Evaluation of zeolite as a component in organic growing substrates for tomato transplant production

Zeolite in substrates for growing plants has been shown to reduce nutrient leaching and to increase water retention. Zeolite was incorporated in organic growing substrates to evaluate the effects of this mineral on the growth of tomato transplants. Initially, 25 substrates were evaluated and the most promising were chosen for further investigation. In a second experiment, tomato (Lycopersicon esculentum ‘Matrix F1’) seedlings, at two to three leaves stage, were transplanted into six organic growing substrates. Three of these substrates had zeolite incorporated at 7% (by volume) and in the other three substrates zeolite was replaced with perlite and vermiculite at 5 and 2% respectively (by volume). Tomato seedlings were harvested at week five (first harvest) and week six (second harvest). At both harvests no significant differences in stem diameter, stem height and leaf area were found. However, shoot and root dry weights of seedlings grown in one of the three substrates containing zeolite were significantly lower (α=0.05) than those grown in its non-zeolite counterpart. At the first harvest shoots and roots from the substrate with zeolite weighed 31 and 29% less respectively than shoots and roots from the non-zeolite substrate and 26 and 28% less respectively at the second harvest. Results suggested that zeolite in organic growing substrates for tomato transplant production does not provide benefits. Although zeolite minerals could potentially increase the pH and nutrient buffering capacity of growing substrates, a low incorporation rate would limit this effect. It is not economically feasible to include zeolite at >7% due to its high bulk density and consequently high shipping cost. Therefore zeolite at ≥7% (v/v) inclusion rate is not recommended for organic growing substrates used for producing tomato transplants.