Grain and starch granule morphology in superior and inferior kernels of maize in response to nitrogen

Maize (Zea mays L.) contributes approximately 55% of China's grain production. The effects of nitrogen (N) on maize grain morphology and starch granules remain elusive. In this study, a field experiment in clay loam soil was conducted using three maize hybrids (Suyu 30, Suyu 20, and Suyu 29) and four N levels (0, 360, 450, and 540 kg ha^-1) in 2010 and 2012. The results indicated that increased grain length and width, starch granule number, surface area, and volume, was associated with the application of 450 kg ha^-1 of N. Differences between superior (ear base) and inferior (apical) grains decreased under highest yield treatments. The effects of N levels on inferior grains was more than that on superior grains. The starch granules of superior grains showed more polygonal, and bigger shape than inferior grains. The results revealed that N levels affected size and morphology of starch granules and grains. The application of 450 kg N ha^-1 resulted in larger-sized starch granules and less difference between superior and inferior grains.