A mixing model to predict selected parameters in mixing container media

The aim of the study was to get accurate data on the effects of mixing container media components and to match these data against models for mixing container media. It was accepted that the mixing of two container media components was related linearly to the amounts of material mixed, for parameters such as degradability. For other parameters the extra material necessary to compensate for the effect of interstitial filling had to be taken into account. Four different two component mixes were measured for 36 different ratios in all. Moisture content, air content, shrinkage, density and EC and pH were measured for each mixture. A formula based on measured densities of the components and the mix was used to predict moisture/air content in the mixes. It is concluded that the formula and the underlying method underestimate the water content in relatively wet materials such as peat-coir products and overrate the moisture content for relatively dry materials such as peat and flax straw mixes. The increase in density of the mix may be calculated either by measuring the volume loss or the density increase of one or more test mixes, from modelling a simplified particle size distribution, or from an empirically calculated relationship with particle size distribution parameters.