运用红边参数估算叶片叶绿素含量

Soil samples collected from several sites along an altitudinal transect on the eastern slope of the Tibetan Plateau were analyzed for hexachlorobenzenes(HCHs) and dichlorodiphenyltrichloroethanes(DDTs).The results showed that HCHs and DDTs were found in the soil samples from the remote high altitude areas away from source regions,which confirmed the long-range atmospheric transport phenomenon of these organochlorine pesticides(OCPs) insecticides.The OCP concentrations in the soils had a significant negative correlation with altitude;they showed a trend to increase with decreasing altitude,but the increase was not continuous,being interrupted at some moderate-altitude sites on the transect.The distances from the source region,landforms,soil properties,and physical-chemical properties of OCPs were more important than total organic carbon content to the distribution of OCPs in soils disturbed by human activities.An analysis of the compositions of HCH isomers and DDTs revealed predominantly low ratios of α-HCH to γ-HCH,ranging from 0.06 to 4.79,which suggested current lindane inputs.On the other hand,low p,p-DDT/p,p-DDE and o,p-DDT/p,p-DDT ratios were observed,indicating mainly aged historical DDT residues in the study area.     

Interactive effects of wind speed,vegetation coverage and soil moisture in controlling wind erosion in a temperate desert steppe,Inner Mongolia of China

The rapid desertification of grasslands in Inner Mongolia of China poses a significant ecological threaten to northern China. The combined effects of anthropogenic disturbances(e.g., overgrazing) and biophysical processes(e.g., soil erosion) have led to vegetation degradation and the consequent acceleration of regional desertification. Thus, mitigating the accelerated wind erosion, a cause and effect of grassland desertification, is critical for the sustainable management of grasslands. Here, a combination of mobile wind tunnel experiments and wind erosion model was used to explore the effects of different levels of vegetation coverage, soil moisture and wind speed on wind erosion at different positions of a slope inside an enclosed desert steppe in the Xilamuren grassland of Inner Mongolia. The results indicated a significant spatial difference in wind erosion intensities depending on the vegetation coverage, with a strong decreasing trend from the top to the base of the slope. Increasing vegetation coverage resulted in a rapid decrease in wind erosion as explained by a power function correlation. Vegetation coverage was found to be a dominant control on wind erosion by increasing the surface roughness and by lowering the threshold wind velocity for erosion. The critical vegetation coverage required for effectively controlling wind erosion was found to be higher than 60%. Further, the wind erosion rates were negatively correlated with surface soil moisture and the mass flux in aeolian sand transport increased with increasing wind speed. We developed a mathematical model of wind erosion based on the results of an orthogonal array design. The results from the model simulation indicated that the standardized regression coefficients of the main effects of the three factors(vegetation coverage, soil moisture and wind speed) on the mass flux in aeolian sand transport were in the following order: wind speedvegetation coveragesoil moisture. These three factors had different levels of interactive effects on the mass flux in aeolian sand transport. Our results will improve the understanding of the interactive effects of wind speed, vegetation coverage and soil moisture in controlling wind erosion in desert steppes, and will be helpful for the design of desertification control programs in future.     

The influence of raindrop induced saltation on particle size distributions in sediment discharged by rain-impacted flow on planar surfaces

A mechanistic model was used to simulate the downstream movement of particles travelling in suspension, by raindrop induced saltation and flow driven saltation on planar surfaces ranging from 2 m to 30 m in length. Results were produced for two rainfall events, one of high intensity, the other of moderate intensity, and a mixture of particle sizes ranging from fine material to 0.9 mm sand. Initially, the composition of the sediment discharge was controlled by the composition of the soil matrix and the rate the raindrop driven transport systems were capable of transporting the particles from zones near the downstream boundary. As time progressed, material transported from upslope provided a degree of protection in these zones and controlled the composition of the sediment discharge. The protection provided reduced the discharge of fine material but had little effect of the composition of the discharge of the coarser material during a given rainfall event so that it remainder finer than that of the soil matrix. However, in the long term, the slow movement of the coarsest material into the zones controlling sediment discharge led to coarsening of the sediment discharge so that it tended to the composition of the soil matrix at the steady state. The time taken to reach that steady state may be considerable, and increases with plot length, so that many many storms may occur before the steady state condition is reached.     

Effects of Soil Moisture Depletion for One Month before Flowering on Dry Matter Production and Ecophysiological Characteristics of Wheat Plants in Wet Soil during Grain Filling

Abstract

The period from mid-March to April in the wheat-growing season in Japan corresponds to a wet period known as “Natanezuyu”. After this wet period, the weather remains rather dry until June. Fluctuations in soil moisture conditions during the growing season might be expected to affect the growth of wheat. Therefore, we compared the grain yield, dry matter production and ecophysiological characteristics of wheat grown with adequate moisture during the ripening stage after it had been grown under adequate (W-plot) or deficient (D-plot) soil moisture conditions for about one month before heading. The grain yield in the D-plot was higher by about 15 to 40% than that in the W-plot, with greater dry matter production. The larger dry weight in the D-plot resulted from a higher rate of crop growth before and after heading, which was due to a larger leaf area and higher net assimilation rate. During the ripening stage, leaf senescence of plants was delayed and the rate of photosynthesis fell more slowly in the D-plot than in the W-plot. Root systems developed better, resistance to water transport from root to leaves was lower, the exudation rate of roots was higher, and the cytokinin activity in xylem exudates from roots was higher in the D-plot. These characteristics of roots might have caused the significant difference in the growth and physiology of the aboveground parts of the plants. Our results indicate that encouragement of the development of the root systems, for example, by drainage during the wet period might be important for improving the grain yield of wheat in Japan.     

Transport and the rural economy: Institutions and institutional change in Ambeso Village,Indonesia

This paper is concerned with the interaction between transport improvements and the rural economy. An institutional approach, based primarily on the new institutionalism theory, was used as the theoretical basis for the analysis. Using the evidence from Ambeso Village of Tana Toraja District, Indonesia, the paper examines the way transport improvements have been introduced and provided opportunities for positive change as well as individual responses to these opportunities. The paper ends by emphasising the role of institutions in the interaction between transport and the rural economy and the need for transport policy and research to transcend its traditional boundaries and address the complexities of institutions and institutional change.     

车载GPS的几种通讯方式及比较

车载GPS利用GPS、计算机、现代通信以及自动化等现代高新技术来实现对车辆的实时监控和调度。其中,通讯手段的选择是车载GPS功能实现的关键技术。目前,常用的通讯方式有GSM/SMS、GPRS、CDMA。为此,将在介绍车载GPS的基础上,针对常用的通讯方式进行阐述和比较。     

Effect of Pesticides On Certain Soil Biological and Biochemical Indices of a Paddy Soil

A 21-day laboratory incubation experiment was conducted to investigate the impact of pesticides (Triazophos, Butaehlor and Jinggangmycin) on a paddy field soil health under controlled moisture (flooded soil) and temperature (25℃ ) conditions. The electron transport system (ETS)/dehydrogenase activity displayed a negative correlation with pesticides concentrations, and the activity was affected adversely as the concentration of the pesticides increased. The higher doses of pesticides,5 and 10 folds field rates, significantly inhibited ETS activity, while lower rates failed to produce any significant reducing effect against the control. The relative toxicity level of pesticides in decreasing the ETS activity was in the following order:Triazophos＞Jinggangmycin＞Butachlor, irrespective of their rates of application. The pesticides caused an improvement in the soil phenol content and it increased with increasing the concentration of agrochemicals. The pesticide incorporation did not produce any significant change in soil protein content. The response of biomass phospholipid content was nearly similar to ETS activity. The phospholipid content was decreased with the addition of pesticides in the given order of Triazophos＞Jinggangmycin＞Butachlor; and the toxicity was in the order: 10 FR (times of field rate)＞5 FR＞1.0 FR＞0.5 FR＞control.     

我国农用运输车的现状与前景浅析

就我国农用运输车的现状进行了分析并提出建议     

Analysis on Optimal Service Frequency of Public Transport Considered with Generalised Cost

The service frequency is an important factor which shows the supply and service level of public transportion. By considering the effect of occupancy rate on generalised cost firstly, the authors establish a new public transport model based on generalised cost. Then from the view of optimal pricing, this paper constructs two optimal service frequency models by the aim of maximizing social welfare and maximizing profit separately. The result shows that, without the effect of externalities, the two optimal service frequency is the same. Finally, this paper use some parameters of generalised cost, which coming from a city, to simulate this model, and the result shows it is feasible.