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The rare earth elements (REE) content, particle-size distribution, and clay mineralogical composition were analyzed for the paddy soils collected from the central region of the Mekong River, Laos, to study the origin and inherent potentiality of soils. REE as the chondrite-normalized curve or the plot of Ce/Eu against Eu/Sm were found to be useful for grouping soils according to their origins. The...
Chemical characteristics of highly humified humic acids (Type A HAs) from the subsoil of paddy fields (paddy soil HAs) and from the surface layer of ando soils (ando soil HAs) were compared based on the analyses of elemental composition, molecular size distribution, and 13 C CPMAS NMR spectra. Humic acids were extracted successively with 0.1 M NaOH and 0.1 M Na 4 P 2 O...
An eight-season rice-wheat rotation field experiment was conducted on two paddy soils in Siyang County and Liyang City of Jiangsu Province, respectively, to study the influence of different potash application patterns on crop yields and K-supplying power of the soils. The potash application patterns were: 216 kg K 2 O ha -1 in the rice season and no K in the wheat season; 216...
The microbial biomass, activity and substrate utilization pattern of seven Chinese paddy soils with different heavy metal concentrations in the vicinity of a Cu-Zn smelter was investigated. Microbial biomass and basal respiration were negatively affected by the elevated metal levels. Two important biological parameters, namely, the microbial biomass-C (C mic )/organic C (C o...
The southern Lake Tai area is an important agricultural area distributed with 500,000 ha of paddy soils. Based on the current soil phosphorus status, it is predicted that phosphorus in agricultural runoff from paddy fields is now one of the most dangerous threats to the quality of water in Lake Tai and the application of phosphorus fertilizers should be controlled. Phosphorus adsorption maxima based...
The processes and characteristics of nitrogen mineralization in paddy soils of the Taihu Region of China were studied with 120-day anaerobic incubation at 25 and 35 o C. Results showed that the organic nitrogen mineralized ranged from 4.0% to 9.4% of total N (60-241 mg kg -1 ) and that the mineral N was only correlated with total N (partial correlation analysis). The pH changed...
The impact of heavy metal pollution on growth and water quality has become a public concern. Fractionation of soil lead (Pb) is an important approach of chemical characterization and can provide useful information on its bioavailability. A greenhouse study was undertaken to estimate the availability of Pb fractions to rice in two paddy soils of Inceptisol (Fluventic Umbrepts) and Ultisol (Plinthudic...
Soil structure is known to affect water and solute movement and to characterize soil quality. For paddy fields, the soil structure has not been explored nor discussed in detail with respect to rice crop nutrient uptake and root development. The objectives were to visualize the size and connectivity of structural pores including arrangement of aggregates and to quantify the vertical bulk density distribution...
Physical protection in aggregates has been commonly accepted as a fundamental mechanism for soil organic carbon (SOC) sequestration for China's paddy soils. However, the role of chemical protection of physically protected SOC has not yet been evaluated. Herewith the authors report a cross-site study on SOC binding forms of both bulk soils and different particle size fractions (PSFs) obtained by low-energy...
China's rice paddies, accounting for 19% of the world's total, play an important role in soil carbon (C) sequestration. In order to reduce uncertainties from upscaling spatial processes of the DeNitrification–DeComposition (DNDC) model for improving the understanding of C sequestration under recommended management practices (RMPs), we parameterized the DNDC model with a 1:1,000,000 polygonal soil...
Paddy field is generally subjected to many cycles of alternative flooding and drying (AFD) during rice growing. The AFD cycles can create a large variation in soil structure that subsequently affects soil water and nutrient retention and migration. This study aimed to investigate the temporal change in soil shrinkage behaviour and to evaluate its consequences on water percolation in two paddy fields...
DPAA is often found as one of the major degradation products in soil and groundwater contaminated with diphenylcyanoarsine or diphenylchloroarsine. These compounds were produced mainly during the World Wars as chemical warfare agents. This study investigated the effect of DPAA contamination on soil bacterial and archaeal community structures under anaerobic conditions in a model experiment using 16S...
Understanding the spatial and temporal variations in toposequential methane (CH 4 ) emission is essential for assessing and mitigating CH 4 emission from rice cascades in mountainous watersheds. To assess the toposequential variation in CH 4 emission among different field positions, two cascades of double-cropping paddy rice fields were investigated in Yen Chau district, Northwest...
We hypothesize that the dynamics of water soluble arsenic (As), chromium (Cr), molybdenum (Mo), and vanadium (V) in soils might be controlled by the period of flooding due to changes of redox potential (E H ), pH, and carriers of metals such as dissolved organic carbon (DOC), iron (Fe), manganese (Mn) and sulfate (SO 42− ). Therefore, we aimed to assess the impact of different...
Soil cracks generated in paddy fields upon drying may be main pathways of preferential flow. In this paper we aimed to characterize soil cracks in paddy field and to assess their role in preferential flow. Two paddy fields, one cultivated for 20years (YPF) and the other cultivated for more than 100years (OPF), were subjected to either alternate flooding and drying (AFD) or continuous flooding (CF)...
The field Donnan Membrane Technique (DMT) has been used successfully to measure in-situ free trace metal concentrations in surface waters. However, it has not been applied previously in submerged soil systems including flooded paddy rice fields. We tested this technique in a column experiment with a flooded paddy soil contaminated with trace metals and compared the DMT measurements with predictions...
It is tempting to develop green energy biotechnology to supplement the depletion of fossil fuel resources and to reduce the greenhouse gas emissions. It has been recently demonstrated that paddy soil can be used to construct the sediment-type microbial fuel cells (MFCs). The mechanisms involved in electricity generation and its effects on methanogenesis, however, remain poorly understood. In the present...
Soil may fail in a number of ways during tilling, depending on soil conditions and the type of implement. The present paper investigates soil structures and several soil physical and mechanical properties associated with different failure patterns in two agricultural soils (upland and paddy). The dry bulk density, soil cohesion, internal friction angle, and cone index decreased remarkably after brittle...
Uptake of trace metals by crops is determined by the solubility of trace metals. In paddy soils, flooding and drainage influence redox chemistry and consequently trace metal solubility and thus uptake by rice plants. Current knowledge on how the dynamics in redox chemistry affect the solubility of trace metals in contaminated paddy soils is still limited. The objectives of our study were to investigate...
The soil structure of paddy soil is very dynamic from the aggregate to the pedon scale because of intensive anthropogenic management strategies. In this study, we tested the hypothesis that long-term inorganic and organic fertilizations can affect soil structure at different scales. Microstructure assessed by soil aggregates (3–5mm in diameter) and macrostructure assessed by small soil cores (CoreS)...
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