Combined application of biochar with fertilizer promotes nitrogen uptake in maize by increasing nitrogen retention in soil

Combined application of biochar with fertilizers has been used to increase soil fertility and crop yield. However, the coupling mechanisms through which biochar improves crop yield at field scale and the time span over which biochar affects carbon and nitrogen transformation and crop yield are still little known. In this study, a long-term field trial (2013-2019) was performed in brown soil planting maize. Six treatments were designed: CK-control; NPK-application of chemical fertilizers; C1PK-low biochar without nitrogen fertilizer; C1NPK, C2NPK and C3NPK-biochar at 1.5, 3 and 6 t ha(-1), respectively, combined with chemical fertilizers. Results showed that the delta N-15 value in the topsoil of 0-20 cm layer in the C3NPK treatment reached a peak of 291 parts per thousand at the third year (2018), and demonstrated a peak of 402 parts per thousand in the NPK treatment in the initial isotope trial in 2016. Synchronously, SOC was not affected until the third to fourth year after biochar addition, and resulted in a significant increase in total N of 2.4 kg N ha(-1) in 2019 in C3NPK treatment. During the entire experiment, the N-15 recovery rates of 74-80% were observed highest in the C2NPK and C3NPK treatments, resulting in an annual increase in yields significantly. The lowest subsoil delta N-15 values ranged from 66 parts per thousand to 107 parts per thousand, and the N-15 residual rate would take 70 years for a complete decay to 0.001% in the C3NPK. Our findings suggest that biochar compound fertilizers can increase C stability and N retention in soil and improve N uptake by maize, while the loss of N was minimized. Biochars, therefore, may have an important potential for improving the agroecosystem and ecological balance. Graphic abstract

Automated summary

The combined application of biochar with fertilizers can increase N stability in soil, improve N uptake by crops, and minimize N loss. Biochars have the potential to improve the agroecosystem and ecological balance.