Relationships between growing media fertility, percolate composition and fertigation strategy in peat-substitute substrates used for growing ornamental shrubs

Abstract

The composition of root-zone solution of container grown Viburnum tinus L. ‘Eve Price’, Nerium oleander L. ‘Émile Shaut’ and Euonymus japonicus Thunb. were studied in two different localities (France and Spain). The growing media assayed were binary mixtures prepared with Finnish sphagnum peat, the following peat-substitutes: cattle manure compost, forest waste compost, pine bark compost, yard compost and raw coir. Perlite was used as inorganic amendment in one mixture. The composition of the root-zone solution was monitored by the induced percolate (IP) method and the applied nutrient solution (NS) was modulated by dilution in the experiments carried out in the French location or by increasing the volume applied to manage the electrical conductivity in the experiments conducted in the Spanish location. Modulation of the NS–water ratio resulted in a linear relation of percolate composition to NS composition. That relation was not present when the NS was not diluted. The results indicate that a steady-state nutrient level in the root zone can be achieved when a modulated and relatively low concentration of NS is applied by fertigation. Release of nutrients, especially nitrates, occurs during growing period. The biostability of the substrates and the initial availability of phosphorus and potassium determine the composition of the leachates. The results proved that the IP method can be used to monitor nutrient levels in the root zone and its use can enhance the nutrient-use efficiency in commercial nurseries.