Crop Rotations for Sustainable Intensification : Knowledge-based Design Focusing on Nitrogen Dynamics and Yield Formation

This dissertation investigates how crop rotation design and nitrogen (N) management can contribute to achieving high and stable yields while improving nitrogen use efficiency (NUE) in arable cropping systems. The research is based on a long-term crop rotation experiment conducted at a high-yielding site in Northern Germany.

At the cropping-system level, yield formation and N offtake were primarily driven by prevailing weather conditions. Nevertheless, crop sequence effects were clearly detectable, particularly in winter crops and under low to moderate N fertilization levels. Diversified crop rotations that included non-cereal crops, catch crops, and spring-sown crops improved NUE, yield stability, and the productivity of winter wheat and winter oilseed rape. In contrast, cereal-dominated rotations were associated with lower NUE and yield penalties.

A major methodological contribution of the dissertation is the development of a transferable spectral reflectance framework for canopy monitoring. By separating primary canopy traits, such as green area index, from derived variables, such as biomass and N uptake, the framework enabled robust predictions across crops, growth stages, growing seasons, and sensing platforms. The approach provided high-temporal-resolution information on canopy development and crop N status, establishing a foundation for adaptive, in-season N management.

Using winter wheat as a case study, the dissertation examined how preceding crops influence N dynamics and yield formation. Differences among crop sequences could not be explained solely by total N availability. Non-cereal preceding crops increased both N uptake and grain yield within identical N fertilization treatments, indicating improvements in internal NUE and yield formation processes.

Overall, the dissertation demonstrates that knowledge-based crop rotation design combined with adaptive N management can make a significant contribution to the sustainable intensification of arable cropping systems. Through the integration of long-term field experimentation and transferable canopy monitoring approaches, it advances the mechanistic understanding of N dynamics and yield formation and provides a foundation for improving NUE in complex cropping systems.