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A number of remediation measures have been used in paddy fields to alleviate serious cadmium (Cd) contamination, which may pose a public health risk through the food chain. In this study, a field trial was conducted in paddy fields with slight–moderate Cd contamination to investigate the remediation effects of combined remediation measures (CRMs), including the use of Cd-safe rice (Oryza sativa L.) cultivars, water management modes (WMMs), lime application (LA), soil amendment application (SAA), and foliar silicon (Si) fertilizers. Two groups of field trials were designed including CRMs with selenium (Se) and without selenium (non-Se) application. The results show that soil measures (LA + SAA) can increase the soil pH by 0.99 and decrease the soil DTPA-extracted Cd content by 34.19% (p < 0.05). All measures used in the present study significantly decreased the Cd content in husked rice and yield, except for the WMMs; the CRMs achieved the best results, and Se application enhanced the effects of all measures. This study shows that CRMs significantly decreased the Cd content in husked rice by 58.10%; this value increased to 72.69% after Se application (p < 0.05). These results provide useful information for selecting remediation measures in paddy fields with slight–moderate Cd contamination. [ABSTRACT FROM AUTHOR]

It is expected that microorganisms capable of arsenic (As) accumulation and volatilization can be used to remediate As-contaminated environments. In this paper, the arsenite [As(III)] resistance, accumulation, and volatilization properties of Trichoderma asperellum SM-12F1, Penicillium janthinellum SM-12F4, and Fusarium oxysporum CZ-8F1 were investigated. The results indicated that all three fungal strains exhibited significant As(III)-resistance. After being exposed to 40 and 80 mg/L As(III) for five days, the dry mycelium weights of P. janthinellum SM-12F4 and F. oxysporum CZ-8F1 were significantly increased compared to the controls. The spiked As(III) initially inhibited and subsequently promoted fungal growth (mainly in the logarithmic growth phase). The maximal biomasses of 0.25, 0.29, and 0.29 g for T. asperellum SM-12F1, P. janthinellum SM-12F4, and F. oxysporum CZ-8F1 after exposure to As(III), respectively, were all higher than their corresponding controls without As(III). When exposed to 40 mg/L As(III) for five days, the efficiencies of As(III) accumulation for T. asperellum SM-12F1, P. janthinellum SM-12F4, and F. oxysporum CZ-8F1 were 53.02, 13.67, and 13.65 µg/g/day, respectively, and the efficiencies of As(III) volatilization were 51.87, 54.34, and 46.35 µg/g/day, respectively. It seems that these fungal strains can be used in the future to tackle As-contaminated environments. [ABSTRACT FROM AUTHOR]

The restoration of vegetation in the abandoned land requires support of water resources, but as drought events occur frequently in Southern China, especially significant in purple hilly region of central Hunan the restoration is often difficult. As a result, the vegetation is rare in purple hilly region and the eco-environment is very fragile, and soil degradation and erosion are very severely. Since 1990s, more and more dry-land in the hilly region was abandoned by the farmers because of the enlarging gap between the prices of farm products and manufactured products. After dry-land was abandoned, the pioneer plants inhabit first and vegetation succession begin, which affect soil characteristics, microbiology and microclimate. Conversely, the soils in the region also affect the type, distribution and dynamic change of vegetation through providing water and mineral nutrients. Earlier studies reveal that vegetation restoration improves soil structure, increase proportion of soil porosity, and soil water storage capacity for vegetation succession. Vegetation restoration is one of the primary measures to improve eco-environment of the purple hilly region. Our objective was to determine the impact of natural vegetation restoration in abandoned dry-land and the impact of succession stages on soil physical properties and soil water characteristics . In this paper, four natural lands with various succession stages on abandoned dry land from the purple hilly region were selected to study soil water storage capacity and related soil physical properties by using "adjacent plot comparing method". The results showed that: no obvious changes occurred in subsoil (20-40 cm) bulk density among different succession stages (P>0.05). However, there was notable changes in surface soil layer (0-20 cm), the order of the average values was as follows: dryland > herbosa > arbor-shrub community >shrub community, and the value of soil bulk density was 1.38 g/cm3,1.3 g/cm3,1.24 g/cm3 and 1.19 g/cm3, respectively, indicating that vegetation restoration incurred lower bulk density of surface soil. The results also showed that the quality distribution of soil particle varied obviously (P<0.05). The content of gravel (1-2 mm) and coarse sand (0.25-1 mm) in herbosa was higher comparing with dry land. The content of gravel and coarse sand decreased and that of silty clay (<0.05 mm) and fine sand (0.05-0.25 mm) increased in stage of arbor-shrub and shrub community. In the same soil layer for different succession stages, there was higher proportion (P<0.05) of finer soil particle content in arbor-shrub and shrub community, however, soil particle content in vertical structure of profile varied obviously in succession middle stage and it was uniform in arbor-shrub stage. In addition, the results showed that the soil capillary porosity of surface soil in herbosa stage was significantly lower (P<0.05) than the other types of vegetation, indicating vegetation succession on abandoned dry land can increase soil capillary porosity. Non-capillary porosity varied indistinctively in different succession stages. All soil total porosity of surface soil was higher than subsoil at different succession stages and there was significant level (P<0.05) in herbosa stage, showing that vegetation succession affected soil total porosity. Moreover, the results showed that soil water-storage capacity had the same changing pattern with soil porosity in different succession stages. Soil capillary and total water-storage capacity of topsoil with various succession stages increased (P<0.05), which showed that vegetation restoration might raise soil water storage capacity. Last, correlation analysis of various soil physical properties indicated that soil water storage capacity mainly determined by soil bulk density, porosity, coarse sand (0.25-1 mm) and silt and clay (<0.05 mm) content. We concluded that vegetation succession stages altered soil surface physical properties greater than the subsurface soil. The decrease in bulk density and increase in porosity helped to improve soil water holding capacity and hence improved the environment for vegetation establishment. [ABSTRACT FROM AUTHOR]

A field experiment was conducted on two soil types in the Changsha suburb of Hunan Province to study the effects of hydroquinone (HQ), dicyandiamide (DCD) and thiourea (TU) on the nitrate content in soil and pakchoi and on the yield of pakchoi. The results showed that all the test nitrification inhibitors could significantly decrease the nitrate content in soil and pakchoi during whole growth stage, among which, DCD had the best effect, but the effect was differed on different soil types. Nitrification inhibitors could increase pakchoi yield, DCD was also the best one, and the effect was significantly better on vegetable garden red soil than on vegetable garden alluvial soil. The nitrate content in soil and pakchoi was the highest about 40 days after pakchoi transplanting.

Through adsorption-desorption experiment and incubation test, this paper studied the phosphate adsorption and desorption characteristics of several fly ashes. The test fly ashes contained 0.545 - 4.540 g x kg(-1) of total P and 19.55 - 163.0 mg x kg(-1) of available P, which were significantly higher than those in soils. The P adsorption capacity of fly ashes increased with increasing added P, while their P adsorption rate was in adverse. Fly ashes had a higher P adsorption rate but a lower P desorption rate than soils, mainly because fly ashes had more P adsorption sites and stronger bound energy. In this study, Langmuir, Freundlich, and Temkin equations were fit to the measured data, and the MBC value in Langmuir equation, a value in Freundlich equation, and k2 value in Temkin equation could be used as a comprehensive index to characterize the potential phosphate adsorptivity of fly ashes. The larger these values were, the stronger the P adsorptivity was. The MBC, a and k2 value of 5 fly ashes collected from different locations was in order of Xiangtan power factory (5 167.7, 4 056.2 and 831.5) > Yueyang paper factory (1 650.7, 2803.4 and 711.9) >Huaneng power factory (303.0, 1677.6 and 368.7) > Zhuzhou power factory (34.7,413.48 and 213.8) > Dongting nitrogen fertilizer factory (34.7, 413.48 and 213.8). The P fixation by fly ashes generally increased with their increasing water content, and their phosphate adsorption was mainly specific adsorption and chemical precipitation, suggesting that the P fixation and the water content of fly ashes should be considered when fly ash was used as soil amendment or as compound fertilizer filling substance.

Three paddy soils with higher content of fixed ammonium in Hunan Province were used as test soils in pot experiment to study the seasonal variation of their fixed ammonium content and its bioavailability during rice growth period. The results showed that the fixed ammonium content in the paddy soils changed constantly during rice growth. Applying N fertilizer and organic manure increased the fixed ammonium content, which was decreased through the N uptake by rice plants. The recently fixed ammonium was almost fully available to rice, while the native fixed ammonium was partly available. The release of fixed ammonium during rice growth was newly alluvial sandy soil > purple clayey soil > alluvial sandy soil, and was greater a early growth stage than at later growth stage.

By the method of Silva and Bremner, the fixed ammonium content of chief paddy soil types in Hunan Province and its influencing factors were studied. The results showed that the content of fixed ammonium in plough layer ranged from 141 mg.kg-1 to 353 mg.kg-1, averaged 272 +/- 67 mg.kg-1, and accounted for 11.2% of total soil N. The content of fixed ammonium was in order of alluvial sandy soil > purple clayey soil > newly alluvial sandy soil > yellow clayey soil > reddish yellow clayey soil. There were four distribution models of fixed ammonium in the soil profiles: 1) fixed ammonium content increased with the increase of depth in the profiles; 2) fixed ammonium content decreased with the increase of depth; 3) there was no distinct change; and 4) abrupt increase or decrease was found in the profiles. The percentage of fixed ammonium to total N in soils always increased with the increase of depth. The fixation of NH4+ by soil was the strongest under 30 degrees C. Long-term submergence benefited to the fixation of NH4+ in newly alluvial sandy soil, purple clayey soil, and alluvial sandy soil, while the alternation of drying and wetting contributed to the fixation of NH4+ in yellow clayey soil best. The content of fixed ammonium in tested soil was correlated with the content of clay < 0.01 mm at the significant level, and not correlated with the content of clay < 0.001 mm, total N, organic N, and matter.