Effect of monosilicic acid on hydrolytic polymerization of Fe(III) and structure hydrolytic products

To analyze the mechanism of retarded hydrolytic polymerization of Fe(III) and crystallization of the hydrolytic products in the presence of H₄SiO₄, we measured the changes in the monomeric Fe(III) concentration as a function of pH, H₄SiO₄ concentration, and aging time, and characterized the hydrolytic reaction products by a combination of methods. The monomeric Fe(III) concentration in solutions with higher H₄SiO₄ concentrations was significantly higher than that in an Si-free solution but the differences gradually narrowed with aging time. Chemical equilibrium calculation showed that the concentration of the FeH₃SiO₄ ²⁺ complex was not high enough to account for the reduced rate of hydrolytic polymerization. Electron microscopy and infrared spectroscopy showed that the hydrolytic products were ferrihydrite or Si-containing ferrihydrite and their particle size decreased with increasing H₄SiO₄ concentration. On the basis of these observations, we concluded that the interfering effect of H₄SiO₄ on the hydrolytic polymerization involved two mechanisms: 1) the coexistence of H₄SiO₄ delayed the kinetics of the hydrolytic polymerization of Fe(III) to a certain extent due to the formation of an FeH₃SiO₄ ²⁺ complex, and 2) H₄SiO₄ retarded the growth of Fe(III) hydroxides by binding onto the active sites of the hydrolytic products.     

Measurement of Si adsorption and “Active Si” in a soil amended with slag fertilizers by using stable isotope 30SP

The silicic acid adsorption by a soil (Eutric Gleysols) where slag fertilizers were applied was measured by the addition of a silicic acid solution labelled with ³⁰Si after soil incubation, in order to study the effect of slag application on the specific Si adsorption by the soil and to estimate the amount of Si in the soil solid phase which can easily enter the soil solution. It was evident that the application of slags increased the ability of soil to adsorb Si. It was also shown that the ³⁰Si added was diluted with not only the Si present in the soil solution but also the Si dissolved from the soil solid phase. We proposed the use of the term “active” for Si in soil which can take part in the isotopic dilution within 1 h. The amount of active Si in the soil solid and liquid phases (D ₆₀ - value) was calculated from the ³⁰Si content in the soil solution and compared with the amount of Si taken up by rice plant (Oryza sativa L.), which was determined in our previous study. The buffering capacity of the soil for Si, which can reflect the ability of soil to maintain the Si concentration in the soil solution constant when Si is added to or removed from the soil, was also determined. The D ₆₀ - value and the Si buffering capacity of the soil increased by slag application. These increases were large when the alkalinity of the applied slags was high. The correlation study revealed that the D ₆₀ - value was a better index of Si availability of the soil than the amount of Si dissolved from the soil solid phase during the incubation when the slags were previously applied.     

Solubility relationships of silica in soils

Abstract

Twenty‐one mineral soils of different physicochemical properties were used in this study. Soil suspensions, 30 grams of soil in 150 ml of distilled water, were shaken for 96 hours at 200 rpm and 25±1°C.

The activity of H₄SiO₄°, maintained in soil suspensions after shaking for 96 hours, was higher than quartz, cristobalite, and tridymite suggesting that comparatively more soluble forms of silica may be present in soils. All the soils, except Soil P and Soil Q, used in this study supported lower activity of Si than amorphous SiO₂. The average activity of H₄SiO₄° was 10^?3.08 M. It may be reasonable, for general purposes, to assume soil Si level as 10^?3.1 M. The activity of H₄SiO₄° found in soil suspensions was independent of soil pH. None of the selected physicochemical properties of soils was significantly correlated (at 5% significance level) to the activity of H₄SiO₄° in soil suspensions.     

Effects of pretreatment and solution chemistry on solubility of rice‐straw phytoliths

Rice is a Si‐accumulator plant, whereby Si has physio‐chemical functions for plant growth. Its straw contains high shares of plant silica bodies, so‐called phytoliths, and can, when returned to the soil, be an important Si fertilizer. Release of Si from phytoliths into soil solution depends on many factors. In order to improve prognosis of availability and management of Si located in phytoliths, in this study we analyzed the effect of pretreatment of rice straw by dry and wet ashing and the soil‐solution composition on Si release. Dry ashing of rice straw was performed at 400°C, 600°C, and 800°C and wet ashing of the original straw and the sample from 400°C treatment with H₂O₂. To identify the impact of soil‐solution chemistry, Si release was measured on separated phytoliths in batch experiments at pH 2–10 and in presence of different cations (Na⁺, K⁺, Mg²⁺, Ca²⁺, Al³⁺) and anions (Cl^–, NO$ _3^- $ , SO$ _4^{2-} $ , acetate, oxalate, citrate) in the concentration range from 0.1 to 10 mmol_c L^–1. After burning rice straw at 400°C, phytoliths and biochar were major compounds in the ash. At an electrolyte background of 0.01 mol_c L^–1, Si released at pH 6.5 was one order of magnitude higher than at pH 3, where the zeta potential (ζ) was close to zero. Higher ionic strength tended to suppress Si release. The presence of cations increased ζ, indicating the neutralization of deprotonated Si‐O^– sites. Monovalent cations suppressed Si release more strongly than bivalent ones. Neutralization of deprotonated Si‐O^– sites by cations might accelerate polymerization, leading to smaller Si release in comparison with absences of electrolytes. Addition of Al³⁺ resulted in charge reversal, indicating a very strong adsorption of Al³⁺, and it is likely that Si‐O‐Al‐O‐Si bonds are formed which decrease Si release. The negative effect of anions on Si release in comparison with deionized H₂O might be due to an increase in ionic strength. The effect was more pronounced for organic anions than for inorganic ones. Burning of rice straw at low temperatures (e.g., 400°C) appears suitable to provide silicon for rice in short term for the next growing season. High inputs of electrolytes with irrigation water and low pH with concomitant increase of Al³⁺ in soil solution should be avoided in order to keep dissolution rate of phytoliths at an appropriate level.     

Solubility characteristics of proto-imogolite sols: how silicic acid can de-toxify aluminium solutions

Proto-imogolite sols can be considered as highly dispersed forms of proto-imogolite allophane, the most widespread type of allophane in volcanic and non-volcanic soils world-wide. The solubility characteristics of such sols define the conditions of precipitation of allophanes in soils, and the maximum concentrations of aluminium released during acidic episodes from soils, such as podzols, that contain allophane. Direct measurement of Al, Si and pH values in equilibrium with proto-imogolite sols, approached from higher and lower pH, indicated a solubility equation: where log*K_so lay in the range 7.14 to 7.23 after equilibration for 4–24 weeks at 22 + 2°C in 17 of the 20 systems studied. The mean value of log *K_SO at 298 K was calculated as 7.02. This value indicates that proto-imogolite will be more stable than amorphous aluminium hydroxides at H₄SiO₄ concentrations above 5 × 10^?6m , but less stable than bayerite below 10^?3m H₄SiO₄, and than gibbsite below 10^?2m . Proto-imogolite is more stable than micro-crystalline gibbsite in 10^?4m H₄SiO₄, a typical minimum concentration in soil solutions and streams in landscapes where podzols are present. The rapid formation of proto-imogolite effectively prevents the formation of gibbsite seeds in soil, except in highly leached and warm environments, i.e. in older landscapes in the tropics. Although the presence of 10^?4m silicic acid has been found to eliminate the acute toxicity to fish exhibited by solutions containing 6–7 μm Al at pH 4.96, little or no proto-imogolite would form under these conditions. Silicic acid would, however, prevent the precipitation of aluminium hydroxides, and could inhibit the formation of the A1₁₃ polycation. These polymeric species are a likely cause of the increased toxicity exhibited by partially neutralized aluminium solutions.     

Evaluation of industrial wastes as sources of fertilizer silicon using chemical extractions and plant uptake

Six inorganic industrial‐waste materials (coal fly ash, bauxite‐processing mud, steel slag, two samples of air‐cooled blast furnace [BF] slag, and one sample of water‐cooled BF slag), along with wollastonite, were evaluated as fertilizer‐Si sources. Evaluation was carried out by analyzing total and extractable Si fractions in the materials, by incubating them at two rates with a Si‐deficient soil and measuring potentially available extractable Si and by measuring yield and Si uptake by two successive rice crops grown in the fertilized soils. Of the waste materials used, fly ash had the highest total Si content (29%) but a negligible quantity was present in extractable forms. Steel slag and bauxite‐processing mud had only 5%–7% Si content while BF slags contained 14%–18% Si. All materials, other than fly ash, increased the amount of extractable Si present in the soil. Additions of steel slag and bauxite‐processing mud caused greater increases in Si extractability than the air‐cooled BF slags while water‐cooled BF slag–treated soils contained notably high acid‐extractable Si. Because of the alkaline nature of the materials, and their reaction products, there was a positive relationship between extractable soil Si and soil pH. However, an equilibration experiment using NaSiO₃ as the Si source confirmed that Si solubility in the soil decreased with increasing pH. Dry‐matter yields of rice, at the lower rate of Si addition, were increased by all treatments other than fly ash. The higher rates of steel slag and bauxite‐processing mud caused yield depressions. Total Si uptake by rice was increased by all treatments, other than fly ash, and was greater at the higher rate of Si addition. It was concluded that the BF slags are the most effective waste materials as fertilizer‐Si sources and that, in slag‐amended soils, CaCl₂ and NH₄ acetate are the most reliable soil‐test extractants.     

High monosilicic acid supply rapidly increases Na accumulation in maize roots by decreasing external Ca2+ activity

Both calcium (Ca²⁺) and silicon (Si) improve plant performance under salt (NaCl) stress. Although these two mineral elements share numerous similarities, the information on how their extracellular interactions in the root apoplast affect uptake of sodium (Na⁺) is still lacking. Here, we investigated the effect of high Si supply in the bioavailable form of monosilicic acid (H₄SiO₄) on the activity of Ca²⁺ in the external root solution, and subsequent root uptake and compartmentation of Na in maize (Zea mays L.). In the short‐term experiments (6 h), 14‐d‐old maize plants were exposed to various concentrations of Ca²⁺ at three different pH‐values (6.5, 7.5, and 8.5) and two Si concentrations, i.e., low (1 mM) and high (4 mM) supply of H₄SiO₄. The activity of Ca²⁺ and Na⁺ in the external solution as well as the root concentrations of total and cell sap and BaCl₂‐exchangeble apoplastic fractions of both elements were analyzed. The pH of the nutrient solution affected neither the ion activities nor the root accumulation of both Ca²⁺ and Na⁺. At higher pH values (7.5 and 8.5) the interactions of Ca²⁺ and Si at high Si supply led to a decrease of Ca²⁺ activity and, hence, an increase of Na⁺ : Ca²⁺ activity ratio in the external root solution. Concomitantly, despite the elevated exchangeable apoplastic fraction of both Ca²⁺ and Na⁺, the total and cell sap concentrations were remarkably decreased for Ca²⁺ and increased for Na⁺ by the addition of 4 mM H₄SiO₄. This work demonstrates that at high Si supply extracellular Ca‐Si interactions leading to lowered activity of Ca²⁺ might rapidly compromise the ameliorative effect of Ca²⁺ on Na⁺ accumulation in roots. Practically, Si over‐fertilization of saline and, in particular, sodic soils may further promote the accumulation of Na⁺ in root tissues hours after Si application and, hence, increase a potential risk of Na⁺ toxicity.     

Silicon Decreases Transpiration Rate and Conductance from Stomata of Maize Plants

ABSTRACT

To characterize the effect of silicon (Si) on decreasing transpiration rate in maize (Zea mays L.) plants, the transpiration rate and conductance from both leaves and cuticula of maize plants were measured directly. Plants were grown in nutrient solutions with and without Si under both normal water conditions and drought stress [20% polyethylene glycol (PEG) concentration in nutrient solution] treatments. Silicon application of 2 mmol L^?1 significantly decreased transpiration rate and conductance for both adaxial and abaxial leaf surface, but had no effect on transpiration rate and conductance from the cuticle. These results indicate that the role of Si in decreasing transpiration rate must be largely attributed to the reduction in transpiration rate from stomata rather than cuticula. Stomatal structure, element deposition, and stomatal density on both adaxial and abaxial leaf surfaces were observed with scanning electron microscopy (SEM) and a light microscope. Results showed that changes in neither stomatal morphology nor stomatal density could explain the role of Si in decreasing stomatal transpiration of maize plants. Silicon application with H₄SiO₄ significantly increased Si concentration in shoots and roots of maize plants. Silicon concentration in shoots of maize plants was higher than in roots, whether or not Si was applied. Silicon deposits in cell walls of the leaf epidermis were mostly in the form of polymerized SiO₂.     

在实验酸性硫酸盐条件和酸性硫酸盐土壤上可溶性铝的控制

The controls of soluble Al concentration were examined in three situations of acid sulfate conditions:1) experimental acid sulfate conditions by addition of varying amounts of Al(OH)3(gibbsite) into a sequence of H2SO4 solutions;2)experimental acid sulfate conditions by addition of the same sequence of H2SO4 solutions into two non-cid sulfacte soil samples with known amounts of acid oxalate extractable Al; and 3) actual acid sulfate soil conditions.The experiment using gibbsite as an Al-bearing mineral showed that increase in the concentration of H2SO4 solution increased the soluble Al concentration,accompanied by a decrease i the solution pH, Increasing amount of gibbsite added to the H2SO4 solutions also increased soluble Al concentration,but resulted in an increase in solution pH.Within the H2SO4 concentration range of 0.0005-0.5mol L^-1 and the Al(OH)3 range of 0.01-0.5g(in 25 mL of H2SO4 solutions),the input of H2SO4 had the major control on soluble Al Concentration and pH .The availability of Al(OH)3，however,was responsible for the spread fo the various sample points,with a tendency that the samples containing more gibbsite had a higher soluble Al concentration than those containing less gibbsite at equivalent pH levels.The experimental results from treatment of soil samples with H2SO4 solutions and the analytical results of acid sulfate soils also showed the similar trend.     

Establishing Soil Silicon Test Procedure and Critical Silicon Level for Rice in Louisiana Soils

Calibration of crop responses to applied silicon (Si) serves as a basis for developing Si fertilizer recommendation guidelines. A greenhouse experiment was set up in a randomized complete block design with five replications, two sources of Si (wollastonite and slag) and four Si rates (0, 170, 340 and 680 kg ha^?1) to calibrate plant-available Si for growing rice in Louisiana soils. Silicon concentrations were determined in soils using seven different extraction procedures. Based on a quadratic model (p < 0.05), the estimated soil Si critical level using 0.01 M calcium chloride (CaCl₂) for Sharkey clay soil was 110 mg kg^?1 while for Crowley silt loam and Commerce silt loam, levels were 37 and 43 mg kg^?1, respectively. These results suggest that suitability of an extractant that gives the best estimate of plant-available Si could considerably depend on soil type and it is unlikely that there is a universal extractant for all soils.     

Aluminosilicate phases during initial clay formation: H+-Al3+–oxalic acid–silicic acid–Na+ system

The solid phases and the precipitation boundary characterizing the system H⁺-Al³⁺-oxalic acid-silicic acid-Na⁺ are discussed. Model experiments have been used to throw more light on two environmental problems: the formation of sparingly soluble aluminium silicates in oceans and alkaline lakes, which could be determining aluminium and silicate concentrations in pore waters of sediments, and the validity of inorganic and organic mechanisms of podzolization and their significance for soil science. pH and Tyndallometric measurements were performed at constant ionic strength of 0.6 M NaCl at 25°C. Three phases Al(OH)₄, H₄SiO₄ (phase Vi^a), Al₂, (OH)₆.H₄SiO₄ (phase VI^b) and NaAl(OH)₄.(H₄SiO₄), (phase VIII) determine the precipitation boundary. Phase NaAl(OH)₄.H₄SiO₄ (phase VII precipitates at 0.4pH units above NaAl(OH)₄.(H₄SiO₄)₂. Using a set of previously determined binary and ternary complexes, and phases of the subsystems, the following formation constants were deduced: Phases VI^a and VI^b are described as end-members of the allophane series with Si: Al ratios of 1:1 and 1.2. Phase VI^b was identified with protoimogolite allophane. These two phases are good model clays for podzolic soils and are extremely soluble at pH < 4. Sodium phases could be hydrous feldspathoids. These phases are possible in sediments of seawater or saline lakes. It is suggested that organic and inorganic mechanisms of podzolization operate sequentially and that neither of them alone can completely describe the process.     

A contemporary overview of silicon availability in agricultural soils

Our current understanding of silicon (Si) availability in agricultural soils is reviewed and knowledge gaps are highlighted. Silicon is a beneficial rather than essential plant nutrient and yield responses to its application have been frequently demonstrated in Si‐accumulator crops such as rice and sugarcane. These crops are typically grown on highly weathered (desilicated) soils where soil solution Si concentrations are low. Increased yields are the result of simultaneous increases in plant tolerance to a wide range of biotic (plant pathogens, insect pests) and abiotic (water shortage, excess salts, metal toxicities) stresses. Traditionally, soil solution Si is viewed as being supplied by dissolution of primary and secondary minerals and buffered by adsorption/desorption of silicate onto Al and Fe hydrous oxide surfaces. In recent years it has become recognized that phytogenic cycling of Si [uptake of Si by plants, formation of phytogenic silica (SiO₂ · nH₂O) mainly in leaves and subsequent return of this silica to soils in plant litter] is the main determinant of soil solution Si concentrations in natural forests and grasslands. Considerable diminution of the phytogenic Si pool in agricultural soils is likely due to regular removal of Si in harvested products. A range of extractants (unbuffered salts, acetate‐based solutions, and acids) can provide valuable information on the Si status of soils and the likelihood of a yield response in rice and sugarcane. The most common Si fertilizers used are industrial byproducts (e.g., blast furnace slag, steel slag, ferromanganous slag, Ca slag). Since agriculture promotes soil desilication and Si is presently being promoted as a broad spectrum plant prophylactic, the future use of Si in agriculture is likely to increase. Aspects that require future research include the role of specific adsorption of silicate onto hydrous oxides, the significance of phytogenic Si in agricultural soils, the extent of loss of phytogenic Si due to crop harvest, the role of hydroxyaluminosilicate formation in fertilized soils, and the effect of soil pH on Si availability.     

Catalase and ascorbate peroxidase activities are not directly involveded in the silicon‐mediated alleviation of ferrous iron toxicity in rice

Silicon (Si) is the second most abundant element in the soil and can alleviate several abiotic stresses in many plant species. However, the mechanisms involved in alleviating ferrous iron (Fe²⁺) toxicity by Si are still largely unknown, and no study has investigated the role of Si on the Fe²⁺‐induced oxidative stress and antioxidant system in rice. Four cultivars of Asian and African rice (Oryza sativa L. and Oryza glaberrima Steud) were grown for 4 weeks under hydroponic conditions with or without Fe²⁺ (250 mg Fe²⁺ L^?1) and with or without Si (250 mg SiO₂ L^?1). The plants that were treated with Fe²⁺ suffered Fe²⁺ toxicity, and Si helped to alleviate the toxicity symptoms. The bronzing index and the Fe concentration in the foliar tissue increased in the presence of Fe²⁺ but decreased significantly with the application of 250 mg SiO₂ L^?1. The concentration of malonyldialdehyde, that is commonly used as an indicator of oxidative stress, increased in the foliar tissue in the presence of 250 mg Fe²⁺ L^?1 in the nutrient solution. The application of 250 mg SiO₂ L^?1 in the plant nutrient solution treated with Fe²⁺ considerably limited the increase of malonyldialdehyde. However, no significant effect of Si application on the activities of antioxidant enzymes (catalase and ascorbate peroxidase) and non‐enzymatic antioxidants (total ascorbate, reduced ascorbate, oxidized ascorbate, and the ratio of the reduced to oxidized forms) was observed in the rice plants that were grown in the presence of Fe²⁺. These results suggest that Si does not act directly on the antioxidant defense system of rice but reduces the plant Fe²⁺ concentration, which reduces the oxidative stress.     

Solubilization of phosphate by rice plants growing in reduced soil: prediction of the amount solubilized and the resultant increase in uptake

Previous work has shown that rice plants growing in reduced soil are able to solubilize P by inducing an acidification in the rhizosphere through H⁺ produced in Fe²⁺ oxidation by root–released O₂, and by the direct release of H⁺ from the roots to balance excess intake of cations over anions. In this paper, equations for the diffusion and interaction of P and acid in soil are developed to predict the resultant increase in P uptake by the roots. Good agreement was obtained between the profiles of P and pH in the rhizosphere measured in the previous experiments, and those predicted using the equations with independently measured parameter values. The equations showed that solubilization accounted for over 80% of the P taken up. Measurements of the solubilization parameters in a range of reduced rice soils showed that H⁺ addition increased the quantity of P that could be desorbed per unit weight of soil and the concentration of P in solution, in all the soils tested. The quantity of P solubilized per unit H⁺ added at a given solution P concentration varied about 50–fold between soils, with a median of 11.9 mmol P per mol H⁺. The native soil solution P concentration varied 50–fold (median = 0.91 UM) and the soil pP buffer power (the quantity of P desorbed per unit decrease in –log of the P concentration in solution) varied 100–fold (median = 0.36 mmol kg^?1 pP^?1); the soil pH buffer power varied 7–fold (median = 0.075 mmol kg^?1 pH^?1). Calculations indicated that, in most of the soils tested, rice plants would depend upon solubilization for the bulk of their P.     

Extractable Silicon in Soils of the South African Sugar Industry and Relationships with Crop Uptake

Reports of sugarcane yield responses to silicon (Si), coupled with mounting evidence that elevated crop Si levels reduce both biotic and abiotic stresses, account for the interest in the Si nutrition of this crop. In terms of managing Si supplies to sugarcane in South Africa, uncertainties exist regarding, first, the reserves of plant-available Si in soils, and second, the reliability of soil-test methods for predicting Si availability. In this study, extractable Si was measured in 112 soils collected from sugarcane-producing fields in South Africa. Soils were selected on the basis of dominant soil types and included Inceptisols, Alfisols, Mollisols, Vertisols, Oxisols, Entisols, and Ultisols, varying widely in chemical properties, texture, and extent of weathering. Extractants employed were 0.01 M calcium chloride (CaCl₂) and 0.02 N sulfuric acid (H₂SO₄). Silicon extracted with 0.02 N H₂SO₄ ranged from 2 to 293 mg kg^?1, whereas with 0.01 M CaCl₂ the range was 5 to 123 mg kg^?1. With both extractants, extractable Si decreased significantly with decreasing pH, exchangeable calcium (Ca), and total cations. In soils with potassium chloride (KCl)–extractable Al+H levels of greater than 0.5 cmol_cL^?1, extractable Si levels were consistently low, suggesting that soluble Al is implicated in reducing plant-available Si levels. Extractable Si levels were not related to the Bache and Williams P-sorption indices of soils. In the second part of the investigation, sugarcane leaf Si concentrations from 28 sites were related to soil extractable Si levels. The CaCl₂ soil test proved markedly superior to H₂SO₄ as a predictive test for leaf Si levels.     

Chemical Composition of Precipitation, Throughfall and Soil Solutions at Two Forested Sites in Guangzhou, South China

Rain water at two forested sites in Guangzhou (south China) show high concentrations of SO₄ ^2?, NO₃ ^? and Ca²⁺ and display a remarkable seasonal variation, with acid rain being more important during the spring and summer than during the autumn and winter. The amount of acid rain represents about 95% of total precipitation. The sources of pollutants from which acid rain developed includes both locally derived and long-middle distance transferred atmosphere pollutants. The seasonal variation in precipitation chemistry was largely related to the increasing neutralizing capacity of base cations in rainwater in winter. Soil acidification is highlighted by high H⁺ and Al³⁺ concentrations in soil solutions. The variation in elemental concentration in soil solution was related to nitrification (H⁺, NH₄ ⁺ and NO₃ ^?) and cation exchange reaction (H⁺, Al³⁺) in soil. The negative effect of soil acidification is partly dampened by substantial deposition of base cations (Ca²⁺, Mg²⁺ and K⁺) in this area.     

Trends of Major Inorganic Species at the Small Watershed Ecosystem in Northern Tama Hills, the Western Tokyo Metropolitan Area, Japan

Acid rain impacts on the small forested watershed in northern Tama Hills in the western Tokyo metropolitan area Japan were investigated by surveying the trends of major inorganic species in rain and spring water during the years from 1991 to 1997. The ecosystem had been stressed by the annual H⁺-deposition of around 0.43 kmol/ha. The spring water outflow corresponded to ca. 27% of the precipitation. Budgets for the precipitation input and spring water output gave good balance for Cl^?,?0.01 ±0.09 kmol/ha, net gains for H⁺, NO₃ ^? and SO₄ ^2?, and to the contrary, relatively large net losses for Na⁺, Mg²⁺, Ca²⁺, Si(as H₄SiO₄) and HCO₃ ^?, thus suggesting the dissolution of chemical weathered products of silicate minerals. Further, in spring water, some concentration relationships were found: CNa⁺ = 376.5?2.05CCl^? (R²=0.748), CNa⁺=12.69+0.5556CHCO₃ ^? (R²=0.872) and CH₄SiO₄=130.0 + 1.108CHCO₃ ^? (R²=0.816). Evidently, the spring water chemistry reflected probable geochemical changes in the soil layer of the watershed. Mass balance in the ecosystem and estimation of the spring water output of chemical weathered products were investigated     

Effect of long-term intensive rice cultivation on the available silica content of sawah soils: Java Island,Indonesia

Abstract

The dramatic increases in rice productivity and cultivation intensity through the implementation of green revolution (GR) technology using high yielding varieties (HYVs) of rice and chemical fertilizers were not long lasting in Indonesia. The stagnancy of rice productivity in recent years without any scientific reasons presents a challenge for agronomists and soil scientists in Indonesia. This study describes the effects of long-term intensive rice cultivation on the change in available silica (Si) in sawah soil. The term sawah refers to a leveled and bounded rice field with an inlet and an outlet for irrigation and drainage. Soil samples collected by Kawaguchi and Kyuma in 1970 and new samples taken in 2003 from the same sites or sites close to the 1970 sites were analyzed and compared. From 1970 to 2003, the average content of available Si decreased from 1,512 ± 634 kg SiO₂ ha^?1 to 1,230 ± 556 kg SiO₂ ha^?1 and from 6,676 ± 3,569 kg SiO₂ ha^?1 to 5,894 ± 3,372 kg SiO₂ ha^?1 in the 0–20 cm and 0–100 cm soil layers, respectively. Cultivation intensity differences between seedfarms planted with rice three times a year and non-seedfarms rotating rice and upland crops appeared to affect the changing rates of available Si within the study period. In the 0–20 cm soil layer, the average content of available Si decreased from 1,646 ± 581 kg SiO₂ ha^?1 to 1,283 ± 533 kg SiO₂ ha^?1 (?22%) and from 1,440 ± 645 kg SiO₂ ha^?1 to 1,202 ± 563 kg SiO₂ ha^?1 (?17%) in seedfarms and non-seedfarms, respectively. Differences in topographical position also influenced the decreasing rate of available Si in this study. Using similar management practices and cultivation intensity, upland sampling sites lost more Si compared with lowland sites. Planted rice under a rain fed system with no Si addition from rain water in an upland position may be a reason for the higher loss of Si, particularly in non-seedfarms. The Si supply from irrigation water might have contributed to the slowdown in the decreasing rate of available Si in Java sawah soils.     

Acid and mineral components determining the exchangeable acidity in mineral horizons of taiga soils of the Komi Republic

Analysis of acid components in soil-KCl suspension filtrates from the mineral horizons was performed on the basis of analytical data reported between 1958 and 2003, including the data on more than 60 soil profiles (about 300 horizons) from the taiga zone of the Komi Republic. It was shown that the acid ions Al³⁺, H⁺ (exchangeable hydrogen), and Fe³⁺ and the basic ion H₃SiO ₄ ^? are the main components determining the pH of filtrates. Groups of horizons with the predominance of specific ions were separated.     

四种常规方法提取伊利石有效钾的机制比较

采用化学分析、X射线衍射、中红外光声光谱以及原子力显微镜的方法,比较了0.2 mol L~(-1)四苯硼钠法、1 mol L~(-1)沸硝酸法、2 mol L~(-1)冷硝酸法和2 mol L~(-1)热盐酸法浸提伊利石中有效钾的机制。结果表明,四苯硼钠法浸提时,伊利石中钾素释放量达到全钾量的59.5%,且基本均通过层间交换反应予以释放,结构离子铁、铝和硅释放量极低;采用三种酸溶液浸提时,其钾素释放量仅占全钾量的1.53%~2.46%,通过层间交换反应释放的钾量占释放量的比例为88.4%~94.0%。四苯硼钠浸提时伊利石层间距扩大,产生次生过渡矿物,并形成富硅表层,但在伊利石表面无溶蚀特征;三种酸溶液浸提时伊利石结构无改变,但其结晶度降低,且表面有明显的溶蚀特征。因此,土壤矿物层间钾是作物可利用有效钾的主要来源,三种酸溶液浸提方法一方面低估了有效钾容量,另一方面提取了一部分不能为植物所利用的结构态钾,不适宜于用来评价伊利石及土壤有效钾库容量。