The researchers studied how nitrogen fertilizer affects starch accumulation and enzyme activities in rice grains. They found that adding nitrogen fertilizer to rice plants can decrease soluble sugar in developing grains and slightly reduce starch content. Amylose and amylopectin levels in the grains increased as they grew heavier. Enzyme activities involved in starch synthesis peaked around 10-15 days after flowering and then decreased. Nitrogen fertilizer boosted some enzyme activities in the grains during later growth stages but decreased others. Fertilizing at the booting stage had a better effect than at the tilling stage.