Stimulated fine root growth benefits maize nutrient uptake under optimized nitrogen management

Optimized nitrogen (N) management reduces total N application without sacrificing crop yield. However, the underlining mechanisms have not been well investigated, especially lacking the evidence from roots. Here we performed a two-year field experiment with maize grown under zero-N, conventional N and optimized N applications and examined grain yield, N, phosphorous (P) and potassium (K) uptake and root length in diverse diameter classes. Results showed that both conventional N and optimized N managements significantly increased plant nutrient contents and grain yield compared with zero-N treatment, but no obvious difference was observed between the two N-fertilized treatments. Notably, the response of different nutrients to N application was not synchronous temporally over the growth period, following the order of N first, P second and K last. Though N application generally had minor impact on total root length and root biomass, optimized N regime significantly increased fine root (diameter ≤ 0.2 mm) length compared with conventional N at the eighth leaf emerged stage. The stimulated fine root growth under optimized N management is beneficial for adequate N uptake during the key growth stage, which determines subsequent PK acquisition and final crop yield. Our findings highlight the importance of fine roots in maize NPK uptake and a better understanding of the response of fine roots to changes in N availability may therefore be critical for optimizing N input in maize farming system.