Creating a “family tree” on fertilizer inventory use in life cycle assessment of oil palm: visualization of earlier studies and its implications

Abstract

This review develops and applies a visualization method for understanding how chemical fertilizer inventory data, including greenhouse gas (GHG) emission factors and fossil fuel energy requirements, have been used in previous life cycle assessment (LCA) studies of oil palm and discusses how inconsistencies detected in previous studies can be decreased. As a visualization method for previous publications, a “family tree” was constructed using a directed graph (digraph) representation. Each node in the graph indicates an article, and an arrow from the source to a destination illustrates that the former article was cited in the latter article as a source of the background inventories. Bibliographical data extracted from the Web of Science were used for constructing the genealogy of fertilizer inventory use. Several groups (“families”) were identified through creation of the family tree. The most noticeable group was formed around the LCA database ecoinvent, which has the maximum number of out-flows (arrows from the node), suggesting a considerable influence of ecoinvent in the LCA of oil palm. In addition, temporal and spatial inconsistencies (outdated technological assumptions and substitutional use of European data) were detected in the visualization; therefore, the severity of the inconsistencies was discussed through an analysis of scenario uncertainty in nitrogen fertilizer production. The importance of devoting attention to fertilizer production technologies rather than simply to regional differences was clarified. This study demonstrates the usefulness of applying visualization methods in understanding the overall configuration of earlier studies. It is expected that the visualization and its implications constitute a way forward to good practices in inventory analysis.