Nitrogen, phosphorus and potassium accounts in the Brazilian livestock agro-industrial system

摘要

We estimated the inventories of nitrogen (N), phosphorus (P) and potassium (K) in the Brazilian livestock agro-industrial system (BLAS) using a dynamic substance flow accounting approach based on the industrial metabolism concept. Our main objective was to derive indicators of sustainability: evolution of total NPK mass involved in the system, dependence on international exchanges, and relative use efficiency of NPK in livestock farms. We considered cattle, poultry and pigs. Annual accounts were estimated for 1992-2013. In methodological terms, we innovate by proposing a greater disaggregation of the productive chain, the establishment of herd dynamics as a central driver of the accounting approach and the interconnection between consecutive annual flows. The total mass of NPK involved increased significantly as well as the generation of waste and emissions to the environment. The exchanges between Brazil and the world also increased considerably. NPK use efficiencies increased for cattle and poultry. In pig production, P use efficiency rose. Our general message is that the increased efficiency in animal production provided by better livestock farm management seems to have little positive environmental effect if the activity is not considered as part of a larger circular economy (i.e. if there is no effort to reuse resources, especially non-renewable ones, such as P and K, and to reduce those that cause damage to the environment, as compounds derived from N and P), and if the growth rate of production in absolute termsto meet national and international demandsis proportionally higher than the specific technological gains for each livestock segment.