China has been cultivating rice since ancient times. The continuous development of ancient water management allowed rice cultivation to expand. During the Warring States period, large-scale irrigation projects arose in Shaanxi and Henan, promoting the cultivation of rice in the Yellow River Basin. By the third century BC, rice cultivation had also developed in the northeastern regions. By the Northern Song dynasty, rice was predominantly grown south of the Yangtze River. By the Southern Song dynasty, the south had become a major rice-producing area. The rice fields in the Jiangnan region were known by names such as Xutian, Hutian, and Shatian.
Why is rice cultivated in paddy fields? This is because its ancestors originated in the warm and humid swamps of the south, preferring to grow in shallow water areas. Over millions of years, influenced by environmental conditions, its physical structure and living habits have evolved. Ancient people understood its nature, a knowledge that has been passed down to this day.
Water is vital for all crops. For rice, the role of water is particularly significant. Firstly, rice is extremely intolerant of drought. A dry field quickly leads to drought stress. Cultivating rice in paddy fields allows it to have enough water. Its body absorbs water from the roots while releasing it through the leaves, maintaining balance. If this balance is disrupted, it cannot survive normally. Regular irrigation of paddy fields ensures it gets enough water.
Rice’s long, slender roots prefer to grow in soft, wet mud and even thrive submerged in water. If the roots of dryland crops like cotton were submerged, they would not survive, but rice is the opposite. Rice roots can absorb oxygen dissolved in the water. They also have special air channels that allow air to reach the roots. If not grown in paddy fields, its roots could not live this way.
Rice not only needs water but also nutrients to thrive in paddy fields. The fertilizer in paddy fields dissolves slowly into the water, becoming diluted, and the rice roots absorb it along with the water. If in dry land, the fertilizer would be too concentrated for the rice to absorb. The most important elements in fertilizer are nitrogen, phosphorus, and potassium. Nitrogen is essential for growth and for producing chlorophyll. Crops absorb two types of nitrogen: nitrate nitrogen and ammonium nitrogen. Rice prefers ammonium nitrogen, which is abundant in paddy fields.
There are many benefits to cultivating rice in paddy fields. For example, the air above the water is more humid, preventing the rice from drying out too quickly. The water layer also helps regulate temperature: it’s warmer when the weather is cold and cooler when it’s hot, protecting the roots and young shoots from damage. Regular irrigation from the water also brings in air and nutrients. After the field is flooded, weeds are also less likely to grow.
Thus, the life of rice is inseparable from water; it must be constantly surrounded by water.