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Effect of Seed Moisture Content, Field Weathering, and Combine Cylinder Speed on Soybean Seed Quality¹

Two varieties of soybeans were harvested at varying dates and at varying seed moisture contents in 1959, 1960, and 1961. Two harvest methods, hand shelling and machine harvesting, were used at each date of harvest. With the machine harvest method combine cylinder speeds of 500, 700, and 900 rpm were used.

In all 3 years there was a general trend for the whole seed from later dates of harvest to have a lower percentage of normal seedlings in laboratory germination and field emergence tests, a higher percentage of splits and cracked seedcoats, and smaller average seed size as measured in grams per 100 seed and by a screening method. Exceptions to this general rule occurred in 1961 when the initial quality of the seed was very high.

With only a few exceptions, hand harvested seed-lots had higher viability and a lower incidence of splits and cracked seedcoats than machine harvested seed-lots. Within the machine harvested seed-lots, harvesting at lower cylinder speeds produced seed with a higher percentage of normal seedlings in laboratory germination and field emergence tests, a lower percentage of abnormal seedlings in laboratory tests, a lower percentage of splits and cracked seedcoats, and larger average seed size. There was some indication that the threshing effect split a larger percentage of the larger soybean seed within each seed-lot.

² Former Instructor (presently Assistant Professor, Department of Agronomy, Iowa State University of Science and Technology), Associate Professor, and Professor and Chairman, Department of Field Crops, University of Missouri.

Received for publication August 26, 1965.