Combined application of biochar and nitrogen fertilizer promotes the activity of starch metabolism enzymes and the expression of related genes in rice in a dual cropping system

BACKGROUND: Overuse of chemical fertilizer highly influences grain filling rate and quality of rice grain. Biochar is well known for improving plant growth and grain yield under lower chemical fertilization. Therefore field trials were conducted in the early and late seasons of 2019 at Guangxi University, China to investigate the effects of combined biochar (B) and nitrogen (N) application on rice yield and yield components. There were a total of eight treatments: N1B0, 135 kg N ha(− 1)+ 0 t B ha(− 1); N2B0,180 kg N ha(− 1)+ 0 t B ha(− 1); N1B1,135 kg N ha(− 1)+ 10 t B ha(− 1); N1B2,135kg N ha(− 1)+ 20 t B ha(− 1); N1B3,135 kg N ha(− 1)+ 30 t B ha(− 1); N2B1,180 kg N ha(− 1)+ 10 t B ha(− 1); N2B2,180 kg N ha(− 1)+ 20 t B ha(− 1); and N2B3,180 kg N ha(− 1)+ 30 t B ha(− 1). RESULTS: Biochar application at 30 t ha(− 1)combined with low N application (135 kg ha(− 1)) increased the activity of starch-metabolizing enzymes (SMEs) during the early and late seasons compared with treatments without biochar. The grain yield, amylose concentration, and starch content of rice were increased in plots treated with 30 t B ha(−1)and low N. RT-qPCR analysis showed that biochar addition combined with N fertilizer application increased the expression of AGPS2b, SSS1, GBSS1, and GBSE11b, which increased the activity of SMEs during the grain-filling period. CONCLUSION: Our results suggest that the use of 20 to 30 t B ha(− 1)coupled with 135 kg N ha(− 1) is optimal for improving the grain yield and quality of rice. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12870-021-03384-w.