The Relationship Between the Equilibrium Moisture Content of Grass Mixtures and the Temperature and Humidity of the Air

Abstract

Equations are presented for the calculation of equilibrium moisture content for forages from air relative humidity and temperature. Most equilibrium moisture content data are derived from experiments with small samples of the material stored in sealed containers with acid solutions of a known concentration. The data presented here were obtained by extended drying of the samples, with air at closely controlled conditions. The relationship between air conditions and the equilibrium moisture content is shown to be the same for the data presented here and the previously published data. Four models, of varying complexity, were fitted to the data, the simpler models are suitable for a range of 25 to 90% relative humidity while the most complex covers the range 0 to 90% humidity. The relationships were found to cover a wide range of forage from rye-grass mixtures to lucerne.The effects of errors in the determination of the relative humidity on the predicted value of equilibrium moisture content were analysed. This analysis showed that the prediction of equilibrium moisture content is very sensitive to errors in relative humidity measurement at high relative humidities. At the lower relative humidities, the errors in measurement are not so sensitive; for example at 55% relative humidity the percentage error in the estimation of equilibrium moisture content is roughly of the same order as the error in measurement.