A review of factors influencing organic matter decomposition and nitrogen immobilisation in container media
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Authors
Date
1999
Type
Journal Article
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Abstract
The organic fraction of a potting mix is subject to decomposition and, therefore, is
important in relation to nitrogen (N) immobilisation. Immobilisation of N is the
reduction in plant available N (i.e., nitrate or ammonium) as a result ofmicroorganisms
using this N as they decompose organic materials with a high carbon (C)
content. The organic portion of potting mixes usually constitutes 50% or more of
their volume and in New Zealand Pinus radiata bark and sphagnum peat are the
most commonly used materials. Pinus radiata sawdust, tree fern fibre, composted
mixed vegetation, and other sources of bark or sawdust are also used on a limited
scale. Spent mushroom compost has also been successfully used in bark and peat
container media overseas although there have been reports ofproblems with its use
in New Zealand. It has good physical properties and is a useful source of nutrients
except for N. Spent mushroom compost may cause temporary N immobilisation,
after which N is slowly mineralised from it. Spent mushroom
compost also has a highsoluble salt content that can be ameliorated by leaching, and
a pH of 6.5-8.1.
This paper seeks to review the factors causing decomposition of these organic
materials and the implications of these processes on N immobilisation.