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Emergence Force by Cotton Seedlings¹

Economic returns from crops require establishment of a good plant stand. Soil crusting reduces seedling emergence and stands of many crops throughout the world. One of the most important crops adversely affected by crusting is cotton (Gossypium hirsutum L.). The force exerted by germinating plants such as cotton often determines the seedling's abdity to rupture and emerge from under the soil crust. However, the force exerted by an emerging cotton seedling has not been determined. Studies were conducted in the laboratory to determine and better understand the emergence force of cotton seedlings.

The force exerted by cotton seedlings under different soil moisture conditions and temperatures was determined using a force transducer. The transducer mv output, which is a linear function of the force exerted against the transducer button, was continuously monitored with a mv recorder.

Emergence force was a linear function of volumetric soil moisture, number of seedlings, and cross-sectional area of the emerging hypocotyls. The size of the hypocotyl was a function of soil moisture and temperature. Maximum diameters of the cotton hypocotyl at 22, 27, 32, and 40 C were 0.32, 0.41, 0.34, and 0.26 cm, respectively, and the maximum forces exerted were about 350, 600, 400, and 200 g, respectively. The time required for maximum exertion by the seedling was dependent upon temperature, ranging from 40 to 48 hours at 32 C and 50 to 60 hours at 27 C. These findings suggest that planting methods, planting dates, and cultivar improvement may offer possible ways to minimize or circumvent crusting effects and increase emergence.

Key Words: Soil crust • Gossypium hirsutum L. • Hypocotyl • Transducer • Temperature • Soil moisture

² Professor, Texas Agric. Exp. Stn., Texas A&M Univ. Agric. Res. and Ext. Ctr. Vernon, Tex.

Received for publication August 27, 1979.