Thesis Abstract of AGS Students

On-farm research of soybean yield Gap

Buntuke Wichaisri (1988)

Soybean yield gap study was conducted in the farmer's fields at Banmae village, Sanpatong District, Chiang Mai Province. Major yield limiting factors at the farm level were identified through site-diagnosis before designing the experiments. Water shortage at the end period of growing season and socio-economic conditions were found to be the main decisive factors for farmer's technological choices. The objectives of the study were to identify constraints to soybean yield and to test recommended technologies in order to develop proper recommendation for existing farm resources. The factors, namely variety, fertilizer and weed control each at two levels i.e. improved practices and farmer's practices were tested in the fields. The improved technologies consisted of Nakornswan 1 variety, 25 kg/rai of 12-24-12 fertilizer grade and postemergence herbicide (Fluazifob-butyl) at the rate of 80 g/rai of active ingredient. The farmer's practices were SJ 5 variety, 17 kg/rai of 16-20-0 fertilizer grade and no chemical weed control. The study employed randomized complete block design with three sets of experiments using complete factorial, minifactorial and supplemental trials, each with two replications involving 15 farmers' fields. Analysis of data revealed that yields obtained from the treatments using recommended technologies were lower than those from farmer's practice. Evaluation of contributing factors indicated that Nakornswan 1, the early maturity variety, produced lower yield and economic return than SJ 5. It was also found that the use of fertilizer grade 12-24-12 at the rate of 25 kg/rai resulted in improving average yield but not acceptable benefit-cost ratio due to high labor cost involved in the application of this fertilizer. Chemical weed control appeared to be the only effective technology which increased both average yield and economic returns and was recommended to farmers in the area.

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