High nitrogen input increases the total spikelets but decreases the high-density grain content in hybrid indica rice

Nitrogen (N) application strongly affects both the total spikelets and grain weight in rice (Oryza sativa L.), thereby affecting grain yield. Grain weight is closely related to the grain-filling process after the heading stage, and can be regarded as a combination of grain size and grain density (GD). However, there is a lack of information about the response of GD in rice to N. Here, we examined in a lager panicle hybrid indica rice at two field experimental sites the responses of grain traits (including GD), grain yield, and yield components to various N treatments and their relationships with each other. In this study, the grains with six GD ranges were fractionated into the light grain (1.00 g ml−1 ≤ GD