Potential for bioenergy generation and nutrient recycling in horticultural crop production systems in New Zealand

Renewable energy can be produced from a number of sources, including plant biomass. One of the most efficient technologies to generate bioenergy from plant biomass is on-farm anaerobic digestion (AD) producing biogas. Biogas can be used as an equal substitute to natural gas for industrial, commercial and residential use, and/or can be converted to electricity, heat or vehicle fuel using established technologies. Using purified biogas for transport is a highly effective greenhouse gas mitigation strategy. Various organic feed stocks can be converted into biogas: we have identified a large variety of purpose-grown bioenergy crop species (such as Jerusalem artichoke, forage sorghum, whole triticale) under New Zealand conditions, but feedstocks can also include farm and orchard waste streams (reject fruit, clippings, thinning and so on), groundcover biomass and other locally sourced organic municipal and industrial bio-waste as well. A novel biofuel cropping system was developed based on AD technology. It makes full use of the nutrients in the digestate with a unique closed-loop nutrient supply feature that conserves nutrients in the feedstock and recycles them back to the farm and orchard as bio-fertiliser. This eliminates the need for external fertilizer. This paper will explore the considerable potential for bioenergy generation and nutrient recycling in horticultural production systems in New Zealand.