ABSTRACT
The emergence of soybeans [Glycine max (L.) Merr.] in the field is a function of the interaction of the seeds and the soil environmental factors. Stress during the emergence period of soybean production results in either inadequate numbers of plants for profitable production or a highly diverse plant population which makes crop management difficult. Important environmental factors include soil temperature, soil moisture, aeration, soil insects, and soil mechanical impedance. Gilman et al. (7) have found that less than optimum levels of temperature or moisture may weaken the seed and render it more susceptible to other factors of the environment and, consequently, reduce emergence. Nonuniform stands increase the difficulty in determining the optimum time of performing subsequent production operations. Poorly timed operations usually reduce profits, and for the grower, this means that the crop must be managed more effectively. Efficient management requires an understanding of the system which the grower is attempting to control. The ultimate understanding of a system can be represented by a model whereby the system can be simulated. Modeling can be very beneficial, even if the initially developed models are not sufficient for accurate simulation (3). Modeling and computer simulation of plant growth has increased greatly in recent years. Hatfield and Egli (9) developed prediction equations for soybean hypocotyl elongation as a function of soil temperature and depth of planting (2) and Wanjura et al. developed equations which describe the rate of shoot and hypocotyl elongation in corn and cotton, respectively. The equations developed by Blacklow (2) and Wanjura (13) were incorporated into computer models which made it possible to predict the time of emergence as a function of soil temperature. Von Bertalanffy (12) has developed a growth function for animals, and Richards (10) 638has shown that when limitations imposed by its theoretical background are discarded, it may have wide applications in empirical botanical studies, facilitating comparisons between sigmoid curves of different shapes.
