Impact of biochar‐based slow‐release N‐fertilizers on maize growth and nitrogen recovery efficiency

Abstract Biochar has been used to address several environmental problems and may be efficacious as a carrier of N‐fertilizer in slow‐release N‐fertilizer (SRF) formulations. Our objective was to compare the efficacy of SRF pellets formulated with different mass ratios of biochar and urea with traditional N‐fertilizers for improving N use efficiency by maize ( Zea mays L.) grown under greenhouse conditions. Two different soil types, four SRF formulations with different biochar‐to‐urea (BCN) ratios (1:2 BCN, 1:3 BCN, 1:4 BCN, and 1:6 BCN), three traditional N‐fertilizers (urea, urea ammonium nitrate, and S‐coated urea), and unfertilized controls for each soil were tested. The accelerated urea release test showed significantly less loss of urea for the SRF over time than the traditional N‐fertilizers. The biochar‐based SRF formulations significantly ( p < 0.05) decreased nitrate leaching loss for both soils relative to the traditional fertilizers. All the SRF formulations increased maize shoot (1%–34%) and root (0%–23%) biomass, N‐recovery efficiency (17%–50%), and soil potential mineralizable‐N relative to urea and S‐coated urea. The results also indicate that the BCN ratio in the SRF formulation can be used to influence the timing of N release and plant N uptake. The results of the greenhouse study suggest that biochar‐based SRFs have potential agronomic and environmental benefits; however, more research is needed to assess their agronomic value under field conditions.