Print PageNitrous oxide (N2O) is a major greenhouse gas (GHG), with a global warming potential (GWP) 298 times higher than carbon dioxide (CO2). Largely due to the application of synthetic nitrogen (N) fertilizers, agricultural cultivation of soils is the prominent source of anthropogenic N2O emissions worldwide. Hence, reducing N2O emission from cropping systems should contribute substantially to the mitigation of global warming. However, to date, few farming strategies have been developed to mitigate N2O emissions in large part because of lack of knowledge of how practices influence emissions. For woody perennial cropping systems, even fewer studies have investigated annual soil N2O emissions, let alone completed a regional scale assessment of baseline emissions.
Here we present an evaluation of statewide N2O emissions estimates from a woody perennial cropping system - California almond orchards - which produces 100% of the US and over 80% of the world almond supply. IPCC three-tier approach was applied. Our Tier 2 method used crop- and irrigation type-specific N2O emission factors (EF’s), and also disaggregated the ecosystem N input by region and irrigation type; our Tier 3 method adopted DeNitrification-DeComposition (DNDC), a process-based biogeochemical model. The compiled data set includes information of climate, soil, tree growth, trace gas emissions, field management practices and statewide orchards distribution.
Results/Conclusions
Our results indicated that climatic factors and management practice played a substantial role in N2O emissions from almond orchards. According to this analysis, the Southern San Joaquin Valley generates approximately 60% of the annual statewide N2O emissions for this crop, followed by the Northern San Joaquin Valley at about 30%, leaving only 10% for the Northern most extent of production in the Sacramento valley. Temperature and precipitation were the main drivers for this geographical difference in N2O emissions. Moreover, orchards using micro-sprinklers generated over half of the annual statewide N2O emissions, followed by the conventional drip irrigation systems at 40%, leaving less than 10% for the flood irrigation systems.
Because we applied condition-specific EF’s for IPCC Tier 2 calculation, it gave a much less, and more accurate, N2O emission estimate than Tier 1 method, although it demands on more detailed data to undertake the estimation. Tier 3 DNDC modeling is still in progress and is expected to provide a better estimate than the other two approaches provided that it is successfully calibrated for California almond orchards.
