Of insects and seeds

Abstract

This study was carried out in Pang Prarachatan village, which is located in Chiang Rai province of northern Thailand. The farmers in this village construct bench terraces to reduce soil erosion and increase plant productivity. However, severe soil erosion occurs frequently on the bare bench terraces. This study investigates the impact of bench terracing on soil erosion. The use of weeds and plant residues to control soil and nutrient losses were also investigated using model slope plots and an artificial rainfall system. Finally, the knowledge gained from this study was transferred to the farmers through a workshop in the village, and their acceptance of the results was evaluated by means of a questionnaire. The severity of soil erosion is thought to vary according to the structure of the bench terrace and the ground cover conditions. Rills are the primary form of erosion on bare bench terraces. In addition, some rills develop into gullies that can run from the upper terrace down to the lower terrace. Nevertheless, rills and gullies are rarely found on weed-covered terraces. Moreover, the results of an erosion experiment using model slope plots and artificial rainfall systems showed that plots covered with weeds and plant residues had much less surface runoff and soil and nutrient losses than bare soil. The amounts of nitrogen and phosphorus absorbed by weeds were 4.7 and 2.3 times smaller than the nitrogen and phosphorus losses due to soil erosion, respectively. The results of the field surveys and model slope experiment were announced to the farmers through participatory workshop in August 2003. The first questionnaire, conducted just after the workshop, clearly showed that around 90% of the farmers agreed to cover their slopes with weeds and plant residues so long as it did not affect soil fertility and plant growth. However, the second questionnaire, conducted in January 2004, showed that only 29% of farmers were covering the bench terraces or non-terraced slopes in their farmlands with weeds and plant residues. Therefore, participatory activities should continue to be held regularly in order to ensure greater acceptance and practice of soil conservation on the part of the farmers.