Red Yellow Soil Research Articles

콩에 대한 근류균과 균근균의 혼합 접종효과

The dual inoculation response of soybean with rhizobium and mycorrhiza was examined in pot vermiculite and field soils. In order to select a symbiotically compatible mycorrhiza with Bradyrhizobium japonicum, a highly germinating spore among 60 strains from 32 upland soils in southern part of Korea was obtained in Acaulospora sp., Gigaspora sp. and Glomus sp., respectively. As a result of dual inoculation of Glycin max cv. Dajangkong and Eunhakong both with cells of B. japonicum YCK 213 and 10 spores of each mycorrhiza in vermiculite pot, only Glomus sp. treatment together with the rhizobium showed significant increase () both in shoot dry wt and nodule mass of not Eunhakong but Dajangkong. In red-yellow soils with pH 5.2() and 203 mg of Lancaster P per kg of soil, in which cells of B. japonicum and spores of mycorrhizae per gram of soil were naturalized, grain yield of G. max cv. Dajangkong was increased to 3.9% by dual inoculation both of cells of B. japonicum and 10 spores of mycorrhizae per two seeds under condition applied with 30 kg and 34 kg per hectare compared to conventionally fertilized plot (2.75 MT ) added with 30 kg N . However, there was not significant.

Elemental composition of agricultural soils in Japan in relation to soil type, land use and region

To evaluate representative elemental composition of agricultural soils in Japan and to investigate the relationship between elemental composition of agricultural soils and their soil type, land use and region in Japan, 180 soil samples were collected from the surface layer of paddy or upland fields in Japan and their total contents of 20 elements were determined. Total concentrations of aluminum (Al), iron (Fe), calcium (Ca), magnesium (Mg), titanium (Ti), phosphorus (P), manganese (Mn), barium (Ba), vanadium (V), strontium (Sr), zinc (Zn), copper (Cu) and nickel (Ni) were determined by ICP-AES and those of potassium (K) and sodium (Na) by atomic absorption spectrophotometry after wet digestion of the finely ground samples with nitric acid (HNO3), hydrofluoric acid (HF) and perchloric acid (HClO4). Total concentration of selenium (Se) was determined by HPLC after treatment of the wet digested solution (HNO3 and HClO4) of the samples with 2,3-diaminonaphthalene and extraction with cyclohexane. Total concentrations of carbon (C) and nitrogen (N) were determined by the dry combustion method, and those of silicon (Si) and oxygen (O) were determined by calculation. The medians of the total concentrations of the 10 major elements were 504 g O kg−1, 291 g Si kg−1, 76.6 g Al kg−1, 36.8 g Fe kg−1, 24.8 g C kg−1, 15.0 g K kg−1, 14.3 g Na kg−1, 11.9 g Ca kg−1, 8.78 g Mg kg−1 and 3.82 g Ti kg−1, which accounted for 98.7% of the total. The medians of the others were 2.15 g N kg−1, 1.43 g P kg−1, 705 mg Mn kg−1, 394 mg Ba kg−1, 140 mg V kg−1, 125 mg Sr kg−1, 90.5 mg Zn kg−1, 24.5 mg Cu kg−1, 14.3 mg Ni kg−1 and 0.42 mg Se kg−1. In terms of soil type, volcanic soils had relatively high Al, Fe, C, N and P contents and alluvial soils had relatively high Si, K and Ba contents, whereas red yellow soils had extremely low Ca, Mg and Na contents. In terms of land use, upland soils had significantly higher Al, Fe, C, Ca, Mg, Ti, N, P, Mn, V and Se contents and lower Si, K and Ba contents than paddy soils. Cluster analysis of elemental composition of agricultural soils grouped regions in Japan into three groups: (1) Okinawa region, (2) Hokkaido, Tohoku, Kanto, Chugoku and Kyushu regions, and 3) Hokuriku-Chubu, Kinki and Shikoku regions, reflecting their soil types. In conclusion, these data can be used as basic information on which development of sustainable agriculture and promotion of environmental conservation is to be established.

西南地区红黄壤坡耕地可蚀性研究

针对西南地区典型红黄壤坡耕地，采用同时Wischemeier、Williams的计算公式、诺谟图查值、美国通用水土流失方程(USLE)K值表查值法开展土壤可蚀性研究，结果表明：A、B、C土层的K总平均值分别在0.222~0.369、0.329~0.413、0.430~0.560和0.405~0.595之间(见表3)。各种方法计算出来的K值差距甚大，变异系数差别也很大，用Sharply A.与Williams J. R.提出的公式计算出的K值变异系数小，相对稳定和精确，是红黄壤坡耕地K值计算的适宜方法；红黄壤坡耕地A层的K值随着年份的增长，呈下降的趋势，整个土层可蚀性强、抗侵蚀弱，侵蚀的危害大。通过4年不同种植制度和利用类型的影响，不同土层的K值都下降，其中A层下降1.26%~12.34%，B层下降1.29%~13.80%，C层下降1.26%~10.82%，A、B、C三层平均下降3.17%~11.64%。不同种植制度和利用类型坡耕地K值下降幅度不一样，除工程梯化处理外，草地、分带轮作、经果林、粮草间作、植物篱、混交林处理的K值下降幅度都高于农民习惯，下降幅度从高到低的排列顺序是：草地 > 分带轮作 > 经果林 > 粮草间作 > 植物篱 > 混交林。种树种草，有利于坡耕地可蚀性的改善和耕地质量的提高。玉米与其它植物间套作，提高覆盖度和增加生物种类，也有利于坡耕地可蚀性的改善。 With Wischemeier and Williams’s design formulas, nomograph and USA Universal Soil Loss Equation (USLE) K-value table, the study to typical sloping farmland on red-yellow soils in southwest showed that the mean K-values of A, B and C layer were 0.262 - 0.476, 0.308 - 0.578 and 0.237 - 0.595 (table 3), respectively. The K-value and variation coefficient were very different with different utilization methods, and Sharply and Williams’s calculation formula in EPIC model was relatively constant and accurate, as the suitable utilization method. The K-value of A layer trended down with age, and the whole A layer had a serious harm of soil erosion with strong erodibility and weak anti-erodibility. The K-values of A, B and C layer turned down 1.29% - 13.80%, 1.29% - 13.80% and 1.26% - 10.82% with different planting systems and land use types in 4 years, and the whole layer turned down 3.17% - 11.64%. The drops in K-value of different planting systems and land use types were not same: Excepted terracing treatment, others drop more than CK, and grass > rotation > fruit forest > grass and crop intercropping > hedgerow > mixed forests. Planting trees and grasses was conducive to improve the erodibility and the quality of the sloping farmland. The maize intercropped and relay intercropped with other plants could improve the coverage and species of the sloping farmland, could also improve the erodibility of the sloping farmland.

논토양 종류가 메탄배출에 미치는 영향

논토양 종류가 메탄배출에 미치는 영향을 구명하기 위하여 적황색토인 화동통과 회색토인 신흥통을 공시하여 벼 재배기간중 메탄배출량, 산화환원전위 및 토양중 산화물 함량을 분석하였다. 적황색토에서 메탄배출이 회색토에 비해 유의하게 낮았으며, 산화환원전위는 상대적으로 높았다. 적황색토는 회색토에 비해 쉽게 환원될 수 있는 Active oxide 함량은 낮은 반면, 상대적으로 안정성이 높은 Free oxide의 함량이 높았다. 따라서 논토양 종류별 메탄배출은 벼 재배기간중 산화환원전위와 토양중 Geothite, Hematite 등과 같은 메탄산화제의 함량에 영향을 받는 것으로 나타났다. Anaerobic decomposition of organic materials in flooded rice fields produces methane (<TEX>$CH_4$</TEX>) gas, which escapes to the atmosphere primarily by transport through organs of the rice plants such as arenchyma etc., Although the annual amount of methane emitted from a given area is influenced by cultivation periods of rice and organic/inorganic amendments etc., soil type also affects methane emission from paddy soil during a rice cultivation. A field experiment was conducted to evaluate effects of soil type on <TEX>$CH_4$</TEX> emission in two paddy soils. One is a red-yellow soil classified as a Hwadong series (fine, mixed, mesic family of Aquic Hapludalfs), and the other is a gley soil classified as a Shinheung series (fine loamy, mixed, nonacid, mesic family of Aeric Fluvaquentic Endoaquepts). During a flooded periods, redox potentials of red-yellow soil were significantly higher than gley soil. <TEX>$CH_4$</TEX> emission in red-yellow soil (<TEX>$0.21kg\;ha^{-1}\;day^{-1}$</TEX>) was lower than that in gley soil (<TEX>$5.25kg\;ha^{-1}\;day^{-1}$</TEX>). In the condition of different soil types, <TEX>$CH_4$</TEX> emissions were mainly influenced by the content of total free metal oxides in paddy soil. The results strongly imply that iron- or manganese-oxides of well ordered crystalline forms in soil such as goethite and hematite influenced on a <TEX>$CH_4$</TEX> emission, which is crucial role as a <TEX>$CH_4$</TEX> oxidizers in paddy soil during a rice cultivation.

Eolian Origin of 2: 1 Layer Silicates and Fine Quartz in Andosols and Red-Yellow Soils Developed on Limestones and Basalts

Eolian Origin of 2: 1 Layer Silicates and Fine Quartz in Andosols and Red-Yellow Soils Developed on Limestones and Basalts

Effects of contamination of single and combined cadmium and mercury on the soil microbial community structural diversity and functional diversity

To assess the effects of single and combined pollution of cadmium (Cd) and mercury (Hg) on soil microbial community structural and functional diversities, an incubation experiment was conducted, by employing two soils, namely, the marine sediment silty loam soil and the yellowish-red soil, in which five levels of Cd, Hg and Cd and Hg in combination were added. After being incubated for 56 days, the phospholipid fatty acids (PLFAs) profile and sole carbon source utilization pattern (BIOLOG) of the samples were tested. The results showed that the composition of the microbial communities changed significantly at different levels of metals application. The principal component analyses (PCA) of PLFAs indicated that the structure of the microbial community was also significantly altered with increasing levels of metals, with increasing PLFAs biomarkers for fungi and actinomycetes, and increasing ratio of Gram-positive to Gram-negative bacteria. Sole carbon source utilization pattern analysis revealed that single and combined application of Cd and Hg inhibited significantly the functional activity of soil microorganisms, the functional diversity indices [Richness (S), Shannon-Wiener indices (H) and Evenness (EH)] were significantly lower in polluted soils than those in non-polluted soils, which also significantly altered with increasing levels of metals. PCA for the sole carbon source utilization pattern also indicated that the metal contamination could result in a variable soil microbial community. The results revealed that the combination of Cd and Hg had higher toxicity to soil microbial community structural and functional diversities than the individual application of Cd or Hg.

Transport and Deposition of Suspended Soil Colloids in Saturated Sand Columns

Understanding colloid mobilization, transport, and deposition in the subsurface is a prerequisite for predicting colloid-facilitated transport of strongly adsorbing contaminants and further developing remedial activities. This study investigated the transport behavior of soil-colloids extracted from a red-yellow soil from Okinawa, Japan. Different concentrations of suspended-soil colloids (with diameter <1 μm) were applied, at different flow velocities and pH conditions, to 10-cm long water-saturated columns repacked with either Narita (mean diameter D50=0.64 mm) or Toyoura (mean diameter D50=0.21 mm) sands. The transport and retention of colloids were studied by analyzing colloid effluent breakthrough curves (BTCs), particle size distribution in the effluent, and colloid deposition profiles within the column. The results showed a significant influence of flow velocity: Low flow velocity caused tailing of colloid BTCs with higher reversible entrapment and release of colloids than high flow velocity. Th...

Nitrogen and phosphorus runoffs into a stream from an upland basin with high stocking density in a red-yellow soil area

Nitrogen and phosphorus runoffs into a stream from an upland basin with high stocking density in a red-yellow soil area

Locating the taxonomical position of argic horizons and cambic horizons in Japanese Red-Yellow soils

Locating the taxonomical position of argic horizons and cambic horizons in Japanese Red-Yellow soils

Soil nitrogen status in Tieguanyin tea plantation of Fujian Province

为了解铁观音茶园土壤氮素供应能力, 对福建安溪、永春和华安14个铁观音生产乡镇150个铁观音茶园表土及相应茶叶进行了调查。结果表明: 供试茶园土壤全氮含量处于中低水平, 平均值为0.79 g·kg^-1, 碱解氮含量处于中高水平, 平均值为95.56 mg·kg^-1, 全氮含量与碱解氮含量呈显著正相关。有机质及阳离 子交换量与土壤全氮和碱解氮含量均呈极显著正相关。不同土壤类型全氮含量依次为水稻土改种>黄壤>红 壤>黄红壤>赤红壤, 质地黏重的土壤氮含量较高。茶树新梢氮含量变幅为8.1～141.8 g·kg^-1, 平均值为23.7 g·kg^-1, 与土壤碱解氮含量无显著相关性。土壤碱解氮含量是否能作为茶园土壤供氮能力的指标以及在铁观音茶树的营养诊断时茶树新梢的氮素含量是否能作为茶树缺素的诊断指标有待进一步研究。福建铁观音茶园土壤应注意增施有机肥, 避免过度施用速效氮肥。

The difference of potassium dynamics between yellowish red soil and yellow cinnamon soil under rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation

To increase the use efficiency of potassium (K) fertilizer, special attention was paid to the dynamics of soil K in the root zone and non-root zone. Difference in K dynamics between yellowish red soil and yellow cinnamon soil under rapeseed (Brassica napus L.)rice (Oryza sativa L.) rotation was studied using a rhizobox system. Results showed that soil water soluble K (Sol-K) and exchangeable K (Ex-K) in the root zone of both soils were reduced in the early stage of rapeseed growth. Along with plant growth and K uptake, soil Sol-K in the inner (0–20 mm to root zone), middle (20–40 mm) and outer (40–60 mm) compartments of the non-root zone of yellowish red soil migrated towards the root zone. As a result, soil Ex-K was transformed into Sol-K. The changes in soil Sol-K and Ex-K in the non-root zone of yellow cinnamon soil were similar to yellowish red soil, and soil non-exchangeable K (Nonex-K) in the root zone also decreased significantly. In the early stage of rice growth, waterlogging promoted diffusion of soil Sol-K from non-root zone to root zone and transformation of Ex-K into Sol-K. Along with the growth of rice and K uptake, soil Ex-K in each compartment of yellowish red soil decreased significantly. Soil Sol-K and Ex-K in the yellow cinnamon soil declined to a certain extent, and then remained unchanged, while soil Nonex-K kept on decreasing. It revealed that the plants first absorbed K in the root zone, of which K reserve was replenished by a gradual diffusion of K from the non-root zone. The closer to the root zone, the greater the contribution to K uptake by plants. Within one rotation cycle, Ex-K and Sol-K in yellowish red soil were the main forms of K available to the plants, and little Nonex-K could be absorbed. However, in the yellow cinnamon soil, Nonex-K was the main form of K available to the plants, followed by Ex-K and Sol-K.

Evaluation of Soil Tests for Plant‐available Mercury in a Soil–Crop Rotation System

A reliable soil test is needed for estimating mercury (Hg) availability to crop plants. In this study, four extraction procedures including 0.1 M hydrochloric acid (HCl), 1 M ammonium acetate (NH4OAc) (pH 7.0), 0.005 M diethylenetriaminepentaacetic acid (DTPA), and 0.1 M calcium chloride (CaCl2) (pH5.0) were compared for their adequacy in predicting soil Hg availability to crop plants of a rice–cabbage–radish rotation system. The amounts of Hg extracted by each of the four procedures increased with increasing equilibrium time. The optimal time required for extraction of soil Hg was approximately 30 min, though it varied slightly among the four extractants. The amounts of Hg extracted decreased with increasing soil/solution ratio, and a soil/solution ratio of 1:5 appeared to be adequate for soil Hg availability tests. The amounts of Hg extracted increased in the order of NH4OAc < CaCl2 < DTPA < HCl in silty loam soil (SLS) soil, and the order was NH4OAc < CaCl2 ≈ DTPA < HCl in yellowish red soil (YRS) soil. Significant positive correlations among the four extractants were obtained in SLS soil. In contrast, the correlations were poor in YRS soil, especially for HCl. There were significant correlations between concentrations of Hg in edible tissue of three plants and the amounts of soil Hg extractable to the four extractants for soil–rice system and soil–radish system, but not for soil–Chinese cabbage system. The 0.1M HCl extraction overall provided the best estimation of soil‐available Hg and could be used to predict phytoavailability of Hg in soil–crop systems.

Effect of different organic amendments on the resistance and resilience of the organic matter decomposing ability of soil and the role of aggregated soil structure

The effect of organic amendment on the resistance and resilience of the organic matter decomposing activity was compared between soils amended with compost and with chemical fertilizers. The impact of metam sodium disinfection on cellulose-decomposing activity and on the number of nematodes in three types of soils was periodically measured. In an andosol, cellulose-decomposing activity was significantly suppressed by soil disinfection only in the chemically fertilized soil (CF-soil) and not in the soils to which cow manure compost and okara (the residue in tofu production)/coffee compost was added. In a brown lowland soil, cellulose-decomposing activity was significantly suppressed by soil disinfection in the CF-soil, but not in the soils to which higher amounts of cow manure compost and pig manure compost had been added. In a red-yellow soil, cellulose-decomposing activity was significantly suppressed by soil disinfection in all soils, but its resilience was higher in the soils to which cow manure compost or coffee compost was added compared with the CF-soil. Total numbers of nematodes were markedly decreased by soil disinfection in all soils. These results may suggest that the resistance and resilience of cellulose-decomposing activity against soil disinfection were enhanced by organic amendments, while disinfection had fatal effects on soil nematodes. In most of the organically amended soils, the mean weight diameters of aggregates were larger compared with the CF-soils, suggesting that highly structured soil pore networks may provide shelters for the soil microbes responsible for cellulose decomposition against disinfection. This hypothesis was supported by the result that the resistance of cellulose-decomposing activity against soil disinfection decreased when the soil structure was destroyed by grinding in a mortal and pestle.

시설 상추에 대한 Rhodobacter sp. SA16 처리 효과

This experiment was conducted to determine the development of mixed organic fertilizer using photosynthetic bacteria and mass production of mixed microbial compound for the environment -friendly agriculture. Photosynthetic bacteria, Rhodobacter sp. SA16 was isolated from soil collected by plastic film house. The SA16 strain was identified based on 16S rDNA sequence analysis and it is closely related to Rhodobacter sp. (100% similarity). The mixed organic fertilizer using SA16 was made of N-P2O5-K2O=60-10-20 g kg -1 with combined soybean cake, sesame cake, powdered blood, fish meal, powdered bones and red-yellow soil. The mixed organic fertilizer 0.45, 0.90 and 1.35 Mg ha -1 application in Ihyeon series was treated based on soil testing for lettuce cultivation in plastic film house. These results showed that the yield was increased the 18 and 19% over control by the mixed organic fertilizer application 0.45 and 0.90 Mg ha -1 , respectively. In the physical properties of the soil, the porosity of mixed organic fertilizer 1.35 Mg ha -1 treatment was highest at 58.8%. Our results clearly revealed that the organic fertilizer using Rhodobacter sp. SA16 and mass production of mixed strains could be a useful technology in pursuing environment-friendly agriculture.

Comparação de classificadores de imagens digitais na determinação da cobertura do solo

Com o objetivo de comparar dois classificadores de imagens para a estimativa da cobertura vegetal do solo, foram avaliadas as coberturas proporcionadas pela semeadura de leguminosas e de gramíneas, sob diferentes espaçamentos, preparo do solo e condições de céu com e sem nuvens. O experimento foi conduzido em quatro parcelas experimentais de perda de solo, com 22 m x 3,5 m, instaladas em um Argissolo Vermelho-Amarelo. Os tratamentos consistiram: a) mucuna-cinza (Mucuna pruriens) em nível; b) crotalária (Crotalaria juncea) em sulcos dispostos em nível; c) milho (Zea mays L.) em sulcos dispostos em nível, e d) milho semeado no sentido do declive. Foram tomadas fotografias das parcelas dos 15 aos 85 dias após a semeadura para posterior análise, utilizando o Sistema Integrado para Análise de Raízes e Cobertura do Solo (SIARCS) e um algoritmo baseado na emissividade das bandas do verde e do vermelho (SEROBIN). A maior cobertura do solo foi obtida na parcela cultivada com crotálaria (85,8%), a qual também foi alcançada em menor tempo (56 dias após semeadura). Por outro lado, as menores coberturas foram proporcionadas pelos tratamentos milho em nível e milho morro abaixo (38,6 e 35,2%, respectivamente). As exatidões globais foram de 0,96 e 0,92, para as classificações realizadas com os programas SIARCS e SEROBIN, respectivamente, não havendo, no entanto, diferença estatística entre os dois classificadores utilizados, de acordo com o teste Z aplicado, a 5% de probabilidade.

Adsorption–Desorption Characteristics of Mercury in Paddy Soils of China

Mercury (Hg) has received considerable attention because of its association with various human health problems. Adsorption-desorption behavior of Hg at contaminated levels in two paddy soils was investigated. The two representative soils for rice production in China, locally referred to as a yellowish red soil (YRS) and silty loam soil (SLS) and classified as Gleyi-Stagnic Anthrosols in FAO/UNESCO nomenclature, were respectively collected from Jiaxin County and Xiasha District of Hangzhou City, Zhejiang Province. The YRS adsorbed more Hg(2+) than the SLS. The characteristics of Hg adsorption could be described by the simple Langmuir adsorption equation (r2 = 0.999 and 0.999, P < 0.01, respectively, for the SLS and YRS). The maximum adsorption values (Xm) that were obtained from the simple Langmuir model were 111 and 213 mg Hg(2+) kg(-1) soil, respectively, for the SLS and YRS. Adsorption of Hg(2+) decreased soil pH by 0.75 unit for the SLS soil and 0.91 unit for the YRS soil at the highest loading. The distribution coefficient (kd) of Hg in the soil decreased exponentially with increasing Hg(2+) loading. After five successive desorptions with 0.01 mol L(-1) KCl solution (pH 5.4), 0 to 24.4% of the total adsorbed Hg(2+) in the SLS soil was desorbed and the corresponding value of the YRS soil was 0 to 14.4%, indicating that the SLS soil had a lower affinity for Hg(2+) than the YRS soil at the same Hg(2+) loading. Different mechanisms are likely involved in Hg(2+) adsorption-desorption at different levels of Hg(2+) loading and between the two soils.

Statistical and geoestatistical characterization of heavy metal concentrations in a contaminated area taking into account soil map units

Soil map units were taken into account in geostatistical prediction of heavy metals concentrations in a contaminated site of Fuyang Valley, Zhejiang Province, China. To compare the spatial variabilities of Cu, Zn, Pb and Cd concentrations in different soil map unit or combination of soil map units, a total of 94 samples distributed in three map units (Yellowish-red soil, Gravelly-yellowish-red soil and Gritty-yellowish-red soil) were collected in this area. The values of Cu, Zn, Pb and Cd concentrations were natural logarithm transformed to fit normal distribution. The variations of four heavy metal concentrations in Gravelly-yellowish-red soil was similar to that in Gritty-yellowish-red soil, but they were different to that in Yellowish-red soil. Then, the 94 soil samples were grouped into two classes (samples of Yellowish-red soil, and samples of Gravelly-yellowish-red soil or Gritty-yellowish-red soil). Semivariogram analysis revealed that all the four heavy metal concentrations in the study area showed moderate to strong spatial dependency, and local spatial variability (i.e. the variance between soil map units) played an important role in their spatial prediction. The spatial distribution maps of the four heavy metals were drawn by using only the measured data and by using the measured data plus taking into account soil map units, respectively. The results showed that spatial prediction by taking into account soil map units could reveal the huge spatial variability of the heavy metals, much better than the prediction without using soil map information in this contaminated site.

Selection of better extractants to indicate Pb bioavailability in lead-contaminated agricultural soils of Zhejiang Province

The accumulation of Pb in the food chain is one of the great concerns as it can cause chronic health problems and the available Pb is easily absorbed by crops. To shed light on Pb bioavailability in lead-contaminated agricultural soils of Zhejiang Province, a series of plant growth experiments were performed in a greenhouse to select more suitable extractants from five commonly used extractants (0.1 M HCl, 1 M NH4OAc, 0.1 M CaCl2, DTPA-TEA and Mehlich 3). The results showed that 1 M NH4OAc can extract Pb best, indicating the Pb bioavailability, then, DTPA-TEA and 0.1 M HCl in the tested soils. In case 1 M NH4OAc was used as an extractant, the critical Pb concentrations in soils were 50.19 mg/kg, 21.16 mg/kg and 114.00 mg/kg (1 M NH4OAc extracted Pb) in silty loam, yellowish-red soil and purplish soil, respectively. When the values exceed the above ones, the contents of Pb in Chinese cabbage leaves will exceed the Chinese Tolerance Limit of Lead in Foods (GB14935-94), as a result, potential ecological risk and hazard to human health via the food chain will appear.

C and N stocks under three plantation forest ecosystems of Chinese fir, Michelia macclurei and their mixture

Chinese fir (Cunninghamia lanceolata), a type of subtropical fast-growing conifer tree, is widely distributed in South China. Its plantation area covers more than 7 × 106 hm2, accounting for 24% of the total area of plantation forests in the country. In recent decades, the system of successive plantation of Chinese fir has been widely used in southern China due to anticipated high economic return. However, recent studies have documented that the practice of this system has led to dramatic decreases in soil fertility and forest environment as well as in productivity. Some forest ecologists and managers recognize the ecological role performed by broadleaf trees growing in mixtures with conifers, and a great deal of studies on mixture effects have been conducted, particularly on mixture species of temperate and boreal forests, but these research results were not completely consistent. Possibilities include dependence of the mixture effects in large part to specific site conditions, the interactions among species in mixtures and biological characteristics of species. Although some researchers also studied the effects of mixtures of Chinese fir and broadleaf tree species on soil fertility, forest environment and tree growth status, little information is available about the effects of Chinese fir and its mixtures with broadleaves on carbon and nitrogen stocks. The experimental site is situated at the Huitong Experimental Station of Forest Ecology, Chinese Academy of Sciences, Hunan Province (26°40′–27°09′ N, 109°26′–110°08′ E). It is located at the transition zone from the Yunnan-Guizhou Plateau to the low mountains and hills of the southern bank of the Yangtze River at an altitude of 300–1,100 m above mean sea level. At the same time, the site is also a member of the Chinese Ecosystem Research Network (CERN), sponsored by the Chinese Academy of Sciences (CAS). This region has a humid mid-subtropical monsoon climate with a mean annual precipitation of 1,200–1,400 mm, most of the rain falling between April and August, and a mean temperature of 16.5°C with a mean minimum of 4.9°C in January and a mean maximum of 26.6°C in July. The experimental field has red-yellow soil. After a clear-cutting of the first generation Chinese fir (Cunninghamia lanceolata) plantation forest in 1982, three different plantation forest ecosystems, viz. mixture of Michelia macclurei and Chinese fir (MCM), pure Michelia macclurei stand (PMS) and pure Chinese fir stand (PCS), were established in the spring of 1983. A comparative study on C and N stocks under these three plantation forest ecosystems was conducted in 2004. Results showed that carbon stocks were greater under the mixtures than under the pure Chinese fir forest and the pure broad-leaved forest, and the broadleaves and the mixtures showed higher values in nitrogen stocks compared with the pure Chinese fir forest. The spatial distribution of carbon and nitrogen stocks was basically consistent, the value being greater in soil layer, followed by tree layer, roots, understory and litter layer. The carbon and nitrogen stocks in soil layer were both highly correlated with the biomass in understory and litter layer, indicating that understory and forest litterfall exerted a profound effect on soil carbon and nitrogen stocks under plantation ecosystems. However, correlations among soil carbon, nitrogen stocks and below ground biomass of stand have not been observed in this study.

Effects of pH, organic acids, and competitive cations on mercury desorption in soils

The effects of pH, organic acids, and competitive cations on Hg 2+ desorption were studied. Three representative soils for rice production in China, locally referred to as a yellowish red soil (YRS), purplish clayey soil (PCS), and silty loam soil (SLS) and classified as Gleyi-Stagnic Anthrosols in FAO/UNESCO nomenclature, were, respectively, collected from Jiaxin County, Deqing County, and Xiasha District of Hangzhou City, Zhejiang Province. Most of the added Hg 2+ was adsorbed at low initial concentrations (<2 mg l −1). Desorption of the adsorbed Hg 2+ in 0.01 M KCl (simulating soil solution) was minimal, but was significantly enhanced by the change of pH, and the presence of organic acids or competitive cations. The desorption of Hg 2+ in the soils decreased with pH from 3.0 to 5.0, leveled off at pH 5.0–8.0, but increased with pH from 7.0 to 9.0. The presence of organic ligands enhanced Hg 2+ desorption in the soils except for YRS, in which the addition of tartaric, malic, or oxalic acid reduced Hg 2+ desorption at low concentrations (<10 −4 M), but Hg 2+ desorption generally increased with organic acid concentration. Citric acid was most effective in increasing Hg 2+ desorption, followed by tartaric acid and malic acid; and oxalic acid was the least effective. Desorption of adsorbed Hg 2+ increased with increasing concentrations of added Cu 2+ or Zn 2+. Applied Cu 2+ increased Hg 2+ desorption more than Zn 2+ at the same loading rate. Capsule The effects of organic acids and competitive cations on Hg desorption in soil–water system are related to their concentrations, basic chemical properties, and soil properties.