SOIL-MOISTURE, TEMPERATURE, AND DRYING INFLUENCE ON SOYBEAN EMERGENCE

Soybean [Glycine max (L.) Merr.] emergence is influenced by the intera ction of initial seed zone soil water content and temperature. Stress due to soil water content that is great enough for seed imbibition but too low for radicle emergence from the testa reduces emergence. Previ ous research has not determined whether emergence is reduced by soil d rying after the seeds have imbibed water. Our objective was to evaluat e soybean emergence influenced by initial seed zone soil water content and soil drying at three day/night soil temperature regimes (17/8, 21 /12, and 25/16 degrees C) as the number of days of soil water deficit and temperature stress increased. The experiment was conducted under c ontrolled temperature conditions using an incubator. Emergence depende d on both initial seed zone soil water content and temperature. As the number of days of soil moisture deficit increased, soil drying reduce d emergence at initial soil water contents of 0.07 and 0.09 kg kg(-1). If the radicle had emerged from the testa and the soil water content was reduced below the initial soil water content due to drying, emerge nce was reduced. If seed imbibition occurred, but the initial soil moi sture was too dry for the radicle to emerge from the testa, emergence decreased as the number of days of stress increased. The results show that the influence of seedbed drying on percent emergence depended on the initial soil water content and the number of days until adequate s oil water content was restored.