Phosphorus buffering capacity of substrate clays and its significance for plant cultivation

摘要

Peat is commonly used as the main component of horticultural substrates, but it has a very low buffering capacity for the anionic macronutrient phosphorus (P), which can be increased by the addition of clays. The aim of this study was to characterize the P adsorption capacity of different substrate clays and to evaluate its significance for plant P uptake. Substrate clays were characterized with a single-point batch experiment and adsorption and desorption isotherms. The data were fitted to the Langmuir equation for a calculation of the maximum adsorption capacity. Additionally, the contents of oxalate extractable Fe and Al (Sigma Fe-ox + Al-ox) were determined. The influence of a varying P adsorption capacity of the clays on the P availability to plants in the respective peat-clay substrates and pure peat was investigated in a growth experiment with Impatiens walleriana fertigated with 0, 17, and 35 mgP L-1 solution, respectively.