Wet rice is rice grown in flooded fields, called paddies, where standing water covers the soil for most of the growing season. It is the dominant method of rice farming across southern and eastern Asia and produces the vast majority of the world’s rice supply. The fields are kept under about 5 to 15 centimeters (2 to 6 inches) of water, creating conditions that rice thrives in but most other plants cannot tolerate.
How Wet Rice Differs From Dry Rice
The distinction comes down to water. Wet rice, also called lowland or paddy rice, grows in fields that are deliberately flooded and kept submerged. Dry rice, sometimes called upland rice, grows in ordinary well-drained soil on hillsides or plateaus, relying on rainfall alone, much like wheat or corn. Both produce edible rice grain, but wet cultivation is far more common globally because it yields more food per acre and offers built-in pest control through the flooding itself.
Wet rice paddies have a naturally impermeable or compacted subsoil layer that prevents water from draining away. Farmers build low earthen walls, called bunds or levees, around each field to hold the water in place. This creates a shallow, controlled pool that stays in place for roughly three-quarters of the growing season before the field is drained ahead of harvest.
Why the Fields Stay Flooded
Flooding serves a precise biological purpose: weed suppression. Rice is the only major cereal crop capable of germinating underwater. That trait gives it an enormous competitive advantage. When a paddy is flooded to even 2 to 4 centimeters, most common weed species simply cannot emerge. Studies have shown that continuous flooding at just 2 centimeters reduces the emergence of certain sedge weeds to less than 10% of what would appear in merely wet soil, and 4 centimeters of water is enough to stop some species entirely.
Before modern herbicides existed, this was the primary way rice farmers controlled weeds, and it remains effective today. Farmers traditionally grow seedlings in a small nursery plot, then transplant them into the flooded paddy once the plants are large enough to stand above the waterline. This size advantage, combined with the flooded soil, means weeds that try to germinate at ground level are fighting a losing battle from the start.
Water Use and Environmental Cost
Wet rice is water-intensive. According to the International Rice Research Institute, producing 1 kilogram of rough (unmilled) rice requires an average of about 2,500 liters of water supplied to the field through rainfall or irrigation. Of that, roughly 500 to 1,000 liters is water the plant actually transpires through its leaves. The rest is lost to evaporation from the flooded surface, seepage into deeper soil layers, and percolation through the paddy floor.
With global rough rice production around 600 million tons per year, the water demands are staggering. This is why rice farming dominates water use in many Asian countries and why researchers have explored alternatives like intermittent flooding, where fields are allowed to dry briefly between soakings, to cut water use without destroying yields.
Where and How It Is Grown
Wet rice cultivation takes place in coastal plains, river deltas, and lowland basins across tropical, subtropical, and temperate climates. The two main subspecies of cultivated rice map roughly onto geography. Indica rice dominates in the tropics and subtropics (think Southeast Asia, India, and southern China), while Japonica rice is more common in cooler, higher-latitude areas like Japan, Korea, and northern China. Both are overwhelmingly grown using wet paddy methods.
Despite using only a small fraction of total agricultural land in many countries, wet rice feeds the majority of the rural population across the Far East. Its productivity per unit of land is high enough that densely populated regions have depended on it for thousands of years. The system rewards careful water management and labor-intensive transplanting, which historically shaped the social organization of entire communities around planting and harvest schedules.
How Flooding Affects the Grain Itself
The waterlogged soil in a paddy changes the chemistry of what ends up in the rice grain. One notable effect involves arsenic. Flooded soils release arsenic from soil particles into the water, which the rice plant then absorbs. Research has found that constantly flooded fields produce rice with arsenic concentrations around 0.21 mg/kg, compared to 0.14 mg/kg in rice grown under aerobic (non-flooded) conditions. That is a roughly 50% increase. Growing rice in drier soil consistently lowers arsenic accumulation in the grain.
On the other hand, flooding has the opposite effect on cadmium, another toxic metal. Cadmium concentrations in rice grain drop dramatically under flooded conditions, falling from 0.21 mg/kg in aerobically grown rice to just 0.02 mg/kg in constantly flooded paddies. So the same water management practice that raises arsenic levels actually protects against cadmium contamination.
Mineral nutrition shows a similar tradeoff. Wetland rice varieties tend to contain higher zinc concentrations in the grain, with studies reporting 39 to 59 mg per kilogram in wetland varieties compared to 17 to 26 mg per kilogram in upland varieties. However, the waterlogged soil itself can reduce the availability of water-soluble zinc, and anaerobic conditions in flooded soil produce harmful substances that can inhibit root growth and the plant’s ability to absorb beneficial trace elements. The net result depends on the specific variety, the soil, and whether zinc fertilizer is applied.
Why It Remains Dominant
Wet rice persists because no other system matches its combination of high yields, natural weed control, and adaptability to monsoon climates where seasonal flooding happens anyway. The standing water essentially turns a liability (too much rain) into an asset. Farmers in river deltas and floodplains work with their landscape rather than against it, channeling water that would otherwise cause damage into productive paddies.
The system does face pressure from water scarcity and concerns about methane emissions from flooded soils, which contribute to greenhouse gas output. But for roughly half the world’s population that depends on rice as a staple food, the paddy remains the foundation of the food supply.