Intercropping with BNI-sorghum benefits neighbouring maize productivity and mitigates soil nitrification and N2O emission

Sorghum (Sorghum bicolor) roots are well-known for the release of Biological Nitrification Inhibitors (BNIs), such as sorgoleone (SGLN) and methyl 3–4-hydroxyphenyl propionate (MHPP). However, the deployment of sorghums with BNIs in agriculture practices has not been widely investigated and evaluated. In this study, sorghum and maize were intercropped in field and pot cultivation to investigate the Biological Nitrification Inhibition (BNI) effect of sorghum on the productivity of both crops and soil nitrification. Inorganic N content (NO3– and NH4+), N2O emission, and the abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in soil were analyzed. The results showed intercropping with sorghum have the potential to improve crop productivity, as indicated by the Land Equivalent Ratio greater than 1.0. Intercropping with sorghum reduced the transformation rate of NH4+ to NO3– in soils and the emission of N2O, as compared to monoculture of maize. Additionally, the abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) under intercropping mode were reduced by 41% and 28% in field trials, and reduced by 59% and 23% in pot experiments, respectively. Incubation of the same soils with SGLN and/or MHPP showed that the combined treatment of both BNIs strongly inhibited nitrification and N2O emission, along with lower AOB and AOA abundances, as compared with those under the sole treatment of SGLN or MHPP. Our results indicated that the root exudates of sorghum play a significant role in inhibiting soil nitrification due to the overlapping or amplified effect of various BNIs, which contribute to the nitrogen nutrition of the neighbouring crops under intercropping mode. Therefore, intercropping with BNI crops provides an eco-friendly strategy to improve crop production with reduced N2O emission.