Abstract:Soil crusts hinder water infiltration rate, thus increasing runoff and triggering soil erosion.Purplish soil is one of the most important types of soil in China and readily erodible.To study how soil crust is formed helps us understand how soil erosion proceeds and construct a physical erosion model.In recent years, works have been reported on characteristics and models of soil erosion in the purplish soil region of China.However, st ill not much is known about format ion of soil crusts and its effect on soil erosion process in purplish soil.In order to understand development of soil crusts on the surface of purplish soil and acquire scientific data for erosion risk assessment, a group of experiments were conducted.In the laboratory, two treatments (uncovered and covered with nets) were designed for samples of purplish soil collected in Lizikou Catchment, Sichuan Province.They were subjected to simulated rainfall.Results show that the purplish soil developed a stable layer of crust, 7~8 mm thick in 30 minutes; mechanical illuviation is the main factor of soil crusting, which was weakened by raindrops that beat the surface soil stimulating formation of a thin compacted layer; distribution of soil pores affects water infiltration and shear strength, which was demonstrated in the covered treatment where the total porocity was low, but evenly distributed, while the water permeability was high, because no compacted layer was formed at the init ial stage of the rainfall, thus lowering shear strength.

Abstract:When raindrops hit the soil, they trigger rain splash and formation of soil crust.Researchers used to pay attention to interactions of them.However, the relationships between the two varying with particle size of the soil have seldom been reported.Under simulated rainfalls in laboratory, splash erosion and soil crust development of Loess soils different in particle-size are observed and analyzed.Results show that distinct differences exist in amount of rain splash between soil samples.Soil samples about 0.15 mm in particle-size are the most susceptible to rain splash.Within a given duration of rainfall, the development of soil crust also varies with particle-size of the soil, which explains variation of splash rate.

Abstract:Ridge-tillage is an effective farming practice for soil and water conservation, extensively used in rainfed cropland in semi arid regions, however, its mechanism of controlling wind erosion is unclear and calls for further research.In the experiment field with ridges 25 cm high and 1 5 m in between, synchronous observation was made of wind profiles from 0 m to 4 m at windward, bed between ridges and leeward.Aerodynamic parameters of these sites, including hourly average wind velocity, aerodynamic roughness, friction velocity, and absolute and relative fluctuation intensity of wind velocity, were analyzed.Results indicate that hourly average velocities of the layer of 0~1 m at the site in between ridges and the leeward site were obviously lower than at the windward site, and the biggest drop was observed at the height of 0.3 m.Horizontally, the parameters, such as extent of the decrease in wind velocity, aerodynamic roughness and friction velocity, were all decreased with the distance of the observation point from the ridge.And all the three parameters were the biggest at the site between ridges whereas the smallest at the windward site, 1.5 m from the ridge.Increasing with wind velocity, absolute fluctuation intensity was a logarithm function of the height in the vertical direction whereas relative fluctuation intensity of wind velocity decreased with height in the 0~1 m layer of the profile, and changed little in the layers above 1 m, but increased with the decrease in distance of the observation site leeward from the ridge at the height of 0.05 m.It is the highest at the site between the ridges, bringing the shear stress of airflow on soil surface up to the peak, which is obviously unfavorable to wind erosion control.

Abstract:Development of biological crusts result ing from establishment of art ificial vegetation in the desert will significantly change water holding capacity and evaporation process of the soil.An indoor evaporation method was used to study evaporation characteristics of the soils covered with or without biological crusts.Results show that the longer the history of sand dune fixation, the thicker the biological crusts and the sub-soil layer below them, the lower its bulk density, and the higher the soil water holding capacity; which was more significant with moss-crust-covered soil than algae-crust-covered.And so was it in terms of soil evaporation rate after the soils were saturated with water.The process of evaporation, however, could be clearly divided into three stages (p<0.05).In the first stage (constant in evaporation rate), biological crusts contributed to evaporation, but in the second stage (declining in evaporation rate), they inhibited evaporation.Based on analysis, it is held that it is the higher waterholding capacity of the biologic crusts that enhance the possibility of soil water evaporation at the first stage, and inhibit evaporation by holding water in the soil when the soil gets dried up.

Abstract:A typical slope in the Caijiachuan watershed, Loess Plateau of China was an object of research.A total of 313 soil moisture monitoring points were laid out in a 20 m×20 m grid pattern in the experiment site for measuring soil moisture in two layers, 0~30 cm and 30~60 cm, with TDR (time domain reflectrometry) in 2005.Based on the data, a soil moisture dis tribution map was plotted with the Kriging method and then superposed over on the topographic factor maps of aspect, slopes and elevation, derived from DEM, thus forming a database of relationships between soil moisture and different topographic factors for analysis of effects of different topographic factors on soil moisture, and variat ion of soil moisture attributed to topographic factors.Results show that in the 0~30 cm soil layer, the topographic factors were in the order of aspect > elevat ion> slope in effect on soil moisture, while in the 30~60 cm soil layer, the sequence is slope> elevation> aspect The cluster analysis of aspects and slopes indicated that aspects could be sorted into two categories: 292.5°~360° (0°)~112.5°(shady slope) and 112.5°~292.5°(sunny slope), and so could slopes, 5°~20° and 20°~35° according to their effects on soil moisture.Based on the sorting models for fitting functional relations between soil moisture and the topographic factors were established and coefficients of the relations worked out.Assuming the soil moisture modulus is set as 1 when a shady slope is 5°~20° in gradient, and it is 0.99 on a sunny slope the same in gradient, 0.82 on a shady slope, 20°~35° in gradient, and 0.80 on a sunny slope the same in gradient.

Abstract:The presence of dissolved organic carbon (DOC) is considered as one of the key factors that facilitate movement of heavy metals, and the effect varies with the type of DOC.In this study, a miscible displacement approach, where soil-water-saturation and constant flow velocity were maintained in soil columns, was applied to investigation of mobility of humic acid (HA) and citric acid (CA), and their effects on Cu mobility in soil columns.Results show that CA was higher than HA in mobility in sandy soil and red paddy soil, and both HA and CA showed facilitating effect on Cu mobility in soils.The effect of CA was more obvious than that of HA, probably because CA may cause higher solution pH than HA and smaller in molecular weight.More interestingly, though the mobility of Cu was extremely low in the two studied soils, it seems that the potential mobility of Cu was higher in the heavy red paddy soil than in the light sandy soil.The results suggest that the enhancement of Cu mobility in the soils after irrigation with water high in DOC content is related mainly to the presence of mobile Cu-organic complexes in the soil solution.Further longterm and field experiments are required to validate the findings.

Abstract:Ionic-strength and pH are two most important chemical factors affecting transport of Kaolinite colloids.A lysimeter experiment using a column of saturated quartz was carried out to determine effects of ionic intensity (0.001 5～0.03mol L^-1) and pH (5～9) on mobilization of Kaolinite colloids.Results show that deposition of Kaolinite colloids increased with rising ionic intensity and so did retardation of the transport of colloids.The deposition of Kaolinite colloids is the lowest in neutral environment (pH7.10) and the highest in acid porous media (pH4.98).

Abstract:With the rapid urbanization of the Chengdu Plain, the risk of periurban soils exposing to heavy metal pollution is aggravating gradually, however, so far no ready-made research method is handy to study quantitatively impact of socio-economic development on soil heavy metal pollution.An attempt was made to study internal relationships between Cd content in soil and its affecting factors related to the socio-conomy of the urbanization of the Chengdu Plain with the aid of the BP Artificial Neural Network, which was made up of one input layer of 12 inputs, one output layer and one hidden layer.The network fit extremely well with precision reaching 97.02%.This BP network model was used to predict Cd content in peri-urban soils, with results 84.19% in precision, which is obviously higher than 71.mer in predicting heavy metal pollution.Then the predicted data of each affecting factor in year 2005 and year 2010 were input into the network, and merged with the previous samples.The model was trained over again to renew the network weight values.Thus soil Cd content in each county in the Chengdu Plain in year 2005 and year 2010 was predicted55% of the traditional regression model, showing superiority of the for.

Abstract:The mobility, bioavailability and toxicity of soil metals are most likely controlled by sorption-desorption reactions.A better understanding of the sorption-desorption processes and mechanisms is crucial for assessment and remediation of heavy metal polluted soils, and for prediction of the metal sorption capacity of soils.Laboratory batch experiments were carried out to study Cd sorption by four representing soils from Yangtze River Delta in China.The thermodynamic parameters including K°, ΔG°, ΔH° and ΔS° were calculated by using sorption data for two different temperatures 25±0.5℃ and 35±0.5℃.Results showed that Cd sorption can be well described by Freundlich model.The sorption K f values decreased in the order: Lithic Ochri-Aquic Cambosols (238.8 dm³kg^-1) > Endogleyic Fe-accumulic Stagnic Anthrosols (115.4 dm³kg^-1) > Typic Gleyic Stagnic Anthrosols (54.40 dm³kg^-1) > Fe-accumulic Gleyic Stagnic Anthrosols (10.74 dm³kg^-1).The Cd sorption capacity of Lithic Ochri-Aquic Cambosols was 24 times as much as that of Fe-accumulic Gleyic Stagnic Anthrosols.The Cd sorption capacity of soils decreased after removal of organic matter.For four tested soils, Cd sorption increased with solution pH.The K° and ΔS° values increased with temperature, while ΔG° values decreased with temperature.The negative values of ΔG° suggested that Cd sorption was a spontaneous process.The positive ΔH° values indicated that Cd sorption was an endothermic process for four tested soils.

Abstract:An experiment of leaching of latosol developed from basalt with simulated acid rain was carried out.Results show 1) simulated acid rain caused a large amount of leaching loss of soil base ions, among which potassium was the easiest to get leached and calcium and magnesium were the highest in amount; the lower the pH values and the longer the duration of simulated acid rain, the higher the leaching amount of soil base ions; 2) after 5 days of leaching with simulated acid rain, the amount of soil exchangeable base ions decreased with the increase in leaching time; and the effect varied with pH of the simulated acid rain; 3) a short-time of leaching (≤5 d) increased contents of soil exchangeable Ca²⁺,K⁺,and the content of Mg²⁺ (when pH was ≤3.0) in the soil;however, a long-time of leaching (≥10 d) did reversely;and the content of soil exchangeable Na⁺ was always decreased no matter how long the leaching time was; and 4) leaching with simulated acid rain, triggered weathering of some soil minerals, thus releasing base ions, and turning some soil exchangeable ions into non-exchangeable ones as well.

Abstract:Interactions between charged soil clay particles and cations in the field of energy has long been a subject attracting all soil chemists.Efforts are made to introduce equations for calculating mean free binding energy and mean free adsorption energy between cations and charged soil clay particles and the application of Wien effect in dilute suspensions, to the study on energy relationships between cations of K⁺, NH₄⁺, Ca²⁺, and Cd²⁺ and clay particles of yellow-brown soil, brown soil, and black soil.Results show that 1) mean free binding energies between cations of K⁺, and NH₄⁺ and the clay particles are in the range of 6 3~ 7 1 kJ mol^-1, and slightly higher with K⁺ than with NH₄⁺; 2) mean free binding energies between ions of Ca²⁺, and Cd²⁺ are in the range of 7.2~ 9.4 kJ mol^-1.With the same cation, the soils follow the order of yellow-brown soil< brown soil< black soil in binding energy.The mean free adsorption energies, ΔG_ad, of the four cations with the three soils under the same high field strengh, e.g., 150 kV cm^-1, show that the values of K⁺ and NH₄⁺ are quite close in yellow brown soil and brown soil, being 0.9 and 0 8 kJ mol^-1, respectively; but in black soil, the value of NH₄⁺ is higher than that of K⁺ by 0.1 kJ mol^-1.The adsorpt ion energies of Ca²⁺ in yellow-brown soil and black soil are 0.3 and 0.6 kJ mol^-1 higher respectively, than that of Cd²⁺.The adsorption energies of divalent cations are 1~ 1.5 times higher than that of monovalent cations.

Abstract:People used to focus on the relationship between the greenhouse gases in the atmosphere and the soil organic carbon (SOC) as mutual source or sink, and little has been done on effect of greenhouse gases on decomposition and transformation of SOC per se, and properties of its fractions.SOC can be divided into humic acid (HA), fulvic acid (FA), humin (HM) and non-humic substances.Formation, decomposition and transformation of SOC (HA, FA and HM) are all known mainly to be soil biochemical processes, which, however, belong to the issue of thermodynamic stability, if they are addressed from the aspect of energy changes from the initial to the final states of SOC.There are a number of factors that affect SOC stability in soil.However, as long as thermodynamic stability is concerned, only the following three,i.e.water activity, partial pressures of oxygen and carbon dioxide, may do, when the temperature is set to be 25℃.This is based on the understanding that any kind of organic matter is made of water, oxygen and carbon dioxide and can be decomposed eventually to the three substances.In order to explore effect of CO₂ concentration on formation and transformation of SOC, an indoor incubation experiment with organic material added the but no crop planted is conducted under controlled conditions varying in CO₂ concentration.Dynamic changes in amounts of total organic carbon (TOC), water soluble substances (WSS), extracted humic substances (HE), HA and HM in the soil were determined, and contents of water floating substances (WFS) and FA in the corn stalks under incubation for 180 days, calculated with the revised humus composition method.Results show that the "newly formed" net TOC decreased in amount gradually with corn stalk decomposing, and the net HE increased in the first 7 days, and then decreases.The absolute amount of HM, however,decreased gradually.The proportion of HA to HE (PQ) exhibited an increasing trend in the beginning, and then leveled off, indicating that the formation of FA is faster than that of HA in the initial stage of incubation.HA and FA transformed reciprocally for a period of time, and reached dynamic balance finally with the incubation going on.The contents of TOC, WSS, HE and HM in the treatment 30% in CO₂ concentration (V/V) were significantly higher than in the treatment 3% in CO₂ concentration and normal in CO₂ concentration (0.037 5%), and WSS and HM were more sensitive to CO₂ concentration, but the difference between treatments 3% and normal CO₂ concentration was not significant.The three treatments are in the order of 30% CO₂ > 3% CO₂ > normal CO₂, in terms of PQ of extractable humus, suggesting that high CO₂ concentration is beneficial to the formation and stability of FA rather than HA.

Abstract:A typical undulating tract of farmland in the Black Soil region of Northeast China was taken for a case study to analyze impact of soil erosion and deposition on loss, transportation and accumulat ion of SOC through measuring contents of water stable aggregates of different sizes, particulate organic carbon and aggregate-bound organic carbon in surface layers and typical soil profiles in different topographic positions.Results show that water stable macro aggregate, mineral-bound organic carbon (MOC) and aggregate-bound organic carbon decreased in content with increasing rate of soil erosion at three sampling sites on the upper slope, and the contents of particulate organic carbon (POC) and POC/ SOC ratios were lower at the deposition sites, especially in foot-slope, at the erosion sites, while the contents of MOC and MOC/ SOC ratios displayed a reverse trend.The depth distribution of organic carbon of various particle-size fractions at the foot slope was characterized by obvious accumulation and deep burying of eroded materials; and accumulation was getting more and more obvious with decrease in particle size of the organic fraction.The above-listed findings reflect that soil erosion tends to transport organic carbon associated with fine part icles and micro-aggregate, and then accumulates in depressed deposition sites.The eroded materials, such as micro-aggregates, particulate organic matter (POM) in the buried layer form stable macro aggregates through deep burying, which eventually promotes sequestration of SOC in the deposition sites.

Abstract:A plot (20 m×30 m) was delineated for study in the Maolan karst virgin forest, containing 7 types of microhabitats: rocky surface, soil surface, rocky soil surface, rocky gullies, rocky crevices, stone pits and stone caves.The soil organic carbon (SOC) contents in the plot ranged from 40.1 g kg^-1 to 203.5 g kg^-1.The variation coefficients of SOC contents of the plot and the microhabitats were 43% and 41%, respectively, 22%～42% between microhabitats of the same, and 14%～57% within a microhabitat, suggesting high spatial variation of the SOC contents in the plot.In order to improve comparability of the data available for the study of soil degradation in the karst ecosystem, a representative sampling method is advanced for collecting samples in a sampling site formed of sampling points of the same microhabitat, which is delineated based on soil area weight.It goes like this: select several types of microhabitats whose respective sum of land areas exceeds 95% of the total soil area of the sample plot, determine quantity of the soil sample of each microhabitat that forms the representative soil sample of the plot by area weight, and the soil sample of each selected microhabitat is mixed out of soil samples from land patches of the same type of microhabitat, and their quantities are determined by area weight.Using this method, the surface area-weighted value of the SOC content in this plot was figured out to be 92.1 g kg^-1.

Abstract:GLEAMS (Groundwater Leaching Effect of Agricultural Management Systems) is a model developed by scientists of the U.S.Department of Agriculture, and is mainly used to evaluate environmental effects of farming practices.The model was used to simulate the cycling of soil nitrogen in the peri-urban areas of Nanjing.Results showed that during the period fromJuly 2003 to July 2005, nitrogen input reached 3 810 kg hm^-2, of which 3 750 kg hm^-2 came from fertilization and animal waste, the rest 57.0 kg hm^-2 was from rainfall and irrigation.Nitrogen output was composed of leaching 1 100 kg hm^-2, runoff 43.0 kg hm^-2, crop uptake 960 kg hm^-2, volatilization 260 kg hm^-2 and denitrification 913 kg hm^-2, thus forming a surplus of 531 kg hm^-2 left in the soil as residue.On such a basis, nitrogen recovery ratio was calculated to be merely 21.6%～25.2%.The results indicate that the agricultural system has low fertilizer use efficiency, but causes much pollution to the groundwater.The findings serve as a scientific basis for exploration of optimal fertilization recommendations and eco-environmental improvement in the region.

Abstract:It is a common way to apply NH₄⁺ and K⁺ together in farming.Effects of NH₄⁺ on movement and transformation of K⁺ in fertilizer microsites in red soil and Fluvo-aquic soil were studied through an incubation experiment using soil columns.The fertilizers used in the experiment were NH₄Cl and KCl.Compared with the treatment of application of K⁺ alone, the treatment of addition of NH₄⁺ did not show any effect on diffusion distance of fertilizer K but did increase the concentration of water-extractable K in fert ilizer microsites.In the soil close to the fertilizer placement site, the concentration of exchangeable K was decreased as a result of the addition of NH₄⁺, which was not so apparent in Fluvo aquic soil as in red soil.Besides, the addition of NH₄⁺ significantly decreased the concentration of nonexchangeble K in fertilizer microsites, suggesting that the addition of NH₄⁺ reduced K fixat ion in soil crystal lattices, thus increasing the risk of K leaching in the two soils.

Abstract:Ammonia volatilization in relation to N application rate and climate factors was studies through field experiment in red soil under the crop rotat ion of Smooth Crabgrass (Digitaria ischaemum) in spring and Winter Radish (Raphanus sativus) in autumn.Results indicate that ammonia volatilization in Treatments N90, N160 and N230 in spring dragged on for 10~17 days, and peaked at the 6th~8th day after urea application, reaching N 0.11, 0.57 and 1.84 kg hm^-2d^-1, respectively, and the total amount of N loss through ammonia volatilization was N 0.67~5.16 kg hm^-2, accounting for 0.74%~2.24% of the total N applied In autumn, in Treatments N70, N130, N190 and N250 (the ratio of basal and sidedressing is 7.3) ammonia volat ilization occurred both after application of basal fertilizer and tillering fertilizer and lasted 10~11 days, with peaks reaching N 0.02, 0.05, 0.06 and 0.09 kg hm^-2d^-1 for the basal fertilizer, and N 0.05, 0.22, 0.38 and 0.72 kg hm^-2d^-1 for the tillering fer tilizer respect ively.The total amount of N loss through ammonia volatilization was N 0.37~3.04 kg hm^-2, accounting for 1.31%~3.69% of the total N applied to Winter Radish (Raphanus sativus).

Abstract:The aims of the work were to investigate effect of NH₄⁺ on Arabidopsis seedlings of different accessions growing in agar medium or hydroponics in root characteristics, morphology and physiology.Results indicate primary root length, lateral root length and root surface area of Arabidopsis all decreased with increasing NH₄⁺, but root average diameter went up first and then down with increasing NH₄⁺.Difference between ecotypes of Arabidopsis in response to elevated NH₄⁺ was obvious, but no similar phenomenon was found when the seedlings were exposed to the same concentration of K+.Further study on two significantly different accessions of Arabidopsis (Col-0 tolerant to NH₄⁺ and JA22 sensitive to NH₄⁺) show that the effect of NH₄⁺ was significantly lower on Col-0 than on JA22 in inhibiting root length, and so was it in promoting root average diameter, but no much difference was observed between them.Treated with 30 mmol L^-1 NH₄⁺, Col-0 was significantly higher than JA22 in biomass of the shoots, but much lower in chlorophyll content, and they are more or less the same in water content.And in terms of NH₄⁺ uptake rate, Col-0 was at least 3 times higher than JA22.Therefore, it could be concluded that the Arabidopsis growth inhibited by NH₄⁺ was not attributed to rhizosphere acidification, absence of NO₃^-, high ion intensity or high availability of NH₄⁺ to plants.

Abstract:Although the enhanced biological phosphorus removal (EBPR) process is widely applied in wastewater treatment to remove phosphorus biologically, it is difficult to predict and control its effect, which is unstable and would often decline suddenly in large-scale municipal sewage treatment plants, on account of lack of knowledge about microbiological and molecular mechanisms of the EBPR process.An experiment was carried out using Pseudomonas putida GM6, a strain of high-efficiency phosphorus-accumulating bacteria isolated and identified in the lab, to quickly reactivate the phosphorus removing capacity of sludge.In order to learn how GM6 colonize in the reactor, Pseudomonas putida GM6 was first labeled with gfp gene through triparent conjugation, and then introduced into a sequencing batch reactor (SBR) installation, low in phosphorus removing efficiency in the lab to investigate how GMTR colonize in activated sludge.The initial count of GMTR introduced into the sludge accounted for 1.5%～3% of the total count of bacteria in the sludge, and rose up to 9.2% after 21 days, indicating GMTR colonized firmly in the sludge.At the same time, variation of phosphorus-accumulating capacity of R2 was studied after inoculation.It was found that phosphorus removal rate gradually increased 5 days after inoculation, and up to 96% at D 21.And phosphate concentration in the effluent lingered around 0.2 mg L^-1 after 28 days.The findings demonstrate that the strain of Pseudomonas putida GM6 is quick to initiate its biological phopshorus removing function in wastewater and may serve as scientific basis for large-scale engineering application.

Abstract:Soil irrigation with wastewater and reclaimed water is a common practice in North China.Its potential ecological risk of accumulation of genotoxic substances is a major concern worth studying.In this paper, in vitro umu/SOS test and in vivo Comet assay were used to assess accumulation of genotoxic substances in the soil irrigated with reclaimed water in suburbs of Beijing.Relative genotoxicity was determined by weight of the soil (G) needed to show positive (or to reach 2 in induction ratio R), and Tail Moment (TM) was cited in Comet assay to characterize genotoxicity of the soil.Results showed G decreased and TM increased along with the increase in amount of reclaimed water used in irrigation, implying that the use of reclaimed water in irrigation could result in increase in genotoxicity of the soil.A significant relationship was observed between G and TM, suggesting that genotoxic substances in the soil irrigated with reclaimed water are mainly organic contaminants.It could be concluded that the umu/SOS test combining with the Comet assay could be used to screen out high risk soil samples rapidly and effectively.

Abstract:A case study of Kaifeng was carried out on soil animals in urban ecosystem and influence of heavy metals pollu tion on their community structure.Kaifeng is a city in Henan Province, sitting at 113°52'~115°02' E Long., 34°12'~35°01'N Lat..Under the warm temperate continental monsoon climate, it enjoys an annual mean temperature of about 14.0~14.2℃ and an annual mean precipitation of 627.5~ 722.9 mm.In May of 2004, soil samples (0~20 cm) were collected randomly in 5 different types of land, i.e.cropland, urban green land, the culture & educat ion land, resident ial land, and industrial land.And in September the same year, soil animals were collected by the hand sorting method (sampling plot area 30 cm×30 cm, two replicates in each land types), Tullgren funnel method (100 cm³ soil materials), and Baermann funnel method (25 cm³ soil materials) from soils (0~5 cm, 5~10 cm, 10~15 cm, and 15~20 cm) in corresponding soil sampling sites.

Abstract:The consumption of P fertilizer has been increasing dramatically in China and so has the content of available P in the soil since the 1980's.However, how the change will affect production and application of P fertilizer in China remains to be unclear and a concern related to food safety and environment safety.Relationship between P balance and change in soil Olsen-P in eight different types of arable soils were evaluated.Results show that on average, about 3.1% of the annual P surplus in the arable land in China was considered as Olsen-P.In the period from 1980 to 2003, the cumulative P surplus reached about 392 kg hm^-2, from which it can be inferred that currently the content of Olsen-P in the arable land of China is about 19 mg kg^-1.If soil available phosphorus is to be increased to and maintained around 40 mg kg^-1 in the future thirty years, the demand for phosphorus fertilizer will rise to 12.5 million tons in 2020 and then drop to 10.5 million tons in 2035.

Abstract:Soil collembolan is deemed as an epitome of soil invertebrate and medium-sized soil animals because of its abundance in species and hugeness in biomass.So it plays an important role and demonstrates its unique advantages over other soil animals in the assessment of heavy metal contamination of environment; This review first briefly summarizes some methodological systems and major parameters (community structures, species character, survival,growth,reproduction, metallothionein, and enzyme) used in the study of ecotoxicology and other related biomarkers in applying Collembola in ecological risk assessment of polluted soils.In the end of this review, problems existing in and prospects of the application of Collembola in the ecological risk assessment of heavy metal contamination of soils are analyzed and discussed.

Abstract:施用氮肥是提高作物产量的重要措施,但不合理施用是导致氮肥利用率偏低的主要原因之一,减少农田中氮肥的损失是提高利用率和降低环境污染的共同基础。寻求一种快速、可靠、廉价、非破坏性的作物氮素营养水平田间诊断方法,然后建立一个通用的施氮模型,对指导作物氮肥管理具有重要意义。

Abstract:根据最新的考古发现,中国种植水稻的历史可以追溯到公元前4000多年^[1]。据考证,位于长江三角洲的昆山市正仪镇绰墩山古水稻土遗址的地下42~57cm与100~116cm均为古水稻土层,历史耕作时间分别距今约3320a和6280a^[2]。氮素是作物生长发育所需的重要营养元素^[3],稻田土壤的供氮能力是影响水稻生长的关键因子,是评价土壤肥力的主要指标之一^[4]。土壤供氮能力主要包括供氮量和供氮过程两个方面^[5],而硝化活性又是评价土壤供氮能力的一个重要指标^[6]。

Abstract:氮素是作物生长所必需的营养元素之一。在一般情况下,作物能够吸收利用的氮素形态有多种。但从营养学角度来说,植物生长的主要氮源为NH₄⁺-N和NO₃^--N^[1,2]。由于作物本身遗传特性和营养特点以及环境条件的差异,作物对NH₄⁺-N和NO₃^--N的吸收利用和适宜性也有不同^[3,4]。对蔬菜作物来说,大多数蔬菜喜好NO₃^--N,但它们的喜硝特性并不是绝对的,许多喜硝作物在NO₃^--N供应充足的前提下,如果同时供应适量的NH₄⁺-N,作物生长可以得以明显改善^[5~8]。其最佳配比随作物生育期不同而不同^[9]。

Abstract:土地荒漠化已经逐渐威胁到人类的生存,是人类共同面对的全球重大环境问题,也是人类研究的热点问题之一。土壤是由水、空气和粒径不同的各类物质组成的具有不规则形状和自相似性的多孔介质,具有一定分维特性^[1]。近年来许多学者运用土壤颗粒的分形维数来综合反映荒漠化土壤的质地、结构及均匀程度,表征荒漠化的程度,分形几何已成为定量描述荒漠化土壤特性的新方法^[2~7]。但目前尚未见到关于在人工植被恢复荒漠化逆转过程中土壤分形特征变化的报道。本文采用已有的分形模型,对青海省治沙站建站以来人工植被恢复荒漠化逆转过程中土壤颗粒分形维数变化特征进行研究,为荒漠化逆转特征描述和荒漠化程度的定量化评价提供新的方法。

Abstract:土壤微团聚体是有机无机复合体经过多次聚合而形成,以不同粒级微团聚体的形式组合在土体内,土壤微团聚体的组成密切影响着土壤的保水、供水性能,是土壤中水分和养分保贮和释供的关键,与土壤肥力水平存在着明显的相关关系^[1]。土壤微团聚体对土壤理化及生物学性质有多方面的重要作用,而不同粒级的微团聚体所起的作用又各不相同,它们影响着土壤肥力水平的高低^[2~5]。