Modeling the Three Phases of the Soaking Kinetics of Seeds

Several models can be used to describe the seed soaking curve, which, under optimal conditions, occurs according to a three-phase pattern. Among these models, the Peleg model stands out by its wide use. However, phase III (of germination itself) is not captured by this and other common models in seed soaking curves. The soaking curves of pea (Pisum sativum L.), lentil (Lens culinaris Medik.), onion (Allium cepa L.), welsh onion (A. fistulosum L.), maize (Zea mays L.), and millet [Pennisetum glaucum (L.) R. Br.] seeds, diverging for physical and morphological properties, were obtained with the following objectives: (i) to propose models to fully describe the kinetics of soaking of seeds, capturing the three stages of the process; (ii) to identify the most appropriate model for each species; (iii) to identify the phases of the soaking process; (iv) to relate physical and morphological properties of seeds, such as bulk density, sphericity, with the soaking kinetics. Five models were fitted: third degree polynomial, Peleg model, logistic model, an adaptation of the logistic model and an adaptation of the Peleg model, both adaptations with the addition of an exponential term with two parameters. The species P. sativum (pea) and L. culinares (lentil) did not present the third stage of the process. In this case, the Peleg model shall be used. On the other hand, the other species presented the three phases. The adaptation of the Peleg equation was quite effective in modeling the seed soaking curve of those species. The water absorption capacity is negatively correlated with the seed's sphericity and density.