Fresh maize yield in response to nitrogen application rates and characteristics of nitrogen-efficient varieties

Efficient nitrogen management is crucial in developing sustainable strategies aimed at enhancing yield while mitigating negative environmental impacts. However, limited research has focused on this aspect in the production of fresh maize. Therefore, this study analyzed nitrogen application rates and yield for 40 sweet and 44 waxy maize varieties in Zhejiang Province, China from 2015 to 2019 across five sites. Nitrogen application rates were categorized as relatively high (RHN: >300 kg ha-1 for sweet maize, >320 kg ha-1 for waxy maize) or relatively low (RLN). An increase in nitrogen application rates for both sweet and waxy maize significantly reduced nitrogen fertilizer partial productivity (R2=0.616, P<0.01; R2=0.643, P<0.01), indicating that the optimum nitrogen application rate in this study might be the lowest values (160 kg ha-1 for sweet maize and 180 kg ha-1 for waxy maize). The kernel number per ear of sweet maize had a potentially more significant impact on fresh grain yield compared to the 1,000-fresh kernel weight both under RLN and RHN. In waxy maize, 1,000-kernel weight contributed more to fresh grain yield under RLN, and kernel number ear-1 and 1,000-kernel weight cooperatively affected yield under RHN. In this study, it was observed that sweet maize required taller plant and ear height, along with an optimal ear-plant height ratio, to enhance dry matter accumulation and increase source size, particularly under RLN, to achieve a higher fresh grain yield. In contrast, a lower ear height and ear-plant height ratio of waxy maize probably contributed more to increased kernel number and weight under RLN, likely due to a lower ear height can reduce the distance between sink and source, enabling more efficient photoassimilate allocation to the ear.