Stagnic Anthrosols Research Articles

Soil microbial population as affected by tillage and rice cultivation modes in Stagnic Anthrosols and Lateritic Red Earth soils in Southern China

The microbial population (MP) is considered to be a relatively important part of soil health, quality, and productivity. Therefore, this study aimed to access the effects of tillage and rice cultivation modes on soil MP in Stagnic Anthrosols and Lateritic Red Earth soils. The treatments were as follows: (i) MDS: land tilled twice with a moldboard plow and hill-seeding of pregerminated seeds with a direct seeding machine of four to six seeds per hill at a planting space of 25 × 15 cm, (ii) RDS: land tilled twice with a rotary tiller and hill-seeding of pregerminated seeds with a direct seeding machine of four to six seeds per hill at a planting space of 25 × 15 cm, (iii) MMT: land tilled twice with a moldboard plow and 15-day-old seedlings were mechanically transplanted with a transplanting machine at a transplanting hill of four to six seedlings and at a transplanting space of 25 × 15 cm, and (iv) RMT: land tilled twice with a rotary tiller and 15-day-old seedlings were mechanically transplanted with a transplanting machine at a transplanting hill of four to six seedlings and a transplanting space of 25 × 15 cm. The findings showed that MDS improved the MP and increases rice yield. MDS showed a high increase in MP in both locations and the rice productivity of 32.81% (1H; first harvest) and 13.91% (2H; second harvest) and 16.48% (1H) and 18.13% (2H) for Zeng-Cheng and Yi-Yang, respectively. In conclusion, MDS was found to be better in improving the MP and increasing rice yield and could be adopted as a suitable approach for improving soil health, quality, and productivity.

Cadmium mobility in three contaminated soils amended with different additives as evaluated by dynamic flow-through experiments

As arable land has become an important sink for cadmium (Cd), soil is being recognized as a major source of metals to the food chain. It becomes, therefore, essential to investigate metal mobility in contaminated soils and to identify suitable remediation strategies. For this, immobilization of Cd was evaluated in contaminated stagnic anthrosol: S1, gleysol: S2 and fluvisol: S3 under flow through conditions. Ten treatments including control were tested alone or in composite form firstly at natural Cd contents (0.58–0.69 mg kg−1). Here, T2 (lime), T5 (biochar) and T10 (composite amendment) were found better in reducing the Cd concentration in the soils’ leachates, so, their efficacy was further investigated in the same soils of higher Cd contents (1 and 2 mg kg−1 imposed by soil spiking). Amendments significantly reduced the leachate metal contents especially in 1 mg kg−1 spiked soils. Characterization of T2, T5 and T10 revealed their structural transformations in all the studied soil types, while active functional groups e.g. C–O, CO, O–H, Si–O–Si, ester and alcoholic groups were notably involved in Cd precipitation or adsorption on amendments surface. Variations in Cd speciation in these soils exhibited the exchange of Cd to more stable fractions with tested amendments. These continuous-flow experiments confirmed the strong efficiency of T2, T5 and T10 in reducing the Cd concentration in the leachate of three soils. This study has strong implications in understanding the role of different amendments in controlling the fate, leaching behavior and immobilization of Cd in diverse soil types.

Evaluation of selenium bioavailability to Brassica juncea in representative Chinese soils based on diffusive gradients in thin-films (DGT) and chemical extraction methods

Selenium (Se) is an essential micronutrient for humans but is toxic when consumed in excess through the food chain, such as vegetables. Therefore, it is imperative to understand the relationship between the bioavailability of Se in soil and its uptake in edible parts of vegetables. This study investigated Se bioavailability of Brassica juncea in six representative Chinese soils treated with different concentrations of exogenous selenate fertilizer (0–2 mg·kg−1) by comparing diffusive gradients in thin-films (DGT) and chemical extraction methods. The correlation coefficients between the Se uptake by Brassica juncea and soil available Se determined by different extraction methods was as follows: DGT > KCl > Water > EDTA > KH2PO4 > NaHCO3 extractions. In addition, soil properties were correlated between Brassica juncea and soil Se concentrations determined by chemical extraction methods, while the DGT method was independent of soil properties. DGT was more suitable for the measurement of Se thresholds for Udic Ferrisols, Mollisols, Stagnic Anthrosols, Fluviogenic Loamy Paddy soil, Silty Loam soil, and Calcaric Regosols with values of 373.34, 648.68, 436.29, 589.84, 295.35, and 464.95 μg·L−1, respectively. Thus, DGT may be an effective method for the prediction and evaluation of Se bioavailability to Brassica juncea in different soil types.

Effect of Eisenia foetida on the metal uptake by Sedum plumbizincicola in different types of contaminated soils

Sedum plumbizincicola is a native cadmium/zinc (Cd/Zn) hyperaccumulator in China. At present, it has been applied to remediation of Cd contaminated soils. As the large differences in the removal efficiency of Cd and Zn for different soil conditions, the enhancement measure is important for the phytoremediation process. There have been many studies on the effects of earthworms on plant growth. But the effects on the growth of S. plumbizincicola and heavy metal removal efficiency have been rarely reported. There were 2 pot experiments: S. plumbizincicola was planted on 3 types of soils: Perudic Luvisols, Stagnic Anthrosols, and Udic Cambisols inoculated with Eisenia foetida to explore the effect of Eisenia foetida on the growth and Cd/Zn absorption of S. plumbizincicola. Stagnic Anthrosols with higher Cd effectiveness was selected in the second season pot experiment for further research the combined effect of earthworm and rich straw. The results of the first pot experiment showed that the addition of earthworms in acidic Perudic Luvisols increased the shoot biomass of S. plumbizincicola by 106% compared with the control treatment, and the Cd and Zn uptake increased by 72.0% and 36.0%, respectively. The soil available Cd was reduced by the addition of earthworms. The other two soils inoculated with earthworms had no enhancement on phytoremediation, addition of earthworms together with straw could improve the growth of S. plumbizincicola and the Cd/Zn uptake in Stagnic Anthrosols. The above results indicated that adding earthworm can enhance the phytoremediation of Cd/Zn hyperaccumulator, and the addition of straw is an important synergistic technique for earthworm-enhanced phytoremediation of S. plumbizincicola.

Immobilization and sorption of Cd and Pb in contaminated stagnic anthrosols as amended with biochar and manure combined with inorganic additives

The present study evaluated the efficiency of pre-selected composite amendments (CA-1: biochar-lime-sepiolite-zeolite and CA-2: manure-lime-sepiolite) for immobilization and sorption of Cd and Pb in field and batch sorption experiments. The field experiment was performed in a co-contaminated clay purple soil (stagnic anthrosols). Along with a control experiment (T1), CA-1 and CA-2 were tested at different rates including 750, 1500, 3000 and 6000 kg ha−1 by growing wheat as the test crop. The obtained results revealed that the highest dose of both composites (T5: 6000 kg ha−1 and T9: 6000 kg ha−1) increased the soil pH to 6.85 and 6.81, respectively as compared to the control (5.63). DTPA-extractable Cd and Pb contents decreased with composite treatments (T7 and T4) at harvest stage samples. Metal fractionation depicted that application of amendments decreased the exchangeable fraction at harvesting stage. Application of CA-2 and CA-1 (3000 kg ha−1) significantly increased the plant biomass (by 28% and 24%, respectively) and grain yield (by 26% and 22%, respectively) of wheat. Furthermore, batch sorption experiment results revealed that Langmuir adsorption model better fitted the sorption results with R2 values ranging between 0.99 and 0.91 for Cd and Pb, respectively. CA-1 and CA-2 exhibited the maximum adsorption capacity for Cd with no significant difference among treatments but Pb adsorption capacity was highest in CA-1 followed by CA-2 and control. The results of our experiments revealed that the application of organics combined with inorganic materials enhanced Cd and Pb immobilization and sorption, consequently reducing metals availability in laboratory and field conditions. Moreover, for field trials, application of the composite amendments at 3000 kg ha−1 emerged as the suitable treatment for tested wheat-grown area.

Composition of clay minerals and their pedogenetic and taxonomic implications for Stagnic Anthrosols derived from different parent materials in Hunan Province, China

The aims of this study were to investigate the composition of clay minerals in soils derived from different parent materials and to elucidate how parent materials and pedogenic environment affect the distribution of clay minerals and reveal the implications for pedogenetics and taxonomy in Stagnic Anthrosols. Clay mineralogy and physicochemical properties of the Hydragric horizon of Stagnic Anthrosols derived from granite (GR), plate shale (PS), quaternary red clays (QRC), limestone (LS), purple sandy shale (PSS) and fluvial-lacustrine deposit (FLD) located in Hunan Province of China were analysed to explore the relationships between the conditions influencing the formation of the soil and the composition of clay minerals. Results indicated that the composition of clay minerals is closely related to both parent material and type of Stagnic Anthrosols: the soils derived from GR, PS and QRC, which are mostly classified as Fe-accumulic-Stagnic Anthrosols, are dominantly 1:1 type kaolinite and vermiculite and illite/vermiculite mixed layer minerals of widespread distribution. However, soils derived from LS, PSS and FLD were mainly classified as Hapli-Stagnic Anthrosols and are mainly composed of 2:1 type illite/smectite mixed layer minerals, where chlorite is commonly found. Illite is widely distributed and its content varies the least among different parent materials. An extremely significant relationship between pH and kaolinite, chlorite and mixed layer minerals was noted, and the two kinds of mixed layer minerals showed highly significant negative correlation. This study revealed that the types and quantities of clay minerals in the soil are closely related to the types of parent material. This reflected better direction and degree of development in Stagnic Anthrosols, which is related to the physicochemical properties of parent material and can be used as one of the bases for the classification of soil groups and subgroups within the soil family for Stagnic Anthrosols in Chinese Soil Taxonomy.

Stability and transport of titanium dioxide nanoparticles in three variable-charge soils

The exposure pathways and environmental impacts of titanium dioxide nanoparticles (TiO2 NPs) released into soils could be significantly influenced by their stability and transport behaviors. The aim of this study was to investigate the stability and transport of TiO2 NPs in three variable-charge soils and to determine the key factors controlling these behaviors. Three surface (0~15 cm) variable-charge soils derived from quaternary red clay, humid ferralsols and stagnic anthrosols collected from Yingtan, Jiangxi Province (YT-H and YT-S, respectively), and humid ferralsols collected from Fuyang, Zhejiang Province (FY-H), were used in this study. Batch sedimentation experiments of TiO2 NPs in soil suspensions were performed for 10 h to quantify their stability. Transport of TiO2 NPs in soil columns was conducted with and without the presence of fulvic acid (FA). Apart from soil organic matter (SOM) and iron oxides, there was no significant difference between the tested soils. Batch experiments showed that TiO2 NPs were more stable in the YT-S soil suspension with high dissolved organic matter than in the YT-H and FY-H soil suspensions. In the column experiments, all TiO2 NPs were retained in YT-H and YT-S, while 11% of the TiO2 NPs were eluted from FY-H with a low amorphous iron oxide content. The significant retention of TiO2 NPs in the soils could be attributed to the straining and adsorption of TiO2 NPs on the surface of soil particles. FA enhanced the transport of TiO2 NPs in YT-H and FY-H by dispersing the TiO2 NPs and reducing their adsorption onto soil particles, while all the TiO2 NPs dispersed in the FA solution were still deposited in YT-S with a high amorphous iron oxide content. The stability of TiO2 NPs in three variable-charge soil suspensions was dependent on the SOM. However, the mobility of TiO2 NPs in soils was not directly related to their stability in the soil suspensions. The difference in amorphous iron oxide content could induce the disparity in mobility of TiO2 NPs in soils.

夜间增温对稻田甲烷排放的影响及其高光谱估算

PDF HTML阅读 XML下载 导出引用 引用提醒 夜间增温对稻田甲烷排放的影响及其高光谱估算 DOI: 10.5846/stxb201707201304 作者: 作者单位: 南京信息工程大学气象灾害预报预警与评估协同创新中心/江苏省农业气象重点实验室,南京信息工程大学气象灾害预报预警与评估协同创新中心/江苏省农业气象重点实验室,南京信息工程大学气象灾害预报预警与评估协同创新中心/江苏省农业气象重点实验室,南京信息工程大学气象灾害预报预警与评估协同创新中心/江苏省农业气象重点实验室,南京信息工程大学气象灾害预报预警与评估协同创新中心/江苏省农业气象重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41375159）；江苏省自然科学基金项目（BK20131430） Methane emission in response to nighttime warming and its hyperspectral estimation in a paddy field Author: Affiliation: Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters/Jiangsu Key Laboratory of Agricultural Meteorology,Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters/Jiangsu Key Laboratory of Agricultural Meteorology,Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters/Jiangsu Key Laboratory of Agricultural Meteorology,Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters/Jiangsu Key Laboratory of Agricultural Meteorology,Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters/Jiangsu Key Laboratory of Agricultural Meteorology Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:昼夜不对称增温是全球气候变化的主要特征之一，有关夜间增温对稻田甲烷（CH4）排放影响的报道尚不多见。通过田间模拟试验，研究了被动式夜间增温下水稻田CH4排放及高光谱的特征，并用高光谱数据对稻田甲烷排放进行定量模拟。田间试验设夜间增温（NW）和对照处理（CK），夜间增温即在整个水稻生育期的夜间（19：00-6：00）用铝箔反射膜覆盖水稻冠层。结果表明，夜间增温显著促进水稻拔节期和抽穗期-灌浆期CH4排放。水稻冠层近红外光谱反射率表现为，在分蘖期和拔节期时，NW>CK；而在抽穗-灌浆期和成熟期时，CK>NW。水稻冠层光谱反射率、一阶导数光谱及光谱特征值均与CH4排放通量显著相关，相关系数最大可达0.8（P < 0.01），其中以"蓝边面积"（SDb）构成的二次多项式模型模拟精度和检验精度综合最佳，决定系数R2分别为0.70和0.72。研究结果对稻田CH4排放通量遥感监测的可行性提供了理论依据和技术支持。 Abstract:Asymmetric diurnal warming is one of the main features of global climate change, but the effects of nighttime warming on CH4emission from paddy fields is unclear. A field experiment with rice was conducted at the Station of Agricultural Meteorology, Nanjing University of Information Science and Technology, Nanjing, China, to investigate the effects of passive nighttime warming on CH4 emission in a paddy field and rice canopy hyperspectral characteristics. CH4 emission flux was estimated with hyperspectral data. The tested rice was hybrid rice cv. Y Liangyou 3399. The tested paddy soil was classified as a Typic Stagnic Anthrosol. The experiment was designed with two levels of warming, i.e., nighttime warming(NW) and control(CK). NW was created by covering the rice canopy with an aluminum foil reflective film at night(19:00-6:00).CH4 emission was measured by the closed chamber method at one-week intervals during the rice-growing period. The results showed that NW significantly increased CH4 emission at the rice jointing and heading-grain filling stages. Compared to CK, NW increased the reflectance of the near-infrared spectrum on the canopy at the tillering and jointing stages, but decreased at the heading-grain filling and maturity stages. Positive correlations were observed in the relationships of CH4 emission with spectral reflectance and the first derivative and the characteristic value of the spectrum. After comparing correlation coefficients (R2) of the fitting models and prediction models, the quadratic polynomial model by 'Area of Blue Edge' (SDb) was found to be the best model(fitting model R2=0.70, prediction model R2=0.72) for estimating CH4 emission. The results of this study provide a theoretical basis for and demonstrate the feasibility of non-destructively monitoring of CH4 emission in paddy fields. 参考文献 相似文献 引证文献

Elevated Atmospheric CO2 and Drought Affect Soil Microbial Community and Functional Diversity Associated with Glycine max

Abstract Under the background of climate change, the increase of atmospheric CO2 and drought frequency have been considered as significant influencers on the soil microbial communities and the yield and quality of crop. In this study, impacts of increased ambient CO2 and drought on soil microbial structure and functional diversity of a Stagnic Anthrosol were investigated in phytotron growth chambers, by testing two representative CO2 levels, three soil moisture levels, and two soil cover types (with or without Glycine max). [...]

Effects of Elevated CO2 and Drought on Plant Physiology, Soil Carbon and Soil Enzyme Activities

AbstractGlobal climate models have indicated high probability of drought occurrences in the coming future decades due to the impacts of climate change caused by a mass release of CO2. Thus, climate change regarding elevated ambient CO2 and drought may consequently affect the growth of crops. In this study, plant physiology, soil carbon, and soil enzyme activities were measured to investigate the impacts of elevated CO2 and drought stress on a Stagnic Anthrosol planted with soybean (Glycine max). Treatments of two CO2 levels, three soil moisture levels, and two soil cover types were established. The results indicated that elevated CO2 and drought stress significantly affected plant physiology. The inhibition of plant physiology by drought stress was mediated via prompted photosynthesis and water use efficiency under elevated CO2 conditions. Elevated CO2 resulted in a longer retention time of dissolved organic carbon (DOC) in soil, probably by improving the soil water effectiveness for organic decomposition and mineralization. Drought stress significantly decreased C:N ratio and microbial biomass carbon (MBC), but the interactive effects of drought stress and CO2 on them were not significant. Elevated CO2 induced an increase in invertase and catalase activities through stimulated plant root exudation. These results suggested that drought stress had significant negative impacts on plant physiology, soil carbon, and soil enzyme activities, whereas elevated CO2 and plant physiological feedbacks indirectly ameliorated these impacts.

Remediation of metal-contaminated paddy soils by chemical washing with FeCl3 and citric acid

Batch extraction experiments were conducted to investigate the chemical washing of metal-contaminated paddy soils using mixtures of ferric chloride (FeCl3) and citric acid (CTA). The effects of the extractants (FeCl3, CTA, or FeCl3 + CTA) and washing cycles (single-step or multistep washing) on the metal removal efficiency were studied. FeCl3 + CTA increased metal removal efficiency to some extent compared to single FeCl3 or CTA. When the liquid-to-solid ratio was 2:1 with three washes and two rinses, a mixture of 10 mmol L−1 FeCl3 and 20 mmol L−1 CTA removed 78.9% Cd, 15.8% Cu, 34.0% Zn, and 18.1% Pb from a Typic Fe–accumuli–Stagnic Anthrosols. Using multistep washing instead of single-step increased the metal extraction effect. Moreover, the removal efficiency and speciation of metals in different soils and changes in soil properties in washed soils were also studied. The removal rate of Cd was higher than that of Zn, Cu, or Pb because of the higher proportions of acid-soluble forms of Cd in the soils. The removal of metals from different soils depended on the distribution of metal speciation and soil type. Soil pH, CEC, exchangeable Ca, and exchangeable Mg decreased significantly after soil washing. We conclude that chemical washing of metal-contaminated paddy soils with mixtures of FeCl3 and citric acid may be a feasible technique for soil remediation.

Effect of Farming Practices on the Variability of Phosphorus Status in Intensively Managed Soils

Phosphorus (P) in agricultural soils is an important factor for soil quality and environmental protection. Understanding of P and its fractions in soils on a regional scale is imperative for effective management or utilization of P and the improvement of P availability in soils. To study spatial variability and changes of soil P and its fractions as affected by farming practices, soil samples were taken in Rugao County, Jiangsu Province of China, an intensive agricultural area in the Yangtze River Delta region, in years of 1982 (n = 1 514), 1997 (n = 1 651), and 2002 (n = 342). High spatial variabilities of Olsen P and total P (TP) were observed throughout the study area. Loamy Stagnic Anthrosols and clay or loamy Aquic Cambosols had significantly higher concentrations of Olsen P and TP than sandy Ustic Cambosols and Aquic Cambosols. Olsen P and TP were increased from 1982 to 2002. The accumulations of Olsen P and TP in the cultivated soils were likely related to the increased application of P fertilizer, organic input, and soil incorporation of crop residues as well as conversion of soil use. Accumulated soil P was dominantly in labile and semi-labile P fractions. These P fractions may be utilized by future crop production by adjusting management practices, but they also pose a serious threat to nearby water bodies. Future strategies should include decreasing P fertilization in soils and supporting sustainable management. The information from this study can be used to monitor changes in soil fertility and environmental risks so that the use of fertilizers can become more rational.

Anthropogenic mercury sequestration in different soil types on the southeast coast of China

Soil is a major pool of anthropogenically emitted mercury (Hg) and will in turn be a source of atmospheric Hg contamination. It was hypothesized that accumulation of anthropogenic Hg in the soil at a regional scale is associated with the amount of Hg emitted to the atmosphere and soil type. A total of 448 horizon samples were collected from the typical soil types of the Yangtze River Delta and Pearl River Delta. Titanium (Ti) was selected as a reference element to discriminate anthropogenic Hg from the Hg associated with pedogenic processes. Soil pools of anthropogenic Hg were quantified to show the difference in Hg sequestration among soil types and regions. Soil pools of anthropogenic Hg ranged from 0.70 to 6971 g/ha in the Yangtze River Delta (YRD) and from 35.81 to 13098.71 g/ha in the Pearl River Delta (PRD). The estimated soil Hg pools were well correlated with the amounts of Hg emitted in these two regions. Soil properties, namely organic matter content, amorphous iron oxides, and cation exchange capacity, were significantly (p < 0.01) and positively correlated with soil Hg accumulation. Meanwhile, soil organic matter was the most important factor to determine the depth distribution of Hg in soil profile of the majority of soils. Perudic Cambisols and Stagnic Anthrosols which contained higher content of amorphous iron oxides had the highest soil Hg pools, indicating the importance of amorphous iron oxides other than organic matter to the Hg retention in soil. Soil and soil horizons with low pH and high salinity did show a low accumulation of Hg probably due to the remobilization of Hg under such conditions. In addition to the amount of Hg emitted, soil types may be a major factor in controlling the sequestration of anthropogenic Hg in both regions. Stagnic Anthrosols are an important pool for retention of anthropogenic Hg.

Phytoavailability of cadmium (Cd) to Pak choi (Brassica chinensis L.) grown in Chinese soils: a model to evaluate the impact of soil Cd pollution on potential dietary toxicity.

Food chain contamination by soil cadmium (Cd) through vegetable consumption poses a threat to human health. Therefore, an understanding is needed on the relationship between the phytoavailability of Cd in soils and its uptake in edible tissues of vegetables. The purpose of this study was to establish soil Cd thresholds of representative Chinese soils based on dietary toxicity to humans and develop a model to evaluate the phytoavailability of Cd to Pak choi (Brassica chinensis L.) based on soil properties. Mehlich-3 extractable Cd thresholds were more suitable for Stagnic Anthrosols, Calcareous, Ustic Cambosols, Typic Haplustalfs, Udic Ferrisols and Periudic Argosols with values of 0.30, 0.25, 0.18, 0.16, 0.15 and 0.03 mg kg−1, respectively, while total Cd is adequate threshold for Mollisols with a value of 0.86 mg kg−1. A stepwise regression model indicated that Cd phytoavailability to Pak choi was significantly influenced by soil pH, organic matter, total Zinc and Cd concentrations in soil. Therefore, since Cd accumulation in Pak choi varied with soil characteristics, they should be considered while assessing the environmental quality of soils to ensure the hygienically safe food production.

Chromium-resistant bacteria promote the reduction of hexavalent chromium in soils.

Knowledge of the chromium (Cr) redox process in soil is important in addressing Cr bioavailability and risk assessment of contaminated soils. In this study, seven representative agricultural soils with different physicochemical properties were used to investigate the importance of microbially mediated Cr(VI) reduction and the response of soil bacterial community to Cr contamination. Chromium application increased soil bacterial diversity in Periudic Argosols, Calcaric Regosols, Stagnic Anthrosols, Mollisols, Typic Haplustalfs, and Ustic Cambosols, with an exception of Udic Ferrisols. The soil bacterial community responded to Cr contamination through changes in bacterial community structure, with Cr-resistant bacteria becoming the dominant species, and the percentage of Cr-resistant bacteria of total cultivable bacteria was 89.9, 75.2, 92.8, 65.3, 72.8, 77.3, and 65.4%, respectively, for Periudic Argosols, Udic Ferrisols, Calcaric Regosols, Stagnic Anthrosols, Mollisols, Typic Haplustalfs, and Ustic Cambosols. , , , , , , , , , and were identified as the Cr-resistant bacteria. Moreover, our results demonstrated that microbial reduction was an important Cr(VI) reduction pathway, and the relative contribution of microorganisms to Cr(VI) reduction was 14.4, 44.0, 20.6, 34.9, 21.9, 21.7, and 22.0%, respectively for Periudic Argosols, Udic Ferrisols, Calcaric Regosols, Stagnic Anthrosols, Mollisols, Typic Haplustalfs, and Ustic Cambosols. Soil properties, especially Fe(II) and soil particle distribution, affected the microbially mediated Cr(VI) reduction. These results provide useful information for the bioremediation of Cr-contaminated soils under a wide range of environmental conditions.

Cadmium phytoavailability to rice (Oryza sativa L.) grown in representative Chinese soils. A model to improve soil environmental quality guidelines for food safety

Food chain contamination by cadmium (Cd) is globally a serious health concern resulting in chronic abnormalities. Rice is a major staple food of the majority world population, therefore, it is imperative to understand the relationship between the bioavailability of Cd in soils and its accumulation in rice grain. Objectives of this study were to establish environment quality standards for seven different textured soils based on human dietary toxicity, total Cd content in soils and bioavailable portion of Cd in soil. Cadmium concentrations in polished rice grain were best related to total Cd content in Mollisols and Udic Ferrisols with threshold levels of 0.77 and 0.32mgkg−1, respectively. Contrastingly, Mehlich-3-extractable Cd thresholds were more suitable for Calcaric Regosols, Stagnic Anthrosols, Ustic Cambosols, Typic Haplustalfs and Periudic Argosols with thresholds values of 0.36, 0.22, 0.17, 0.08 and 0.03mgkg−1, respectively. Stepwise multiple regression analysis indicated that phytoavailability of Cd to rice grain was strongly correlated with Mehlich-3-extractable Cd and soil pH. The empirical model developed in this study explains the combined effects of soil properties and extractable soil Cd content on the phytoavailability of Cd to polished rice grain. This study indicates that accumulation of Cd in rice is influenced greatly by soil type, which should be considered in assessment of soil safety for Cd contamination in rice. This investigation concluded that the selection of proper soil type for food crop production can help us to avoid the toxicity of Cd in our daily diet.

Accumulation of Chromium in Pak Choi (Brassica chinensis L.) Grown on Representative Chinese Soils

Anthropogenic chromium (Cr) pollution in soils poses a great threat to human health through the food chain. It is imperative to understand Cr accumulation properties in common vegetables because the proportion of vegetables consumed has increased with the improvement of living standards. This study investigated Cr accumulation in pak choi ( L.) grown on six representative agricultural soils in China. Chromium concentration in the edible parts of pak choi generally increased with soil Cr concentrations following the order: Ustic Cambosols > Periudic Argosols > Mollisols > Calcaric Regosols > Stagnic Anthrosols > Udic Ferrisols. Simple correlation analysis indicated that Cr concentration in pak choi was significantly correlated with the total Cr, Mehlich-3-extractable Cr, and Cr(VI). Stepwise multiple regression analysis also demonstrated that the phytoavailability of Cr was strongly correlated with the extractable fraction by Mehlich-3, total Cr concentration, soil organic matter, and Fe(II). Critical Cr concentrations in these six soils were evaluated for pak choi based on the maximum safe level for daily intake of Cr. Total soil Cr can be used as Cr thresholds for potential dietary toxicity in pak choi. Mehlich-3-extractable Cr is most suitable to be used as Cr thresholds for Periudic Argosols, Udic Ferrisols, Mollisols, and Ustic Cambosols, with values of 20.7, 15.8, 21.2, and 20.4 mg kg, respectively, whereas Cr(VI) is most suitable for Calcaric Regosols and Stagnic Anthrosols, with values of 26.5 and 28.0 mg kg, respectively.

Model for Evaluation of the Phytoavailability of Chromium (Cr) to Rice (Oryza sativa L.) in Representative Chinese Soils

Anthropogenic chromium (Cr) pollution in soils poses a great threat to human health through the food chain. It is imperative to understand Cr phytoavailability to rice (Oryza sativa L.), which is a major staple food crop for the largest population of people on Earth. This study was aimed to establish a model for evaluation of the phytoavailability of Cr to rice in six representative Chinese soils based on soil properties. Simple correlation analysis indicated that Cr concentration in polished rice was significantly correlated with total Cr, Mehlich-3 extractable Cr, and Cr(VI) in soil. Stepwise multiple regression analysis also demonstrated that the Cr phytoavailability was strongly correlated with soil total Cr, Mehlich-3 extractable Cr, Cr(VI) concentration, soil organic matter, Fe(II), and particle size distribution. Critical Cr concentrations in the six soils were evaluated for rice based on the maximum safe level for daily intake of Cr. Mehlich-3 extractable Cr are the most suitable Cr thresholds for Periudic Argosols, Udic Ferrisols, Mollisols, and Ustic Cambosols with values of 1.54, 0.56, 0.42, and 2.18 mg kg(-1), respectively, while Cr(VI) are adequate thresholds for Calcaric Regosols and Stagnic Anthrosols with values of 0.68 and 0.84 mg kg(-1), respectively.

Reduction Kinetics of Hexavalent Chromium in Soils and Its Correlation with Soil Properties

The toxicity of chromium (Cr) to biota is related to its chemical forms and consequently to the redox conditions of soils. Hexavalent Cr[Cr(VI)] may undergo natural attenuation through reduction processes. In this study, the reduction kinetics of Cr(VI) in seven soils and its relationships with soil properties were investigated with laboratory incubation experiments. The results indicate that the reduction of Cr(VI) can be described by a first-order reaction. The reduction rates of Cr(VI) in the seven soils decreased in the order: Udic Ferrisols > Stagnic Anthrosols > Calcaric Regosols > Mollisol > Typic Haplustalf > Periudic Argosols > Ustic Cambosols. Simple correlation analysis revealed that the reduction of Cr(VI) in soils was positively related to organic matter content, dissolved organic matter content, Fe(II) content, clay fraction, and to the diversity index of the bacterial community but negatively correlated with easily reducible Mn content. Using stepwise regression, the reduction of Cr(VI) in soil could be quantitatively predicted by the measurement of dissolved organic matter content, Fe(II) content, pH, and soil particle size distribution, with a fitting level of 95.5%. The results indicated that the reduction of Cr(VI) in natural soils is not controlled by a single soil property but is the result of the combined effects of dissolved organic matter, Fe(II), pH, and soil particle size distribution.

Long-term effect of fertilizer application on rice yield, potassium uptake in plants, and potassium balance in double rice cropping system

A 27 years field experiment was conducted on a Fe-Accumli Stagnic Anthrosol to evaluate the effects of long-term application of fertilizer, pig manure (PM), and rice straw (RS) on rice yield, uptake, and usage efficiency of potassium, soil K pools, and the nonexchangeable K release under the double rice cropping system in South Central China. Common cropping pattern in the study was early rice-late rice-fallow (winter). The field treatments included CK (no fertilizer applied), NP, NK, NPK, and NK + PM, NP + RS, NPK + RS. The pig manure and rice straw was applied in both the early rice and late rice cropping season. The ranking order of 27 years average annual grain yield were the CK<NK<NP<NK + PM<NP + RS<NPK<NPK + RS treatments. The negative yield change trends were observed in the CK and NP and NK treatments of unbalanced nutrient application in the case of omitted-K and P-omitted. The positive yield change trends were observed in balanced applications of NPK and combined application of fertilizer (NPK) with pig manure (NK + PM) or rice straw (NP + RS and NPK + RS). The application of K fertilizer (NPK) increased grain yield by 56.7 kg·hm−2·a−1 over that obtained with no K application (NP). The combined application of pig manure with fertilizer (NK + PM) increased by 82.2 kg·hm−2 per year compared with fertilizer application alone (NK). The combined application of rice straw with fertilizer (NP + RS and NPK + RS) increased on the average of 34.4 kg·hm−2 per year compared with fertilizer application alone (NP and NPK). In all fertilizer, pig manure and rice straw combinations, K uptake change trends in rice plants of the early rice was positive except for CK and NP treatments. The results showed that the total removal of K by the rice plants exceeded the amounts of total K applied to the soil in all treatments, which showed a negative K balance. This ranged from 106.3 kg·hm−2·a−1 in CK treatment to 289.6 kg·hm−2·a−1 in the NPK + RS treatment. Continuous annual application of 199.2 K kg·hm−2 to rice resulted in an accumulation (58 kg·hm−2) of exchangeable K (1 mol NH4OAc extractable K) in 0–45 cm soil depth over the study period, despite the higher average annual uptake of K by the system (225.7 kg·hm−2). However, nonexchangeable K increased substantially from 1090 kg·hm−2 to 1113 kg·hm−2 and 1140 kg·hm−2 in the 0–45 cm soil layer in NPK + RS and NPK treatments after 27 years of the continuous double rice cropping system, respectively. Thus, long-term rational application of K fertilizer may increase sustainable K fertility of the continuous double rice cropped system.