Events & Media


A PhD Dissertation Defense

"Life-cycle assessment of agricultural systems with an emphasis on technology change,
marginal yield, and regional characteristics"

Yi Yang
PhD Candidate
Bren School

Monday, June 1, 2015
9:00 a.m.
Bren Hall Pine Room (3526)

Faculty Advisor: Sangwon Suh
Committee Members: Arturo Keller, Roland Geyer, Reinout Heijings

Driven by rapid adoption of, and sustained improvements in, genetic technologies and agronomic management practices, agricultural productivity has experienced a substantial growth worldwide since the start of the Green Revolution in the 1960s. This growth has enabled us to escape from the well-known Malthusian Trap. With our success, however, comes what is also known as “the other inconvenient truth”: modern agriculture has become one of the major drivers of global environmental change and is pushing the earth system beyond its safe operating boundaries. Further, even more challenges lie ahead of us as we must feed a growing number of mouths while increasingly diverting food to fueling our cars (i.e., biofuels).

In this talk, I will present three chapters related to agricultural systems in the United States. The first two chapters focus on the environmental consequences of corn expansion driven partly by biofuels policies aimed at boosting ethanol production. In the first chapter, I build life-cycle inventories that reflect the regional heterogeneity in management practices and emissions in order to evaluate the environmental implications of land use change from cotton to corn. In the second chapter, I quantify the carbon payback time associated with growing corn for ethanol on marginal land. The analysis takes into account two key elements — marginal yield and technological advances — that were neglected in previous studies. The third chapter focuses on the environmental impacts of major crops in the United States (corn, soybean, cotton, and wheat) and how these impacts may have changed in the past decade. In particular, I evaluate whether the adoption of genetically modified organisms (GMO), such as herbicide-resistant corn and cotton, has reduced the ecological toxicity impact of those crops.


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