Liebig or Mitscherlich?

More efficient use of nutrients, especially nitrogen, is essential for more sustainable agricultural systems. Currently, around half of the nitrogen applied to global cropland is not recovered by the first crop. Besides adoption of improved management practices, reducing the impacts of nitrogen application also requires more fundamental insights into yield response curves to nitrogen, to inform sustainable application rates. Based on data from 25 long term experiments, Grinsven et al. (2022) recently showed that total nitrogen required for a certain fraction of the locally attainable yield, is independent of the size of that attainable yield. This was postulated by Mitscherlich in 1924, but not supported by empirical data, and in contrast with Liebig and others who suggested nitrogen requirements for a given target yield change with the attainable yield. Here, we assessed if these findings hold when tested on a larger dataset of short-term experiments. We compiled data on 532 yield response curves across five European countries (Denmark, Spain, the Netherlands, United Kingdom and Sweden). We show that yield responses follow a Mitscherlich curve with an R2 of 0.88 for spring barley and R2 of 0.90 for winter wheat. These findings highlight the strong dependency of nitrogen requirements on attainable yields, determined by biophysical factors (such as soil and climates) and management (such as irrigation). Our findings give new fundamental insights into yield responses to available nitrogen. This may support differentiation of nitrogen fertilizer recommendations and environmental legislations across agro-ecological zones.