Soybean yield gap analysis in paddy field after rice in Chiang Mai

Soybean yields at farmer's field are generally lower than those indicated by trials at research station. This study was concentrated in soybean yield gap from the aspect of agronomic components. The on-farm trial was tested on 11 farmers' fields in Mae Rim district and 13 farmers' fields in Mae Tang district, Chiangmai from December 1988 to April 1989. In this study, 14 farmers received recommendation and free package of inputs (good seed, fertilizer, herbicides and insecticide) and 10 farmers received only recommendation. For Chiang Mai 60 variety, the mean soybean yields with inputs were 46.8 % and 76.9 % higher than those without inputs at Mae Rim and Mae Tang districts, respectively. For SJ.5 variety, the mean soybean yields with inputs were 11.27 % and 11.3 % higher than those without inputs at Mae Rim and Mae Tang, respectively. The yield gap of soybean resulted from low quality, seeds, non application of herbicide and chemical. Futhermore, the available phosphorous in the soil was inadeguate for soybean production. Moreover, weeds were the main problem for growing soybean as well. In addition, lack of correct knowledge and experience to use production technology, inadequated capital (credit/loan) and opportunity to be employed off-farm contributed to the soybean yield gap as weel. In the second year, the on-farm trial was conducted in two locations from December 1989 to April, 1990. Ten and 16 farmers' fields were selected for the trial at Hang Dong and Sanpatong district, Chiang Mai, respectively. Yields of soybean grown in rice straw burned and unburned straw with either small mechanized planter (INVERTED-T) or bamboo stick were not significantly different. However, soybean yields with herbicide applying and straw mulching were higher than those with no weed control supporting the first year observation that weeds were the main problem of soybean growing. The dimonstration plots were conducted in 20 locations. Land preparation by straw burning, straw cutting and left straw in the field with two planting methods (using INVERTED-T and bamboo stick) did not produce different soybean yield. However, economic consideration showed that soybean grown with INVERTED-T in unburned staw reduced cost of production per unit area.