Designing rockets and growing media

Rational and efficient design of a system typically demands a target endpoint, plus the means to determine progression from one prototype to another in pursuit of that endpoint. If both endpoint and prototypes can be quantified using numerical parameters, then that progression should be amenable to a mathematical description. We will first illustrate this idea using a toy example of rocket design, in which the endpoint is escape velocity and prototype rockets are described numerically using fuel capacity and engine thrust as parameters. Moving to growing media, we motivate numerical parametrisation of media and the development of mathematical relationships linking mixtures. The objective is a predictive model that can be used to rationally design a growing media mix in pursuit of a target crop type and growing system. We propose that this approach offers an alternative to 'look-see' growing trials for assessing growing media performance. Focusing on physical properties, we describe growing media materials and mixtures using three parameters: Air filled porosity, dry bulk density and available water. Materials and mixtures of materials are then represented as points in a three-dimensional parameter space. Plant performance is mapped out over this space via the output of systematic growing trials. A target, for example 'peat-like', can be expressed in terms of its physical parameters. Insight on how to progress a trial mixture toward the target can then be extracted from trends in plant performance, coded as mathematical relations involving media parameters. This mimics the rocket example, in which engine and fuel tank parameters can be used to compare designs and to assess progress toward the goal of escape velocity. This UK Government and industry sponsored project, 'Transition to responsibly sourced growing media use within UK Horticulture' (SP1215/CP138), is a collaborative effort involving growers, industry consultants, growing media producers and academics.