Changes in Irrigation Practices likely Mitigate Nitrous Oxide Emissions from California Cropland

Crop production with intensive nitrogen (N) application is an important source of atmospheric nitrous oxide (N2O). However, there remains large uncertainty in quantifying cropland N2O emissions and their mitigation potential, especially in regions where cropping systems and farming management practices are highly diverse. Because N2O production in soils is tightly linked to N application rate and type, soil moisture, and oxygen status, improving irrigation is a potential strategy for N2O mitigation. We applied a process-based biogeochemical model, DeNitrification-DeComposition, to evaluate the influence of irrigation management on N2O emissions from California cropland, where cropping systems are extremely diverse and irrigation management has changed rapidly. We constructed a database containing data on weather, crop types and areas, soil properties, and farming management practices and predicted N2O emissions from California cropland under four typical irrigation methods (surface gravity, sprinkler, drip, and subsurface drip). We also assessed impact on N2O emissions of large-scale changes in irrigation management experienced in California from 2001 to 2010 that was driven by the demand of reducing water use in agriculture. Simulations under different irrigation methods indicated that drip and subsurface drip irrigation reduced N2O emissions by 55% and 67%, respectively, compared to surface gravity irrigation. We estimated baseline N2O emissions from California cropland as 7.94x10(3) metric ton (MT)N/year under actual irrigation management in 2002. The large-scale changes in irrigation management likely reduced N2O emissions by 7.3% from 2001 to 2010. This study showed the potential for reducing N2O emissions by using low-volume irrigation.