Nitrogen contents of the soil and leaves at the observation sites were evaluated (Figure 1). Although, nitrogen content in soil at Ranong Province (3.06-3.62%) was higher than the soil in Lao PDR (1.82 to 2.26%), total nitrogen in leaves at Ranong Province (9.84-11.89%) was lower than those of leaves at Lao PDR (12.63 to 17.45%). Optimizing nitrogen is necessary to regulate vegetative growth and to promote flower induction and bud differentiation, as well as increase fruit set (Menino et al., 2003).