Effects of Mixed Controlled Release Nitrogen Fertilizer with Rice Straw Biochar on Rice Yield and Nitrogen Balance in Northeast China

A 3-year fixed site experiment was carried out on a Planosol in Northeast China to study the effects of biochar and controlled-release nitrogen fertilizer on rice yield, nitrogen-use efficiency, residual nitrogen, and nitrogen balance in soil-crop system. Five treatments were established: control (CK), bare urea (BU), controlled-release urea (CRU), 50% BU + 50% CRU (MBC), and 50% BU + 50% CRU + biochar (MBCB) treatments. The results showed that, compared with the BU treatment, the yield, N-use efficiency (NUE) and N agronomic efficiency (NAE) of the CRU treatment increased by 12.2%, 33.9% and 4.3 kg kg(−1), respectively; while the soil residual N and N surplus at harvest decreased by 11.6% and 10.7%, respectively. Compared with the MBC treatment, the yield, NUE and NAE of the MBCB treatment increased by 10.2%, 16.5% and 4.0 kg kg(−1), respectively; while the soil residual N and N surplus at harvest decreased by 10.8% and 12.3%, respectively. Therefore, mixed application of bare urea, controlled-release urea and biochar was effective for obtaining high rice yield, and high fertilization efficiency as well as for sustainable agricultural development in Northeast China.