首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 62 毫秒
1.
The quantity: potential relationships for Ca→K exchange in six soils were evaluated, where potential is defined by ΔGK,Ca+Mg. Using the percentage K saturation of the CEC as the index of quantity, the Worcester Series soil, rich in hydrous micas, was shown to have the highest concentration of K selective sites, and Newport Series soil, with mainly kaolinitic clay, the lowest. The other soils, containing mainly smectites, had intermediate K selectivities. An algebraic transformation of this relationship to separate the effects of exchangeable K and CEC showed that 0.01 m CaCl2 released more K than m ammonium acetate. From the exchangeable K : ΔG relationship, two regions of K buffering were observed for all but the Newport soil, the transition occurring at a mean ΔGK,Ca+Mg value of ?20.7 kJ mol?1, signifying the K concentration below which K from ‘perlpheral’ regions of micaceous minerals is released. This may explain why the percentage K saturation of the CEC of a soil cropped exhaustively (without K manuring) in the field does not drop below a minimum value. Based on pot experiments, exhaustion and optimum K potentials (ΔGexh and ΔGopt) were derived from second-degree polynomials fitted to the response curves of plant dry matter yield against ΔGK,Ca+Mg for five soils, the Worcester soil showing little response. ΔGexh was inversely related to the 2 : 1 layer silicate content of the soil (r2=0.98 and 0.94 for ryegrass and fescue respectively), and similarly, ΔGopt, to their CEC values (r2=0.74 and 0.77). Potassium uptake was more closely correlated with exchangeable K than with ΔGopt.  相似文献   

2.
The solubility and the enthalpy of dicarboxylic acids have been determined in water at intervals between 278.5 and 543.5 K. At 298.15 K, the values derived were: Δsol H m (m?=?1.33 mol kg?1)?=?29.80 kJ mol?1for oxalic acid; Δsol H m (m?=?16.03 mol kg?1)?=?12.82 kJ mol?1 for malonic acid; Δsol H m (m?=?0.75 mol kg?1)?=?28.20 kJ mol?1 for succinic acid; Δsol H m (m?=?8.77 mol kg?1)?=?48.01 kJ mol?1 and Δsol H m (m?=?0.17 mol kg?1)?=?40.30 kJ mol?1 for glutaric and adipic acid respectively. The solubility value exhibits a prominent odd–even effect with respect to terms with even number of carbon atoms with the odd carbon numbers showing much higher solubility. Observations made in the atmospheres suggest that this odd–even effect may have implications for the relative abundance of these acids in aerosols.  相似文献   

3.
Heats of adsorption and adsorption isotherms of ammonia gas were measured at 300 K (27 °C) on outgassed soil saturated with Na+, K+, NH4+, Ca2+, or Mg2+ ions. The Ca and Mg soils adsorbed apparently one more NH2 molecule per exchangeable ion than the Na and K soils, mostly in the relative pressure range o to 0.005, but not much more than the NH4 soil. The initial heat of adsorption was c. 75 kJ mol-1 on the Ca and Mg soils and c. 60 kJ mol-1 on the other soils. The results suggest that most NH, is sorbed on these soils through reactions not involving exchangeable cations.  相似文献   

4.
  相似文献   

5.
Exchange behaviour of potassium versus magnesium was studied on surface soil samples of 3 Ustochrepts from a semiarid tropical region in relation to different levels of cattle farmyard manure (FYM, 0, 2.5, 5 and 10%). Magnesium saturated soil samples were equilibrated with KCl + MgCl2 solutions having a range of equivalent ion fraction of K from 0 to 1 in the equilibrium solutions. The experimental results were analysed and interpreted, using different exchange selectivity quotients and thermodynamic parameters. Application of FYM caused a small but consistent increase in the K-preference over Mg as depicted from the normalized exchange isotherms. Standard free energy of K-Mg exchange were strongly negative (ΔGo-6.97 to ?9.47 kJ eq?1 by Gaines and Thomas approach; ΔG'o ?10.85 to ?14.15 kJ M?1 by Babcock and Duckart approach), suggesting a strong thermodynamic preference for K over Mg in these soils. For comparable treatments, ΔGo were about ?0.84 to ?1.25 kJ eq?1 more negative for K-Mg, compared to K-Ca system reported earlier. ΔGo for 10% FYM treatments became more negative over the controls by 2.34, 1.40 and 0.53 kJ eq?1 for Hissar, Panipat and Pehowa soils, respectively. All the selectivity quotients scrutinized in this investigation, viz., Gapon (KG), Vanselow (Kv) and thermodynamic (KN) were strongly K-saturation dependent; the dependence becoming more pronounced with the addition of FYM.  相似文献   

6.
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 CO2‐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 CO2‐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, CO2‐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 CO2‐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 CO2 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   

7.
The direct application of Sokoto phosphate rock to restore phosphorus in the savanna soil of Nigeria has not been very successful. The dissolution of Sokoto phosphate rock was investigated in three electrolyte solutions – 0.01 m CaCl2, NaCl and KCl – at pH range 3.5–7.0 under laboratory conditions to provide solubility and kinetic data that are required to develop guidelines for direct application in the field. The phosphate rock dissolved in the salt solutions in the order KCl > NaCl > CaCl2. Particle size and ionic strength had no significant effect on the dissolution. The standard free energy of reaction ΔG°R in an acidic solution with no basic cations was ?38 kJ mol?1. If Ca2+ ions were in the acidic solution, then ΔG°R increased to 210 kJ mol?1, 170 kJ mol?1 for Na+ ions, and 107 kJ mol?1 for K+ ions in the solution. The theoretical solubility constant (Ks) calculated from the relation ΔG° = ?RT ln Ks gave Ks = 106.7 in an acidic solution without basic cations, but decreased to 10?36.8 with Ca2+ ions in solution, 10?29.8 with Na+ ions, and 10?18.8 with K+ ions in solution. At pH ≥ 5.5, the dissolution was more constrained by Ca2+ ions or basic cations in solution than by availability of protons. The kinetics of the dissolution reaction was best described by a power function: Ct = atb, where Ct is the amount of P released from the rock phosphate at time t, and a and b are fitting parameters. An Elovich and a parabolic diffusion expression equally gave satisfactory fits to the dissolution data, suggesting that the rate of dissolution was limited by a combination of film‐ and intra‐particle diffusion. To utilize this rock phosphate as an effective source of P, management practices that increase Ca sinks and the supply of protons to the soil are necessary. In the savanna, increasing the soil's organic matter greatly enhances cation exchange capacity and availability of protons. The practice should provide adequate sinks for Ca2+ and the acidic environment required for the release of P from rock phosphate.  相似文献   

8.
Ion exchange preferences for NH4+ and K+ by soil exchanger surface can greatly affect the NO3? leaching into groundwater and nitrogen-use efficiency in agricultural production. Since NH4+ and K+ salts are usually applied together as fertilizers, the binary K→NH4 exchange of two benchmark Botswana soils, Pellustert and a Haplustalf, was studied to determine the selectivity coefficients and the thermodynamic exchange constant with special reference to N economy. The Vanselow and the Gaines and Thomas coefficients indicated preference for NH4+ by the Pellustert and K by the Haplustalf across the exchanger phase composition. The equilibrium constant (Kex) was 1.807 for the Pellustert and 0.174 for the Haplustalf. The exchange free energy (ΔGex0) was ?1.467 kJ mol?1 for the Pellustert and 4.334 kJ mol?1 for the Haplustalf. Negative ΔGex0 for the Pellustert is consistent with preference for NH4+ to K+ in contrast to positive ΔGex0 for the Haplustalf. The greater stability of NH4X than KX complex in the Pellustert, and KX than NH4X in the Haplustalf, would mean increased residence time of NH4+ in the Pellustert than the Haplustalf. The implication of short residence time of NH4+ in soil is rapid nitrification, thereby leading to NO3??N leaching losses and possible groundwater contamination.  相似文献   

9.
The plant minimal exchangeable K (EPl,min) defines the lower accessible limit of the most available pool of soil K to plants. It is also an index of long‐term K reserve in soils. However, its estimation by the classical method of exhaustion cropping is laborious. This study aimed at comparing EPl,min values obtained by the exhaustion cropping method with EPl,min values estimated by an alternative approach based on the cationic exchange capacity (CEC) of the infinitely high selective sites for K (i.e., always saturated with K) in the K‐Ca exchange (EK‐Ca,min). A set of 45 soil samples, corresponding to the various fertilization K treatments of 15 long‐term K fertilization trials, was used in this study. The selected soil samples presented a wide range of texture, CEC, and exchangeable K. The plant minimal exchangeable K was found more or less independent of the K treatment, whereas EK‐Ca,min increased when the soil exchangeable K content increased. The plant minimal exchangeable K was systematically lower than EK‐Ca,min, showing that EK‐Ca,min is at least partially available to the plant. Hence, EK‐Ca,min is not a surrogate of EPl,min. Conversely, the plant minimal exchangeable K was strongly, positively correlated to soil CEC (measured at soil pH; r2 = 0.90***). This soil property can consequently be used as a proxy of EPl,min.  相似文献   

10.
Non-exchangeable potassium (Knex) contributes to soil K availability and several extractants are used to access its contribution. This study evaluated sodium tetraphenylboron (NaBPh4) as a soil test of K availability in 20 soils from Northern Greece. Winter wheat (Triticum aestivum L. var. ‘Yecora’) was sown in a greenhouse pot experiment and five cropping cycles were carried out until K-depletion. Soils were analyzed with NH4OAc and NaBPh4 (1 and 5 min incubation periods). Critical levels of K ranged between 130–140 and 330–340 mg K kg?1 of soil for NH4OAc and NaBPh4 (1 min incubation period), respectively, and between 32 and 35 g K kg?1 of wheat dry matter. NaBPh4-K (1 min) related better with K concentration and uptake compared to NH4OAc for each cropping cycle (r2 = 0.45–0.83 and 0.44–0.89) and for all soils (r2 = 0.58 and 0.51). Similar results obtained in soils low in exchangeable K (r2 = 0.41 and 0.39). Correlation between NH4Oac- and NaBPh4-extractable K was weaker among soils below the critical level (r = 0.70) compared to those above (r = 0.93). Inclusion of illitic K and cation exchange capacity in a multiple linear regression between NH4OAc- and NaBPh4-extractable K showed that they significantly contributed to NaBPh4-extractable K.  相似文献   

11.
Mean NH3 losses after nine days incubation at 18°C and 60% FC were 3.1±2.9% and 7.6±6.0% of applied urea-N from the pasture and tillage counterparts of 10 soil series. These losses were highly correlated with buffered CEC and maximal pH values (pHm) generated three days after urea application. NH3 volatilization was apparently controlled by buffered CEC and initial pH (R2= 72–87%) and was related to variations in soil organic matter and texture (R2= 77–81%). Losses in the acid pasture soils were attributed largely to initial pH differences, and in the tillage soils to buffered CEC only. Evolution was greater from the tillage than from the pasture equivalent in eight series. This was attributed to differences in CEC, including buffered CEC and pH-dependent charge, caused by differences in OM content primarily but also in texture between the two soil groups. Differences in NH3 evolution from urea in pasture and tillage soils, in general, are not related to pH differences.  相似文献   

12.
Apple (Malus domestica, Borkh) and pear (Pyrus communis, L.) trees responded to nitrogen (N), phosphorus (P), and potassium (K) fertilizers. In low P soils, leaf, and fruit P concentrations were increased and yield was improved with moderate rates of mono‐ammonium phosphate (MAP) fertilizers. Improved fruit quality including fruit firmness, red fruit color of ‘Delicious’ apples, and a lower incidence of fruit disorders of apples (bitter pit) and pears (alfalfa greening and cork spot) was frequently associated with trees that were fertilized with calcium nitrate [Ca(NO3)2] (CN). Although yield was often improved in experiments containing N‐P‐K or MAP fertilizers, long‐term use of N‐P‐K or MAP could be associated with a higher incidence of fruit disorders and a lower soil pH than with CN fertilizer at equivalent rates of N.  相似文献   

13.
The aim of this study was to investigate the potential of silicon (Si) for alleviating Ultraviolet-B (UV-B) radiation stress based on changes in biomass, physiological attributes and photosynthetic characteristics of two soybean (Glycine max L.) cultivars, Kenjiandou 43 (‘K 43’) and Zhonghuang 35 (‘ZH 35’). The cultivars were raised with and without Si in the greenhouse, and then subjected to ambient, ambient + 2.7 kJ m?2d?1and ambient + 5.4 kJ m?2d?1of UV-B radiation. Depending on cultivar, plants suffered severe growth limitations under UV-B radiation, but the application of Si alleviated the adverse effects on growth and development by increasing the stem length, net photosynthetic rate (PN) and leaf chlorophyll content. Concurrently, it decreased the stomatal conductance (Sc) and intercellular carbon dioxide (CO2) concentration (Ci). In response to the UV-B radiation stress, the antioxidant enzyme activities of superoxide dismutase (SOD) increased by 41.2–72.7%, peroxidases (POD) by 49.5–85.7%, malodialdehyde (MDA) by 6.7–20.4% and soluble protein by 4.2–7.6%. The overall results indicated that media treatment with Si might improve soybean growth under elevated UV-B radiation through positive changes in biomass and some physiological attributes that were dependent on cultivar.  相似文献   

14.
Sixteen soils and 4 soil preparations were cropped exhaustively with ryegrass in the glasshouse and monocalcium phosphate potentials (½pCa+pH2PO4=1) were measured after each of 6 consecutive harvests. The amounts of phosphorus (Q) removed from the soils by ryegrass accounted for 95·1–96·6 per cent of the variance in 1 for 3 soils and 2 soil preparations (P < 0·001), for 88·4–93·7 Per cent of the variance for 6 soils and 2 soil preparations (0·001 < P < 0·01), for 71·6–82·6 per cent of the variance for 3 soils (0·01 < P < 0·05) and for insignificant amounts of the variance for 4 soils. Values of ΔI/ΔQ ranged from 7 × 10–4 to 431 × 10–4½pCa+pH2PO4/ppm P removed from soil. ΔI/ΔQ tended to decrease (i.e. the soils were more buffered) with increasing clay contents and with increasing amounts of NaHCO3-soluble P and to increase (i.e. the soils were less buffered) with increasing amounts of CaCO3. Variations in organic C did not significantly affect ΔI/ΔQ. The following equation accounts for 81 per cent of the variance in ΔI/ΔQ for all soils except those in equilibrium with octacalcium phosphate: ΔI/ΔQ× (104) = 225·9–4·17(% clay)+8·01(% CaCO3)–1·38(ppm NaHCO3-soluble P).  相似文献   

15.
The electric charge characteristics of five Ando (B) and two Red-Yellow B horizon soils and two weathered pumices were studied by measuring the retention of NH4+ and Cl? at different pH values and NH4Cl concentrations. The magnitude of their negative charge (CEC; meq/100g) was dependent on pH and NH4Cl concentration (C; m) as represented by a regression equation: log CEC =apH +blog C +c. The values of the coefficient a (0.017 to 0.342), b (0.031 to 0.274) and c (1.41 to ? 1.26) were correlated and depended on the kind of clay minerals present. A similar equation: log AEC =a’ pH +b’ log C+c’ was also found for the positive charge in the Ando soils, but there was little difference in the values of a’(?0.204 to ?0.251), b’(0.181 to 0.253) and c’(2.06 to 2.46) between the soils. It was shown that the equations generally hold for soils with constant and/or variable charges and describe adsorption equilibria in which NH4+ and H+, and Cl? and OH? compete for cation- and anionexchange sites, respectively. The significance and utility of the coefficients is discussed.  相似文献   

16.
The electric charge characteristics of four Ando soils (A1 and μA1) and a Chernozemic soil (Ap) were studied by measuring retention of NH4+ and Cl– at different pH values and NH4Cl 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 NH4Cl 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   

17.

Purpose

Recent research has focused on using water treatment residuals (WTRs) as cost-effective materials to remove potential environmental contaminants. To better understand and predict how WTRs affect the mobility and retention of nickel (Ni) in soils with time, it is crucial that the kinetics and thermodynamics of these reactions be understood. Such information is lacking in the literature and would aid in evaluating the suitability of WTR as a soil amendment for adsorbing Ni contaminant. Accordingly, we focused on investigating the retention of Ni in differing soils and the subsequent influence of WTR application on Ni retention.

Materials and methods

To examine the effects of WTR application on the characteristics of Ni retention, equilibrium, and kinetics, sorption batch experiments were performed on three soils having different properties. The sorption data were applied to the first-order kinetic model, and the Arrhenius equation was used to determine the thermodynamic parameters.

Results and discussion

The quantity of Ni sorbed by the soils followed the trend Typic Torrifluvent > Typic Calciorthids > Typic Torripsamment. Soil sorption isotherms shift toward a higher sorption of Ni indicating addition of more sorption sites as a result of WTRs’ application. Data generated at different temperatures for soils and WTR-amended soils fitted well to Freundlich isotherm and first-order kinetic models. The energy of activation (E a) and enthalpy (ΔH #), entropy (ΔS #), and free energy of activation (ΔG #) related to Ni sorption were calculated using the Arrhenius equation. The activation energy (E a) values (51.65–130.0 kJ mol?1) and the positive ΔH # values characterize Ni sorption process onto the sorbents studied as chemisorption with an endothermic nature. The large negative ΔS # values (?262 to ?290 J?mol?1) and the large positive ΔG # values (88.11–89.14 kJ mol?1) indicate the involvement of an associative mechanism in the Ni sorption process.

Conclusions

WTR addition has led to an overall increase in Ni sorption by the amended soils. Such increase in Ni sorption provides evidence that WTR has the potential for land application as a Ni sorbent in soil remediation techniques. The sorption capacity of the soils and WTR-amended soils enhanced with an increase in temperature. Therefore, to truly understand the potential fate and mobility of Ni in the natural environment, temperature, in particular, should be considered.  相似文献   

18.
Risk assessment of heavy metals in soil requires an estimate of the concentrations in the soil solution. In spite of the numerous studies on the distribution of Cd and Zn in soil, few measurements of the distribution coefficient in situ, Kd, have been reported. We determined the Kd of soils contaminated with Cd and Zn by measuring metal concentrations in the soil and in the soil solution and attempted to predict them from other soil variables by regression. Soil pH explained most of the variation in logKd (R2 = 0.55 for Cd and 0.70 for Zn). Introducing organic carbon content or cation exchange capacity (CEC) as second explanatory variable improved the prediction (R2 = 0.67 for Cd and 0.72 for Zn), but these regression models, however, left more than a factor of 10 of uncertainty in the predicted Kd. This large degree of uncertainty may partly be due to the variable degree of metal fixation in contaminated soils. The labile metal content was measured by isotopic dilution (E value). The E value ranged from 18 to 92% of the total metal content for Cd and from 5 to 68% for Zn. The prediction of Kd improved when metals in solution were assumed to be in equilibrium with the labile metal pool instead of the total metal pool. It seems necessary therefore to discriminate between ‘labile’ and ‘fixed’ pools to predict Kd for Cd and Zn in field contaminated soils accurately. Dilute salt extracts (e.g. 0.01 m CaCl2) can mimic soil solution and are unlikely to extract metals from the fixed pool. Concentrations of Cd and Zn in the soil solution were predicted from the concentrations of Cd and Zn in a 0.01 m CaCl2 extract. These predictions were better correlated with the observations for field contaminated soils than the predictions based on the regression equations relating logKd to soil properties (pH, CEC and organic C).  相似文献   

19.
Cation exchange characteristics of the K:Ca saturated forms of five soils were measured at 25°C and 50°C. The rates of isotopic exchange of 42K and 45Ca were too fast to be measured except that of 42K in the K:Ca Harwell soil at 25°C. The slower isotopic exchange of K in this soil was attributed to the presence of a zeolite, clinoptilolite. The intra-particle diffusion coefficient, Di, of K in this soil increased with K-saturation to a maximum at about 40 per cent K, probably because of the ‘blocking’ action of the larger hydrated Ca ions at small K-saturations in clinoptilolite. The CEC, measured by isotopic exchange along the K:Ca adsorption isotherm, decreased with increasing temperature probably because some interlayer spaces collapsed. The standard free energy, enthalpy, and entropy changes were negative for the reaction Ca-soil+2K+? 2K-soil+Ca++. These results seem to show that K is more strongly bound than Ca by the soil and that the Ca-preference shown by the isotherm at small external electrolyte concentration is caused by entropy changes in solution. Calculated activity coefficients of the exchangeable ions changed with K-saturation similarly at both temperatures but values at 50°C were smaller than at 25°C.  相似文献   

20.
Surface and subsurface horizons of 16 representative sugarcane growing soils with varying soil properties in the eastern region of Thailand were collected to determine the potassium (K) fertility status and its availability by using the quantity/intensity relationship (potential buffering capacity of K (PBCk)). The results showed that most soils had a low K fertility status and lack of reserved K from K-bearing minerals. The PBCk values of the studied soils ranged from 3.75 to 168 cmol kg?1/(mol L?1)1/2, and the coarse-textured soil group showed much lower PBCk values; these results suggested a low capability of these soils to replenish K removal by plant uptake compared with that of the fine-textured soil group. The negative delta K (ΔK°) values of the coarse-textured soil group also indicated a large quantity of readily available K for plant uptake that easily leaches at the same time. The higher K activity ratio (ARke) of the coarse-textured soil group (>0.001 mol L?1)1/2) than that of the fine-textured soil group (<0.001 mol L?1)1/2) suggested that readily available K was desorbed from the non-specific sites of 1:1 clay minerals and specific sites of 2:1 clay minerals, respectively. The ΔK° value of the studied soils was more significantly correlated to K concentration in sugarcane stalks (R2 = 0.64) than that of readily available K content (R2 = 0.54). Therefore, the results of this study suggested that ΔK° represents a better parameter to estimate K availability in these soils compared to conventional ammonium acetate (NH4OAc)-extractable K content.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号