Rice hulls and peat replacement in substrates for vegetable transplant production

The choice of substrates for vegetable and ornamental plant production is an aspect of basic importance. Because of its overall appropriate characteristics, peat is the main substrate used in the nurseries. However, because of peat high water retention, other substrate components are sometimes added in order to improve its hydraulic properties. Because of the increasing price of peat and environmental concerns related with its extraction, researchers have been searching for materials that can replace it, at least partially, in the substrates. In this perspective, rice hulls appear to be potentially interesting because they are a cheap organic by-product and because of their capacity to increase porosity in growing media mixes. In this research, substrates containing 0, 25, 50, 75 and 100% of rice hulls in substitution of peat moss were chemically characterized. Whenever possible, the analytical CEN methods for substrates were used. Then, in order to evaluate the suitability of these mixes as substrates for transplant production, experiments were carried out on one cultivar of tomato and pepper and two cultivars of chicory. Plants were grown in a greenhouse with daily fertigation. The chemical profile showed that all the substrates could be employed for cultivations in nursery as features as pH, electrical conductivity and organic carbon are compatible with literature recommendations. Some concerns can rise from the unbalanced nutrients content. Regarding the agronomic experiment, different responses were observed among species. Pepper and tomato were negatively influenced by increased % of rice hulls in the substrates and rice hulls then not suitable for peat replacement in substrate with these plants. Differently, despite varietal differences, chicory appeared to be better suited to the cultivation on substrates containing rice hull. Rice hulls appeared to be suitable (not exceeding 50% on a volume basis though) as component of growing media formulation but the requirements of the species and the cultivars need to be considered.