A fertilization strategy to reduce Nitrogen contamination

In recent decades, the growing demand for food to meet both human and livestock requirements has resulted in an uptick in the utilization of fertilizers to enhance crop productivity. Excessive fertilizer usage disrupts the nitrogen (N) cycle, causing detrimental environmental effects, including the release of greenhouse gases and ammonia into the atmosphere, as well as the accumulation of nitrates in the soil. These nitrates, washed away by rainfall, contaminate water bodies and contribute to eutrophication. Given these environmental challenges and the current upward trend in fertilizer costs, numerous solutions have emerged to reduce fertilizer application without compromising crop yields and, by extension, the livelihoods of farmers and livestock breeders.

The international research team, led by Alberto Sanz-Cobeña (UPM) and Benjamín Sánchez (INIA-CSIC), has conducted an examination of the factors contributing to imbalances resulting from the application of nitrogen fertilizers. They have also assessed various approaches to mitigate or prevent these imbalances. Benjamín Sánchez Gimeno, a research scientist at the INIA-CSIC Department of Environment and Agronomy, elaborates, “We have scrutinized the advantages and potential drawbacks of eight nitrogen fertilization strategies in the Region of Murcia, an area susceptible to over-fertilization of its agricultural lands, which has led to several instances of pollution in the Minor Sea in recent years.”

This research, published in the Environmental Research Letters journal, adopts a comprehensive approach by examining the nitrogen (N) dynamics within the agricultural and food system of the Murcia region. It combines this investigation with a detailed geospatial analysis of specific locations and crops where excessive fertilization has been documented. This analysis encompasses a historical perspective, including estimates of nutrient flows from 1860 to 2018. Additionally, it explores the agricultural system at various spatial scales, ranging from areas smaller than 1 km2 to the entire region, as well as systemic scales, encompassing crop zones, pastures, livestock areas, urban regions, and the agri-food system as a whole. The study concludes that there is a disconnection in the N balance between the agricultural and livestock components of the agri-food system, resulting in an excess of nitrogen in specific areas that the system cannot manage.

To propose solutions, the authors have also analyzed 8 fertilization scenarios based on the total or partial reduction of synthetic fertilizers, as proposed by the European Union’s “Farm to Fork” strategy, or the application of technological measures to increase the efficiency of these fertilizers. “The methodology used for this analysis is also integrative, combining models that consider the impact of proposed solutions on the emission of toxic substances into the atmosphere, such as ammonia and greenhouse gases, and the potential leaching of N in the soil, as well as on crop yields,” emphasizes Benjamín Sánchez.

Among all the scenarios studied, the most beneficial is the elimination of urea-containing fertilizers, as it would significantly reduce ammonia emissions (52-86%) into the atmosphere, potentially leachable N (15-21%), and greenhouse gases (19%), with minimal production losses (0-2.5%). However, the authors emphasize that “to reduce the imbalances found, it is necessary, first and foremost, to couple agricultural production with livestock, ensuring a closure of nutrient flows in the Region of Murcia.”

Moreover, a significant finding of the research underscores the advantage of directing reduction efforts towards particular crops and problematic regions, rather than implementing broad, generic reductions. In this context, the authors advocate for a reduction in fertilizer usage in irrigated horticultural and citrus crops. These crops occupy 40% of the cultivated land and contribute to 67% of excessive fertilization in the area, while also being notably present in the vicinity of the Minor Sea. This approach, coupled with enhanced practices and greater circularity, aligns with the strategies endorsed by the European Union.

This research is a component of the Agroscena-UP Project, which received funding from MCIU under PID2019-107972RB-I00 (led by Alberto Sanz-Cobeña and Luis Lassaletta). Additionally, Benjamín Sánchez received co-financing through the European Union EJP-SOIL program, where he served as the scientific coordinator for Spanish initiatives associated with the program.