During the late rainy season, the permanent hill fields that surround a cluster of hilltribe villages in the Chiang Dao district of northern Thailand radiate various hues of green. These verdant fields, belonging to ethnic Lisu, Lahu, Akha, Palaung and Karen farmers, are covered in a patchwork of green manure/cover crops (gm/ccs) that include rice bean (Vigna umbellata), cowpea/black bean (Vigna unguiculata), lablab bean (Lablab purpureus), peanut (Arachis hypogaea) and jack bean (Canavalia ensiformis).
The extensive plantings of gm/ccs are part of a legume-maize relay cropping system that local farmers developed in the early 1980s. Relay cropping is a type of intercropping with two or more crops grown simultaneously during part of their life cycles. The second crop is often planted after the first crop has reached its reproductive phase, but before it is ready to harvest (Van Keer, et al.).