Impact of irrigation and nitrogen fertilization on the energy balance and energy return on investment of Jatropha production

Abstract

The aim of this research was to perform the energy analysis of Jatropha in two water management (full irrigation and rainfed) and four levels of nitrogen fertilization: "150% (N150)", "100% (N100)", "50% (N50)", and "0% (N0)" of the fertilization recommendation for the crop. The study was developed in the experimental field area located at Piracicaba/SP, Brazil, during the third growing season of Jatropha. Material and energy flow, energy balance (EB), and the energy return on investment (EROI) were determined for all water and nitrogen levels. The component that most contributed as energy input were fuels for all conditions (17.71 GJ ha-1). Among all the treatments, the highest energy incorporation (37.48 GJ ha-1) was observed in the N150 under irrigation. The increase for nitrogen applied, along with the irrigation usage, resulted in higher fruit yield and consequently input energy, despite the need for a greater energy investment. Without counting the residues in the analysis, only the N150 under irrigation was energetically efficient, presenting EROI of 1.04. Considering the residues, "N150" and "N100" with irrigation presented EROI of "1.15" and "1.06", respectively. Irrigation promoted an increase of "52", "63", "34" and "203%" in EROI for fertilization levels "N150", "N100", "N50", and "N0", respectively.