Cover crop and soil improver
The main attributes of velvet bean are its fast growth and its long growing season in frost-free environments. It is thus possible for velvet bean to protect the soil through the wet monsoon season (FAO, 2011; Cook et al., 2005).
Velvet bean is an N-fixing legume that has no specific rhizobium requirements, but N fixation is favoured by warm temperatures (FAO, 2011).
As a leguminous species velvet bean is reported to improve soil fertility: it provides more than 10 t DM aboveground biomass/ha, and below ground it fixes some 331 kg N/ha, equivalent to 1615 kg ammonium sulfate/ha (Cook et al., 2005; Buckles et al., 1998; Wulijarni-Soetjipto et al., 1997). Velvet bean also yields 100 kg K/ha, and 20 kg P/ha (Buckles et al., 1998). It is widely grown in Central America, either relay planted with maize or as a rainy season fallow crop in rotation with dry season maize. It was reported to improve maize yield by between 500 kg and 2 t/ha after a one-year fallow (ILRI, 2004; Wulijarni-Soetjipto et al., 1997).
Velvet bean is mainly grown as a cover crop and green manure because it can establish very quickly without requiring complete soil preparation (Cook et al., 2005). In intercropping systems including maize and velvet bean, the fast growing legume accumulates nutrient through N fixation and it protects the soil from heavy rains in the wet season. Once slashed into a thick mulch, the velvet bean foliage protects the soil from erosion and prevents weed germination. Velvet bean also has a positive effect on soil moisture (Buckles et al., 1998).
As a cover crop, velvet bean sown in rubber plantations can yield about 2 t/ha of fresh organic matter within 6 months (Wulijarni-Soetjipto et al., 1997). In Sri Lanka, it has been planted as a cover crop in coconut plantations (Ravindran, 1988). It used to be an important cover crop in citrus and banana plantations (Wulijarni-Soetjipto et al., 1997).
Weed and pest control
Velvet bean has an overall beneficial effect on companion crops in intercropping systems due to its pest and disease resistance. When established, the crop smothers weeds effectively (FAO, 2011). Velvet bean is one of the most suitable crops for reclaiming land infested with weeds, notably Cynodon dactylon, Cyperus species, Saccharum spontaneum and Imperata cylindrica (Hellin, 2006; Wulijarni-Soetjipto et al., 1997). In Brazil, it is recommended for use in rotation with cotton to limit Fusarium oxysporum infestation. It can also effectively control nematode infestation by species such as Meloidogyne incognita (Wolf et al., 2003; Wulijarni-Soetjipto et al., 1997).