On-farm fertilizing materials in organic horticulture: agronomic performance, energy use and GHG emission evaluation

Anaerobic digestate (AD), a sub-product of cattle manure treatment to produce biogas, could be used for agricultural purposes after co-composting. The aim of this research was to evaluate in organic horticulture the co-composted AD, obtained using two different aerobic stabilization processes (not aerated and aerated composting), by assessing (i) the energy requirements and the GHG emissions of on-farm co-composting; (ii) the agronomic performance of the co-composted AD, compared to a commercial organic (CF) fertilizer, on fennel, tomato and zucchini crops; (iii) the environmental sustainability of the different analyzed systems, through the energy and the carbon footprint analyses. The AD co-composting was a feasible way to valorize organic wastes by producing organic fertilizers. These fertilizers could substitute the CF, leading to similar production capacity, energetic and carbon efficiencies. In particular, despite the greater carbon stocks generated by CF, the carbon efficiency was higher in co-composted AD than CF for both fennel and tomato cultivation systems. The GHG emission analysis for the agricultural operations indicated that CF treatment determined the highest CO(2)emissions. Therefore, an appropriate management of the fertilization strategies could allow reducing the GHG emissions.