Thesis Abstract of AGS Students

On-farm assessment of soybean yield constraints by agronomic survey

Chanchai Sangchyoswat (1988)

On-farm assessment of soybean yield constraints was conducted by monitering farmers' fields in Mae Taeng irrigated area of Hangdong and Sanpatong district during 1987/1988 growing season. The cultural practices of farmers as well as physical and biological environment including soil and plant nutrients, crop water stress level, weeds, diseases and insects damage, soybean growth and development stages, yield and yield component were recorded. Analyses of the relationship between environmental factors and yield components were carried out in order to identify factors which limit soybean yield.

The frontier analysis of soybean yield under farmer management revealed that optimum level for each yield component was 1,300 seeds per square meter, 18.8 grams per 100 seeds, 1,200 pods per square meter and 50 plants per square meter. Number of pods per node was found to be affected by potassium and phosphorus contents in the leaves and crop water stress index at stage of pod formation (R3). An increase in number of pods per node subsequently contributed to an increase in number of pods per sqaure meter. On the other hand if the number of nodes per square meter increased, the pods per square meter will be increased. Increasing number of plants per square meter will increase number of nodes per square meter. However, over optimum number of plants per square meter caused by excessive seeding rate used by the farmers resulted in reduction in number of pods per square meter. Crop water stress at the stage of seed formation (R6), phos-phorus content in the leaves and excessive number of plant per hill affected grain weight of SJ 5 and SJ 4 varieties.

Results from the study suggest that soybean yield constraints may be alleviated by using the optimum seeding rate together with the application of phosphorus and potassium fertilizer. For planting area at the tail-end of the irrigated canal, early drought tolerant soybean varieties should be introduced. Furthur on-farm trials on the above factors should be emphasized to improve recommendation for soybean production.

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