1. Introduction
Thailand is located in Southeast Asia, where monsoons are common. Soil erosion is a serious problem affecting crop productivity and the incomes of farmers in mountainous areas. Soil erosion is severer on steep slopes, where government agents seldom go, especially along the border of Thailand and Myanmar. Most of the people in the mountainous areas of Thailand belong to ethnic minority groups that differ from those in the lowlands of Thailand. Legally, people are not allowed to cultivate slopes with grades greater than 35%. However, many ethnic groups have settled here and have been cultivating the land for hundreds of years. Recent population increases have forced them to practice deforestation and intensive cultivation to survive. These practices have resulted in soils of low fertility and insufficient food to feed the
population. Thai governmental officers from the Department of Land Development and the Royal Forestry Department have promoted several conservation techniques for reducing soil erosion. However, severe soil erosion still occurs in the mountainous areas. The Department of Land Development, which deals with agricultural land development, recommends that farmers living on slopes with grades between 12% and 35% construct bench terraces or hillside ditches combined with buffer strips of vegetation such as vetiver (Vetiveria zizanioides) or napier grass (Pennisetum purpureum) (Attaviroj, 1996) to control erosion. While terrace paddy cultivation is traditional for some ethnic groups in Thailand, using such techniques for upland crops is new, and most farmers are not familiar with soil and water conservation practices for terraces for upland crops. Moreover, in traditional slash-and-burn farming, farmers prefer to keep the slopes bare with no ground cover or buffer strips, which exposes the soils to storm rainfall and surface runoff. Rill and gully erosion predominate on the slopes between the bench terraces, but not in conventional fields. Therefore, many farmers still hesitate to construct bench terraces as a conservation measure. The objectives of this study are: to survey the structure
and erosion characteristics of bench terraces in farmlands in northern Thailand, to investigate effects of weed cover on
reducing soil erosion, and to observe how participatory methods can improve the farmers’ acceptance and implementation
of the remediation strategies.