中国北方土壤风蚀问题研究的进展与趋势

土壤风蚀是中国北方土地退化的主要原因之一。国内土壤风蚀的研究工作相对比较薄弱，所取得的进展主要包括区域性的土壤风蚀分布地带性规律和不同时间尺度的准周期性规律，描述性的风蚀强度分级与危害评价，单因子风蚀过程的风洞实验，农田风蚀防治等方面。今后的研究趋势主要表现在土壤风蚀的物理本质、影响因素及发展动态的综合研究，土壤理化性质与表面性质对抗蚀性的影响及其与风蚀的反馈关系，土壤风蚀的基本过程及防治原理，土壤风蚀预报方程与数字模拟，土壤风蚀影响评价模型，土壤风蚀与土地利用以及全球变化的关系，各种观测与实验设备的研究等方面。

Effect of Plant Fiber-Polyacrylamide Blend on Retention and Evaporation Water at Arid and Semi-Arid Soils of Algeria

Soil and water conservation is essential for sustaining food production and for preserving the environment in arid and semi arid lands （ASALs） where conditions for agriculture and other land use systems are often harsh and unpredictable. The ASALs of Algeria are an important source of a variety of non wood forest products like Stipa tenacissima L. plant （esparto grass）. This research was conducted to determine the effects of different low concentration （〈 I%） polyacrylaJnide, Stipa tenacissima L. fiber （esparto grass fibers） and its mixtures with the polymer at water retention in arid and semi arid soil. All samples are characterized by infrared spectroscopy, X-ray Diffractometry, thermal analysis TG DSC and scanning electron micrographs （SEM）. The results showed that polymer blend in soil could improve better soil physical proprieties decreased evaporation and increase water retention in arid soils compared with application of any other blend at the same concentration. The use of Polyacrylamide-Cellulose blend appears to promise for reducing the labor cost of irrigation at arid and semi-arid soils, and offers safe and environmentally friendly inexpensive materials. The importance of Polyacrylamide-Cellulose blends to alleviate poor physical properties and retain water in these arid regions to sustain plant growth.

Maize （Zea mays L.） Growth and Grain Yield under Conventional and Site-Specific Nitrogen Management in a Dryland Farming System

Large amount of pre-plant nitrogen （N） fertilizer results in low N use efficiency due to poor synchrony between soil N supply and maize N demand, especially during N sensitive growth stages. The objectives of the study were to compare growth and yield of maize （Zea rnays L.） under conventional and site-specific N management in a dryland farming system. The study, which was designed as randomized complete block design was conducted over three site-years under continuous maize cropping system in the semi-arid regions of the Limpopo Province in South Africa. Treatments of the study consisted of three N management strategies on a maize field planted to drought resistant SNK 2147 hybrid maize cultivar. Treatments were： （i） no N application （NO）, （ii） site-specific N at variable rates ranging between 18 kg N/ha and 33 kg N/ha based on soil analysis results （N l） and （iii） conventional and uniform N application broadcasted during planting at 58 kg N/ha （N2）. Sufficiency index as indication of N deficiency was determined using CCM-200 on maize leaves based on leaf numbers during maize vegetative growth stages V6, V10 and Vl4, and thereafter N was applied only when needed. The highest maize grain yield of 5.2 Mg/ha for N 1 was significantly higher （P 〈 0.05） than 3.2 Mg/ha and 4.0 Mg/ha of N0 and N2 in site-year I, respectively. Maize grain yield of 2.2 Mg/ha （Nl） at site-year ll was significantly higher （P _〈 0.05） than 1.7 Mg/ha of the NO. The maize growth and yield under N2 and N1 was compared, N1 required between 43% and 69% lesser N fertilizer as compared to N2 over site-years, and resulted in higher maize height, number of leaves per plant, leaf length, and leaf area than that of conventional N management strategy. Therefore, site-specific N management strategy sustains and improves growth and yield of maize using minimal N fertilizer as compared to conventional approach in low fertility soils of semi-arid regions in dryland farming systems. In examining the results of this study, there was a consistent benefit of site-specific N management strategy on improving growth and yield of maize while saving fertilizer use in small-scale dryland maize farming system.

Relationship Between Microbial Community and Soil Properties During Natural Succession of Abandoned Agricultural Land

The changes of microbial biomass carbon (MBC) and nitrogen (MBN) and microbial community in the topsoil of the abandoned agricultural land on the semi-arid Loess Plateau in China during the natural succession were evaluated to understand the relationship between microbial community and soil properties. MBC and MBN were measured using fumigation extraction, and microbial community was analyzed by the method of fatty acid methyl ester (FAME). The contents of organic C, total N, MBC, MBN, total FAME, fungal FAME, bacterial FAME and Gram-negative bacterial FAME at the natural succession sites were higher than those of the agricultural land, but lower than those of the natural vegetation sites. The MBC, MBN and total FAME were closely correlated with organic C and total N. Furthermore, organic C and total N were found to be positively correlated with fungal FAME, bacterial FAME, fungal/bacterial and Gram-negative bacterial FAME. Natural succession would be useful for improving soil microbial properties and might be an important alternative for sustaining soil quality on the semi-arid Loess Plateau in China.

Climate Change and Water Resources： Strategies and Practices for Improved Water Management in Arid Countries

Assessment report of the Intergovernmental Panel on Climate Change （IPCC） highlighted the complex linkages between climate change and water. The likely warmer climate induced by the climate change is set to alter hydrological cycle and the shifting pattern of the rainfall would affect the spatial and temporal distribution of runoff, soil moisture, and surface and groundwater reserves. Therefore, there is an urgent need to assess the impacts of climate change on water and devise adaptation measures including management structures and processes by which one can deal with this challenge. The paper highlights with the global overview of climate change impacts on water in the arid region, supported and substantiated through scientific evidence drawn from IPCC reports and other relevant documents. This paper provides an overview of water resource management challenges including transboundary geopolitical concerns documented across the world and emphasizes the importance of an integrated framework for adaptive policy making. Further, it examines the viable water resource management options for various sectors and regions and showcases some of the international best practices in adaptation and mitigation. The paper also explains the complementary role of traditional knowledge in coping with climate change risks and uncertainties and the need for a balanced view in designing adaptation and mitigation strategies.

Challenges of Implementing Participatory Irrigation Management for Food Security in Semi-arid Areas of Tanzania

Participatory irrigation management （PIM） is theoretically assumed to reduce poverty significantly, but its practical experience and challenges are yet researched and documented in Tanzania. The study aimed at assessing challenges observed during implementation of PIM approach for food security in semi-arid areas of Tanzania. Data were collected through questionnaire, participatory rapid appraisal （PRA） tools, key informants interview, Focus Group Discussion （FGD）, observation and literature review. Data collected from questionnaire were analyzed using SPSS. Data fi＇om other methods were analyzed using content analysis. The study revealed that PIM approach has contribution in improving food security at household level due to involvement of communities in water management activities and decision making, which enhanced availability of irrigation water and increased crop production. However, there were challenges observed during implementation of the approach, including the minimum participation of beneficiaries in decision making during planning and designing stages, which means that inadequate devolution of power among scheme owners, inadequate and lack of transparency on income expenditure in water utilization associations （WUAs）, water conflict among WUAs members, conflict between farmers and livestock keepers and conflict between WUAs and village government leaders regarding training opportunities and status. The rules and regulation of WUAs were not legally recognized by the national courts and few farmers who planted trees around water sources. However, it was realized that some of the mentioned challenges were rectified by farmers themselves and facilitated by government officials. The study recommends that the identified challenges need to be rectified for farmers to realize more on the importance of PIM approach as it was realized in other Asian countries.

Hydrological Services by Mountain Ecosystems in Qilian Mountain of China: A Review

Hydrological service is a hot issue in the current researches of ecosystem service, particularly in the upper reaches of mountain rivers in dry land areas, where the Qilian Mountain is a representative one. The Qilian Mountain, where forest, shrubland and grassland consist of its main ecosystems, can provide fresh water and many other ecosystem services, through a series of eco-hydrological process such as precipitation interception, soil water storage, and fresh water provision. Thus, monitoring water regulation and assessing the hydrological service of the Qilian Mountain are meaningful and helpful for the healthy development of the lower reaches of arid and semi-arid areas. In recent 10 years, hydrological services have been widely researched in terms of scale and landscape pattern, including water conservation, hydrological responses to afforestation and their ecological effects. This study, after analyzing lots of current models and applications of geographical information system（GIS） in hydrological services, gave a scientific and reasonable evaluation of mountain ecosystem in eco-hydrological services, by employing the combination of international forefronts and contentious issues into the Qilian Mountain. Assessments of hydrological services at regional or larger scales are limited compared with studies within watershed scale in the Qilian Mountain. In our evaluation results of forest ecosystems, it is concluded that long-term observation and dynamic monitoring of different types of ecosystem are indispensable, and the hydrological services and the potential variation in water supplement on regional and large scales should be central issues in the future research.v

Drought Tolerant Criterion of Wheat Genotypes Using Carbon Isotopes Discrimination Technique

Drought tolerant analysis using carbon isotopes discrimination could be useful tool to decide a genotype with high adaptation to drought. A pot culture experiment was conducted in glass house at the IAEA （International Atomic Energy Agency） laboratories, Seibersdorf, Austria to analyze drought tolerant of wheat genotype using carbon isotopes discrimination technique. Four wheat genotypes viz., LU-26s, Bhittai, Roshan, Taifu, were tested. There were two treatments： Control （normal irrigation） and Drought （@ 30% field capacity of the control treatment）. Drought treatment was imposed after two weeks of germination. The experiment was continued up to 10 weeks after germination and was terminated at flowering stage. The data were recorded in terms of plant height, number of tillers, shoot dry weight and carbon isotopic ratio （δ）. Results showed that genotype LU-26s was found to have best performance under drought condition, with minimum decrease in the growth parameters i.e., plant height, number of tillers and shoot dry weight. High CID （carbon isotopes discrimination） values were also observed in genotype LU-26s, showing close positive correlation between SDW （shoot dry weight） and CID. It is therefore concluded that carbon isotopes discrimination can be an important criterion for the selection of wheat genotypes for drought prone areas.

18～20世纪初党河下游河道变迁研究

党河是流经敦煌的一条重要河流,现为一条独立的水系。翻检清至民国一些文献资料,发现党河在清初还有余流分两支分别注入哈拉湖和疏勒河。约在道光年间河流西北一支发生断流,民国初年两支均断流,党河从此成为一条独立河流。文章试从自然和人类活动两个方面分析其变迁的原因,认为党河地区的屯田灌溉是导致党河断流的主因。

The effects of giant cloud condensation nuclei on the structure of precipitation in hailstorm clouds

The Regional Atmospheric Modeling System (RAMS) has been used to investigate the effects of varied giant cloud condensation nuclei (GCCN) concentrations on precipitation characteristics of the spring hailstorms in a semi-arid region. The simulation result shows that this variation has significant effects on the storm microphysical processes as well as on the surface precipitation. The coverage of hail and hail mixing ratio maxima in cloud increases with greater GCCN concentrations. The accumulation zone structure benefits the growth of hail particles. Higher GCCN concentrations lead to more supercooled rain water and cloud water available for freezing. This simulation also shows that increasing GCCN concentrations may produce more rainfall on the surface but less hail precipitation, and the total accumulated precipitation increases while the ice phase precipitation decreases. This effect is stronger in polluted air than in clean air. The surface flow field changes with different GCCN concentrations. The identification index of spring hailstorm is different from that of summer hailstorm with a different aerosol background.