An on-farm diagnostic survey on the extent and causes of variability of upland rice yields was carried out during 1993-96 in Mae Haeng, Chiang Mai Province, in upper northern Thailand (600-700 masl).
Farmers’ varieties were characterized from physiological, agronomic, and genetic points of view. Data were obtained over four successive wet seasons from a total of 423 small squares (1 m2) from 63 farmers’ fields representing an extensive range of upland rice cropping conditions under a predominant swidden cultivation system. Plots were monitored every 2 wk to quantify key physiological and agronomic parameters needed to understand yield buildup patterns of various types of cultivars. Isozyme analysis was carried out to assess the genetic variability of farmers’ upland rice varieties.