13 graphs; 22 ref. Summary (En)

In this study, the yield and growth responses of four rice cultivars to seven irrigation and three nitrogen levels were evaluated using the line source sprinkler system. Visual observations on the degree of drought tolerance and measurement of leaf water potential (LWP) were also made. The effect of drought stress was least on the traditional variety Kinandang Patong and greatest on the modern variety IR 20. Increasing nitrogen levels from D (no nitrogen fertilizer) to 60 and 120 kg N/ha increased the degree of water stress. This also resulted in decreased LWP especially when the total water applied was minimal. At all nitrogen levels, Kinandang Patong had significantly higher LWP than IR 20. There was a curvilinear increase in the number of days to heading and a linear decrease in plant height and dry matter production with decrease in total water applied. The yield-water-fertilizer relationship of the four cultivars revealed different production surfaces. The early-maturing IR 52 gave the highest grain yield at 120 kg N/ha and maximum water application of 850 mm. Without nitrogen fertilizer (0 kg N/ha), Kinandang Patong gave the highest predicted yield with 550 mm water applied. At 120 kg N/ha, and 550 mm water, IR 36 was superior in yield to other rice tested. Result suggest that in areas of uncertain moisture supply, nitrogen application rate should be reduced from that normally used for irrigated rice culture

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