GROWING PEPPER ON ECOLOGICALLY SOUND SUBSTRATES

The two main environmental problems of substrate culture are on the one hand the cumulating waste caused bij the substrate mats and on the other hand the effluence of the overdosed nutrient solution from the substrate mats into the soil, resulting in eutrophication of the soil and the ground water.

These problems were tackled by the rather laborious procedure of recycling the rockwool and glasswool mats and by recirculating the drained solution.

Since 1984 we have been examining alternative solutions for the problems related to the substrate, one of which was the inert recycled polyurethane-ether foam (PUR) which has now been used in the culture for 10 years while being treated with steam every year. Because of its inert properties the substrate does not interfere with the administered nutrient solution and its recirculation can be limited to adjustment in function of the consumption by the plants.

In 1988 we started to study the possibilities of growing vegetables on various one-year organic substrates including the fir firbre substrate HORTIFIBRE. Here we noticed both microbiological and chemical reactions of the substrate with the administered nutrient solution. Thus EC, NO₃, P, Ca, and the trace elements Fe, Mn, Cu, and B were strongly reduced in the nutrient solution in the mats, whereas pH, K, Cl, SO₄ and HCO₃ were increased.

As long as we cannot control these reactions, technical interventions in the growing process will be necessary, including adjustment of the trickling frequency, temporary increase of the EC and NO₃ during the first 10 weeks of root taking. For the recirculation of the drainwater this implies, of course, a higher frequency of analyses.