Different rates of biochar application change 15 N retention in soil and 15 N utilization by maize

Biochar application to soil may impact soil nitrogen (N) dynamics, but the effects on N uptake and utilization by crop remain largely unknown, especially the effects of the rate of biochar application. To investigate the effects of biochar on soil 15 N retention rate and 15 N utilization efficiency ( 15 NUE) by maize, a six‐month 15 N isotope tracer technique combined with in situ pot experiment was conducted in Mollisol. The experiment included four treatments: no biochar applied (CK) and biochar applied at the rates of 12 t ha −1 (P12), 24 t ha −1 (P24) and 48 t ha −1 soil (P48). Compared with CK, biochar application reduced soil bulk density and 15 N loss rate, and significantly improved total N and 15 N retention amount in the 0–30 cm soil depth. The P24 treatment had the largest increase in 15 N retention rate throughout the 0–40 cm depth. After biochar application, the 15 N uptake and 15 NUE were significantly increased in the grain and leaf, which promoted grain yields. Contrary to this, the P48 treatment appeared to lower 15 N uptake and 15 NUE compared with P12 and P24. In conclusion, biochar application improves the potential of the soil to retain N and the improvement in 15 N uptake and utilization are more pronounced in maize leaves and grain. Moreover, biochar application promotes 15 N utilization in maize plant and improves maize yield. However, when biochar application rate is high (i.e. P48 treatment), the 15 N retention by the soil and 15 N utilization by the maize are reduced markedly compared with P12 and P24.