4th Grade - Science

LESSON PROBLEM: Botany: How is irrigation of rice different from irrigation of other crops?


Rice is an important food staple with as many as 40,000 varieties. It is grown on every continent, except Antarctica. As you can imagine, the growing conditions from place to place can vary widely also. In general, there are two methods for growing rice, either as upland rice or as irrigated rice. These two methods vary according to the complexity of the farming methods, the geography of the land and the source of water. The common factor for either method is the need for and use of water. Rice grows best in flooded fields called paddies. In the United States rice is farmed to make efficient use of resources like water and land.

Upland Methods Vs. Irrigated Methods

Upland Rice
About sixty percent of the rice grown in the world is considered "upland" rice. This is rice that is grown on fields that totally depend on rainfall to flood the paddies. The rice farmer first prepares his field to make it level. Levees are then constructed around and through the fields to hold the rainfall on the field. The levees keep the water at the best depth for the variety of rice the farmer is growing. Upland rice is grown in areas of the world where there is a lot of rainfall, such as Southeast Asia, Brazil, Bangladesh and Indonesia.

Upland rice is also grown in areas of the world where the land is more hilly, such as in the Himalayas, Laos and Philippines. In most of these hilly regions, the sloping land is leveled into steps so that rice can be grown. This is what is meant by terracing. It is necessary to level the ground because horizontal ground is needed so the water can stay on the land. The collected rainwater is allowed to flow from the highest step to the lowest levels.

Flood Prone Areas
Some areas where rice is an important crop tend to flood. Special varieties of rice called flood-prone or floating rice are grown in these areas. It is cultivated in uncontrolled flooded river valleys. It grows very quickly and has long stems. The panicle floats on the surface of water. The panicle is the swelling head of the rice plant, which is full of grains. The rice is harvested by people sitting in boats or it is harvested after the flood waters recede. This method is used in many areas of Asia, especially China, Cambodia, Bangladesh, and Thailand.

Irrigated Rice
Modern rice farmers, such as those in the United States, use irrigation to produce rice. In this method, rice farmers are able to control the flow and amount of water needed to produce the rice. Irrigation insures that the farmer will get a lot of rice and a quality grain. With irrigation, the farmer does not need to rely on weather that might not always produce the water needed for his rice crop. Water is drawn from nearby rivers or wells to flood the fields. Rice fields, where water is controlled by the farmer, produce about forty percent of the rice produced in the world. U.S. rice farmers use irrigation and other farming techniques that use water efficiently. They use laser and computer assisted machinery to create perfectly leveled rice fields with an exact placement of the levees in order to keep water at an even depth of about two to three inches. Special equipment is often used to recycle the water and to keep it at an even depth.

Mechanized Farming in the U.S.A.
In the United States, machines are used to level vast amounts of land to make large paddies. While the paddies in hilly areas, such as the Philippines, might be smaller than a football field, in the U.S. the largest rice farm covers approximately 15,000 hectares, which is equal to 36,000 acres. The average size rice farm in the U.S. is about 336 acres. Here space-age technology, computers, lasers and airplanes are used to prepare the soil and sow the rice seeds on large farms. Machines are used at each stage of rice cultivation from preparing the land and sowing the seeds to harvesting, milling and packaging.

To prepare the fields for planting, heavy equipment, aided by computers and laser guidance systems, shift the soil and level the fields to provide an even gentle slope to the fields to insure uniform flooding during the growing season. Water control levees are precisely placed to control and conserve the water on the fields.

The water for the rice fields is pumped from nearby rivers, canals or wells and is kept on the fields throughout the growing season at a depth of 2 to 3 inches. Modern irrigation systems are often used to conserve water. Today, a rice farmer, in the United States, can use up to two-thirds less water than they may have used thirty years ago.

Acres of fields can be quickly seeded either by grain drills that plant the seeds to an exact depth before the field is flooded or airplanes are used to cast seed over flooded fields. Harvest begins when the rice grain has matured. The water is first drained from the fields and combines then cut the rice, separate the grain from the stalk and pump the grain into trucks which will transport the grain to the drying/storage facilities. Here the rice is stored at precise moisture levels to keep the grain at peek quality until it is ready to mill. Following harvest, U.S. farmers reflood the rice field to provide a wetland habitat for migrating waterfowl, such as ducks and geese. The flooded fields provide food and shelter for the waterfowl. It also has benefits to the farmers. Water left on the field helps reduce soil erosion and improves water quality.

Draw an illustration for each of the different methods of rice farming. Include a caption stating how each one is unique.

Refer to books that tell about mechanized rice farming used in the U.S.A., and try to find out how it affects the rate and productivity of rice

  • panicle
  • irrigation
  • spikelet
  • terracing
  • mechanization
  • stepping

Click here to play Rice Rampage!
How is Rice Grown:
Farming rice is hard work. Click here to learn more about the Stages of Farming Rice.
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