Partial replacement of chemical fertilizers with animal manures in an apple orchard: Effects on crop performance and soil fertility

The combined use of chemical fertilisers with organic materials in crop fertilization is an essential approach to transition towards a more sustainable and resilient agriculture in Europe. In an apple orchard, chemical fertilisers (CF) were partially (25 to 57%) replaced with animal manure (cattle slurry - CS, acidified cattle slurry - ACS, cattle solid manure - CsM, and poultry manure - PM), based on the crop's nitrogen (N) requirements. Apple production and soil properties were monitored during a 3-year experiment. At the end of the third year, leaf N was higher in the control treatment (CTRL, 100% CF). Apple production was, on average, higher in the CS treatment, although not significantly different from the CTRL. Fruit analysis showed that replacing CF with animal manures did not significantly impacted fruit quality (weight, oBrix and firmness). Soil organic carbon (SOC), N and exchangeable potassium (K+) were significantly higher in the manure treatments. The increase in soil K+ in the manure treatments consequently increased soil K/magnesium (Mg) ratio, slightly mitigating K and Mg antagonism, as seen by the increase in fruit K. However, K content was still deficient in fruits and leaves in all treatments. It can be concluded that the partial replacement of chemical fertilisers by animal manures (CS, ACS and PM) had a positive effect on soil health with no decrease of apple production.