Energy consumption and carbon footprints of New Zealand dairy systems: Comparison of pastoral and barn dairy farming systems : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

Abstract

Over the last years, New Zealand dairy farming has expanded both in dairying area and milk production and became more intensive in terms of energy inputs. The usage of higher energy inputs are responsible for significant direct and indirect fossil energy consumption, which produces carbon dioxide (CO₂) emissions both on-farm through consumption of fossil fuels in machinery and off-farm during the production of fertilizers and imported feed supplements inputs. The aim of this research study was to estimate and compare energy consumption, efficiency and related carbon footprints of New Zealand pastoral (PDFs) and barn dairy farming systems (BDFs). The estimation of energy use and associated carbon emissions (CO₂) will help to identify an energy and emission efficient dairy farming system for the future of the New Zealand dairy industry. Accordingly, the energy efficiency of both dairy systems was evaluated based on the Data Envelopment Analysis (DEA) approach. The study was conducted on 50 dairy farms including 43 pastoral and 7 barns, in Canterbury, New Zealand. Canterbury represents 16% of the total dairy land and comprises 19% of total dairy cows of New Zealand. In this study, energy consumption was defined as energy involved to produce the milk until it leaves the farm gate. The data were collected through a survey questionnaire for the dairy season 2016-17. The energy inputs considered in this study are those involved in on-farm milk production excluding post-processing components. On average, the energy consumption of pastoral (PDFs) and barn (BDFs) dairy systems was estimated as 50538 MJ ha⁻¹ and 55833 MJ ha⁻¹ respectively. In the total energy consumption, electricity (35.5%) and fertilizer (29.9%) were the main energy inputs in PDFs, while in BDFs, electricity (34.8%) and imported feed supplement (24.1%) were the leading energy inputs. The difference in total energy consumption was 5295 MJ ha⁻¹ indicating that pastoral (PDFs) systems used 9.5% less energy compared to barn dairy farming systems (BDFs). Energy related total annual carbon footprints (CO2) of pastoral (PDFs) and barn (BDFs) dairy systems were equivalent to 2857 kgCO₂ ha⁻¹ and 3379 kgCO₂ ha⁻¹ respectively. In terms of individual energy input contribution to total carbon footprints, machinery (27%) and fertilizer (25%) were the major carbon sources in PDFs, while in BDFs, imported feed supplements (30%) and machinery (24%) were the dominant sources of carbon emissions. From a system comparative perspective, pastoral (PDFs) system have 15% lower carbon footprints than the barn dairy system (BDFs) with total difference of 522 kgCO₂ ha⁻¹. Based on the Data Envelopment Analysis (DEA) approach, the energy efficiency results highlighted the average technical, pure technical and scale efficiencies of pastoral (PDFs) as 0.84, 0.90, 0.93 respectively and for barn dairy systems (BDFs) as 0.78, 0.84, 0.92 respectively, indicating that energy efficiency is slightly better in the PDFs systems compared to BDFs. Further, this study suggested energy auditing and usage of more renewable energy sources for on-farm energy efficiency improvement in both dairy systems.