Rice (Oryza sativa L.) in tropical Asia is mostly grown under lowland conditions with one to three crops per year, depending on rainfall or availability of irrigation water, and the use of modern short-duration varieties. The adoption of legumes into rice-based cropping systems offers opportunities to increase and sustain productivity and income of smallholders in Southeast Asia ( Whitmore et al., 2000 and Wijnhoud et al., 2003).