Biochar Improves the Properties of Poultry Manure Compost as Growing Media for Rosemary Production

Compost represents a sustainable alternative for peat (P) replacement in soilless plant cultivation, but its use can be limited by several inadequate physical and physicochemical properties. Biochar can alleviate some of the limitations of compost for its use as growth media by improving the physical properties, decreasing salinity and making the phytotoxic compounds unavailable for plants. We studied the physical and physicochemical properties of holm oak biochar (B), poultry manure compost (PMC), poultry manure composted with biochar (PMBC), a commercial peat (P) and multiple combinations of these materials as growth media, and their effect on the rooting and growth of rosemary. PMBC and PMC showed similar physical and physicochemical properties as growing media, and they both were phytotoxic when used in a rate above 50% (by volume) in the growing medium. However, when used at proportion of 25%, PMBC was less phytotoxic than PMC and enhanced the percentage of rosemary cutting rooting. The incorporation of B in the growing medium instead of P (either at 50% or 75% in volume) increased the stability of the growing media and the percentage of rooted cuttings, but it did not affect plant growth significantly. Our results demonstrate the potential of substituting peat by a combination of poultry manure compost and biochar for the formulation of growth media