Water Management - 86


 

 

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Project Leader and Principal UC Investigators

J.F. Williams, Cooperative Extension, University of California, Sutter-Yuba counties

 

Objective

  • Determine the most beneficial practices for rice growth, yields and weed control.

The rice water management studies were conducted by the University of California's Statewide Integrated Pest Management Project, with support funds coming from the state. Harvesting equipment and some labor were provided by Rice Research Board funds. General objectives of the Integrated Pest Management Project are improved pest control techniques, reduced pesticide load in the environment, increased use of natural pest controls, and development of programs that are environmentally and economically acceptable.

Six water management systems were compared using the same plots for the second year in Sutter County. All water management treatments were compared with and without the use of herbicides, making a total of 12 treatments.

Three of the water management treatments compared shallow (2 inches), moderate (5 inches), and deep (8 inches) water for the first 75 days, after which all were maintained at 8 inches.

The fourth water management treatment was to flood the field, sow the rice seed into the water and then drain immediately. As soon as the rice seedlings became anchored in the mud, the field was reflooded to a 5-inch depth for the next 75 days and then raised to 8 inches for the remainder of the season.

The fifth treatment was to flood the field to 5 inches, sow the rice seed and hold this water depth until 8 days after Ordram application. The field was then completely drained until the rice recovered, then reflooded to 5 inches for 75 days, after which an 8-inch water depth was used.

The sixth and last treatment was to flood to 8 inches until 8 days after Ordram application, then dropping to a 5-inch depth for 75 days, after which the 8-inch depth was maintained.

None of the water management treatments gave satisfactory yields without herbicide use, but significantly higher yields were obtained from continuous flooding, initially at 8 inches and then dropping to 5 inches until the plants were well established. This is treatment six as described above and is referred to as the "old method" that was widely used before herbicides were available.

Where pesticides were used, the so called "old method" was the best in 1985, the first year of the experiment. However, in 1986, the best treatment, as measured by yields, was the shallow water held at 2 inches for 75 days, then increased to 8 inches. Next best, but nearly 900 pounds per acre less, was the intermediate water depth (5 inches) for 75 days, followed by 8 inches of water for the remainder of the season. It appears that where weeds are not a problem, shallow water during the early stages of rice development is beneficial, probably because shallow water favors tiller development.

Eight widely grown rice varieties were compared at shallow, intermediate and deep water management in 1986. Yields showed that varieties with vigorous seedlings, such as S-201 and M-101, are relatively unaffected by water depth, while the varieties with less vigorous seedling growth, such as M-201 and M-202, are adversely affected by deep water. The long-grain variety L-202, although low in seedling vigor, was not appreciably affected by water depth.

 

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