Assessment of the performance of Cromarty’s equation to predict seed equilibrium moisture content during drying

Abstract

For conventional seed (gene)banking of orthodox seeds, it is essential to effectively dry the seeds and maintain a low moisture content (MC). Cromarty’s equation describes the MC and relative humidity (RH) relationship of drying seeds, based on their oil content, and can be used to predict the MC seeds would reach when dried to equilibrium in a controlled environment (RH, temperature). However, the equilibrium MC-RH relationship (‘isotherm’) varies not only between seeds of different species and depending on temperature, but also on whether seeds are losing (desorbing) or gaining (adsorbing) moisture. The reliability of Cromarty’s equation in predicting the equilibrium MC for drying different seed species was examined and compared with the Guggenheim-Anderson-De Boer (GAB) equation, to model both desorption and adsorption data. Cromarty’s equation provided a good fit to the desorption data for oilseed rape and barley ( R 2 = 0.98). For yellow mustard, seed MC was overestimated and for lupin, wheat, buckwheat and pea, the MC equilibria predicted by Cromarty’s equation were closer to the adsorption data. Overall, the GAB equation provided a better fit of the data. While Cromarty’s equation is a useful tool for estimating the MC of seeds under a given environment, it should be used with caution in critical situations.