The Miyun Reservoir is the most important water source for Beijing Municipality, the capital of China with a population of more than 12 million. In recent decades, the inflow to the reservoir has shown a decreasing trend, which has seriously threatened water use in Beijing. In order to analyze the influents of land use and cover change (LUCC) upon inflow to Miyun Reservoir, terrain and land use information from remote sensing were utilized with a revised evapotranspiration estimation formula; a water loss model under conditions of human impacts was introduced; and a distributed monthly water balance model was established and applied to the Chaobai River Basin controlled by the Miyun Reservoir. The model simulation suggested that not only the impact of land cover change on evapotranspiration, but also the extra water loss caused by human activities, such as the water and soil conservation development projects should be considered. Although these development projects were of great benefit to human and ecological protection, they could reallocate water resources in time and space, and in a sense thereby influence the stream flow. 相似文献
This paper describes how the CERES-Wheat simulation model can be used to estimate tillage effects on soil water regimes of a silty clay soil in Foggia, Southern Italy. The four tillage treatments compared are traditional mouldboard ploughing, ripper subsoiling, surface disc-harrowing and minimum tillage with rotary hoeing under continuous durum wheat cropping. For each tillage treatment the CERES-Wheat model was used to calculate the water balance for several layers in the root zone.
The water balance routine of the model estimates the water content within saturation and the lower limit at any time. Inputs required by the model are some basic information about the site, weather, genetic parameters and management practices as well as some soil properties, such as albedo, bulk density, organic matter and N contents. The model was calibrated by estimating the genetic parameters for the minimum tillage treatment in the season 1984–1985. The same set of parameters was used for the subsequent validation procedure. Statistical tests proved that the match between measured and simulated soil water content values was quite good. The simulation results also showed some differences among different tillage treatments. The model predicted the lowest plant extractable soil water values and a different water content distribution along the soil profile of the ripper subsoiling in comparison with the other tillage treatments. The soil water content was lower until 20–40 cm depth and higher at 40–60 cm depth in the ripper treatment as compared with the others. In deeper layers differences became non-significant. This might be due to the cracks produced by the ripper through which rainfall infiltrated in deep layers. 相似文献
According to the biphasic model of growth response to salinity, growth is first reduced by a decrease in the soil osmotic potential (Ψo), i.e., growth reduction is an effect of salt outside rather than inside the plant, and genotypes differing in salt resistance respond identically in this first phase. However, if genotypes differ in Na+ uptake as it has been described for the two maize cultivars Pioneer 3906 and Across 8023, this should result in differences in Na+ concentrations in the rhizosphere soil solution and thus in the concentration of salt outside the plant. It was the aim of the present investigation to test this hypothesis and to investigate the effect of such potential differences in soil Ψo caused by Na+ exclusion on plant water relations. Sodium exclusion at the root surface of intact plants growing in soil was investigated by sampling soil solution from the rhizosphere of two maize cultivars (Across 8023, Pioneer 3906). Plants were grown in a model system, consisting of a root compartment separated from the bulk soil compartment by a nylon net (30 μm mesh size), which enabled independent measurements of the change of soil solution composition and soil water content with increasing distance from the root surface (nylon net). Across 8023 accumulated higher amounts of sodium in the shoot compared to the excluder (Pioneer 3906). The lower Na+ uptake in the excluder was partly compensated by higher K+ uptake. Pioneer 3906 not only excluded sodium from the shoot but also restricted sodium uptake more efficiently from roots relative to Across 8023. This was reflected by higher Na+ concentrations in the rhizosphere soil solution of the excluder 34 days after planting (DAP). The difference in Na+ concentration in rhizosphere soil solution between cultivars was neither due to differences in transpiration and thus in mass flow, nor due to differences in actual soil water content. As the lower Na+ uptake of the excluder (Pioneer 3906) was only partly compensated by increased uptake of K+, soil Ψo in the rhizosphere of the excluder was more negative compared to Across 8023. However, no significant negative effect of decreased soil Ψo on plant water relations (transpiration rate, leaf Ψo, leaf water potential, leaf area) could be detected. This may be explained by the fact that significant differences in soil Ψo between the two cultivars occurred only towards the end of the experiment (27 DAP, 34 DAP). 相似文献
Abstract. Fertilizer and manure application rate and timing are often based on the optimal nitrogen rate and not on potassium (K) requirements. This can lead to excess or shortage of K depending on the crop and rotation. In grass‐dominated agricultural production, including many organic farming systems, K has become a critical element, especially in areas dominated by coarse‐textured or organic soils. In this paper we review K management in relation to long‐term sustainability of both the soil resource and the production of crops of high yield and quality. One question for the future is whether we can adopt management options that favour efficient use of K and secure a sustainable future for global K reserves. For example, is it possible to enhance the release rate of K from soil mineral sources so that we require less fertilizer K from K‐bearing salt deposits? A reduction in external K inputs requires improved on‐farm recycling of K in order to reduce losses. We also need a better understanding of soil processes and soil–plant interactions and decision‐support tools to predict the potential K release from mineral weathering. Certain areas dominated by young, clay‐rich soils can potentially supply enough K, whereas other areas with coarse sandy or organic soils have a very low weathering potential and would thus need external inputs of K. 相似文献
Coordinating distribution of water resources of a river across more than one administrative regions is a critic issue connected with rational resource development and environment conservation among different administrative bodies and finally with the resolving problems about water resources distribution among them . By the quantitative analysis and based on META-game theory, this paper has analyzed the conflicts over water distribution among several administrative bodies within the Heihe river basin, and established mathematic models to obtain reasonable recommendation that might benefit and be acceptable to each part in the conflicts in order to end the long time dispute over water distribution in these regions. 相似文献