Energy analysis of Jatropha curcas under irrigation and rainfed at the Southeast Brazilian humid subtropical

Abstract

Jatropha (Jatropha curcas L.) is an oil seed species, adaptive to different climate and soil conditions. It is known due to its high-oil-content seed, being an option for biodiesel production and presenting competitive yields under irrigated condition. This study was developed in an experimental area located in a humid subtropical region of Brazil and the objective was to evaluate Jatropha’s energy balance under irrigation and rainfed condition during the first four years of its cycle. First, the material flows were determined, which supported the calculation of, energy input and output flows were obtained. These were used to determine the energy indices: energy balance (EB), and energy return on investment (EROI) for both conditions. Fertilizers had the highest contribution on energy input (42.58 GJ ha^-1, 37.7% in irrigated area and 45.9% in rainfed area) followed by fuel consumption (32.96 GJ ha^-1, 29.8% in irrigated area and 35.5% in rainfed area). Total energy input for the first four years in the irrigated area was 114.84 GJ ha^-1 (which 19.22% was due to the irrigation) and 92.8 GJ ha^-1 in the rainfed area. The output energy flows were 73.78 and 47.88 GJ ha^-1 for irrigated and rainfed areas, respectively. In this study, a negative value for EB and unviable EROI (< 1) were obtained. However, EROI showed evolution when evaluated year-by-year, reaching values above 1 in the 4^th year for both systems, as expected from perennial crops. Considering just the period evaluated, this crop was not sustainable for energy production, but this is a long lifespan crop and for the following years it is expected yield levels like the last one and values positive of energy balance.