Biochar organic fertilizers from natural resources as substitute for mineral fertilizers

Biochars are new, carbon-rich materials that could sequester carbon in soils improve soil properties and agronomic performance, inspired by investigations of Terra Preta in Amazonia. However, recent studies showed contrasting performance of biochar. In most studies, only pure biochar was used in tropical environments. Actually, there is little knowledge on the performance of biochar in combination with fertilizers under temperate climate. Therefore, we conducted an experiment under field conditions on a sandy Cambisol near Gorleben in Northern Germany. Ten different treatments were established in 72-m2 plots and fivefold field replicates. Treatments included mineral fertilizer, biogas digestate, microbially inoculated biogas digestate and compost either alone or in combination with 1 to 40 Mg ha−1 of biochar. Soil samples were taken after fertilizer application and maize harvest. Our results show that the biochar addition of 1 Mg ha−1 to mineral fertilizer increased maize yield by 20 %, and biochar addition to biogas digestate increased maize yield by 30 % in comparison to the corresponding fertilizers without biochar. The addition of 10 Mg ha−1 biochar to compost increased maize yield by 26 % compared to pure compost. The addition of 40 Mg ha−1 biochar to biogas digestate increased maize yield by 42 % but reduced maize yield by 50 % when biogas digestate was fermented together with biochar. Biochar-fertilizer combinations increased K, Mg and Zn and reduced Na, Cu, Ni and Cd uptake into maize. Overall, our findings demonstrate that biochar-fertilizer combinations have a better performance than pure fertilizers, in terms of yield and plant nutrition. Therefore, an immediate substitution of mineral fertilizers is possible to close regional nutrient cycles.