On the Loess Plateau of China, facing the vulnerable environment, local people have to try their best to guarantee the security of food, and at the same time, to control the most serious soil erosion in the world. The...On the Loess Plateau of China, facing the vulnerable environment, local people have to try their best to guarantee the security of food, and at the same time, to control the most serious soil erosion in the world. The paper introduces two typical models of ecological agriculture: ecological agriculture with commodity and agri- culture with soil and water conservation. According to the local natural condition, the model of eco-agriculture with commodity could be characterized by the structure of “agriculture-byproduct”, “agriculture-fruit” or “agri- culture-forestry-husbandry”. The development of agriculture with soil and water conservation has decreased the soil erosion rate from 12,184 ton/km2 in 1980 to 458.4 ton/km2 in 1999, while the farmers’ income has increasingly risen. Analyses on the two models’ benefits both in terms of ecological and agricultural economy show that there is a great possibility to construct or restore good eco-environment with comprehensive control in the hilly-gully area of north Shannxi. Further more, the paper points out the potential problems of foodstuff production and stockbreeding development in forming ecological agriculture and eco-environmental restoration.展开更多
The rural settlements accounted for a great proportion of overall building land in China,but it still expanded in recent years along with urbanization and gradually decreasing rural population.To explore the reason fo...The rural settlements accounted for a great proportion of overall building land in China,but it still expanded in recent years along with urbanization and gradually decreasing rural population.To explore the reason for this phenomenon,an analy- sis has been made based on the investigation in a traditional agri- cultural region.This study found that socioeconomic factors,in- cluding the scale of families and its quantity,the improvement of rural public infrastructure,the change of population and the pres- sure of arable land,have effects on the expansion.The view on land tenure which has shaped in farmers minds in the long haul makes them dispose their houses cautiously,and this was the main cause of the fact that one household own more than one plot.In addition,the limitations of rural land institution are unconducive to inspiriting the transfer of farmers' building land and redevel- opment of the idle housing land.展开更多
We report a unique shell margin that differed from the usual shell structure of Pinctada fucata.We observed empty organic envelopes in the prismatic layer and the formation of the nacreous layer in the shell margin.Al...We report a unique shell margin that differed from the usual shell structure of Pinctada fucata.We observed empty organic envelopes in the prismatic layer and the formation of the nacreous layer in the shell margin.All the characteristics of the growing margin indicated that the shell was growing rapidly.To explain this anomaly,we propose the concept of "jumping development".During jumping development,the center of growth in the bivalve shell jumps forward over a short time interval when the position of the mantle changes.Jumping development explains the unusual structure of the anomalous shell and the development of annual growth lines in typical shells.Annual growth lines are the result of a discontinuity in the shell microstructure induced by jumping development.展开更多
文摘On the Loess Plateau of China, facing the vulnerable environment, local people have to try their best to guarantee the security of food, and at the same time, to control the most serious soil erosion in the world. The paper introduces two typical models of ecological agriculture: ecological agriculture with commodity and agri- culture with soil and water conservation. According to the local natural condition, the model of eco-agriculture with commodity could be characterized by the structure of “agriculture-byproduct”, “agriculture-fruit” or “agri- culture-forestry-husbandry”. The development of agriculture with soil and water conservation has decreased the soil erosion rate from 12,184 ton/km2 in 1980 to 458.4 ton/km2 in 1999, while the farmers’ income has increasingly risen. Analyses on the two models’ benefits both in terms of ecological and agricultural economy show that there is a great possibility to construct or restore good eco-environment with comprehensive control in the hilly-gully area of north Shannxi. Further more, the paper points out the potential problems of foodstuff production and stockbreeding development in forming ecological agriculture and eco-environmental restoration.
文摘The rural settlements accounted for a great proportion of overall building land in China,but it still expanded in recent years along with urbanization and gradually decreasing rural population.To explore the reason for this phenomenon,an analy- sis has been made based on the investigation in a traditional agri- cultural region.This study found that socioeconomic factors,in- cluding the scale of families and its quantity,the improvement of rural public infrastructure,the change of population and the pres- sure of arable land,have effects on the expansion.The view on land tenure which has shaped in farmers minds in the long haul makes them dispose their houses cautiously,and this was the main cause of the fact that one household own more than one plot.In addition,the limitations of rural land institution are unconducive to inspiriting the transfer of farmers' building land and redevel- opment of the idle housing land.
基金supported by the National Natural Science Foundation of China (Grant Nos. U0831001 and 40876068)the National High Technology Research and Development Program of China (Grant Nos. 2010CB126405 and 2010AA09Z405)
文摘We report a unique shell margin that differed from the usual shell structure of Pinctada fucata.We observed empty organic envelopes in the prismatic layer and the formation of the nacreous layer in the shell margin.All the characteristics of the growing margin indicated that the shell was growing rapidly.To explain this anomaly,we propose the concept of "jumping development".During jumping development,the center of growth in the bivalve shell jumps forward over a short time interval when the position of the mantle changes.Jumping development explains the unusual structure of the anomalous shell and the development of annual growth lines in typical shells.Annual growth lines are the result of a discontinuity in the shell microstructure induced by jumping development.
