Optimizing Container Soil Amendment: The “Threshold Proportion” and Prediction of Porosity1

Abstract The quantity of amendment required to ensure adequate aeration in container soils is usually determined by empirical tests on a series of mixtures containing different amounts of the amendment In this study, the “threshold proportion” or minimum amount of amendment required before aeration improvement begins, was demonstrated to be controlled by amendment interporosity. This concept is the basis for a method of predicting total and aeration porosity of any container soil mixture.