A MODIFIED ECOLOGICAL FOOTPRINT MODEL AND ITS APPLICATION TO AGRO-ECONOMIC ECOSYSTEM BEFORE AND AFTER GRAIN FOR GREEN POLICY IN THE WATERSHED SCALE ON THE LOESS PLATEAU IN CHINA

Based on the theory of emergy analysis and the introduced concept of emery density, a modified ecological footprint model was established to evaluate the environmental status of sustainability in the given region. The main process was to use this model to transform all kinds of energy flows of the eco-economic systems into the corresponding biological productive units and then combine with emergy density to calculate ecological footprint and ecological carrying capacity. With the agricultural eco-economic system of zhifanggou watershed in hilly-gullied loess region as an example, we applied the modified and traditional model of ecological footprint to analysis the changes of this region before and after grain for green policy. By using the modified model, we could find that the carrying capacity per capita was 0.256hm(2)/cap and 0.201hm(2)/cap separately before and after grain for green policy, while the ecological footprint per capita was 0.183 hm(2)/cap and 0.118hm(2)/cap separately. All results showed an ecological surplus. And the index of sustainability was 0.528 and it belonged to the slight sustainability condition before this policy, but after this policy, the index of sustainability was 0.630 and it belonged to the middle sustainability condition. Meanwhile, the results of ecological footprint per capita were 0.733hm(2)/cap and 0.650hm(2)/cap separately. By using the traditional model, the ecological carrying capacities were 1.559hm(2)/cap and 1.781hm(2)/cap separately before and after grain for green policy. And they all showed ecological surplus and belonged to the middle sustainability condition. From all the above, the results all showed that the calculation results of the modified ecological footprint model were more realistic situations of zhifanggou watershed and the conclusion was more reasonable than the traditional one.