LAUSR

BACKGROUND The importance of biochar-based fertilizers in agroecosystems has been increasingly understood. However, no studies have evaluated the effects of partial substitution of urea with biochar-based urea on rice yields and soil microbial communities. Therefore, we investigated rice yields, bacterial communities and gene abundances involoved in nitrogen in silty clay and sandy loam soil paddy fields treated with urea (U), all substitution of urea with biochar-based urea (BSU), partial substitution of urea with biochar-based urea in basal and tillering fertilizers (BSU1), and partial substitution of urea with biochar-based urea in panicle fertilizers (BSU2). RESULTS Compared with U, applying biochar-based urea increased rice yields, with BSU2 being the most notable. Principal coordinate analysis revealed that bacterial communities under BSU2 treatment in both soils were significantly different from those under U and BSU treatments, most probably due to the decrease in pH caused by the decrease in the concentration of ammonium. The relative abundances of Subdivision3_genera_incertae_sedis, Azotobacter, Geobacter, Buchnera, and Terrimonas in silty clay soils and Saccharibacteria_genera_incertae_sedis and Geobacter in sandy loam soils significantly increased under BSU2 treatment and were positively correlated with rice yields, indicate the inprovements of rice yield were associated with changes in bacterial communities. Based upon amoA/narG related to nitrate accumulation and norB/nosZ related to nitrous oxide emissions, BSU2 enabled a lower the risk of nitrate leaching and nitrous oxide emissions in both soils, as compared to U and BSU treatments. CONCLUSION The BSU2 has a stronger yield-increasing effect than the biochar-based urea alone and a lower the risk of nitrogen pollution, which is beneficial to the sustainable development of paddy fields. This article is protected by copyright. All rights reserved.