[Effects of site condition on litterfall and related nutrient return in Pinus luchuensis plantations].

Over three years study on the dynamics of litterfall and related nutrient return in Pinus luchuensis plantations at different sites of northern Okinawa Island, Japan showed that the annual litterfall biomass ranged from 6.54 to 8.05 Mg x hm(-2) x yr(-1), with a peak from June to July. Typhoons had a strong influence on the timing and mass of litterfall. There were significant differences in nutrient concentrations among the different components of litterfall. The annual total nutrient input from litterfall ranged from 113.4 to 154.6 kg x hm(-2) x yr(-1), of which, N input was the greatest and contributed 42.2% of the total. The nutrient input was in order of N > Ca > K > Mg > Na > P. Due to the significantly different site conditions, there were significant differences in annual litterfall mass and related nutrient inputs between the two sampling stands. The annual mean litterfall mass of the sampling stand P1 on the lower slope reached 8.05 Mg x hm(-2) x yr(-1), which was 23.1% greater than that of P2 on the upper slope. The annual mean nutrient inputs were N 66.04, P 1.63, K 17.42, Ca 48.31, Mg 14.65 and Na 6.57 kg x hm(-2) x yr(-1), and were 39.7%, 48.8%, 39.4%, 32.9%, 24.8% and 49.3% higher in P1 than in P2, respectively. The nutrient use efficiency in litter production was higher in P2 (e.g., N 138, P 5945 and K 523) than in P1 (e.g., N 122, P 4934 and K 462), which should be attributed to the relatively lower fertility of soil in P2. The results from the study suggested that Pinus luchuensis plantation in Okinawa was a high efficiency system.