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.     

A rapid method to determine cation exchange capacity and exchangeable bases in calcareous,gypsiferous, saline and sodic soils

Summary

A simple, single‐step extraction with LiEDTA for the estimation of CEC and exchangeable bases in soils has been developed. Multivalent cations are stripped from the soil adsorption sites by the strongly chelating agent EDTA, and are replaced by Li. In soils without CaCO₃ or water soluble salts, exchangeable divalent cations (Ca, Mg) are chelated by EDTA and exchangeable monovalent cations (Na, K) are replaced in a single extraction step using 0.25–2.5 g of soil and 10.0 ml of extractant.

In calcareous soils the CEC can be determined in the same way, but for the extraction of exchangeable Ca and Mg, another separate extraction is needed because dissolution of calcite by EDTA is unavoidable. This extraction is done with as much NaEDTA as needed to extract only exchangeable Ca and Mg in a 1:2 (m/V) soil/alkaline‐50% (V/V) aethanolic solution to minimize dissolution of calcite.

In gypsiferous soils gypsum is transformed into insoluble BaSO₄ and soluble CaEDTA by LiBaEDTA thus avoiding interference of Ca from dissolution of gypsum, which renders the traditional methods for determining CEC unsuitable for such soils. To determine exchangeable Ca and Mg, Na₄EDTA is used as for calcareous soils.

In saline/sodic soils replacement of Na by Li is incomplete but the Na/Li‐ratio at the complex after extraction is proportional to the molar Na/Li‐ratio in the extracts, so that the CEC and original exchangeable sodium (ESP) content can be calculated. Additional analysis of Cl and, if necessary, SO₄ in the extracts of saline soils can be used to correct for the effect of dissolution of the salts on the sum of exchangeable cations.

This new method is as convenient as the recently developed AgTU (silverthiourea), but is better suitable for calcareous and gypsiferous soils.     

THE INFLUENCE OF MAGNESIUM AND OF EASILY WEATHERED MINERALS ON HYDRAULIC CONDUCTIVITY CHANGES IN A SODIC SOIL

Exchangeable Mg appears to have no specific effect on soil hydraulic conductivity of A and C horizons of a sodic sandy loam soil (montmorillonite and kaolinite clay minerals) leached with solutions which cause clay swelling to be the dominant mechanism reducing conductivity (SAR < 20, electrolyte concentration 10 meq per litre). There is some evidence of a specific effect when these soils are subsequently leached with water which causes clay dispersion to become important. Fresh loess in the A horizon dissolves in percolating rainwater, causing difficulties in the replication of experiments. It seems to give a small degree of ‘self protection’ to soil structure, a property likely to be operating in other soils affected by recent loess deposits.     

Validation of water sorption‐based clay prediction models for calcareous soils

Soil particle size distribution (PSD), particularly the active clay fraction, mediates soil engineering, agronomic and environmental functions. The tedious and costly nature of traditional methods of determining PSD prompted the development of water sorption‐based models for determining the clay fraction. The applicability of such models to semi‐arid soils with significant amounts of calcium carbonate and/or gypsum is unknown. The objective of this study was to validate three water sorption‐based clay prediction models for 30 calcareous soils from Iran and identify the effect of CaCO₃ on prediction accuracy. The soils had clay content ranging from 9 to 61% and CaCO₃ from 24 to 97%. The three water sorption models considered showed a reasonably fair prediction of the clay content from water sorption at 28% relative humidity (RMSE and ME values ranging from 10.6 to 12.1 and −8.1 to −4.2, respectively). The model that considers hysteresis had better prediction accuracy than the other two that do not. Moreover, the prediction errors of all three models arose from under‐prediction of the clay content. The amount of hygroscopic water scaled by clay content decreased with increasing CaCO₃ content. The low organic carbon content of the soils and the low fraction of low‐activity clay minerals like kaolinite suggested that the clay content under‐predictions were due to large CaCO₃ contents. Thus, for such water‐sorption based models to work accurately for calcareous soils, a correction factor that considers the reduction of water content due to large CaCO₃ content should be included.     

Effect of ground water high in Mg on cation exchange of Na-illite in the presence of CaCO3

Ground waters with electrical conductivity of 4.9–7.4 mmhos/cm, a pH of 7.7–8.8 and a Mg/Ca ratio of 0.8–41.5 were equilibrated with a Na-illite in the presence and absence of CaCO₃. In the presence of CaCO₃, exchangeable Ca, exchangeable $\text{Ca+Mg}$ and the exchangeable Ca/Mg of the equilibrated clay increased but exchangeable Mg and Na decreased. The pH values of the ground waters were positively correlated with (1) exchangeable Ca, (2) exchangeable $\text{Ca+Mg}$, and (3) exchangeable Ca/Mg ratio, both in the presence and absence of CaCO₃.     

Zur Pedogenese und Klassifikation von Marschböden des Unterweserraumes. I. Gesamtnährstoffe,Carbonatgehalt, Kationenbelag und Diatomeenflora als Indikatoren für Sedimentations-Bedingungen und Bodenentwicklung

Development and Classification of Marsh Soils from the Unterweser Region, West Germany. I. Total Nutrients, Carbonate Content, Exchangeable Cations and Diatom Flora as Indicators of the Role of Sedimentation Conditions in Soil Development This study was carried out to see how much sedimentation conditions determine the properties– in particular the Ca/Mg ratio – of marsh soils (fluvaquents of coastel areas). The following results show, that the marsh soils properties are not determined by different sedimentation conditions: – The vertic fluvaquents don't have a higher clay content than the mollic and aeric fluvaquents – The total (t) contents of P, Ca, Mg, K and Na varied because of different soil development – The Ca_t/Mg_t ratio in soils with CaCO₃ was higher than in soils without CaCO₃, and – related to the Ca_a/Mg_a ratio – it can also be used as a classification characteristic (a = exchangeable) – The Ca_a/Mg_a ratio varied greatly because of differences in exchangeable Ca content. Vertic fluvaquents sometimes, but not often, have a higher content of exchangeable Mg than the mollic and aeric fluvaquents. Comparing maps of the Weser area as it appeared at various times in the Holocene with the soil map, shows that the sedimentation pattern is invariably brackish-marine. This is further confirmed by the diotom flora of the soils tested. Thus the properties of marsh soils, long believed to be dependent on sedimentation conditions, are the product of different continuance and intensity of soil development.     

Changes to a soil on irrigation with a sanitary landfill leachate

A detailed soil column leaching experiment was set up to investigate the changes in properties to a soil as a result of irrigation with an alkaline sanitary landfill leachate (pH 10.3). Chemistry of the soil was drastically altered as a consequence of the interaction. The soil was titrated from pH 5 to pH 10 and was changed from an exchangeable Mg dominated soil to an exchangeable Ca dominated soil. Magnesium was displaced by ion exchange reaction at acid pH, but at pH 10, 14.2 meq 100 g^?1 of Mg, i.e. up to three times the cation exchange capacity of Mg, was adsorbed in non-exchangeable forms at the immediate surface of the soil column by specific adsorption reactions. The leachate-treated soil was not stable on distilled water leaching. Structural breakdown led to clay dispersion and reduction in pore space, resulting in a 64 times reduction in hydraulic conductivity, 1.6 × 10^?4 to 2.5 × 10^?6 cm s^?1. The structural breakdown could be explained in term of the increase in Na adsorption ratio of the treated soil and the subsequent reduction in electrolyte concentration following the distilled water treatment.     

Hydraulic conductivity of calcareous soils as affected by salinity and sodicity. I. effect of concentration and composition of leaching solution and type and amount of clay minerals of tested soils

Abstract

Although there is generally no physical problem with salt‐affected soils when irrigated with saline and sodic waters, physical deterioration of the soils often results when leached with good quality (low salt and low sodium) irrigation water or by rain. Two major mechanisms of swelling and dispersion of clay particles have been proposed to be responsible for reduction in hydraulic conductivity (HC). The type and amount of clay minerals are major factors influencing the swelling and dispersion properties of soil in the presence of saline‐sodic solutions. The study was initiated to improve the understanding of swelling and dispersion processes in response to saline‐sodic conditions, particularly the role of the type and amount of clay minerals of the tested soils and the concentration of the leaching solutions. The study was conducted in a series of two leaching experiments. In the first experimental soil samples were leached with solutions of different combinations of 100 meq (NaCl+CaCl₂)L^‐1 and sodium adsorption ratio (SARs) 5, 10, 15, and 20. In the second, 8 samples of them selected to be leached with solutions of the same SARs of 5, 10, 15, and 20, but the higher concentration of 1000 meq (NaCl+CaCl₂)L^‐1. The changes in the HCs were determined through the concept of “the Sensitivity Index‐SI values”;. In general, solutions with lower concentrations and higher SAR resulted in greater reductions in the soil HC (i.e, SI value), and the SI values and SAR level showed a negative linear relationship. With respect to the regression equations between the SI values and the swelling/dispersion processes, and the relatively coarse texture as well as the mineralogical composition of the tested soils which shows the dominant clay minerals in almost all tested soils is non‐expanding dispersive quartz, illite and chlorite, it may be concluded that the slaking of the soil structure is responsible for blockage of the conducting pores and reduction in the HCs of the tested soils.     

Effect of potassium on soil structure in relation to hydraulic conductivity

The effect of exchangeable K⁺ on soil structure and permeability has been studied. A loamy sand, a light clay and a heavy clay soil were leached with solutions adjusted to potassium adsorption ratios (PAR) of 0.0, 0.72, 3.74 and ∞. Exchangeable K⁺ percentage (EPP) and hydraulic conductivity (HC) were measured on the leached soils. SEM observations on undisturbed soil samples were used to evaluate changes in soil structure and pore size.

EPP values for the three soils ranged as follows: 0.8–1.3, 5.5–9.2, 16.0–21.0 and 58.0–76.0 for PAR's of 0.0, 0.72, 3.74 and ∞, respectively. HC incrased slightly (20%) up to EPP values of about 20% for the loamy sand and heavy clay soil, while a decrease in HC corresponding to any increase of EPP was observed for the light clay soil. This soil was richer in illite and also exhibited higher affinity for K⁺. At the highest EPP values (58.0–76.0) HC of the three soils decreased to about 20% of the values measured for the Ca²⁺ saturated soils.

SEM observations were performed and Ca²⁺ saturated soils compared with the K⁺ enriched ones. Ca²⁺ treated loamy sand exhibited discrete clay aggregates located in the spaces between sand particles or attached to them. K⁺ enrichment resulted in the formation of a dense network of clay microaggregates filling up the pore space. The microaggregate structure of the two Ca²⁺ clay soils changed to a dense layer composed of much smaller particles following K⁺ enrichment. Pores were mostly smaller than 10 μm in the K⁺ soil compared to several tens of microns in the Ca²⁺ form.

SEM observations and the fact that clay content did not vary with depth suggest that dispersion of clay microaggregates and their rearrangement in situ were the major mechanisms involved in HC reduction, rather than long-range clay migration and the formation of a clay enriched layer with impeded drainage.     

Waste water renovation through soil percolation

A laboratory experiment simulating high-rate effluent renovation by soil percolation involved leaching secondary sewage effluent through columns of three differing soils. Analyses of P in 22 leachate collections and distribution of both organic and inorganic P in column sections revealed the mechanisms of P removal, the influence of differing soil properties, and the effect of continuous utilization. Renovation of effluent P was greatest with percolation through columns of acid Milner soil which contains abundant Al and Fe, and, although Squilax soil removed more P from initial leachings due to its higher exchangeable Ca content, Glenmore soil was the more suitable of these two alkaline soils over the long term. The leachate N0₀3-N levels were lower than the original N0₃-N content of effluent for the first ten leachings but N0₃-N enrichment occurred for the last effluent percolations through all three soils. Analyses of Ca, Mg, K, and Na in leachates and soil columns indicated losses of exchangeable cations from the calcareous Squilax and Glenmore soils enriched effluent content and the accumulation of the cations in the acid soil reduced concentrations in effluent that passed through Milner soil.     

Zinc and copper in some soils of Egypt as related to other soil properties

Total Zn in alluvial and calcareous soils (average 138 and 70 ppm respectively) was significantly related to their contents of CaCO₃ (negatively), O.M. and clay (positively). Extracting Zn by Na₂EDTA gave the highest values for both soil types. Total Cu contents varied widely from 26 to 111 ppm in alluvial and from 15 to 30 ppm in calcareous soils. They were negatively correlated with the CaCO₃ contents. The pot experiments showed that EDTA(NH₄)₂CO₃, Na₂EDTA and DTPA are reasonable extractants for available Zn from both soil types. DTPA was efficient for all soils investigated, while Na₂ EDTA and EDTA-citrate were specific for extracting Cu from calcareous soils.     

Determination of CEC and exchangeable Ca and Mg in non-saline calcareous soils

A method is proposed for determination of CEC and exchangeable cations in non-saline calcareous soils. The saturating solution used, 0.5 d Lithium formate in 80% methanol at pH 8.2, does not dissolve CaCO₃.The method is simple and less laborious than any other known method.     

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.     

Clay dispersion in relation to changes in the electrolyte composition of dialysed red-brown earths

Dialysis and re-suspension of red-brown earths showed dispersion in distilled water independent of the adsorbed cations. Whenever the electrolyte concentration is below the critical coagulation concentration the soil and clay will disperse. Mechanical disturbance greatly enhances the dispersion process. The experiments suggest that the dispersion was influenced by the released salt in the suspensions. The changes with time in the electrolyte composition of dialysed soils and clays showed that the ‘homoionic’ systems are unstable with possible interference with clay dispersion by the generated electrolytes. The importance of free electrolytes, especially calcium, in the management of dispersive red-brown earths is indicated.     

ON THE POSSIBILITY OF CHARACTERIZING CALCIUM PHOSPHATES IN CALCAREOUS SOILS BY ISOTOPIC EXCHANGE

Characterization of calcium phosphates depended upon the nature and the amount of phosphate used to react with reagent-grade CaCO₃. Formation of octa-calcium phosphate (OCP) was inferred from the solubility equilibria after reacting CaCO₃ with KH₂PO₄ solutions. Isotopic exchange measurements confirmed the presence of OCP, when the amount of P retained exceeded 44 μrnoles/g CaCO₃. The determined surface-Ca to surface-P molar ratios were close to the theoretical Ca/P ratio of 1.33 in OCP. As P retained on CaCO₃ decreased the surface Ca/P ratio markedly increased because of interference from surface Ca of the CaCO₃. When CaCO₃ was reacted with monocalcium phosphate (MCP), solubility equilibria indicated the formation of dicalcium phosphate dihydrate (DCPD). Isotopic exchange measurements, however, showed an average Ca/P ratio of only 0.375. This value corresponds to the composition of the metastable triple point solution (MTPS) formed on MCP dissolution rather than to the Ca/P ratio in DCPD. MCP application decreased the measured surface-Ca (exchangeable Ca) either for soil or Ca-resin, because of blocking of the exchange sites by the MCP reaction products and, consequently, a lower rate of isotopic exchange. Surface phosphorus of the two investigated calcareous soils proved to be proportional to the lowering in pH initiated by MCP application. Characterization of MCP reaction products in calcareous soils may thus prove infeasible, in view of the unexpected reduction in surface-Ca and the pH dependency of surface P.     

DOWNWARD MOVEMENT OF DOLOMITE,KIESERITE OR A MIXTURE OF CaCO3 AND KIESERITE THROUGH THE UPPER LAYERS OF AN ACID FOREST SOIL

Liming and fertilization are important tools for improving the chemical status of acid, base poor forest soils. The downward movement of dolomite, kieserite and a mixture of CaCO₃ and kieserite was investigated by monitoring the leachates and exchangeable cation composition from single and combined horizon columns, reconstructed from an acid brown forest soil profile (0–15 cm). Upon entering the soil, Mg ions from kieserite displaced base cations and acidity (H and Al ions) from exchange sites, which subsequently moved down with the mobile SO₄ ^2- anions. Total leaching during the initial SO₄ ^2- pulse was similar with the CaCO₃ + kieserite mixture. Compared to the single kieserite treatment, the joint application of CaCO₃ greatly increased the proportion of Ca in the leachates from all horizons. It also decreased the leaching of acidity from the surface Oe horizon and prevented pH from dropping under this layer. With both treatments, the redistribution of magnesium with SO₄ ^2- anions resulted in a rapid increase in exchangeable Mg contents throughout the studied columns. Due to the important charge increase in the Oe horizon and to kinetic restraints imposed on dissolution, downward movement of Ca and Mg ions from dolomite was very limited. Mg was however much more mobile than Ca. In the CaCO₃ + kieserite and dolomite treatments, the migration of alkalinity and base cations with time was associated with a decrease in exchangeable acidity and an increase in ECEC in the two upper soil layers. By the end of the monitoring period, overall net Mg retention in the 0–15 cm columns increased in the order kieserite < CaCO₃ + kieserite << dolomite with respectively 20, 35 and 85% of cumulated inputs remaining in the columns. The corresponding net Ca retention amounted to 82 and 96% of cumulated inputs for the CaCO₃ + kieserite and dolomite treatments, respectively. Results from this study complement those obtained in the field by clearly demonstrating the mechanisms involved in the downward movement of some fertilizers commonly used to increase the base saturation of acid forest soils.     

Use of hydraulic conductivity to evaluate the suitability of Vertisols for deep-rooted crops in semiarid parts of central India

Abstract. Detailed morphological, physical, chemical, mineralogical and micromorphological studies were carried out to identify properties that influence the yield of deep-rooted crops in 29 Vertisols of semiarid central India, since existing land evaluation methods are not adequate to explain the yield of cotton obtained by farmers. The studies indicated that among the soil parameters, CaCO₃ in the clay fraction, the exchangeable Ca/Mg ratio, exchangeable sodium percentage (ESP) and saturated hydraulic conductivity (HC) were the yield-influencing factors. The pedogenetic relationships between the semiarid climate, formation of pedogenic calcium carbonate, exchangeable Ca/Mg, ESP and HC have been established. In view of the pedogenetic processes that ultimately impair the drainage of soils, evaluation of Vertisols for deep-rooted crops on the basis of HC alone may help in planning and management of soils, not only in the Indian semiarid tropics, but also in similar climatic areas elsewhere.     

酸化及施碳酸钙对土壤各形态锰的影响

以灰潮土为对照 ,研究了华中地区 3种已明显发生酸化的土壤在施用碳酸钙前后各形态锰的变化情况。结果表明 ,已酸化的红壤、棕红壤和黄褐土施用碳酸钙降低了土壤酸度 ,土壤交换态锰随 pH值上升而降低 ,其降幅分别为 42 % ,49%和 39% ;其它形态锰的增减随各土而异 ,残留态锰较稳定 ,变幅小。作为对照 ,灰潮土虽与前 3种已酸化土壤一样种植过多茬作物 ,但其交换态锰含量仍甚微。无论是否施用碳酸钙 ,在灰潮土的交换态锰、碳酸钙结合态锰和易还原态锰 3种形态锰中 ,易还原态锰占 80 %以上 ,说明易还原态锰是其活性锰的主要部分     

Downward Movement of Soil Cations in Highly Weathered Soils Caused by Addition of Gypsum

Abstract

Besides supplying calcium (Ca) and sulfur (S) to plants, gypsum has recently been used in agriculture to ameliorate some soil physical and chemical properties, especially to alleviate aluminum phytotoxicity in subsoils. When applied in large quantities, however, gypsum may leach significant amounts of nutrients from the plow layer. This study was conducted to assess the effect of gypsum addition to the soil on the magnitude of cation leaching as well as the relationship of leaching with some soil properties in a group of seven Brazilian soils. Rates of gypsum equivalents to 0, 5.0, 10, and 20 t ha^?1 (0, 2.5, 5.0, and 10 g kg^?1) were mixed with triplicate soil samples consisting of 3.0 kg of dry base soil. After 60 days of incubation at room temperature (15–25°C), the experimental units were packed into polyvinyl chloride leaching columns (32‐cm‐high×10 -cm-diameter) at a density of 0.9 g cm^?3. Thereafter, they were percolated once a week with a volume of distilled water equivalent to 1.5 times the total soil porosity over 11 weeks. Soil samples were collected before the first and after the last percolation, for chemical analysis. Averaged across soils, 11 percolation events leached about 26% of each Ca, magnesium (Mg), and potassium (K) from the treatment without gypsum. Averaged across soils and rates, addition of gypsum leached 41–94% of added Ca, 13–90% of exchangeable Mg, and 13–58% of exchangeable K, and the highest losses occurred on the sandiest soils. The relationship between soil parameters and Ca leaching varied with gypsum rate: in the treatments that received gypsum, leaching was negatively related to cation exchange capacity (CEC), clay, and organic matter, and positively correlated with sand; in the treatment with no gypsum, leaching correlated with the same parameters above, nevertheless, all coefficients presented opposite signs. Leaching of K caused by gypsum was negatively associated with clay and positively with sand, whereas leaching of Mg was poorly correlated with any soil parameter. Gypsum is a good source to promote high and fast downward movement of Ca in the soil profile, but rates must be cautiously chosen because of excessive leaching of Mg especially on soils with low CEC.