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1.
A 90‐day laboratory incubation study was carried out using six contrasting subtropical soils (calcareous, peat, saline, noncalcareous, terrace, and acid sulfate) from Bangladesh. A control treatment without nitrogen (N) application was compared with treatments where urea, ammonium sulfate (AS), and ammonium nitrate (AN) were applied at a rate of 100 mg N (kg soil) –1. To study the effect of N fertilizers on soil carbon (C) turnover, the CO 2‐C flux was determined at nine sampling dates during the incubation, and the total loss of soil carbon (TC) was calculated. Nitrogen turnover was characterized by measuring net nitrogen mineralization (NNM) and net nitrification (NN). Simple and stepwise multiple regressions were calculated between CO 2‐C flux, TC, NNM, and NN on the one hand and selected soil properties (organic C, total N, C : N ratio, CEC, pH, clay and sand content) on the other hand. In general, CO 2‐C fluxes were clearly higher during the first 2 weeks of the incubation compared to the later phases. Soils with high pH and/or indigenous C displayed the highest CO 2‐C flux. However, soils having low C levels ( i.e., calcareous and terrace soils) displayed a large relative TC loss (up to 22.3%) and the added N–induced TC loss from these soils reached a maximum of 10.6%. Loss of TC differed depending on the N treatments (urea > AS > AN >> control). Significantly higher NNM was found in the acidic soils (terrace and acid sulfate). On average, NNM after urea application was higher than for AS and AN (80.3 vs. 71.9 and 70.9 N (kg soil) –1, respectively). However, specific interactions between N‐fertilizer form and soil type have to be taken into consideration. High pH soils displayed larger NN (75.9–98.1 mg N (kg soil) –1) than low pH soils. Averaged over the six soils, NN after application of urea and AS (83.3 and 82.2 mg N (kg soil) –1, respectively) was significantly higher than after application of AN (60.6 mg N (kg soil) –1). Significant relationships were found between total CO 2 flux and certain soil properties (organic C, total N, CEC, clay and sand content). The most important soil property for NNM as well as NN was soil pH, showing a correlation coefficient of –0.33** and 0.45***, respectively. The results indicate that application of urea to acidic soils and AS to high‐pH soils could be an effective measure to improve the availability of added N for crop uptake. 相似文献
2.
The electric charge characteristics of four Ando soils (A 1 and μA 1) and a Chernozemic soil (Ap) were studied by measuring retention of NH 4+ and Cl – at different pH values and NH 4Cl concentrations. No positive charge appeared in the Ando soils at pH values 5 to 8.5 except for one containing allophane and imogolite. The magnitude of their negative charge (CEC; meq/l00g soil) was dependent on pH and NH 4Cl concentration (C; N) as represented by a regression equation: log CEC = a pH + b log C + c, where the values of a and b were 0.113–0.342 and 0.101–0.315, respectively. Unlike the Chernozemic soil, Ando soils containing allophane, imogolite, and/or 2:1–2:1:1 layer silicate intergrades and humus showed a marked reduction of cation retention as pH decreased from 7 to 5. This was attributed to the charge characteristics of the clay minerals and to the carboxyl groups in humus being blocked by Al and Fe. 相似文献
3.
Recent studies indicate that aerobic rice can suffer injury from ammonia toxicity when urea is applied at seeding. Urea application rate and soil properties influence the accumulation of ammonia in the vicinity of recently sown seeds and hence influence the risk of ammonia toxicity. The objectives of this study were to (i) evaluate the effects of urea rate on ammonia volatilization and subsequent seed germination for a range of soils, (ii) establish a critical level for ammonia toxicity in germinating rice seeds and (iii) assess how variation in soil properties influences ammonia accumulation. Volatilized ammonia and seed germination were measured in two micro‐diffusion incubations using 15 soils to which urea was applied at five rates (0, 0.25, 0.5, 0.75 and 1.0 g N kg ?1 soil). Progressively larger urea rates increased volatilization, decreased germination and indicated a critical level for ammonia toxicity of approximately 7 mg N kg ?1. Stepwise regression of the first three principal components indicated that the initial pH and soil texture components influenced ammonia volatilization when no N was added. At the intermediate N rate all three components (initial pH, soil texture and pH buffering) affected ammonia volatilization. At the largest N rate, ammonia volatilization was driven by soil texture and pH buffering while the role of initial pH was insignificant. For soils with an initial pH > 6.0 the risk of excessive volatilization increased dramatically when clay content was <150 mg kg ?1, cation exchange capacity (CEC) was <10 cmol c kg ?1 and the buffer capacity (BC) was <2.5 cmol c kg ?1 pH ?1. These findings suggest that initial pH, CEC, soil texture and BC should all be used to assess the site‐specific risks of urea‐induced ammonia toxicity in aerobic rice. 相似文献
4.
PurposeThe majority of biochar studies use soils with only a narrow range of properties making generalizations about the effects of biochar on soils difficult. In this study, we aimed to identify soil properties that determine the performance of biochar produced at high temperature (700 °C) on soil pH, cation exchange capacity (CEC), and exchangeable base cation (Ca2+, K+, and Mg2+) content across a wide range of soil physicochemical properties. Materials and methodsTen distinct soils with varying physicochemical properties were incubated for 12 weeks with four rates of biochar application (0.5, 2, 4, and 8% w/w). Soil pH, CEC, and exchangeable base cations (Ca2+, K+, and Mg2+) were determined on the 7th and 84th day of incubation. Results and discussionOur results indicate that the highest biochar application rate (8%) was more effective at altering soil properties than lower biochar rates. Application of 8% biochar increased pH significantly in all incubated soils, with the increment ranging up to 1.17 pH unit. Biochar induced both an increment and a decline in soil CEC ranging up to 35.4 and 7.9%, respectively, at a biochar application rate of 8%. Similarly, biochar induced increments in exchangeable Ca2+ up to 38.6% and declines up to 11.4%, at an 8% biochar application rate. The increment in CEC and exchangeable Ca2+ content was found in soils with lower starting exchangeable Ca2+ contents than the biochar added, while decreases were observed in soils with higher exchangeable Ca2+ contents than the biochar. The original pH, CEC, exchangeable Ca2+, and texture of the soils represented the most crucial factors for determining the amount of change in soil pH, CEC, and exchangeable Ca2+ content. ConclusionsOur findings clearly demonstrate that application of a uniform biochar to a range of soils under equivalent environmental conditions induced two contradicting effects on soil properties including soil CEC and exchangeable Ca2+ content. Therefore, knowledge of both biochar and soil properties will substantially improve prediction of biochar application efficiency to improve soil properties. Among important soil properties, soil exchangeable Ca2+ content is the primary factor controlling the direction of biochar-induced change in soil CEC and exchangeable Ca2+ content. Generally, biochar can induce changes in soil pH, CEC, and exchangeable Ca2+, K+, and Mg2+ with the effectiveness and magnitude of change closely related to the soil’s original properties. 相似文献
5.
Heavy metal distribution and clay contents in soils . In soil profiles differing considerably in horizon pattern and parent material the contents of Mn, Zn, Cu and Co were correlated with those of clay (and CEC), of total Fe (and dithionite soluble Fe) and - after relation to clay - with C. The correlations with clay, CEC, Fe t and Fe d were in all cases positive and highly significant, though differing between the different metals and between the references. Deviations for all elements are due to lithogenic differences in soils from mesozoic sediments and for Mn also due to its lower pedogenic stability. The correlations with C were not significant, since O horizons were not yet investigated. The ‘mobility’ of the heavy metals ( = EDTA + NH 4O Ac-extractable in relation to total amount) in topsoils could be more correlated (negative) with the reserves than with other soil features. Relating the ‘immobile’ heavy metal contents to the other soil features considerably improved the correlations. 相似文献
6.
Phosphorus (P) adsorbed by iron (Fe) oxyhydroxides in soil can be released when the Fe(III) minerals are reductively dissolved after soil flooding. However, this release is limited in tropical soils with large Fe contents and previous studies have suggested that P sorbs or precipitates with newly formed Fe(II) minerals. This hypothesis is tested here by scavenging Fe 2+ in flooded soils by increasing the cation exchange capacity (CEC) of soil through resin application (30 cmol c kg ?1; Na‐form). Three soils from rice paddies with contrasting properties were incubated in aerobic and anaerobic conditions with or without resin and with or without addition of organic matter (OM) to stimulate redox reactions. Dissolved Fe was 0.1–1.1 mm in unamended anaerobic soils and decreased to less than 0.07 mm with resin addition. Anaerobic soils without resin and aerobic soils with or without resin had marginal available P concentrations (<2 mg P kg ?1; anion‐exchange membrane P). In contrast, available P increased 3‐ to 14‐fold in anaerobic soils treated with resins, reaching 16 mg P kg ?1 in combination with extra OM. Application of Ca‐forms of resin did not stimulate P availability and dissolved Ca concentrations were larger than in unamended soils. Resin addition can increase P availability, probably by a combination of reducing solution Fe 2+ (thereby limiting the formation of Fe(II) minerals) and increasing the OM solubility and availability through reducing dissolved Ca 2+. The soil CEC is a factor controlling the net P release in submerged soils. 相似文献
7.
The island of Milos (Greece), part of the South Aegean volcanic arc with a typical Mediterranean climate, is covered with volcanic deposits of different ages. The objective of this study was to investigate the physicochemical and mineralogical properties of the soils developing on these volcanic deposits and their classification. Samples were taken from seven locations of soil on different parent material and of different ages. There were substantial differences in their particle size distribution, with sand ranging from 19% to 92%, silt from 3.5% to 50%, and clay from 5% to 46%. Organic matter content was low (< 2.0%). The soil pH ranged from 5.6 to 8.0. In two of the profiles, CaCO 3 equivalents of 1.4% to 24.6% were found and a calcic horizon identified. The cation exchange capacity (CEC) and specific surface area (SSA) varied between profiles ranging from 3 cmol (+) kg − 1 to 47 cmol (+) kg − 1 and 30 m 2 g − 1 to 380 m 2 g − 1, respectively. The soils exhibited high base saturation. The amounts of Al, Fe and Si extracted with ammonium oxalate (Αl o, Fe o and Si o) were particularly low (< 0.1%, < 0.17%, and < 0.1%, respectively) which demonstrates the absence of amorphous clay-silicate minerals (allophane). Fe extracted with dithionite citrate bicarbonate — DCB (Fe d) was greater than Fe o sharing the dominance of crystalline Fe oxides. Al and Si extracted with hot 0.5 M NaOH (Al 2Ο 3NaOH and SiΟ 2NaOH) and with Τiron-C 6H 4Na 2O 8S 2, (Al 2Ο 3Τ and SiΟ 2Τ). SiΟ 2NaOH and SiΟ 2Τ were particularly high (mean values 3.4% and 4.5%, respectively), showing that amorphous silica was present. The clay fraction of the soil was dominated by the presence of 2:1 (vermiculite and smectite) and 1:1 (kaolinite) clay-silicates. Al o+ 1/2Fe o was low (< 0.18%), while the P-retention in most soils was less than 15%. These soils do not exhibit andic properties and hence cannot be classified as Andisols. The silica saturation index (ISS) may be used for these soils to describe a pedogenetic environment rich in Si which favours the formation of pedogenic amorphous silica. The climate is the major determinant of the evolution of these soils. 相似文献
8.
The electrokinetic behavior of colloidal particles in three waterlogged soils at 38°C was investigated with reference to the stability changes of soil colloidal suspensions under reductive conditions. The dispersed clay particles of the three soils exhibited a negative zeta (ζ) potential. The absolute value of the ζ-potential, |-ζ|, of these soils in the earlier period of waterlogging decreased, which caused the flocculation of clay particles. The concentrations of divalent cations, i.e., Fe 2+ and Ca 2+ in the soil solutions were estimated to be higher than their critical flocculation concentrations (CFCs) on the basis of the observed CFCs of Fe 2+ and Ca 2+ for the clay suspension of halloysite as a reference. With the progression of the reduction process, clay particles of one soil still exhibited a low |- ζ| and flocculated. The concentrations of Fe 2+ and Ca 2+ in the soil solutions were estimated to be higher than their CFCs, respectively. The clay particles of two sandy soils, however, showed an increase in |- ζ| due to the increase in pH and dispersed. The concentrations of Fe 2+ and Ca 2+ in the soil solutions were estimated to be lower than their CFCs, respectively. The stability changes of the soil colloidal suspensions by these divalent cations under sequential soil-reduction can be explained by the alteration of the Stern potential (- ψ s ), which determines the repulsion energy related to the potential energy of interaction between two particles. The apparent decrease in the Ca 2+ concentration of the soil solutions in the later period of waterlogging was explained largely by the re-adsorption of water-soluble Ca 2+ on the exchange sites of soil clays with the decrease in the Fe 2+ concentration in the soil solution. 相似文献
9.
Abstract Eight methods to determine exchangeable cations and cation exchange capacity (CEC) were compared for some highly weathered benchmark soils of Alabama. The methods were: (1) 1N NH 4OAc at pH 7.0 by replacement (for CEC only), (2) 1N NH 4OAc at pH 7.0 (summation of basic cations plus 1N KCl extractable Al), (3) 1N NH 4OAc at pH 7.0 (summation of basic cations plus exchangeable H +), (4) 0.1M BaCl 2 (summation of basic cations plus exchangeable Mn, Fe and Al), (5) Mehlich 1 (summation of basic cations plus 1N KCl extractable Al), (6) Mehlich 1 (summation of basic cations plus exchangeable H +), (7) Mehlich 3 (summation of basic cations plus 1N KCl extractable Al), and (8) Mehlich 3 (summation of basic cations plus exchangeable H +). The 0.1M BaCl 2 was chosen as the standard method for the highly weathered soils and the other methods compared to it. The results indicated that the 1N NH 4OAc replacement method gave significantly higher CEC values compared to the summation methods. This was probably due to the overestimation of the field CEC caused by measurement of pH dependent cation exchange sites in these soils. There was, however, close agreement between the BaCl 2 method and the summation methods that included extractable Al. The generally good agreement between these summation methods suggests that the Mehlich 1 and Mehlich 3 extractants, commonly used to determine available nutrients in the southeastem USA, may also be used to measure effective CEC of some acid‐rich sesquioxide benchmark soils of Alabama. However, 1N KCl extractable Al as opposed to exchangeable H + should be included in the computation. 相似文献
10.
Abstract Selected chemical properties of an artificially acidified agricultural soil from northern Idaho were evaluated in a laboratory study. Elemental S and Ca(OH) 2were used to manipulate the soil pH of a Latahco silt loam (fine‐silty, mixed, frigid Argiaquic Xeric Argialboll), which had an initial pH of 5.7. A 100 day incubation period resulted in a soil pH manipulation range of 3.3 to 7.0. Chemical properties evaluated included: N mineralization rate, extractable P, AI, Mn, Ca, Mg and K and CEC. N mineralization rate (assessed by anaerobic incubation) decreased with decreasing soil pH. Nitrification rate also decreased as NH 4 +‐N accumulated under acid soil conditions. Sodium acetate extractable P was positively linearly correlated (R 2= 0.87) with soil pH over the entire pH range evaluated. Potassium chloride extractable Al was less than 1.3 mg kg ‐1of soil at pH values higher than 4.4. Consequently, potential Al toxicity problems in these soils are minimal. Extractable Mn increased with decreasing soil pH. Soil CEC, extractable Mg, and extractable K all decreased with increasing soil pH from 3.3 to 7.0. Extractable Ca levels were largely unaffected by changing soil pH. It is likely that the availability of N and P would be the most adversely affected parameters by soil acidification 相似文献
11.
The roles of fine-earth materials in the cation exchange capacity (CEC) of especially homogenous units of the kaolinitic and oxyhydroxidic tropical soils are still unclear. The CEC (pH 7) of some coarse-textured soils from southeastern Nigeria were related to their total sand, coarse sand (CS), fine sand (FS), silt, clay, and organic-matter (OM) contents before and after partitioning the dataset into topsoils and subsoils and into very-low-, low-, and moderate-/high-stability soils. The soil-layer categories showed similar CEC values; the stability categories did not. The CEC increased with decreasing CS but with increasing FS. Silt correlated negatively with the CEC, except in the moderate- to high-stability soils. Conversely, clay and OM generally impacted positively on the CEC. The best-fitting linear CEC function (R 2, 68%) was attained with FS, clay, and OM with relative contributions of 26, 38, and 36%, respectively. However, more reliable models were attained after partitioning by soil layer (R 2, 71–76%) and by soil stability (R 2, 81–86%). Notably FS's contribution to CEC increased while clay's decreased with increasing soil stability. Clay alone satisfactorily modeled the CEC for the very-low-stability soils, whereas silt contributed more than OM to the CEC of the moderate- to high-stability soils. These results provide new evidence about the cation exchange behavior of FS, silt, and clay in structurally contrasting tropical soils. 相似文献
12.
15NO 3? was immobilized in a calcareous clay and a calcareous sandy soil during incubation of each soil with glucose and wheat straw. Changes in the distribution of immobilized 15N amongst soil extracts and soil fractions of different particle size and density were determined during periods of net N immobilization.The nature of the organic-C amendment, but not soil type, significantly influenced both the distribution of the immobilized 15N and the pattern of changes of the organic- 15N of soil fractions with time. In straw-amended soils, approx. 20% of the organic- 15N became associated with a light fraction, sp. gr. < 1.59, the remainder becoming distributed mainly amongst the silt and clay fractions. In glucoseamended soils, very little (< 1.2%) of the 15N was immobilized in the light fraction, sp. gr. < 1.59, most being rapidly distributed amongst the silt and clay fractions. During a period of complete immobilization, organic- 15N was transferred from the fine clay to the silt and coarse clay fractions.Silt, coarse clay and fine clay components from glucose-amended soils sampled at the end of the net immobilization phase were further fractionated densimetrically into light (sp. gr. < 2.06) and heavy (sp. gr. > 2.06) subfractions. The organic- 15N of respective light subfractions accounted for 43–64% of the total organic- 15N of the silt, 1–9% of that of the coarse clay and 19–21% of that of the fine clay fractions. 相似文献
13.
An investigation of the effect of aquic conditions on Fe-oxides distribution and magnetic susceptibility ( χlf) was conducted on selected soils from Southern Iran. Seven pairs of adjacent soil pedons with different soil moisture regimes (aquic and non-aquic), were selected. The average concentrations of poorly crystalline Fe (Fe o) and total free Fe (Fe d) in aquic soils were 0.2 and 0.07% respectively, and 0.45 and 0.9% in non-aquic soils, respectively. The ratio of Fe o/Fe d varied from 0.03 to 0.64. χlf ranged from 1.8 to 113 × 10 ?8 m 3 kg ?1 in the soil studied. The variation of χfd ranged from 0.0 to 9.65%. The χfd values observed in non-aquic soils were larger than in aquic soils (4.00% vs. 1.37%). Positive correlations were observed between χ and clay contents in both aquic and non-aquic soils; however, non-aquic soil samples showed a larger coefficient of determination. A positive correlation existed between χfd and χ in aquic and non-aquic soils. Higher values of χfd were observed at the soil surface of non-aquic soil samples than at deeper levels, suggesting a greater proportion of ultrafine grains. Of the soil properties that were assessed, clay, cation exchangeable capacity (CEC), Fe d, Fe o/Fe d ratio, χlf and χfd contents, changed significantly in response to the aquic condition. 相似文献
14.
The CEC was determined for humic acid preparations by changing the conditions for the CEC procedure and the CEC values obtained were compared with those of clay minerals. Humic acid was extracted from Kodonbaru and Kuriyagawa surface soils, Iwanuma peat, and straw with 0.1 M Na 4P 2O 7-0.l M NaOH. The CEC was measured by a method which eliminates washing for the removal of excess saturating salt. The CEC of humic acid became larger as humification progressed, and increased in the order: Straw<Iwanuma<Kuriyagawa<Kodonbaru. An equilibrium of cation exchange for the humic acid preparations was attained in a short time in contrast with that for allophane. No effect of salt concentration on the CEC of the humic acid preparations was recognized. The CEC of humic acid was also determine using the procedure in which tbe excess salt was removed by washing with water. Practically no decrease of CEC with decreasing salt concentration was found. When the pH of the salt solution WBB reduced, the em: of the humic acid decreased, though the extent of the decrease was smaller than that of allophane. The CEC of halloysite and montmorillonite did not decrease through reduction of the pH of the salt solution. It was considered that humic acid is a stronger acid than allophane and a weaker acid than halloysite and montmorillonite. The difference between the CEC of humic add measured with Ca 2+ and Ba 2+ was small. Little temperature effect was observed for humic acid. 相似文献
15.
The sorption of chromium (Cr) species to soil has become the focus of research as it dictates the bioavailability and also the magnitude of toxicity of Cr. The sorption of two environmentally important Cr species [Cr(III) and Cr(VI)] was examined using batch sorption, and the data were fitted to Langmuir and Freundlich adsorption isotherms. The effects of soil properties such as pH, CEC, organic matter (OM), clay, water-extractable SO 4 2– and PO 4 3–, surface charge, and different iron (Fe) fractions of 12 different Australian representative soils on the sorption, and mobility of Cr(III) and Cr(VI) were examined. The amount of sorption as shown by K f was higher for Cr(III) than Cr(VI) in all tested soils. Further, the amount of Cr(III) sorbed increased with an increase in pH, CEC, clay, and OM of soils. Conversely, the chemical properties of soil such as positive charge and Fe (crystalline) had a noticeable influence on the sorption of Cr(VI). Desorption of Cr(VI) occurred rapidly and was greater than desorption of Cr(III) in soils. The mobility of Cr species as estimated by the retardation factor was higher for Cr(VI) than for Cr(III) in all tested soils. These results concurred with the results from leaching experiments which showed higher leaching of Cr(VI) than Cr(III) in both acidic and alkaline soils indicating the higher mobility of Cr(VI) in a wide range of soils. This study demonstrated that Cr(VI) is more mobile and will be bioavailable in soils regardless of soil properties and if not remediated may eventually pose a severe threat to biota. 相似文献
16.
The structural stability of eight samples representing three soil profiles from tropical and subtropical regions of China (Latosol, Red Earth and Yellow Brown Earth) was studied by dispersion treatments. The samples were treated with the following solutions in order without previous mechanical disruption: (I) H 2O, (II) 0.1 N NaCl, (III) 0.002% Na 2CO 3, (IV) 0.1 N NaOH, (V) acid oxalate, (VI) 0.1N NaOH. These procedures were designed to disperse soil samples by removal of potentially aggregating substances and by anion adsorption. After each treatment the clay dispersed was separated by sedimentation and its mineralogical composition was studied by XRD, Mössbauer spectroscopy and magnetic susceptibility measurements to assess the role of mineralogy in the maintenance of soil structure. The amounts of iron extracted by Na-dithionite–citrate–bicarbonate were 9.6–10.8% in the Latosol, 3.1–3.4% in the Red Earth and 0.9–2.1% in the Yellow Brown Earth. It was concentrated in clay fractions and existed mainly as superdispersed particles. The hematite/goethite ratio varied from 1.7 for the Latosol to 0.2 for the Yellow Brown Earth. The clay fraction of the Yellow Brown Earth is vermiculitic and has a permanent negative charge. This soil's structural stability is mainly influenced by exchangeable Ca 2+. In the Latosol and the Red Earth, surfaces with variable (pH-dependent) charges prevail because of the large free Fe-oxides contents. Alkaline treatment (IV) promoted most dispersion of these soils, indicating the mainly electrostatic nature of interactions between mineral particles. Thus, the role of the Fe oxide minerals in these soils is one of aggregation rather than cementation. The aggregation properties of the Latosol and Red Earth are relict paleosol features inherited from an earlier period of cooler and wetter climate than the present. 相似文献
17.
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
18.
Laboratory experiments were conducted with sodic soils of varying exchangeable sodium percentage (ESP) (82, 65, 40, and 22) and a normal soil (ESP 4) to study the changes with time in soil pH, pCO 2, Fe 2+ and Mn 2+ under submerged conditions with and without 1.0 per cent rice husk. In all the soils pCO 2, Fe 2+ and Mn 2+ increased after flooding, reached the maximum value and then either maintained or declined slightly. The release of Fe 2+ and Mn 2+ was maximum in normal soil and decreased with increase of ESP in sodic soils. Addition of rice husk brought about a conspicuous increase in Fe 2+ and Mn 2+, the maximum increase being in lowest ESP soil. Flooding reduced the pH of all soils. The effect was more pronounced in the presence of rice husk. The kinetics of pCO 2 indicated that accumulation of CO 2 was higher in normal soil and least in highest ESP soil. The addition of rice husk showed an average increase of 0.0074 atm pCO 2 in comparison to rice husk untreated soils. 相似文献
19.
Abstract Soil cation exchange capacity (CEC) measurements are important criteria for soil fertility management, vaste disposal on soils, and soil taxonomy. The objective of this research was to compare CEC values for arable Ultisols from the humid region of the United States as determined by procedures varying widely in their chemical conditions during measurement. Exchangeable cation quantities determined in the course of two of the CEC procedures were also evaluated. The six procedures evaluated were: (1) summation of N NH 4OAc (pH 7.0) exchangeable Ca, Mg, K, and Na plus BaCl 2 ‐ TEA (pH 8.0) exchangeable acidity; (2) N Ca(OAc) 2 (pH 7.0) saturation with Mg(OAc) 2 (pH 7.0) displacement of Ca 2+; (3) N NH 4OAc (pH 7.0) saturation with NaCl displacement of NH 4 +; (4) N MgCl 2 saturation with N KCl displacement of Mg 2+; (5) compulsive exchange of Mg 2+ for Ba 2+; and (6) summation of N NH 4OAc (pH 7.0) exchangeable Ca, Mg, K, and Na plus N KCl exchangeable AJ. The unbuffered procedures reflect the pH dependent CEC component to a greater degree than the buffered methods. The compulsive exchange and the summation of N NH 4OAc exchangeable cations plus N KCl exchangeable Al procedures gave CEC estimates of the same magnitude that reflect differences in soil pH and texture. The buffered procedures, particularly the summation of N NH 4OAc exchangeable cations plus BaCl 2 ‐ TEA (pH 8.0) exchangeable acidity, indicated inflated CEC values for these acid Ultisols that are seldom limed above pH 6.5. Exchangeable soil Ca and Mg levels determined from extraction with 0.1 M BaCl 2 were consistently greater than values for the N NH 4Oac (pH 7.0) extractions. The Ba 2+ ion is apparently a more efficient displacing agent than the NH 4 + ion. Also, the potential for dissolving unreacted limestone is greater for the Ba 2 + procedures than in the NH 4 + extraction. 相似文献
20.
Laboratory and greenhouse experiments were conducted to determine the influence of soil properties on adsorption and desorption of boron (B) as well as to estimate the degree of reversibility of adsorption reactions. The utility of Freundlich and Langmuir equations for characterizing the plant availability of applied B in soils was established using soybean [ Glycine max (L.) Merr.] as a test crop. The adsorption-desorption study revealed that Fe 2O 3 and clay were primarily responsible for retaining added B in all the 25 different soils under investigation. Organic carbon, pH and cation exchange capacity (CEC) positively influenced the adsorption of B while free Fe 2O 3, organic carbon and clay retarded release of B from these soils. The degree of irreversibility (hysteresis) of B adsorption/desorption increased with increase in organic carbon and CEC of these soils. Freundlich isotherm proved more effective in describing B adsorption in soils as compared to Langmuir equation. The split Langmuir isotherm demonstrated that any of the adsorption maxima, calculated from lower, upper or entire isotherm, could be of practical use. Contrary, bonding energy coefficient, calculated either at lower or higher equilibrium concentration failed to show any practical benefit. Regression models as a function of B application rate and adsorption equation parameters to predict B uptake from applied B, demonstrated the utility of Langmuir and Freundlich equation parameters. 相似文献
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