The agricultural land resources of China are relatively limited because of its large population.Therefore,balancing the land use for industrialization,urbanization,and food security is a big challenge.In recent years,...The agricultural land resources of China are relatively limited because of its large population.Therefore,balancing the land use for industrialization,urbanization,and food security is a big challenge.In recent years,rural hollowing in China has resulted in numerous of abandoned rural houses,and the areas with abandoned houses need to be restored into agricultural land with effective land consolidation techniques.This study used the method of benefit-cost analysis and the data collected through field surveys conducted in Yucheng City in the northwest of Shandong Province in March 2009,to examine how hollow villages (HVs) to be created and how to solve the problem.The qualitative and quantitative analyses indicate following results.1) The situation of HVs is becoming increasingly severe under rapid industrialization and urbanization in Yucheng City.2) Poor infrastructure in rural areas and incomplete urbanization are the main factors that have led to the rural hollowing in many major rural regions of China.3) In order to resolve the problem caused by HVs and increase agricultural land,reconstructing rural communities in the countryside is necessary.4) A new mechanism in the provision of compensation funds by developed regions to the villages in less-developed regions must be established.展开更多
Roughness length and zero-plane displacement over three typical surfaces were calculated iteratively by least-square method, which are Yucheng Experimental Station for agriculture surfaces, Qianyanzhou Experimental St...Roughness length and zero-plane displacement over three typical surfaces were calculated iteratively by least-square method, which are Yucheng Experimental Station for agriculture surfaces, Qianyanzhou Experimental Station for complex and undulant surfaces, and Changbai Mountains Experimental Station for forest surfaces. On the basis of roughness length dynamic, the effects of roughness length dynamic on fluxes were analyzed with SEBS model. The results indicate that, aerodynamic roughness length changes with vegetation conditions (such as vegetation height, LAI), wind speed, friction velocity and some other factors. In Yucheng and Changbai Mountains Experimental Station, aerodynamic roughness length over the fetch of flux tower changes with vegetation height and LAI obviously, that is, with the increase of LAI, roughness length increases to the peak value firstly, and then decreases. In Qianyanzhou Experimental Station, LAI changes slightly, so the relationship between roughness length and LAI is not obvious. The aerodynamic roughness length of Yucheng and Changbai Mountains Experimental Station changes slightly with wind direction, while aerodynamic roughness length of Qianyanzhou Experimental Station changes obviously with wind direction. The reason for that is the terrain in Yucheng and Changbai Mountains Experimental Station is relatively flat, while in Qianyanzhou Experimental Station the terrain is very undulant and heterogeneous. With the increase of wind speed, aerodynamic roughness length of Yucheng Experimental Station changes slightly, while it decreases obviously in Qianyanzhou Experimental Station and Changbai Mountains Experimental Station. Roughness length dynamic takes great effects on fluxes calculation, and the effects are analyzed by SEBS model. By comparing 1 day averaged roughness length in Yucheng Experimental Station and 5 day averaged roughness length of Qianyanzhou and Changbai Mountains Experimental Station with roughness length parameter chosen by the model, the effects of roughness le展开更多
Rural off-farm employment,rapid loss of agricultural land,and advanced technology popularization had led agricultural production in Chinese typical rural areas come at a critical transformation and upgrade stage.Based...Rural off-farm employment,rapid loss of agricultural land,and advanced technology popularization had led agricultural production in Chinese typical rural areas come at a critical transformation and upgrade stage.Based on sample survey data gathered from 401 households in Yucheng City,Shandong Province,this paper focuses on the characteristics and mechanism of agricultural transformation in typical rural areas of the eastern China.It was found that 74.3% of households surveyed kept at least one member engaging in off-farm employment,and 57.1% looked forward to expanding the operational scale of arable land,while just 13.7% had actually transferred their agricultural land.Since growing off-farm employment does not result in the collapse of traditional subsistence agriculture,therefore,agricultural production in Yucheng City is at an incomplete transformation phase from traditional small-holder farming to modern scale economy.It is caused by both macro environments and family characteristics,while urban-rural dual structure,imperfect rural development policy and agricultural technology popularization make peasant economy strengthen upon maintenance,and small-holder farming becomes peasant's natural response owing to pluriactivity,local off-farm employment,reverse elimination,etc.In order to achieve smooth agricultural transformation of typical rural areas in the eastern China,it needs to promote professional differentiation among peasants,under clear policies adopted by central government.Providing comprehensive services for agricultural production and improving production skills and knowledge of farmers who are still living in the countryside will effectively stimulate the process of agricultural transformation.展开更多
Using data on leaf area density and wind profiles above and within canopies of wheat,rice,soybean and corn,the center-of-pressure method (CPM),originally proposed by Thom (1971),is first validated in the field.A physi...Using data on leaf area density and wind profiles above and within canopies of wheat,rice,soybean and corn,the center-of-pressure method (CPM),originally proposed by Thom (1971),is first validated in the field.A physically-based model for directly calculating zero-displacement height (d) is derived.The comparison between the friction velocity (u_*) estimated with CPM and that with eddy correlation technique shows that CPM not only works well in the field,but also produces more steady and accurate estimates of aerodynamic parameters (which are hardly affected by atmospheric thermal stability),than those with the widely-used log-profile fitting method in diabatic atmosphere. The results presented in this paper also demonstrate that the ratios of d,z_0 to crop height h usually vary with canopy ar- chitecture,atmospheric stratification and turbulent exchange intensity,and are not just constants as commonly assumed or used.d/h raises with an increase of relative height of the maximum foliage layer and wind extinction coefficient within the canopy.Only for crops with short stem and moderate foliage density,can the relations d= 0.64h,z_0=0.08h keep stable.In addition,for long stem crops or sparse canopies,the fairly large shear stress at the soil surface and the va- riation of the exponent in the relationship between drag coefficient and wind speed undoubtedly influence the accuracy of CPM to a certain extent.展开更多
基金Under the auspices of Knowledge Innovation Programs of Chinese Academy of Sciences (No.KZCX2-EW-304)National Natural Science Foundation of China (No.40635029,40871257)
文摘The agricultural land resources of China are relatively limited because of its large population.Therefore,balancing the land use for industrialization,urbanization,and food security is a big challenge.In recent years,rural hollowing in China has resulted in numerous of abandoned rural houses,and the areas with abandoned houses need to be restored into agricultural land with effective land consolidation techniques.This study used the method of benefit-cost analysis and the data collected through field surveys conducted in Yucheng City in the northwest of Shandong Province in March 2009,to examine how hollow villages (HVs) to be created and how to solve the problem.The qualitative and quantitative analyses indicate following results.1) The situation of HVs is becoming increasingly severe under rapid industrialization and urbanization in Yucheng City.2) Poor infrastructure in rural areas and incomplete urbanization are the main factors that have led to the rural hollowing in many major rural regions of China.3) In order to resolve the problem caused by HVs and increase agricultural land,reconstructing rural communities in the countryside is necessary.4) A new mechanism in the provision of compensation funds by developed regions to the villages in less-developed regions must be established.
基金This work was supported the Key Project of the NSFC (Grant No. 40471099) the National Basic Research Project (Grant No.G2002CB412501) the Knowledge Innovation Project of Institute of Geo-graphic Sciences and Natural Resources Research, CAS (Grant No. KZCX1-SW-01-01A).
文摘Roughness length and zero-plane displacement over three typical surfaces were calculated iteratively by least-square method, which are Yucheng Experimental Station for agriculture surfaces, Qianyanzhou Experimental Station for complex and undulant surfaces, and Changbai Mountains Experimental Station for forest surfaces. On the basis of roughness length dynamic, the effects of roughness length dynamic on fluxes were analyzed with SEBS model. The results indicate that, aerodynamic roughness length changes with vegetation conditions (such as vegetation height, LAI), wind speed, friction velocity and some other factors. In Yucheng and Changbai Mountains Experimental Station, aerodynamic roughness length over the fetch of flux tower changes with vegetation height and LAI obviously, that is, with the increase of LAI, roughness length increases to the peak value firstly, and then decreases. In Qianyanzhou Experimental Station, LAI changes slightly, so the relationship between roughness length and LAI is not obvious. The aerodynamic roughness length of Yucheng and Changbai Mountains Experimental Station changes slightly with wind direction, while aerodynamic roughness length of Qianyanzhou Experimental Station changes obviously with wind direction. The reason for that is the terrain in Yucheng and Changbai Mountains Experimental Station is relatively flat, while in Qianyanzhou Experimental Station the terrain is very undulant and heterogeneous. With the increase of wind speed, aerodynamic roughness length of Yucheng Experimental Station changes slightly, while it decreases obviously in Qianyanzhou Experimental Station and Changbai Mountains Experimental Station. Roughness length dynamic takes great effects on fluxes calculation, and the effects are analyzed by SEBS model. By comparing 1 day averaged roughness length in Yucheng Experimental Station and 5 day averaged roughness length of Qianyanzhou and Changbai Mountains Experimental Station with roughness length parameter chosen by the model, the effects of roughness le
基金Under the auspices of National Natural Science Foundation of China (No 40635029, 40771014)National Key Technologies R&D Program of China (No 2006BAB15B05)
文摘Rural off-farm employment,rapid loss of agricultural land,and advanced technology popularization had led agricultural production in Chinese typical rural areas come at a critical transformation and upgrade stage.Based on sample survey data gathered from 401 households in Yucheng City,Shandong Province,this paper focuses on the characteristics and mechanism of agricultural transformation in typical rural areas of the eastern China.It was found that 74.3% of households surveyed kept at least one member engaging in off-farm employment,and 57.1% looked forward to expanding the operational scale of arable land,while just 13.7% had actually transferred their agricultural land.Since growing off-farm employment does not result in the collapse of traditional subsistence agriculture,therefore,agricultural production in Yucheng City is at an incomplete transformation phase from traditional small-holder farming to modern scale economy.It is caused by both macro environments and family characteristics,while urban-rural dual structure,imperfect rural development policy and agricultural technology popularization make peasant economy strengthen upon maintenance,and small-holder farming becomes peasant's natural response owing to pluriactivity,local off-farm employment,reverse elimination,etc.In order to achieve smooth agricultural transformation of typical rural areas in the eastern China,it needs to promote professional differentiation among peasants,under clear policies adopted by central government.Providing comprehensive services for agricultural production and improving production skills and knowledge of farmers who are still living in the countryside will effectively stimulate the process of agricultural transformation.
文摘Using data on leaf area density and wind profiles above and within canopies of wheat,rice,soybean and corn,the center-of-pressure method (CPM),originally proposed by Thom (1971),is first validated in the field.A physically-based model for directly calculating zero-displacement height (d) is derived.The comparison between the friction velocity (u_*) estimated with CPM and that with eddy correlation technique shows that CPM not only works well in the field,but also produces more steady and accurate estimates of aerodynamic parameters (which are hardly affected by atmospheric thermal stability),than those with the widely-used log-profile fitting method in diabatic atmosphere. The results presented in this paper also demonstrate that the ratios of d,z_0 to crop height h usually vary with canopy ar- chitecture,atmospheric stratification and turbulent exchange intensity,and are not just constants as commonly assumed or used.d/h raises with an increase of relative height of the maximum foliage layer and wind extinction coefficient within the canopy.Only for crops with short stem and moderate foliage density,can the relations d= 0.64h,z_0=0.08h keep stable.In addition,for long stem crops or sparse canopies,the fairly large shear stress at the soil surface and the va- riation of the exponent in the relationship between drag coefficient and wind speed undoubtedly influence the accuracy of CPM to a certain extent.
