Emergy efficiency of land-use systems in the brazilian semi-arid region

Abstract

Emergy analysis is used to evaluate agricultural management systems in order to diagnose their efficiency in using economic and natural resources. In this study, emergy analysis was used to evaluate an agroforestry production model and compare it to the traditional production model used in the semi-arid region of the northeast of Brazil. The agroforestry model comprises three subsystems: agrosilvopastoral (ASP), silvopastoral (SP) and preserved caatinga (CAT). For the traditional model, three subsystems were evaluated: an area under cultivation (AC); an area lying fallow for six years (F6); and an area fallow for nine years (F9). For each model and its respective subsystems, all input and output energy flows were identified. These flows were later quantified and transformed into emergy using their respective transformity values. The emergy performance of the systems and subsystems was evaluated by the indices: transformity (Tr), emergy investment ratio (EIR), emergy yield ratio (EYR), emergy renewability index (%R), environmental load rate (ELR), and emergy sustainability index (ESI). It was found that the agroforestry model uses a lower quantity (-13%) of natural resources than the traditional model. However, the agroforestry model uses 64% more resources from the economy than used in AC. More than 55% of the emergy required in the ASP and AC subsystems comes from services. The subsystems that required a greater amount of emergy and achieved less efficiency were SP in the agroforestry model and AG in the traditional model. Values for Tr were lower in CAT (2.6E+03) and higher in AC (2.4E+05). The ELR was low in all areas, ranging from 0.00 in F6 and F9 to 0.58 in SP. Values for %R ranged from 60.76 in AC to 99.98 in F6. The agroforestry system displayed better emergy performance due to a lower values for Tr and ELR, and greater renewability.