Effects of graphene carriers on nitrogen forms, nitrogen cycling enzyme activities in soil and maize yield and quality

With the development of nanotechnology, the entry of nanomaterials like graphene into the soil environment may lead to a series of unknown consequences, which mainly affect soil nitrogen forms, enzyme activities and maize yield and quality. Four different amount graphene was applied to soil, soil aggregate, nitrogen content and enzyme activities were determined at the tasseling stage (VT), silking stage (R1) and maturing stage (R6) respectively. The results showed that graphene treatments significantly reduced soil bulk density and increased the total content of soil aggregates > 0.25 mm. G2 and G3 treatments notably increased GMD and MWD of soil aggregates, G1-G4 treatments significantly raised WSA, and ELT and D values decreased significantly. There was no significant difference in total nitrogen (TN) content from the VT to R6 growth period compared with the CF treatment, G2, G3, and G4 significantly increased available nitrogen (AN) content. Graphene treatments (G1-G3) increased ammonium nitrogen (NH ₄ ⁺ -N) content at VT and R1; and G1-G4 significantly increased nitrate nitrogen (NO ₃ ⁻ -N) content from VT to R6. The activities of nitrate reductase, nitrite reductase and hydroxylamine reductase first rose then fell, and graphene improved protease compared with CF. The yield in the G3 treatment significantly increased by 10.81%. Compared to CF, maize kernel’s albumin, gluten and alcohol soluble protein content first increase then decrease with increasing graphene application, Consider comprehensively, our results indicate that 5 g·kg ^− 1 graphene was the most appropriate treatment in this experiment.