顶推机换填法整修既有线路基

顶推式换土机设备用于既有线路基填料的更换是国外一种有别于传统施工工艺的新的路基整修改造方法 ,最大特点是路基改造不影响邻线行车 ,本文从设备的结构、功能。

SPATIAL AND TEMPORAL DYNAMICS OF SOIL ORGANIC CARBON IN RESERVED DESERTIFICATION AREA——A Case Study in Yulin City, Shaanxi Province, China

Soil organic carbon (SOC) was considered to be a key index in evaluation of soil degradation and soil C sequestration. To discuss the spatial-temporal dynamics of SOC in arable layer in reversed desertification area, a case study was conducted in Yulin City, Shaanxi Province, China. Data of SOC were based on general soil survey in 1982 and repeated soil sampling in 2003. Soil organic carbon content (SOCC) was determined by K2Cr3O7-FeSO4 titration method, and soil organic carbon density (SOCD) was calculated by arithmetic average and area weighted average method, respectively. On average, SOCC and SOCD of the arable layer in the study area from 1982 to 2003 had increased 0.51g/kg and 0.16kg/m2, respectively. Considering main soil types, the widest distributed Arid-Sandic Entisols had lowest values and increments of SOCC and SOCD during the study period; while the second widest Los-Orthic Entisols had higher values and increments of SOCC and SOCD, compared to the mean values of the whole region. The results indicated that reversed desertification process was due to the modification of land use and management practices, such as natural vegetation recovery, planting grass, turning arable land to grassland, and soil and water conservation etc., which can improve SOCC and SOCD and thus enhance soil C sequestration.

Release of Soil Nonexchangeable K by Organic Acids

The amounts of soil nonexchangeable K extracted with 0.01 mL/ L oxalic acid and citric acid solutions and that with boiling 1 mL/ L HNO3 for ten minutes were remarkably significantly correlated with each other, and the amount extracted with the oxalic acid solution was higher than that with the citric acid solution. The soil nonexchangeable K release was comprised of two first-order kinetic processes. The faster one was ascribed to the interlayer K in outer sphere, while the slower one to that in inner sphere. The rate constants of the soil nonexchageable K were significantly correlated with the amounts of nonexchangeable K extracted with boiling ImL/ L HNO3 for ten minutes. Study on the fitness of different kinetic equations indicated that the first-order, parabolic diffusion and zero-order equations could all describe the release of soil nonexchangeable K. well, but Elovich equation was not suitable to describe it.

Changes of Soil Water, Organic Matter, and Exchangeable Cations Along a Forest Successional Gradient in Southern China

Information on the distribution patterns of soil water content （SWC）, soil organic matter （SOM）, and soil exchangeable cations （SEC） is important for managing forest ecosystems in a sustainable manner. This study investigated how SWC, SOM, and SEC were influenced in forests along a successional gradient, including a regional climax （monsoon evergreen broad-leaved forest, or MEBF）, a transitional forest （coniferous and broad-leaved mixed forest, or MF）, and a pioneer forest （coniferous Masson pine （Pinus rnassoniana） forest, or MPF） of the Dinghushan Biosphere Reserve in the subtropical region of southern China. SWC, SOM, and SEC excluding Ca^2＋ were found to increase in the soil during forest succession, being highest in the top soil layer （0 to 15 cm depth） except for Na^＋. The differences between soil layers were largest in MF. This finding also suggested that the nutrients were enriched in the topsoil when they became increasingly scarce in the soil. There were no significant differences （P = 0.05） among SWC, SOM, and SEC. A linear, positive correlation was found between SWC and SOM. The correlation between SOM and cation exchange capacity （CEC） was statistically significant, which agreed with the theory that the most important factor determining SEC is SOM. The ratio of K^＋ to Na^＋ in the topsoil was about a half of that in the plants of each forest. MF had the lowest exchangeable Ca^2＋ concentration among the three forests and Ca^2＋：K^＋ in MPF was two times higher than that in MF. Understanding the changes of SWC, SOM, and CEC during forest succession would be of great help in protecting all three forests in southern China.

Chemical Fractionation and Sorption of Phosphorus in Greek Inceptisols

Phosphorus fractionation and sorption, both separately and jointly, were studied in two cultivated Inceptisols in Northern Greece. Hedley＇s extraction was used to separate soil phosphorus （P） into inorganic Pi （geochemical） and organic Po （biological） fractions. Direct extractable P by Olsen （Olsen-P）, by Mehlich llI （M3-P） and by ammonium oxalate （Pox） was also determined. Phosphorus sorption was carried out with 1：10 soil/solution ratio and sorption parameters were derived from the Langmuir model to the experimental data. Most of the total P occurred in inorganic P forms （74% of Pt）, while organic P comprised only 26% of the Pt. Among the various inorganic P forms relatively large amount of residual P （111 mg kg^-1） was observed, while occluded P in calcium phosphate minerals （d.HCI-Pi） and in Fe, Al-oxides （c.HCI-Pi） existed in equal amounts （83.1 and 83.7 mg kg^-1 respectively）. The phosphorus sorption parameters showed positive relationships with clay content, cation exchange capacity and the sum of exchangeable calcium plus magnesium. Overall, this study indicated that Ca and Mg compounds strongly influence the P chemistry in moderately weathered soils, with relatively high concentration of primary P minerals.

Effect of Distances from Different Trees Species on the Properties of Mollic Horizon

The study area is located in Duhok province-Kurdistan region-Northern Iraq and including two locations the first location is situated in Galbook village and the vegetation cover is trees of （Quercus aegilops L.）, the second location is situated in Koradeer village that covered with threes of Prunus dulcis （Mill.） Webb.. Disturbed surface soil samples at depth 0-30 cm were collected at four different distances （1, 5, 10 and 15 m） from the tree with randomized selection three trees in each study location. Soil organic matter decreases with increasing distances from tree in both locations under two different trees species, which is attributed to the effect of tree crown. Ordinarily, organic matter content in both locations correspond to the requirements of Mollisols. Statistical analysis of data showed significant differences in organic matter content between locations. Cation exchange capacity is high under tree crown and decreasing with distances from tree in both locations, as a result of decreasing organic matter and increasing calcium carbonate with distances. Commonly soil pH is slightly increased with increasing distances from tree because of increasing calcium carbonate with distances and decreasing organic matter content. Calcium was not uniform with distances and Mg decreasing with distances in both locations. The values of fine clay/coarse clay and fine clay/total clay of soil samples confirm development of the soils under study. Porosity percentage under tree crown is high and decreasing with distances. Soil bulk density was increased with distances in both locations, as a result of decreasing organic matter content with distances. This study aims to explain the effect of tree distances and species on the mollic horizon properties.

Process and Mechanism for the Development of Physical Crusts in Three Typical Chinese Soils

To compare the development of physical crusts in three typical cultivated soils of China, a black soil （Luvic Phaeozem）, a loess soil （Haplic Luvisol）, and a purple soil （Calcaric Regosol） were packed in splash plates with covered and uncovered treatments, and exposed to simulated rainfall. Meshes covered above the surfaces of half of soil samples to simulate the effects of crop residue on crusting. The results indicated a progressive breakdown of aggregates on the soil surface as rainfall continued. The bulk density and shear strength on the surface of the three soil types increased logarithmically as rainfall duration increased. During the first 30 min of simulated rainfall, the purple soil developed a 7-8 mm thick crust and the loess soil developed a 3-4 mm thick crust. The black soil developed a distinguishable, but still unstable, crust after 80 rain of simulated rainfall. Soil organic matter （SOM） content, the mean weight diameter （MWD） of soil aggregates, and soil clay content were negatively correlated with the rate of crust formation, whereas the percentage of aggregate dispersion （PAD）, the exchangeable sodium percentage （ESP）, and the silt and sand contents were positively correlated with crusting. Mechanical breakdown caused by raindrop impact was the primary mechanism of crust formation in the black soil with more stable aggregates （MWD 25.0 mm, PAD 3.1%） and higher SOM content （42.6 g kg-1）. Slaking and mechanical eluviation were the primary mechanisms of crust formation in the purple soil with low clay content （103 g kg-1）, cation exchange capacity （CEC, 228 mmol kg-1）, ESP （0.60%）, and SOM （17.2 g kg-1）. Mechanical breakdown and slaking were the most important in the loess soil with low CEC （80.6 mmol kg-1）, ESP （1.29%）, SOM （9.82 g kg-1）, and high PAD （71.7%） and MWD （4.6 mm）. Simulated residue cover reduced crust formation in black and loess soils, but increased crust formation in purple soil.

Sorption of Water-Extractable Organic Carbon in Various Clay Subsoils: Effects of Soil Properties

Clay-rich subsoils are added to sandy soils to improve crop yield and increase organic carbon （C） sequestration; however, little is known about the influence of clay subsoil properties on organic C sorption and desorption. Batch sorption experiments were conducted with nine clay subsoils with a range of properties. The clay subsoils were shaken for 16 h at 4 ℃with water-extractable organic C （WEOC, 1 224 g C L-1） from mature wheat residue at a soil to extract ratio of 1：10. After removal of the supernatant, the residual pellet was shaken with deionised water to determine organic C desorption. The WEOC sorption was positively correlated with smectite and illite contents, cation exchange capacity （CEC） and total organic C, but negatively correlated with kaolinite content. Desorption of WEOC expressed as a percentage of WEOC sorbed was negatively correlated with smectite and illite contents, CEC, total and exchangeable calcium （Ca） concentrations and clay content, but positively correlated with kaolinite content. The relative importance of these properties varied among soil types. The soils with a high WEOC sorption capacity had medium CEC and their dominant clay minerals were smectite and illite. In contrast, kaolinite was the dominant clay mineral in the soils with a low WEOC sorption capacity and low-to-medium CEC. However, most soils had properties which could increase WEOC sorption as well as those that could decrease WEOC sorption. The relative importance of properties increasing or decreasing WEOC sorption varied with soils. The soils with high desorption had a low total Ca concentration, low-to-medium CEC and low clay content, whereas the soils with low desorption were characterised by medium-to-high CEC and smectite and illite were the dominant clay minerals. We conclude that WEOC sorption and desorption depend not on a single property but rather a combination of several properties of the subsoils in this study.