ACCUMULATION OF NUTRIENTS IN EXPANDED CLAY USED FOR INDOOR PLANTINGS

Specimens of expanded clay material were sampled in three horizontal layers from containers with indoor plantings grown under different fertilization regimes for 21 months.
From the analysis of ground and unground material using different extraction solutions and varying shaking times the following results can be summarized:

The accumulation of nitrogen, phosphorus and potassium in expanded clay rises absolutely with increasing fertilization levels.
The relative recovery of the fertilized nutrients reaches from about 15 (N) to nearly 30 (P,K) %.

The nutrients can diffuse into the clay granules and can be released again.

Nitrogen and potassium remain water soluble.
Consequently both nutrients move to a great extent up to the top layer by capillary action.

Phosphorus accumulates as compounds of lower solubility.
Therefore, phosphorus remains mainly in the lower layer.

From the results it can be concluded that expanded clay is able to produce a quite considerable buffer effect.
For this reason the usual amount of water soluble fertilizers applied to indoor plantings can be raised.
This means that water soluble fertilizers are also applicable in the case of longer fertilization intervals instead of slow release fertilizers on an ion exchange basis.

International Symposium Growing Media and Plant Nutrition in Horticulture

E. Meinken

buffer effect, extraction solution, grinding, shaking time, horizontal layer, recovery

https://doi.org/10.17660/ActaHortic.1997.450.38