Materia orgánica carbonizada como componente de sustrato para el cultivo en contenedor

Six mixes of carbonized organic matter (COM) and coir fibre (CF) were assayed as growing media for potted vegetable (tomato and cress), ornamental (petunia and marigold) and shrub (mastic and myrtle) cultivation. Two COM were used: 1) HTC = biochar from forest and garden wastes produced by hydrothermal carbonization; and 2) Cisco = partially burned olive mill and stone waste. The seven substrates were HTC:FC and Cisco:FC mixes at 50:50, 25:75, 10:90 and 0:100 (CF control) proportions by volume. The physical and physico-chemical properties of the raw materials and the substrates were determined. Whilst the raw materials showed inadequate physical properties for their use as only components in growing media (low air content and too high water content for HTC and the opposite for Cisco), the mixes with CF showed adequate properties in the case of HTC although the air content was still too high in the case of Cisco mixes. Both COM were alkaline (pH for HTC = 8.6; pH for Cisco = 9.7). Whilst mixing HTC with CF (pH = 6.0) decreased substrate pH, mixing Cisco with CF decreased only slightly the original Cisco pH indicating that Cisco had a strong buffer capacity. Electrical conductivity was acceptable for HTC (136 mS m-1) but markedly high for Cisco (918 mS m-1) and decreased significantly in the mixes as the proportion of CF increased. As expected, the germination bioassays carried out with lettuce and cress seeds indicated that Cisco was potentially phytotoxic whilst HTC was not. In the growing assays HTC at higher proportions (25% to 50%) caused a decrease in plant growth, more remarkably in the vegetables and shrubs than in the ornamental specimens. This effect was probably due to nitrogen immobilization in the medium. The plant response to Cisco differed among species in relation to their tolerance to salinity. Petunia, marigold and myrtle did not survive in media containing 25% or 50% Cisco. For cress and mastic growth decrease was the more remarkable the more Cisco was present in the substrate. Tomato grew well in substrates containing up to 25% of Cisco but growth decreased in Cisco at 50%.