Thesis Abstract of AGS Students

On-farm study of soil and water management for soybean (Glycine max. (L.) Merrill)

Nadh Tasachabutara (1988)

An on-farm study of soil and water management for soybean was conducted in the year 1987 in paddy fields at the Ground Water Development Project, Sri Nakhon and Sawankalok district, Sukhothai province. The objective of the study was to compare various soil and water management methods with that practiced by farmers in order to find alternative methods that help improve productivity of the farms and the project. Design of the study was split plot with two tillage methods as main plots. The first tillage method was minimum tillage followed by seed drilling with Inverted-T seeder. The second was conventional tillage followed by hand broadcasting. The subplots were three irrigation interval i.e., 15, 20 and 25 days during the growing period. Irrigation water was applied as flooded basin in all irrigation methods.

The results showed that the minimum tillage method reduced irrigation water by half com paring to the conventional tillage method. The amount of water per application for the plots employed the minimum tillage treatment was 7.1 cm comparing to 13.9 cm in the conventional tillage plots. Seeding rate used by Inverted-T seeder in the minimum tillage tratment was 15 kg/rai which was half of that using the conventional tillage followed by hand broadcasting. Seed germination in the minimum tillage and the conventional tillage treatments were 81% and 52% respectively.

It was found that there were significant interactions between tillage methods and irrigation interval. Minimum tillage followed by irrigation at 15 and 20-day interval yielded 319 and 328 kg/rai respectively. The yield were significantly higher than those from the plots subjected to conventional tillage at all irrigation interval. However, soybean yield in the plots which received irrigation water at 25-day interval following the minimum tillage, was not significantly differed from those received irrigation water at 20-day interval with conventional tillage and hand broadcasting.

Minimum Tillage and planting by an Inverted-T seeder with 20 days irrigation interval could increase the irrigated area by about 113 rai per well. This method gave the return above the variable cost of 1,860 baht/rai and benefit cost ratio (B/C) of 2.7. Conventional tillage and hand broadcasting with 25 days irrigation interval, the common practice in the study area, gave the return above variable cost of 739 baht/rai and benefit cost ratio of 1.6. The results suggest that minimum tillage with an Inverted-T seeder followed by 20 days irrigation interval is feasible and may be implemented in the Ground Water Development Project in the study area.

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