Yield,Nutrient Uptake,and Changes in Soil Chemical Properties as Influenced by Liming and Iron Application in Common Bean in a No-Tillage System

Soil acidity is the principal limiting factor in crop production in Oxisols, and deficiency of micronutrients has increased in recent years because of intensive cropping. A field experiment was conducted over three consecutive years to assess response of common bean (Phaseolus vulgaris L.) to lime and iron (Fe) applications on an Oxisol in a no-tillage system. Changes in selected soil chemical properties in the soil profile (0- to 10- and 10- to 20-cm depths) with liming were also determined. Lime rates used were 0, 12, and 24 Mg ha^–1, and Fe application rates were 0, 50, 100, 150 200, and 400 kg ha^–1. Both lime and Fe were applied as broadcast and incorporated in the soil. Grain yields of common bean were significantly increased with the application of lime. Iron application, however, did not influence bean yield. There were significant changes in soil profile (0- to 10-cm and 10- to 20-cm depths) in pH, calcium (Ca²⁺), magnesium (Mg²⁺), hydrogen + aluminum (H⁺ + Al³⁺), base saturation, acidity saturation, cation exchange capacity (CEC), Ca²⁺ saturation, Mg²⁺ saturation, potassium (K⁺) saturation, and ratios of Ca/Mg, Ca/K, and Mg/K. These soil chemical properties had significant positive association with common bean grain yield. Averaged across two depths and three crops, common bean produced maximum grain yield at pH_w 6.3, Ca²⁺ 3.8 cmol_c kg^–1, Mg²⁺ 1.1 cmol_c kg^–1, 3.5 H⁺ + Al³⁺ cmol_c kg^–1, acidity saturation 41.8%, CEC 7.5 cmol_c kg^–1, base saturation 57.4%, Ca saturation 45.2%, Mg saturation 14.2%, K saturation 9.1%, Ca/Mg ratio 3.1, Ca/K ratio 22.6, and Mg/K ratio 6.7.     

土壤水溶性盐基离子的高光谱反演模型及验证

土壤水溶性盐基离子是诊断土壤盐渍化类型与盐渍化程度的重要依据,利用光谱技术快速获取土壤水溶性盐基离子含量数据,可为土壤盐渍化类型与盐渍化程度的诊断提供新的技术和手段。该研究通过采集新疆5个不同地区399个土样的反射率与水溶性盐基离子数据并进行31种光谱预处理方法,分析了不同水溶性盐基离子(HCO3-、Cl-、SO42-、K+、Na+、Ca2+、Mg2+)与高光谱反射率之间的相关性;采用K-S(Kennard-Stone)方法挑选出299个样品,针对每种离子使用偏最小二乘回归(partial least squares regression,PLSR)分别建立32个高光谱定量反演模型,优选最佳反演模型,并单独使用100个样品对估测模型进行检验。结果表明:不同离子的最佳反演模型所使用的预处理方法存在差异,其中仅有Cl-和Ca2+、SO42-和Mg2+所使用的预处理方法相同,其他离子则不同;不同离子的反演精度也不同,HCO3-和Ca2+构建的模型相对分析误差(relative percent deviation,RPD)分别为2.67、2.57,模型具有很好的预测能力。Cl-、SO42-和Mg2+所构建的模型RPD分别为2.05、2.10和2.14,表明这三者建立的模型具有较好的预测能力。K+建立的模型RPD仅为1.11,不能对样品进行预测。Na+构建的模型RPD为1.83,表明该离子所建模型只能对样品进行粗略估测。研究结果为探究水溶性盐基离子的高光谱反演增添了新的内容,为土壤盐渍化监测的深入和推进提供了新的思路和方法。     

日光温室番茄缺镁与土壤盐分组成及离子活度的关系

研究了石灰性土壤日光温室不同栽培年限及番茄不同程度缺镁的土壤水溶盐分中离子组成、比例及Mg2+、Ca2+、K+离子活度等的变化及关系.结果表明:随着栽培年限的增加,温室土壤水溶盐分中Ca2+、K+、NO3-含量显著增加;水溶性盐分中阳离子以Ca2+为主,栽培5 a后NO3-成为阴离子主要成分;土壤中NO3-含量的增加是导致土壤盐分累积的主要因素.随番茄缺镁程度的加剧,土壤水溶性盐中Ca2+、K+、NO3-、全盐量及Ca2+/Mg2+、K+/Mg2+摩尔比均呈增加趋势,番茄出现缺镁的土壤含盐量达到盐渍化水平.随着土壤盐分含量增加,Ca2+、Mg2+活度均呈指数下降趋势,番茄缺镁的土壤溶液中Mg2+和Ca2+活度显著低于不缺镁土壤,(K+)/(Mg2+)、(Ca2+)/(Mg2+)活度比显著高于不缺镁土壤,(K+)/(Mg2+)活度比随缺镁程度加剧达显著差异,番茄缺镁的土壤溶液(K+)/(Mg2+)活度比大于1.盐分累积使Mg2+活度大幅降低以及K+富集对植物吸收Mg2+的拮抗作用是石灰性土壤上番茄缺镁的主要诱因.     

Release of sulphate-sulphur, potassium, calcium and magnesium from spent mushroom compost under field conditions

 The release of SO₄ ^2–-S, K⁺, Ca²⁺ and Mg²⁺ from soil amended with spent mushroom compost (SMC), a byproduct of mushroom production, was measured in leachate from field lysimeters for 30 weeks. Rates of application were 0 and 80 t ha^–1 moist SMC. The SMC contained 1.7% K, 6.5% Ca, 0.4% Mg and 1.2% S (of which 87% is SO₄ ^2–-S), and has a C : S ratio of 26. The break-through curves of ion leaching were polymodal indicating the preservation of soil structure in the lysimeters and its influence on leaching. SO₄ ^2–-S release from SMC was rapid (first-order exponential) and was very similar to the release from a laboratory incubation. The release of K⁺, Ca²⁺ and Mg²⁺ was described using first/zero-order models which were also used to describe their release in the laboratory. The rate and amount of Ca²⁺ release was similar in the field and laboratory, but the amount of K⁺ (and to a lesser extent Mg²⁺) release was less in the field than in the laboratory. Recoveries of SMC applied nutrients in leachate were 80% of S (263 kg ha^–1), 3% of K (14 kg ha^–1), 16% of Ca (284 kg ha^–1) and 37% of Mg (40 kg ha^–1). Little if any S was mineralised. Using SMC could provide plants with S, K, Ca and Mg but there is potential for SO₄ ^2–-S losses via leaching. Received: 7 April 1999     

REACTIONS OF AMMONIA WITH SOIL. I

Heats of adsorption and adsorption isotherms of ammonia gas were measured at 300 K (27 °C) on outgassed soil saturated with Na⁺, K⁺, NH₄⁺, Ca²⁺, or Mg²⁺ ions. The Ca and Mg soils adsorbed apparently one more NH₂ molecule per exchangeable ion than the Na and K soils, mostly in the relative pressure range o to 0.005, but not much more than the NH₄ soil. The initial heat of adsorption was c. 75 kJ mol^-1 on the Ca and Mg soils and c. 60 kJ mol^-1 on the other soils. The results suggest that most NH, is sorbed on these soils through reactions not involving exchangeable cations.     

Effects of calcium lignosulphonate on Mehlich‐III extractable calcium,magnesium, and potassium quantity‐intensity relationship in the soil with or without potassium dihydrogen phosphate

Abstract

Calcium lignosulphonate (CaLS), a waste product from the pulp and paper industry, is expected to affect reaction of K fertilizer in the soil, thus influences their availability to crops. A clay soil (Typic Humaquept) was incubated with various amounts of CaLS (0 to 150 g kg^‐1 soil) and potassium dihydrogen phosphate (0–25.64 mmol kg^‐1 soil) for 240 h under moist conditions at 5 and 15°C. Subsamples were extracted with deionized water and the Mehlich‐III (M3) solution for the analyses of pH, and P, Ca, K and Mg concentrations and K adsorption (K_ad). Higher temperature reduced M3 extractable K (K_M3). CaLS and K additions increased M3 extractable Mg (Mg_M3) with Ca contributed more than did K as indicated by the standardized estimates. Additions of CaLS increased K_M3. Potassium adsorption decreased with the increases in CaLS addition rates. Significant positive linear relationships were observed between K_ad and the concentration ratio of [K⁺]/[Ca²⁺]^½, suggesting that the potassium buffering capacity of the soil was reduced by the additions of CaLS, with the desugared CaLS being more effective than the non‐desugared CaLS. The increased slope values with the increases in CaLS additions of the linear relationships between K_M3 and [K]/[Ca²⁺]^½ indicated that CaLS improved the quantity and intensity relationships and increased the power of the soil supplying plants with K.     

Modelling of sorption experiments and seepage data of an Amazonian Ultisol subsoil under cropping fallow

The results of physico-chemical investigations of an Ultisol subsoil under a 2-year old fallow in eastern Amazonia are presented. Subsoil chemistry was studied using 4 different approaches: i) concentrations of H, Na, K, Ca, Mg, Mn, Al, and Fe in seepage water were measured under field conditions, ii) the equilibrium soil chemistry was studied in sequential batch experiments where the soil was treated with different solutions, iii) results of batch experiments were simulated with a chemical equilibrium model, and iv) the seepage data were calculated using selectivity coefficients obtained by modelling the batch experiments. The model included multiple cation exchange, precipitation/dissolution of Al(OH)₃ and inorganic complexation. Cation selectivity coefficients were pK_x/Ca^sel: X = Na: 0.3, K: 0.8, Mg: ?0.1, and Al: 0.4. The amount of cations sorbed ranged from ?0.2 to 2.0 (K), ?0.7 to 2.3 (Mg), ?1.6 to 1.8 (Ca), ?4.8 to 3.6 (Al) and 0.0 to 8.5 (Na) mmol_c kg^?1. The model predictions were good with values lying within 0.3 pH units (for the pH range 3.7 to 7.2), and 3% of CEC for individual cations. The most important proton buffer reaction seemed to be the dissolution of gibbsite and a large release of Al into the soil solution. When selectivity coefficients obtained by the modelling procedure were used to predict the field data for cation concentrations in the seepage water, they decreased in the following order: Na > K > Ca > Mg > Al. These calculated values were similar to the measured order: Na > Ca > K ≈ Mg > Al. Thus the options for managing these soils should be carefully chosen to avoid soil acidification which may result from inappropriate use of fertilizer during the cropping period.     

Growth, Net Photosynthetic Rate, Nutrient Status and Secondary Xylem Anatomical Characteristics of Fagus Crenata Seedlings Grown in Brown Forest Soil Acidified with H2SO4 Solution

Dry matter production, net photosynthetic rate, leaf nutrient status and trunk anatomical characteristics of Fagus crenata seedlings grown in brown forest soil acidified by adding H₂SO₄ solution were investigated. The soil acidification leaded to decreased (Ca+Mg+K)/Al molar ratio in the soil solution. Dry mass per plant of the seedlings grown in the soil treated with H⁺ at 120 mg·L^?1 was significantly reduced compared with the control value at 0 mg·L^?1. When net photosynthetic rate was reduced in the seedlings grown in the soil treated with H⁺ at 120 mg·L^?1, the carboxylation efficiency and maximum net photosynthetic rate at saturated CO₂-concentration were lower than the control values. The addition of H⁺ to the soil at 120 mg·L^?1iinduced a reduction in the concentration of Ca in the leaf. By contrast, the concentration of Al in the leaf was increased with increasing the amount of H⁺ added to the soil. The annual ring formed in the seedlings grown in the soil treated with H⁺ at 120 mg·L^?1 was significantly narrower than that at 0 (control), 10, 30, 60 or 90 mg·L^?1. Based on the results obtained in the present study, we conclude that Fagus crenata is relatively sensitive to a reduction in the (Ca+Mg+K)/Al molar ratio of soil solution compared with Picea abies.     

基于电导率和结构稳定性阳离子比的微咸水灌溉水质评估方法

电导率（Electrical Conductivity,EC）和结构稳定性阳离子比（Cation Ratio of Soil Structural Stability,CROSS）是评估微咸水对土壤渗透性能影响的重要指标。虽然CROSS全面地考虑了Na+、K+、Ca2+和Mg2+对土壤结构稳定性的复杂影响,但CROSS的离子浓度系数在不同地区的适用性存在差异,有必要根据当地的水质条件确定基于EC和CROSS评估方法的分类标准。该研究旨在分析CROSS替代钠吸附比（Sodium Adsorption Ratio,SAR）评估水质危害的合理性以及其在河套灌区的适用性。在河套灌区不同区域采集73份地下水水样,并采用EC和SAR、EC和CROSS对其进行评估。结果表明,基于2种方法的地下水分类结果中,仅有34.25%的水样分类结果相同,并且不同的CROSS计算方法（基于阳离子相对絮凝能力（Flocculation）的CROSSf、相对分散能力（Dispersion）的CROSSd和优化的（Optimal）CROSSopt）在河套灌区的适用性也不相同。建议采用CROSSd或CROSSopt,并结合土壤盐分和离子浓度评估河套灌区地下水水质。该评估方法更全面地考虑了地下水和土壤中的离子组成对土壤渗透性能的影响,有效避免了不合理的微咸水利用导致的土壤结构恶化等问题,可为微咸水的安全可持续利用提供理论支撑。     

ADSORPTION OF LEAD, COPPER, ZINC, COBALT, AND CADMIUM BY SOILS THAT DIFFER IN CATION-EXCHANGE MATERIALS

The adsorption of Zn²⁺, Pb²⁺, Cu²⁺, Co²⁺, and Cd²⁺ (M²⁺) by soils was measured at concentrations ranging from 10-⁷ to 10-² M in 10-³ to 10-² M CaCI₂. Exchange between Ca²⁺ and M²⁺, and solubility products [M²⁺][OH^?]² indicate that M²⁺ is not precipitated as hydroxide but is adsorbed on cation-exchange sites. The proportion of selective adsorption sites with specified values of the selectivity coefficient calculated using Ca as reference ion, increased in the order montmorillonite < humus, kaolinite, < allophane. imogolite < halloysite, iron oxides. Raising the soil pH by Ca-saturation increased both the amount and affinity of adsorption. Selectivity of adsorption increased in the order Mg, Ca < Cd, Co < Zn < Cu, Pb, and the selectivity coefficient varied from < 1 to > 10 000. The formation of the coordination complexes of heavy metal with deprotonoted OH and COOH groups as ligands is suggested as a possible mechanism of selective adsorption.     

Lime and Cattle Manure in Soil Fertility and Soybean Grain Yield Cultivated in Tropical Soil

Most tropical soils have high acidity and low natural fertility. The appropriate application of lime and cattle manure corrects acidity, improves physical and biological properties, increases soil fertility, and reduces the use of chemical and/or synthetic fertilizers by crops, such as soybean, the main agricultural export product of Brazil. This study aimed to assess the effects of the combination of the application of dolomite limestone (0, 5, and 10 Mg ha^?1) and cattle manure (0, 40, and 80 Mg ha^?1) on grain yield and the chemical properties of an Oxisol (Red Latosol) cultivated with soybean for two consecutive years. The maximum grain yield was obtained with the application of 10 Mg ha^?1 of lime and 80 Mg ha^?1 of cattle manure. Liming significantly increased pH index, the concentrations of calcium (Ca²⁺) and exchangeable magnesium (Mg²⁺), and cation exchange capacity (CEC) of soil and reduced potential acidity (H⁺ + Al³⁺), while the application of cattle manure increased pH level; the concentrations of potassium (K⁺), Ca²⁺, and exchangeable Mg²⁺; and CEC of the soil. During the 2 years of assessment, the greatest grain yields were obtained with saturation of K⁺, Ca²⁺, and Mg²⁺ in CEC at the 4.4, 40.4, and 17.5 levels, respectively. The results indicated that the ratios of soil exchangeable Ca/Mg, Ca/K, K/Mg, and K/(Ca+Mg) can be modified to increase the yield of soybean grains.     

Yield,Nutrient Uptake,and Soil Chemical Properties as Influenced by Liming and Boron Application in Common Bean in a No‐Tillage System

Abstract

In Oxisols, acidity is the principal limiting factor for crop production. In recent years, because of intensive cropping on these soils, deficiency of micronutrients is increasing. A field experiment was conducted on an Oxisol during three consecutive years to assess the response of common bean (Phaseolus vulgaris L.) under a no‐tillage system to varying rates of lime (0, 12, and 24 Mg ha^?1) and boron (0, 2, 4, 8, 12, 16, and 24 kg ha^?1) application. Both time and boron (B) were applied as broadcast and incorporated into the soil at the beginning of the study. Changes in selected soil chemical properties in the soil profile (0- to 10‐ and 10- to 20‐cm depths) with liming were also determined. During all three years, gain yields increased significantly with the application of lime. However, B application significantly increased common bean yield in only the first crop. Only lime application significantly affected the soil chemical properties [pH; calcium (Ca²⁺); magnesium (Mg²⁺); hydrogen (H⁺)+ aluminum (Al³⁺); base saturation; acidity saturation; cation exchange capacity (CEC); percent saturation of Ca²⁺, Mg²⁺, and potassium (K⁺); and ratios of exchangeable Ca/Mg, Ca/K, and Mg/K] at both soil depths (0–10 cm and 10–20 cm). A positive significant association was observed between grain yield and soil chemical properties. Averaged across two depths and three crops, common bean produced maximum grain yield at soil pH_w of 6.7, exchangeable (cmol_c kg^?1) of Ca²⁺ 4.9, Mg²⁺ 2.2, H⁺+Al³⁺ 2.6, acidity saturation of 27.6%, CEC of 4.1 cmol_c kg^?1, base saturation of 72%, Ca saturation of 53.2%, Mg saturation of 17.6%, K saturation of 2.7%, Ca/Mg ratio of 2.8, Ca/K ratio of 25.7, and Mg/K ratio of 8.6. Soil organic matter did not change significantly with addition of lime.     

塔里木盆地柽柳灌丛沙堆盐分分布特点研究

为明确处于稳定阶段柽柳灌丛沙堆内土壤盐分的分布规律及其对环境可能产生的影响,以塔里木盆地北缘洪积冲积扇末端为研究区,分析了灌丛沙堆内与堆间地盐分的分布特征及其与柽柳灌丛凋落物年产量的关系.研究结果表明,柽柳灌丛沙堆表层土壤(0-30 cm)盐分明显低于堆间地表层土壤盐分,相关分析表明,柽柳灌丛凋落物产量的增加是抑制盐分表聚的一个重要因素.而沙堆深层土壤(30-120 cm)盐分则明显高于堆间地相同深度的土壤盐分,呈明显的富集状态,即形成了明显的“盐岛”.盐岛内主要富集K+,Na+,C1和HCO3-这4种离子,其余离子(SO24-,Ca2+,Mg2+)则呈均匀分布或随机分布.以上结果表明,柽柳灌丛沙堆是土壤盐分局部汇集的小型盐分库,它的演变趋势会对干旱区绿洲生态系统的稳定性产生潜在的影响.     

Genotypic variation in foliar nutrient concentrations, δ13C,and chlorophyll fluorescence in relation to tree growth of radiata pine clones in a serpentine soil

This study investigated the genotypic variation in foliar nutrient concentrations, isotopic signature (δ¹³C), and chlorophyll fluorescence (F_v/F_m) and tree growth of 40 radiata pine clones grown on a New Zealand serpentine soil, and the relationships between growth and physiological traits of these clones from improved and unimproved groups. Genotypic variation in growth and physiological traits existed within (i.e., clonal) and between groups, with larger variation among clones. The clonal repeatabilities were greater for foliar nitrogen (N), calcium (Ca), magnesium (Mg), boron (B) concentrations, δ¹³C, and Ca : Mg ratio (0.35–0.64) than for growth traits (0.14–0.27) and other physiological traits (0.08–0.24). Significant phenotypic correlations were found between growth traits and foliar phosphorus (P), potassium (K), sulfur (S), iron (Fe), and K : Mg and Ca : Mg ratios and F_v/F_m (positive), and foliar Mg (negative). This study indicates that the trees on this serpentine soil generally suffered from multiple nutrient deficiencies and imbalances and the clonal variation in growth performance was more related to their capabilities of acclimation to nutrient than water stresses. Overall, the clones that absorbed more P, K, S, and Fe and less Mg from the soil grew better on this serpentine soil. For unimproved clones, the most limiting nutrients for tree growth were foliar K and Fe, while for improved clones it was foliar K.     

苏打盐渍土地区芦苇地土壤盐分离子空间变异与群落关系研究

对松嫩平原西部苏打盐渍土地区芦苇小区土壤盐分离子和植被群落进行了分析,结果表明土壤盐分离子空间变异显著,四种阳离子(Na+、K+、Ca2+、Mg2+)变异系数为0.60~1.22,四种阴离子(HCO3-、CO32-、C l-、SO42-)变异系数为0.35~1.41。离子中,Na+在阳离子中含量最高,HCO3-在阴离子中含量最高。群落间比较,碱茅+芦苇群落八大离子浓度均大于芦苇群落(p<0.05)。且土壤电导率、pH,以及株高、生物量、覆盖度也高于芦苇群落(p<0.01),因此随着土壤电导率、离子浓度的增加,芦苇小区土壤碱化程度加重,植被生长指标减小,植被群落也由芦苇群落向含有碱地植被的碱茅+芦苇群落过渡。     

胀果甘草原生境土壤盐分特征分析

 通过野外调查采样和土样化学测定,分析胀果甘草原生境下土壤盐分的特征。结果表明:研究区土壤盐分普遍较高且表聚作用明显,土壤表层0～10 cm土层盐分均值高达32+.08g/kg,属典型的强度盐渍化土;土壤盐分组成中,含阳离子Ca2+、Na+、Mg2+、K+和阴离子Cl-、SO24、HCO-3,不含CO2-3,土壤盐分的特征因子为Ca2+、C1-、SO2-4、NaCa+,其盐渍类型主要为硫酸盐-氯化物型,重碳酸盐是土壤盐分的次要成分;该生境土壤中在整个垂直剖面上Ca2+的含量丰富,属典型钙质土。     

Soil Water Chemistry and Revegetation of a Limed Clearcut in a Nitrogen Saturated Forest

A clearcut stand of Pinus sylvestris in Flanders (Belgium) was limed with 3 ton/ha dolomite and reforested with Acer pseudoplatanus and Fagus sylvatica. Soil water monitoring revealed an overall decrease of ion concentrations and an annual peak in September due to seasonal nitrification. Liming reduced concentrations of NO₃ ^- and Al³⁺ and raised concentrations of K⁺ and Mg²⁺ and the molar ratio of (Ca+Mg)/Al. Liming also stimulated release of SO₄ ^2-, which prevented a rise of pH, except during nitrification peaks. Liming had no effect on height increment of Fagus but stimulated Acer, which suffered from severe deficiencies of calcium (Ca), magnesium (Mg), potassium (K), and phosphorus (P) without treatment. Nitrogen (N) was not growth-limiting for Fagus or Acer and liming had no effect on N concentrations in leaves of both species. Liming had a strong impact on ground vegetation. Nutrient-demanding species expanded while species that tolerate nutrient-poor conditions decreased. It is argued that changes in ground vegetation had a greater impact on reduction of NO₃ ^- concentration in soil water than increased tree growth.     

柚木优良无性系根系养分吸收动力学研究

以4个柚木优良无性系1年生苗木为试材,采用营养液培养和离子消耗曲线模拟方法,测定了根系的Ca2+、Mg2+、K+、NO-3吸收动力学参数。结果表明,以根系总吸收面积和总干重计算的Ca2+、Mg2+、K+、NO3-最大吸收速率相接近。在Ca2+、Mg2+、K+、NO3-最大吸收速率(Vmax)及离子流入速率(α值)指标上,不同基因型之间差异较大,而在养分离子吸收亲合力(Km)指标上,则没有明显差异。缅甸种源无性系VI-23根系对Ca2+、Mg2+、NO3-的Vmax及α值均为最大,而印度种源无性系70-12根系则对K+的Vmax及α值为最大,表明缅甸种源无性系VI-23为Ca、Mg和NO3--N硝态氮高效吸收基因型,印度种源无性系70-12为钾高效吸收基因型。     

Relationship between water soluble and exchangeable soil cations for estimating plant uptake and leaching potential

Abstract

The relationship between water soluble and exchangeable cations (Ca, Mg, Na, and K) was investigated for surface horizons of 195 soils including many taxonomic categories and a wide range in physical and chemical properties from around the world. This will provide information on exchangeable soil cation solubility for use in estimating plant uptake and leaching potential. Amounts of water soluble and exchangeable cations were not consistently related (r² of 0.50, 0.08, 0.77, and 0.49 for Ca, Mg, Na, and K). High correlations were biased by high water soluble and exchangeable cation levels of a few soils that had 3.8‐ and 2.5‐fold greater mean than median values. The ratio of exchangeable to water soluble cations was closely related to cation saturation (r² of 0.87, 0.95, 0.95, and 0.93 for Ca, Mg, Na, and K, respectively). As the degree of saturation of the exchange complex by a certain cation increased, solubility Increased. A change in saturation had less effect on K than on Na, Mg, and Ca solubility. Only exchangeable soil cations (NH₄OAc extractable) are routinely measured and reported in soil survey reports, thus, water soluble levels may be determined from cation saturation. This will allow estimation of the amounts of cation that can potentially move in solution through the soil or be taken up by plants. Use of cation saturation, in addition to exchangeable content, will better characterize soil cation availability by representing quantity, intensity, and buffer factors.     

设施土壤盐分的累积、迁移及离子组成变化特征

通过对我国不同地区设施栽培现状的野外调查和取样分析,研究了设施栽培条件下土壤盐分的累积、迁移及离子组成变化特点。结果表明:1)设施栽培条件下,土壤含盐量的变化幅度大,且均明显高于露地土壤,各研究区域内已有40%8～9%的土壤含盐量超过了作物正常生长的临界浓度。2)设施栽培的可持续利用周期较短,连续种植到4年左右的设施土壤,其耕层盐分的累积量可达到作物的生长障碍临界点,之后因设施使用率的下降以及采取的措施而有所降低,但仍高于露地土壤。设施连续使用会导致土壤环境质量的不断恶化。3)设施土壤剖面(0100.cm)盐分含量均高于相邻露地,盐分含量随土层深度增加而降低,其中耕层(020.cm)的盐分含量显著高于其下各层;盐分离子在土壤剖面的运移同时存在着明显的向底层迁移和向表层聚集两种方式,但以表聚为主;此外,盐分离子的大量累积和向底层迁移,特别是NO3-的淋溶已严重影响到部分地区的地下水水质。4)设施栽培后,土壤中的NO3-、SO42-、Cl-、Ca2+、Mg2+、K+、Na+均有不同程度的累积,阴离子以NO3-和SO42-为主,阳离子以Ca2+为主。盐分的大量累积以及某些离子的相对富集在一定程度上引起了作物养分的供需失衡、土壤酸化、棚室内CO2供应不足等生产问题。