Fertilizers play a significant role in ensuring food security and building soil health, but excess nutrients pose a risk for water quality. Chemical fertilizers provide nutrients in plant-available form to feed the crop, and they are widely used to increase crop yield. Organic fertilizers, on the other hand, provide fewer quickly available nutrients, but they do provide organic matter to build the soil. This organic matter has positive impacts on soil structure, soil biology, and soil water holding capacity, and it delivers nutrients to the crops after mineralization. To investigate the long-term effect of different fertilization strategies we tested the following the following hypotheses: Fertilizers that primarily feed the crop do initially have high yields, but they see decreasing yields over time. On the other hand, fertilizers that primarily build the soil do initially have low yields, because of the low availability of nutrients, while the yields increase over time, with increasing soil health, and mineralization of nutrients from the organic matter.

To test these hypotheses, a twenty year-long field experiment was set up in Flevoland, the Netherlands. The experiment was carried out on a working organic farm, where our study plots were part of the standard crop rotation on the farm. Eight different strategies were tested, including artificial fertilizer, different manures, and composts.

The results show that yield is comparable for fertilizers that primarily build the soil and fertilizers that primarily feed the crop, while the combined treatment has significantly higher yields. We find that building soil health can significantly increase crop yield, both on the short-term and on the long-term. However, yields remained low for fertilizers with a sole focus on building the soil, because even after twenty years of high organic matter application, they do not provide enough plant-available nutrients. We conclude that a (partial) substitution of chemical fertilizers with organic fertilizers can contribute to crop yield and soil health, while it has further environmental benefits such as lowering the sector’s carbon footprint.