Abstract:Based on field surveys, soil samples were collected systematically at the YPC loess-paleosol site, Yuzhou County, Henan Province for analysis of contents of macro-and micr-oelements and their variations with XRF and comparison with the curves of magnetic susceptibility and particle-size distribution. It was found that K₂O/Na₂O ratio, eluvial coefficient and contents of micro-elements with Rb as an indicator varied regularly with the layers of the Holocene aeolian loess-paleosol profile, i. e. they peaked in the paleosol (S₀), and were lower in the modern topsoil (MS) and the lowest in the loess (L₀, L_t, L₁), Whereas SiO₂/Al₂O₃ ratio and content of Sr went the other way in the profile, showing that during the stage of S₀ and MS formation, the climate was warm and humid, and pedogenesis and secondary clayification were stronger; and during the stage of loess accumulation, the climate turned very dry and with frequent dust storms and pedogenesis was weakened. Comparison of these chemical parameters with magnetic susceptibility showed that transference of these elements was mainly controlled by the Holocene climate. The contents of most macro-elements were much higher, the contents of most micro-elements were much lower, and the magnetic susceptibility was much lower too, and the content of most fine sands in the particle-size composition was much higher in the YPC loess-paleosol profile than in the Luochuan profile which is located in the hinterland of the Loess Plateau, which suggested that the sources of Holocene loess-paleosol in the upperreaches of the Huaihe River Basin evidently differed from that of the Loess Plateau. Considering the fact that the Yellow River overflowed and changed route frequently, leading to deposition during the Holocene and the prevailing North-East wind in the Huang-Huai plains caused formation of flowing sands, it can be concluded that the loess in the Huaihe River Basin was deposition of Aeolian sands from nearby sources, i. e. the Yellow River alluvial deposition, which was weathered and conveyed by North-East wind. Then aeolian sand deposited, accumulated and weathered on the spot to form loess-paleosol.

Abstract:Scientific accurate quantification of topographic feature of watershed is one of the key issues in establishing an extensively applicable model for prediction of soil erosion on a watershed scale on Loess Plateau. Based on the fractal theory and with the aid of the GIS technology and multianalysis method, coupling relationship between sediment yield from rainfall erosion and topographic features was studied in the Chabagou watershed, which lies on Loess Plateau. Results show that the coupling relationship model, into which fractal information dimension of topographic feature of watershed is introduced, can simplify the relationship between runoff and sediment yield that varies from branch to branch of the Chabagou watershed to a uniform mathematic expression. As a whole, the relative error of the prediction of sediment transport modulus of the Xizhuang and Shejiagou watersheds using the model is low. It is feasible and reliable to use fractal information dimension of topographic features of watershed as an index to quantify topographic features of watershed, which is one of the important influencing factors in establishing models for soil erosion prediction on a watershed scale.

Abstract:To analyze soil quality in relationship to land use/cover in landscape at a village level in hilly regions South China, village landscape maps were plotted out of high resolution (1m) IKONOS satellite imagery using a standardized ecological landscape classification (land form, land use, land cover, ecotope) and mapping system. Results demonstrate that: Under different land use landscapes, soils in the 0～15 cm layer differ sharply in soil bulk density (SBD) (highest in Constructed of 1.42 g cm^-3), soil organic material (SOM) (highest in Paddy soil of 18.67 g kg^-1) and soil total nitrogen (TN) (highest in Paddy soil of 0.95 g kg^-1). The land use landscape of the region mostly consists of Forests (52.05%), Rainfed land (22.30%) and Paddy soil (11.6%). The stock of soil nutrients is mainly affected by soil area. In the 0～15 cm soil layer, the Forest has the highest soil nutrient stock, about 55.05% in SOM, 53.88% in TN, and 46.23% in soil total phosphorus (TP) of total region, respectively. Under different land cover landscapes, there also are significant differences in SBD (highest in Sealed cover of 1.42 g cm^-3), SOM (highest in Mixed cover of 15.96 g kg^-1) and TN (highest in Mixed cover of 0.68 g kg^-1). The land cover landscape of the region is composed of Perennial cover (54.50%), Annual cover (15.15%) and Mixed cover (22.92%). The soils nutrient stock in the 0～15 cm layer under Perennial cover are the highest, about 55.01%, 54.53%, and 59.02% in SOM, TN and TP of total region, respectively. Because of little human disturbance, no significant difference is found in SBD, SOM, TN and TP of 15～30 cm soil layer in different types of land use/cover. Compared with soils in woodlands and paddy fields with high in vegetation cover, soils in residential areas, barelands under intensive human distur-bance and lands with low in vegetation cover are high in SBD but low in soil nutrient content.

Abstract:Simulation results of water yield, sediment yield and other natural processes in the Lianshui basin, China were presented for analysis of their tempo spatial variation and simulation accuracy. Simulation needs a warm up'stage at the begin ning, especially for simulation of sediment yield. Simulation accuracy decreases with the number of years in simulation. For sim ulation of water yield, the mean accuracy over 3 years is 98.32%, and over 8 years it is 90.27%, while for simulation of sedi ment yield, the mean accuracy over 2 years is 88.83%, and over 8 years it is 82.51%, which suggests that the method can be used to medium or long term dynamic monitoring of water and sediment yields in a basin. As for monthly simulation accuracy, the mean over 3 years is 83.84% and the mean over 8 years is 86.05% for water yield, and the mean over 2 years is 68.80% and the mean over 8 years is 59.70% for sediment yield. Simulation results of the method can also be applied for natural re sources management in a basin.

Abstract:Acquisition of soil solute transport parameters is a precondition for predicting solute transport using the numerical model in practice. A new and simple method is recommended here for estimating transport parameters of D and R using changes in depth of the solute front with time by means of one order approximate solution of CDE (Convective dispersive equa tion, CDE). Time domain reflectometry (TDR) was used to determine the time when the solute front arrived at different fixed points in the soil column and at the same time effluent from the column was collected for parameters estimation with the BTC (Breakthrough curve, BTC) fitting method using the CXTFIT program at the bottom of the soil column. By comparison the retar dation factors, R, derived with the two methods are more or less the same, however the convective dispersive coefficient D esti mated with the solute front information method is generally smaller than the one with the BTC fitting method. One of the factors resulting in the smaller D is the lag of the measured solute front behind the theoretic one, which is testified by comparing the for mer with the latter calculated using the parameters figured out with the BTC fitting method. Comparison between the measured BTC and the calculated BTC shows that the two have the same dispersive process in sand soil and the same times soil solute made the initial breakthrough and complete breakthrough, which demonstrates that the parameters estimated based on solute front information is somewhat applicable, but the precision of this method need further improvement.

Abstract:In the industry-oriented peri-urban region of Wuxi, Jiangsu Province, concentrations of total and DTPA extractable Cu, Zn, Pb and Cd were determined of 119 topsoil samples collected from an area of 8 km² and factors dominating spatial distributions of these elements were studied. Concentrations and coefficient of variation of soil heavy metals in this area were found increasing and so were significant positive correlations between concentrations of DTPA extractable metals and of their respective totals. Spatial variations of Cu, Zn and Cd in the soils were induced mainly by the industry therein. However the patterns of their spatial distribution hardly indicated any similarity probably because of the dispersiveness in distribution and diversity in type of the industrial plants in the study area. Concentrations of Pb were found high in the soil close to the city and decreased with distance away from the city. Highway and land use didn't show any close relationship with the variation of heavy metal concentrations in the soil, which was obviously obscured by the impact of the industry. It is, therefore, strongly recommended that a reasonable and orderly layout be made for industrial plants, so as to control the scope of soils polluted with heavy metals.

Abstract:Spatial distribution of soil organic carbon (SOC) is one of the key issues of the study on SOC sequestration, and plays a crucial role in understanding SOC storage dynamics. A research project on distribution of SOC in soil aggregates, profile, and field of purple paddy soil that is widely distributed in the Sichuan basin, was initiated in 1990.Results show that the highest organic carbon content in aggregates was discovered in the fraction of 2～0.25 mm in particle size, while total organic carbon (TOC) in aggregates was mainly distributed in the fractions of 0.25～0.02 mm and 0.02～0.002 mm. The content of SOC in aggregates trended to be greater (enrichment coefficient, EC > 1.5) in macroaggregates (> 0.25 mm) at depth of 0～10 cm under non-tillage ridge culture. In conventional fields under flat culture, paddy-upland rotation and ridge culture, SOC concentration decreased slowly with the increase in depth. Organic carbon content was significantly (p< 0.05) different between treatments. Distribution of soil organic carbon and some related properties of the topsoil layer of the experiment field demonstrated significant spatial variation, forming stripes and patches. The treatment of non-tillage ridge culture was the highest in SOC content, reaching 30.71 g kg^-1, while the treatment of conventional flat culture the lowest being only around 16.50 g kg^-1. Longterm non-tillage ridge culture may lead to enrichment of SOC in macroaggregates of the surface soil layer and differentiation between layers of the soil profile.

Abstract:Dynamics of soil organic carbon (SOC) under cultivation shifts has been in debate in soil C cycling studies. In this study, 2 adjacent fields of Wunitu paddy soil (one with rice-rape rotation and another with double corn for 3 years after rice and rape) were chosen to study the SOC dynamics. Both topsoil and whole profile was sampled. C pools of total organic carbon (TOC), dissolved organic carbon (DOC) and soil microbial biomass carbon (SMBC) was determined for bulk soils from the two fields respectively. Soil particle size factions (PSFs) were separated using low energy ultrasonic dispersion and the TOC of them determined using CNS analyzer. Selected samples of bulk soil and PSFs from both rice and corn fields were used for ¹³C natural abundance measurement with Finnigan MAT251 mass spectrometer. TOC of topsoil decreased drastically after 3 years of continuous corn cultivation although marked increase of DOC and SMBC was observed in the corn field. This was in coincident with the decrease of SOC in the sand PSF despite no remarkable changes in the other PSFs from the corn filed. Significantly heavier carbon could be detected either in bulk samples or in a single PSF from the corn field than from rice field. Calculation using the data of δ¹³C ‰(PDB) indicated that 80% of young carbon inputted by corn residues was allocated in the topsoil of 0～20cm and mainly found in the coarse PSF as well as in the pools of DOC and SMBC. The calculated short mean residence time (MRT) found with bulk sample and coarse fraction from the corn field in contrast to from the rice field suggested a coupling of rapid TOC decrease and fast aggregate turnover in the cornfield. Therefore, the TOC decline in the corn field was attributed to the disruption of aggregates that, in turn, released labile carbon from physical protection. Drastic decline of indigenous SOC at C 4 t hm^-2 a^-1 in the paddy soil after corn cultivation was in disagreement with the findings reported for American and European dry croplands and implicated a possible instability under alternation of cropping systems of SOC accumulated in paddies due to destruction of physical protection in coarse PSFs.

Abstract:Two variable charge soils and one acid constant charge soil were chosen to investigate the effect of salicylic acid on migration of Al with leaching experiment. The results showed that the different soils had different adsorption capacity for salicylic acid due to the difference in soil mineral compositions, and thus the effect of salicylic acid on the migration of Al in different soils was different. The Ferralosols with high content of free iron oxides has the great adsorption capacity for salicylic acid and thus small promotion of the acid on migration of Al was observed in this soil. The content of free iron oxides in Ferrosols was lower than that in Ferralosols, the adsorption capacity for salicylic acid in the former was also smaller than that in the latter. Therefore at the earlier stage of leaching experiment, the effect of salicylic acid on migration of Al was small, but the great promotion was observed in the soil at the latter stage of leaching experiment, especially at high initial concentration of salicylic acid. The Argosols has small adsorption capacity for salicylic acid, the organic acid showed obvious promotion on Al migration in the soil at high initial concentration of the acid after the start of leaching experiment. The results also indicated that the migration of Al was also related to the pH of soil systems. Low pH promoted the dissolution of Al and the migration of Al in soils as well.

Abstract:Kinetics of ammonium fixation in several types of cultivated upland soils and paddy soils derived from represen tative parent materials in Hunan province, China, was studied through sampling in fields, and incubation and determination in laboratory. Results showed that fixation of added NH₄⁺ in the tested soils, whether paddy or upland, all increased with fixation time, and the fixing rate for added NH₄⁺ was high at the initial stage, especially at the initial 8~12 hours of reaction, and grad ually slowed down afterward. After 24 hours, the fixation of added NH₄⁺ reached equilibrium basically. Both the first order equation and Elovich equation were the most applicable to describing NH₄⁺-fixation kinetics in the tested soils. The parabolic dif fusion equation had some good fitting results, too. But the zero level equation was not applicable. The kinetic parameters obtained through the first-order equation, i. e., theoretical maximum fixation capacity (A), reaction rate constant (b) and half reaction time, varied with soil types. The paddy soils were lower in theoretical maximum fixation capacity (A) and half reaction time, but much higher in reaction rate constant (b) than the upland soils.

Abstract:Three rice genotypes differing in nitrogen absorption efficiency (NAE), namely Wuyou 244 low in NAE, R832 12 medium in NAE and Shuiyuan 349 high in NAE, were planted in a pot experiment to investigate physiological and morphological characteristics of the roots of these plants growing with optimum nitrogen supply at the jointing stage, and their relat ionships with NAE. Results showed that Shuiyuan 349 was much higher than R83212 and Wuyou 244 in total length, density, surface area and dry weight of roots, and the highest in total absorption area (St), active absorption area (Sa) and ratio of Sa/St of roots, which were essential conditions for efficient nitrogen absorption. Moreover, Shuiyuan 349 was also higher in energy consumption, oxidizing capacity, reducing capacity and activities of nitrate reductase, glutamine synthetase, glutamate synthase and glutamate dehydrogenase in roots, which accelerated carbohydrate synthesis and nitrogen uptake and assimilation in roots, and enhanced bleeding intensity, free amino acid and soluble sugar content in roots, thus resulting in significantly high nitrogen content and accumulation in shoots. Stepwise regression indicated that root density, root total absorption area and nitrogen content in shoots at the jointing stage were the main characters of high efficient nitrogen absorption of rice and could be regarded as reliable indicators for efficient nitrogen management and genetic improvement of rice.

Abstract:This hydroponics experiment studied the differences in use of different forms of nitrogen (N) by starved rice crop (Oryza sativa L. ssp. Japonica cv. Wuyunjing 7 #). Re-supply of N stimulated growth of shoot but decreased biomass accumulation of roots, particularly by the single form of ammonium. In comparison to either ammonium or nitrate alone, mixture sup ply of the two forms of N increased total N uptake and translocation of N to shoot as well as activation of glutamine synthetase in the roots and nitrate reductase in the leaves. Concentration of total chlorophyll, particularly chlorophyll a in the ammonium supplied leaves was significantly higher than that nitrate supplied leaves. It suggests that balanced supply of both ammonium and nitrate through rational management of water and fertilization could improve both uptake and use efficiency of N by rice crop.

Abstract:According to the latest archaeological discoveries in the low Yangtze River Delta of China, in history rice cultivation can trace back to B. C. 4 000 in China. A mini-pot-culture experiment was carried out to evaluate effects of rice cultivation on microbial functional diversity and ammonia-oxidizing bacterial number in ancient paddy soils that have been buried under-ground for thousands of years, and in present paddy soil as well. A huge population of ammonia-oxidizing bacteria (AOB), about 0.416～1.235 MPN mg^-1 dry soil, was observed in the present paddy soil, while only a limited number of AOB, about 0.013～0.055 MPN mg^-1 dry soil, was detected in the ancient paddy soils after incubation for one or two months in greenhouse. Rice cultivation without N fertilization decreased the number of soil AOB significantly, while rice cultivation with ammonium sulfate fertilization increased its number within a short period of time, but sodium nitrate fertilization did not show any significant effect on soil AOB. The present paddy soil was much lower than the ancient paddy soils in carbon-source utilization capability, and in Shannon index, Simpson index and McIntosh index of microbial community to a varying extent. Rice cultivation, however,significantly increased carbon-source utilization capability of the microbial community as a whole in the present paddy soil, and raised the three indices therein up to the level of the ancient soils. The increase was slowed down by N fertilization. Rice cultivation and N fertilization did not significantly affect these functional diversity indices of the microbial community in the ancient paddy soils, and no significant difference was observed between the 3 320 a and 6 280 a ancient paddy soils.

Abstract:A modified UV spectrophotometry is compared with the phenoldisulfonic acid colorimetry, MgO distillation and FeSO₄-Zn reduction method, and copperized cadmium reduction method in determining NO₃^- concentration in soil extracts of nine different types of soils. In the UV spectrophotometry, the value of correction factors (f) is determined by measuring the absorbance of the soil extract solution in the absence of NO₃^-. The mean value of f is 2.2. Statistically, it is highly correlated between the four methods in determination value, particularly in mineral soils with low organic matter (less than 50 g kg^-1). All results show no significant difference between UV spectrophotometry and phenoldisulfonic acid colorimetry. However, the f value still needs to be readjusted in soils with high organic matter (more than 50 g kg^-1). In general, UV spectrophotometry is simple and rapid, and it can be applied to rapid analysis of large batches of soil samples.

Abstract:Sampling designing based on spatial distribut ion and variability of soil properties is an important issue in recent studies on soil sampling. In the present study, the variance quad tree method (VQT), combined with the semivariogram function, was used to design an optimal sampling scheme in a field of coastal saline soils. The ordinary kriging method was adopted to interpolate the sampling points fixed with the regular grid method and the VQT method, respectively, and their prediction errors were subsequently calculated for accuracy comparison. Results reveal that with the same size of samples, the VQT sampling scheme was much smaller than the grid one in prediction error, and hence its sampling efficiency was improved by 16% to 25%. The advantage of the VQT method is that this scheme samples sparsely in fields relatively even in soil properties and more inten sively in fields varying sharply. Thus it not only characterizes variability within the sampling area, but also improves sampling ef ficiency, and hence saves sampling cost.

Abstract:Field experiments were carried out to study effects of seawater irrigation on yield compositions and ion distribution of different varieties of Helianthus tuberosus growing in coastal mudflat along semiarid regions in 2005. Results show: (1) Nanyu No. 2 was higher than the others in biomass of the roots and aerial parts, and Nanyu No. 5 and Nanyu No. 3 were taller than the others in all treatments, but the effect on diameter of the main stems of the plants varied sharply with treatment. In the treatment of irrigation with 30% seawater, Nanyu No. 1 was not affected in biomass accumulation in roots and aerial parts, but the others to a varying extent. (2) The plants differed sharply in yield between varieties. Nanyu No. 2 was the highest when irrigated with 30% seawater, and so did they in single tuber weight, total sugar and Inulin content. Nanyu No. 1 and Nanyu No. 2 were the highest in single tuber weight. (3) Concentrations of Cl^- and Na⁺ in roots, stems and leaves of all varieties increased with the seawater concentration, but significant differences did exist between varieties. Na⁺ content was lower in leaves than in roots and stems. Judging by biomass accumulation, yield of tubers, total sugar and Inulin contents in tuber, and ion distribution, Nanyu No. 1 and Nanyu No. 2 were more adaptive to planting in coastal mudflat along semiarid regions with seawater irrigation than other varieties.

Abstract:Ecotoxicology of sulfamethazine on soil microbial activity and its degradation and transfer in the soil were investigated. Results show that 1 mg kg^-1 concentration of sulfamethazine in soil resulted in an apparent decrease in populations of bacteria and fungi (p < 0.05). Moreover, sulfamethazine was observed hardly degrading in soil, with a half life of 223.9 d and 102.4 d in sterilized and unsterilized soil respectively. And the thin layer chromatogram and leaching test indicated that sulfamethazine was liable to transfer and get leached, with R_f being more than 0.7, and its transfer and leaching rates were subject to the impact of pH and increased in acidic and alkaline developing agents, suggesting that sulfamethazine, as veterinary antibiotic, is a new environmental contaminant strong in ecotoxicology and mobility, low in degradation rate in soil, thus posing a potential pollut ion risk to water bodies.

Abstract:Adsorption/desorption of Cry1Ab crystal protein extracted from cry 1Ab-transgenic sorghum in six types of soils were determined, and effects of concentration of Cry1Ab protein in the solution and physical and chemical property of 6 types of soils on adsorption/desorption of the protein were studied. Results show that adsorption and desorption of Cry1Ab protein in the 6 soils were obviously different. Paddy soil fromred clay was the highest in Cry1Ab adsorption, and followed by typic podzolic soil, blue purple clay soil, paddy soil from quaternary red clay, yellow loamy paddy soil and paddy soil derived from red sand-stone in a decreasing order, while typic podzolic soil was found the highest in Cry1Ab desorption and followed by blue purple clay soil, paddy soil derived from red sandstone, paddy soil from quaternary red clay, paddy soil from red clay and yellow loamy pad dy soil. A significant positive correlation was found between the concentration of Cry1Ab in the solution added and the adsorption or desorption of the protein by the soils, with coefficients being 0.86 and 0.99, respectively. Effects of organic matter content and pH of the soil on adsorption were posit ive and significant, with coefficients being 0.83 and 0.82, respectively. The correla tion between the adsorption and the content of total nitrogen orreadily available phosphorus was positive, while it was negative between the desorption and the content of total nitrogen, readily available phosphorus or readily available potash. Consequently the adsorption and desorption of Cry1Ab in the soils were controlled jointly by concentration of Cry1Ab protein and physical and chemical propert ies of the soil.

Abstract:Being the largest freshwater lake in China, the Poyang Lake has widely aroused attention worldwild. As early as in 1992,the Poyang Lake Nature Reserve was enrolled into "the Ramsar List of Wetlands of International Importance". The Poyang Lake wetland, a unique ecosystem on earth, plays important roles in keeping ecological and hydrological balances, regulating climates, reducing pollution, and providing habitats for wildlife. According to the analysis of the ecological environment of the Poyang Lake Region, such as vegetation, wetland biological diversity, land use, water and soil erosion, soil alkalization, etc. Its main problems are defined. For example, serious degradation of the wetland vegetation, aggravation of water and soil erosion, prevalence of schistosomiasis, decrease in biological diversity, and so on. At the same time, with Notion of Science Development as guidance and from the strategic point of view, countermeasures are put forward, such as making an overall plan, rationalizing layout, exploitating reasonably, paying attention to ecoenvironment protection, which may serve as reference and basis for decision-making for sustainable development of the Poyang Lake as well as its Region.

Abstract:Soil C sequestration has been a research area of increasing significance in study of Earth surface processes and global change. The understanding of capacity, biophysical potential and mechanisms involved in soil C sequestration has been demanded by the assessment of global biophysical potential of GHGs mitigation for the post-Kyoto period. In this paper, the main research achievements in soil C sequestration study are overviewed focusing C capacity and protection mechanisms. While much has been dedicated to the C pools and C sequestration, there is a good number of studies showing that chemical binding, transformation of OC are both involved in C capacity and stabilization as well as the physical protection in coarse particle size fractions. Interaction of soil-plant(crop)-microbes in soil crop system may exert significant role in C sequestrat ion in cropland soils which will become a frontier of C study by holistic approaches in the near future. Finally, a conceptual model of C sequestration of agricultural soils is proposed and suggestions for further study of C sequestration in China are given with emphasis on the processes under interact ive effect of land management and crop production trends in the framework of global change biology systems.

Abstract:Rapid urbanization and industrialization often and increasingly cause soil contamination. Accumulation of toxic chemicals in soil may affect growth, reproduction and survival of plants, animals and micro-organisms in the terrestrial eco-systems, and may even threaten ecosystems quite a distance away from the source of pollution. Therefore, ecological risk assessment (ERA) is used to predict ecological domino effects triggered by contamination of the soils, and quantitatively measure magnitude and probability of risks. This article gives a brief introduction of ERA methodology developed in America and Europe, and reviews, current advances, existing problems and future trends in ERA research and development, hoping that through this effort development in ERA of polluted soils and establishment of risk-based Soil Environmental Quality Guidelines in China would be promoted.

Abstract:土壤侵蚀是全球性的严重环境问题。揭示土壤侵蚀过程,建立土壤侵蚀模型将为土地合理利用规划、水土保持措施优化配置、水土流失监测及水土保持减水减沙效益评价等生产实践提供重要科学依据和技术工具。土壤侵蚀预报模型按建模方法可分为经验模型与物理模型等,其中,经验模型主要是基于土壤侵蚀观测资料,采取统计分析的方法模拟侵蚀产沙量与降雨、植被、土壤、地形等影响因子之间的关系。自1953年刘善建^[1]在国内首次建立了坡面土壤侵蚀预报方程以来,不同学者根据各地的实际情况,建立了诸多不同的土壤侵蚀经验模型^[2~6]。

Abstract:耕地是土地的精华,是农业生产不可替代的重要生产资料,是保持社会和国民经济可持续发展的重要资源^[1]。耕地地力是指在当前管理水平下,由土壤本身特性、自然背景条件和基础设施水平等要素综合构成的耕地生产能力^[1]。对耕地地力进行评价是提高资源利用效率,推进农业结构调整,降低农业生产成本,指导科学施肥等工作的需要。对耕地资源的评价方法很多,大体可归为两类:一类是定性的评价方法,如分级划等的等级法,另一类是半定量的,如指数法或参数法^[2,3]。

Abstract:近年来,国内外学者对土壤入渗特征进行了大量研究,提出了具有不同特点和用途的入渗模型^[1~5]。随着土壤水分运动理论的发展,模型的发展日益趋于简单化、数值化、理论化,各模型之间的关系越来越紧密,许多学者试图通过对土壤入渗模型中特征参数的对比分析,建立模型参数间的关系,从而为获取相关土壤入渗参数提供手段,便于土壤入渗模型的实际应用^[6~9]。描述土壤水分入渗过程的模型很多,其中Philip和Green-Ampt入渗模型具有明确的物理意义,应用较广泛。王全九等建立了Philip和Green-Ampt两个入渗模型参数间的理论关系,并用实验结果进行了合理性验证^[8]。

Abstract:土壤风干-润湿过程可加剧土壤有机质矿化反应^[1],其矿化来自于土壤非生物有机质分解和土壤微生物在干湿变化过程中死亡两个过程^[2]。因此,干湿变化可能对土壤有机质及养分循环产生重要的影响。国内外的相关研究主要集中于干湿变化过程中土壤对磷素的吸附作用及有机磷矿化作用^[3]、微生物量碳的变化及有机碳矿化作用^[1,4]等等,实验对象多为肥沃或酸性土壤。

Abstract:土壤中氮(N)素营养往往是陆地森林生长发育的限制因子,土壤的供氮特性影响着森林生态的生产力、生态功能及生态结构^[1],因此森林土壤N素研究始终受到高度的关注。然而,许多因素控制和影响着森林土壤中N的循环及迁移,包括气候、植被、地形环境及各种扰动因素^[2~5],土壤中N的含量及形态则是最基本的要素。通常土壤中的N有90%以上是以有机形态存在^[6],掌握土壤中有机N的结构组成对于深入了解氮素的地球化学循环有重要意义。但是,由于分析技术与手段的限制,人们对于土壤中有机N种类及其形成机制还并不完全清楚。

Abstract:茶叶(Camellia sinensis)是重要的经济作物,茶树具有耐酸耐铝毒等特性,适合在热带亚热带的酸性土壤种植。由于茶园的施肥管理,茶树凋落物归还土壤以及根系分泌物等原因,茶园土壤随着植茶年龄的增加,土壤理化性质会发生一系列变化。如土壤pH值下降,钙、镁等盐基离子和微量元素相对缺乏^[1~4],而铝、氟和多酚类物质逐渐在茶园土壤中富集^[5,6],形成了非常独特的茶园土壤生态系统。

Abstract:硅酸盐细菌是土壤中一类能分解硅酸盐类矿物,破坏其晶格结构,使矿物钾转化成有效钾释放出来供植物生长的细菌^[1]。它不仅能溶磷解钾,亦有固氮的作用^[2]。目前的种类主要有,环状芽孢杆菌(Bacillus circulans)、胶质芽孢杆菌(B.mucilaginosus)和土壤芽孢杆菌(B.edaphicus)三个种的菌株^[3,4]。由于硅酸盐细菌的独特作用,已广泛应用于采矿、冶金、微生物肥料、饲料工业上^[2]。我国在硅酸盐细菌的生物学功能方面已进行了大量的工作,尤其是在硅酸盐细菌作为生物肥料方面^[5~9],但是对硅酸盐细菌的分类地位和遗传多样性研究较少。