018/2019 and 2019/2020 in a salt-affected soil to explore the combined effects of plant growth-promoting rhizobacteria (PGPR) and potassium (K) silicate on maintaining the soil quality, performance, and productivity of faba bean plants irrigated with either fresh water or saline water. Our findings indicated that the coupled use of PGPR and K silicate under the saline water irrigation treatment had the capability to reduce the levels of exchangeable sodium percentage (ESP) in the soil and to promote the activity of some soil enzymes (urease and dehydrogenase), which recorded nearly non-significant differences compared with fresh water (control) treatment, leading to reinstating the soil quality. Consequently, under salinity stress, the combined application motivated the faba bean vegetative growth, e.g., root length and nodulation, which reinstated the K+/Na+ ions homeostasis, leading to the lessening or equalizing of the activity level of enzymatic antioxidants (CAT, POD, and SOD) compared with the controls of both saline water and fresh water treatments, respectively. Although the irrigation with saline water significantly increased the osmolytes concentration (free amino acids and proline) in faba bean plants compared with fresh water treatment, application of PGPR or K-silicate notably reduced the osmolyte levels below the control treatment, either under stress or non-stress conditions. On the contrary, the concentrations of soluble assimilates (total soluble proteins and total soluble sugars) recorded pronounced increases under tested treatments, which enriched the plant growth, the nutrients (N, P, and K) uptake and translocation to the sink organs, which lastly improved the yield attributes (number of pods plant−1, number of seeds pod−1, 100-seed weight). It was concluded that the combined application of PGPR and K-silicate is considered a profitable strategy that is able to alleviate the harmful impact of salt stress alongside increasing plant growth and productivity.

Effects of gypsum, irrigation and tillage on a sodic Yellow Kandosol at Carnarvon, Western Australia

Context Kandosol soils are widely distributed in Australia and are frequently used for irrigated cropping. However, under intensive irrigated cropping they can degrade due to poor structural stability where surface soil aggregates break down as a result of slaking and dispersion; the slaking is associated with low soil organic carbon levels (<1.0 g/100 g) on these frequently cultivated soils, and the dispersion is related to the moderate level of exchangeable sodium percentage (ESP) combined with low electrical conductivity (EC) levels in the soil solution. Aims To investigate the effects of applied gypsum (0, 2 and 10 t/ha), irrigation with water of low EC (0.5 dS/m) and low sodium adsorption ratio (≤2), and two tillage practices, i.e. conventional tillage (CT) and reduced tillage (RT), on the structure of a marginally sodic (ESP 6) Yellow Kandosol soil. Methods The experiment was conducted at Carnarvon, Western Australia. Key results After 2 years the soil EC (1:5) and ESP levels were significantly reduced on all plots at the three gypsum rates. The three gypsum rates also significantly affected exchangeable calcium (Ca) and magnesium (Mg) and soluble Ca and Mg levels, as well as pH and dispersion values. Micromorphological examination indicated less dispersed clay with gypsum application. Conclusions The EC results indicated that the soil will require frequent re-application of gypsum to maintain electrolyte levels and prevent dispersion. With some of the variables, RT compared to CT demonstrated greater through-flow, which was attributed to the presence of more macropores in RT. Implications A change in management from semi-arid chenopod shrublands used for grazing to intensely cultivated horticulture will require careful consideration of factors causing soil structural instability.

Carbon Mineralization under Different Saline—Alkali Stress Conditions in Paddy Fields of Northeast China

Soil organic carbon (SOC) mineralization (conversion of carbonaceous material to carbon dioxide) plays a central role in global carbon cycle. However, the effects of SOC mineralization under different saline–alkali stress conditions are poorly understood. In order to understand the carbon mineralization processes, four paddy fields with different saline and alkali degrees were chosen as the experimental samples and the soil CO2 emission fluxes at nine different time steps of the whole simulation experiment were observed. The physical and chemical properties of soils of four field conditions were compared for the dynamic changes of CO2 flux in the progress of paddy field cultivation simulations. The results showed that the first three fields (P1, P2, and P3) were weakly alkaline soils and the last one (P4) was strongly alkaline soil. The SOC content of each plot was significantly different and there was a near-surface enrichment, which was significantly negatively correlated with the degree of alkalization. The accumulation process of the SOC mineralization during the incubation time was consistent with the first-order kinetic model. In the initial stage of mineralization, the amount of CO2 released massively, and then the release intensity decreased rapidly. The mineralization rate decreased slowly with time and finally reached a minimum at the end of the incubation period. This study indicates that the SOC mineralization process is affected by a variety of factors. The main factors influencing SOC mineralization in the saline–alkaline soils are the exchangeable sodium percentage (ESP), followed by enzyme activities. Salinization of the soils inhibits the rate of soil carbon cycle, which has a greater impact on the carbon sequestration than on the carbon source process. The intensity and completeness of the SOC mineralization reactions increase with increasing SOC contents and decrease with increasing ESP levels.

Atterberg limits and shrink/swell capacity of soil as indicators for sodium sensitivity within a gradient of soil exchangeable sodium percentage and salinity

Soil sodification and salinization present a global soil degradation risk to agricultural production since they affect soil hydraulic properties. Soils containing smectite clays have been found to be most sensitive to sodicity although little research exists directly relating sodicity to clay swelling under varying levels of salinity and Exchangeable Sodium Percentage (ESP). The goal of this study is to determine whether soil swelling related measurements can be a proxy to determine soil sensitivity to exchangeable sodium. This study examined the response of three smectitic soils treated with salt solutions having concentrations ranging between 5 and 40 mmolc dm−3 and ESP levels between 0 and 50% to create differing degrees of sodicity. Whole soil Atterberg limits and the coefficient of linear extensibility (COLE) were measured prior to and after treatments. Liquid limit, plasticity index and the coefficient of linear extensibility increased for all three soils after treatment with a salt concentration of 5 mmolc dm−3 at an ESP of 25 and 50% and 10 mmolc dm−3 at an ESP of 50%. Comparing liquid limit of low salinity treatment at 50% ESP to low salinity 0% ESP revealed the presence of swelling smectite clay and the sensitivity of the soils to sodicity and a soil measurement to identify soil sodicity risk.

Long-term performance of flue gas desulfurization gypsum in a large-scale application in a saline-alkali wasteland in northwest China

Flue gas desulfurization (FGD) gypsum has been used as an amendment to reduce soil salinization and alkalinization worldwide. However, the effective and safe use of FGD gypsum in agricultural land is still debatable in some countries, although many studies have reported its beneficial effects on soil management. Therefore, a study was conducted on wasteland (600 ha) close to the Yellow River in Inner Mongolia, China. The main aim of this research was to evaluate the long-term effects of FGD gypsum application on soil salinity and sodicity, crop production and heavy metals in soils and crops. The results showed that soil pH and exchangeable sodium percentage (ESP) in topsoil (0–20 cm) decreased dramatically during the first year, while a substantial reduction of electrical conductivity (EC) occurred during the second year after FGD gypsum application. Four years later, the EC, pH and ESP levels in reclaimed soils were 58.3%, 92.2% and 95.2% lower, respectively, than those in the initial soils. In addition, the FGD gypsum application altered the major water-soluble ion composition of dissolved salts, showing high Ca2+ and SO42− concentrations and low concentrations of HCO3−, CO32− and other water-soluble ions. After reclamation, the crop yields gradually increased over time, and the sunflower and corn yields reached more than 90% of the levels of local production of these crops. Moreover, the heavy metal (Cd, As, Pb, Hg and Cr) contents of the FGD gypsum-reclaimed soils and crops was far lower than the established standards and below detectable limits. This study provides convincing evidence of the benefits of the large-scale use of FGD gypsum to reclaim saline-alkali soils.

Extensive reclamation of saline-sodic soils with flue gas desulfurization gypsum on the Songnen Plain, Northeast China

Previous studies have reported that flue gas desulfurization (FGD) gypsum can be used as an amendment for saline-alkali soils. However, little information is available regarding the effects of FGD gypsum on soil quality and crop production at large scales. Thus, we evaluated the changes in the soil salinity, sodicity, soluble ion levels, paddy rice (Oryza sativa L.) yield and heavy metal levels in soil and rice after reclamation with FGD gypsum and paddy planting over three years. Data (90 samples) were also collected from three neighbouring saline-sodic fields (1780 ha). As expected, soil salinity and sodicity decreased significantly after two years of reclamation. The levels of electrical conductivity (EC) and the sodium absorption ratio (SAR) decreased rapidly in the first year, and the pH and exchangeable sodium percentage (ESP) decreased substantially in the second year. Averaged across the experimental sites, the mean EC, pH, ESP and SAR levels of the soils two years after reclamation decreased by 38.6%, 14.6%, 61.2% and 87.8%, respectively, compared to those of the initial soils. In addition, the concentrations of water-soluble Na+ and CO32− + HCO3− were 97.5% and 96.8% lower, respectively, two years after reclamation than the concentrations before reclamation. The paddy rice yield increased over time with reclamation; the mean level in the second year was 7.4 t ha−1 or 80% of the yield harvested from the managed fields of neighbouring farmers. Moreover, the heavy metal (Cd, Cr, Hg, Pb and As) contents of both soils and rice were lower than the established standards and below detectable limits after FGD gypsum application. These results confirm that FGD gypsum is a safe and effective way to reclaim saline-sodic soils and worthy of widespread application on the Songnen Plain in Northeast China and in similar ecological areas.

Influence of Incubation Periods on Extractable Fluoride and Phosphorous at Different Exchangeable Sodium Percentage Levels

The laboratory incubation experiment was accomplished to study the effect of incubation periods on the extractable Fluoride (F) and Phosphorous (P) in soil at different exchangeable sodium percentage (ESP) levels. The soils of different ESP levels (30, 45 and 60) were prepared by applying different amount of sodium bicarbonate dissolved in distilled water to the calculated volume of saturation percentage of the soil. The observed ESP of the prepared soil was 27.1, 43.7 and 54.9. Incubation studies were conducted with fluoride levels ranging from 40 to 160 mg/kg and phosphorus levels from 12.5 to 50 mg/kg with incubation periods of 1, 3,7, 14, 21, 28 and 35 days at temperature of 25±2℃. Moisture was maintained at field capacity by addition of distilled water. The results showed that the extractability of fluoride in soil increased with increasing levels of F and P application along with increased ESP. The increase was 100 percent at ESP 54.9 compared to ESP 6.2 at F level of 160 mg/kg at 1st day of incubation period. Similarly, Olsen’s extractable phosphorus in soil increased with increasing levels of F, P and ESP. It increased by 66 percent at ESP 54.9 compared to ESP 6.2 at P level of 50 mg/kg at 1st day of incubation period. However, extractability of both F and P decreased with increase in incubation periods. Fluoride extractability decreased by 65 percent at ESP 6.2 and 25 percent at ESP 54.9 with increasing days from 1st to 35th day of incubation period. Olsen’s extractable phosphorus decreased by 37 percent at ESP 6.2 and 48 percent at ESP with increasing days from 1st to 35th day of incubation period.

Genesis and Classification of Sodic Soils in the Northern Pantanal

ABSTRACT The simultaneous occurrence of high levels of exchangeable sodium percentage (ESP) and alkalinity in soils imposes restrictions on plant development and affects physical properties such as porosity, bulk density, permeability, and hydraulic conductivity. Although sodic soils are frequent in the flood plain of the Sao Lourenco River, northern Pantanal, Brazil, few studies focus on their formation and classification, especially with regard to specific processes and detailed classification into lower categorical levels by the different systems available. The aim of [...]

Saline-sodic soil and organic matter addition in the cultivation of the colored cotton ‘BRS Topázio’

he prevailing climate of the semiarid region in the northeastern region of Brazil along with inadequate irrigation management, have caused the formation of halomorphic soils, which have hampered agricultural production and environmental sustainability of this region. Therefore, this study aimed to evaluate the emergence and initial growth of the cotton cultivar ‘BRS Topázio’ cultivated in soil with different levels of exchangeable sodium percentage (ESP) and concentrations of organic matter (OM) in a greenhouse from April to June 2014. The experiment was set in a randomized block design in a 5 × 4 factorial scheme, with three replicates, and the treatments consisted of five ESP levels (13.6, 22.4, 30.1, 39.0, and 48.0) and four OM concentrations (0, 5, 10, and 15% based on soil volume). Soils with an ESP ranging from 13.6 to 48.0 did not interfere with the emergence and number of leaves of cotton at 10 days after seeding (DAS). At 44 DAS, in the period preceding the flowering stage, ESPs ranging from 27 to 30 promoted greater plant height, stem diameter, and shoot fresh and dry matter. Increasing OM increased the emergence percentage and emergence speed index and, at 44 DAS, increased plant height, stem diameter, and shoot fresh and dry matter. Increasing OM mitigated the effect of the exchangeable sodium up to an ESP of 30 on the number of leaves, plant height, stem diameter, and leaf area at 10 DAS, and up to mean ESPs of 28.5 and 34.0 for the number of leaves and leaf area, respectively, at 44 DAS.

Long term irrigation with treated wastewater (TWW) and soil sodification

Use of treated wastewater (TWW) for irrigation has grown noticeably in recent years, especially in arid and semi-arid regions. The sodium adsorption ratio (SAR) in TWW is considerably higher than that in its fresh water of origin. Recently, there is evidence showing that subsurface (depth >30 cm) exchangeable sodium percentage (ESP) levels in Israeli orchards may reach 6–9 which is higher than expected following long-term irrigation with TWW having SAR <5. Our objectives were to (i) determine the ESP in soil profiles of orchards exposed to irrigation with TWW, and (ii) examine the relationships between the SAR of the irrigation water, the SAR of the soil solution and the ESP of the studied soils. Soil samples were taken from different depths (up to 120 cm) in orchards grown on two different soil types that had been irrigated for >10 years with TWW. In each soil sample non-adjusted SAR and adjusted SAR (SARadj) of the saturated paste and ESP were determined. In all sampled sites except one, accumulation of adsorbed sodium in the soil subsurface was noted. The obtained ESP levels were higher than those expected based on the SAR of the TWW. A satisfactory agreement was noted between ESP data and the non-adjusted SAR and SARadj of the soil solution. These observations suggest that a chemical equilibrium exists between the soil exchange phase and the soil solution and that the properties of the latter were not always dictated by those of the irrigation water.

Modification of the McNeal Clay Swelling Model Improves Prediction of Saturated Hydraulic Conductivity as a Function of Applied Water Quality

A review of the McNeal clay swelling model, including its underpinning assumptions and the method for determining its parameters, was undertaken. Limitations of the model include model parameter identification, the fixed threshold exchangeable sodium percentage level at which hydraulic conductivity begins to decline, and the assumption that the expanding clay will always be 10% of the soil. To overcome these problems, an improved form of the model that accommodates a range of clay content is proposed. The modified model was used to estimate the reduction in saturated hydraulic conductivity in the three McNeal groups of soils containing different percentages of expanding clay. The model produced good agreement between the observed and estimated saturated hydraulic conductivities over the entire range of irrigation salinity (3–200 mmolc/L) and sodicity used for the original swelling model. The modified model was also successfully validated against three new sets of relative hydraulic conductivity data. The generalization of interlayer clay swelling in the modified model is more appropriately described as determining the dispersive potential of a given solution, rather than physical interlayer swelling. Consequently, this modified model more accurately predicts the reduction in saturated hydraulic conductivity as a function of the sodicity and salinity of the applied water.

Screening of sodicity tolerance in Aloe vera: An industrial crop for utilization of sodic lands

In this study an experiment was carried out for two years to assess the effects of various exchangeable sodium percentage (ESP) levels on growth, gel yield, aloin content and nutrient content of Aloe vera. A. vera suckers were planted at 10 (control), 15, 30, 45 and 60 ESP levels in pots. Suckers planted up to 30 ESP level survived well, while, those planted at 45 ESP picked up their growth in second year. But suckers planted at 60 ESP died. Number of suckers, leaf numbers and leaf biomass increased significantly in both the years at 15 and 30 ESP as compared to control and 45 ESP. The gel content also increased at 15 ESP level in both the years from the control plants but decreased significantly at 30 and 45 ESP, whereas, aloin content increased significantly up to 30 ESP after that decreased at 45 ESP. Concentration of nitrogen (N), calcium (Ca) and magnesium (Mg) decreased significantly from 15 to 45 ESP, while, the concentration of phosphorus (P) and sodium (Na) increased correspondingly. Nitrogen use efficiency (NUE) was less at 15 ESP and P use efficiency was high at control and 45 ESP. It is concluded that sodic soils up to 30 ESP can be utilized for the cultivation of A. vera.

Cyanophycean Algae Inhabiting Sodic Soil Exhibit Diverse Morphology: An Adaptation to High Exchangeable Sodium

A soil pot experiment was conducted in soils containing two exchangeable sodium percentage (ESP) levels i.e. normal (4.37) and high (54.5) ESP levels. The soils used in experiment were collected from different natural conditions to asses the algal biodiversity and changes in morphology of algae. The genera reported at high ESP were Oscillatoria, Lyngbya and colony of Anabaena while in normal soil these were absent. The heterocyst chain was also observed in soil of high ESP while in normal soil it was not reported. The width of heterocyst was much different than those reported. The chemical properties of soil e.g. pH, exchangeable sodium and ESP were decreased while organic carbon and total nitrogen contents were increased after one year algal growth. Key words: Cyanophycean algae, heterocyst, sodic soil, exchangeable sodium percentage. doi: 10.3126/eco.v15i0.1937 ECOPRINT 15: 15-21, 2008

Infiltrability in soils from south-western Africa: effects of texture, electrical conductivity and exchangeable sodium percentage

The effects of particle size, electrical conductivity (EC) and exchangeable sodium percentage (ESP) on infiltra-bility were investigated in 35 soils from Namibia and western South Africa. Samples were grouped as follows: sand (5–9% clay + silt), loamy sand (16–20%) and silty loam (73–80%). Subgroups included: low EC and low ESP (LL); low EC and high ESP (LH) and high EC and ESP (HH). Infiltrability was measured using a rapid laboratory syringe method. To investigate dispersion and flocculation processes the effect of four mobile phases on infiltrability was examined. Mobile phases included distilled water (W), a gypsum solution (G), a 1:5 soil suspension in gypsum solution (GS), and a 1:5 soil suspension in water (WS). Infiltrability was highest in the sand group, and lowest in the silty loam group. Electrical conductivity and ESP effects varied between particle size groups. In the silty loam group, EC and ESP effects were not significant due to swelling of clay minerals and rapid blockage of soil pores with dispersed particles. In the sand group, soils with high ESP (22) had significantly lower (p<0.05) infiltrability than soils with low ESP (4) levels. The application of gypsum in these soils enhanced infiltrability and minimized the negative effect of high ESP. The ameliorating effect of gypsum was apparent in treatment GS, but not treatment G, which highlights the dominant effects of mechanical disturbance and clay dispersion on crust formation and infiltrability.

Cyclic Use of Sodic and Non-Sodic Canal Waters for Irrigation in Cotton-Wheat Cropping System in a Semi-Arid Region

ABSTRACT A 6-year field study (1996 to 2002) was conducted on a sandy loam soil to investigate the effect of different irrigation cycles involving sodic water (SW) and good-quality canal water (CW) on soil properties and crop yields in a cotton-wheat rotation. The treatments were: irrigation with CW, irrigation with SW (residual sodium carbonate 10 mmolc L−1) and different combinations of CW and SW applied in a cyclic mode starting with CW or SW. Irrigation with SW increased soil pH, sodium adsorption ratio (SAR), exchangeable sodium percentage (ESP) and bulk density (BD), and decreased final infiltration rate (FIR). From the third year onward, wheat and seed-cotton yields in the SW treatment declined by 5.9% and 16.5% yr−1, respectively. Compared with SW alone, alternating irrigation between CW and SW helped maintain significantly lower pH, SAR, and ESP levels, improve FIR and BD of the soil, and achieve higher crop yields. Exchangeable sodium percentage of the soil (0 to 0.30 m layer) measured 6 years after initiation of the experiment explained 94% and 83% variation in wheat and seed-cotton yields, respectively. Compared with SW, significantly higher wheat and seed-cotton yields were obtained in irrigation cycles starting with CW involving one SW (2CW:SW, CW:SW) or SW followed by two CW irrigations (SW:2CW). Decline in seed-cotton yield was relatively greater (18% to 23%) than that in wheat (9% to 10%) in irrigation cycles starting with SW (SW:CW, 2SW:CW) and involving only one CW.

Effect of freezing and thawing processes on some physical properties of saline–sodic soils mixed with sewage sludge or fly ash

Dispersion of saline–sodic soils was rather difficult to leach. Therefore, negative effects of freeze–thaw on soil physical properties should be reduced by inexpensive and practical methods. This study investigates the effect of freeze–thaw cycles (3, 6, and 9) on wet aggregate stability, bulk density, and permeability coefficient in three soils with different electrical conductivity and exchangeable sodium percentage levels (soil I: 5.30 dS m −1, 47.51%; soil II: 42.80 dS m −1, 55.45%; soil III: 36.30 dS m −1, 59.34%) which consist of different proportions of sewage sludge and fly ash by volume (10%, 20%, and 30%). The experiment was conducted under laboratory conditions using disturbed and non-cropped soil samples mixed with sewage sludge and fly ash. Soils mixed with sewage sludge produced higher aggregate stability and permeability coefficients and lower bulk density values as compared to the soils mixed with fly ash. Sewage sludge added with a rate of 30% eliminated the negative effects of freeze–thaw processes on wet aggregate stability. Freeze–thaw processes did not affect the bulk density of the soils II and III, which were mixed with sewage sludge. However, fly ash addition decreased the bulk density of these soils very significantly after nine freeze–thaw cycles. Addition of sewage sludge or fly ash with rates of 20% and 30% significantly increased the permeability coefficients in soil I after nine freeze–thaw cycles. Results indicated that addition of sewage sludge and/or fly ash to saline–sodic soils could be alternative way for reducing negative effects of freezing–thawing on soil wet aggregate stability, bulk density, and permeability coefficient.

Native CaCO3 Mineral Dissolution and Its Contribution to Sodic Calcareous Soil Reclamation Under Laboratory Conditions

Efficient and sustainable reclamation of sodic soils is important to agricultural production. With the help of a peristaltic pump, laboratory-leaching experiments for sodic calcareous soils with exchangeable sodium percentage (ESP) of 1, 12.5, and 19 were conducted under atmospheric CO2 partial pressure to investigate native CaCO3 mineral dissolution and its contribution to the rehabilitation of moderate sodium-affected soils at the water flow velocities of 2 and 18 mm h−1, respectively. The electrical conductivity (EC), pH, and the Ca2+, Mg2+, Na+, K+, Cl−, and HCO3 − concentrations in the leachates were measured. The exchangeable Na+ contents in the soils after leaching were measured and their ESPs were calculated. Results indicated that both soil sodicity and water flow velocity significantly affected native CaCO3 dissolution and sodic soil reclamation. Almost all of the Ca2+ to substitute the adsorbed Na+ came from the native CaCO3 dissolution. The CaCO3 dissolution rate decreased logarithmically with leachate volume and increased with the initial ESP level. The leachate EC increased with the initial soil ESP level and decreased with flow velocity. The total detected cation concentrations in the leachates within the first six pore volumes (PV) were greater than 3.0–4.6 mmolc L−1.Low flow velocity was favorable to the improvement of the reclamation rate and reclamation efficiency of sodic soils. After the leaching of six PV, 24.1–36.0% of the Na+ adsorbed in the soils with initial ESPs of 12.5 and 19 were removed. Without the aid of extraneous chemical amendments, the gradual reclamation of moderate sodic calcareous soils under suitable management is possible.