Water is scarce in the North China Plain and the limited precipitation is not enough to satisfy the water requirement for wheat growth. In order to avoid reduction of output caused by scarcity of water, irrigation is necessary to supplement water. This paper discusses the relationship between the amount of irrigation and the yield of wheat. Statistical analysis of experimental data of irrigation indicates that the relationship between yield of wheat and irrigation presents a quadratic parabola in North China. We fit the model of wheat water production function by adopting least squares theory on the basis of field experimental data of wheat. Water production function is quadratic function and its math expression is Y=-0.0027ET 2+2.8647ET-127.91. Water productivity is divided into three different development stages according to the changing rule of water use efficiency and the relationship between yield and water consumption. Water consumtion being less than 217.66mm is identified as the first stage when yield rises with the rise of water consumption, and productivity rises gradually at this stage. Water consumption at the second stage rises from 217.66mm to 530.50mm and the yield still rises with the rise of water consumption, but the range of rise reduces. The productivity rises slowly.Water consumption at the third stage exceeds 530.50mm and the yield reduces with the rise of water consumption. Negative rise occurs and productivity declines. The analysis of wheat irrigation production function under typical irrigation system indicates that the best point of irrigation efficiency of wheat is not the highest point of utilization ratio of water or the highest point of yield. The best point of irrigation efficiency of wheat is decided by the principle that marginal revenue is equal to the marginal cost. When marginal benefit equals marginal cost, net income of irrigation of wheat is the biggest. The maximal net income is 4816.49 yuan/ha, and irrigation water is 265.00mm at this time. Compared with the irrigation of the maximal yield, it saves 17.85mm of water . Making rational use of wheat water irrigation production function and its regularity can realize the better unification of water-saving, high-yield and high-efficiency of wheat.
The pattern, process and their relationships are fundamental issues in geography. Patterns and processes in nature, such as ecosystem distribution, regional climatic changes, land use and land cover, and rainfall or runoff series, display complex behavior and often intertwine with scale problems. Many scale-dependent phenomena have been exemplified in scientific researches, and scale issues are found at the center of methodological discussions in both physical and human geography. However, some existed research works failed to make a distinction among the concepts of scale and scaling, to employ consistent scaling paradigm, and to adopt an objective criterion for assessing the scaling effects in geography. This paper attempts to calibrate those deviations and to present new branch subject of geography-Scaling Methodology of Geography. After introducing scaling approaches, upscaling and downscaling, in geography, we place a focus on the research objects, categories and contents of proposed subjects, and three basic principles, scientific principle, economic principle and operational principle, are proposed in scaling works. Finally, ten key issues are presented for establishing the scaling methodology of geography. The key questions are as follows: (1) how does spatial heterogeneity scale in scaling ? (2) how do ratio variables change with scale in scaling? (3) how do dominating processes change with scale in scaling? (4) how does property of processes change with scale in scaling? (5) how does sensitivity change with scale in scaling? (6) how does predictability change with scale in scaling? (7) what is sufficiency for simple aggregation and disaggregation in scaling? (8) how do disturbance factors change with scale in scaling? (9) can scaling transcend several scales and scale fields? (10) is noise factor changeable with scale in scaling?
This paper presents a new method to simulate the dynamics of multiple land uses based on the integration of neural networks,cellular automata and GIS. Recently, cellular automata (CA) have been increasingly used to simulate urban growth and land use dynamics. However, simulation of multiple land use changes using CA models is difficult because numerous spatial variables and parameters have to be utilized. Conventional CA models have problems in defining simulation parameter values, transition rules and model structures. In this paper, a three-layer neural network with multiple output neurons is designed to calculate conversion probabilities for competing multiple land uses. The neural-network-based CA model is directly developed in a GIS environment by using ARC/INFO GRID AML. The GIS provides both data and spatial analysis functions for constructing the neural network. Real data are conveniently retrieved from the GIS database for calibrating and testing the model. The GIS functions are also used for the neural network calculations. The neural network has multiple output neurons to generate conversion probabilities at each iteration. Land use conversion is decided by comparing the conversion probabilities. The model is carried out by iterative looping the neural network for simulating multiple land use changes. Complex global patterns can be generated from local interactions through the neural network. The simulation results are not deterministic because a stochastic variable is used and site attributes are dynamically updated at the end of each loop. The proposed method can overcome some of the shortcomings of the currently used CA models in simulating complex urban systems and multiple land use changes by significantly reducing the tedious work in defining parameter values, transition rules and model structures. The model has been successfully applied to the simulation of land use dynamics in the Pearl River Delta.
With the help of remote sensing data and GIS, by using the indices of the landscape pattern, such as fractal dimension, patch density, fragment index, landscape diversity index etc., this article presents the dynamic change of Kaifeng city from 1988 to 2002. The results show that: (1) There were a rapid increase in the patch number from 1988 to 2002 in the study area,the patch number increased from 28784 in 1988 to 32311 in 2002. The whole shape turned irregular and the fragment of the landscape degree became serious, from 1.1308 in 1988 to 1.1334 in 2002. (2)The construction area, water area, and green-land increased individually from 8049.97hm 2, 4756.86 hm 2, and 1076.31 hm 2 in 1988 to 11852.60 hm 2, 6486.21 hm 2 and 2125.52 hm 2 in 2002; the farmland (mainly the irrigable land), non-used land and orchard area decreased individually from 10937.97 hm 2, 2500.56 hm 2, and 1454.67 hm 2 in 1988 to 4206.42 hm 2, 1104.84 hm 2, and 623.83 hm 2 in 2002. (3) The center of high-density construction area was shifted to southwest, green-land to northeast and water area to southeast. (4)The high-density construction area changed rarely, but low-density construction area was mainly transformed to high-density construction area; farmland mainly to construction area and non-used land to farmland and green-land. (5)Urbanized index and landscape used degree increased a little from 20.08% to 29.57%, and the landscape used index increased a little from 293.0532 to 315.8277. (6)Human activity has important influence on the urban landscape, but the Yellow River has a great influence on the landscape pattern of Kaifeng city, because the study area is located near the Yellow River with an abnormal geographic background. Irrigation from the Yellow River made a lot of non-used land turn to farmland, and diverting water from the Yellow River made water area increase greatly.
Flood hazard is one of the most harmful disasters in the world for over 40% of the natural hazard damage are caused by flood hazard every year. With the developments of socio-economy, people come to realize that they should not only depend on engineering measures but also use non-structural measures such as flood forecasting, damage evaluation and flood regulation to reduce flood damage. At the same time, along with deepening and broadening of research content on flood control and multi-disciplinary infiltration, people pay increasingly more attention to the studies of multi-disciplinary integrated flood control measures. Meanwhile it is possible to apply computer simulation, remote sensing and GIS technologies to the research field of flood control as well as to the analysis of flood-inundated simulation by GIS on floodplain based on the research of flood prevention and reduction. In southeast China coastal areas there are many size medium or small rivers that flow into the sea separately. Because the flood regulation and storage capacities are low with short flow concentration duration, flood hazard is grave. Besides these basins are situated in the China's developed region, especially in recent years, with rapid growth of economy, enlargement of industrial and city scale, as well as expansion of population, flood losses have also drastically increased. So research on flood hazard prevention and reduction has become an urgency. As floods occur mainly on flood plain in this region, this paper, taking the lower reaches of the Fenghua river in Yongjiang basin of Southeast China as an example, discusses the application of the approaches and methods of remote sensing and GIS to flood-simulation in floodplain. It firstly explores the rainfall runoff characteristics in this basin and floodplain flood routing rules. Supported by remote sensing and GIS the rainfall runoff and two-dimension flood routing models are built, the parameters of models and coefficients of two-dimension numerical calculation models are determined with GIS. Meanwhile the evaluating model of flood submerged area and the damage assessment models are built supported by digital elevation models (DEM) as well as socioeconomic database. Finally a satisfactory calculating result of actual simulated verification is obtained by using remote sensing, telemetering and GIS information. The research indicates that geographic information system and remote sensing create favorable condition for flood-inundated simulation on floodplain. There will be great promise for the application of GIS to the studies of flood prevention and reduction. This research will also provide valuable experience for the flood preventioll and reduction decision-making studies of this region.
The spatial distribution of marine economy in China includes 11 provinces having littoral zones, islands and vast expanse of sea areas. China has taken marine resources development as an important content in the national development strategies and regarded marine economic development as a great action to revitalize the national economy since the 1990s. China has proposed the plan of forming several marine economically strong provinces by 2010,which can provide relevant conditions not only for building China into a well-to-do society, accommodating workforce, alleviating the employment problems but also for developing western regions and revitalizing old industrial base in Northeast so as to promote overall development of the national economy and quicken the pace of economic growth. In the research, some quantitiative methods and models for analysing regional space differentiations are used to analyse the spatial agglomeration and diffusion degree of marine industry and marine tertiary industrial structure of various provinces for the purpose of revealing the mechanisms and laws for the formation of the marine economy of every province. Countermeasures for building marine economically strong provinces in China are put forward.
By using the multi-stage nested Theil decomposition method and the wavelet analysis of the Theil index sequence, this paper studies the spatial and temporal scales of regional economic disparities in China from 1952 to 2000. The main conclusions are: (1) the regional economic disparities in China, including the disparities within-province, between-provinces, within-region (the eastern, central and western regions) and between-regions, have existed since 1952. (2) The first stage decomposition of Theil index shows that the dynamic trend of disparity in the eastern region is consistent with that of whole China. The disparity in the central and western regions remains small, and the evolution is rather slow. The disparity between the three regions has been continuously increasing. (3) The second stage decomposition of Theil index reveals that the within-province disparities is the most significant component of all in the overall regional inequalities, which is more significant than that of the between-province and between-region disparities components, constituting the important part of the overall regional inequalities. In addition, the influence of within-province disparities in the eastern region on the overall regional inequalities is more significant than that of in the other two regions, and, the influence in the western region is more significant than that of in the central region. (4) Based on the decomposition and approximation of Theil index sequence using wavelets by different time scales, we elicit a conclusion that the evolutionary process of regional economic disparity in China is not a simple inverted U-shaped pattern but a compound of several U-shaped patterns. The result tells us the evolutionary process of regional economic disparity in China does follow the inverted U-shaped patterns a time scale of 16 years. That is to say that the regional inequality tends to rise in the first stage of economic development, and falls slowly over the peak in the second stage of economic development. However, if we shorten the time scale to 8 or 4 years, then a link of several U shaped patterns will appear.
As a concept based on greenway development, heritage corridor, which combined recreation and tourism development with ecological restoration and cultural conservation, has come into being in the United States since the 1980s. With rapid development in the study of greenway network, plans of heritage greenway network were proposed for heritage conservation as part of ecological infrastructure in regional scale in recent years worldwide. As many cases have shown, suitability analysis is the key in greenway planning study. Some approaches of greenway suitability analysis given in the former cases were too complicated and too much data dependent to be applicable in the Chinese condition. With GIS (geographic information system) technology and MCR (minimum cumulative resistance) model being used, a new approach of heritage corridor suitability analysis is designed to analyse and identify the suitability of potential areas for heritage corridors. This approach is featured in the following aspects: 1) A heritage corridor is defined as a linear landscape element that combines the function of recreational activities, heritage protection and ecological processes. 2) In addition to the physical faccors of heritages, the process of recreational use is the major concern in the definition of the suitability of a heritage corridor. 3) Recreational activities associated with heritages are considered as a horizontal process going across the landscape. This process is taken as an active process which overcomes the cumulative landscape resistance affected by land uses and covers. The less accumulative resistance a user is going to experience across the landscape, the more suitable the landscape is designated as heritage corridors. 4) The suitability of a landscape for a heritage corridor is therefore represented through the relative accumulative resistance in the process that a user experiences across the landscape towards or between heritage sites. 5) The calculation of accumulative landscape resistance is based on the cost-distance from the sources (heritage sites) to any points in the landscape.Different land uses and covers contribute differently to the resistance, and their weights are based on the evaluation by experts and inquiry of the local people. A case study in a rapidly urbanizing region, Taizhou City of Zhejiang Province, is presented.
Urban housing spatial structure can be viewed as the substantial expression of urban development history. The housing spatial structure of Guangzhou city is typical in that it lies on the front of opening zone and, furthermore, it is one of the three largest cities in China. Basing on the housing data of Guangzhou's 5th Census, the paper employs factor and cluster methods to analyze 5 key factors taking from 40 variables of 77 sub-districts (F>70%). They are housing constructed years, housing sources, kitchen equipments, toilet equipments and housing floors. The results of the factor scores help to divide the houses in urban built-up area of Guangzhou city into four types with different features: Ⅰ) Pre-establishment Housing Area (in which houses constructed before the founding of P. R. China); Ⅱ) Government Welfare Housing Area (Ⅱa: in which houses constructed for public servant from the time of the founding of P. R. China to the Reform and Opening) and Enterprise Welfare Housing Area (Ⅱb: in which houses constructed for people serving public owned enterprises from the time of the founding of P. R. China to the Reform and Opening); Ⅲ) 1980s Housing Area (houses with relatively rough equipment constructed during the 1980s); Ⅳ) 1990s Housing Area, in which Commercial Houses (Ⅳa) and Privately Constructed Houses (Ⅳb) centralized. The results can be used to explain the formation mechanism of Guangzhou's housing spatial structure. 1) As a result of Guangzhou's development, housing spatial structure turns on concentric circles from inside to outside. The quality of houses in the former urban area (inside circles) is poorer than that in the outer because they are the origin of the city. Some underdeveloped villages were surrounded by built-up area with urban expansion, while some of them were developed apart from the urban. 2) City planning distorted the concentric circle structure. 3) City reconstruction changed the homogeneous situation of the former urban area. 4) Although the housing reform institute changed houses' tenure, their public-owned attribute has not been broken. 5) Outskirts of the city become the hot area of real estate development, which result in the highest ratio of commercial housing in the outside of the built-up area. As a conclusion, the paper deduces the structure mode of housing spatial structure in the large cities of China: The Pre-establishment Housing Area normally lies in the inner circle. The second circle is the Welfare Housing Area. The Commercial Housing Area mainly centralized in the 3rd circle, which surrounds those relatively underdeveloped villages originally far from urban built-up area and some special function area constructed in the culture and education areas in the 1980s. The broad suburban housing area and industrial area together formed the 4th circle.
The origin and development of cities of Northeast China have a long history along with the formation of their peculiar civilization. But, before the 20th century, the level of urbanization in Northeast China lagged behind that in Central China for a long period of time due to some historical reasons. Modern cities of Northeast China originated in the early 20th century. Since the 20th century, Northeast China had gone through the immigrating and opening-up policies of the Qing government, later been invaded and occupied by the imperialist nations such as Russia and Japan for several decades. After the founding of the People's Republic of China, Northeast China has ever been the key region of China's industrialization. Today, due to economic growth and dramatic reform of economic structure, Northeast China's urban development has stepped into the rapid developing period, and been one of the regions with the highest standard of urbanization in China except for several municipalities directly under the central government, and made the great contribution to Chinese economy. Compared with other cities of China, cities of Northeast China have a special political and economic background, and clearly reflect the feature of synchronous developing and mutual promoting in the course of both urbanization and industrialization. In the paper, the authors identify the development mechanism of cities of Northeast China in the 20th century by revealing the relationships between the development of cities of Northeast China and their economic and social development. Simultaneously, the authors also analyze the historic role of the development of cities of Northeast China and some current major problems restricting their development in the course of renewing the old industrial base of Northeast China.
Study of a historic sediment in the south margin of the Tarim Basin, where is influenced by the Westerlie force evidently, shows that the mass susceptibility correlates positively with carbonate δ13C and strongly with the components of 56.37-224.4μm(especially with components of 70.96-200μm), but correlates negatively with the components of 0.56-35.57μm (especially with components of 17.83-31.70μm.). The correlation among three proxies bears profound significance of climate and environmental changes. When temperature declined in the extreme arid area, the relative humidity increased greatly, resulting in restrains of evaporation and prosperity of vegetation, protecting the land surface from erosion, and only relative finer debris can be carried to deposit in lake, carbonate δ13C declined. Less oxidation strength during a relatively cold period led to lower mass susceptibility. Conversely, when temperature increased, relative humidity declined sharply and resulted in increase in evaporation, the vegetation cover reduced so that the erosion intensity on the land surface increased, leading to coarser component being loaded and deposited in lake and rise in carbonate δ13C. Strengthened oxidation during a relatively warm period resulted in an increase in mass susceptibility. Based on the interpretation of the proxies and widely regional comparison, this paper identifies 8 characteristic climatic periods during the last 4.0ka. Most significantly, the similarity which can be observed between the fluctuation of climate proxies in this paper (especially the proxies of grain size ) and the Greenland GISP2 ice core δ18O record shows that climate change of the studied area may have global background, and on the other hand, it also incarnates evident regional characteristics.
The south coastal plain of Laizhou Bay is one of the typical salt-water intruded areas, whose occurrence and development have a close relation with the environmental evolution since late Pleistocene. This paper deals mainly with the systematic palynological, microfossil, granularity research and 14C dating on more than 29 samples from a column core with a depth of 29m of core A1 for the purpose of revealing the characteristics of paleoenvironmental evolution since late Pleistocene.According to the systematic study, 7 phases of the paleo-climate fluctuations and paleo-vegetation successions since late Pleistocene are identified. And 7 climate periods can be listed in the ascending order for the convenience of correlation: ①120-85kaBP, the analysis of spores,pollens and sediments shows that the then climate evolved from cold into warm and a little dry gradually;②85～76kaBP,obvious manifold pteridophyte and exiguous granularity of sediments showed a local humid environment with swamps and lakes developed in the lower reaches of the Weihe River; ③76～50kaBP,equal to the secondary Ice Age of Dali, characterized by grassland vegetation type with conifer in domination, and coarse sediments showed a barren terrestrial environment;④50～24kaBP,cold,wet-resistant hydrophyte such as bulrush lived on the coastal wetlands where the sea interacted with rivers, being a littoral environment; ⑤24～10kaBP,the worst period of Quaternary natural environment, the south coastal plain of Laizhou Bay was dry grassland and loess deposition environment; ⑥10～4kaBP,owing to the warm and wet weather, sea level was high and transgression occurred; the local marine-deposited stratum embodied exuberant hydrophyte and aquatic plants. The maximal transgression of Holocene ended at 4kaBP;⑦4～0kaBP,the modern sedimentary environment which inclines to dry. Three warm and wet periods and two cold periods can be found. Of which, the warm period of 85-76 kaBP is corresponded with the late Yangkou seawater transgression and there is no evidence of early Yangkou seawater transgression, the warm period of 50-24kaBP is corresponded with the Guangrao seawater transgression and the warm period of 10-4kaBP is corresponded with Kenli seawater transgression, the duration of the latter one is longer than Bohai and east of Laizhou Bay. The three periods formed the foundation for the salt-water intrusion in this area.
This study has chosen the shrubs of Caragana opulens Kom., a natural zonal vegetation in the semiarid area on northwest Loess Plateau, and compared its soil moisture from 09.9m to those of re-vegetated shrubs of C.korshinskii Kom., re-vegetated almond forest, natural grassland （protected） dominated by Stipa breviflora, intensively grazed grassland and continuous cropland. Soil moistures were measured at the depth over 3m with an interval of 0.2m beneath and with an interval of 0.3m. The purpose was to testify the hypothesis that the zonal natural shrub vegetation consumes less soil water than re-vegetated shrub and forest vegetations. The results show that the soil moisture of natural shrub of C.opulens Kom. was largely higher than those of re-vegetated shrub of C.Korshinskii Kom. and almond forest beneath 1m in soil profile, close to those of intensively grazed grassland and cropland,but slightly lower than cropland. The average soil moisture in 09.9m soil profiles of natural shrub of C.opulens, re-vegetated shrub of C.korshinskii, re-vegetated almond forest, natural grassland, intensively grazed grassland and cropland were 9.5%, 7.4%, 7.7%, 8.5%, 9.3% and 9.8%, respectively.and the average soil water moisture from 19.9m are 10.2%, 7.6%, 8.1%, 9.0%, 10.6% and 10.0% respectively. The soil moisture of natural shrub land of C.opulens was higher than the soil moisture of natural grassland between the soil layer of 04m, but beneath 4m, their soil moistures were essentially the same. All vegetation types have resulted in a continuous dry soil layer within which the soil moistures were hard or unavailable to vegetation. The thickness of hard or unavailable water moisture layers of natural shrub of C.opulens , re-vegetated shrub of C.korshinskii,re-vegetated almond forest, natural grassland, intensively grazed grassland and cropland were 2, 5.6, 4.2, 3.6, 3.3 and 1.0m, respectively. According to previous studies, the layer of unavailable soil moisture above 2m in soil profile is rechargeable by annual precipitation in the study area, but it hardly can be recharged by precipitation for unavailable soil water layers beneath 2m. From this initial study, we concluded that the natural shrubs of C.opulens consumes less soil water than re-vegetated shrubs of C.korshinskii, re-vegetated almond forest, underlining the importance of the role of zonal vegetation in the vegetation reconstruction in the study area.
On the basis of analyzing ecogeographical models and studying those methods being realized at the present time, a new research method integrated by ARC/INFO and VC++ is put forward, which can overcome those limitations existed in the previous methods and techniques. In the operational process of our methods , before the Holdridge life zone model and ecological diversity model are simulated, the original data are interpolated and become grid data. Based on the daily surface air temperature and precipitation data observed at 735 stations in China from 1960 to 2002, and through runing these models with our available methods and techniques, we obtained the serial maps of temporal and spatial distribution of Holdridge life zones and the value of Holdridge life zone diversity in China. After finishing all simulations, we carried out a series of analyses with these results. First, according to the serial maps of temporal and spatial distribution of Holdridge life zones, we found changes in spatial distribution of Holdridge life zones correspond well with the changes of the climatic factors and land cover. Second, through comparing and analyzing Holdridge life zone diversity, annual mean biotemperature and annual mean precipitation in our research period of time, some rules and phenomena are archived in China: 1) The fluctuated changing pattern occurs in the Holudridge life diversity, biotemperature and precipitation. 2) While the fluctuated directions of precipitation and biotemperature are the same, the fluctuated direction of the Holdridge life diversity accords with them. However, 3) while the fluctuated directions of precipitation and biotemperature are reversed,more intensive fluctuated changing pattern would occur in the Holdridge life zone diversity and the fluctuated intensity and scope would increase with the enlargement of the reversed ratio. Furthermore, through analysing the Holdridge life zone diversity, shape index of patches and patch connectivity of the Holdridge life zone in China during the 1960s, 1970s, 1980s and 1990s, we attained the analytical results that the Holdridge life zone diversity, the number of patches and the number of patch types present a decreasing trend at ratios of 0.0692%, 1.7293% and 1.3515% in every ten years, respectively. Whereas the shape index of patches and the patch connectivity present an increasing trend at ratio of 0.2526% and 3.7928% in every ten years. Finally, we discuss the relationship between life zone diversity and eco-environmental stability according to the above results.
The Ejin natural oasis landscape lies in the lower reaches of the Heihe river basin in the arid inland regions of northwestern China. With decreasing water resources from the upper reaches of the Heihe river basin, many serious ecological and environmental issues in the Ejin natural oasis have become more and more pressing in recent years. Using remote sensing techniques, GIS, and landscape pattern analysis software APACK, the landscape patterns changing characteristics, and the eco-environmental effects for Ejin natural oasis landscape are studied based on Landsat Thematic Mapper data in 1987 and Landsat Enhanced Thematic Mapper Plus data in 2001. The main results show that: 1) During the past 15 years, both the water area and main oasis area sharply decreased. The degree of oasis desertification process, at present, is more serious than before. 2) The most intense conversion among different landscape types was occurring in the transitional zone between oasis landscapes and desert landscapes. 3) As a result of the change of Ejin natural oasis landscape, the landscape patches shape complexity and its heterogeneity were obviously reduced. Moreover, the landscape texture became more and more coarser, the landscape diversity was decreasing and the landscape stability turned into unsteady. 4) Sharply decreasing surface water from the upper reaches of Heihe river basin is the vital factor for Ejin natural oasis landscape degradation in the past 15 years. The eco-environmental effects for Ejin natural oasis landscape induced by landscape change include the acceleration of groundwater mineralization degree, the degeneration of groundwater quality, the degradation of natural oasis vegetation, the decrease of species diversity, the increasing threats of sandstorms, the increasing quantity of ecological refugee and so on. In conclusion, the landscape condition of Ejin natural oasis landscape, today, is much worse than in the past years, with bad unsustainable developing trend.
The water and nitrogen applications are the two main factors that affect the nitrate leaching on farmland. The field experiment was conducted to analyze the nitrate leaching and yield under different nitrogen and water application rates in summer maize field. The result indicated that there was no distinct yield difference between the higher water treatment (with soil moisture controlled between 70%FC and 100%FC in 0～50cm) and the lower one (between 55%FC and 85%FC), while the nitrogen rate had evident effect on yield with the yield reaching the maximum at about 200 kg N ha-1,and significant effect on nitrate leaching. Higher water application could accelerate the leaching of nitrate evidently. Under higher water level, the soil nitrate concentration peaks appeared at deep layers more easily than those under lower water level as an indication of nitrogen leaching, meanwhile the nitrate concentrations of soil water at depth of 200 cm were all higher than the national drinking water limit (10 mg NO-3-N L-1). Comparatively, under lower water treatment the nitrate leaching depths are all less than those under higher water treatment, but NO-3-N L-1 concentrations of soil solution under level of 200 and 300 kg N ha -1at the depth of 200 cm still exceeded the national drinking water limit (10 mg NO-3-N L-1). When NO-3-N in 100cm soil profile came to about 450 kg N ha-1 the soil NO-3-N concentration at soil depth of 200cm would rapidly rise to 130 mg L-1 from 40 mg L-1 ,at the same time the nitrogen rate just reached 230kg N ha-1,which mean that the nitrogen rate should be under about 230kg N ha-1.
Intake excess of arsenic (As) can damage human health and may cause diseases. Routes of As intake are respiratory for dust and fumes, and oral for As in water, soil, beverage, and food. Consumption of vegetables from contaminated soils may be harmful to consumers health. In 1999, a serious As poisoning incident due to As contamination happened, more than 300 people were hospitalized in Dengjiatang, Chenzhou City, Hunan Province. Some 50 ha of paddy fields were contaminated and the farmlands were wasted for 4 years, though the source of As contamination had been cut off by local authority in time. Only a few vegetable fields can still be cultivated on the fields. There are few reports on revegetation or potential risk study of wasted As-contaminated farmland.We investigated the As concentration of plants and soils on the fields with different levels of As contaminations. Processes of natural revegetation of waste paddy and health risk of cosumed vegetables cultivated were investigated in the As-contaminated erea. It was found that revegetation in As-contaminated soil was significantly affected by the As-contaminated level. The amount of plant species was small and the weed biomass was the greatest in soil contaminated with low arsenic. The weeds grown on soil contaminated with medium level of As had the highest amount of plant species. The amount of plant species was the least and biomass of weed was the lowest in soil contaminated with high level of As. The species diversity was reduced by the present of Paspalum sp., a dominated weed, in the wasted fields. As concentrations in the edible parts of most vegetables were higher than the maximal permissible limit of As in food. Intake of As from consumed vegetables was 4.1 μg/kg body wt. per day in spring and summer, and 2.9 μg/kg body wt. per day in autumn and winter, respectively, both of which exceeded the level (2.1 μg/kg body wt. per day) set by World Health Organization (WHO).
