Effects of nitrogen fertilizer on post-silking dry matter production and leaves function characteristics of low-nitrogen tolerance maize

In order to clarify the features of dry matter production and leaf function during post-silking stage in maize varieties with different low-nitrogen tolerance, a field experiment with 6 levels of nitrogen application rates 0 kg(N)hm^-2 (B1)、90 kg(N)hm^-2 (B2)、180 kg(N)hm^-2 (B3)、270 kg(N)hm^-2 (B4)、360 kg(N)hm^-2 (B5), 450 kg(N)hm^-2 (B6) was conducted using low-nitrogen tolerant maize cultivar ‘Zhenghong 311’ and low-nitrogen sensitive maize cultivar ‘Xianyu 508’ as experimental materials. The results showed that nitrogen application significantly increased dry matter accumulation, leaf area index and leaf photosynthetic rate. It also alleviated the reductions of both chlorophyll and nitrogen contents of maize leaf at post-silking stage due to nitrogen deficiency, which was in turn reduced leaf C/N ratio at late growth stage, and increased maize yield. Dry matter accumulation, photosynthetic rate and leaf area index at post-silking stage and yield of low-nitrogen tolerant cultivar ‘Zhenghong 311’ increased by 30.5%, 9.2%, 35.0% and 8.8%, respectively, compared with those of low-nitrogen sensitive cultivar ‘Xianyu 508’. Chlorophyll content in leaves of ‘Zhenghong 311’ enhanced by 4.85% compared to that of ‘Xianyu508’ at post-silking stage. Low-nitrogen tolerant maize cultivar ‘Zhenghong 311’ maintained high chlorophyll content to ensure high dry matter production. There was no significant difference in leaf nitrogen content between two maize cultivars after silking stage. Compared with silking stage, however, leaf nitrogen content decreased by 31.5% for ‘Zhenghong 311’ and by 34.9% for ‘Xianyu 508’ at maturity stage. C/N ratio in leaf of ‘Xianyu 508’ was higher than that of ‘Zhenghong 311’ by 5.95% at post-silking stage. Compared with low-nitrogen sensitive cultivar ‘Xianyu 508’, low-nitrogen tolerant cultivar ‘Zhenghong 311’ kept higher photosynthetic rate and leaf area index during post-silking period, the amplitude of decline in both chlorophyll and nitrogen contents was alleviated, and C/N ratio in leaf kept lower level at later growth stage, all which were beneficial for prolonging leaf functional period, delaying leaf senescence, and increasing dry matter accumulation and yield of ‘Zhenghong 311’. In summary, nitrogen fertilizer effectively increased dry matter accumulation, leaf area index and grain yield. It reduced the increase of C/N ratio in leaf of ‘Zhenghong 311’. However, ‘Xianyu 508’ needed high nitrogen fertilization application to maintain effective leaf photosynthetic rate and nitrogen content.