With the "eternal rye" experiment, laid out by Julius Kuhn in 1878, the Institute of Agricultural and Nutritional Sciences of the Martin Luther University Halle-Wittenberg has the second oldest long-term fertilization trial of the world after Rothamstedt (UK). In addition, four more long-term fertilization experiments as well as one soil development trial exist in Halle, all founded by Karl Schmalfuss in 1948/49. Wolfgang Merbach and Annette Deubel summarize the most important results and draw conclusions for the continuation of these internationally important experiments.