An Index Model for Predicting Seed Germination and Emergence Rates

We present a germination and emergence model that can be used as a sub-model in an individual-based model of population dynamics. Seed germination and seedling elongation rates were measured in petri dishes in the laboratory for ivyleaf morningglory, velvetleaf, corn, and soybean seeds, as functions of temperature and water potential. The analysis yielded a set of indices: the germination temperature index (GTI), the germination water index (GWI), the emergence temperature index (ETI), and the emergence water index (EWI). The seed populations were divided into 100 discrete cohorts, with each cohort (i), having its own germination rate (GR) as the product of a reference rate and the germination indices, or GR i = GR i REF × GTI × GWI. After germination, the emergence rate (ER) was the product of a reference rate and emergence indices, or ER i = ER REF × ETI × EWI. The model was tested against the timing of emergence in the field for seeds planted 1, 2, 4, and 8 cm deep in natural or rain-excluded environments. The predictions were more accurate for all depths combined than for any particular depth.