A study was made of the biogeochemical cycling of the second generati on Chinese fir plantation at its fast growing stage. The results indicate that the total input of N, P, K by rainfall is 39.970 kg·hm -2 a -1 , and the output in runoff accounts for 9.883 kg·hm -2 a -1 . The net diversification ratio of output and input is 75.3%. N ranks the highest of net accumulation among the three nutrient elements (N, P, K) and its diversification ratio reaches 83.54%. The biogeochemical cycling is in the order: N>K>P. and the cycling velocity of N, P,...