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Craig Beyrouty*, R.J. Norman, N.A. Slaton
Department of Agronomy, University of Arkansas, Fayetteville,
Arkansas USA 72701
All of the commercially produced rice in the United States is lowland irrigated. However, the timing of floodwater application is not the same throughout the rice producing regions. Either rice is drill seeded into a non-flooded soil, with a permanent flood applied at the 4- to 5-leaf stage, or germinated rice seed is broadcast by airplane into a standing flood. In both cases, the flood is usually removed from the soil approximately two weeks before the grain is mechanically harvested. Nitrogen is usually applied as a single pre-flood broadcast application or is split into two or three smaller quantities applied up to reproductive growth. Rice cultivars bred for commercial production in the United States vary considerably in growth characteristics, most notably in maturity and stature. Many of the newer cultivars are short-season semi-dwarfs that are capable of absorbing high levels of nutrients and producing excellent grain yields. Less than 1% of the rice grown in the U.S. is short grain, while 28 and 72% are medium and long grain, respectively.
Rice is grown in seven of the 50 states in the U.S., these being: Arkansas, California, Florida, Louisiana, Mississippi, Missouri, and Texas. In 1995, the average rough rice grain yield in the U.S. was 6400 kg/ha with a range of 5900 to 9100 kg/ha among the seven rice producing states.
Rice Production in Arkansas
Arkansas produces about 40% of the U.S. rice and ranks number one in hectares planted and kilograms per hectare produced. Nearly 55% of the rice in Arkansas is produced on silt loam soils located in the eastern one third of the state. The remainder of the soils are clay and sandy loams. This region of the state is ideally suited for rice production because it consists of alluvial soils deposited by the Mississippi river and located on flood plains and terraces. The landscape is flat to slightly undulating and many of the soils have impeded drainage. Rice was first grown on 0.4 hectares in 1902 and peaked at 0.6 million harvested hectares of rice in 1981.
The average farmer in Arkansas is 49 years old and operates a farm typically consisting of 200 to 800 ha of which less than 200 ha is usually dedicated to rice. The average size of a rice field is 26 ha. Rice is usually grown in rotation with soybean but can follow corn, rice, sorghum, cotton, or fallow.
Several varieties of rice are grown that represent very short, short, or midseason maturity groups and are long or medium grain types. Days to 50% heading range from 77 to 82 for the very short season varieties to 89 to 101 for the medium maturing varieties. Selection of appropriate rice varieties is assisted through use of the RICEVAR computer program available through the Cooperative Extension Service. Seedbed preparation generally consists of disking in early spring, land planing to smooth the field and eliminate depressions, and cultivating to prepare a firm, shallow seedbed. Levees are built between fields to contain the 5 to 10 cm depth flood applied at the 4- to 5-leaf stage. Levees are spaced such that there is no more than a 0.6 cm vertical interval between adjacent levees. Planting is generally conducted on dry seedbed and the dates vary between early April to mid June, but is not recommended to begin until the average daily temperature is at or above 21C. For most varieties, the optimum stand density is 15 to 20 plants per square foot. In order to achieve this final stand, the initial seeding density is recommended to be 40 seeds per square foot. This seeding density is increased 10% when seeding is done on a date earlier than recommended, 20% for broadcast seeding or if seeded into a clay soil or into a poorly prepared seedbed, or 30% if water seeded. RICESEED is a computerized seeding rate and drill calibration program available through the Cooperative Extension Service that provides a recommended seeding rate for the variety chosen and the specific situation described.
The DD50 program is used by 70% of the rice producers in Arkansas to assist with 28 management decisions such as herbicide application, critical times to scout for insects and diseases, and N application. It is a modification of the growing degree day concept which uses temperature to predict rice development. It calculates the daily heat units above 50F and predicts days to reach a specific stage of plant development based upon heat units required to reach that stage. Heat units are calculated from 30 year weather data and predictions are adjusted during the season if temperatures vary considerably from the average.
Nitrogen is usually recommended as a 3-way split application, with 50 to 80% of the N applied preflood and the remaining N split applied at internode elongation and 7 days after internode elongation. Urea is the N source of choice and is often applied aerially by plane. Weed, disease, and insect control is accomplished by following recommendations provided by the Arkansas Cooperative Extension Service. Recommendations are based upon research and many are listed in the Rice Production Handbook, a joint publication by the University of Arkansas and Cooperative Extension Service.
Much of the research conducted on rice is supported from funds supplied by the Arkansas Rice Research and Promotion Board. Funds administered by this board are contributed by rice producers in Arkansas to support rice research and the promotion of rice to the general public.