Why are the rice harvest months different in the south and the north?

South and north rice in which month is it harvested? As everyone knows, only by accurately grasping the rice harvest time, sowing at the right time and harvesting at the right time can yields be increased. Below, let us take a look together at the rice harvest times in the south and the north.

North China is a single-cropping rice region. Single-season rice must be sown before Qingming and transplanted at the end of April and the beginning of May (if conditions permit, it can also be transplanted at Guyu). Northeast China is an early-maturing single-cropping rice region. The sowing time is around April. For double-cropping rice in the north, the first rice crop has a growth period of 104 days, and the second rice crop has a growth period of 87 days. These are generally early-maturing varieties. They avoid winter. To grow double-cropping rice in the north, extra-early-maturing varieties must be developed.

In the south, the first rice crop is raised from seedlings in mid-April of the Gregorian calendar and can mature and be harvested in early August, about 104 days. The second rice crop is transplanted while the previous crop is being harvested. It is harvested before the ground freezes. Taking the middle and lower Yangtze Plain in the south as an example, early rice is sown in mid-April, transplanted in early May, and harvested in late July, immediately followed by late rice transplanting (known as double rush), which generally must be completed before Liqiu, and late rice is harvested from late October to November.

For nearly half a century, Neolithic rice remains in the Yangtze River basin and to its south have spanned from 4,000 to 10,000 years ago, while Neolithic rice remains in the Yellow River basin date back only 4,000 to 5,000 years, indicating that rice in the north was introduced northward from the south into the Yellow River basin in the late Neolithic period. In the late Neolithic period, the average annual temperature in the north was about 2C0 higher than now, and rainfall and lakes were also greater than today, so rice quickly took root and grew in places in the north with sufficient water sources. After entering recorded history, the general trend of the northern climate developed toward aridity, rainfall gradually decreased, lakes and rivers gradually shrank, and the rice area naturally shrank as well. Although rice is still cultivated in the north to this day, its characteristic is that it has not been grown on a large scale. The current distribution is one area in Xinjiang, the Gansu Hexi Corridor, the Inner Mongolia Hetao region, and the Ningxia Yellow River irrigation district; one area in northern Shaanxi, northern Shanxi, and parts of Hebei; and one area in parts of Liaoning, Jilin, and Heilongjiang in the northeast. Most of what is grown is japonica rice.

Indica rice is mainly distributed across the vast areas of South China, and once it reaches the Yangtze River basin it no longer goes north; japonica rice is mainly distributed in the Yellow River basin and to its north. What is the reason for this? From the process of rice domestication, the first to be domesticated was indica rice. This is easy to understand, because wild rice is distributed south of the Yangtze River. Indica rice inherited the characteristics of wild rice and is naturally warmth-loving and not cold-tolerant. Below, let us compare the climatic differences between South China and North China and their relationship with rice growth and development, which can deepen our understanding of the indica-japonica issue.

The climate of South China is characterized by the highest temperatures, the greatest heat resources, the most abundant rainfall, and the longest rice-growing period. The annual monthly average temperature in South China is above 10°C, and the average annual rainfall is above 1500 to 2000 mm. During the rice-growing period, the average temperature is 22 to 26°C, and the difference between daytime and nighttime temperatures is only 5 to 8°C, so two rice crops, early and late, can be grown in one year. In North China, such as the Beijing-Tianjin region, the climate is characterized by an average temperature during the rice-growing period of 19 to 21°C, a day-night temperature difference of as much as 12 to 15°C, and a monthly average temperature of 10°C

for only a little more than six months, with average annual rainfall above 500 mm. The time allowing rice growth is only about five months (even shorter in the northeast rice region), so only early rice types with one crop a year can be grown.