Factors affecting potassium fixation in calcareous soils of southern Iran

Potassium fixation capacity and mineralogical analysis of 24 representative soils, collected from southern Iran, were studied. Potassium fixation analysis was performed by adding six rates of K from 0 to 1000 mg kg^?1 soil in a plastic beaker and shaking for 24 h. Mineralogical analysis showed that the clay fractions were dominated by smectite, chlorite, mica, palygorskite, vermiculite and quartz. In general, the studied soils fixed 8.5–55% of the added K. The potassium fixation capacity of the studied soils was significantly correlated with smectite content (r ² = 0.87), clay content (r ² = 0.60), cation-exchange capacity (r ² = 0.79) and NH₄OAc-K. Wetting and drying treatment and incubation time had significant effects on K fixation. The average percentage increase in K fixation following the wetting and drying treatment was 24 and 30% for surface and subsurface soils, respectively. The average percentage increase in K fixation with increasing residence time was 79 and 56% for surface and subsurface soils, respectively. Because K fixation is a diffusion process, time and increased concentration of soluble K (because of soil drying) are factors affecting the rate of K diffusion from a soil solution to the interlayer positions of the expansible 2:1 clay minerals.     

Kinetics of nonexchangeable‐potassium release and plant response in some calcareous soils

Nonexchangeable K⁺ constitutes a slowly available reserve that may significantly influence K⁺ fertility of soils. Laboratory and greenhouse experiments were conducted to characterize the K⁺ supply and nonexchangeable K⁺–release kinetics in 10 calcareous soils using 0.01 M CaCl₂ and 0.01 M oxalic acid extractions. Total K⁺ uptake by wheat (Triticum aestivum L.) grown in the greenhouse was used to measure plant‐available K⁺. The release of K⁺ was characterized by an initial fast rate followed by a slower rate. The nonlinear relationship in the early stages of the K⁺ release may be attributed to the edge sites, and release of K⁺ from interlayer exchange sites may be responsible for the second part of the K⁺ release. Kinetics of K⁺ release was described best with power function, which showed the best fit of the four models tested. Parameters of kinetics models in 0.01 M CaCl₂ were significantly related to K⁺ uptake by wheat. Potassium release was also correlated to initial NH₄OAc‐extratable K⁺ and to HNO₃‐extractable K⁺.     

铵、钾同时存在时, 土壤对铵的优先吸附

Ten soils collected from different parts of China were used in a series of experiments to study fixation of NH4^ and K^ by soils.When K^ was added concurrently with or prior to NH4^ ,the soils were found to fix more moles of NH4^ than those of K^ ,irrespective of the mole ratios of NH4^ to ^ that were added.     

Ability of sorption–desorption experiments to predict potassium leaching from calcareous soils

When potassium (K⁺) fertilizers are applied to the soil, K⁺ is subject to displacement through the soil profile. Leaching can play an important role in agricultural K⁺ losses that can decrease groundwater quality. To avoid overfertilization, estimation of K⁺ leaching from soil is important. The ability of the soils to retain K⁺ against leaching varies according to the adsorption coefficient of the soils. The aim of this study was to relate the K⁺ leaching from a wide range of calcareous soils to the values obtained from a sorption–desorption experiment. The soil columns were leached with 10 mM CaCl₂ solution and the leachate was analyzed for K⁺. The breakthrough curves for K⁺ were different, and the amounts of K⁺ leached varied considerably between different soils. In these calcareous soils where crops are irrigated with water containing significant concentrations of Ca²⁺ and other cations, large amounts of K⁺ will be leached. Cumulative K⁺ leached after five pore volumes leaching with 10 mM CaCl₂ was significantly (r = 0.776, p < 0.01) related to the equilibrium K⁺ concentration. The results of this study enabled us in many cases to estimate the K⁺ leaching from soil without conducting column experiments, minimizing the laborotary work.     

Potassium release from sand,silt and clay fractions in calcareous soils of southern Iran

The release of non-exchangeable potassium from 24 calcareous soils of divergent mineralogy, from southern Iran, was examined. Sand, silt and clay particles were fractionated after dispersion with an ultrasonic probe. Samples were extracted with 0.01 M CaCl₂ for 30 successive 2-h periods. The clay fraction released the largest amount of K in each soil. Cumulative K released ranged from 175 to 723, 35 to 128, and 71 to 146 mg kg^?1 contributing 20–90, 4–39 and 2–54% for clay, silt and sand fractions, respectively. The lower proportion of K released from sand and silt fractions can be explained by the presence of a high content of CaCO₃ and quartz in these fractions. The release kinetics for the non-exchangeable K data showed that parabolic diffusion and power function were the best fitting kinetic models. This indicated that slow diffusion of K from the mica interlayer positions is the main rate-controlling process. Cumulative K released and constant b values of parabolic diffusion model correlated significantly with the mica content of the clay fraction.     

Calcium carbonate solubilization through H‐proton release from some legumes grown in calcareous saline‐sodic soils

Increasing levels of CO₂ and H⁺ proton in the rhizosphere from some legumes may play an important role in calcite dissolution of calcareous salt affected soils. Soils planted with white and brown varieties of cowpea (Vigna unguiculata L.) and hyacinth bean (Dolichos lablab L.) relying on either fertilizer N (KNO₃) or N‐fixation were compared against soils to which gypsum was applied and a control without plants and gypsum application to study the possibility of Ca²⁺ release from calcite and Na⁺ leaching. As compared to plants relying on inorganic N, leachates from all pore volumes (0·5, 1·0, 1·5, 2·0 pore volume) in lysimeters planted with N‐fixing hyacinth bean contained significantly higher concentrations of HCO with lower concentrations from lysimeters planted with white cowpea relying on N‐fixation. However, the lowest concentrations of HCO were recorded in the gypsum and control treatments. In initial leaching, lysimeters planted with N‐fixing plants maintained similar leachate Ca²⁺ and Na⁺ concentrations compared to gypsum amended soils. However, gypsum amended soils were found to have a prolonged positive effect on Na⁺ removal. It might be concluded that some legumes that are known to fix N in calcareous salt affected soils may be an alternative ameliorant to the extremely expensive gypsum through calcite solubilization and a consequent release of Ca²⁺. Copyright © 2009 John Wiley & Sons, Ltd.     

Extraction of potassium from some kaolinitic soils of the tropics

Abstract

Three methods for soil potassium extraction (M NH₄OAc pH 7, 0.01 M AgTU and 30 % hot H₂SO₄) were compared for a variety of kaolinitic soils of the tropics. The AgTU‐extractable K was much higher than the M NH₄OAc‐extractable K when vermiculite clay was present in the soil. The correlation between both was given by an R value of 0.937. The amounts of K extracted by 0.01 M AgTU and by hot H₂SO₄ were approximately the same. The R value for these two methods was 0.843.

It is suggested that the AgTU extractant could be used for determination of plant‐available K in soil and for testing for the presence or absence of vermiculite clay in soils.     

Release of interlayer potassium in Norwegian grassland soils

Potassium (K) release from sources that are not initially exchangeable is attributed to depletion of interlayer K of micas and clay minerals or weathering of feldspars. The aim of the present study was to estimate the K release from interlayer K. Soil samples from 17 field experiments in ley on a range of mineral soils in Norway were used in the study. The change in K‐fixation capacity was used as an estimate of depletion of interlayer K. It was assumed that the increase in K‐fixation capacity during 3 yr of cropping was equivalent to the amount of K depleted from the interlayer positions. Mean K fixation increased in the majority of the soils during 3 yr of grass cropping both with and without K application. The increase in K fixation indicated that without K application, the K uptake from interlayer K amounted to 43%, 28%, and 26% of the K yield for clay soils, high‐K sandy soils, and low‐K sandy soils, respectively. Including K uptake from exchangeable K in the topsoil and from subsoil, the explained K uptake amounted to 79%, 69%, and 81% for the three groups of soil, respectively. Simple linear‐regression analyses showed that the change in K fixation during 3 yr of grass cropping was best explained by the percentage of clay in the soil.     

Potassium isotherm partitioning based on modified quantity‐intensity relation and potassium buffering characterization of soils of North India

Background : Potassium (K) availability in soil and plant uptake is restrained by the dynamic interactions among the different pools of K. Aims : To understand these interactions, a study was undertaken to assess the quantity–intensity (Q/I) and buffering characteristics of rainfed maize (Zea mays L.) growing soils. Ten contrasting soils were evaluated for K partitioning changes in exchangeable K (ΔEK) and non‐exchangeable K (ΔNEK) pools in the soil‐solution phase and buffering characteristics using a modified version of Q/I approach. Results : The partitioned Q/I isotherms showed strong adsorption with the increase in K concentration ratio (CR^K) and the changes due to ΔEK were higher than changes due to ΔNEK. Total buffering capacity (PBC^K) significantly correlated (r = 0.92, p <0.01) with clay content with a major share contributed by buffering capacity owing to non‐exchangeable K ( ${\mathrm{PBC}}_{\Delta \mathrm{NEK}}^K$) rather than exchangeable K ( ${\mathrm{PBC}}_{\Delta \mathrm{EK}}^K$). The fixation capacity (β) factor, the magnitude of added K converted into a non‐exchangeable pool, ranged from 41 to 63%, whereas release (α) factor, the magnitude of added K converted to the exchangeable pool, ranged from 19 to 36%. Both threshold solution K (CK_r) and threshold exchangeable K (EK_r) values were found to be high in Satran clay loam (S2) and lower in Doon silty clay loam (S3) soils. The equilibrium exchangeable K (EK_o) was found close to minimum exchangeable K (E_min) in Doon silty clay loam (S3) and Babaweyl sandy clay loam (S1) soils and overall E_min constituted about 8.94 to 0.57% of the EK_o. Conclusion : It may be concluded that K Q/I isotherm partitioning provides a valuable insight to assess the dynamic relations. The ratio of α/β (K recharge index) could be used to evaluate the K enrichment capacity of soil to K additions while EK_r and E_min can be potentially useful in the elucidation of exchangeable K as K fertility index especially in soils with poor K fertilizer management.     

Effect of long‐term fertilization and manuring on potassium release properties in a Typic Ustochrept

A long‐term fertilizer experiment, over 27 years, studied the effect of mineral fertilizers and organic manures on potassium (K) balances and K release properties in maize‐wheat‐cowpea (fodder) cropping system on a Typic Ustochrept. The treatments consisted of control, 100% nitrogen (100% N), 100% nitrogen and phosphorus (100% NP), 50% nitrogen, phosphorus, and potassium (50% NPK), 100% nitrogen, phosphorus, and potassium (100% NPK), 150% nitrogen, phosphorus, and potassium (150% NPK), and 100% NPK+farmyard manure (100% NPK+FYM). Nutrients N, P, and K in 100% NPK treatment were applied at N: 120 kg ha^—1, P: 26 kg ha^—1, and K: 33 kg ha^—1 each to maize and wheat crops and N: 20 kg ha^—1, P: 17 kg ha^—1, and K: 17 kg ha^—1 to cowpea (fodder). In all the fertilizer and manure treatments removal of K in the crop exceeded K additions and the total soil K balance was negative. The neutral 1 N ammonium acetate‐extractable K in the surface soil (0—15 cm) ranged from 0.19 to 0.39 cmol kg^—1 in various treatments after 27 crop cycles. The highest and lowest values were obtained in 100% NPK+FYM and 100% NP treatments, respectively. Non‐exchangeable K was also depleted more in the treatments without K fertilization (control, 100% N, and 100% NP). Parabolic diffusion equation could describe the reaction rates in CaCl₂ solutions. Release rate constants (b) of non‐exchangeable K for different depth of soil profile showed the variations among the treatments indicating that long‐term cropping with different rates of fertilizers and manures influenced the rate of K release from non‐exchangeable fraction of soil. The b values were lowest in 100% NP and highest in 100% NPK+FYM treatment in the surface soil. In the sub‐surface soil layers (15—30 and 30—45 cm) also the higher release rates were obtained in the treatments supplied with K than without K fertilization indicating that the sub‐soils were also stressed for K in these treatments.     

Black carbon estimation in French calcareous soils using chemo‐thermal oxidation method

We studied the black carbon (BC) content of ca. 405 samples from French topsoil and artificial soil and carbonate mixtures. Our protocol involved three main steps: (i) decarbonation by HCl, (ii) elimination of non‐pyrogenic organic carbon in a furnace at 375 °C, and (iii) quantification of residual carbon by CHN analysis. BC content increased for calcareous soils according to their carbonates content. Subsequent analyses confirmed the existence of a methodological artefact for BC determination only in calcareous soils. Decarbonation changes the thermal properties of organic matter, creating more recalcitrant carbon than in the initial sample. Higher CaCO₃ and organic carbon content results in a more pronounced artefact. The reversal of the first two steps of the chemo‐thermal oxidation method (i.e. thermal oxidation before soil decarbonation) eliminates this artefact. Overall, our results suggest that BC content may have been overestimated in a large number of studies on calcareous soils.     

Isolation and characterization of potassium solubilizing bacteria in some Iranian soils

The ability of a few soil bacteria to transform unavailable forms of potassium (K) to an available form is an important feature in plant growth-promoting bacteria for increasing plant yields of high-K-demand crops. In this research, isolation, screening, and characterization of six isolates of K solubilizing bacteria (KSB) from some Iranian soils were carried out. The ability of all isolates were tested in three treatments including acid-leached soil, biotite, and muscovite by analyzing the soluble K content after 5 days of incubation at 28 ± 2°C. Identification and phylogenetic analyses were also carried out by morphological, biochemical, and 16S rDNA analyses. Among the six efficient isolates, five isolates belonged to Bacillus megaterium (JK3, JK4, JK5, JK6, and JK7), while isolate JK2 belonged to Arthrobacter sp. The soluble K contents in all isolated-treatments were significantly (p < 0.01) higher than the contents in nonbacteria treatment. Herein, isolate JK2 had lower potential for K solubilization (910 mg kg^?1) compared with other isolates in acid-leached soils. The six bacterial strains showed higher solubilized K in biotite treatment than other two treatments. Overall, it can be concluded that the isolates belong to B. megaterium are the most efficient KSB under in vitro condition.     

The effect of pig slurry on exchangeable potassium in calcareous soils

Pig slurry in quantities of 200, 400, 500, 600, 800, and 1000 m³ ha^-1 year^-1 was added to two calcareous soils, which differed in concentration and type of clay minerals. The soils were cultivated with two successive crops of pepper and tomatoes grown in containers. A control was given no slurry. The soils were analysed after harvesting for exchangeable K⁺. Differences in exchangeable K⁺ were studied in relation to the concentration and type of clay minerals. The soil with the higher clay content and of the illite type retained K in the exchangeable form to a much greater extent than the soil with the low clay content. In the soil with the lower clay content, of the interstratified illitic — montmorillonite type, very little K was incorporated into the exchange complex. The exchange capacity being low, the amount of K added had little effect on the level of exchangeable K⁺.     

动力学模型在土壤钾素释放特征描述中的运用及其与化学方法提取的钾素之间的相关性研究

Potassium (K) release characteristics in soil play a significant role in supplying available K. Information on K-release characteristics in soils of central Iran is limited. The objectives of this study were to determine K release characteristics and correlations of K release rate constants with K extracted by different chemical methods in surface soils of ten calcareous soils of central Iran. The kinetics of K release in the soils was determined by successive extraction with 0.01 mol L^-1 CaCl₂ in a period of 2--2 017 h at 25±1 ^oC. Soil K was extracted by distilled water, 0.5 mol L-1 MgNO₃, 0.002 mol L^-1 SrCl₂, 0.1 mol L^-1 BaCl₂, 0.01 mol L^-1 CaCl₂, 1 mol L^-1 NaCl, 1 mol L^-1 boiling HNO₃, 1 mol L^-1 NH₄OAC, Mehlich 1, 0.002 mol L^-1 SrCl₂ 0.05 mol L^-1 citric acid, and ammonium bicarbonate-diethylenetriamine pentaacetic acid (AB-DTPA). A plot of cumulative amounts of K released showed a discontinuity in slope at 168 h. Thus, two equations were applied to two segments of the total reaction time (2--168 and 168--2017 h). Cumulative amounts of K released ranged from 55 to 299 mg kg^-1 in 2--168 h and from 44 to 119 mg kg^-1 in 168--2 017 h. Release kinetics of K in the two time segments conformed fairly well to parabolic diffusion, simplified Elovich, and power function models. There was a wide variation in the K release rate constants. Increasingly higher average concentrations of soil K were extracted by distilled water, Mehlich 1, SrCl₂, CaCl₂, SrCl₂ + citric acid, AB-DTPA, MgNO₃, NaCl, NH₄OAc, BaCl₂ and HNO₃. Potassium release rate constants were significantly correlated with K extracted. The results of this study showed that information obtained from mathematical modeling in two reaction time segments can help to estimate the K-supplying power of soils.     

Labile pools of copper and zinc in calcareous soils as measured by DTPA and plant extraction

Abstract

Labile pools of Cu and Zn were measured on two calcareous soils from Saudi Arabia, using successive extraction with DTPA, and successive cropping followed by extraction with DTPA after cropping. The examined soils differed in their ability to supply Cu and Zn. The first DTPA extraction removed a major proportion of the labile pool, particularly in the sandy soil. The two soils showed a general decrease in extractable Cu and Zn with progressive extractions, with DTPA extractable Cu declining more rapidly than Zn. DTPA extractable Cu and Zn determined after cropping were highly correlated with DTPA extractable Cu and Zn values obtained after successive extractions. The results gave evidence on both the contribution of element dissolution from insoluble forms with progressive extraction or cropping, and the usefulness of the DTPA extractant for monitoring the availability of Cu and Zn in these calcareous soils.     

Clay mineralogical and ammonium fixation characteristics of some tropical upland rice soils

Abstract

In view of the agronomic and economic significance of NH₄ fixation in soils, an attempt has been made to relate this to the most reactive mineral constituents of soils ‐ the clay minerals, under the temperature‐moisture regimes normal to tropical upland rice soils. Laboratory fixation study was done with NH₄, concentrations similar to those common in soils upon N fertilization, and under alternate wetting and drying at ambient temperatures rather than at 100°C as in many published studies.

Results of the investigation show that soil clays with dominant vermiculite and montmorillonite fix the greatest proportion of applied NH₄ (94 and 91%), followed by beidellite (72%) and x‐ray amorphous (45–64%) clays. Fixation is negligible (10%) in the clay with mineral suite consisting of hydrous mica, halloysite, and chlorite. Crystallinity of minerals seems to influence NH₄ fixation appreciably.     

施钾对茶园土壤钾素及平衡的影响

盆栽选取四川、重庆典型的砂岩黄壤、灰岩黄壤、酸性紫色土为供试土壤,田间选取在砂岩黄壤上生长了25年的茶园,连续5年研究了施用钾肥(硫酸钾)对茶园土壤钾库及钾素平衡的影响。结果表明:施用钾肥能显著提高土壤钾库的各类钾素,但其绝对含量都呈逐年下降的趋势。土壤中各类钾素的变化因土壤类型而异,土壤各类钾素的增量均为灰岩黄壤砂岩黄壤酸性紫色土。不施钾肥(CK)的盆栽茶树、田间茶树分别每年从土壤取走钾素0.10.g/kg。盆栽三种土壤的钾素年平均流失量分则别为0.18.g/kg(灰岩黄壤)、0.09.g/kg(砂岩黄壤)、0.07g/kg(酸性紫色土),可见种植茶树施用K肥很有必要。     

Potassium fixation of some calcareous soils after short term extraction with different solutions

This investigation was done to determine the release of potassium (K) from five calcareous soils of southern Iran using 0.025 M CaCl₂, HCl and citric acid during six successive extractions and to study the K fixation capacity of the soils after K release experiment. Mineralogical study indicated that Vertisols and Mollisols were dominated with smectites; while other soils had illite, chlorite, palygorskite and smectite. Results indicated that citric acid extracted more K than CaCl₂ and HCl (137 vs. 111 and 113 mg kg^?1, respectively). The analysis of calcium (Ca), magnesium (Mg) and K concentrations in the solutions suggests that the exchange of K with soluble Ca and Mg (originated from dissolution of carbonates by acidic solutions) is the main mechanism of K release, but citrate is able to dissolve K-bearing minerals and release K in slightly calcareous soils. Soils with more illite released more K. Potassium fixation capacity of soils increased after extractions of soils with different extractants from 324 to 471 mg kg^?1, with no significant difference. It is suggested to apply more K fertilizers in K-depleted calcareous soils and use of different solutions for extracting K from soil minerals may be a temporary and short term solution.     

Adsorption isotherms of some heavy metals under conditions of their competitive adsorption onto highly calcareous soils of southern Iran

Recently, application of sewage sludge or effluents resulted in raising the concentrations of some heavy metals in some agricultural soils of Iran. Experiments were conducted to evaluate the competitive adsorption of lead (Pb), copper (Cu), zinc (Zn), and cadmium (Cd) on six calcareous soils. Adsorption characteristics were evaluated by equilibration of 1 g of each soil sample with 20 ml of 0, 10, 20, 30, 40, 50, 100, or 200 mg L^?1 of their nitrate solutions and 0.01 M NaNO₃ as background electrolyte. Furthermore, solid/liquid distribution coefficients (K_d) of studied metals, as an index of soil capacity to resist a change of the soil solution concentration, were calculated. Results indicated that amounts of adsorbed Pb, Cu, Zn, and Cd increased with increase in their concentrations in the contact solutions, but this trend was more pronounced for Pb and Cu than the others. For all studied soils and metals, Langmuir equation described the adsorption behavior fairly well. Furthermore, Langmuir and Freundlich equation parameters were positively correlated to cation exchange capacity (CEC) and smectite contents; whereas, they were negatively correlated to sand content. Considering K_d values, the selectivity sequence of the metal adsorption was Pb > Cu > Zn > Cd. Therefore, the risk of leaching and also plant uptake of Zn and Cd will be higher as compared to those of the other elements.