Introduction Organic and recycling fertilizers are often ammonium dominated and soil injection or fertilizer placement is often related to higher uptake efficiency (Nkebiwe et al. 2016). The controlled uptake long-term ammonium nutrition (CULTAN) fertilization technique consists of injecting a concentrated ammonium solution into the soil and aims to positively impact crop physiology and N use efficiency, thus often reducing losses to the groundwater. Aims: This study assesses whether CULTAN can contribute to lower N leaching while maintaining yields in temperate regions with an annual precipitation of around 1000 mm or higher. Methodology We analysed a 12-year lysimeter study with two consecutive 6-year crop rotations and a 3-year field study with winter wheat and maize in Switzerland. CULTAN was compared to a conventional surface application of ammonium nitrate fertilizer (ConvF). To evaluate the effects of CULTAN compared to ConvF across both experiments, yield and N leaching or soil mineral N were measured and N use efficiency was calculated. More details can be found in Bernert et al. (2024). Results and discussion CULTAN achieved at least similar yields compared to ConvF in both studies and had a 38% lower yield-scaled N leaching in the lysimeters. In both studies, CULTAN displayed higher nitrogen recovery efficiency (NRE) compared to ConvF, with an increase ranging from 8% to 17% depending on crop type, although a statistical significance was only found for winter wheat in the field study. NRE and N leaching were only weakly correlated, indicating that other N pathways are affected in the CULTAN fertilization system (Bernert et al 2024). Finally, we suggest that the timing and placement of the CULTAN injection need to be better adapted to the plant physiology and pedoclimatic conditions for optimal nutrient use and crop yields. A brief conclusion is that in areas of high nitrate concentration in the groundwater, CULTAN can be an effective fertilization strategy complementing loss reduction measures. Acknowledgements The authors would like to thank C. Humphrys and V. Prasuhn for conducting the experiment and helping with the data collection and discussion, R. Flisch for the field experiment data and helpful comments, M. Häberli, G. Steger, and P. Briner AG for practical discussions and helpful comments. This study was financed by the Swiss Federal Office for the Environment (Grant number: BAFU-D-7C3D3401/785) and by Agroscope Core Funding..
