WATER MANAGEMENT AND LOCATION EFFECTS ON ROOT AND SHOOT GROWTH OF IRRIGATED LOWLAND RICE

In the United States rice (Oryza sativa L.) is entirely flood irrigated. Delaying the application of the floodwater beyond the recommended time is practiced by some Arkansas producers and may (with supplemental rainfall) potentially reduce the water inputs required to produce a crop. Water stress, however, may affect root growth characteristics which could impact fertility management decisions relative to continuous flood culture. Therefore a field study was initiated to identify the responses of root and shoot growth and yield to water management and location. Two water management treatments were imposed on the 'Tebonnet' cultivar, i) normal water management where a flood was applied at the four- to five-leaf stage (continuous flood), and ii) flood delayed (but with supplemental irrigation) until 1.25 cm internode elongation. Studies were located on two soils in eastern Arkansas, a Sharkey clay and Crowley silt loam in 1988 and 1989. The floodwater was removed from plots approximately 10 d before harvest. Although there was no treatment effect on total root length, root length densities showed an inconsistent proliferation in response to the delayed flood at the 0-10 cm and 30-40 cm soil depths. This proliferation in root length density differed between locations and years. Delayed flood reduced plant height in 1988 only up to heading and there was a trend for reduced leaf area index in both years. Grain yield was not significantly affected by water management. Yield was greater, however, for rice grown on the Crowley soil than the Sharkey soil by nearly 1100 kg/ha. This yield increase may have been due to higher tiller production on the Crowley soil. Root lengths differed between locations with higher root lengths measured on the Sharkey. Results suggest that delayed flooding does not severely stress the rice plant and yields similar to those achieved with continuous flood can be obtained.