Abstract:A new method was proposed to evaluate the accuracy of DEM by combining the pixel slope evaluation method with numerical value evaluation method.Results obtained from two types of DEM experiment sites,the Miyun Reservoir in Beijing and Jiangsu Province showed that the new method for DEM evaluations was characterized by credibility,accuracy,quickness,intuitiveness,and objectivity,and could quickly turn out a precise DEM after correcting a few mistakes in general imaginary of DEM.The accurate values are true to the reality.Since the method can make errors standing out in DEM and hence easy to correct,it is very useful to work out a precise,intuitionistic and actual DEM.The new method has been fully proved in establishing DEM of Jiangsu Province and the upstream region of the Miyun Reservoir in the Haihe watershed.

Abstract:Ever since the Miocene time,aeolian dust has been falling down over Northwestern China,forming the Loess Plateau.The dust sedimentations have never been intermitted even in the soilforming periods when the climates were warmer and wetter.The peculiarity of the pedogenic processes of the loess lies in the synchronization of the soil forming processes and sedimentation of aeolian dust,thus making the profile thick and uniform,with complex properties.The parent materials of the paleosols are not the underlying loess,but the aeolian materials,which were accumulated constantly during the soilforming processes.There is not typical buried A horizon in the paleosols.It is not reasonable to classify paleosol profiles into A,B and C horizons.Owing to the continuous input of dust with plenty of carbonate,the pedogenic strength of the paleosols is steadily weakened,and thus has even not yet reached the level of the Brown Soil in most cases in Loess Plateau.

Abstract:Effects of five low-molecular-weight organic acids,i.e.,acetic acid,citric acid,maleic acid,malic acid,and oxalic acid,on electrokinetic properties of two latosols-Kunming latosol and Xuwen latosol were investigated in this work.The results showed that under the experimental conditions with the increase in the concentration of acetic acid,the potentials of Kunming latosol and Xuwen latosol were gradually shift ing to the positive direction,and then the movement increased in velocity significantly,till the potential leveled off.With the increase in the concentration of citric acid,however,the potentials of Kunming latosol and Xuwen latosol moved towards a further negat ive direction,with the velocities being more or less the same between the two latosols within the range (0~0.15 mmol L^-1) of the tested concentration.With the pH value ranging between 3.2 and 6.0,the potentials of the two latosol suspensions containing different organic acids showed a decreasing order of acetic acid> maleic acid> malic acid> citric acid> oxalic acid;and the potentials of suspensions containing the same organic acid were always higher for Kunming latosol than for Xuwen latosol.In the presence of different organic acids the isoelectric point (IEP) of the two latosols followed the same order as that of potentials mentioned above;and as for the same treatment,IEP of Kunming latosol was 0.5~1.0 pH unit higher as compared with that of Xuwen latosol.

Abstract:Dynamics of organic carbon and total nitrogen under different types of land use in Napahai marsh wetland,northwest Yunnan was studied with the sequential coring and in-situ exposure method.The results show that soil organic carbon and total N varied significantly both vertically and horizontally.The content of organic matter was 110.67 g kg^-1 in the primary marsh soil,85.30 g kg^-1 in the swampy meadow topsoil and only 22.66 g kg^-1 in the deep soil layer,and decreased horizontally from primary marsh to swampy meadow,meadow and to cropland by 22.92%~69.64%.Total N followed organic matter in the same trend in spatial distribution,showing a significant correlation coefficient vert ically (r_(top)=0.93,r_(deep)=0.96).But it had a low correlation coefficient horizontally with NH₄⁺-N(r=-0.74) and NO₃^--N (r=-0.65).Besides,a significantly negative correlation was observed between NH₄⁺-N (NO₃^--N) and hydrolysable N (r=-0.81,r=-0.76).The C/N was high (average 23.69) in the primary marsh,showing that primary marsh in Napahai wetland had low mineralization rate,a high nitro-gen accumulation rate and a carbon fixation rate,which also explains that soil organic carbon and total N in Napahai wetland are degrading with human disturbances.

Abstract:Soil organic C plays a key role in carbon cycle and carbon storage in the natural ecosystem.The soil carbon stocks under native vegetations in China were estimated by making use of 2 440 profiles from the second national soil survey and the vegetation map (14 000 000) of China,and map the distribution of soil carbon density under native vegetations.With the aid of a simplified vegetation classification system,the digitalized vegetation map units were sorted into 6 categories and 26 types of vegetation.The median carbon stocks of the soils in China are 8.23 kg m^-2 in 0~100 cm soil layer,and 2.67 kg m^-2 in 0~20 cm topsoil.The difference in the soil carbon density among vegetation categories is prominent.The soil carbon density in 0~100 cm under forests,scrubs,deserts,steppes,meadows and croplands is 11.59,7.25,3.14,5.29,14.90 and 8.07 kg m^-2,re spectively.On the basis of vegetation types,the total soil carbon stocks were calculated at 69.38 Gt in 0~100 cm and 23.81 Gt in 0~20 cm.In 0~100 cm,the soil carbon stock under forests (17.39 Gt) was the highest,accounting for 25% of the total in China despite the fact that the forest soil amounted to only 15.81% of the total territory of the country.Under croplands,it was 14.69 Gt or 21.2%,a little higher than the percentage (19.18%) of the soil in area.Though the soil under the vegetation of meadows and swamps was low (8.64%) in percentage in area,its carbon storage amounted to 12.22 Gt or 17.63%.The soil carbon stocks under steppes were 14.69 Gt or 10.76% of the total,lower than the percentage (14.86%) of the soil in area,and it was 3.93 Gt or only 5.66% under deserts,much lower than the percentage (13.17%) of the soil in area.

Abstract:Development of precision farming calls urgently for remote sensing techniques capable of providing timely accu rate ground information.Estimation of soil moisture from reflectance measurements in the solar spectral domain (400~2 500 nm) was investigated.For this purpose,18 soils representing a large range of permanent characteristics were gathered for the test.Reflectance data were measured in the laboratory during the soil drying process with a high spectral resolution spectroradiometer.Five approaches were compared.The first one was based on single-band reflectance and on calibration of the reflectance data by the reflectance of the corresponding soil under dry conditions,the second and the third approaches on either reflectance deriva tives or absorbance derivatives and the fourth and fifth approaches on differences between reflectance and absorbance observed in two non consecutive bands.In the first step,the relationships were calibrated over half the dataset (nine soils) with emphasis on selection of the most pertinent spectral bands.Results showed that,for the first approach,the bands corresponding to the highest water absorption ca pacities (1 944 nm) yielded the best soil moisture retrieval performance.For the second and third approaches,the bands corre sponding to sharp edges of the water absorption features performed better (1 834 nm for the reflectance derivatives and 1 622 nm for the absorbance derivatives).The fourth and fifth approaches could be considered as a generalization of the derivative approach when bands were no longer consecutive.The best performance was achieved when the bands were not too far apart.The best overall retrieval performances were achieved with the absorbance derivatives and the absorbance difference,confirming the non linear character of the relationship between soil moisture and reflectance.

Abstract:A pot experiment was conducted in a glasshouse to clarify and quantify the effect of soil water regimes on dry matter production,water-use efficiency (WUE),and carbon isotope discrimination (CID) of different plant parts of upland rice (Oryza sativa L.) measured at the tillering and maturing stages,and to understand the relationship between WUE and CID.Three water regimes were imposed: saturated condition (W1),70% of saturation moisture (W2),40% of saturation moisture (W3).Results of the experiment showed that biomass accumulation decreased by 45% at the tillering stage,and by 16%~19% at the maturing stage with soil water regime changing from W1 to W2,and by 73% and by 55%~57% with soil water regime from W1 to W3.On the other hand,above ground dry matter-based WUE (WUE_A) and total dry matter based WUE (WUE_T) increased with rising water stress by 0.07~0.28 g kg^-1 at the tillering stage,and by 0.07~0.45 g kg^-1 at the ma turing stage.The values of CID of the plant varied from 17.0 to 20.6 with significant differences among plant parts,which can be lined in an order of rootCID values of all the analyzed plant parts significantly decreased with rising water stress.A consistent negative relationship between the CID values of leaves and WUE_A(and WUE_T) was ob served.

Abstract:A graphing method is proposed in this paper for estimating parameters of solute transport in soils based on the convection-dispersion equation (CDE).The ratio of flux concentration changing with the time (dc/dt) is obtained on data of breakthrough curves (BTCs) of solute transport in a semiinfinite soil column.Using graphing software,for example,the Microsoft Excel,can draw two curves of t^1.5 dc/dt and dc/dt in respect to time.Each curve has a single peak.The two curves are used to estimate the retardation factor (R) and dispersion coefficient (D₀) in the CDE.Hypothetical examples and displacement experimental data of the two soils were used to validate the new graphing method for its accuracy and stability of the estimation of the two parameters.The stability of parameter estimation is evaluated by the standard deviations of est imated parameters against their average value.The accuracy of the new method is assessed by comparing it with other two most used methods that are the CXTFIT and the equal-slope method.The results show that the method high both in accuracy and in stability.The new method is particularly good for est imating parameter R.The method is a deterministic method and it is simple in terms of calculation.It also has the advantages of uniqueness and no initial guess of parameters over the CXTFIT method.The new method provides an alternative approach to estimating parameters of solute transport in soils.It is simple,accurate,stable,and saves time.

Abstract:Based on a modified Leenheer fractionation scheme,dissolved organic matter (DOM) extracted from Huang-nitu under different land use were fractioned according to their polarities and charge characteristics by using XAD-8 resin.The characteristics were studied with the aid of elemental analysis,¹H-NMR and CP/ MAS-¹³C-NMR spectroscopy.It was preliminarily found that of the total DOM extracted from the paddy soils,HIM predominated,accounting for about 35%,HON accounted for 7%~15% and HOB for a little.As is shown by the elemental analysis,¹H-NMR and ¹³C-NMR spectra,HON was characterized mainly by longchain alkylate with 77.13% of aliphatic C.N from the DOM could be found primarily in fraction HON.Comparison between the spectra of HOA and fulvic acids (FA) indicated that both contained a large amount of carboxylic groups and that the former contained more carbohydrates and less aromaticity.Finally,fraction AIM consisted of high-branched polyphenols and humic bound carbohydrates,and fraction HIM contained a high amount of carbohydrates.

Abstract:Accumulation of cadmium and nonprotein thiols (NPT) in rice (Oryza sativa L.) seedling as affected by short-term treatment of different combinations of sulfate and cadmium was studied.The results showed that short-term(6 days) Cd stress did not cause significant decline of the seedling biomass,but the interaction between cadmium and sulfate did affect cadmium accumulation in rice seedlings.It was observed that increasing sulfate supply could considerably enhance cadmium transport from root to shoot,thus resulting in higher accumulation of cadmium in leaf.Both of cadmium only stress and higher level of sulfate supply increased NPT content in seedlings,particularly in roots,although level of the phosphate buffer-extractable proteins in plants was kept on changed.Supply of cadmium and sulfate together could further increase NPT content in seedlings,indicating a positive effect of the interaction on NPT.It was concluded that sufficient supply of sulfate could improve rice tolerance to cadmium stress but also enhance cadmium accumulation in the leaf.

Abstract:A kinetic method is presented for characterizing the physiological state of microorganisms capable of carrying out specific metabolic function in red soils taken from a lead-zinc mining area.The results showed that soil microbial community metabolic profiles were inhibited by mixed heavy metals pollution,exhibiting non linear correlation with the incubation time,and the shape of the color development curve was generally sigmoidal.Test well OD values over time suggested a kinetic model based on the density-dependent logistic growth equation.The kinetic parameters generated by the model can be used as surrogates for single-time-point data in constructing carbon source utilization patterns.The kinetic parameter K and r values decreased signifi cantly with level of mixed heavy metals pollution.The higher pollution degree,the lower microbial community profiles,the lower microbial metabolic processes and the microbial growth rate.Principal component analysis (PCA) single-time-point microplate data and parameters of the kinetic model showed that parameters K and s could be effectively used to differentiate degrees of heavy metal pollution in the mining zone with efficiency higher than AWCD.Change in dynamic characteristics of the microbial community functional diversity well reflects differences in model of microbial communities utilizing C sources in the soils polluted with mixed heavy metals,and change in soil microbial community functional diversity in particular eco environment like mining zones,thus revealing to some extent functional mechanism of microbial communities in environment under heavy metal stress.

Abstract:Four arbuscular mycorrhizal fungi (AMF) inocula were produced in the sterilized soil under glasshouse conditions.Effectiveness and infectivity of the inocula were tested in pot culture with the most probable number (MPN) test method.The results indicated that biomass of inoculated plants was significantly higher than that of non-inoculated control plants (p<0.01),and the number of propagules was in the range of 95~1 400 per gram inocula.The field trials were carried out by means of producing pre-inoculated seedlings prior to transplanting.The infection rate of maize roots increased rapidly at early stage of the plant growth and then leveled off.The yield of the maize inoculated with inoculum A (Glomus constrictum),C (three Glomus species) or D (G.intraradices) was significantly enhanced (p< 0.05),and so was the content of starch and phosphorus in grains of the maize.

Abstract:In a pot experiment,pots of maize inoculated with G.intraradices Schenck & Smith and G.etunicatum Becker & Gerdemann were treated with herbicides.The dosages of herbicides applied in the pots were the same as in the fields.The results showed that the herbicides (acetochlor,butachlor,glyphosate-isopropylammonium,aventis,dicamba,and fluroxypyr) had significant impacts on biomass of the maize,infection rate of AM mycorrhiza fungus,and hyphal enzyme activity of alkaline phosphatase (ALP) and succinate dehydrogenase (SDH),and amount of AM mycorrhiza fungal hypha in the soil.Samples collected at the 10th week showed that aventis had greatest impact on biomass of the maize (21.1~31.3 g),and glyphosate isopropylammoniun had the least (59.7~65.5g),while the biomass in the control was 85.4~95.7 g.In terms of impact on infection rate,Butachlor ranks first among the six,resulting in an infection rate of 13.7%~18.1% and Fluroxypyr the last (30.4%~36.6%),while the infection rates in the control were 63.0%~88.2%.Butachlor remained to be the first in terms of impact on ALP and SDH activities of AM mycorrhiza fungal hypha (ALP 8.1%~10.4% and SDH 10.6%~14.6%),and Fluroxypyr the last (ALP 17.0%~20.6% and SDH 23.1%~28.2%),whereas the control showed 38.0%~50.3% and 49.7%~72.4%,respectively;Besides,herbicides also affected significantly total amount of the hyphae of AM mycorrhiza fungus in the soil.

Abstract:A yeast strain Gb identified as Debaryomyces sp.was isolated from sludge of a chemical plant by acclimatization.This strain was capable of growing in media with 20% Na₂SO₄ and utilizing phenol as sole carbon and energy sources.Effects of environmental factors on growth of this strain and degradation of phenol were tested.It was found that the optimal condition for growth and phenol degradation of this strain was phenol 1 000 mg L^-1,Na₂SO₄ 5%,pH 5.5 and temperature 30.The optimal volume is 100 ml in a 250 ml conic flask.This strain can degrade 95% phenol in 3 days when Na₂SO₄ was 5% and phe nol was 1 000 mg L^-1.The osmoregulation mechanism of this strain was studied.It was found that the intracellular level of tre halose increased with the increase of salinity,indicating that Debaryomyces sp.can use trehalose as osmoprotectant in hyper saline environment.The physiological characteristics of the strain were also studied,yielding some basic parameters useful for biodegrading of high salt concentration phenol wastewater.

Abstract:Experiments in lab indicated that the persistence of Bt insecticidal crystal protein (BICP) in soil and its effects on soil phosphatase activity were different between forms of BICP introduced into the soil.In the first treatment of the experiments,Bt was applied directly into the soil with results showing that BICP concentration in the soil increased gradually along with the incubation time and reached the peak value on D15 and then decreased.On D30 the concentration of BICP was almost the same as at the initial stage after the application.In the second treatment,Bt cotton tissues were used.The results showed that BICP concentration in soil decreased along with the incubation time.There was a rapid decline at the initial stage of the in cubations and the trend leveled off in the middle and late stages.On D56 of the incubation,BICP in soil was at 44.7% (ZK) and 56.1% (GK) of the initial values.In the third treatment,Bt cotton was planted in pots.Analysis of the soil showed that during the whole growth period,the concentration of BICP in the rhizospherice soil of Bt cotton was significantly higher than that of non Bt cotton.The treatment with Bt and Bt cotton tissues showed a trend of the soil phosphatase activity being higher than that in CK.But the phosphatase activity in the rizhospherice soil of Bt cotton was lower than that of non-Bt-cotton.Whatever forms of BICP were introduced into soil,the difference in soil phosphatase activity between treatments different in BICP concen tration treatment was significant.

Abstract:Investigations were carried out on horizontal and vertical distributions of soil gamasida in Picea and Abies forest,Larix gmelini forest,Alnus hirsuta forest,Betula platyphylla forest and broad-leaved and Pinus koraiensis mixed forest in the Xiaoxing'anling.The results indicate that Gamasellus montanus and Zercon xiaoxinganlingensis are distributed extensively in all habitats,and only in one type of habitat has a huge variety of gamasida species and the more the species exist in the habitat,the more obvious the extensively habitats is.According to Jaccard's similarity index analysis,the soil gamasida communities in Larix gmelini forest are the most similar to those in Alnus hirsuta forest,and the soil gamasida communities in Picea and Abies forest and Alnus hirsuta forest are the least similar to those in Alnus hirsuta forest and Betula platyphylla forest.The vertical distribution of soil gamasida generally shows surface enrichment,but it is different in each habitat.The higher the organic matters and total N in soil,the more the species of soil gamasida and the bigger their populations are.Most of soil gamasida tend to live in slightly acid habitats.

Abstract:Investigations were carried out on structure of salt gland and secretion characteristics of salt excretion from xero-halophyte Reaumuria soongorica and their relationship with salt distribution in the soil and the plant under arid and saline-alkali conditions.Na⁺ and SO₄^2- were the prominentions in the soil solutions,as well as in the plant tissues,followed by K⁺,Mg²⁺,and Cl^-,and the content of Ca²⁺ was the lowest.The internal salt contents,which were lower in the branches than in the leaves,were diurnally approximately constant.Na⁺,K⁺,Ca²⁺,Mg²⁺,Cl^-,and SO₄^2- could be secreted from its multi-cellular salt gland.The excretion rate was higher during the day than during the night and in the morning than in the afternoon,as was affected by temperature.Among the excretedions,Cl^- was the highest,followed by Na⁺ and SO₄^2-,and then K⁺,Ca²⁺ and Mg²⁺ the lowest.In comparison with the salt content in the leaves,Cl^- excreted from the salt grand was much higher over otherions.The ratio of Na/K in the secreted fluid were higher than that in the plant tissues.The above-described findings showed that the salt content in the plant was related to the salt content in the soil as well as the plant s characteristics of absorbing the elements;and the excretion of the salt grand was affected by temperature and irradiation and its high selectivity of ions.Such high selectivity for ions in absorption and excretion of Reaumuria soongorica is of high significance to the plant in adapting to the saline alkaline habitat.

Abstract:A four year field trial was carried out to determine the effect of application rate and form of K fertilizer on mulberry (Morus atropurpurea Roxb.) during 1999~2002 and a silk worm (Bombyx mori Linne) experiment to determine their consequential effect on silk cocoon yield and quality in summer of 2001.The results showed that in comparison with the leaf yield in Treatment Zero K,it increased by 23.9%,31.7% and 36.0% in Treatments K₂O 150,300 and 375 kg hm^-2 a^-1,respec tively,and that when the K application rates were the same,the two different forms of K fertilizer,K₂SO₄ and KCl,were quite similar to each other in effect on mulberry leaf yield.Crop response to K application seemed to increase with the time of the experiment and the post-effect of the application was also quite significant.Leaf nutrient determination showed N,K and S contents increased whereas Ca,Mg and Zn decreased with K application in the form of K₂SO₄,but no change for P content.The results showed that mulberry nutrient uptake increased greatly with K application,which led to better fertilizer utilization efficiency.As a result,the essential amino acids,total amino acid,protein,sugar and fat contents in the leaves increased with the K application rate.KCl also improved leaf quality but not so much as K₂SO₄ did.The silk cocoon quality test showed that silk worms fed with mulberry leaves from K treatments produced cocoons better in quality in terms of silk worm weight,cocoon weight,reelable cocoon rate,filament length,reelability and silk neatness.The higher the K application rate,the better the cocoon quality.And the effect of K₂SO₄ was more significant than that of KCl in this aspect when the K application rates were the same.

Abstract:A novel rice cultivation in aerobic soil in China has made it possible to intercrop the rice with legumes,which is one of the ways in sustainable production of rice.Pot experiments using 15 N isotope dilution method were carried out to study biological nitrogen fixation by groundnut and nitrogen transfer from groundnut to associated rice in aerobic soil at three N fertilizer application rates (15 kg hm^-2,75 kg hm^-2 and 150 kg hm^-2).Decomposition experiment of groundnut root labeled by 15 N foliar enrichment was also conducted at the same time to investigate the contributed nitrogen transfer from the decomposition of groundnut root to the associated rice.The results showed that at 15 kg hm^-2 and 75 kg hm^-2 N fertilizer application rates the dry weights of rice in intercropping condition were increased by 23.5% and 12.2% respectively compared with rice in monocropped condition.The total N accumulated in rice in intercropped was 135 and 144 mg plant^-1 at the N fertilizer application of 15 and 75 kg hm^-2 respect ively while they were 117 and 131 mg plant^-1 in monocroopped treatment respectively,showing that inter-cropping could significantly increase the dry weight and nitrogen content of rice,especially at low N application rate.The dry weight and nitrogen content of groundnut intercropped were not significantly different from that monocropped.At three N application rates,biological N fixation(BNF) rates by groundnut were 72.8%,56.5%,35.4% and 76.1%,53.3%,50.7% in mono-and intercropped condition respectively,indicating that the BNF by groundnut was significantly increased in intercropped condition and the BNF decreased with increasing N fert ilizer application rates.The N transferred rates and the amount of N trans-ferred were 12.2%,9.2%,6.2% and 16.3 mg plant^-1,13.0 mg plant^-1 and 10.4 mg plant^-1,respectively,with N fertilizer application rates of 15 kg hm^-2,75 kg hm^-2 and 150 kg hm^-2,indicated N transfer decreased with increasing N fertilizer application rates in rice/groundnut intercropping system.Using 15 N foliar labeled method,it was shown that the decomposition of groundnut root had a significant contribution to N transfer happened in groundnut associated with rice system.

Abstract:Regression isogram was employed to analyze temporal and spatial variation of soil moisture in cornfield mulched with straw and plastic film.The results showed that soil moisture in CK,Treatment SM (straw mulching),and Treatment PM (plastic film mulching) all followed the same trend of going down first and then rising up' with the time in the experimental period of 250 d;and then the trend turned downward again with the depth in profile to 150 cm.The decreasing in soil moisture with the time was parallel to the rising intensity of soil water consumption by corn.The lowest soil water zone occurred much earlier and much closer to the soil surface in CK than in Treatments SM and PM.Treatment PM dropped the most rapidly in soil water content and its lowest soil water zone had a trend of extending downward,whereas Treatment SM had the highest soil moisture content in the lowest soil water zone.The soil moisture of cornfield in CK and the 2 treatments began to increase continuously from the late growth period of corn to the end of the experiment (Jan.4,2003),much more in the upper layer than in the middle layer or bottom layer.It can thus be inferred that regression isogram can be used to reflect the trend and pattern of the temporal and spatial variation of soil moisture and has the characteristics of being simple and time-saving,explicit in graph,vast in information,and easy to analyze.Therefore,it can be used as a good tool for collation and analysis of soil moisture data.

Abstract:Due to the inhibited nitrification in the bulk soil of lowland rice field,researches on nitrogen nutrition of rice mainly focus more on ammonium than nitrate.In fact,the roots of rice can excrete O₂ to surrounding soil and this can convert NH₄⁺ to NO₃^- in the process of nitrification at root surface or in rhizosphere.Rice roots are actually always exposed in a mixture of NH₄⁺ and NO₃^- although the predominant species of mineral nitrogen in the soil collected from the lowland rice field is ammonium.This paper reviews the nitrification process in the rhizosphere of rice,and discussed the stimulation of nitrate on the absorption and utilization of ammonium by rice from both the uptake rate and root growth.The pathways involved in the local and sys temic responses to NO₃^- supply were also discussed.In terms of the local stimulation by NO₃^- on the lateral roots,the nutritional function and signal function of NO₃^- were clarified in details from its effect on carbohydrate,amino acid,phytohormones.Finally some issues on nitrate nutrition of rice are proposed to be studied further.

Abstract:长江三峡地区地面覆盖和土地利用类型及其面积的确定,是通过TM或MSS等卫星数字图像计算机分类实现的^[1～5]。它与传统使用的航空像片目视判读获得的结果相比,二者有多大的一致性或差异呢?当然这是在认为二者都有可信性的前提下来作比较的。对说明这个问题的有利条件是,在我们用数字卫星图像计算机分类确定长江三峡地区地面覆盖与土地利用的同时,中国水电部遥感中心也用航片目视判读法确定了长江三峡地区的地面覆盖与土地利用类型。只需将二者加以比较就可以了。但二者比较有不少的困难。首先,二者的研究和工作范围不同。

Abstract:土地利用/地表覆盖变化及其对环境的影响是目前全球变化研究中的一个热点。我国经济的快速发展引起的工业化和城镇化过程影响了土地利用的变化,特别是东部经济发达区农业用地被迅速侵占,这反过来影响了社会经济的可持续发展。利用遥感(包括可见光谱、高光谱和微波)可以提取土地利用/地表覆盖的变化信息,1999年起国家针对大中城市的土地利用年际变化启动了遥感动态监测项目。通常的方法是对多时相遥感数据分别进行分类,然后通过对分类结果进行比较,提取变化信息^[1～2],Nelson将这种方法称为分类后比较法^[3]。

Abstract:余江县位于江西省东北部武夷山区向鄱阳湖平原的过渡地段,东经116°41'～117°09',北纬28°04'～28°37',是我国中亚热带低丘岗地红壤的典型地区。据1989年土地资源普查结果,全县国土总面积927km²。境内水、光、热资源丰富,多年均温176℃,年均日照18524h,年降雨量17660mm,无霜期262d,有利于农作物生长。生产经济条件较好,1998年全县耕地面积20400hm²,人均耕地0062hm²;人均纯收入达2116元;耕地农机总动力294kWhm^-2耕地化肥施用量675.83kg hm^-2。为促进生态农业的发展,特对该县农业50 年的发展态势进行分析评价。

Abstract:海水灌溉农业是国际范围内新兴的热点研究领域。在我国海水灌溉农业研究还刚刚起步。为探索海水灌溉对滨海盐土发育演变的影响,作者从2000年起,在半干旱的山东莱州地区进行海水灌溉下滨海盐土水盐运动的田间试验研究,以率定不同气候带土壤发育安全的海水灌溉指标与参数,探索可行的土壤水盐调控技术体系,并根据田间试验结果安排原状土柱室内模拟试验,以深入探讨其作用机制。本文仅就田间盐分运动试验结果进行讨论。

Abstract:CO₂是土壤空气的重要组成,土壤空气CO₂浓度一般高于大气几倍到数十倍,甚至上百倍^[1]。土壤空气中CO₂主要来源于土壤呼吸,其浓度主要决定于生物因素(植物根系、土壤微生物活性等)和环境因素(土壤温度、含水量等)^[2～4]。土壤空气CO₂浓度可以反映和影响土壤向大气释放CO₂的通量^[4,5],同时对植物根系生长发育、土壤微生物活动和各种养料物质转化也有很大影响^[1]。研究了解土壤空气CO₂浓度剖面分布、季节动态及其影响因素,有助于人们认识土壤中CO₂产生、累积、输运以及向大气排放的生物和物理过程,制定和实施合理的农作措施以改善作物生长环境和减少土壤向大气排放的CO₂。国外已在森林、草地和农田土壤上开展了较长时间的土壤空气CO₂浓度观测研究^[4~7],但我国的研究和报道很少^[8,9]。本文通过土壤剖面不同深度CO₂浓度的定位观测,初步揭示了土剖面CO₂浓度的分布特征、季节动态及其受水热条件的影响。

Abstract:核辐射危害人类健康,是造成多种全身性疾病,如造血功能障碍,白血病、神经系统疾病和恶性肿瘤 等的重要诱因^[1]。与所有的食品相比较,烟叶中的 天然²³⁸U、²³²Th、²²⁶Ra 和¹³⁷Cs 等放射性核素含量较高 而引起对人体的危害^[2,3]。因此,有效降低烟叶中的放射性核素含量对于保护吸烟者的身体健康至关重要。