Efficiency and feasibility of Best Management Practices to reduce nutrient loads in an agricultural river basin

Excessive use of mineral fertilizers and inappropriate tillage operations are two main drivers of land degradation. The European Green Deal (EUGD) aims to restore the natural functions of ground and surface soil by 2030. EU Member States will be called upon to include mitigation measures in their own management programs. In this context, the current work aimed to evaluate the feasibility of Best Management Practices (BMPs), generally used to counteract soil erosion, in achieving nutrient load reduction, and evaluate their economic convenience in the private and public sector. The Soil and Water Assessment Tool (SWAT) was used to model point and diffuse nutrient sources in the Carapelle basin (Apulia, Italy) and to simulate BMP scenarios. Contour farming (CF), no tillage (NT), reforestation (RF), and two additional scenarios, including the 20% reduction of fertilizers in CF and NT, (CFR) and (NTR), were simulated following the EUGD strategy. For the current land uses, the riverine export of nitrogen (TN) and phosphorous (TP) were -49 kg ha-1y-1 and -0.044 kg ha-1y-1, respectively. CF and NT increased N-NO3 load both into surface runoff and in terms of leaching. Conversely, RF showed a reduction of NNO3 losses. CFR and NTR scenarios decreased N-NO3 load both in surface runoff and leached of -20%. CFR and NTR represented the best alternative among the analyzed scenarios both for their lower production costs at the farm level and for their savings in terms of nutrient and soil losses. RF was economically profitable in sloped areas, thus representing BMPs that may be implemented in combination with other practices to have a greater impact at the basin scale. BMP implementation requires significant investments (public and private). The results of this study provide the scientific basis for decision-making for agriculture and watershed management.