Contribution to the HiStory series in Plant Nutrition

ABSTRACT Three nitrogen issues dominated the scientific debates from the middle of the 19th century: (1) Is fertilization with nitrogen necessary at all, which was prominently questioned by Justus von Liebig. (2) How can one explain the special nature of legumes with regard to the nitrogen budget in agricultural systems. And (3) once the need for nitrogen fertilization of non‐leguminous plants had been recognized, how can one provide nitrogen fertilizer once the deposits of fossil nitrogen, such as Chile saltpeter, are exhausted. Liebig postulated that plants could cover their nitrogen requirements by taking up ammonia from the atmosphere, so nitrogen fertilization was not necessary. However, this hypothesis contradicted the practical experience of many farmers, who achieved higher yields with additional nitrogen fertilization. Agricultural scientists such as John Bennet Lawes and Joseph Henry Gilbert in England and Julius Adolph Stöckhardt and Emil Wolff in Germany intensively conducted the debate. Lawes and Gilbert carried out numerous field trials that proved that nitrogen fertilization significantly increased the yields of many crops, calling Liebig's nitrogen theory into question. Finally, the academically trained farmer Albert Schultz‐Lupitz made a decisive contribution to renewing the debate. Through his field trials, he realized that legumes in crop rotation leave nitrogen in the soil, allowing subsequent cereal crops to thrive without additional nitrogen fertilization. This “Lupitz fertilization system” suggested that legumes could use atmospheric nitrogen, which contradicted previous doctrine. Schultz‐Lupitz's findings once again made nitrogen a central topic of discussion.