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| Usefulness of clay in substrate mixtures | |
Plants grown in peat based media that contain clay result in more compact growth compared with mixtures without clay. The positive effect of clay is ascribed to its Cation Exchange Capacity (CEC). The positive effect of the clay varies according to its composition, attached minerals, dry matter and grade (from fine powder through to course granules). The positive effect of clay on plant growth is also due to certain physical effects and interaction with the cultivation systems (irrigation frequency and fertilization) which appear to play an important role in effectiveness of clay products in mixtures. Clay products showed a large influence on the water uptake and water holding characteristics of mixtures with peat. Very fine graded clay products showed a strong effect on the content of Easily Available Water (EAW) and an greater velocity of water uptake under very dry conditions. The measurement of EAW in clays is a very useful tool in assessing the relative value of a given type of clay content in a substrate mixture. The effectiveness of clay on the buffering of nutrients was only found for cations and phosphorus. Measurement of CEC and of the occupation of the CEC by means of a barium chloride extract showed to be effective in the classification of clay products. J.B.G.M. Verhagen ‘Effectiveness of clay in peat based growing media’ ISHS Acta Horticulturae 644: International Symposium on Growing Media and Hydroponics. www.actahort.org |
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