The greenhouse gas （GHG） footprint of an agricultural system is a measure of the climate change impact potential （CCIP） exerted by the formation of its product（s）, its accurate quantification is essential for de...The greenhouse gas （GHG） footprint of an agricultural system is a measure of the climate change impact potential （CCIP） exerted by the formation of its product（s）, its accurate quantification is essential for determining the green value added tax of agricultural products for food markets, which in turn may drastically change the current patterns of food consumption and production towards a product life cycle oriented economy. This paper reviews the literature regarding GHG footprints of crop cultivation systems.The review concludes that few studies have fully considered the categories/ items of net GHG emissions from an investigated crop cultivation system, and thus probably led to biases in footprint estimation. Most studies to date have even neglected changes in the soil organic carbon stocks of ecosystems with annual crops, while process-oriented biogeochemical models so far have seldom been involved in GHG footprint quantification.To help with solving these problems or drawbacks, the authors propose a generic methodological framework for quantifying GHG footprints of crop cultivation systems free from grazing, which takes into account all direct/indirect GHG contributors within a ＇cradle-to-gate＇ life cycle. The authors then provide example values of some GHG emission factors, such as those from machinery operations and other agricultural inputs, extracted from the literature. In addition, direct measurements or model simulations of other major on-farm emission factors are emphasized. The need to further update this methodological framework in future studies, especially by adapting it to mixed crop-livestock production systems, is also indicated.展开更多
This paper deals with a kind of fourth degree systems with perturbations. By using the method of multi-parameter perturbation theory and qualitative analysis, it is proved that the system can have six limit cycles.
基金supported jointly by the National Key R&D Program project of China[grant number 2017YFF0211704]the National Natural Science Foundation of China[grant number41761144054]
文摘The greenhouse gas （GHG） footprint of an agricultural system is a measure of the climate change impact potential （CCIP） exerted by the formation of its product（s）, its accurate quantification is essential for determining the green value added tax of agricultural products for food markets, which in turn may drastically change the current patterns of food consumption and production towards a product life cycle oriented economy. This paper reviews the literature regarding GHG footprints of crop cultivation systems.The review concludes that few studies have fully considered the categories/ items of net GHG emissions from an investigated crop cultivation system, and thus probably led to biases in footprint estimation. Most studies to date have even neglected changes in the soil organic carbon stocks of ecosystems with annual crops, while process-oriented biogeochemical models so far have seldom been involved in GHG footprint quantification.To help with solving these problems or drawbacks, the authors propose a generic methodological framework for quantifying GHG footprints of crop cultivation systems free from grazing, which takes into account all direct/indirect GHG contributors within a ＇cradle-to-gate＇ life cycle. The authors then provide example values of some GHG emission factors, such as those from machinery operations and other agricultural inputs, extracted from the literature. In addition, direct measurements or model simulations of other major on-farm emission factors are emphasized. The need to further update this methodological framework in future studies, especially by adapting it to mixed crop-livestock production systems, is also indicated.
基金Project supported by the National Natural Science Foundation of China (No.10371072)the New Century Excellent Ttdents in University (No.NCBT-04-038)the Shanghai Leading Academic Discipline (No.T0401).
文摘This paper deals with a kind of fourth degree systems with perturbations. By using the method of multi-parameter perturbation theory and qualitative analysis, it is proved that the system can have six limit cycles.
