A Regional Assessment of Four Green Manure/Cover Crop Species Suited to Tropical Southeast Asia

Abstract

While maintaining adequate levels of soil fertility can be a challenge on any farm, maintaining those levels on the resource-limited smallholder farms of the tropics requires options that are also affordable, practical, and appropriate in such challenging conditions. This research endeavor was designed to compare the adaptability and potential of four legume species promoted as Green Manure/Cover Crops (GMCC’s) in Southeast Asia. Cowpea (Vigna unguiculata), Jackbean (Canavalia ensiformis), Lablab (Lablab purpureus), and Ricebean (Vigna umbellata) were planted in field trials in five diverse countries across Southeast Asia in 2016, including Cambodia, Myanmar, Thailand, Bangladesh, and the Philippines. Data was collected to assess the production of above-ground biomass, percentage of ground cover, and timing of growth cycles at each site. Although results varied from country to country based on soil-type, climatic conditions, and growing degree days, Jackbean consistently outperformed other GMCC species in terms of biomass production, yielding up to 12 t ha^-1 on a dry-weight basis in Bangladesh and the Philippines. Of the four crops compared, cowpea consistently delivered the shortest growth cycle, reaching the pod formation stage in the fewest number of days across all five sites. These results provide informative answers regarding the growth habits and life cycles of these four crops across five diverse sites, and serve to enhance the capability of smallholders in Southeast Asia to select appropriate species needed for soil improvement purposes in a wide-ranging set of cropping systems.