ISHS Acta Horticulturae 648: South Pacific Soilless Culture Conference - SPSCC
CHANGES IN ORGANIC GROWING MEDIA DURING STORAGE |
| Author: | W.R. Carlile |
| Keywords: | storage; growing media; peat; bark; timber by-products |
| Abstract:
Over half of all growing media produced in the UK is now sold in pre-packed form through nurseries, garden centres and multiple retailers, contrasting with the situation in the 1970s and 1980s where media were principally used by professional growers – normally within a short time of preparation. Bags of growing media may now remain on point-of-sale premises for up to a year. During this time, changes in the physical, chemical and microbiological status of media may occur. These were first highlighted by Bunt in the 1950s for the John Innes media, where mineralisation of the hoof and horn fertiliser then used in such media resulted in increases in pH following release of ammoniacal N. Nitrification and subsequent accumulation of nitrate was also seen to occur in stored John Innes media. Peat-based media came to dominate the UK (and European) growing media market in the 1970s and 1980s and peat is till the principal component of seed, potting and multipurpose media. Peat media are usually fertilised with straight inorganic nutrients and the only change that may occur in storage is a slow rise in pH from dissolution of calcium and magnesium added as chalk or dolomitic limestone. The breakdown of slow release fertilisers added to peat media has on occasions caused problems of high salinity following storage. Many peat-free media may incur problems during storage. The principal polymer in peat is lignin, which is resistant to microbial degradation. Coir also contains a high proportion of lignin, but materials such as bark, timber waste, wood fires and paper waste have a high cellulose and hemicellulose content, and microorganisms readily degrade these polysaccharides. Structural breakdown of materials may occur, and microbial growth may lead to utilisation of nutrients- especially nitrogen - added to media. Furthermore, the appearance of microbial growth in bagged media is unsightly and may deter consumers. Solutions to these problems include careful selection of materials for use in peat-free growing media; use of appropriate composting techniques to allow microbial utilisation of readily available carbon sources; and blending of materials to counteract storage problems associated with individual components. | |
Download Adobe Acrobat Reader (free software to read PDF files) | |
