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1.
Abstract

Speciation study of microelements in soils is useful to assess their retention and release by the soil to the plant. Laboratory and greenhouse investigations were conducted for five soils of different agro‐ecological zones (viz., Bhuna, Delhi, Cooch‐Behar, Gurgaon, and Pabra) with diverse physicochemical properties to study the distribution of zinc (Zn) among the soil fractions with respect to the availability of Zn species for uptake by rice plant. A sequential extraction procedure was used that fractionated total soil Zn into water‐soluble (WS), exchangeable (EX), specifically adsorbed (SA), acid‐soluble (AS), manganese (Mn)‐oxide‐occluded (Mn‐OX), organic‐matter‐occluded (OM), amorphous iron (Fe)‐oxide‐bound (AFe‐OX), crystalline Fe‐oxide‐bound (CFe‐OX), and residual (RES) forms. There was a wide variation in the magnitude of these fractions among the soils. The studies revealed that more than 90% of the total Zn content occurred in the relatively inactive clay lattice and other mineral‐bound form (RES) and that only a small fraction occurred in the forms of WS, EX, OM, AFe‐OX, and CFe‐OX. Rice (Oryza sativa L.) cultivars differ widely in their sensitivity to Zn deficiency. Results suggested that Zn in water‐soluble, organic complexes, exchange positions, and amorphous sesquioxides were the fractions (pools) that played a key role in the uptake of Zn by the rice varieties (viz., Pusa‐933‐87‐1‐11‐88‐1‐2‐1, Pusa‐44, Pusa‐834, Jaya, and Pusa‐677). Isotopic ally exchangeable Zn (labile Zn) was recorded higher in Typic Ustrochrept of Pabra soil, and uptake of Zn by rice cultivars was also higher in this soil. The kinetic parameters such as maximum influx at high concentrations (Imax) and nutrient concentration in solution where influx is one half of Imax (Km) behaved differentially with respect to varieties. The highest Imax value recorded was 9.2×10?7 µmol cm?2 s?1 at the 5 mg kg?1 Zn rate for Pusa‐933‐87‐1‐11‐88‐1‐2‐1, and the same was lowest for Pusa‐44, being 4.6×10?7 µmol cm?2 s?1 at the 5 mg kg?1 Zn rate. The Km value was highest for Pusa‐44 (2.1×10?4µmol cm?2 s?1) and lowest for Pusa‐933‐87‐1‐11‐88‐1‐2‐1 (1.20×10?4µmol cm?2 s?1). The availability of Zn to rice cultivars in Typic Ustrochrepts of Bhuna and Delhi soils, which are characterized by higher activation energy and entropy factor, was accompanied by breakage of bonds or by significant structural changes.  相似文献   

2.
Eight soils from the Gulf of Kalloni in Lesvos Island, Greece, most of which were of low clay and low organic matter content, were used in a series of leaching experiments. The aim was to investigate the role of sewage sludge on Zn leaching and determine the soil properties that affect it. It was found that sludge addition at a low application rate (10 t ha?1) decreased Zn leaching significantly by 30%. From a regression analysis it was found that eluted Zn was reduced with increasing Fe oxides content, probably due to Zn adsorption onto them, and that Zn transport increased with clay content. This indicates that Zn leaching was facilitated by the downward movement of clay particles, which was also suggested by the erratic Zn breakthrough observed in many soils. This was further confirmed by the fact that colloid concentrations increased with clay content in the soils (R?=?0.85, P?<?0.05). The results show that the addition of sewage sludge to low organic matter and clay content soils at moderate application rates enhances soil organic carbon and increases metal retention capacity.  相似文献   

3.
Abstract

The apparent recovery of applied zinc (Zn) by plants is very low in calcareous soils of Iran because most of it is retained by the soil solids. Subsamples of 24 surface soil (clay 130–530 g kg‐1; pH 7.7–8.4; electrical conductivity 0.63–3.10 dS m‐1; organic matter 6.0–22.0 g kg‐1; cation exchange capacity 8–20 cmol kg‐1; calcium carbonate (CaCO3) equivalent 180–460 g kg‐1) representing 13 soil series in three taxonomic orders were equilibrated with zinc sulphate (ZnSO4) solutions and the amount of Zn disappeared from solution after a 24‐h shaking period was taken as that adsorbed (retained) by the soil solids. The adsorption data were fitted to Freundlich (X=ACB) and Langmuir [X=(K‐bC)/(1+K#lbC)] adsorption isotherms. Backward stepwiseprocedure was used to obtain regression equations with isotherms coefficients as dependent and soil properties as independent variables. Freundlich A and Langmuir K were found to be highly significantly related to pH and clay and increasing as these soil properties increased. But Langmuir b was related only to clay and Freundlich B showed no significant relationship with any of the properties studied. The distribution coefficient (also called maximum buffering capacity), calculated as the product of Langmuir K and b, was also found to be highly significantly related to pH and clay. It is concluded that pH and clay content of calcareous soils are the most influential soil properties in retention of Zn.  相似文献   

4.
This study was to determine if diffusion of soil ammonium may explain why many sandy soils have greater nitrogen (N)–supplying capacity to rice than clay soils. A laboratory procedure using transient-state methods measured the linear movement of soil ammonium (NH4) in tubes packed with five field soils under aerobic conditions. Ammonium diffusion was measured by sectioning tubes after 48 h of equilibration and then measuring NH4 by steam distillation. Effective diffusion coefficients, De, and NH4 diffusion distance, d, per day ranged from De = 4.6 × 10?5 cm2 d?1 and 1.5 cm d?1 for Katy sandy loam to De = 2.9 × 10?7 cm2 d?1 and 0.11 cm d?1 for League clay. Ammonium diffusion distance d was strongly related to soil clay content and hence was predicted by d = Y × {[100/(% clay)] ? 1}, where Y is set to 0.1. Predicted d and measured d were highly related (R2 = 0.99).  相似文献   

5.
The sorption of zinc (Zn) by two acid tropical soils, Mazowe clay loam (kaolinitic, coarse, Rhodic Kandiustalf) and Bulawayo clay loam (coarse, kaolinitic, Lithic Rodustalf), was studied over a wide range of Zn solution concentrations. Samples of the two soils used in the experiments were collected at both uncleared, uncultivated (virgin) sites and cultivated sites. The two virgin soils showed similar abilities to bind Zn. Mazowe soil (40 g organic matter kg?1) presented the highest affinity for Zn. Yet, Bulawayo soil (23.5 g organic matter kg?1) sorbed almost the same amount. Bulawayo soil had higher pH and Fe and Mn-oxide content than Mazowe soil. Once cultivated, the two soils behaved quite differently. After 50 years, Mazowe soil had lost 60% of its organic matter and effective cation exchange capacity (ECEC). In this soil, Zn sorption capacity had also been decreased by 60%. Clearing and 10 years under cultivation had affected neither the organic matter content nor the ECEC of Bulawayo soil. For this soil, Zn sorption was even higher in the cultivated soil, presumably due to an increase in the amount of Fe and Mn oxide from subsoiling. Zinc sorption was dependent upon pH, with retention dramatically increasing in the pH range 6–7. Sorption occurred at pH values below the point of zero charge (PZC), indicating that the sorption reaction can proceed even in the presence of electrostatic repulsion between the positively charged soil surface and the cation. In the two soils, the reversibility of the sorption reaction was very low. More than 90% of the sorbed Zn was apparently strongly bonded.  相似文献   

6.
Counter-diffusion coefficients of Rb86 and Sr89 counter diffusing against H+ ions were measured in Dundee silt loam and Sharkey clay soils at differing soil bulk-densities. The cation exchange complex of each soil was saturated with either Rb+, Sr++, or H+ and washed free of salts before making diffusion measurements. The water content of the soil on an oven-dry weight basis was maintained at a constant value for all bulk-densities; 14.2 and 28.0 per cent for the Dundee and Sharkey soils respectively. These moisture contents correspond to a tension of 2/3 bar for sieved soil. The diffusion coefficients were dependent upon concentration. Average counter-diffusion coefficients were calculated and related to soil bulk-density. Soil compaction of Dundee silt loam had little or no effect upon the counter diffusion of Rb86. The average counter-diffusion coefficients of Sr89 in Dundee silt loam and Sharkey clay were significantly and linearly related to bulk-density; as bulk-density increased the average counter-diffusion coefficients increased. The average counter-diffusion coefficients were approximately 0.5–0.75 of the corresponding self-diffusion coefficients measured previously in these soils. The applicability of counter- and self-diffusion data to practical field problems are discussed.  相似文献   

7.
We carried out mid-infrared (mid-IR) spectral interpretation of soils 0–5 and 5–15 cm deep in selected alternative crop rotations (ACR) treatments and an adjacent native prairie soil. Ashing and spectral subtraction shows that absorbance at 3700–2850 and 1700–1550 cm?1 indicates organic absorbance. Prairie soils, with their greater carbon (C) content, have different spectral properties from the cropped soils. Prairie soils have greater absorbance at the 2950–2870 cm?1 and the 1230 cm?1 CH bands. The soils from the different depths had different spectral properties, with the soils 0–5 cm deep having stronger absorbance at the 1055 cm?1 carbohydrate band, at 1270–1460 cm?1, and at the 1730 cm?1 ester band. The soils 5–15 cm deep are characterized by greater absorbance at the clay band. Soil C and nitrogen (N) correlated negatively with the 3700 cm?1 clay band and the 1830 cm?1 quartz band and correlated positively with the 2920 cm?1 because of aliphatic CH absorbance.  相似文献   

8.
A sample of Harwell soil containing 36 percent fine clay (< 0.3 μm) and 14 per cent coarse clay plus fine silt (0.3–5μm) was separated into fractions, and the K-supplying power of soil and fractions measured by cropping with ryegrass, exchange with Ca resin and double-label isotopic exchange with 42K and 45Ca ions. Mineralogical examination of the fractions coupled with the cropping experiments showed that the K-supplying power of the soil to ryegrass can be explained by the presence of a zeolite, clinoptilolite-heulandite, in addition to the clay minerals, mica, and interstratified illitic smectite, commonly found in a glauconitic clay-rich soil. The 0.3–5 μm fraction, containing much zeolite, has an exchange diffusion coefficient for K ions to Ca resin of 1.8 × 10?16 cm2sec?1 compared with a value of 5.7 × 10?20 for the < 0.3μm fractions in which interstratified illitic smectite is the dominant mineral. Isotopic exchange shows that all Ca ions in fractions < 50μm are isotopically exchangeable. In fractions coarser than 20μm, some of the K ions in felspar and mica were not exchangeable within the duration of the experiments.  相似文献   

9.
Abstract

Sorption of zinc (Zn) in a calcareous soil was studied using a miscible displacement procedure. Sorption of Zn in soil can be described by a second‐order equation and by a diffusion equation based on the overall higher value of correlation coefficient and the lower value of standard error. The results show that the sorption of Zn in soil was increased by elevated temperature and pH. The maximum of Zn sorbed in soil increased, but the rate coefficient decreased with increasing pH. The maximum of sorbed Zn and rate coefficient tended to increase with elevated temperature. The value of activation energy (Ea) estimated with different kinetic equations was found to be variable and in the range of 5.0–17 kJ.mol‐1. The relative diffusion rate coefficient (D/r2), estimated using a diffusion equation, was found to be in the order of 10‐6 sec‐1. The intra‐aggregate diffusion and/or film diffusion of Zn may be a rate‐limiting process in the sorption of Zn in soils.  相似文献   

10.
Abstract

Zinc (Zn) deficiency is a widespread micronutrient disorder in crops grown in calcareous soils; therefore, we conducted a nutrient indexing of farmer‐grown rainfed wheat (Triticum aestivum, cv. Pak‐81) in 1.82 Mha Potohar plateau of Pakistan by sampling up to 30 cm tall whole shoots and associated soils. The crop was Zn deficient in more than 80% of the sampled fields, and a good agreement existed between plant Zn concentration and surface soil AB‐DTPA Zn content (r=0.52; p≤0.01). Contour maps of the sampled areas, prepared by geostatistical analysis techniques and computer graphics, delineated areas of Zn deficiency and, thus, would help focus future research and development. In two field experiments on rainfed wheat grown in alkaline Zn‐deficient Typic Haplustalfs (AB‐DTPA Zn, 0.49–0.52 mg kg?1), soil‐applied Zn increased grain yield up to 12% over control. Fertilizer requirement for near‐maximum wheat grain yield was 2.0 kg Zn ha?1, with a VCR of 4∶1. Zinc content in mature grain was a good indicator of soil Zn availability status, and plant tissue critical Zn concentration ranges appear to be 16–20 mg kg?1 in young whole shoots, 12–16 mg kg?1 in flag leaves, and 20–24 mg Zn kg?1 in mature grains.  相似文献   

11.
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12.
Increased zinc (Zn) concentration in seed may sometimes improve human health. The influence of rate and placement of three Zn sources (ZnEDTA, ZnSO4, and Rayplex‐Zn) on Zn concentration in navy bean (Phaseolus vulgaris L.) seed grown on a Calciaquoll was studied in the greenhouse. Application of 4 and 8 mg Zn/kg mixed throughout the soil increased seed Zn concentration by approximately 60 and 68%, respectively, and the responses were similar with the three Zn sources. The mixed‐throughout‐the‐soil ZnEDTA, ZnSO4, and Rayplex‐Zn treatments applied at 8 mg Zn/kg reduced seed phosphorus (P) concentration by 10,13, and 15%, respectively. The corresponding reductions with 4 mg Zn/kg were 10, 8, and 13%, respectively. Banding ZnEDTA, ZnSO4, and Rayplex‐Zn at 4 mg Zn/kg in 17‐cm‐long, 3‐cm‐deep bands reduced seed Zn concentration by 8, 34, and 31 % compared to their mixed‐throughout‐the‐soil counterparts. A significant Zn source x placement interaction resulted from marked reduction in Zn uptake as a result of banding ZnSO4 and Rayplex‐Zn. Banding of ZnSO4 and Rayplex‐Zn in calcareous soils is less likely to increase the Zn concentration of navy bean seed than is banding of ZnEDTA.  相似文献   

13.
A cloud point extraction (CPE) procedure has been developed for the determination of water-soluble and acid-soluble zinc (Zn) in soils by flame atomic absorption spectrometry. Deionized water and 0.1 mol L–1 hydrochloric acid (HCl) were selected as extracting agents. In the proposed approach, 2-(5-bromo-2-pyridylazo)-5-diethylam-inophenol (5-Br-PADAP) was used as a chelating agent, and polyethylene glycol octyl phenyl ether (OP) was selected as the surfactant. Some factors including the pH of analytical solution, concentrations of the chelating agent and surfactant, equilibration temperature and time, and salt effect, which would affect the extraction efficiency and subsequent determination of Zn, were studied and optimized. Under the optimized conditions, the calibration graph was linear in the range of 5.0?×?10–3 to 0.5 μg mL–1, and preconcentration of 20 mL sample solution gave an enhancement factor of 25. The detection limit was 4.93?×?10–3 μg mL–1. Recoveries in the range of 95.0–110% were obtained. Some metal ions including iron (Fe2+), cobalt (Co2+), and manganese (Mn2+) would interfere with the determination of Zn. The interference from these ions can be eliminated using thiourea (0.5% w/v) and triethanolamine (0.5% w/v) as masking agents. The proposed method was applied to the determination of water-soluble and acid-soluble Zn in soils, which were collected from the suburbs of Zhengzhou, and satisfactory results were obtained. To have more understanding of the soils, we determined the total content of Zn in soils. The results showed that the water-soluble and acid-soluble Zn contents in different soils are not correlated with the total content. For example, the total content of Zn for the soil from a farm in north loop was very low, but the percentage of water-soluble Zn was very high.  相似文献   

14.
The concern for groundwater pollution by agrichemicals through solute movement within the soil is widespread. Zeolite is a type of soil amendment that is utilized to improve physical properties of soil and ameliorate polluted soil. The high negative charge of the zeolite and its open space structure allows adsorption and access of heavy metals and other cations and anions. The objectives of this research were (i) to determine the effects of different application rates of zeolite (0, 2, 4, and 8 g kg?1) on the immobile water content and mass exchange coefficient in a loam soil and then (ii) to determine the effects of optimum application rate of zeolite on the immobile water content and mass exchange coefficient of sandy loam and clay loam soils in saturated conditions by a mobile and immobile (MIM) model. In a disturbed soil column, a method was proposed for determination of MIM model parameters, that is, immobile water content (θim), mass exchange coefficient (α), and hydrodynamic dispersion coefficient (Dh). Breakthrough curves were obtained for different soil textures with different zeolite applications in three replicates, by miscible displacement of chloride (Cl?1) in disturbed soil column. Cl?1 breakthrough curves were evaluated in terms of the MIM model. The results showed that the pore water velocity calculated based on the total soil volumetric water content (θim+ θm) and real pore water velocity calculated based on the mobile water content (θm) increased in the loam soil with an increase in zeolite application rate, so that, between these different rates of zeolite application, the maximum value of pore water velocity and real pore water velocity occurred at zeolite application rates of 8.6 and 11.5 g kg?1, which are indicated as the optimum application rates. However, the comparison between different soils showed that the zeolite application rate of 8 g kg?1 could increase pore water velocity of sandy loam and loam soils by 31% more than that of clay loam soil. The immobile water content and mass exchange coefficient of loam soil were correlated with the zeolite application rate and reduced with an increase in the rate of applied zeolite. In a comparison between different soils at zeolite application rate of 8 g kg?1, the immobile water contents of the zeolite-treated soil decreased by 57%, 60%, and 39% on sandy loam, loam, and clay loam soils, respectively, compared with the untreated soil. Furthermore, zeolite application could reduce mass exchange coefficient by 9%, 43%, and 21% on sandy loam, loam, and clay loam soils, respectively. A positive linear relationship was found between θim and α. Zeolite application increased real pore water velocity of sandy loam soil by 39% and 46% compared with loam and clay loam soils, respectively. In other studies there was a decrease in ammonium and nitrate leaching due to the zeolite application, and therefore, an increase in real pore water velocity due to zeolite application in sandy loam soil, as compared with the loam and clay loam soils, may not show more rapid movement of solute and agrichemicals to the groundwater.  相似文献   

15.
Zinc solubility in clay and soil suspensions was controlled by chemisorption at pH 4.5 – 7.0. The solubility in clay mineral suspensions was in the order palygorskite < montmorillonite « kaolinite and reflected the high affinity of zinc to palygorskite and the high CEC of montmorillonite. The solubility in soil suspensions was in the order Haplustoll < Torrifluvents and reflected the effect of high CEC and organic matter content of the first. The slopes of the pH-pZn curves, calculated zinc potential and sequential desorption data suggested that Zn++ ? Zn(OH)2 aqueous controlled the solubility of zinc in soil and clay mineral suspensions at pH 7.5 – 9.0. The slopes of the pH–pZn curves of two soils were, however, modified by the possible peptization of organic matter and Zn(OH)2.  相似文献   

16.
Abstract

Zinc adsorption by 10 (pH 4.0–6.5) cultivated mineral soils from Finland was studied in batch experiments. Additions of Zn ranged up to 600 mg kg?1 of soil and the corresponding equilibrium concentrations were 0.1–13 mg 1?1. In each soil, Zn adsorption conformed to the Freundlich isotherm. Despite a relatively low initial Zn adsorption by the acidic soils, each of the soils proved to have a high potential to adsorb Zn, but the capacity was highly pH dependent. In addition to the conventional Freundlich adsorption isotherms, calculated separately for each soil, extended Freundlich-type isotherms that also incorporate soil pH and other soil characteristics were used to describe Zn adsorption of several soils simultaneously in one equation. The pH-dependent Freundlich adsorption isotherm proved to serve as a practical tool to assess Zn adsorption by soils varying in pH and other characteristics.  相似文献   

17.
ASSESSMENT OF SOIL POTASSIUM RESERVES AVAILABLE TO PLANT ROOTS   总被引：1，自引：0，他引：1  
Successive extraction with Ca-saturated sulphonated resin is used to remove potassium from soils. The kinetics of K-release are analysed mathematícally to define three simultaneous rate processes by the amounts and rate-functions associated with them. The diffusion coefficient (3 × 10-19 cm2 sec-1) calculated for the slowest process (suggested to be from the mineral matrix) is of the same magnitude as that for illitic clay minerals. The effect of K manuring on these parameters is evaluated from measurements on soils from the Nil and K-fertilised plots of the Rothamsted Classical Experiments. Based on this analysis, a procedure is suggested for deriving from a smaller number of observations the amount of K a soil would release in a given time, and the contribution of each process to this amount is demonstrated.  相似文献   

18.
The self diffusion coefficients of zinc (DaZn), determined by half cell technique, were found to be greatly influenced by variations in soil characteristics such as volumetric moisture content, bulk density, temperature, carrier zinc concentration and soil pH. The DaZn values showed exponential decrease with increase in soil pH but with increasing volumetric moisture content, DaZn values showed logarithmic increase. The highest DaZn value was obtained at a compaction of 1.50 g/cm3. Increase in temperature from 5°C to 30°C showed 4 to 20 times increase in DaZn values. An attempt was made to study the relationship between soil characteristics and DaZn values for 87 illitic soils differing in physical and chemical properties. The simple and multiple correlation coefficients did not account for more than 21 per cent of variations indicating that DaZn values cannot be predicted accurately from soil properties.  相似文献   

19.

Purpose

In view that soils are bodies and that processes such as storage and release of water, carbon, nutrients and pollutants, and aeration and rooting happen in these bodies, it is of interest to know the density of elements and compounds in soils. On the basis of soil bulk and element density of organic carbon (OC), N, and heavy metals in soils and of horizon thickness, stocks of these elements for garden soils were calculated.

Materials and methods

Fourteen gardens in four allotments of the northwestern part of the Ruhr area, Germany were investigated. The research included 14 vegetable patches, 13 lawns, 2 compost heaps, and 1 meadow. Volume samples were taken. The soil analysis included pH, soil bulk density, and OC, N, Pb, Cd, Zn, Cu, and Ni contents.

Results and discussion

The soils were from sandy loam to loamy sand. The pH was slightly acid and C/N ratio about 20. Soil bulk density was between 0.8 and 1.4 g cm?3 and mean bulk density was 1.1 g cm?3. Mean OC content was for compost 7.4 %, vegetable patches 5.2 % (0–30 cm depth), and lawns and meadow 5.8 and 5.2 % (0–5 cm depth). OC density for compost was 76 mg cm?3, vegetable patches 56 mg cm?3, and lawns 67 mg cm?3 (0–5 cm). Mean OC stock in 0–30 cm soil depth in vegetable patches was 16.4 kg m?2, lawns 15.5 kg m?2, and meadow 11.1 kg m?2. N contents were between 0.06 and 0.46 %. For compost, the mean was 0.39 %, vegetable patches 0.27 % (0–30 cm), lawn 0.28 %, and meadow 0.26 % (0–5 cm). Mean stock of N in 0–30 cm depth for vegetable patches was 0.84 kg m?2, lawn 0.76 kg m?2, and meadow 0.55 kg m?2. For heavy metals in compost, vegetable patches, lawn and meadow, Cd contents were in the range of 1.7 to 3.0 mg kg?1, Pb 49 to 152 mg kg?1, and Zn 52 to 1830 mg kg?1. The amounts stored per square meters in 30 cm depth were for Cd 0.6–1.1 g, Pb 15–52 g, Zn 41–440 g, Cu 4–39 g, and Ni 1–8 g.

Conclusions

Allotment gardens have a high capacity to store CO2 as OC. Roughly, there will be 7–8 million tons of OC stored in the 1.3 million allotment gardens of Germany. The high amount of 8000 kg N ha?1 could damage the groundwater when released by wrong soil management. Cd, Zn, Pb, Cu, and Ni amounts of 7.8, 1000, 300, 135, and 30 kg ha?1, respectively, are a lasting burden.
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20.
Rate of zinc (Zn) release from solid to solution phase by organic acids can influence Zn availability in calcareous soils. The objective of the present study was to investigate the effect of different concentrations (1.1, 2.2, and 3.3 mM) of oxalic acid and citric acid on the kinetic release of Zn from two calcareous soils from Eastern Iran. The two organic acids showed significant difference in Zn release from studied soils. Cumulative Zn release during 72 h ranged from 5.85 to 10.4 mg kg?1 in soil 1 and ranged from 8.7 to 16.9 mg kg?1 in soil 2 using different concentrations of oxalic acid. The amount of cumulative Zn release after 72 h in soil 1 ranged from 13.65 to 28.77 mg kg?1 and from 17.63 to 23.13 mg kg?1 when different concentrations of citric acid was used. In general, Citric acid released 38% more Zn from soils than oxalic acid. The release of Zn from soils increased with citric acid concentration but decreased with increasing of oxalic acid concentrations in the solution. The simplified Elovich equation best described Zn release as a function of time (r2 = 0.93 and SE = 0.78). From the present study, Zn release from soils can be limited by the higher concentration of oxalic acid, while citric acid is suitable for enhancing soil lability of Zn.  相似文献   

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