Abstract: The N cycle of rubber-tea-chicken eco agricultural model,a typical tropical agro forestry system in Wenchang municipality of Hainan province,was studied with quantitative experiment and qualitative analysis,compared with rubber and rubeer tea systems.The results showed that the N cycling rate,N output and soil surplus N of chicken garden were all the highest,being 43%,196.5% kg·hm^-2 and 237.6 kg·hm^-2,respectively.The N output/input rate of chicken sub-system was 91%,and the transformation rate was very high. Compared with the other two systems,the chicken garden had a decreased external N input rate, and its internal cycling N was the highest,being 824.1 kg·hm^-2.rubber-tea chicken agro forestry system had a rational N cycling structure,and its N cycle was most active.

Key words: Agro-forestry system, Eco-agricultural model, N cycle, rubber-tea-chicken, Cd, paddy soil, rice, risk assessment