Inaccurate use of nitrogen (N) fertilizers causes severe environmental problems such as the emission of the greenhouse gas nitrous oxide and nitrate leaching into groundwater. The sources of N available to the plant are affected by spatial variability and the timely synchronization between N inputs and crop N demand, which can be addressed via site-specific N management. This study [1] tests a combination of digital and standard methods to provide decision-support for N fertilization in winter wheat in Switzerland. The hypothesis was that site-specific and variable rate (VR) fertilization reduces N input compared to standard uniform application (ST) without affecting yield, thus increasing N use efficiency (NUE) and reducing N surplus. Used methods were drone imaging, sampling of soil solution and plant and soil analysis. The experimental setup consisted of a multi-plot design with two treatments (VR and ST) and two controls (no and surplus fertilizer) in seven fields over three years (2018–2020) located in northeast Switzerland. Grain yields were in the expected range (6–7 t ha−1) with no significant difference between VR and ST [2]. In contrast, N fertilizer application was reduced in the VR treatments between 5 and 40%, thus increasing NUE. However, a better prediction of N mineralization in the soil and related N uptake by the plants was found necessary to further optimize in-season N fertilization. Therefore, the two components i) the remotely estimated plant N uptake (REN) and ii) nitrate-N in soil solution (NSS) were measured on a weekly basis. The REN and NSS showed a distinct relationship. The timely integration of both was related to improved NUE and reduced N surplus [3]. Finally, a developed concept linked the economic and environmental performance. On average, net revenues in VR were 4% higher than in ST. The surplus N was 32% (21 kg N ha–1) lower in VR compared to ST, due to a reduction in N inputs of 13% without significant yield differences [4]. The point of balanced N supply varied from 180 to 205 kg total available N ha–1. In conclusion, by monitoring and managing the N variability observed in crop and soil, the established methods showed possible solutions to reduce N surplus. Sensor-based monitoring can lead the way to these practices, aiming to maintain profitability quality, and reduce ecological impact.
