Effects of Coating on Seed Imbibition: II. Effect of Coating Rates

Abstract

Coatings may slow water uptake by seeds. To analyze this effect, imbibition of coated and non‐coated maize (Zea mays L.) seeds was determined in gaseous and liquid phases. One coating material was applied at five different rates. Similar experiments were done with porous silica beads in saturated air. The volume and surface of the seeds and silica beads were either measured or calculated, and the thickness of the coating was measured. Water potential and wettability were estimated for the seeds, silica beads, and coating. The mechanical behavior of the coating was observed during imbibition. Data were compared with simulations by a simple model. When the seeds are soaked in a liquid medium, coating had no effect. In saturated air, coatings enhanced seed water uptake at low coating rates and slowed it at higher rates. When applied to silica beads, coating slowed imbibition at all rates of application. Thus, we distinguished between a positive effect which predominates at low coating rates for seeds (wetting or breaching effect of the surfactants on the pericarp wax) and a barrier effect to water uptake which increases with the coating rate. On seeds, these effects may be modified by the appearance of cracks in the coating, which resulted from seed swelling. Two independent estimates of the vapor diffusion properties of the coatings were deduced from experiments performed on seeds and silica beads and they differed by a factor of approximately 1.7. It seems therefore possible to determine coating transport properties with this model.