Necessity for quantified measurement of soil sodicity and selection of suitable gypsum amendment for proper reclamation of sodic soils

<正>Dear Editor,Soil sodicity is the primary limiting factor in sustainable crop production in arid and semiarid regions, where the water scarcity, low rainfall, and poor-quality (salty) groundwater are common occurrence (Datta et al., 2019; Hosain,2019; Minhas et al., 2019; Kumar and Sharma, 2020).Globally, five categories of salt-affected soils have been identified, based on the nature and composition of salts(Szabolcs and Várallyay, 1971; Kovda, 1973; Szabolcs,1989). These soils are sali...     

Influence of forest tree species on reclamation of semiarid sodic soils

Tree plantation is a proven strategy to improve the salt‐affected soils. However, the efficiency of trees to reclaim the soil varies from species to species. This study was therefore, carried out with the objective of assessing the efficiency of 3‐yr old plantations of Prosopis juliflora (Swartz) D.C. (Mesquite), Eucalyptus tereticornis Sm. (Forest Red Gum) and Dalbergia sissoo Roxb. Ex. D.C. (Indian Rosewood) to improve the sodic soil characteristics in Sultanpur districts of Uttar Pradesh, India (26°10′–26°23′N, 81°50′–82°5′E). Soil samples collected from six depths; 0.0–0.1, 0.1–0.3, 0.3–0.6, 0.6–0.9, 0.9–1.2 and 1.2–1.5 m below the surface, were analysed for chemical and physical properties by following standard methods. The infiltration rate (IR) was determined by double concentric infiltrometer and the permeability by constant head permeameter. The trees were measured for their girth at breast height (at 1.33 m from ground) and crown area within a 100 × 100 m sector at each of the sites selected. There were decreases in soil pH (from 10.06 to 9.64) and exchangeable sodium percentage (from 70.6 to 26.9) at the P. juliflora plantation relative to the E. tereticornis and D. sissoo plantations. The organic carbon and nitrogen content increased from 2.0 and 0.18 g/kg to 3.9 and 0.45 g/kg under P. juliflora at the surface (0.0–0.1 m) layer. There was also more exchangeable Ca²⁺, Mg²⁺and K⁺ at exchange sites and a reduction in exchangeable Na⁺ 3 yr after establishing the plantations. There was a significant decrease in surface soil (0.1 m) bulk density from 1.66 to 1.37 (t/m³) but an increase in porosity from 41.2 to 46.3% and water holding capacity from 4.3 to 4.8 g/kg. The IR and soil permeability also increased after 3 yr of tree growth. Prosopis juliflora proved more effective than E. tereticornis and D. sissoo in its ability to enrich a sodic soil with organic matter and establishing better soil–water characteristics.     

Carbon dynamics of sodic and saline soils following gypsum and organic material additions: A laboratory incubation

Carbon fluxes in sodic and saline soils were investigated by measuring the soil microbial biomass (SMB) and soil respiration rates under controlled conditions over 12 weeks. Gypsum (10 t/ha) and organic material, as kangaroo grass (10 t/ha), were incorporated in an acidic and an alkaline saline–sodic soils. Cumulative soil respiration rates were lowest in the sodic and saline soils without amendment, while the highest rates were found in those soils that had organic material addition. The addition of gypsum decreased the cumulative respiration rates in the 0–5 cm layer compared to the addition of organic material and the addition of organic material and gypsum. Similarly, the SMB was lowest in the sodic and saline soils without amendment and highest in the soils which had organic material addition, while the effects of gypsum addition were not significant. The low levels of respiration and SMB were attributed to the low soil organic carbon (SOC) levels that result from little or no C input into the soils of these highly degraded landscapes as the high salinity and high sodicity levels have resulted in scarcity or absence of vegetation. Following the addition of organic material to the sodic and saline soils, SMB levels and respiration rates increased despite adverse soil environmental conditions. This suggests that a dormant population of salt-tolerant SMB is present in these soils, which has become adapted to such environmental conditions over time and multiplies rapidly when substrate is available.     

Use of langbeinite to reclaim sodic and saline sodic soils

Abstract

Langbeinite is a soluble potassium‐magnesium sulfate mineral (K₂SO₄2MgSO₄) found as an evaporite in many regions of the world. Langbeinite was used as a reclaiming material in a fine textured (clay loam) saline sodic soil (Grabe Series). This amendment can be dissolved and directly into the irrigation water, displacing sodium (Na) quickly with minimal water use. This amendment was superior over gypsum as a reclaiming material for a saline sodic soil in batch, column, and greenhouse studies. Langbeinite required 50% less irrigation water than gypsum to displace and leach exchangeable Na from soils. Langbeinite improved the infiltration rates of saline sodic soils, but not as effectively as gypsum. Significant increases in germination percent dry matter production mass of lima bean (Phaseolus lunatus L.) plants were observed when using langbeinite over the gypsum soil amendment.     

苏打盐碱水灌溉的土壤添加石膏肥和有机肥后水溶性碳和微生物碳研究

Microbial biomass carbon (MBC), a small fraction of soil organic matter, has a rapid turnover rate and is a reservoir of labile nutrients. The water-extractable carbon pools provide a fairly good estimate of labile C present in soil and can be easily quantified. Changes in soil MBC and water-extractable organic carbon pools were studied in a 14-year long-term experiment in plots of rice-wheat rotation irrigated with canal water (CW), sodic water (SW, 10-12.5 mmol c L-1 residual sodium carbonate), and SW amended with gypsum with or without application of organic amendments including farmyard manure (FYM), green manure (GM), and wheat straw (WS). Irrigation with SW increased soil exchangeable sodium percentage by more than 13 times compared to irrigation with CW. Sodic water irrigation significantly decreased hot water-extractable organic carbon (HWOC) from 330 to 286 mg kg-1 soil and cold water-extractable organic carbon (CWOC) from 53 to 22 mg kg-1 soil in the top 0-7.5 cm soil layer. In the lower soil layer (7.5-15 cm), reduction in HWOC was not significant. Application of gypsum alone resulted in a decrease in HWOC in the SW plots, whereas an increase was recorded in the SW plots with application of both gypsum and organic amendments in both the soil layers. Nevertheless, application of gypsum and organic amendments increased the mean CWOC as compared with application of gypsum alone. CWOC was significantly correlated with MBC but did not truly reflect the changes in MBC in the treatments with gypsum and organic amendments applied. For the treatments without organic amendments, HWOC was negatively correlated with MBC (r = 0.57*) in the 0-7.5 cm soil layer, whereas for the treatments with organic amendments, both were positively correlated. Irrigation with SW significantly reduced the rice yield by 3 t ha-1 and the yield of rice and wheat by 5 t ha-1 as compared to irrigation with canal water. Application of amendments significantly increased rice and wheat yields. Both the rice yield and the yield of rice and wheat were significantly correlated with MBC (r = 0.49**-0.56**, n = 60). HWOC did not exhibit any relation with the crop yields under the treatments without organic amendments; however, CWOC showed a positive but weak correlation with the crop yields. Therefore, we found that under sodic water irrigation, HWOC or CWOC in the soils was not related to MBC.     

Leaching and reclamation of calcareous saline‐sodic soil by moderately saline and moderate‐SAR water using gypsum and calcium chloride

Lysimeter experiments were conducted with sandy‐clay‐loam soil to study the efficiency of two amendments in reclaiming saline‐sodic soil using moderately saline and SAR (sodium‐adsorption ratio) irrigation water. Gypsum obtained from industrial phosphate by‐products and reagent grade Ca chloride were applied to packed soil columns and irrigated with moderately saline (ECe = 2.16 dS m^–1), moderate‐SAR water (SAR = 4.8). Gypsum was mixed with soil prior to irrigation at application rates of 5, 10, 15, 20, 25, and 32 Mg ha^–1, and Ca chloride was dissolved directly in leaching water at application rates of 4.25, 8.5, 12.75, 17.0, and 21.25 Mg ha^–1, respectively. The highest application rate in both amendments resulted in 96% reduction of total Na in soil. The hydraulic conductivity (HC) of soils receiving gypsum increased in all treatments. The highest HC value of 6.8 mm h^–1 was obtained in the highest application rate (32 Mg ha^–1), whereas the lowest value of 5.2 mm h^–1 was observed with the control treatment. Both amendments were efficient in reducing soil salinity and sodicity (exchangeable‐sodium percentage, ESP); however, Ca chloride was more effective than gypsum as a reclaiming material. Exchangeable Na and soluble salts were reduced with gypsum application by 82% and 96%, and by 86% and 93% with Ca chloride application, respectively. Exchangeable Ca increased with increasing amendment rate. Results of this study revealed that sodium was removed during cation‐exchange reactions mostly when the SAR of effluent water was at maximum with subsequent passage of 3 to 4 pore volumes. Gypsum efficiently reduced soil ESP, soil EC, leaching water, and costs, therefore, an application rate of 20 Mg ha^–1 of gypsum with 3 to 4 pore volumes of leaching water is recommended for reclaiming the studied soil.     

The use of coal fly ash in sodic soil reclamation

An experiment was conducted for two years in northwest India to explore the feasibility of using coal fly ash for reclamation of waterlogged sodic soils and its resultant effects on plant growth in padi–wheat rotation. The initial pH, electrical conductivity, exchangeable sodium percentage and sodium adsorption ratio of the experimental soil were 9.07, 3.87 dS m⁻¹, 26.0 and 4.77 (me l)^−1/2, respectively. The fly ash obtained from electrostatic precipitators of thermal power plant had a pH of 5.89 and electrical conductivity of 0.88 dS m⁻¹. The treatments comprised of fly ash levels of 0.0, 1.5, 3.0, 4.5, 6.0 and 7.5 per cent, used alone as well as in combination with 100, 80, 60, 40, 20 and 10 per cent gypsum requirement of the soil, respectively. There was a slight reduction in soil pH while electrical conductivity of the soil decreased significantly with fly ash as measured after padi and wheat crops. The sodium adsorption ratio of the soil decreased with increasing fly ash levels, while gypsum treatments considerably added to its favourable effects. Fly ash application increased the available elemental status of N, K, Ca, Mg, S, Fe, Mn, B, Mo, Al, Pb, Ni, Co, but decreased Na, P and Zn in the soil. An application of fly ash to the soil also increased the concentrations of above elements except Na, P and Zn in the seeds and straw of padi and wheat crops. The available as well as elemental concentrations in the plants was maximum in the 0 per cent fly ash + 100 per cent gypsum requirement treatment except Na and heavy elements like Ni, Co, Cr. The treatment effects were greater in the fly ash + gypsum requirement combinations as compared to fly ash alone. Saturated hydraulic conductivity and soil water retention generally improved with the addition of fly ash while bulk density decreased. Application of fly ash up to 4.5 per cent level increased the straw and grain yield of padi and wheat crops significantly in both years. The results indicated that for reclaiming sodic soils of the southwest Punjab, gypsum could possibly be substituted up to 40 per cent of the gypsum requirement with 3.0 per cent acidic fly ash. Copyright © 2003 John Wiley & Sons, Ltd.     

Degradation processes and nutrient constraints in sodic soils

Accumulation of excess sodium (Na⁺) in a soil causes numerous adverse phenomena, such as changes in exchangeable and soil solution ions and soil pH, destabilization of soil structure, deterioration of soil hydraulic properties, and increased susceptibility to crusting, runoff, erosion and aeration, and osmotic and specific ion effects on plants. In addition, serious imbalances in plant nutrition usually occur in sodic soils, which may range from deficiencies of several nutrients to high levels of Na⁺. The structural changes and nutrient constraints in such soils ultimately affect crop growth and yield. The principal factor that determines the extent of adverse effects of Na⁺ on soil properties is the accompanying electrolyte concentration in the soil solution, with low concentration promoting the deleterious effects of exchangeable Na⁺ even at exchangeable sodium percentage (ESP) levels less than 5. Consequent to an increase in the use of poor quality waters and soils for crop production, the problems of sodic soils can be expected to increase in future. The mechanisms that explain sodic behaviour can provide a framework in which slaking, swelling and dispersion of clay together with nutrient constraints in sodic soils may be assessed so that the practices to manage such soils can be refined for long‐term sustainable agriculture. Copyright © 2002 John Wiley & Sons, Ltd.     

Comparison of pyrites varying in water-soluble sulfur with gypsum for the reclamation of alkali soils under a rice-wheat rotation

We evaluated the effect of agricultural-grade (AG) pyrites (total sulfur 22%) varying in water-soluble sulfur (1–8%) and gypsum on the soil properties and yields of rice and wheat in alkali soils during the years 1993–1995 at the Gudha and Saraswati experimental farms at the Central Soil Salinity Research Institute, Karnal, India. Gypsum and pyrites were applied on the basis of gypsum requirement (GR) of the soils. Results showed that the efficiency of AG pyrites in decreasing soil pH and exchangeable sodium percentage (ESP) and increasing crop yields was dependent on their water-soluble sulfur content at the time of application to the field. Pyrites with 5.5% and 8% soluble sulfur were as effective as gypsum. The freshly mined pyrite (water-soluble S 1%) was found to be inefficient in reclaiming alkali soils. We also explored the possibility of increasing the water-soluble sulfur content of pyrite by optimizing its storage conditions. When pyrite (1% water-soluble S) was stored under moist conditions by sprinkling water over the bags under a rain shelter, there was an enrichment of indigenous iron- and sulfur-oxidizing bacteria of pyrite, and the water-soluble sulfur increased to 5% within a period of 6 months. However no such increase occurred when pyrite was stored dry. We conclude that the soluble sulfur content of pyrite increased during its storage under moist conditions and should be between 6% and 8% at the time of its application to the field.     

Comparison of pyrites varying in water-soluble sulfur with gypsum for the reclamation of alkali soils under a rice-wheat rotation

We evaluated the effect of agricultural-grade (AG) pyrites (total sulfur 22%) varying in water-soluble sulfur (1–8%) and gypsum on the soil properties and yields of rice and wheat in alkali soils during the years 1993–1995 at the Gudha and Saraswati experimental farms at the Central Soil Salinity Research Institute, Karnal, India. Gypsum and pyrites were applied on the basis of gypsum requirement (GR) of the soils. Results showed that the efficiency of AG pyrites in decreasing soil pH and exchangeable sodium percentage (ESP) and increasing crop yields was dependent on their water-soluble sulfur content at the time of application to the field. Pyrites with 5.5% and 8% soluble sulfur were as effective as gypsum. The freshly mined pyrite (water-soluble S 1%) was found to be inefficient in reclaiming alkali soils. We also explored the possibility of increasing the water-soluble sulfur content of pyrite by optimizing its storage conditions. When pyrite (1% water-soluble S) was stored under moist conditions by sprinkling water over the bags under a rain shelter, there was an enrichment of indigenous iron- and sulfur-oxidizing bacteria of pyrite, and the water-soluble sulfur increased to 5% within a period of 6 months. However no such increase occurred when pyrite was stored dry. We conclude that the soluble sulfur content of pyrite increased during its storage under moist conditions and should be between 6% and 8% at the time of its application to the field.     

Amelioration strategies for sodic soils: a review

Sodic soils are characterized by the occurrence of excess sodium (Na⁺) to levels that can adversely affect soil structure and disturb availability of some nutrients to plants. Such changes ultimately affect crop growth and yield. There are large areas of the world that exist under sodic soils and need attention for efficient, inexpensive and environmentally feasible amelioration. Sodic soil amelioration involves increase in calcium (Ca²⁺) on the cation exchange sites at the expense of Na⁺. The replaced Na⁺ together with excess soluble salts, if present, is removed from the root zone through infiltrating water as a result of excessive irrigations. Records nearly a century old reveal the use of water, crop, chemical amendment, electric current, and tillage as amelioration tools for such soils. Among the amelioration strategies, chemical amendments have an extensive usage. Owing to gradual increases in amendment cost in some parts of the world during the last two decades, this amelioration strategy has become cost‐intensive, particularly for the subsistence farmers in developing countries. In the meantime, phytoremediation with low initial investment has emerged as a potential substitute of chemical amelioration. Phytoremediation works through plant root action that helps dissolve native soil calcite (CaCO₃) of low solubility to supply adequate levels of Ca²⁺ for an effective Na⁺−Ca²⁺ exchange without the application of an amendment. Although significant progress has been achieved in improving amelioration methods, a great deal of work remains to analyse the economics of such methods with focus on (1) the long‐term sustainability of the amelioration projects and (2) the consequences of amelioration for the farmer himself, other growers and society as a whole. Computer modelling may help assess economic viability of different soil amelioration methods to extend results broadly to other similar locations. In addition, computer modelling to stimulate movement and reactions of salts in sodic soils has been a potentially useful complement to experimental data. However, such models need evaluation under field conditions. Copyright © 2001 John Wiley & Sons, Ltd.     

Effect of flooding on physico-chemical changes in sodic soils

Laboratory experiments were conducted with sodic soils of varying exchangeable sodium percentage (ESP) (82, 65, 40, and 22) and a normal soil (ESP 4) to study the changes with time in soil pH, pCO₂, Fe²⁺ and Mn²⁺ under submerged conditions with and without 1.0 per cent rice husk. In all the soils pCO₂, Fe²⁺ and Mn²⁺ increased after flooding, reached the maximum value and then either maintained or declined slightly. The release of Fe²⁺ and Mn²⁺ was maximum in normal soil and decreased with increase of ESP in sodic soils. Addition of rice husk brought about a conspicuous increase in Fe²⁺ and Mn²⁺, the maximum increase being in lowest ESP soil. Flooding reduced the pH of all soils. The effect was more pronounced in the presence of rice husk. The kinetics of pCO₂ indicated that accumulation of CO₂ was higher in normal soil and least in highest ESP soil. The addition of rice husk showed an average increase of 0.0074 atm pCO₂ in comparison to rice husk untreated soils.     

Driving forces for sodium removal during phytoremediation of calcareous sodic and saline–sodic soils: a review

Abstract. Sodic and saline–sodic soils are characterized by the occurrence of sodium (Na⁺) at levels that result in poor physical properties and fertility problems, adversely affecting the growth and yield of most crops. These soils can be brought back to a highly productive state by providing a soluble source of calcium (Ca²⁺) to replace excess Na⁺ on the cation exchange complex. Many sodic and saline–sodic soils contain inherent or precipitated sources of Ca²⁺, typically calcite (CaCO₃), at varying depths within the profile. Unlike other Ca²⁺ sources used in the amelioration of sodic and saline‐sodic soils, calcite is not sufficiently soluble to effect the displacement of Na⁺ from the cation exchange complex. In recent years, phytoremediation has shown promise for the amelioration of calcareous sodic and saline–sodic soils. It also provides financial or other benefits to the farmer from the crops grown during the amelioration process. In contrast to phytoremediation of soils contaminated by heavy metals, phytoremediation of sodic and saline–sodic soils is achieved by the ability of plant roots to increase the dissolution rate of calcite, resulting in enhanced levels of Ca²⁺ in soil solution to replace Na⁺ from the cation exchange complex. Research has shown that this process is driven by the partial pressure of CO₂ (P_CO2) within the root zone, the generation of protons (H⁺) released by roots of certain plant species, and to a much smaller extent the enhanced Na⁺ uptake by plants and its subsequent removal from the field at harvest. Enhanced levels of P_CO2 and H⁺ assist in increasing the dissolution rate of calcite. This results in the added benefit of improved physical properties within the root zone, enhancing the hydraulic conductivity and allowing the leaching of Na⁺ below the effective rooting depth. This review explores these driving forces and evaluates their relative contribution to the phytoremediation process. This will assist researchers and farm advisors in choosing appropriate crops and management practices to achieve maximum benefit during the amelioration process.     

Selection of Leucaena species for afforestation and amelioration of sodic soils

Performance of three exotic species of Leucaena (L. diversifolia, L. shannonii and L. leucocephala) and one local selection of L. leucocephala was evaluated on sodic soil sites (pH 8.6–10.5) in order to select promising species for biomass production and reclamation of these soils. There were significant differences among three species with respect to their field survival (47.7–95.5 per cent), growth in terms of stem volume (40.8–118.6 m³ ha⁻¹) and biomass production (24–70 Mg ha⁻¹) after eight years of growth. L. leucocephala was rated as the most promising species irrespective of seed source, followed by L. shannonii. L. diversifolia could not perform well on these hostile soils. A definite improvement in physicochemical properties of soil particularly in surface layers (0–5 cm) was observed after eight years of plantations as compared to the same at uncultivated site. The soil pH and sodium content decreased followed by an increase in organic carbon, nitrogen and phosphorus content. However, efficiency of different species varied greatly to ameliorate these soils depending on quantity and quality of organic matter lying on the floor. L. leucocephala, irrespective of seed origin, showed greater promise for afforestation of sodic soils because of its potential to produce higher biomass per unit area and greater efficiency to ameliorate fertility status of these soils. The study revealed that matching of species to soil conditions is very important for a successful plantation programme and sustainable development of degraded soil sites. Copyright © 2002 John Wiley & Sons, Ltd.     

Amelioration of calcareous saline sodic soils through phytoremediation and chemical strategies

Abstract. The worldwide occurrence of saline sodic and sodic soils on more than half a billion hectares warrants attention for their efficient, inexpensive and environmentally acceptable management. These soils can be ameliorated by providing a source of calcium (Ca²⁺) to replace excess sodium (Na⁺) from the cation exchange sites. Although chemical amendments have long been used to ameliorate such soils, the chemical process has become costly during the last two decades in several developing countries. As a low‐cost and environmentally acceptable strategy, the cultivation of certain salt tolerant forage species on calcareous sodic and saline sodic soils, i.e. phytoremediation, has gained interest among scientists and farmers in recent years. In a field study conducted at three calcareous saline sodic sites (pH_s=8.1–8.8, EC_e=7.8–12.5 dS m^–1, SAR=30.6–76.1) in the Indus Plains of Pakistan, we compared chemical and phytoremediation methods. There were four treatments; two involved plants: Kallar grass (Leptochloa fusca (L.) Kunth), and sesbania (Sesbania bispinosa (Jacq.) W. Wight). The other two treatments were uncropped: soil application of gypsum and an untreated control. All treatments were irrigated with canal water (EC=0.22–0.28 dS m^–1). The plant species were grown for one season (5–6 months). Sesbania produced more forage yield (34 t ha^–1) than Kallar grass (23 t ha^–1). Phytoremediation and chemical treatments resulted in similar decreases in soil salinity and sodicity, indicating that phytoremediation may replace or supplement the more costly chemical approach. The soil amelioration potential of sesbania was similar to that of the Kallar grass, which suggests that moderately saline sodic calcareous soils can be improved by growing a forage legume with market value.     

Amelioration of sodic soils by trees for wheat and oat production

Prolonged occupation of sodic soils by trees results in the latters' amelioration in terms of decreased pH and electrical conductivity and improved organic matter and fertility status. To assess whether sodic soils reclaimed by tree plantations can be used for growing agricultural crops, a greenhouse pot trial was conducted during winter of 1994–95 (November–April) at the Central Soil Salinity Research Institute, Karnal, India. Wheat (Triticum aestivum, L; cultivar HD 2329) and oat (Avena sativa, L. cultivar local) plants were grown in topsoils (30 cm) collected from 24-year-old plantations of Prosopis juliflora, Acacia nilotica, Eucalpytus tereticornis, Terminalia arjuna and Albizia lebbek that had been established in 1970 on a highly sodic soil (pH₂ 10·2–10·5), and a reclaimed sodic soil from a farm field adjacent to the plantations. The organic carbon content and nutrient status of the soil under the 24-year-old plantations was much higher than that of a reference farm soil reclaimed through gypsum in 1974. Soil amelioration was highest under Prosopis canopies (pH 7·4 and organic carbon 0·89 per cent) in topsoil and minimum in Eucalpytus canopies (pH 8·6 and organic carbon 0·56 per cent). Reduced sodicity and improved fertility resulted in much better growth reference and productivity of the wheat and oat test crops grown on the five plantation soils, than in the reference farm soil. Grain and straw yields of wheat and oats were maximum in Prosopis soil (wheat 61·7 g grains and 87·5 g straw and oats 87·9 g grains and 111·1 g straw per pot) and minimum in Eucalpytus soil (32·3 and 25·3 g, and 42·7 and 58·5 g per pot). Grain yields of both wheat and oats obtained in the Prosopis soil were 4·5 and 3·5 times more, respectively, than obtained in the reference farm soil. The phosphorus concentration in whole plant tissues of wheat and oats was highest in Prosopis soils reflecting the prevailing phosphorus status and better restoration processes of the soils. Potassium concentration was little affected due to different soil treatments. The study clearly indicated that prolonged afforestation of sodic soils by tree plantations, particularly by Prosopis and Acacia trees, may restore the productivity of abandoned soils to much above the present agricultural production levels. The results further suggest that 24 years' occupation of sodic soils by trees, such as Prosopis, Acacia, Eucalyptus, Terminalia and Albizia, did not result in a build-up or accumulation of toxic allelochemicals which could be injurious to wheat and oats cultivation on such soils. © 1998 John Wiley & Sons, Ltd.     

苏打碱土盐分淋洗与饱和导水率的关系

土壤饱和导水率是土壤重要的物理性质之一,反映了土壤入渗和渗漏性质,是计算土壤剖面水通量和排水工程设计的一个重要土壤水力参数[1]。准确地估测农田饱和导水率,对于制定正确的水分和盐分、水分和养分的管理措施及有效地防止污染物对环境的影响,都有十分重要的意义。已有研究表明,饱和导水率受土壤质地、结构、盐分含量与组成、容重或孔隙度、土壤水分特征等诸多因素影响[2-7]。就碱土而言,饱和导水率低是其标志性特征之一[8-10],提高饱和导水率是有效淋洗碱土盐分的基本前提[11]。松嫩平原是国内仅次于黄淮海平原的第二大平原,其西部是中国五大盐渍土分布区域之一[12]。土壤盐分以NaHCO3和NaCO3为主[     

The effect of lime on the response of soils to sodic conditions

The role of CaC0₃ in preventing clay dispersion and losses in hydraulic conductivity (HC) of sodic soils was determined directly by mixing two lime-free soils with 0.5 and 2.0 per cent CaCO₃. Whereas the HC of the lime-free soils dropped sharply when 0.01 n solutions of SAR 20 were displaced with distilled water, mixing the soils with powdered lime prevented both HC losses and clay dispersion. The response of a sandy soil mixed with lime was similar to that of a calcareous sandy soil. The beneficial effect ofCaC0₃ was not so pronounced in soils equilibrated with solutions of SAR 30. The increase in electrolyte concentration, due to CaCO₃ dissolution, was suggested as the mechanism responsible for the beneficial effect of lime.