RETAINING CELL WALL STRUCTURE IN PRODUCING QUALITY COMPOSTS TO REPLACE PEAT AS GROWING MEDIA

There has been abundant research to evaluate the physical properties of peat and other growing media in relation to plant requirements. Much of the methodology has been derived from soil science. However, there has been relatively little work to understand the underlying compositional nature of peat and non-peat growing media. This paper reports comparative studies on some physical and chemical properties of peat, compost and related substrates and considers the importance of retaining plant cell wall structure in order to develop appropriate growing media from non-peat sources. The results showed: 1) commercial peat and peat-based growing media retain a large level of cell wall structure which provides the basis of their functional properties; 2) mature, industrially composted materials lack plant cell wall structure and are unlikely to emulate the properties of peat, 3) controlled composting can facilitate the retention of plant cell wall structure; this provides the basis for the development of a new range of growing media; 4) blending of structurally-sound composts with small quantities of peat or other structured composts can further tailor the properties of the material; 5) the three physical parameters “Moisture Retention”, “Air-filled-Porosity” and “Dry Bulk Density” in conjunction with Principal Compo¬nent Analysis provide a simple yet sound basis for rapid and cheap evaluation of substrates and their structural suitability as growing media.