浅谈几种不同土壤类别的改良利用方法

土壤是农业的基础,也是各类作物生长的基础,不同的土壤类别,其理化性状存在差异,主要是受地质气候、地貌等特征的影响,故产生不同的肥效,进而影响作物产量的提高。人们通过耕种施肥,使不同的低产土壤变成高产土壤。作者经过多年的积累和掌握,就黑垆土、黄绵土、红粘土、淀土、潮土提出了一些改良利用的措施。

Precipitates identification in R_2PdSi_3(R= Pr,Tb and Gd) single crystal growth

Floating zone method with optical radiation heating was applied to growing a class of R2PdSi3（R=Pr,Tb and Gd） single crystals due to its containerless melting and high stability of the floating zone.One serious problem during the single crystal growth,precipitates of secondary phases,was discussed from the following four parts：precipitates from the raw materials and preparation process,precipitates formed during the growing process,precipitates in the melts and precipitates in the grown crystals.Annealing treatment and composition shift can effectively reduce the precipitates which are not formed during the crystallization but precipitated on post-solidification cooling from the as-grown crystal matrix because of the retrograde solubility of Si.

Crystal growth of Gd_2PdSi_3 intermetallic compound

Gd2PdSi3 single crystals were grown by a vertical floating zone method with radiation heating at a zone traveling rate of 3 mm/h. The compound exhibited congruent melting behavior at a liquidus temperature of about 1700 ＆#176;C. The slightly Pd-depleted composition of the crystal, with respect to the nominal Gd2PdSi3 stoichiometry, led to gradual accumulation of Pd in the traveling zone and to a decreasing operating temperature during the growth process. Thin platelet-like precipitates of a GdSi phase were detected in the stoichiometric feed rod growth crystal matrix which can be reduced by annealing treatment. Feed rod composition shift crystal growth was proved to be a better way of getting high quality of Gd2PdSi3 single crystal.

Effect of Y on age hardening response and mechanical properties of Mg-xY-1.5LPC-0.4Zr alloys

Ageing hardening,microstructure and mechanical properties of Mg-xY-1.5LPC-0.4Zr（x=0,2,4,6）alloys（LPC represents La-based rare earth metal）were investigated.It was found that the age hardening was enhanced,the grains became finer and the tensile strength was improved with the increase of Y content in Mg-Y-1.5LPC-0.4Zr alloy.The results show that the formed precipitates responsible for age hardening change from fine hexagonal-shaped equilibrium Mg12RE phase to metastableβ′phase with orthorhombic-bc crystal structure when Y is added into Mg-1.5LPC-0.4Zr alloy,and the volume fraction of precipitate phases also increases.The cubic-shapedβ-Mg24Y5 precipitate phases were also observed at grain boundaries in Mg-6Y-1.5LPC-0.4Zr alloy. The distribution of prismatic shapedβ′phases and cubic shapedβ-Mg24Y5 precipitate phases in Mg matrix may account for the remarkable enhancement of tensile strength of Mg-Y-LPC-Zr alloy.The Mg-6Y-1.5LPC-0.4Zr alloy exhibits maximum tensile strength at peak-aged hardness,and the values are 250 MPa at room temperature and 210 MPa at 250°C.

Effect of Ryegrasses on Soil Runoff and Sediment Control

Living plants and plant roots can reduce runoff and soil erosion. Using a rain simulator, a series of soil erosion experiments were conducted to study the influence of living roots and canopies of ryegrasses （Lolium perenne L.） during the growing season on sediment yields and runoff of a silt loam soil. The results indicated that during the growing season, decrements in runoff and sediment yields increased with time. Sediment yields （τ^2 = 0.999） and decrements in runoff （τ2 = 0.946） were closely related to the root surface area density. The contributions of roots and canopies of ryegrasses to the reductions in runoff and sediment yields were different. Canopies usually contributed more to the runoff decrement than the roots, whereas roots contributed up to 96% of the decrease in sediment yields in the late stage of the growing season.

Free Oxide Distribution in Poorly and Well Drained Soils Developed on Calcareous Alluvial Deposits

A study on the distribution of free iron and manganese oxides was conducted in soils developed on calcareous alluvial deposits under subhumid climatic conditions, in Western Greece. Soil samples from two well drained soils and from two poorly drained soils, classified as Alfisols, were collected and used in this study. After certification of soil homogeneity the acid ammonium oxalate and dithionite-citrate-bicarbonate methods were used to extract free iron and manganese oxides from the samples. Iron oxides extracted by the dithionite-citrate-bicarbonate method (Fed) were significantly higher than the iron oxides extracted by the ammonium oxalate method (Feo), indicating that a considerable fraction is present in crystalline forms,independent of drainage status. A confirmation of free iron oxides and fine clay was detected. The ratios Feo/Fed and (Fed-Feo)/total Fe (Fet) could not be used to distinguish the well drained soils from the poorly drained soils. Manganese movement in a soluble form is independent of the fine clay.

Engineering behavior and sedimentation behavior of lead contaminated soil-bentonite vertical cutoff wall backfills

Soil-bentonite （SB） vertical slurry cutoff wall is a useful treatment for urban industrial contaminated sites. Due to the clay-heavy metal interaction, significant changes would occur in the engineering behavior of SB cutoff walls. However, previous study is limited to kaolinitic soils or montmorillonitic soils along using solidum chloride and/or calcium chloride as target contaminant. In this work, a series of oedometer tests were conducted to investigate the effects of lead （Pb） on the compressibility and the permeability of kaolin-bentonite （KB） mixtures, a simplified model of in-situ SB cutoff wall backfills. In addition, sedimentation tests were conducted to interpret the mechanism controlling the change of compressibility and permeability from the perspective of soil fabric. The Pb-contaminated KB mixtures for oedometer tests and sedimentation tests were prepared with bentonite contents of 0, 5%, 10%, and 15% by dry mass, and they were mixed with pre-determined volume of lead nitrate solution based on designed Pb concentration and solid-to-solution ratio. The Pb concentration was controlled as 0, 0.1, 0.5, 1.0, 5.0, 10, and 50 mg/g with a solid-to-solution ratio of approximate 0.5. The prepared KB mixtures with bentonite contents of 0, 5%, and 10% were chosen for the sedimentation tests. They were freeze-dried and mixed with DDI with a solid-to-solution ratio of 10 g/100 mL. The results indicate that pH, compressibility, and permeability of KB mixture changed considerably with respect to Pb concentration. It is concluded that the fabric of KB mixture, depending on the particle-particle interaction subjected to different ranges of pH and Pb concentration, governs the sedimentation behavior and permeability. The results of liquid limit （WE） cannot be explained in terms of the sedimentation behavior since it is only ionic-dependent.

Comparison of Extraction Techniques with Different Solvents for DDT Analogues in Sediments

Four techniques, Soxhlet extraction (SOX), ultrasonic extraction (USE), fluidized-bed extraction (FBE) and acce-lerated solvent extraction (ASE) with different solvents (methanol, hexane/acetone and acetonitrile) were used for theextraction of DDT analogues in sediments. Results revealed that the four extraction techniques had high recoveries (>86.0%) with low standard deviations (< 12.0%) for most of DDT analogues, meaning that they could all successfully extractDDT analogues in sediments. Accelerated solvent extraction using methanol and hexane/acetone (1:1), fluidized-bedextraction using hexane/acetone (1:1) and the ultrasonic extraction using hexane/acetone (1:1) were comparable or betterthan Soxhlet extraction using hexane/acetone (1:1). Considering solvent- and time-consumption, level of automation,and environmental risk, accelerated solvent extraction with hexane/acetone (1:1) was better than the other extractiontechniques.

Non-Uniform Sediment Transport Downstream from Reservoir

The transport characters of non-uniform sediment before and after the reservoir operation are compared and analyzed. Field data from the Three Gorges Reservoir (TGR), Danjiangkou, and Sanmenxia reservoir indicate that the transport character of coarse particle is various in different reaches. Before the reservoir operation, the dramatic decrease of the hydraulic condition in some reaches is the main reason to cause the coarse particle deposited. After the reservoir operation, almost all grain sized sediment may be eroded, when the reach is eroded seriously. However, the transport character of the coarse particle will be consistent with what it was before, when the reach is not eroded seriously. The deposition amount will be less than its pre-dam value, and it will tend to decrease with the time going on. Erosion of fine particle results from its unsaturation. Longdistance erosion downstream from reservoir is caused by shortage of the supply from riverbed, especially the shortage of fine particle.

Impact of Sediment Supply on Spartina Salt Marshes

During the past century,natural and human modifications of environmental systems have greatly accelerated coastal salt marsh deterioration and shoreline retreat in many regions worldwide. Field investigation,profile analysis,geographical information analysis,and remote sensing were employed in combination to study the effect of sediment on Spartina alterniflora salt marshes of the coast in Jiangsu Province,East China. The results indicated that the propagation of Spartina alterniflora salt marshes was closely related to regional sediment conditions,especially the supply of fine-grained materials. Additionally,because of the dense and high grass in Spartina alterniflora salt marshes,wave energy and tidal currents were baffled and weaker than those of the adjacent,unvegetated mud flats. Fine sediment was hardly resuspended under the low energy conditions in the Spartina alterniflora salt marshes.

Study on the sedimentation capability of bauxite flotation concentrate

The sedimentation behaviors of bauxite flotation concentrates were investigated at different pH values and floceulant dosages. The effects of three types of flocculants （ cationic, anionic and non-ionic polyacrylamide floceulants） as well as the molecular weight of anionic flocculants on the sedimentation of concentrate were studied. It is shown from the experimental results that at the pH 7.0, best sedimentation capability is reached when anionic polyacrylamide flocculant （molecular weight 14 million） is added and the optimal dosage is 30 g/t.

Applications of ionic liquids in electrodeposition of rare earths

The electrodeposition and electrochemical behaviors of rare earths in different ionic liquids are summarized. It is demonstrated that most of the rare earths can be electrodeposited in ionic liquids except cerium. Anion of ionic liquids appears to play a significant role in determining the electrochemical windows, and then deciding whether the corresponding ionic liquids can be used for rare earths electrodeposition. The electrochemical behaviors of the reduction process in ionic liquids are similar to those in high-temperature molten salts. The reduction of RE(III) to RE(II) has different reversibility, but the reaction of rare earths to their zerovalent state is irreversible.

Separation of diaspore from bauxite by selective flocculation using hydrolyzed polyacrylamide

Selective flocculation is a new method to solve the problem of China's bauxite de-silication besides flotation and reverse flotation. The method of selective flocculation of bauxite using hydrolyzed polyacrylamide as flocculant was experimented and evaluated. The results of diaspore and kaolinite single mineral settling tests show that the difference between settlement yield of kaolinite(settling 15 min) and diaspore(settling 3 min) increases from 16% to 60% by adding flocculant at pH=7. Results of selective flocculation experiment of bauxite show that the higher concentrate grade(65.75) and Al-Si ratio(7.34) could be obtained with sodium carbonate as dispersant compared with sodium hexametaphosphate; under the action of flocculating agent, the concentrate grade and Al-Si ratio increase to 67.99 and 9.01. These results could meet the requirements of Bayer production, and the simpler process was expected to cost far less than traditional flotation method and a promising de-silication method of bauxite.

Screening of Degrading Bacteria for Phthalic Acid Esters Under Cadmium Stress and Its Application

In order to enrich the degrading microbial resources for phthalic acid esters(PAEs)under cadmium stress,a degrading bacterium B-7 for di(2-ethylhexyl)phthalate(DEHP)was screened from the strains stored in the laboratory by means of inorganic salt liquid medium containing DEHP and cadmium,and the characteristics of the strain were studied.Strain B-7 was Bacillus amyloliquefaciens,which had high biosafety and excellent degradability to DEHP.The optimum temperature for degradation was 25–40℃,and the optimum pH value was 6–8.Strain B-7 was cultured in inorganic salt medium(MSM)with an initial DEHP concentration of 400 mg/L and cadmium content of 10 mmol/L for 4 d,and its degradation rate of DEHP was up to 93.1%.In addition,the strain had a strong degradation ability to dimethyl phthalate(DMP),diethyl phthalate(DEP),and dibutyl phthalate(DBP).In soil contaminated by cadmium and DEHP,the synergic degradation of B-7 and indigenous microorganisms in soil significantly increased the degradation rate of DEHP,indicating that this strain had potential application value in the field of microbial remediation of soil contaminated by cadmium and PAEs.

Effect of Vegetation and Precipitation upon Runoff and Sediment Production on Slope Lands of the Loess Area in China

According to fixed-position data for 1992-2003 from 16 runoff plots of Caijiachuan watershed which lie in Jixian County, Shanxi Province, in the loess area, this paper studied the relationship between vegetation and runoff and sedimentproduction on slope lands. The results showed as follows: 1) Runoffand sediment production in Robinia pseudoacacia forestand Pinus tabulaeformis forest had a high correlation with precipitation amount and rainfall intensity, but the correlation decreased gradually with the increase of canopy density; 2) The secondary forest had better function of soil and water conservation than artificial R. pseudoacacia forest, and runoff and sedimentproduction in the former in an individual rain event was 65%-82% and 23%-92% lower than thosein the latter, respectively;3) The difference ofrunoff and sediment production in several land uses was very distinct. Runoff and sediment production in Ostryopsisdavidiana forest and the secondary forest were the least; runoff and sediment production in artificial R. pseudoacacia forest and P. tabulaeformis forest were 5-fold as much as those in O. davidiana forest. Besides, runoff and sediment production in mixed stand of apple trees and cropswere 16.14-fold and 2.96-fold higher than that in O. davidiana forest, respectively, but theamount decreased obviously after high-standard soil preparation for theformer;4) Based on gray correlation analysis of variousfactorsaffecting runoffand sedimentproduction on slope lands, it can be seen that stand canopy density and herb and litter biomass werethe most significant ones, whosegray correlation valuesall exceeded 0.6. Therefore, mixed forest with multi-layer stand structure and shrub forest should be developed in vegetation reconstruction of the loess area, which help to increase coverage and litter thicknessto cut down the runoffand sediment production dramatically on slope lands.

Nickel,Lead and Zinc Sorption in a Reclaimed Settling Pond Soil

The wastes used to amend soils sometimes have high concentrations of metals such as nickel(Ni), lead(Pb) and zinc(Zn). To determine the capacity of soils to retain these metals, the sorption capacities of different mine soils with and without reclamation treatments(tree vegetation and waste amendment) for Ni, Pb and Zn in individual and competitive situations were evaluated using the batch sorption technique. The untreated settling pond soil had low capacity for Ni, Pb and Zn retention. The site amended with wastes(sewage sludges and paper mill residues) increased the sorption capacity most, probably because of the higher concentrations of soil components with high retention capacity such as carbon and clay fraction. No significant competition was observed between metals in the competitive sorption experiment, indicating that the maximum of sorption was not achieved by adding 0.5 mmol L^(-1) of metal. We can conclude that, despite the possible additions of Ni, Pb and Zn from wastes to degraded soils, sewage sludges and paper mill residues have a high sorption capacity that would prevent the metals from being in a mobile form.

The precipitation “threshold value” on C_4/C_3 abundance of the Loess Plateau, China

In this paper, we report organic carbon isotopic characterizations from two loess sequences （JY and GL）, spanning the last 20 ka, from the northwest Chinese Loess Plateau （CLP）. The results indicate that the vegetation type is nearly pure C3 plants in the studied region during the Holocene. In contrast to other reported loess sequences in the central-southeast CLP, the relative abundance of the C4 plants decreases from southeast to northwest, with the vegetation types changing from pure C3 to a C4/C3 mixture should near 36°N in the Holocene. From the perspective of the modem temperature and precipitation distribution, the summer temperature has no obvious change at the same latitude, but there are differences in the summer precipi- tation, which exhibit an obvious increase from west to east. Further analysis indicated that the C4 plant abundance decreases with the decreasing summer season precipitation from the southeast to the northwest CLP during the Holocene. We suggest that with the absence of favorable precipitation condition, increasing temperature and decreasing atmospheric CO2 concentration are insufficient to drive an expansion of the C4 plants on the CLP in the Holocene. According to a Holocene precipitation recon- struction, a ＂threshold value＂ of summer precipitation existed, which mainly controlled the expansion of C4 plants. Compared with the modern δ13Csom and climate data on the CLP, both the Holocene and the present ＂threshold value＂ are near the 360-mm summer precipitation line, although the present precipitation line turned slightly southwestward. Our results provide new insights for further research on the C4/C3 variations with precipi- tation and the relationship to global C4/C3 change.