Rice irrigation under limited water supply
1985
Wanna Chankong
The highest grain yield (829 kg/rai) of RD9 variety was obtained from the treatment with the ratio of 0.1 at vegetative stage and total quantities of water applied were 498 millimeters. A positive linear relationship between irrigation practices and plant height, dry matter, number of panicles per tiller, unfilled grain and 1,000 seed weight was also observed. During the growth period of 72 days, the mean actual evapotranspiration rates (ETa) from treatments 1 to 8 were 7.0, 5.7, 5.7, 6.2, 6.2, 6.6, 6.6, 6.0 and 5,8, 5,4m 4,5, 4.7, 5.3, 4.8 and 3.8 millimeter per day for RD 9 and RD7 varieties, respectively. Water use efficiency exhibited an inverse relationship with the total quantity of water applied. However, the low water use of efficiency was found in treatment with water deficit at the flowering stage. The average pan coefficient of treatments 1 to 8 at establishment, vegetative, flowering and yield formation stages were 0.61, 0.98, 1.62, 1.58 for RD9 and 0.61, 0.99, 1.24 and 0.89 for RD7, respectively. The ratio of yield to the actual evapotranspiration was 14 formulating a linear relationship. Irrigation timing was predominant effect on yield response rather than the magnitude of water deficit in each growth period. The average yield response factors (Ky) for treatments 2 to 8 were 0.95, 0.52, 1.75, 1.43, 1.17, 0.83 and 1.07, respectively. The sensitivity factors were 1.12, 0.27, 0.48 at the vegetative, flowering and yield formation stages, respectively. This factor might be used to predict crop yield under other climatic conditions and limited water supply
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