Effects of irrigation-induced salinity and sodicity on soil microbial activity

The effects of irrigation-induced salinity and sodicity on the size and activity of the soil microbial biomass in vertic soils on a Zimbabwean sugar estate were investigated. Furrow-irrigated fields were selected which had a gradient of salinity and sugarcane yield ranging from good cane growth at the upper ends to dead and dying cane at the lower ends. Soils were sampled under dead and dying cane, poor, satisfactory and good cane growth and from adjacent undisturbed sites under native vegetation. Electrical conductivity (EC) and sodium adsorption ratio (SAR) of saturation paste extracts was measured, as well as the exchangeable sodium percentage (ESP). There was a significant negative exponential relationship between EC and microbial biomass C, the percentage of organic C present as microbial biomass C, indices of microbial activity (arginine ammonification and fluorescein diacetate hydrolysis rates) and the activities of the exocellular enzymes β-glucosidase, alkaline phosphatase and arylsulphatase but the negative relationships with SAR and ESP were best described by linear functions. By contrast, the metabolic quotient increased with increasing salinity and sodicity, exponentially with EC and linearly with SAR and ESP.Potentially mineralizable N, measured by aerobic incubation, was also negatively correlated with EC, SAR and ESP. These results indicate that increasing salinity and sodicity resulted in a progressively smaller, more stressed microbial community which was less metabolically efficient. The exponential relationships with EC demonstrate the highly detrimental effect that small increases in salinity had on the microbial community. It is concluded that agriculture-induced salinity and sodicity not only influences the chemical and physical characteristics of soils but also greatly affects soil microbial and biochemical properties.     

松嫩平原盐渍土钠吸附比推算土壤碱化度研究

Soil exchangeable sodium percentage (ESP) and sodium adsorption ratio (SAR) are commonly used to assess soil sodicity.Correlation between ESP and SAR of saturated pasted extract (SAR e) or of 1:5 (m:m) mixture soil to water (SAR 1:5) has been documented to predict ESP from SAR.However limited studies have been undertaken to model soil ESP based on soil SAR in the Songnen Plain,Northeast China.In this study,117 soil samples were used to predict ESP from SAR e and SAR 1:5 of salt-affected soils in western Songnen Plain.Soil ESP was highly related (r 2 > 0.76,P < 0.001) with SAR e and SAR 1:5.ESP of salt-affected soils in the Songnen Plain could be predicted using a logarithmic regression equations of ESP=10.72 · ln(SAR e) 15.36 and ESP=11.44 · ln(SAR 1:5) + 5.48.     

Influence of induced salinity and sodicity on manganese sorption in vertisols and aridisols

Abstract

Salinity and sodicity effects on manganese (Mn) sorption in a mixed sodium‐calcium (Na‐Ca) soil system were studied. Soil samples were taken at 0–30 cm depth from Vertisols (El‐Hosh and El‐Suleimi) and Aridisols (El‐Laota) at three sites in Gezira scheme (Sudan). No Mn was applied to these soils. Prior to analysis the soils were equilibrated with NaCl‐CaCL₂ mixed salt solutions to attain SAR values at different salt concentrations. The results indicated that saline soils sorbed less Mn and had higher equilibrium Mn concentrations. Sodic soils retained more Mn but had low equilibrium concentrations. Sodicity had a pronounced effect only on increasing Mn retention at higher SAR values. Salinity tended to alleviate sodicity effects on Mn retention, but soluble salts that increased soil pH decreased Mn concentration.     

Effects of plant residues and calcite amendments on soil sodicity

The effects of wheat, potato, sunflower, and rape residues and calcite were evaluated in soil that received sodic water. These materials were added to a sandy‐loam soil at a rate of 5%, after which the treated soils were incubated for 1 month at field‐capacity moisture and a temperature of 25°C–30°C. Column leaching experiments using treated soils were then conducted under saturated conditions using water with three sodium‐adsorption ratios (SAR) (0, 10, 40) with a constant ionic strength (50 mmol L^–1). The results indicated that the application of plant residues to soils caused an increase in cation‐exchange capacity and exchangeable cations. Leaching experiments indicated that the addition of plant amendments led to increased Na⁺ leaching and decrease in exchangeable‐sodium percentage (ESP). The ESP of the control soil, after leaching with solutions with an SAR of 10 and 40, increased significantly, but the level of sodification in soils treated with plant residue was lower. Such decreases of soil ESP were greatly affected by the type of plant residues, with the order of: potato‐treated soil > sunflower‐treated soil > rape‐treated soil > wheat‐treated soil > calcite‐treated soil > control soil.     

Field and laboratory approaches for determining sodicity effects on saturated soil hydraulic conductivity

Dilution of high-sodicity soil water by low-sodicity rainfall or irrigation water can cause declining soil hydraulic conductivity (K) by inducing swelling, aggregate slaking and clay particle dispersion. Investigations of sodicity-induced reduction in K are generally restricted to repacked laboratory cores of air-dried and sieved soil that are saturated and equilibrated with sodic solution before tests are conducted. This approach may not yield a complete picture of sodicity effects in the field, however, because of loss of antecedent soil structure, small sample size, detachment of the sample from the soil profile, reliance on chemical equilibrium, and differing time scales between laboratory and field processes. The objectives of this study were to: (i) compare the electrical conductivity (EC), exchangeable sodium percentage (ESP), and sodium adsorption ratio (SAR) in laboratory cores of intact field soil that had, or had not, undergone prior saturation and equilibration with sodic solution; (ii) compare the pressure infiltrometer (PI) field method with the intact laboratory soil core (SC) method for assessing sodicity effects on saturated soil hydraulic conductivity; and (iii) characterize hydraulic conductivity reduction in a salt-affected sandy loam soil and a salt-affected clay soil in Sicily as a result of diluting high-sodicity soil water with low-sodicity water.In terms of EC, ESP and SAR, quasi-equilibrium between soil and infiltrating solution was attainable in 0.08 m diameter by 0.05 m long laboratory cores of intact clay soil, regardless of whether or not the cores were previously saturated and equilibrated with solutions of SAR=0 or 30. In the sandy loam soil, the PI and SC methods produced statistically equivalent linear reductions in K as a result of diluting increasingly sodic soil water (SAR=0, 10, 20, 30) with deionised water. In the clay soil, the PI method produced no significant correlation between initial soil water SAR and K reduction, while the SC method produced a significant log-linear decline in K with increasing soil water SAR. Sodicity-induced reductions in K ranged from 3–8% (initial soil water SAR=0) to 85–94% (initial soil water SAR=30) in the sandy loam, and from 9–13% (initial soil water SAR=0) to 42–98% (initial soil water SAR=30) in the clay. The reductions in K were caused by aggregate slaking and partial blocking of soil pores by dispersed clay particles, as evidenced by the appearance of suspended clay in the SC effluent during infiltration of deionised water. As a result, maintenance of K in these two salt-affected soils will likely require procedures to prevent or control the build-up of sodicity.     

Predicting ESP and SAR by artificial neural network and regression models using soil pH and EC data (Miankangi Region,Sistan and Baluchestan Province,Iran)

Monitoring exchangeable sodium percentage (ESP) and sodium adsorption ratio (SAR) variability in soils is both time-consuming and expensive. However, in order to estimate the amounts of amendments and land management, it is essential to know ESP and SAR variations and values in sodic or saline and sodic soils. Thus, presenting a method which uses easily obtained indices to estimate ESP and SAR indirectly is more optimal and economical. Input data of the current research were 189 soil samples collected based on a regular networking approach from Miankangi region, Sistan plain, Iran. Then, their physicochemical properties were measured. Results showed that SAR = 3.8 × ln(EC) + 22.83 × ln(pH) – 44.37, (R² = 0.63), and ESP = 3.98×ln(EC) + 36.88(pH) – 56.98 (R² = 0.78) are the best regression models for estimating SAR and ESP, respectively. Moreover, multilayer perceptron (MLP), which explains 95–97% of parameters of soil sodicity using EC and pH as inputs, was the best neural network model. Therefore, MLP could be applied for ESP and SAR evaluation with high accuracy in the Miankangi region.     

Salt tolerance of grain crops in relation to ionic balance ability to absorb microelements

A greenhouse experiment was conducted to investigate the effect of exchangeable Na on the growth and absorption of metal elements in barley, rye, and maize. The plants were cultivated in soils whose exchangeable sodium percentages (ESP) were 6.6 (saline soil: Saline), 17.4 (saline-sodic soil: Sodic 1), and 39.6 (sodic soil: Sodic 2), which were prepared from Tottori sand dune soil (Control). The dry weight (DW) and concentrations of metal elements Ca, Mg, Mn, Zn, and Cu) in shoots were analyzed. The shoot DW was smaller with higher ESP, but in barley the difference between all the treatments was no longer observed with time. In Sodic soils, the growth of barley was vigorous, whereas rye growth was poor, and maize plants died by 5 weeks after planting. The Na concentration in shoots of all the species was higher with higher ESP. The K concentration in shoots was low at the early growth stage, but in barley it was higher in the Saline and both Sodic soils than in the Control at the subsequent stages. The concentrations of Ca and Mg in shoots of barley and maize in the Saline and both Sodic soils were higher than those in the Control, but in rye the concentrations were lowest in Sodic 2. The concentrations of Mn, Zn, and Cu in barley shoots in the Saline and bothSodic soils tended to be higher than those in the Control, whereas in rye they were lower than in the Control in both Sodic soils. Barley showed a higher ability to absorb low available microelements than rye and maize. These results indicate that barley is tolerant to sodicity as well as salinity, maize is tolerant to salinity, but is very sensitive to sodicity, and rye is moderately sensitive to both stresses. We suggest that the tolerance of grain crops to ESP involves a tolerance to a high Na concentration in shoots, the ability to keep suitable concentrations of essential cations in the presence of a high concentration of Na in shoots and the ability to absorb low available microelements.     

盐分对土壤呼吸和有机质动力学的影响与土壤电导率相关，而与渗透势的关系更为密切

Osmotic potential (OP) of soil solution may be a more appropriate parameter than electrical conductivity (EC) to evaluate the effect of salts on plant growth and soil biomass.However,this has not been examined in detail with respect to microbial activity and dissolved organic matter in soils with different texture.This study evaluated the effect of salinity and sodicity on respiration and dissolved organic matter dynamics in salt-affected soils with different texture.Four non-saline and non-sodic soils differing in texture (S-4,S-13,S-24 and S-40 with 4％,13％,24％ and 40％ clay,respectively) were leached using combinations of 1 mol L-1 NaC1 and 1 mol L-1 CaC12 stock solutions,resulting in EC (1:5 soil:water ratio) between 0.4 and 5.0 dS m-1 with two levels of sodicity (sodium absorption ratio (SAR) ＜ 3 (non-sodic) and 20 (sodic),1:5 soil:water ratio).Adjusting the water content to levels optimal for microbial activity,which differed among the soils,resulted in four ranges of OP in all the soils:from-0.06 to--0.24 (controls,without salt added),-0.55 to-0.92,-1.25 to-1.62 and-2.77 to-3.00 Mpa.Finely ground mature wheat straw (20 g kg-1) was added to stimulate microbial activity.At a given EC,cumulative soil respiration was lower in the lighter-textured soils (S-4 and S-13) than in the heavier-textured soils (S-24 and S-40).Cumulative soil respiration decreased with decreasing OP to a similar extent in all the soils,with a greater decrease on Day 40 than on Day 10.Cumulative soil respiration was greater at SAR =20 than at SAR ＜ 3 only at the OP levels between-0.62 and-1.62 MPa on Day 40.In all the soils and at both sampling times,concentrations of dissolved organic C and N were higher at the lowest OP levels (from-2.74 to-3.0 MPa) than in the controls (from-0.06 to-0.24 MPa).Thus,OP is a better parameter than EC to evaluate the effect of salinity on dissolved organic matter and microbial activity in different textured soils.     

Effect of Soil Sodicity on Growth,Yield, Essential Oil Composition,and Cation Accumulation in Rose‐Scented Geranium

Abstract

The effect of soil sodicity [exchangeable sodium percentage (ESP)] on the growth, yield, essential oil composition, and cation accumulation of two cultivars (Bourbon and Cimpawan) of geranium (Pelargonium graveolens) were studied in a pot experiment. Irrespective of soil sodicity, two cultivars of geranium differed significantly in their plant height and herb and oil yield. Plant height was not significantly affected with increases in soil ESP from 0.7 (control) to 20.0 and 7.0, respectively, for cultivars (cv) Bourbon and Cimpawan, but further increase in soil ESP decreased the plant height. The herb yield of cv Bourbon significantly increased with increasing soil ESP to 16.0, and the oil yield increased with increasing ESP to 7.0. Further increase in soil ESP decreased the yield. The increase in yield of cv Bourbon was 13.1 and 15.1% in the herb and 40.0 and 15.2% in the oil over the control (ESP 0.7) at soil ESP of 7.0 and 16.0, respectively. Decreases in yield were 3.5, 4.9, 53.3, and 59.3% in the herb yield and 3.8, 5.7, 53.3, and 80.0% in the oil over control (ESP 0.7) at soil ESP of 20.0, 24.0, 28.0, and 30.0, respectively. The herb and oil yield of cv Cimpawan significantly decreased with increase in soil ESP. The decease in yield was 17.7, 20.2, 40.7, 53.1, 70.7, and 72.6% in the herb and 4.0, 6.8, 30.9, 45.4, 83.2, and 84.0% in the oil over control (soil ESP 0.7) at the soil ESP 7.0, 16.0, 20.0, 24.0, 28.0, and 30.0, respectively. The concentration of isomenthone, linalool, citronellyl formate, and geranyl formate in the essential oil increased at low levels of soil ESP (between 16.0 to 24.0) but decreased at high soil ESP (>28). The concentration of l‐citronellol, nerol, and geraniol gradually increased with increase in soil ESP. The increase in the soil ESP enhanced the concentration of sodium (Na) and decreased that of potassium (K) in shoot and root tissues of geranium as compared to control. The concentration of Ca in shoot tissues of cv Bourbon significantly decreased with increase in soil ESP, but in the cv Cimpawan, the Ca concentration was not significantly affected with increase in soil ESP from 0.7 to 16.0, and thereafter the Ca concentration significantly decreased with further increase in soil ESP. The concentration of Na, K, and Ca were relatively higher in shoot than in root tissues. The K/Na and Ca/Na ratios in shoot tissues of both cultivars of geranium decreased with increase in soil ESP. The K/Na and Ca/Na ratios in shoot were not found to be related to the differences in sodicity tolerance of the cultivars of geranium tested in this experiment. The concentration of zinc (Zn) in shoot tissues decreased with increase in soil ESP. The cv Bourbon maintained a higher concentration of Zn in shoot tissues at high sodicity than that of cv Cimpawan. The results suggest that the geranium is slightly to moderately tolerant of soil sodicity stress.     

Spatial prediction of saline and sodic soils in rice‒shrimp farming land by using integrated artificial neural network/regression model and kriging

In the context of widespread saline and sodic soil, mapping and monitoring spatial distribution of soil salinity and sodicity are important for utilization and management in agriculture lands. In this study, two-stage assessment was proposed to predict spatial distribution of saline and sodic soils. First, artificial neural network (ANN) and multiple linear regressions (MLR) model were used to predict sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) based on soil electrical conductivity (EC) and pH. Then, the Kriging interpolation method combined with overlay mapping technique was used to perform saline spatial predictions in the study area. The model accuracy level is evaluated based on coefficient of determination (R²) and root mean square error (RMSE). In the first stage, the values of R² and RMSE of SAR and ESP were 0.94, 0.17 and 0.94, 0.24 for ANN, and 0.35, 0.52 and 0.34, 0.76 for MLR, respectively. Similarly, in the second stage, the RMSE of ANN-Kriging were much closer to 0 and relatively lower than MLR-Kriging and Kriging. The results show that ANN-Kriging can be used to improve the accuracy of mapping and monitoring spatial distribution of saline and sodic soil in areas that develop the rice-shrimp cultivation model.     

Effect of water quality on exchange phase — solution phase behavior of three soils

The effect of total electrolyte concentration (TEC) and sodium adsorption ratio (SAR) of water on ESR‐SAR relationships of clay (Typic Haplustert), clay loam (Vertic Haplustept) and silt loam (Lithic Haplorthent) soils was studied in a laboratory experiment. Twenty four solutions, encompassing four TEC levels viz., 5, 10, 20, and 50 mmol_c l^—1 and six SAR levels viz., 2.5, 5, 10, 15, 20, and 30 mmol^1/2l^—1/2 were synthesized to equilibrate the soil samples using pure chloride salts of calcium, magnesium, and sodium at Mg:Ca = 1:2. SAR of equilibrium solution decreased as compared to the equilibrating solution and more so in waters of low salt concentration and high SAR. At low electrolyte concentration, high SAR values were not attained in the equilibrium solution because of addition of calcium and magnesium from the mineral dissolution and from the exchange phase. Irrespective of TEC, exchangeable sodium in all the soils increased by about 4.5 to 5‐fold and irrespective of SAR, it increased by about 1.4‐ to 1.8‐fold. A positive interaction of TEC and SAR influenced the ESP build‐up and CEC played a major role in the visual disparity in sodication of these soils. At higher TEC levels, considerable increase in ESP was observed when it was corrected for anion exclusion and more so in silt loam followed by clay loam and clay soils. The values for Gapons' constant were in the range 0.0110—0.0176, 0.0142—0.0246, and 0.0189—0.0344 mmol^—1/2l^1/2 in clay, clay loam, and silt loam soils, respectively. Increase in TEC from 5 to 50 mmol_c l^—1 resulted in 5.84, 8.33, and 9.77 % decrease in Gapons' constant of clay, clay loam, and silt loam soils, respectively. The soils exhibited differential affinity for Ca²⁺, Mg²⁺ or Na⁺ under different quality waters. Regression coefficients of ESR‐SAR relationship were lower for low TEC as compared with high TEC waters. The exchange equilibrium was strongly affected by TEC of the solution phase. Variation in soil pH was gradual with respect to TEC and SAR of equilibrating solution and no sharp change was observed. Soluble salt concentration was doubled upon equilibration with low salt waters at all SAR levels in all the soils. However, the salt concentration remained unchanged upon equilibration with high salt waters. Considering pH 8.5 a boundary between soil salinity and sodicity, ESP values attained at TEC 5 mmol_c l^—1 were 7.34, 8.02, and 14.32 for clay, clay loam, and silt loam soils, respectively.     

Factors and processes of soil degradation in vertisols of the Purna Valley,Maharashira, India

The Vertisols of the Purna Valley, which cover the districts of Amravati, Akola and Buldhana in the state of Maharashtra, India, lack any perceptible evidence of salt efflorescence on the soil surface which would indicate the presence of salt, but the drainage conditions are poor. The limited data available indicate that the adverse physical condition of the soils is due to their poor hydraulic conductivity (HC), which is impaired by sodium in the exchange complex. However, the factors and processes that are inherently related to the development of sodicity in these shrink-swell soils are not yet understood. In order to establish the cause-effect relationship, eight Vertisol pedons from methodically selected sites were studied morphometrically in the field, and for their sodicity-related physical and chemical properties in the laboratory. The soils are deep, calcareous, clayey and very dark greyish brown to dark brown in colour. Cracks extend up to the slickenside zones in soils of Pedons 1–3 in the northeastern area of the valley, while they cut through the slickenside zones in soils of Pedons 4–8 in the southwest. The slickenside faces were larger in the soils of the southwest than in those of the northeast. All these soils meet the specifications of the Vertisols order of soil taxonomy. Saturation extracts of the soils had very low electrical conductivity (ECe ⩽ 2 ds m⁻¹). They ranged from moderately alkaline in the northeast, Pedons 1–3, to strongly alkaline in the southwest, pedons 4–8. In soils from the northeast the exchangeable sodium percentage (ESP) was less than 5 throughout the depth of the pedons, whereas in other soils it was up to 6 in the surface horizons and between 7 and 26 in the subsoil horizons; four of these soils qualified as sodic according to the criteria of the United States Salinity Laboratory. The inherently low hydraulic conductivity was due to the dispersion of clay particles caused by a high percentage of exchangeable magnesium (EMP) in the highly smectitic soils, and also to a slight increase in ESP (⩾5). The results of this study suggest that ESP 5 should be used as the lower limit for sodic subgroups of Vertisols, rather than ESP 15 as given in Keys to Soil Taxonomy (Soil Survey Staff, 1994). This is because there are severe limitations to the use of such soils owing to the development of adverse physical conditions even at such a low ESP. The authors emphasize the need to keep this fact in mind during future land resource management programmes on the soils of this valley as well as on similar soils occurring elsewhere. The development of sodicity in the soils of the southwestern part of the valley has been attributed to the semi-arid climatic conditions that have induced the pedogenetic process of depletion of calcium ions from the soil solution in the form of calcium carbonate, thereby resulting in an increase of both the sodium adsorption ratio (SAR) and the ESP with pedon depth. This chemical degradation, which affects the sodicity of Vertisols, appears to be a basic process that needs to be recognised in the future along with those already described as natural processes of soil degradation.     

Effects on soil and paddy–wheat crops irrigated with waters containing residual alkalinity

Degradation of soils by irrigation with ground waters containing residual alkalinity poses a major threat to agriculture in semi‐arid regions, particularly in South Asia. However, there is a lack of indices to define the soil degradation and crop performance under a monsoon climate. Therefore, an experiment was conducted during 2000–2004 to determine the responses of paddy rice and wheat crops in rotation to irrigation with alkaline waters (AW) having similar salinity (electrolyte concentration 30 me L^?1) but varying ionic constituents (sodium adsorption ratio irrigation water, SARiw 10 and 25; adjusted sodium adsorption ratio, adj.R_Na 13.6 and 29.2; residual sodium carbonate, RSC 5 and 10 me L^?1 and Cl:SO₄ 4:1 and 1:4, respectively). The concentration factors, ECe/ECiw (ratio of electrical conductivity of soil's saturation paste extract to that of the irrigation water) were between 1.1 and 1.8 for soils deprived of rainfall, whereas it was almost 1 for soils not sheltered from rain. Similarly, saturation paste extract, SARe, was between 1.6 and 2.0 times SARiw and 2.0–2.3 times SARiw with and without rainfall, and the exchangeable sodium per cent (ESP) 1.0–1.8 times SARiw. Yields of paddy relative to yields of crops irrigated with good‐quality water, averaged 56–74% during the period 2000–2004 compared with 81–88% for wheat, indicating the greater sensitivity of rice to irrigation with AW. Elevated levels of sulphate rather than chloride in the irrigation water lessened the impacts of the residual alkalinity. Production functions showed that the sodicity (ESP) did not solely explain the variation in crop yields because the salinity stress simultaneously inhibited growth. None of the sodicity indices (RSC, SAR and adj.R_Na) adequately defined the relative impacts of AW, although residual alkalinity (RSC) was a better indicator than either of the other two. The monsoon rains played an important role in alleviating the effects of residual alkalinity. Data presented here should support the development of more reliable criteria for the assessment of sodicity/salinity hazards from AW in semi‐arid regions.     

华北地区微咸水应用对土壤水力传导性能的影响

由于淡水资源短缺,中国华北地区微咸地下水灌溉面积逐年增多。该文通过室内土柱淋洗试验,研究了灌溉水盐分浓度和钠吸附比(SAR)对华北地区非碱土(可交换钠百分比ESP0)和碱土(ESP30)饱和水力传导性能的影响。灌溉水盐浓度分别为2.5、10和25mmolc/L,SAR分别为0、10和30(mmolc/L)0.5。去离子(盐浓度0)作为对照处理。试验包括2个土壤碱度、9个灌溉水质组合和1个去离子水处理,共20个试验处理。试验结果显示,非碱土和碱土对微咸水应用的反应机理以及反应程度不同。当黏粒弥散程度较弱时,上部土壤的饱和水力传导度显著大于下层土壤;反之,则各层土壤的水力传导度均较小。在试验水质条件下,非碱土的平均饱和水力传导度的变化范围为0.75～13.25cm/h,而碱土的变化范围为0.06～6.50cm/h。碱土的稳定饱和水力传导度随着灌溉水盐浓度的增加或/和SAR的减小而增大,但在非碱土中稳定饱和水力传导度的变化规律与此基本相反。试验结果对合理应用微咸水灌溉非碱土和碱土具有指导意义。     

Bioreclamation of sodic waste land—a case study

The study reports a case of bioreclamation of a once barren sodic landscape in the middle part of Gangetic alluvial plain at Banthra Research Station (National Botanical Research Institute, Lucknow, India) (80° 45′ – 53′E and 26° 40′ – 45′N) which began about four decades ago. The investigations were carried out to ascertain the changes in soil characteristics caused by different land‐use systems adopted consistently over three decades. The results showed that the anthropogenic effect on alteration of surface texture through addition of sand in soils of Typic Natrustalfs is still distinct but persistent sodicity is retained. The soils of Inceptic Haplustalfs are markedly improved showing pH value around 8 and ESP > 4 with negligible CaCO₃. The soils of Aeric Endoaquepts supporting stands of forest trees are now devoid of sodicity to about 0\5 m depth, whereas the soils of Aeric Halaquepts though under cultivation have mild sodicity. Soils of Typic Halaquepts occurring on a low physiographic position with aquic soil moisture regime have high sodicity. Summarizing the results of changes in the surface (0 – 15 cm) soil characteristics caused by continuous cultivation irrespective of any crop grown on any soil type reveals that there is perceptible reduction in soil pH and ESP after three decades of reclamation using organic amendments coupled with regular cultivation and afforestation in different locations. Copyright © 2000 John Wiley & Sons, Ltd.     

Salinity and sodicity induced changes in dispersible clay and saturated hydraulic conductivity in sulfatic soils

Abstract

Irrigation is becoming a more commonly used practice on glacially derived soils of the Northern Great Plains. Threshold salinity and sodicity water quality criteria for soil‐water compatibility in these sulfatic soils are not well defined. This study was conducted to relate soil salinity and sodicity to clay dispersion and saturated hydraulic conductivity (K_sat) in four representative soils. Soil salinity (EC treatment levels of 0.1 and 0.4 S m^‐1) and sodicity (SAR treatment levels of 3, 9, and 15) levels were established to produce a range of conditions similar to those that might be found under irrigation. The response of each soil to changes in salinity and sodicity was unique. In general, as sodicity increased clay dispersion also increase, but the magnitude of the increase varied among the soils. In two of the soils, clay dispersion across a range of sodicity levels was lower under the 0.4 S m^‐1 treatment than under the 0.1 S m^‐1 treatment and in the other two soils, clay dispersion across a range of sodicity levels was similar between the two salinity treatments. Changes in K_sat were greatest in the finer textured soil (decreasing an order of magnitude across the range of sodicity levels), but was unchanged in the coarse textured soils. Results suggest that these sulfatic soils are more susceptible to sodicity induced deterioration than chloridic soils. These results and earlier field observations suggest that sustainable irrigation may be limited to sites with a water source having a SAR <5 and an EC not exceeding 0.3 S m^‐1 for these sulfatic glacially derived soils.     

Short-term effects of biochar and gypsum on soil hydraulic properties and sodicity in a saline-alkali soil

Salt and sodicity of saline-alkali soil adversely affect the construction of ecological landscapes and negatively impact crop production. The reclamation potential of biochar (BC, wheat straw biochar applied at 1% by weight), gypsum (G, 0.4% by weight), and gypsum coupled with biochar (GBC) was examined in this laboratory-based study by evaluating their effects on a saline-alkali soil (silt loam) with no amendment as a control (CK). Saline ice and fresh water (simulated rainfall) were leached through soil columns to investigate changes in salt content, sodium adsorption ratio (SAR), alkalinity, and pH of the leachate and the soil. Results showed that saturated water content and field water capacity (FWC) significantly increased by 4.4% and 5.6%, respectively, in the BC treatment after a short incubation time. Co-application of biochar and gypsum (GBC) increased soil saturated hydraulic conductivity (Ks) by 58.4%, which was also significantly higher than the sole addition. Electrical conductivity (EC) of the leachate decreased sharply after saline ice leaching; subsequent freshwater leaching accelerated the removal of the rest of the salts, irrespective of the amendment application. However, the application of gypsum (G and GB) significantly enhanced the removal of exchangeable Na+ and reduced leachate SAR. After leaching, the soil salt content decreased significantly for all treatments. The application of gypsum resulted in a significantly lower soil pH, exchangeable sodium percentage (ESP), SAR, and alkalinity values than those recorded for the CK and BC treatments. These results demonstrated that the co-application of gypsum and biochar could improve saline-alkali soil hydraulic conductivity and decrease leaching-induced sodicity over a short period.     

Use of an electromagnetic technique to determine sodicity in saline-sodic soils

Soil sodicity is an increasing problem in arid‐land irrigated soils that decreases soil permeability and crop production and increases soil erosion. The first step towards the control of sodic soils is the accurate diagnosis of the severity and spatial extent of the problem. Rapid identification and large‐scale mapping of sodium‐affected land will help to improve sodicity management. We evaluated the effectiveness of electromagnetic induction (EM) measurements in identifying, characterizing and mapping the spatial variability of sodicity in five saline‐sodic agricultural fields in Navarre (Spain). Each field was sampled at three 30‐cm soil depth increments at 10–30 sites for a total of 267 soil samples. The number of Geonics‐EM38 measurements in each field varied between 161 and 558, for a total of 1258 ECa (apparent electrical conductivity) readings. Multiple linear regression models established for each field predicted the average profile ECe (electrical conductivity of the saturation extract) and SAR (sodium adsorption ratio of the saturation extract) from ECa. Despite the lack of a direct causal relationship between ECa and SAR, EM measurements can be satisfactorily used for characterizing the spatial distribution of soil sodicity if ECe and SAR are significantly auto‐correlated. These results provide ancillary support for using EM measurements to indirectly characterize the spatial distribution of saline‐sodic soils. More research is needed to elucidate the usefulness of EM measurements in identifying soil sodicity in a wider range of salt and/or sodium‐affected soils.     

吉林省大安市苏打碱土碱化参数之间的关系

选择典型苏打碱化土壤,对土壤碱化度(ESP)、钠吸附比(SAR)、残余碳酸钠(RSC)、总碱度和pH等进行了测定计算,分析了各碱化参数之间的关系,得出了各参数之间的相关方程。结果表明,除pH外,苏打碱土各碱化参数之间均具有极显著的相关性,各参数之间关系密切。土壤pH与ESP和SAR之间的关系变异性较大,利用pH推算该区苏打碱土碱化状况将会产生很大的不确定性。