An attempt to analyse the yield difference between the experimental yield of soybean monitored by researchers and actual farm yield done by farmers or the gap between the potential yield in the farm environment and the actual farm yield is made between 1989 and 1990 crops year in rainfed areas of Sawankhalok, Si Satchanalai, Si Nakorn and Si Semroog districts in Sukhothai province. The intend of the agronomic trals was to find solution for farmers. The trial was conducted by employing the IRRI approach. Three types of field experiments were done : complete factorial, minifactorial and maximum yield supplement. Three factors; namely weed control,fertilizer and insect control were tested individually or combining among two factors and three factors. The expermental design used in both 1989 and 1990 trals was RCBD. The results in both years revealed that the difference between treatments were insignificant for yield in all locations. For the demonstration fields, the considerable variations in yield obtained from the farmers with free inputs ranged from 0.75 to 2.50 tha while the yield from the field praticed with farmers' technology ranged from 0.80 to 2.07 tha and the yield gap between the two groups were raged from 7.03% To 19.24 % The contribution of the fertilizer toward the yield appeared to be the greatest (127.08 kg/ha) followred by insect control and weed control (26.04 kg/ha and 16.44 kg/ha) respectively. However, the combine analysis showed no statistical difference among treatments. The adverse climatic condition especially the below average rainfall plur the damaging by pest seemed to be the responseible factors. The result of the 1990 trial plot followed the same trend of the 1989 date. There was no sighificantly difference among yield obta ined from any treatments. The abnormal pattern was, again the responsible factor. The comperison between the famer input plot and the free input plots showed the greater yield of the latter one than the first. It replied the facts that Sukhothai farmers were reluctant to invest more input due to the two executive years of adverse climatic condition