Contribution characteristics of nitrogen accumulation and distribution to grain yield of maize

A two-year field experiment (2019-2020) was conducted in Yongchuan, Chongqing, and Deyang, Sichuan, to investigate the differences in nitrogen (N) accumulation and grain yield formation between maize varieties with contrasting N efficiencies. Additionally, we clarify the contribution characteristics of N accumulation and distribution to the grain yield of maize in Southwest China. Two maize varieties-N-efficient Zhenghong 311 (ZH 311) and N-inefficient Xianyu 508 (XY 508)-were tested under four N levels (0, 120, 240, and 360 kg·ha^-1). Kernel number per ear showed the strongest correlation with N accumulation (R² = 0.8186) and weakest correlation with 100-kernel weight (R² = 0.2479). ZH 311 exhibited a significantly higher ear row number, kernel number per row, total kernel number per ear, and grain yield than XY 508. However, its 100-kernel weight was lower, indicating that N accumulation primarily regulates grain yield by modulating the kernel number per ear. N accumulation peaked during the V12-R1 (12-leaf to silking) stages, with substantial contributions from the SS-V6 (emergence to 6-leaf; R² = 0.7737), V12-R1 (R² = 0.7129), and R1-R3 (silking to milking stage; R² = 0.7277) stages. Root (R² = 0.6804), stem-sheath (R² = 0.8440), and leaf (R² = 0.8590) N accumulation was positively correlated with grain yield. Root N accumulation contributed the most to yield at the R3 stage, whereas stem-sheath N accumulation had a highly significant contribution in the V12, R1, and R3 stages and leaf N accumulation in the V6, V12, and R3 stages. ZH 311 exhibited significantly higher N accumulation at all growth stages, ear row number, kernel number per row, total kernel number per ear, and grain yield compared to XY 508, while its 100-kernel weight was lower. The N-efficient variety ZH 311 increased grain yield by enhancing kernel number per ear in the early stages (thereby expanding sink capacity) and later strengthening the supply from source organs (stems, leaves, and roots) to ensure assimilate availability.