Precision nitrogen fertilization strategies for durum wheat: a sustainability evaluation of NNI and NDVI map-based approaches

Durum wheat, one of the most important staple crops, faces increasing use of fertilizers, particularly nitrogen (N), to meet growing food demand. However, inefficient nitrogen management to meet crop demand can contribute to harms ecosystems. This study focuses on the application of precision fertilization technologies, particularly through variable-rate fertilization based on satellite imagery, to enhance N use efficiency in durum wheat cultivation. To this end, an experiment was conducted during four consecutive growing seasons, from October 2018 to July 2022, in Asciano, Siena, Italy. A total of four N fertilization approaches were evaluated: a uniform N rate, calculated conventionally, and three variable rates based on Sentinel-2 L2A spectral bands. These variable rate approaches include one using the Nitrogen Nutrition Index (NNI), a proportional NDVI-based estimate (NDVIH), and a compensative NDVI-based estimate (NDVIL). Results indicate that the NNI approach, based on satellite imagery, lead to significant N savings without compromising grain yield or quality. This approach also optimizes protein partitioning and dough technical properties, essential factors in various end-use applications. The NNI approach consistently outperforms the other approaches in terms of N fertilizer use efficiency (NfUE). Furthermore, the NNI approach proves to be economically advantageous, with lower social costs and higher rates of return compared to other N fertilization approaches. This emphasizes the economic and environmental sustainability of precision fertilization techniques, specifically NNI, in durum wheat cultivation. This research provides valuable insights for the practical implementation of satellite-based N fertilization strategies, in particular NNI, which offer long-term benefits for sustainable agriculture.