Reduced Nitrous Oxide Emissions in Tomato Cropping Systems Under Drip Irrigation and Fertigation.

In California, agriculture and forestry account for 8% of the total GHG emissions, of which 50% is accounted for by nitrous oxide (N₂O). Furrow irrigation and high temperatures in the Central Valley, together with conventional fertilization, are ideal for the production of food, but also N₂O. These conditions lead to high current fluxes, but also mean there is great potential to reduce N₂O emissions by optimizing fertilizer use efficiency and irrigation practices. Improving fertilizer use efficiency by better coordination of nitrogen (N) availability and crop demand can reduce fertilizer costs and N loss. Smaller, more frequent fertilizer applications increase the synchrony between available soil N and crop N uptake and result in less N loss to the atmosphere. Fertigation allows for more control over how much N is being added and results in lower levels of soil mineral N throughout the season. In our study, we determined how management practices, such as fertilization, irrigation, tillage and harvest, affect direct N₂O emissions in typical tomato cropping systems under two contrasting irrigation managements and their associated fertilizer application method, i.e. furrow irrigation and knife injection versus drip irrigation and fertigation. Across two tomato-growing seasons, this project has demonstrated that shifts in fertilizer and irrigation water management directly effect GHG emissions. Our preliminary data indicates that seasonal N₂O fluxes are three times lower under drip versus furrow irrigation. Environmental parameters of soil mineral N, dissolved organic carbon and soil moisture also varied between the two systems. Used as an index of substrate availability, soil ammonium and nitrate exposure were significantly lower in the drip system. These changes in irrigation water and fertilizer management also increased crop yield in the drip system, highlighting the potential for improved fertilizer use efficiency through the use of fertigation techniques.