Characteristics of energy input and output in fruit tree-grain crop lntercropping ecosystem--A case study from dry valley region in the upper reaches of the MinJinng River

Characters of energy input and output for three typical fruit tree-graln crop intercropping ecosystems in the upper reaches of the Minjiang River are studied．The resuits show that the eficiency of the supplementary energy input is only 1．15～1．52 because of the irrational structure of the energy input．The light use eficiency for the three systems are 0．661%～1．205%．which is higher than single planting．Optimal management such as optimizing the components and structures of the system．improving the supplemental energy input and level，returning non-edible products and utilizing food chain cyclically should be carried out．