Life cycle analysis of greenhouse gas emissions from organic and conventional food production systems, with and without bio-energy options

Abstract

The Nafferton Factorial Systems Comparison experiments were begun in 2003 to provide data on the production and quality effects of a whole spectrum of different crop production systems ranging from fully conventional to fully organic. In this paper, the crop production data for the first 4 years of the experiments have been used to conduct a life cycle analysis of the greenhouse gas (GHG) emissions from organic and conventional production systems. Actual yield and field activity data from two of the treatments in the experiments (a stocked organic system and a stockless conventional system) were used to determine the GHG emissions per hectare and per MJ of human food energy produced, using both the farm gate and wider society as system boundaries. Emissions from these two baseline scenarios were compared with six other modelled scenarios: conventional stocked system, a stockless system where all crop residues were incorporated into the soil, two stocked systems where manure was used for biogas production, and two stockless systems where all crop residues were removed from the field and used for bio-energy production. Changing the system boundary from the farm gate to wider society did not substantially alter the GHG emissions per hectare of land when organic production methods were used; however, in conventional systems, which rely on more off-farm inputs, emissions were much greater per hectare when societal boundaries were used. Incorporating on-farm bioenergy production into the system allowed GHG emissions to be offset by energy generation. In the case of the organic system that included pyrolysis of crop residues, net GHG emissions were negative, indicating that energy offsets and sequestration of C in biochar can completely offset emissions of GHG from food production. The analysis demonstrates the importance of considering system boundaries and the end use of all agricultural products when conducting life cycle analyses of food production systems.