AN EXPLANATION OF LISIANTHUS AND LETTUCE BEHAVIOR: MICROMORPHOLOGICAL FEATURES AND PHYSICAL PROPERTIES OF DIFFERENT GROWING MEDIA

Abstract

The micromorphological features and physical properties of several materials for growing media were compared with response variables from two greenhouse experiments, so as to determine the limiting and/or promoting factors of plant development. The first greenhouse experiment used lisianthus (Eustoma grandiflorum) and included organic (coconut fiber, Cf; and peat moss, Pm) and inorganic (pumice, P; and Perlite, Pe) materials, with varying particle size (1-2 and 2-3.36 mm), using the same organic:inorganic ratio (60:40 v/v), and using bulk material as blank tests. The second experiment used lettuce (Lactuca sativa), with one particle size, but with varying ratios (100 Cf, 75:25, 50:50, 25:75, 100 P v/v) of Cf:P mixtures. Thin sections were prepared from the mixtures of both experiments, to describe sorted degree, distribution patterns and porosity (macro and micro). Furthermore, the water release curve was determined (air capacity, AC; easily available water, EAW) for each treatment in both experiments. In lisianthus, it was observed that using a single particle size Cf:P (1-2 or 2-3.36 mm) renders higher yields, because of the loose packing particles, well sorted material and macro- and micropores, resulting in sufficient EAW (36%) and AC (33%). In contrast, the worst effects were in bulk peat moss, because of the poor sorted, close packing particles, and high micropores content (95%) resulting in a low AC (12%) and EAW (49%), overall. Regarding lettuce, the best ratio resulted in Cf:P 75:25 v/v compared to other ratios, because particles presented a banded distribution pattern generating an heterogeneous porous system (vughs, fissures, and simple and compound packing voids). We conclude micromorphology helps to a better understanding of physical properties of mixtures, and to identify which features for growing materials may improve or restrict lisianthus and lettuce development.