Studies on fertilization effect of middle aged plantations of Larix kaempferi

Fertilization experiments of 4 dosages, three kindsN and P mixed ratio and 2 frequencies were implemented in middle-aged plantations of Larix kaempferi in Kuandian county, Liaoning province. The results showed that the effect of fertilization of all treatments was not significant equally. N fertilizers had a certain effect, growth of stands increased with the increasing of fertilization; but growth tended to decrease after fertilizers was used once more, the increment was largest after 2～3 years, then the difference decreased gradually compared with the control; fertilization was also restricted by site quality, even if a certain economic benefit was obtained in 8 years after N fertilizers was used, but captial input with the interests would outweigh the gain when Larix kaempferi stands were cut-over.