ISHS Acta Horticulturae 294: II Symposium on Horticultural Substrates and their Analysis, XXIII IHC
MICROBIAL ACTIVITY IN GROWING MEDIA - A BRIEF REVIEW |
| Authors: | W.R. Carlile, D.P. Wilson |
| Abstract:
Many investigations have been conducted into the activities of microorganisms during processes of composting of substrate constituents such as bark, animal and plant wastes, as well as domestic refuse. Much less is known of microbial activity within soil-less media prepared from these and other substrates. The microbial flora of substrates prepared from composted materials may be rich and diverse, whereas that of native peats may be low and microorganisms may be absent initially from materials such as perlite, vermiculite and mineral wool. After wetting, fertilisation and in the case of peats, pH adjustment, soil-less media become amenable habitats for the development of microbial populations, Microbial pathogens of media, such as species of Pythium and Phytophthora, as well as some Fusarium wilts may still pose considerable problems in soil-less media. The saprophytic microflora of growing media, though, is much less well researched. Investigations of the saprophytic microflora have largely involved determination of the products of microbial activity, such as nitrate in nitrification processes. However, measurement of respiratory activity, ATP changes as well as direct counting and planting techniques have been used to monitor microbial activity. The low initial population of microorganisms in certain media - notably these containing peat and inorganic constituents such as perlite and mineral wool - may allow establishment of artifically introduced microorganisms. Introduction of antagonistic fungi such as Trichoderma may confer control of certain pathogens, as well as enhancing growth of plants in media. Certain rhizobacteria may exert similar effects. Reductions in the activity of pathogenic microorganisms may further be achieved by use of media constituents, such as some types of bark, which may have suppressive effects on these microorganisms. This manipulation of microbial growth in soil-less media may offer considerable benefits to growers, and may form an integral part of commercial use of soil-less media in the not too distant future. | |
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