Rapid assessment of soil accessible Cr(â ¥) in the field by a portable RGB color sensor.

Field rapid determination of soil accessible Cr(Ⅵ) is of great significance for on-site assessment and decision-making about the health risks of contaminated sites. When the thickness of solutions with various concentrations of Cr(Ⅵ) is constant, there would be a quantitative relationship between the chromogenic difference of Cr(Ⅵ) solutions and the concentration of Cr(Ⅵ). The chromogenic difference could be described by Red (R), Green (G), Blue (B) values. Based on the chromogenic reaction between 1,5-diphenylcarbazide and Cr(Ⅵ), this study first established the calibration curve between the chromogenic difference and the concentration of Cr(Ⅵ) in standard solution with or without 0.01 M CaCl2, using an RGB color sensor. This is the subsequent determination basis of the method for rapidly assessing accessible Cr(Ⅵ) in the field (M-RGB). Then, the concentration of accessible Cr(Ⅵ) of contaminated soil with "hand-shaking + standing" field extraction method was compared with "end-over-end shaking" laboratory extraction method. Finally, the accessible Cr(Ⅵ) of contaminated soil extractants was determined via M-RGB integrating the field extraction method. Results indicated there was a highly significant linear relationship between colorimetric difference value (∆E) and Cr(Ⅵ) concentration in the range of 0.1-3 mg/L (R2 > 0.99, P < 0.01), based on the Euclidean formula for calculating ∆E. The "hand-shaking + standing" field extraction method was effective in obtaining accessible Cr(Ⅵ) extractants with or without 0.01 M CaCl2, with the high extraction efficiency within 100±1%. The concentrations of accessible Cr(Ⅵ) in various polluted soils determined by M-RGB were consistent with that determined by the ultraviolet-visible spectrophotometry, with the relative error within ±5%, and the relative standard deviation ≤ 20%. The spiked recovery experiments showed that the recovery of M-RGB was between 95% and 105%, which means M-RGB could realize the trace analysis for accessible Cr(Ⅵ) in the field.

Differential immobilization of cadmium and changes in soil surface charge in acidic Ultisol by chitosan and citric acid: effect of their functional groups.

Soil organic matter plays an important role in cadmium adsorption and immobilization. Since different organic matter components affect cadmium adsorption processes differently, selecting the right organic substrate and knowing how to apply it could improve cadmium remediation. This study compares the effects of two contrasting organic molecules; chitosan and citric acid, on cadmium adsorption and speciation in acidic Ultisol. The adsorption of chitosan to Ultisol significantly increased the soil positive charge while adsorption of citric acid increased the soil negative charge. At pH 5.0, the maximum amount of cadmium adsorbed in excess chitosan was 341% greater than that in excess citric acid. About 73-89% and 60-62% of adsorbed cadmium were bound to Fe/Mn oxides and organic matter/sulfide at pH 4.0 while this fraction was 77-100% and 57-58% for citric acid and chitosan at pH 5.0, respectively. This decrease in the complexing ability of chitosan was related to the destabilizing effect of high pH on chitosan's structure. Also, the sequence through which chitosan, citric acid, and cadmium were added into the adsorption system influenced the adsorption profile and this was different along a pH gradient. Specifically, adding chitosan and cadmium together increased adsorption compared to when chitosan was pre-adsorbed within pH 3.0-6.5. However, for citric acid, the addition sequence had no significant effect on cadmium adsorption between pH 3.0-4.0 compared to pH 6.5 and 7.5, with excess citric acid generally inhibiting adsorption. Given that the action of citric acid is short-lived in soil, chitosan could be a good soil amendment material for immobilizing cadmium.

Changes in molybdenum bioaccessibility in four spiked soils with respect to soil pH and organic matter.

Investigation of the inherent relationship between soil physicochemical properties and pollutant's bioaccessibility (BAc) by analyzing different soil types may produce erroneous results or bias, owing to the complexity of natural soil characteristics. However, use of single factor analysis (e.g., soil pH, organic matter) facilitates evaluation of the transition. In this study, the inherent relationship between soil properties and the BAc of molybdenum (Mo) was evaluated in two typical variable-charge soils (Ferralosol and Ferrosol) and constant-charge soils (Alfisol and Inceptisol) spiked with Mo after adjusting their pH and organic carbon content. The Unified Bioaccessibility Research Group of Europe (BARGE) Method (UBM) was applied to evaluate the BAc of Mo in the gastric and intestinal phase (GP and IP, respectively). Isothermal adsorption experiment, Tessier sequential extraction, and field emission scanning electron microscope-energy dispersive spectroscopy (FESEM-EDS) analysis were conducted on these spiked soils. The results indicated that the BAc of Mo in IP (27.42-80.41%) was significantly higher than that in GP (2.52-28.53%). A significantly lower level of BAc of Mo was found in the variable-charge soils, when compared with that in the constant-charge soils. Furthermore, significant negative correlations were identified between the BAc and adsorption of Mo, which decreased with soil pH. These negative correlations can be attributed to the increase in soil negative charge density and enhancement of Mo desorption by hydroxyl, which reinforce the repulsion between Mo and soil particles with increasing soil pH; this was further confirmed by the decrease in Mo adsorption with Alfisol pH. The Mo fractions and FESEM-EDS patterns confirmed that the BAc of Mo in GP was negatively correlated with soil organic carbon (SOC) content, possibly owing to an increase in Mo retention by SOC. These findings indicated that the health risk of Mo contamination in low pH and SOC-rich variable-charge soil is relatively low, thus providing references for rationalizing risk assessment and remediating Mo-polluted soil.

More negative charges on roots enhanced manganese(II) uptake in leguminous and non-leguminous poaceae crops.

BACKGROUND: Manganese (Mn) is an essential micronutrient for plants, whereas excess Mn(II) in soils leads to its toxicity to crops. Mn(II) is adsorbed onto plant roots from soil solution and then absorbed by plants. Root charge characteristics should affect Mn(II) toxicity to crops and Mn(II) uptake by the roots of the crops. However, the differences in the effects of root surface charge on the uptake of Mn(II) among various crop species are not well understood. RESULTS: The roots of nine legumes and six non-legume poaceae were obtained by hydroponics and the streaming potential method and spectroscopic analysis were used to measure the zeta potentials and functional groups on the roots, respectively. The results indicate that the exchangeable Mn(II) adsorbed by plant roots was significantly positively correlated with the Mn(II) accumulated in plant shoots. Legume roots carried more negative charges and functional groups than non-legume poaceae roots, which was responsible for the larger amounts of exchangeable Mn(II) on legume roots in 2 h and the Mn(II) accumulated in their shoots in 48 h. Coexisting cations, such as Ca2+ and Mg2+ , were most effective in decreasing Mn(II) taken up by roots and accumulated in shoots than K+ and Na+ . This was because Ca2+ and Mg2+ could compete with Mn(II) for active sites on plant roots more strongly compared to K+ and Na+ . CONCLUSION: The root surface charge and functional groups are two important factors influencing Mn(II) uptake by roots and accumulation in plant shoots. © 2023 Society of Chemical Industry.

Effects of pH variations caused by redox reactions and pH buffering capacity on Cd(II) speciation in paddy soils during submerging/draining alternation.

Incubation experiments were conducted to investigate the influencing factors of pH variation in different paddy soils during submerging/draining alternation and the relationship between pH buffering capacity (pHBC) and Cd speciation in ten paddy soils developed from different parent materials (including 8 acid paddy soils and 2 alkaline paddy soils). The soil pHBC and the changes in soil pH, Eh, Fe2+, Mn2+, SO42- and Cd speciation were determined. The results showed that there was a significant positive correlation between cation exchange capacity (CEC) and pHBC of these paddy soils, indicating that soil CEC is a key factor affecting the pHBC of paddy soils. The contribution of Fe(III) oxide reduction to H+ consumption is far greater than the reduction of Mn(IV)/Mn(III) oxides and SO42- during the submerging. For example, the contribution of the reduction of manganese oxides, SO42- and iron oxides to H+ consumption in the paddy soils from Anthrosol at 15 d submerging was 1.2%, 11.6% and 87.2%, respectively. This confirms that the reduction of Fe(III) oxides plays a leading role in increasing soil pH. Importantly, we noticed that during submerging, soil pH was increased and resulted in the content of available Cd in soils being reduced. This was due to the transformation of Cd to less active forms. Also, there was a significant positive correlation between the change rate of available Cd, the percentage of acid extractable Cd and pH variation. This suggests that the variation in soil pH was responsible for the transformation of Cd speciation. In addition, the change rate of available Cd and the percentage of acid extractable Cd concentration were significantly negatively correlated with soil pHBC. The soil with higher pHBC experienced less pH change, and thus the change rate of available Cd and the percentage of acid extractable Cd concentration were less for the soil. The results of this study can provide a basis for the remediation of Cd-contaminated acidic paddy soils.

Critical values of soil solution Al3+ activity and pH for canola and maize cultivation in two acidic soils.

BACKGROUND: Aluminum (Al) toxicity caused by soil acidification is the main constraint for crop growth in tropical and subtropical areas of southern China. The critical values of soil solution Al3+ activity and pH for crops in acidic soils can provide a useful reference for soil acidity amelioration. RESULTS: A pot experiment in a greenhouse was conducted to investigate the critical values of soil solution Al3+ activity and pH for canola and maize in an Ultisol and an Alfisol. The critical values of soil solution Al3+ activity in Ultisol and Alfisol for canola were 1.5 and 10.0 µmol L-1 , and 13.9 and 30.4 µmol L-1 for maize, respectively. The Al tolerance varied with soil type for the same variety of crop. There was more biomass of roots and shoots and higher plant height under the same Al3+ activity, and thus greater critical values of soil solution Al3+ activity for both crops in Alfisol than those in Ultisol, owing to higher Ca2+ /Al3+ , Mg2+ /Al3+ and K+ /Al3+ ratios in soil solution caused by higher cation exchange capacity and exchangeable base cations in Alfisol, when compared with those in Ultisol. The critical values of soil solution pH for canola and maize in Ultisol were 5.09 and 4.72, respectively; while those in Alfisol were 4.87 and 4.54, respectively. CONCLUSION: The critical values of Al3+ activity were higher for maize than for canola and the critical values for both crops were higher in Alfisol than in Ultisol. The critical soil pH for both crops showed opposite trends to soil Al3+ activity. © 2022 Society of Chemical Industry.

Elucidating the mechanisms determining the availability of phosphate by application of biochars from different parent materials.

The consortium of minerals and organic matter notably alters and affects minerals' surface characteristics and nutrients providence. Organic matter such as biochar can modify the availability status of macronutrients like phosphorus (P). Despite some investigation, the adsorption/desorption of P with pure iron (hydr)oxides and the probable mechanisms involved are still unknown. In the present study, the goethite/hematite or goethite-biochar/hematite-biochar complexes were prepared, and a batch experiment with different P concentrations, time spell, pH, and ionic strength is performed to evaluate the sorption characteristics of P. The results of our study suggest that the P adsorption on mineral surface decreased with the increasing pH. Furthermore, the coexistence of biochar and minerals significantly inhibits P adsorption on the minerals surface. The results of Languimner and Freundlich's equations signify that the biochar-minerals complexes have heterogeneous adsorption sites and the presence of biochar reduces P adsorption on minerals surface. Among four biochars including peanut straw biochar (PC (B1)), rice straw biochar (RC (B2)), canola straw biochar (CC (B3)), and soybean straw biochar (SC (B4)), PC was more effective than other biochars to inhibit P adsorption on minerals surfaces.

Effect of root surface charge on the absorption and accumulation of Cu(II) by different japonica and indica rice varieties under acidic conditions.

Excessive amounts of copper (Cu) in soils causes toxic effects on plants. In this study, 58 rice cultivars were classified into tolerant, moderately tolerant, and susceptible types for Cu(II) toxicity based on 50% germination (LC50). Nine japonica rice varieties (three each from the tolerant, moderately tolerant, and susceptible groups) and six indica rice varieties (three from the moderately tolerant and susceptible groups) were selected for the hydroponics experiments. In the short-term adsorption experiment, Cu(II) adsorbed on rice roots was differentiated into exchangeable, complexed, and precipitated forms. Similarly, it was done for long-term culture. Absorption of Cu(II) by rice roots and shoots was also measured. The results indicated that adsorbed Cu(II) mainly existed as complexed and exchangeable forms on rice roots in the short-term adsorption experiment, and the exchangeable and complexed Cu(II) levels were greater for indica rice than for japonica rice due to the larger negative charge on the indica rice roots. The adsorbed Cu(II) mainly existed as a complexed form in the long-term culture experiment, and the exchangeable Cu(II) level was much lower than that in the short-term adsorption experiment due to the absorption of Cu(II) by rice plants. The indica varieties absorbed more Cu(II) than the japonica varieties. Furthermore, the absorption and accumulation of Cu(II) by the susceptible varieties were greater than by the tolerant and moderately tolerant varieties for both the japonica and indica rice. The absorption and accumulation of Cu(II) in rice roots were much greater than in the shoots. Chlorophyll content, and the lengths and dry matter weights of the rice roots and shoots decreased with increasing Cu(II) concentration. The Cu(II) showed greater toxicity toward indica varieties than japonica varieties, and the greater negative charge on indica roots was one of reasons for the greater exchangeable Cu(II) on the roots, the increase in Cu(II) toxicity, and the higher uptake of Cu(II) by indica rice varieties compared to japonica rice varieties.

Effects of surface charge and chemical forms of manganese(II) on rice roots on manganese absorption by different rice varieties.

The roots of 4 japonica, 4 indica, and 7 hybrid rice varieties were obtained by hydroponic experiment and used to explore the relationship between charge characteristics and exchangeable manganese(II) (Mn(II)) on rice roots and Mn(II) absorption in roots and shoots of the rice. Results indicated Mn(II) adsorbed on rice roots mainly existed as exchangeable Mn(II) after 2 h. The roots of indica and hybrid rice carried more negative charges than the roots of japonica rice. Accordingly, this led to more exchangeable Mn(II) to be adsorbed on roots of indica and hybrid rice after 2 h and more Mn(II) absorbed in the roots of the same varieties after 48 h. However, this was contrary to the result of Mn(II) absorption in rice shoots after 48 h. Coexisting cations of K+, Na+, Ca2+, and Mg2+ reduced the exchangeable Mn(II) on rice roots through their competition with Mn(II) for sorption sites on rice roots, which led to the decrease in Mn(II) absorption in rice roots and shoots. Ca2+ and Mg2+ showed a greater decrease in the Mn(II) absorbed in roots and shoots than K+ and Na+. The reduction of Mn(II) absorption in the roots of indica rice and hybrid rice induced by Ca2+ and Mg2+ was more than that of japonica rice. This was attributed to more negative charges on the roots of the former than the latter. Therefore, the absorption of Mn(II) by rice roots was determined by surface charge properties and exchangeable Mn(II) on the rice roots. The results suggested that Ca2+ and Mg2+ have potential to alleviate Mn(II) toxicity to rice.

Comparing ameliorative effects of biomass ash and alkaline slag on an acidic Ultisol under artificial Masson pine: A field experiment.

Forest soil acidification caused by acid deposition is a serious threat to the forest ecosystem. To investigate the liming effects of biomass ash (BA) and alkaline slag (AS) on the acidic topsoil and subsoil, a three-year field experiment under artificial Masson pine was conducted at Langxi, Anhui province in Southern China. The surface application of BA and AS significantly increased the soil pH, and thus decreased exchangeable acidity and active Al in the topsoil. Soil exchangeable Ca2+ and Mg2+ in topsoil were significantly increased by the surface application of BA and AS, while an increase in soil exchangeable K+ was only observed in BA treatments. The soil acidity and active Al in subsoil were decreased by the surface application of AS. Compared with the control, soluble monomeric and exchangeable Al in the subsoil was decreased by 38.0% and 29.4% after 3 years of AS surface application. There was a minimal effect on soluble monomeric and exchangeable Al after the application of BA. The soil exchangeable Ca2+ and Mg2+ in the subsoil increased respectively by 54% and 141% after surface application of 10 t ha-1 AS. The decrease of soil active Al and increase of base cations in subsoil were mainly attributed to the high migration capacity of base cations in AS. In conclusion, the effect of surface application of AS was superior to BA in ameliorating soil acidity and alleviating soil Al toxicity in the subsoil of this Ultisol.

Method for initially selecting Al-tolerant rice varieties based on the charge characteristics of their roots.

To explore the relationship between charge characteristics of rice roots and aluminum (Al) tolerance of rice, roots of 47 different rice genotypes were obtained by hydroponic experiment. The zeta potentials of roots were determined by streaming potential method, and the Al tolerance and the functional groups of rice were measured by relative root elongation and infrared spectroscopy (ATR-FTIR), respectively. The exchangeable, complexed and precipitated Al(III) sorbed on the root surface of rice was extracted with 1 mol L-1 KNO3, 0.05 mol L-1 EDTA-2Na and 0.01 mol L-1 HCl, respectively. There was a significant correlation between the zeta potentials and the relative elongation of rice roots, indicating that the zeta potentials of rice roots could be used to characterize rice tolerance to Al toxicity. Twelve Al-tolerant rice varieties, 25 medium Al-tolerant rice varieties, and 10 Al-sensitive rice varieties were obtained. The Al-tolerant rice varieties sorbed less complexed Al(III) and total Al(III) because there was lower negative charge on their roots compared to less tolerant genotypes. A correlation analysis showed that there were significant negative correlations between the zeta potential, relative root elongation, and the total Al(III) sorption capacity of the roots, which further confirmed the reliability of using the root zeta potential to characterize rice tolerance to Al toxicity. The results of this paper provide a new method for screening Al-tolerant rice varieties.

Phytotoxicity of Cu2+ and Cd2+ to the roots of four different wheat cultivars as related to charge properties and chemical forms of the metals on whole plant roots.

The relationship between the chemical forms of Cu2+ and Cd2+ adsorbed on the roots of different wheat cultivars and their phytotoxic effects on the plants were investigated. The wheat varieties Dunmaiwang (DMW), Tekang 6 (TK6), Zhongmai895 (ZM895), and Chaojixiaomai (AK68) were used. The zeta potentials of wheat roots, measured by the streaming potential method, were used to characterize root charge properties. Results indicated that the changes in zeta potential at pH 4.01-6.61 were 14.7, 15.53, 13.01, and 12.06 mV for ZM895, AK68, DMW, and TK6, respectively. The negative charge and functional groups on ZM895 and AK68 roots were greater than on DMW and TK6 roots, which led to more exchangeable and complexed Cu2+ and Cd2+ on ZM895 and AK68 roots and increased Cu2+ and Cd2+ toxicity compared to DMW and TK6. Coexisting cations, such as Ca2+, Mg2+, K+, and NH4+, alleviated Cu2+ and Cd2+ toxicity to wheat roots through competition for adsorption sites on the roots, which decreased exchangeable and complexed Cu2+ and Cd2+ on wheat roots. The Ca2+ and Mg2+ were most effective in alleviating heavy metal toxicity and they decreased exchangeable Cu2+ on AK68 roots by 39.14% and 47.82%, and exchangeable Cd2+ by 8.51% and 28.23%, respectively.

Effects of extracellular polymeric substances of Pseudomonas fluorescens, citrate, and oxalate on Pb sorption by an acidic Ultisol.

The continuous production of low molecular weight (LMW) organic acids by plants and microorganisms coupled with the continuous presence of extracellular polymeric substances (EPS) in soils is a guarantee that the mobility of heavy metals in soils will be controlled. The effects of citrate, oxalate, and EPS on the adsorption of Pb by an acidic Ultisol were studied both as a function of pH and ionic strength. Electrokinetic potential measurements were also employed to observe to what extent each ligand affected the surface charge property of the Ultisol. All the ligands shifted the zeta potential of the Ultisol to the negative direction, implying that the surface charge of the soil became more negative. The effect on the zeta potential of the soil was observed in the order of oxalate ˃ citrate ˃ EPS. The quantity of Pb adsorbed at each pH (3.0-7.0) reflected the corresponding change in the zeta potential as induced by each ligand. The presence of the ligands shifted the isoelectric point of the Ultisol from 4.8 to 3.2 for the EPS system and below 3.0 for the citrate and oxalate systems. More Pb was adsorbed in the presence of oxalate than in the presence of citrate and EPS. The two most outstanding mechanisms that governed the adsorption of Pb by the Ultisol were (1) electrostatic attraction which was supported by the increase in negative zeta potential of the Ultisol and, (2) complexation which was supported by the lesser proportion of Pb adsorbed in the citrate system at higher pH and also by the spectroscopic data for EPS. The combination EPS + citrate + oxalate was more effective in enhancing the adsorption of Pb than the combination EPS + oxalate and EPS + citrate.

Effect of different phosphorus sources on soybean growth and arsenic uptake under arsenic stress conditions in an acidic ultisol.

Soil arsenic (As) contamination is a serious concern because of its mark negative impacts on plant growth and physiological processes. In plant-soil system, As competes against phosphorus (P) which depends on charge component of different soil types. The main objective of this study was to investigate the influence of ((NH4)3PO4 (PO43-) and Ca5(PO4)3(OH) (phosphorite)) in ameliorating As stress on plant physiological process against As toxicity and their role in As accumulation. We performed eighteen treatments with different levels of As (0, 35, and 70 mg/kg) and P (0, 100, and 200 mg/kg) against two P sources of PO43- and phosphorite. Overall, more improvement in plant growth was observed by addition of PO43- than phosphorite. Significant increases in plant height (51%), dry biomass (root (49%) and shoot (40%)), chlorophyll contents (88%), total soluble sugars (58%) and plant functional leaves (51%) were observed by PO43- application as compared to their corresponding un-fertilized treatment under As stress conditions. However, proline and MDA contents were decreased by 49% and 71% with PO43- applied, respectively, under As stress. The As and P uptake by soybean were remarkably enhanced by the application of PO43- than phosphorite. Therefore, highly soluble P supplementation has great potential to minimize As-induced damage to plant growth in acidic soils and improve As uptake by plants. The findings obtained in present study will be used as an important tool for amelioration of As polluted acidic soils.

Peanut straw biochar increases the resistance of two Ultisols derived from different parent materials to acidification: A mechanism study.

The mechanisms for increasing soil pH buffering capacity (pHBC) and soil resistance to acidification by peanut straw biochar were investigated by undertaking indoor incubation and simulated acidification experiments using two Ultisols derived from tertiary red sandstone and quaternary red earth. The biochar increased the pHBC and resistance of the two Ultisols to acidification. The addition of 3% biochar increased the pHBC of the two Ultisols by 76% and 25%, respectively. The increased resistance of the soils to acidification led to the inhibition to decrease in soil pH and the activation of soil Al during acidification. The protonation of carboxyl groups on the biochar surface was the main mechanism responsible for resisting acidification of the Ultisols when the pH was between 4.5 and 7.0. The higher soil pH (>6.0) after biochar application and the large number of carboxyl groups on the biochar surface were essential if biochar was to significantly increase the resistance of soils to acidification.

Effects of adhesions of amorphous Fe and Al hydroxides on surface charge and adsorption of K+ and Cd2+ on rice roots.

Iron (Fe) and aluminum (Al) hydroxides in variable charge soils attached to rice roots may affect surface-charge properties and subsequently the adsorption and uptake of nutrients and toxic metals by the roots. Adhesion of amorphous Fe and Al hydroxides onto rice roots and their effects on zeta potential of roots and adsorption of potassium (K+) and cadmium (Cd2+) by roots were investigated. Rice roots adsorbed more Al hydroxide than Fe hydroxide because of the greater positive charge on Al hydroxide. Adhesion of Fe and Al hydroxides decreased the negative charge on rice roots, and a greater effect of the Al hydroxide. Consequently, adhesion of Fe and Al hydroxides reduced the K+ and Cd2+ adsorption by rice roots. The results of attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and desorption of K+ and Cd2+ from rice roots indicated that physical masking by Fe and Al hydroxides and diffuse-layer overlapping between the positively-charged hydroxides and negatively-charged roots were responsible for the reduction of negative charge on roots induced by adhesion of the hydroxides. Therefore, the interaction between Fe and Al hydroxides and rice roots reduced negative charge on roots and thus inhibited their adsorption of nutrient and toxic cations.

Characteristics of biomass ashes from different materials and their ameliorative effects on acid soils.

The chemical characteristics, element contents, mineral compositions, and the ameliorative effects on acid soils of five biomass ashes from different materials were analyzed. The chemical properties of the ashes varied depending on the source biomass material. An increase in the concrete shuttering contents in the biomass materials led to higher alkalinity, and higher Ca and Mg levels in biomass ashes, which made them particularly good at ameliorating effects on soil acidity. However, heavy metal contents, such as Cr, Cu, and Zn in the ashes, were relatively high. The incorporation of all ashes increased soil pH, exchangeable base cations, and available phosphorus, but decreased soil exchangeable acidity. The application of the ashes from biomass materials with a high concrete shuttering content increased the soil available heavy metal contents. Therefore, the biomass ashes from wood and crop residues with low concrete contents were the better acid soil amendments.

Bioaccumulation of nickel by E. sativa and role of plant growth promoting rhizobacteria (PGPRs) under nickel stress.

Phytoremediation potential of plants can be enhanced in association with microbes. Further, many plant growth-promoting rhizobacteria can improve growth under stress. The present study was conducted to investigate the effect of Pseudomonas putida (P. putida) on nickel (Ni) uptake and on growth of Eruca sativa (E. sativa). Three different levels of Ni (low; 150 ug/g, medium; 250 ug/g and high; 500 ug/g) were applied to the soil containing E. sativa seedlings, with or without P. putida. Ni-toxicity was measured by metamorphic parameters including shoot length, root length, biomass, chlorophyll and proline and Ni contents. Inoculation with P. putida increased 34% and 41% in root and shoot length and 38% and 24% in fresh, dry weight respectively, as compared to non-inoculated plants. Similarly, Ni uptake increased by up to 46% following P. putida inoculation as compared to non-inoculated plants. Indole acetic acid, siderophore and 1-aminocyclopropane-1-carboxylate deaminase (ACCD) activity in the growing media enhanced growth and Ni uptake in E. sativa. The present results offer insight on Plant Growth Promoting Rhizobacteria (PGPR), such as P. putida, for the potential to enhance the plant growth by inhibiting the adverse effects of Ni in E. sativa.

Effect of carbon and nitrogen mineralization of chitosan and its composites with hematite/gibbsite on soil acidification of an Ultisol induced by urea.

Chitosan is a biodegradable polymer with a vast range of applications. Along with its metal composites, chitosan has been applied in the remediation of polluted soils as well as a biofertilizer. However, little attention has been given to the degradation of chitosan composites in soil and how they affect soil respiration rate and other physicochemical parameters. In this study, the degradation of chitosan and its composites with gibbsite and hematite in an acidic Ultisol and the effect on urea (200 mg N kg-1) transformation were investigated in a 70-d incubation experiment. The results showed that the change trends of soil pH, N forms, and CO2 emissions were similar for chitosan and its composites when applied at rates <5 g C kg-1. At a rate of 5 g C kg-1, the C and N mineralization trends suggested that the chitosan-gibbsite composite was more stable in soil and this stability was owed to the formation of a new chemical bond (CH-N-Al-Gibb) as observed in the Fourier-transform infrared spectrum at 1644 cm-1. The mineralization of the added materials significantly increased soil pH and decreased soil exchangeable acidity (P < 0.01). This played an important role in decreasing the amount of H+ produced during urea transformation in the soil. The soil's initial pH was an important factor influencing C and N mineralization trends. For instance, increasing the initial soil pH significantly increased the nitrification rate and chitosan decomposition trend (P < 0.01) and thus, the contribution of chitosan and its composites to increase soil pH and inhibit soil acidification during urea transformation was significantly decreased (P < 0.01). These findings suggest that to achieve long-term effects of chitosan in soils, applying it as a chitosan-gibbsite complex is a better option.

Using an inexpensive RGB color sensor for field quantitative assessment of soil accessible Cu(â ¡).

Field rapid determination of soil accessible Cu(Ⅱ) was important for environmental safety and human health risk assessment. In this study, an inexpensive red, green, and blue (RGB) color sensor was used for quantitative color difference analysis of the colored solution for soil accessible Cu(Ⅱ) with bis-cyclohexanone oxalydihydrazone as color reagent to develop a new method for analyzing soil accessible under field conditions. First, the calibration curve for RGB color sensor method was established in the standard solutions of Cu(II). Then the "hand shaking + standing" field extraction method for accessible Cu(Ⅱ) was developed. Finally, the method was applied in contaminated soils in the laboratory and in the field, and set the values determined by atomic absorption spectroscopy (AAS) as the standard ones. Results indicated that in the range of 0.1-5 mg L-1 Cu(II), the RGB Euclidean chromogenic difference values were directly linear correlated with the concentration of Cu(II) (R2 > 0.999). The interference of Fe(Ⅲ) and Mn(Ⅱ) could be eliminated by adding citric acid. The "hand shaking + standing" field extraction method could effectively extract the accessible Cu(Ⅱ) from soil with the high extraction rates. The concentrations of accessible Cu(II) in various polluted soils determined by RGB color sensor method were consistent with that determined by AAS, with the relative error within ±5%, the relative standard deviation ≤ 20%. The recovery of Cu(II) in RGB color sensor method was between 97% and 105%, which could meet the requirements of trace analysis of accessible Cu(Ⅱ) in the field. The high accuracy and precision of RGB color sensor method was reconfirmed in the rapid field quantitative assessment of soil accessible Cu(Ⅱ). Due to that the RGB color sensor was low cost, rechargeable, portable, mobile, ambient light resistant, the method would have a great potential for the determination of accessible Cu(Ⅱ) in contaminated soils.