The relevance of clay as a highly effective buffer material for nutrients and salts in coir pith-based growing media

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Matthias Schellhorn, René Grove, Ralf Diedel, Claus-Peter Witte
Book (published in): 
Posters IPS Convention Bremen 2019 Future Use of Peat and Substitutes in Horticulture
coir, peat, clay, horticulture, growing media



From the experiences gained using growing media with clay as an ingredient in the cultivation of ornamental plants, it is well known that clays make a valuable contribution to the buffering of nutrients, above all potassium and phosphorus. In addition, undesirable pollutants such as manganese can be buffered in growing media by using clays. However, the efficiency of the clays depends significantly on their mineral composition.
In peat-reduced or peat-free growing media, peat substitutes, e.g. coir pith, compost, wood fibres, etc. are used, causing several problems due to their potentially high salt loads and - in comparison with peat - low sorptivity. The possibility of countering the negative effects of alternative basic constituents by adding clays regulating the nutrient balance and salt level in general, which has not been taken into consideration up to the present, shall be explored in a series of experiments.

Recent studies have proved the effect of clays with high sorptivity on the regulation of the nutrient content in the soil solution and on the availability of nutrients for plants grown in coir-based growing media. We used a growing medium composed of coir pith, perlite and vermiculite for nitrogen fertilisation tests with the model plant Arabidopsis thaliana. Our original growing medium seemed to have limited interaction with nutrients, probably leading to high nutrient concentrations in the aqueous phase, causing salt stress symptoms and growth retardation.

By adding Florisol® B-extra bentonite to the medium, salt stress symptoms could be prevented. At the same level of nitrogen concentration, significantly higher fresh mass values could be achieved in the presence of Florisol® B-extra.

These results will stimulate further studies regarding the use of clay in peat-free growing media, especially in order to stabilise the content of nitrogen, as its long-term availability is an acknowledged problem particularly in the case of using wood fibre as basic constituent.