Agro-ecosystem Emergy Evolution and Trend in Hunan Province

Using the emergy analysis method, we conduct trend analysis of changes in the total emergy, input and output structure, various emergy indicators of agro-ecosystem in Hunan Province during the period 1999-2008. The results show that during the study period, total emergy input basically remained stable, but the emergy input structure was constantly optimized, of which the input of non-renewable industrial assistant emergy increased by 38.4%, from 4.00E+22 sej to 5.53E+22 sej, and the input of renewable organic emergy declined from 1.32E+23 sej to 1.20E+23 sej; total emergy yield and yield efficiency of this system were promoted dramatically, and in 2008, the total emergy yield reached 1.69E+23 sej, increasing by 23.8% as against that in 1999, the net emergy yield ratio rose from 0.79 to 0.96; since the environmental loading ratio also tended to rise constantly, from 1.12 to 1.79, the sustainability index of this system also experienced the slow downward trend, from 0.71 to 0.54, always less than 1, indicating that the agriculture in Hunan Province is the high consumption-driven ecosystem in general, with obvious features of extensive development.