Chemical fractionation of seven heavy metals (Cd, Cu, Fe, Mn, Ni, Pb, and Zn) in selected paddy soils of Iran

The content and fractionation of seven heavy metals (Cd, Cu, Fe, Mn, Ni, Pb, and Zn) were determined in 28 surface soil samples (0–20 cm) of agricultural topsoil from Isfahan Province in central Iran. The order of abundance of metals in the soils was Fe (1240.4 mg kg^?1) > Mn (95.7 mg kg^?1) > Pb (51.6 mg kg^?1) > Zn (23.8 mg kg^?1) > Ni (13.4 mg kg^?1) > Cu (7.0 mg kg^?1) > Cd (2.8 mg kg^?1). Iron, Mn, Ni, Pb, and Zn existed in paddy soils mainly in Fe-Mn oxides (53.6 %, 65.2 %, 40.4 %, 40.8 %, 53.3 %, respectively), whereas Cu and Cd occurred essentially as residual mineral phase (41.4 %) and carbonate (36.1 %), respectively. The mobile and bioavailable fractions of Cd, Cu, Fe, Mn, Ni, Pb, and Zn in paddy soils averaged 48.8, 20.8, 0.79, 29.2, 28.5, 41.1, and 24.8 %, respectively, which suggests that the mobility and bioavailability of the seven metals probably decline in the following order: Cd > Pb > Mn ≥ Ni > Zn > Cu ? Fe, suggesting greater contribution of anthropogenic Cd. As Cd in soil is easily accumulated by plants through the root system, the concentration of Cd in these paddy soils could be a concern to human health.     

The effect of waterlogging on electrochemical properties and soluble nutrients in paddy soils

This study was conducted to investigate the influence of waterlogging on availability of nutrients in paddy soils. The five soils were incubated under a waterlogged condition at 30 °C for 12 weeks. The EC, Eh, pH, NH₄, K, Na, Ca, Mg, Cl, P, Fe, and Mn of soil solutions were monitored over the waterlogged period. The Eh values generally dropped to the lowest point within 14 days of waterlogging, then increased, and reached equilibrium after 8 weeks of waterlogging. The soil pH decreased in the first 2–4 weeks of waterlogging. The EC values increased partly due to dissolution of soluble salts in the first 2 weeks. The concentrations of soluble NH₄ were significantly increased with waterlogging, reached maximum values at week 4–6, and then declined to the initial level. Waterlogging increased the concentration of soluble K, Ca, Mg, Fe, and Mn ions, the magnitudes of changes were greatly affected by soil properties. Increases in soluble Na, K, Ca, and Mg were attributed to the increase in solubility of insoluble salts and increase in competition for the exchange sites. Increases in soluble Fe and Mn induced by waterlogging were attributed to the dissolution of Fe and Mn oxides under reduced conditions.     

Pb fractionation and redistribution as affected by applied inorganic amendments under different soil moisture regimes and incubation time in saline–sodic Pb-polluted paddy soil

Bioavailability and mobility of lead (Pb) in soils depend upon their partitioning between solution-solid phases and their further fractionation and redistribution among different solid-phase components. However, the dynamics of Pb in salt-affected (saline–sodic) Pb-contaminated (polluted) paddy soil need more exploration particularly under the influence of application of amendments at varying hydrological regimes and residence time. In this context, an incubation study was conducted to investigate the effect of application of three inorganic amendments (gypsum, rock phosphate and diammonium phosphate) on Pb fractions at two soil moisture regimes (flooding regime and 75% field capacity) and two incubation times (after 2 and 30 days) successively in non-saline/sodic and saline–sodic Pb-polluted paddy soils. After applied treatments, the concentration of Pb in five, i.e., exchangeable (F1), carbonate (F2), Fe–Mn oxide (F3), organic matter and sulfide bound (F4) and residual (F5) fractions, was assessed by sequential extraction. The results showed that the Pb spiked in the soils was significantly (P?≤?0.05) transformed from easily extractable (exchangeable and carbonate) fractions into less labile (Fe–Mn oxide, OM–S bound and residual) fractions. Among tested amendments, gypsum performed better in reducing the lability of Pb followed by DAP.     

Dynamics of cadmium concentration in contaminated rice paddy soils with submerging time

This study examined the change in the speciation of cadmium (Cd) in contaminated rice paddy soils with prolonged submergence. Three Changhua soils (CH1, CH2, and CH3) from central Taiwan and three Taoyuan red soils (TY1, TY2, and TY3) from northern Taiwan with different levels of heavy metal contamination were selected for the study. The Cd, Fe, Mn, soil pH, and Eh in soil solutions were determined as a function of submerging time. During submergence, the Fe and Mn concentration increased, while the SO₄ ^2? concentration decreased. The concentrations of Cd immediately increased in the soil solutions after a short submerging time and then decreased with further submergence. The sequential extraction showed that the exchangeable fraction decreased and the oxide-bound fraction increased after submergence. According to preliminary calculations of the MinteqA2 program, sulfate cannot be reduced to sulfite or sulfide under the soil Eh and pH values observed for the soils after prolonged submergence. Thus, the observed decreases of sulfate concentration may result from sulfate reduction in the micro-environments, which cannot be accounted for by the thermodynamic calculation. The reduction of sulfate to sulfide may subsequently result in the formation of CdS precipitate, which attributes to the decreases of Cd concentrations in the soil solutions after prolonged submergence.     

Rice husk biochar application to paddy soil and its effects on soil physical properties,plant growth,and methane emission

The objective of this study was to investigate the effects of the application of rice husk biochar on selected soil physical properties, rice growth, including root extension, and methane (CH₄) emissions from paddy field soil. Three replication experiments were conducted using outdoor pot experiments utilizing commercial rice husk biochar mixed with paddy soil at a rate of 0 (control), 2, and 4 % (weight biochar/weight soil) in which the rice was cultivated for 100 days under a continuously flooded condition. The physical properties of soils were analyzed before and after the growing periods. Some parameters of rice growth and CH₄ emissions of paddy soils were monitored weekly during the experiment. Root extension was also analyzed after harvesting. The experiments showed that the application of rice husk biochar improved the physical properties of paddy soils. It led to a decrease in bulk density and an increase in saturated hydraulic conductivity, including the total pore volume as well as the available soil water content. The shoot height of rice plants was significantly higher in soil amended with 4 % biochar than that in the control soil. However, other plant growth parameters and root extension were only slightly affected by the application. It was also found that amending soil with biochar led to a reduction of the total CH₄ emissions by 45.2 and 54.9 % for an application rate of 2 and 4 %, respectively, compared with the control. Our results showed that the higher the application rate, the stronger the effect of biochar was observed. More research is still necessary for a better understanding of the underlying mechanisms.     

Mineral characteristics of leaves of plants from different phylogeny grown in various soil types in the temperate region

The objective of this research was to analyze selected minerals in leavesof plants, belonging to 166 species growing in alluvial, low pH, brownforest and serpentine soils. Mineral characteristics of the soils involved werealso determined.For the macronutrients, in trees grown in alluvial soil, N, P, Ca, and Mgconcentrations of leaves were higher in recently evolved plants than inplants with a longer period of evolution; K concentration remained constantregardless of evolution. In grasses grown in alluvial soil, it was difficult todetect the general tendency of mineral concentration. N, P, and Kconcentrations in alluvial soil were closely related to those in low pH andserpentine soils. Ca concentration in alluvial soil was lower than that in lowpH and serpentine soils. Mg concentration in alluvial soils was higher thanthat in low pH soils, while lower than that in serpentine soil. Therefore, N,P, and K accumulated according to the plant characteristics for theseelements, while Ca and Mg accumulation was strongly affected by the soilproperties.For the micronutrients, in trees, Fe and Mn remained constant regardlessof evolution; Zn concentration was lower in recently-evolved plants than inplants with a longer period of evolution. In grasses, Fe, Mn, and Znconcentrations in Caryophyllids were high. Except for Caryophyllids, Fe andCu concentrations remained constant, Mn concentration decreased withevolution, Zn concentration was higher in recently-evolved plants than inplants with a longer period of evolution.     

Mechanical insights into the effect of fluctuation in soil moisture on nitrous oxide emissions from paddy soil

Paddy fields are subjected to fluctuating water regimes as a result of the alternate drying and wetting water management, which often incurs a sensitive change in N₂O emissions from paddy soils. However, how the soil moisture regulates the emission of N₂O from paddy soil remains uncertain. In this study, three incubation experiments were designed to study the effects of constant and fluctuating soil moisture on N₂O emission and the sources of N₂O emission from paddy soil. Results showed that the N₂O emission from paddy soil at 100 % WHC (water-holding capacity) was higher than that at 40, 65, 80, 120, and 160 % WHC, indicating that 100 % WHC was the optimum soil moisture content for N₂O emission under the incubation experiment. Small peak of N₂O flux appeared when the soil moisture content from 250 % WHC decreased near to 100 % WHC, lower than that triggered by nitrogen (N) fertilization, which was mainly owing to the low NH₄ ⁺ concentration at this period. Nitrification dominated the emissions of N₂O from paddy soil at 250 % WHC (54.96 %), higher than that of nitrification-coupled denitrification (6.74 %) and denitrification (38.3 %). The contribution of denitrification to N₂O emissions (44.10 %) was equivalent to that of nitrification (44.45 %) in soil at 100 % WHC, which was higher than that of 250 % WHC treatment. In conclusion, the finding suggested that the peak of N₂O in paddy soils during midseason aeration could be attributed to the occurrence of optimum soil moisture under sufficient N availability, favorable for the production and accumulation of N₂O.     

Nutritional characteristics of the leaves of native plants growing in adverse soils of humid tropical lowlands

Acid sulfate, peat, sandy podzolic, and saline soils are widely distributed inthe lowlands of Thailand and Malaysia. The nutrient concentrations in theleaves of plants grown in these type of soils were studied with the aim ofdeveloping a nutritional strategy for adapting to such problem soils. In sagoand oil palms that were well-adapted to peat soil, the N, P, and Kconcentrations were the same in the mature leaves, while the Ca, Mg, Na,and Fe concentrations were higher in the mature leaves of the oil palm thanof the sago palm. Melastoma malabathricum and Melaleuca cajuputi plantsthat were well-adapted to low pH soils, peat, and acid sulfate soils were alsostudied. It was observed that a high amount of Al accumulated in the M.marabathricum leaves, while Al did not accumulate in M. cajuputi leaves.M. cajuputi plants accumulated large amounts of Na in their leaves or stemsregardless of the exchangeable Na concentration in the soil, while M.malabathricum that was growing in saline-affected soils excluded Na.Positive relationships between macronutrients were recognized between Pand N, between K and N, and between P and K. Al showed antagonisticrelationships with P, K, Ca, Mg, Fe, Zn, Cu, and Na. Na also showedantagonistic relationships with P, K, Zn, Mn, Cu, and Al. Fe showed weakantagonistic relationships with Zn, Mn, Cu, and Al.     

武夷山市5种类型茶园土壤重金属剖面分布特征?

采用野外调查和室内分析相结合的方法,研究武夷山市5种类型茶园土壤（黄壤、红壤、潮砂土、高山草甸土、紫色土）重金属剖面分布特征。结果表明：茶园土壤 Fe、Mn、Cu、Zn、Cd 和 Pb 的含量范围分别为17.35～44.91 g·kg-1、144.81～693.55 mg·kg-1、4.36～57.12 mg·kg-1、74.92～236.27 mg·kg-1、0.09～0.67 mg·kg-1和22.71～91.87 mg·kg-1。不同类型茶园土壤重金属含量差异较大,茶园黄壤 Fe 和 Cu 含量显著高于其它土壤类型;潮砂土和高山草甸土茶园土壤 Mn、Zn 和 Cd 含量显著高于黄壤和红壤;茶园土壤 Pb 含量则以潮砂土最高,黄壤最低。不同重金属元素剖面分布规律略有不同,茶园土壤 Fe含量0～80 cm 深度内并无明显的变化规律;茶园土壤 Mn、Cu 和 Zn 含量在0～20 cm 土层含量较高（潮砂土除外）;黄壤、红壤和紫色土 Cd 和 Pb 含量由上至下呈递减的趋势,潮砂土 Cd 和 Pb 在40 cm 以下土层含量较高。相关分析表明,除了 Zn与 Fe 和 Cu 以外,其它重金属之间存在显著或极显著相关性,表现为多种重金属复合污染;土壤有机碳、全氮、pH、砂砾、粉粒和粘粒对茶园土壤重金属影响较大。     

As contamination alters rhizosphere microbial community composition with soil type dependency during the rice growing season

Rhizosphere microbes play a cardinal role in transformation and crop uptake of arsenic (As), thereby relieving or intensifying the risk of As contamination in the food webs. How rhizosphere microbiomes respond to As contamination in different paddy soils and rice growth stages is still unclear. Here, we conducted a rice pot experiment to address the effects of rice developmental stage and As contamination on the rhizosphere microbial communities in two contrast paddy soils, a yellow clayey paddy soil (YP, pH 5.1, soil organic matter 20.8 g/kg) and red paddy soil (RP, pH 6.2, soil organic matter 46.1 g/kg). The rhizosphere microbial communities were investigated using phospholipid fatty acids analysis at tillering, panicle initiation, and maturity stages. The results showed that rice growing in YP soil accumulated 2-10 times higher contents of As in root than that in RP soil. There was a significant effect of rice growing stage, independent of soil types and As treatment, on rhizosphere microbial community composition in both YP and RP soils as depicted by canonical correspondence analysis. As contamination significantly altered rhizosphere microbial community composition only in YP soil, which showed the soil type dependency of the As contamination effect. In RP soil, the higher content of soil organic matter reduced the impact of As contamination. Soil pH explained more percentage of variation in microbial community composition than soil DOC and DON did. These influences of soil physiochemical properties on heavy metal available and rhizosphere microbial community may lay the foundation for exploration of bioremediation potential.     

Effect of biochar on CH4 and N2O emission from soils vegetated with paddy

Biochar is believed to have positive impact on soil properties and plant yield. Due to the presence of C, it can also enhance CH₄ emission in paddy soils. On the other hand, ammonium sulphate can decrease CH₄ emission due to negative impacts on methanogenesis. Keeping these points in view, a pot experiment was conducted to determine the effect of biochar along with ammonium sulphate on CH₄ and N₂O emission from paddy soil. Analysis revealed that biochar treated soils released more CH₄ compared to untreated. Ammonium sulphate treated soil emitted the highest N₂O whereas biochar addition decreased its emission significantly. Further, total emission was found to be higher for CH₄ (16.9–34.7 g/m²) in comparison to N₂O (?0.05 to 0.02 g/m²) for all treatments. Biochar application has positive impact on plant variables such as panicle number and weight of panicles. This study suggests that biochar application significantly decrease N₂O emission and increase CH₄ emission possibly due to affecting the availability of organic C in the soil to microbial activity for methanogenesis. Another possibility for enhancing CH₄ emission by following biochar could be attributed to the increase in plant biomass.     

Effects of temperature and soil moisture on gross nitrification and denitrification rates of a Chinese lowland paddy field soil

Alternate wetting and drying (AWD) irrigation is widely adopted to save water in rice production. AWD practice shifts lowland paddy fields from being continuously anaerobic to being alternately anaerobic and aerobic, thus affecting nitrogen (N) transformations in paddy field soils. Using the barometric process separation technique, a large number of soil cores sampled from lowland paddy field soil profiles were measured for gross nitrification and denitrification rates under different temperature and soil moisture conditions. The gross nitrification and denitrification rates vary with rice growth stages and range between 1.18–30.8 and 0.65–13.54 mg N m^?3 h^?1, respectively. Results indicate that both gross nitrification and denitrification rates increased with the increase in temperature in all three studied soil layers. Gross nitrification rates significantly decrease with increasing soil moisture while denitrification rates increase, and different soil layers demonstrated different rates of variation to the increase in soil moisture. Gross nitrification rates in the cultivated horizon layer decreased more sharply with the increase in soil moisture. High soil water content is favorable to denitrification of all soil layers.     

转Bt基因水稻Cry1Ab杀虫蛋白在水稻土中的降解

室内研究了转 Bt基因水稻克螟稻 2号和华池B6 叶片中的Cry1Ab杀虫蛋白在稻田水稻土中的降解动态。分别将克螟稻 2号的粉碎叶片和华池B6 的整张叶片埋入 3种土壤 (即老黄筋泥田、青紫泥田和黄松田 )中 ,此后每隔 6～ 10d测定土壤或叶片中的Cry1Ab含量。克螟稻 2号粉碎叶片中的Cry1Ab均以处理后的前 36d,尤其是前 6d的降解较快 ,其中在青紫泥田中最快 ,黄松田中最慢。在处理后 6～ 36d内 ,不同土壤中的Cry1Ab残留量有显著差异 ,黄松田中的明显最高 ,老黄筋泥田中的次之 ,青紫泥田中的为最低 ;此后土壤间的残留量差异逐渐缩小 ,至处理后 78d差异已不明显。土壤淹水可显著加快华池B6 叶片中Cry1Ab的降解 ,且淹水后其降解动态在不同土壤之间十分相似 ;淹水对Cry1Ab降解的促进作用仅发生在前 12d之内 ,此后多数时间内残留量在淹水与非淹水处理间无显著差异。建立了各处理中Cry1Ab降解的动力学指数方程 ,相应地得出了其降解的半衰期。还讨论了土壤有机质和微生物等因子对土壤中Cry1Ab降解的影响。     

大豆锰素营养研究

采用水培试验研究大豆锰素营养,并分析了黄淮海及长江中下游大豆产区几种土壤的有效锰含量。结果表明:(1)大豆植株体内锰的浓度和含量随着培养介质中锰浓度增加而增加,(2)锰主要分布于叶部和根部,茎部最少,(3)锰与磷、铁间存在拮抗关系,(4)黄淮及长江中下游地区,沙土和砂姜黑土缺锰,黄棕壤有效锰含量丰富,淤土和二合土居中。     

云南文山植烟土壤肥力Fuzzy综合评价

以云南省文山烟区7个县的167个植烟土壤样本的养分含量为分析数据,采用 Fuzzy 综合评判法对烟区土壤综合肥力水平进行评价。结果表明,文山烟区主要以红壤和黄壤两种类型为主,植烟土壤中二级肥力占总样本数比例为50.30％,土壤肥力较好。描述性统计分析和Fuzzy综合评判法均表明,棕壤土和水稻土的肥力最高,其IFI值分别为0.797和0.774,红壤和黄壤的土壤肥力中等,其IFI值分别为0.637和0.638,石质土的IFI值为0.584,属于三级肥力土壤,肥力相对较低。     

近30年来桐庐县稻田土壤肥力演变趋势

为了解浙江省桐庐县稻田耕层土壤肥力现状及其演变趋势,利用历史资料和近期地力评价调查数据,探讨了近30年来桐庐县稻田耕层土壤主要肥力指标的变化特征。结果表明,近30年来,桐庐县稻田耕层土壤主要肥力指标发生了较大变化,但变化方向和变化程度因养分种类和区块而异。土壤p H值有轻微的酸化趋势,平均降低0.07个p H值单位;土壤阳离子交换量总体上以中低水平为主;土壤有机质显著降低,平均降幅为17.32%,以分水区块下降最为明显,降幅为24.17%;土壤有效磷和速效钾显著提升,平均增幅分别为173.75%和63.05%。其中,土壤有效磷已出现了累积现象,以桐君区块累积最为明显,增幅高达316.24%;土壤速效钾虽提升显著,但仍处于中等水平,桐君区块提升最多,增幅为112.62%。分析认为,施肥结构和种植制度的改变是引起桐庐县稻田土壤肥力变化的主要原因。     

低分子有机酸对茶园土壤中Al、F、P、Cu、Zn、Fe、Mn的活化效应

本文通过用不同浓度 (0mmol l、 0 5mmol l、 1mmol l、 2mmol l、 5mmol l、 10mmol l) ,不同有机酸(柠檬酸、草酸、酒石酸、苹果酸、琥珀酸 )及氨基酸 (谷氨酸、天冬氨酸 )对土壤中Al、F和几种营养元素 (P、Cu、Zn、Fe、Mn)的浸提实验 ,得出结论 :(1)有机酸及氨基酸对土壤中的Al、F、P、Cu、Zn、Fe、Mn具有活化作用 ,但其活化作用的大小因茶根分泌物的种类和浓度及土壤理化性质而异 ,即一般而言 ,柠檬酸、草酸、酒石酸、苹果酸的活化作用较     

Dynamics of dissolved ions in the soil of abandoned terraced paddy fields in Sado Island, Japan

We investigated the soil and soil water chemistry in abandoned terraced paddy fields (reed stand) and a thicket of deciduous broad-leaved trees (thicket stand) on the same slope in Sado Island, Japan. The soils gathered from these plots were incubated under different water conditions to examine the dynamics of dissolved ions. The organic carbon pool in the soil in the reed stand at the lower slope position was greater than the thicket stand at the middle slope position. The high concentration of base cations and an almost neutral pH of the soil water at the reed stand corresponded with the high exchangeable cation concentrations and base saturation in the soil. These results reflect the mineral-rich groundwater percolating down the slope, which may be produced by chemical weathering. An in situ sulfate reduction in the reed stand at deeper soil horizons was identified. The different water conditions in the incubated soils affected the soil pH(H₂O), transformation of Fe, and dominant anions (NO₃ ⁻, HCO₃ ⁻, and SO₄ ²⁻). These biogeochemical processes were more conspicuous in the reed stand at the lower slope position where the concentrations of organic matter and base cations were high. When the abandoned terraced paddy field is developed for the conservation of the Japanese crested ibis (Nipponia nippon) habitat in Sado Island, the reductive subsoil at the lower slope position should be kept waterlogged to limit sulfuric acid generation.     

THE YIELD AND UPTAKE OF PHOSPHORUS BY GRASSES AND CLOVERS

The yield and phosphorus uptake of grasses and clovers from Welsh soils were studied in 6-inch flower pots. Attempts were made to relate the phosphorus that the plants had been able to absorb to various measurements of the labile phosphorus in the soil. It is shown that in these'phosphate fixing' soils, absorption is not related to the exchangeable phosphorus as measured by equilibration. The values obtained for the latter are very high compared with the small amounts of phosphorus that the plants have been able to absorb, giving support to the view that the conversion of phosphorus to insoluble forms is not the main feature of'fixation' in these soils. Absorption of phosphorus by the grass was, however, related to the Larsen (L) values. In previously unfertilized soils, the fact that the L values were also related to the acetic-soluble phosphorus content confirmed the belief that acetic extraction is a suitable means for assessing the abilities of such soils to provide the necessary phosphorus for plant growth. In soils containing reserves of residual phosphorus, however, much of the phosphorus that contributed to the L values was not extracted by acetic acid, and this method of extraction is unsuitable for use with such soils. Placement of the applied phosphorus near the root zone led to a decrease in L values.     

红壤与茶叶品质的研究——Ⅰ.低丘红壤区茶叶品质成分的调查分析

通过4年主要生化品质成分测定和计算机统计分析,探讨了低丘红壤茶区茶样的自然和加工品质。对比分析结果表明,红壤春茶样,氨基酸、水浸出物、多酚、绿原酸有不同程度偏低,夏茶则比例失调,滋味较差;与此相反,酯类儿茶素、脂肪酸、粗纤维、无机成分中的 Al、Mn、Fe 异常增值,对此进行了综合分析讨论。