Novel Slow-Release NPK Biochar-Based Fertilizers with Acidulated Apatite: Evaluation of the Fertilization Value in a Short-Term Experiment

PurposeCompared with mineral fertilizers, the use efficiency of nitrogen (N), phosphorus (P), and potassium (K) from organomineral matrices increases as biochar is mixed with acidulated apatite to produce slow-release NPK-biochar-based fertilizers (BBFs). The BBFs reduce P losses while improving plant nutrition in Oxisols. Thus, the aim of this study was to synthetize and evaluate the effects of slow-release BBFs produced by mixing coffee waste-derived biochar with acidulated apatite.MethodsThe agronomic efficiency of BBFs was evaluated through the cultivation of maize in greenhouse conditions. The availability of NPK in whole soil and solution and the kinetics of P released by fertilizers in water and citric acid leachates were evaluated as well.ResultsCompared with mineral fertilizers, N and K supplied by BBFs did not improve the nutrition of maize plants. Triple superphosphate (TSP) released nearly all the total P, while the BBFs released less than 10% of the P released by the TSP in the first 24 h. Biochar based-fertilizers, depending on the synthesis route adopted, produced a greater or similar maize biomass. The acquisition of P from BBFs was greater than that of NPK supplied via mineral fertilizers. Thus, BBFs can slow the release of P in water leachates and, simultaneously, release high levels of P in citric acid leachates.ConclusionsThe BBFs formulated with coffee husk-derived biochar and acidulated apatite are a sustainable and efficient approach to producing NPK sources with higher agronomic effectiveness than soluble mineral fertilizers. The BBFs improved the nutritional status and growth of maize and the residual available soil P content in the Oxisols as well (Ferralsols).