Pluri-energy analysis of livestock systems – A comparison of dairy systems in different territories

Summary

This paper introduces a generic assessment method called pluri-energy analysis. It aims to assess the types of energy used in agricultural systems and their conversion efficiencies. Four types of energy are considered: fossil energy, gross energy contained in the biomass, energy from human and animal labor and solar energy. The method was applied to compare smallholder low-input dairy-production systems, which are common in developing countries, to the high-input systems encountered in OECD countries. The pluri-energy method is useful for analyzing the functioning of agricultural systems by highlighting their modes of energy management. Since most dairy systems in South Mali (SM) are low-input systems, they are primarily based on solar and labor energy types and do not require substantial fossil-energy inputs to produce milk. Farms in Poitou-Charentes (PC) and Bretagne (BR) show intermediate values of fossil-energy use for milk production, similar to that found in the literature for typical European systems. However, fossil-energy use for milk production is higher on PC than BR farms because of a higher proportion of maize silage in the forage area; grazing pastures are more common on BR farms. Farms on Reunion Island (RI) require a relatively large amount of fossil energy to produce milk, mainly because the island context limits the amount of arable land. Consequently, milk production is based on large imports of concentrated feed with a high fossil-energy cost. The method also enables assessment of fossil-energy-use efficiency in order to increase the performance of biological processes in agricultural systems. Comparing the low-input systems represented by SM to the high-input systems represented by RI, PC and BR, an increase in solar-energy conversion, and thus land productivity, was observed due to intensification via increased fossil-energy use. Conversely, though fossil-energy use at the herd level increased milk productivity, its effect on gross-energy conversion by the herd was less evident. Partitioning the total on-farm gross energy produced among animal co-products (milk, meat and manure) highlights the major functions of SM herds, which are managed to produce organic crop fertilizers.