Effect and Mechanism of Multiple Land Use Systems on Raising Productivity of Degraded Tropical Soii

Four PEMLU models were established in regenerated rubber plantations in view of degraded phenomena including soil erosion , fertility decline and yield reduction in old rubber plantations. The results indicated that PEMLU models had five functions:(1)decreasing runnoff and soil loss 66. 7% and 65. 1% respectively in FEF model,as compared to the check plots (2) improving soil fertility with the amount of ground - litter being 83 - 280% more than that of the cherk plots and the content of organic matter in FEF model increasing from 0. 54% to 1. 34% 5 (3)promoting the growth of the rubber trees which leads to tapping one year earlier in PEMLU models; (4)increas ing total economic value per hectare with the annual average 2.830-6.650 yuan t and (5)reducing yield loss from natural calamity. A quantitative analysis was made on four PEMLU models by FWBG method. The results showed that the optimal benefits could be well obtained by applying FEF modei and that WRS models was suitable to extend practically to a large scale in Hainan Island owing to its low investment and high benefits.