Biochar and NPK fertilizer co-applied with plant growth promoting bacteria (PGPB) enhanced maize grain yield and nutrient use efficiency of inorganic fertilizer

A field experiment was carried out for two consecutive years to assess the yield response of maize and the use efficiency of nitrogen, phosphorus and potassium following the application of biochar and mixed culture of Bacillus spp and Pseudomonas spp to Inorganic NPK fertilizer. Seven treatments comprising: control, inorganic NPK fertilizer at half rate (HR), inorganic NPK fertilizer at full rate (FR), inorganic NPK fertilizer (HR)+biochar (1500 kg ha-1), inorganic NPK fertilizer (FR) + biochar (1500 kg ha-1), inorganic NPK fertilizer (FR)+biochar (1500 kg ha-1)+P + B, inorganic NPK fertilizer (HR)+biochar (1500 kg ha-1)+P + B were laid in a randomized complete block design. Bulk density reduced only in fields amended with the treatments that included biochar. Also, soil pH increased in all plots that were co-amended with inorganic NPK and biochar. Soil organic carbon, cation exchange capacity, dehydrogenase activity and metabolic quotient significantly increased in the amended plots compared with the control. However, inorganic NPK fertilizer + biochar with mixed bacteria cultures, enhanced organic C, dehydrogenase activity and metabolic quotient compared with NPK alone or NPK + biochar. Nitrogen, phosphorus and potassium uptake and the use efficiency and yield of maize, were superior in treatments that included mixed bacteria cultures compared to the addition of NPK alone or NPK + biochar. Our study showed that the inclusion of mixed culture of bacteria in combination with biochar is a promising strategy to increase grain yield, enhance the use efficiency and reduce the rates of inorganic NPK fertilizer application recommended for cultivating maize in the coastal savannah agroecological zone of Ghana.