9th International Conference LCA of Food San Francisco, USA 8-10 October 2014 A comparative assessment of greenhouse gas emissions in California al- mond, pistachio, and walnut production Elias Marvinney 1,* , Alissa Kendall 2 , Sonja Brodt 3 1 Department of Plant Science, University of California, Davis 2 Department of Civil and Environmental Engineering, University of California, Davis 3 Sustainable Agriculture Research and Education Program, University of California, Davis  Corresponding author. E-mail: emarvinney@ucdavis.edu ABSTRACT A process-based life cycle assessment (LCA) model was constructed for almond, pistachio, and walnut production in California. Agro- chemical inputs, mechanized operations, soil processes, geospatial variation, and biomass accumulation were explicitly modeled based on technical reports, economic cost-and-return studies, field data collection, and grower interviews. Mean annual greenhouse gas (GHG) foot- prints for a typical hectare of orchard, from nursery to hulling/shelling facility gate, were calculated at 4260 kg CO2e ha -1 yr -1 for almond, 3480 kg CO2e ha -1 yr -1 for pistachio, and 4050 CO2e ha -1 yr -1 kg for walnut. These results can be expressed by orchard product (nut kernel) as 1.76 CO2e kg -1 for almond, 0.95 CO2e kg -1 for walnut, and 3.83 CO2e kg -1 for pistachio. Variations in biomass accumulation, yield and orchard lifespan between these crops result in different total life cycle emissions and potential management options for net GHG reduction and credit opportunities under California GHG cap-and-trade legislation. Keywords: perennial cropping systems, orchard, greenhouse gas footprint, almond, walnut, pistachio 1. Introduction Though LCA has been applied to a wide variety of food production systems, orchards have been examined relatively infrequently, with studies focusing on apple (Milà i Canals et al. 2006; Mouron et al. 2006; Page et al. 2011; Hester & Cacho 2003; Alaphilippe et al. 2012), kiwi (Xiloyannis et al. 2011), and citrus (Coltro et al. 2009; Mordini et al. 2009; Beccali et al. 2009; Beccali et al. 2010). Walnut production has also been examined although primarily in the context of timber production (Cambria & Pierangeli 2011). Many of these studies examine a single year for a production system, and thus do not consider the entire orchard life cycle, which includes orchard establishment, tree growth, and eventual removal (Bessou et al. 2012). Also, these studies generally do not consistently address the flow of carbon and nitrogen through the orchard and the woody biomass generated from orchard systems. This study characterizes the greenhouse gas impacts of typical almond, walnut, and pistachio orchard production systems in the U.S. state of California using a comprehensive process-based life cycle assessment model that specifically accounts for carbon and nitrogen flow in biomass accumulation and fertilizer application. These highly industrialized agro-ecosystems are of great economic and environmental importance, occupying more than 500,000 ha of California agricultural land and yielding more than 83% of world almond production, 46% of walnut production, and 37% of pistachio production (USDA Office of Global Analysis 2013). Commercial orchards in California’s Central Valley demand significant agrochemical, water, and fuel inputs throughout their productive lifespans (Beede et al. 2008; Connell et al. 2012; Grant et al. 2007; Micke & Kester 1997). Irrigation accesses groundwater via on-site pumps and surface water via the California Aqueduct system and other surface water transport infrastructure, entailing significant energy inputs for onsite and upstream pumping. Due to its relatively high input intensity, the California nut industry is responsible for significant emissions of greenhouse gases (GHGs) and other atmospheric pollutants. However, perennial cropping systems such as almond, walnut and pistachio orchards have the potential to sequester carbon in soils and biomass as a consequence of their long life cycles and high biomass production (Kroodsma & Field 2006). In California, much orchard waste biomass is used to produce electricity at regional electricity generation plants, widely distributed in California (Wallace & Leland 2007). The potential for sequestration versus emissions offset through use of waste biomass as an energy feedstock is dependent on management characteristics, orchard lifespan, and other factors. We examined the effects of various biomass fates on net orchard GHG and energy consumption footprints, accounting for potential GHG credits from biomass- based energy production and temporary storage in standing biomass under both a business-as-usual scenario based