When seeds sprout, their young roots typically grow into the soil (in the direction of gravity). However, in some cases, after rice seeds sprout, their roots do not grow into the soil but instead turn outwards, above the soil. This is known as “exposure root.” Why does this phenomenon occur?
The main reason is improper water management in the seedbed—often caused by consistently deep water irrigation. Like humans, rice plants also need sufficient air. If the water in the seedbed is too deep, the rice roots cannot get enough air to breathe. As a result, the young roots grow slowly, do not develop properly, and lack the strength to penetrate the soil, leading to the exposure root phenomenon.
Additionally, when rice seeds are germinated at too high a temperature with insufficient water, the young roots may grow too long. When planted in the seedbed under such conditions, the roots lack the strength to penetrate the soil, causing them to flip. If the seedbed dries out and hardens, it becomes difficult for the young roots to establish themselves. Other causes include sudden heavy irrigation or rainstorms that wash away the young roots before they take hold in the soil, leading to exposure root. Sometimes, frogs jumping around in the seedbed or water birds resting in the field and trampling the seedlings can also cause this phenomenon.
Exposure root is detrimental to seedlings because roots exposed outside the soil struggle to absorb water and nutrients. If they cannot get enough water or nourishment, the seedlings will grow poorly, and over time, they may die from lack of sustenance.