253-5 Assessing GHG In California Cropping Systems to Address Climate Change Regulation.

See more from this Division: S04 Soil Fertility & Plant Nutrition
See more from this Session: Symposium--Global Importance and Progress of Reducing Anthropogenic Emissions of Nitrous Oxide From Cropping Systems: I
Tuesday, October 18, 2011: 9:45 AM
Henry Gonzalez Convention Center, Room 211
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William Horwath, University of California-Davis, Davis, CA, Johan Six, University of California, Davis, Davis, CA and Martin Burger, Land, Air and Water Resources, University of California Davis, Davis, CA

The California Global Warming Solutions Act of 2006 (AB 32) mandates that the State develop comprehensive strategies to reduce greenhouse gas (GHG) emissions. Nitrous oxide (N2O) is a potent GHG emitted from intensively managed agro-ecosystems as a result of fertilizer N applications and leguminous cover crops. More than half the GHG emissions from agriculture are attributed to N2O production. Currently, there is a lack of baseline N2O emission data for most cropping systems in the State, and the relationship between N fertilization levels and N2O emission is not well understood at the farming field level. The paucity of N2O emission data has hampered biogeochemical modeling, which requires robust data of N2O emissions to calibrate and validate the models' predictive capability. The objectives of this project are to (1) measure annual N2O emissions for major California crops (vineyards, almonds, tomato, wheat, alfalfa, lettuce, rice) under typical management practices,  (2) determine N2O emission factors for these crop systems at several fertilizer N addition rates, (3) to characterize the effects of environmental factors on the temporal profile of N2O emissions, and (4) to determine NO and NO2 fluxes in these crop systems. Annual emissions in processing tomato systems were 2.5 kg N2O-N/ha with standard fertilization (160 kg N / ha), similar to background emissions and those from a drip irrigated system, and 4.0 and 5.8 kg N2O-N /ha y-1 at fertilizer rates of 225 and 300 kg N /ha.  About half the annual emissions were emitted within 3 d after the first seasonal rainfall event. In other tomato studies, estimated losses of fertilizer N as N2O were 0.38 0.03 kg/ha y-1 in a drip irrigated system and 1.79 0.21 kg/ha y-1 in furrow irrigated system, which was equivalent to 0.19% and 0.73% of the added fertilizer, respectively. In a lettuce production system, annual N2O emissions were about 1 kg N2O-N /ha y-1. In a wheat system, emissions during the growing season in the rainy season were between 1.0 and 1.5 kg N2O-N, with highest emissions occurring after anhydrous ammonium applications. Annual emissions in a vineyard totaled 2.05 kg N2O-N/ha in the first year, when a leguminous cover crop was planted in the tractor row, while emissions reached only 0.17 kg N2O-N/ha in the second year when the tractor rows were fallow. All emissions were generally lower than 1% of the applied N. 

See more from this Division: S04 Soil Fertility & Plant Nutrition
See more from this Session: Symposium--Global Importance and Progress of Reducing Anthropogenic Emissions of Nitrous Oxide From Cropping Systems: I