Spatial characterization of reactive N flows in the agro-food system of a semiarid Mediterranean region

Intensive use of nitrogen (N) within the agro-food system leads to significant N losses to the environment with severe associated environmental impacts. The main drivers are the excessive N fertilization of crops and the increasing production of animal manures fuelled by feed import and concentrated in some regions worldwide. An effective characterization of N budgets in regional agro-food systems, highlighting hotspots of reactive N (Nr) release, is key for the proper design of effective Nr abatement strategies. With the present work we aimed to characterize the main N flows between the key compartments of the agro-food system of one the most relevant agricultural areas in Southern EU, the Murcia Region (Spain) by means of a spatialization the GRAFS approach). This approach allowed to identify and spatialize hotspots where action is urgent. Additionally, several Nr abatement scenarios were assessed in an integrated way (i.e. considering impacts on different pathways of N loss and crop yields and pollution swapping. High N surplus were found in several areas thus enhancing the risk of Nr losses in the form of N2O and NH3 to the atmosphere and leached NO3- to water bodies. The most intensive cropping systems namely outdoor and indoor horticultural crops, citrus and other irrigated orchards concentrated the impacts. The impacts are associated with a large disconnection between crop and livestock systems, which involves the entry of a significant amount of nitrogen in the form of feed, that is transformed into manures in excess with respect to crops. Despite this significant fertilizer source, an excessive use of synthetic N fertilizers in addition to high irrigation triggers soil processes controlling the release of Nr. Agronomic and technological NH3 mitigation techniques were also evaluated. They include the incorporation of organic fertilization, the use of urease inhibitors and the avoidance of urea fertilization. These NH3 abatement measures could have two possible agro-environmental side-effects. On one hand, the potential of increasing crop yields through more Nr available in soil, and, on the other hand, adverse environmental impacts linked to potential losses of Nr (i.e. pollution swapping).