Biochar-based nitrogen fertilizers: Greenhouse gas emissions, use efficiency, and maize yield in tropical soils.

The sustainable development of agriculture depends on increasing N use efficiency (NUE) and consequently reducing N losses from different sources, such as NH volatilization, NO leaching, and NO emissions. While the chemical and physical properties of biochar (BC) in fertilizers have been evaluated to increase NUE, a lack of information exists regarding the effects of BC amendments in tropical soils. We performed a one-year field experiment with tropical soil to evaluate the effects of BC-based N fertilizers (BN) on maize yield and on greenhouse gas (GHG) emissions. The treatments consisted of five fertilizers: ammonium nitrate (AN), urea (U), BN (51% BC, 10% N), BN (40% BC, 17% N), BN (29% BC, 20% N), and a control (without N fertilizer). The N fertilizers (80 kg N ha) were broadcast 20 days after sowing. Yield, grain N uptake, NUE, ammonia volatilization, and GHG emissions were measured. The results demonstrated the potential of BNs to enhance the efficiency of the fertilizers. BN and BN had an average maize yield that was 26% higher than that of U, and BN resulted in a NUE that was 12% higher than what was observed for U. Both the effects on yield and NUE were attributed to lower N release rates of the BN-amended fertilizers compared to that of the conventional soluble N sources. The BC-based fertilizers presented better environmental performance, and BN showed the lowest emission intensity when C sequestration by BC was not considered, with a value that was 14% lower than that of the U treatment. When considering C sequestration by BC, the emission intensity of the C equivalents demonstrated that all BNs presented C sequestration that differed from that of the mineral N sources. BC-based nitrogen fertilizers may have promising applications for sustainable agricultural development by mitigating N losses and increasing C stocks.