ISHS Acta Horticulturae 644: International Symposium on Growing Media and Hydroponics
EFFECTIVENESS OF CLAY IN PEAT BASED GROWING MEDIA |
| Author: | J.B.G.M. Verhagen |
| Keywords: | water retention, capillary water transport, water availability, CEC |
| Abstract:
For many years a diverse range of ornamental plants have been grown in peat based media containing clay. Plants grown on such mixtures result in more compact growth compared with mixtures without clay. This effect was ascribed to the Cation Exchange Capacity (CEC) of the clay types used. Nowadays a wide variety of clay products is applied in peat based growing media. Variation does occur for content and clay type minerals in the product, if materials are dried or not, and for the grade (fine powder till coarse granules). In practice this variation gave various results on the effects of clay addition on the development of plants. Whenever effects were obtained they could not always be ascribed to specific chemical characteristics of clay products. Physical effects and interaction with the cultivation systems (irrigation frequency and fertilization) seemed to play an important role in effectiveness of clay products in mixtures. The research as described in this publication was initiated by the demand for more clarity about the usability of clay products. The objective of the work was to find useful parameters for qualifying the effectiveness of clay products used in growing media. 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 easy available water (EAW) and the velocity of water uptake under very dry conditions. These characteristics showed no relation with the content of clay minerals (expressed as percentage < 2 µm) in the products. Mixtures with a low content of EAW did lead to a retarded growth of Impatiens New Guinea when cultivated dry. Therefore effectiveness on EAW is a very useful tool for cultivation of plants. The velocity of water uptake was influenced positively by clay in uncultivated mixtures. This effect was also found under dry conditions in a culture with Impatiens. The effectiveness 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 to classify clay products. | |
Download Adobe Acrobat Reader (free software to read PDF files) | |
