Irrigation System, Rather than Nitrogen Fertilizer Application, Affects the Quantities of Functional Genes Related to N2O Production in Potato Cropping

The spatial and temporal distribution of water and nitrogen supply affects soil-borne nitrous oxide (N2O) emissions. In this study, the effects of different irrigation technologies (no irrigation, sprinkler irrigation and drip irrigation) and nitrogen (N) application types (no fertilizer, broadcasted and within irrigation water) on N2O flux rates and the quantities of functional genes involved in the N cycle in potato cropping were investigated over an entire season. The volume of irrigation water affected microbial N2O production, with the highest N2O flux rates found under sprinkler irrigation conditions, followed by drip and no irrigation. Nitrifier denitrification was identified as the potential pre-dominant pathway stimulated by fluctuations in aerobic-anaerobic soil conditions, especially under sprinkler irrigation. Regarding the different N application types, increased N use efficiency under fertigation was expected. However, N2O flux rates were not significantly reduced compared to broadcasted N application under drip irrigation. On average, the N2O fluxes were higher during the first half of the season, which was accompanied by a low N use efficiency of the potato crops. Potato crops mainly require N at later growth stages. Due to the different water and nutrient demand of potatoes, an adjusted application of fertilizer and water based on crop demand could reduce N2O emissions.