Study on land evaluation by Karen people in northwest Thailand: Examination of land evaluation method based on indigenous knowledge compared with data related to upland rice growth and yield, and soil physico-chemical properties

Land evaluation of upland rice fields by local farmers was examined from the standpoint of soil and crop characteristics. As a result the nitrogen content of rice plants, the amount of nitrogen absorbed per unit area, the values of plant height the tiller number, and the content of mineralized nitrogen of the surface soils at the late vegetative stage were higher in the fertile land than in the infertile land. It was considered that local farmers assessed the land fertility based on the green color of rice plants and more vigorous plant growth in the rainy season, since it was reported that the green color of rice plants depended on the amount of nitrogen fertilizer applied. The data related to the climatic conditions, rice growth calendar and soil physical properties suggested that the soils in the fertile land were characterized by a clayey soil texture, low permeability, and hence a low decrease rate of the soil water potential at the stages of rice growth, whereas the soils in the infertile land were characterized by a sandy soil texture, high permeability, and hence a high decrease rate of the soil water potential at the reproductive stage. Thus, it was inferred that 10cal farmers considered that the land was fertile if the soil retained a large amount of water even after rain stopped. The characteristics of 'the rice plants grown in fertile land, compared to infertile land were as follows: 1) the panicles were longer, 2) the number of spike lets per panicle was higher, 3) the fluctuations in rice yield were significantly lower, and 4) rice growth and rice yield were not affected significantly even when weeding was omitted once compared to the standard weeding freequency (three times). Therefore, it appeared that the local farmers considered that the land was fertile when panicles were long, when the number of spikelets per panicle was high and when the yield fluctuations in the same field were low.