Rice life is divided into vegetative growth period and reproductive growth period. The reproductive growth period of rice is basically unchanged, but the vegetative growth period changes greatly, so the difference of rice varieties' growth period is mainly the change of vegetative growth period. The vegetative growth period is divided into basic vegetative growth period and variable vegetative growth period. In a certain range, with the increase of temperature and the shortening of sunshine time, the growth rate of general rice varieties is accelerated and the vegetative growth period is shortened. However, after shortening to a certain number of days, even if the temperature and sunshine are suitable, the vegetative growth period will not be shortened. This vegetative growth period is called basic vegetative growth period, also called short-day high temperature growth period. The part of vegetative growth period eliminated by high temperature and short days is called variable vegetative growth period. The growth period of early rice, middle rice and late rice is very different, mainly due to the different length of basic vegetative growth period and variable vegetative growth period. Even the same variety will change the length of growth period in different years, and the same is true.

The variable vegetative growth period of early rice is mainly affected by temperature, and the variable vegetative growth period of late rice is mainly affected by the length of sunshine besides high temperature, which shows that early rice has strong temperature sensitivity and late rice has strong temperature sensitivity and photosensitivity.