Sustainability of Mediterranean crop rotation systems – evaluation from a water and nitrogen perspective

In the Mediterranean climate, agriculture often consists of intensively irrigated and fertilized row crop rotations, which can cause significant pressure on groundwater resources and groundwater-dependent ecosystems. A paradigmatic example is the Campo de Cartagena in south-eastern Spain, which is considered as the vegetable and fruit orchard of Europe. To reduce eutrophication events in the nearby lagoon, the regional authorities recently implemented a new regulation that allows two instead of the traditional three-crop rotations. However, there is little guidance for choosing the type and most suitable timing of potential cover crops. Here, we aim to provide some guidance by applying an agro-hydrological modelling approach that considers local crop varieties and agricultural management practices, and long-term climatic variability. The approach is based on the hydrological model Hydrus 1D, which was calibrated against field-based observations of soil moisture, N₂O emissions, and plant NO₃ uptake for broccoli and fava bean grown in an experimental field site in the Campo de Cartagena. The calibrated model was used to simulate the water and nitrogen cycle under various combinations of crops (broccoli, melon, and lettuce) and cover crops (fava bean, cow pea, and fallow). The daily simulations were run with thirty years of meteorological data to quantify the system’s long-term response and sensitivity to the large interannual climatic variability typically encountered in the study region. The results show the importance of considering climatic variability, especially variations in rainfall, when evaluating the effectiveness of the new policy interventions in terms of both food production and environmental protection.