Thesis Abstract of AGS Students

Annop Kasivivat (1989)

The study on the effect of planting dates and harvesting times on the quality of soybean seeds was undertaken during the 1986/87 crop year in two parts. First was the inquiry into soybean seed production problems among members of farmers' group in San Maha Pon village of Mae Taeng District in Chiang Mai Province which revealed that late planting date would result in low seed quality as rainy season started at harvesting time. Second was the study on the effect of alternative planting dates and harvesting times under field condition on the quality of soybean seeds using split plot design. Planting date was treated as main plot for three planting dates, 20th December, 30th December and 10^th anuary. Supplementary information was collected rom farmers who started planting on 3^rd January.

Soybean seeds quality were evaluated at two stages, physiological maturity (R7) and at field maturity for their moisture content, germination percentages and seed vigor at harvesting time and after being kept under room temperature condition for four months.

The SJ 5 variety planted on 30^th December was found to have highest yield at 476 kg/rai with

10 percent seed damage. Planting on 20^th December and 10th January were not different signi-ficantly in yield level which was averaged at 416 kg/rai but seed damage were 9 and 17 percent, respectively.

The germination percentages of soybean seeds planted on different dates were significantly different after four months storage period as indicated by 91, 89 and 84 percent corresponding to 20^th December, 30th December, and 10^th January planting dates. Seed vigor of soybean planted on 20^th December and 30^th December were different significantly from 10th January, as shown by the indices of 8.0, 7.7 and 7.3, respectively.

The quality of soybean seeds harvested at different stages tested in laboratory were not different significantly. However, after four month storage, seeds obtained from harvesting at the first stage had higher germination percentages than those from the second stage for every planting date with the average of 54 and 43 percent, respectively.

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