Soil Carbon Availability Affects Nitrogen Transformation Under Irrigated Lucerne

Dear Editor, Approximately 55％ of the agricultural land in New Zealand is grazed grassland to support the expanding dairy and meat industries. Intensified management practices such as irrigation, nitrogen (N) fertiliser application, and of forage crop provision are increasingly being adopted to meet the growing production demands. Given its ability in fixing N from symbiont rhizobia, thereby reducing the reliance on inorganic N fertilisers, lucerne (alfalfa, Medicago sativa L.) has been promoted as a forage species for dryland systems. Moreover, its deep roots can gain access to water during dry periods (Moot, 2012). Although grazing systems are economically profitable, 14％of national greenhouse gas emissions in New Zealand are accounted for by agriculturally derived nitrous oxide (N2O) emission. Furthermore, intensi-fied management has been linked to nitrate (NO?3 ) leaching (Cameron et al., 2013) and losses of soil carbon (C) (White-head et al., 2018). Accordingly, identifying management practices that can promote reduction in N2O emission whilst maintaining or enhancing soil C has become a priority.