Assessing the impacts of biochar-blended urea on nitrogen use efficiency and soil retention in wheat production

Improving nitrogen (N) use efficiency (NUE) in crop plants is important to reduce the negative impact of excessive N on the environment. Although biochar-blended fertilizer had been increasingly tested in crop production, the fate of fertilized N in soil and plant had not been elucidated in field conditions. In this study, a novel biochar-blended urea (BU) was prepared by pelleting maize straw biochar, bentonite, sepiolite, carboxymethylcellulose sodium, and chitosan with urea (commercial urea without biochar [CU]). N fertilization in a winter wheat field was treated with BU and CU at both 265 kg N ha(-1) (HL) and 186 kg N ha(-1) (LN). Within a treatment plot, a microplot was fertilized with N-15-labeled urea at a relevant N level. We investigated the influence of fertilizer management on biomass, grain yield, bioaccumulation of nutrient, soil properties, N-15 isotopic abundance, and greenhouse gas emissions. Microscopic and spectroscopic analysis showed that micro/nanonetwork of biochar could bind N to form a loss control agglomerated particle, and organo-mineral coatings on BU may protect N from quick release. Compared with CU, BU significantly increased grain yield by 13% and 38%, and grain N allocation by 19% and 55%, respectively, at HN and LN level. The total recovery of urea N-15 in wheat plant (N-15 based NUE) was 32.8% under CU regardless of N rates but increased to 41.7% (HN rate) and 56.3% (LN rate) under BU. Whereas, the soil proportion (soil residual N-15) was 20.1% and 13.4% under CU but 32.5% and 18.8% under BU, in 0-20cm topsoil, respectively, at HN and LN rate. Compared with the CU, BU had no effect on CO2 and CH4 emissions but significantly reduced the total N2O emission by 23%-28%. These important findings suggested that BU can be beneficial to uplift plant NUE to reduce reactive N loading but boost crop production.

Automated summary

The study found that using biochar-blended urea (BU) fertilizer in winter wheat fields can significantly increase crop yield, increase the proportion of nitrogen allocation in crops, and reduce soil nitrogen residue. Compared to conventional urea (CU), BU also reduces total nitrogen gas emissions, helping to improve plant nitrogen use efficiency.