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Title: Field-based estimates of global warming potential in bioenergy systems of Hawaii: Crop choice and deficit irrigation

Replacing fossil fuel with biofuel is environmentally viable from a climate change perspective only if the net greenhouse gas (GHG) footprint of the system is reduced. The effects of replacing annual arable crops with perennial bioenergy feedstocks on net GHG production and soil carbon (C) stock are critical to the system-level balance. Here, we compared GHG flux, crop yield, root biomass, and soil C stock under two potential tropical, perennial grass biofuel feedstocks: conventional sugarcane and ratoon-harvested, zero-tillage napiergrass. Evaluations were conducted at two irrigation levels, 100% of plantation application and at a 50% deficit. Peaks and troughs of GHG emission followed agronomic events such as ratoon harvest of napiergrass and fertilization. Yet, net GHG flux was dominated by carbon dioxide (CO 2), as methane was oxidized and nitrous oxide (N 2O) emission was very low even following fertilization. High N 2O fluxes that frequently negate other greenhouse gas benefits that come from replacing fossil fuels with agronomic forms of bioenergy were mitigated by efficient water and fertilizer management, including direct injection of fertilizer into buried irrigation lines. From soil intensively cultivated for a century in sugarcane, soil C stock and root biomass increased rapidly following cultivation in grasses selectedmore » for robust root systems and drought tolerance. The net soil C increase over the two-year crop cycle was three-fold greater than the annualized soil surface CO 2 flux. Furthermore, deficit irrigation reduced yield, but increased soil C accumulation as proportionately more photosynthetic resources were allocated below ground. In the first two years of cultivation napier grass did not increase net greenhouse warming potential (GWP) compared to sugarcane, and has the advantage of multiple ratoon harvests per year and less negative effects of deficit irrigation to yield.« less
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  1. Univ. of Hawaii Manoa, Honolulu, HI (United States)
  2. Texas A&M AgriLife Blackland Research and Extension Center, Temple, TX (United States)
  3. United States Dept. of Agriculture-Agricultural Research Service Grassland Soil and Water Research Lab., Temple, TX (United States)
  4. Hawaii Commercial & Sugar, Puunene, HI (United States)
  5. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
Grant/Contract Number:
Published Article
Journal Name:
Additional Journal Information:
Journal Volume: 12; Journal Issue: 1; Journal ID: ISSN 1932-6203
Public Library of Science
Research Org:
Univ. of Hawaii, Honolulu, HI (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Country of Publication:
United States
09 BIOMASS FUELS; 60 APPLIED LIFE SCIENCES; sugarcane; agricultural irrigation; agricultural soil science; carbon dioxide; fertilizers; grasses; bioenergy feedstock; physical geography
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Alternate Identifier(s):
OSTI ID: 1346035