Top-grain filling characteristics at an early stage of maize (Zea mays L.) with different nitrogen use efficiencies

Maize genotypes vary significantly in their nitrogen use efficiencies (NUEs). Better understanding of early grain filling characteristics of maize is important, especially for maize with different NUEs. The objectives of this research were (i) to investigate the difference in apical kernel development of maize with different NUEs, (ii) to determine the reaction of apical kernel development to N application levels, and (iii) to evaluate the relationship between apical kernel development and grain yield (GY) for different genotypes of maize. Three maize hybrid varieties with different NUEs were cultivated in a field with different levels of N fertilizer arranged during two growing seasons. Kernel fresh weight (KFW), volume (KV) and dry weight (KDW) of apical kernel were evaluated at an early grain filling stage. Ear characteristics, GY and its components were determined at maturity stage. Apical kernel of the high N and high efficiency (HN-HE) type (under low N, the yield is lower, and under higher N, the yield is higher) developed better under high N (N210 and N240, pure N of 210 and 240 kg ha−1) than at low N (N120 and N140, pure N of 120 and 140 kg ha−1). The low N and high efficiency (LN-HE) type (under low N, the yield is higher, while under higher N, the yield is not significantly higher) developed better under low N than at high N. The double high efficiency (D-HE) type (for both low and high N, the yield is higher) performed well under both high and low N. Apical kernel reacted differently to the N supply. Apical kernel developed well at an early grain filling stage and resulted in a higher kernel number (KN), kernel weight (KW) and GY with better ear characteristics at maturity.