Drought response of rice at different nitrogen levels using line source sprinkler system

Abstract

In rainfed rice, the nitrogen status of soil and plant is closely related to the moisture regime in the soil. The lower the soil moisture content, the lower the nitrogen use efficiency in the plants. 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 reaction and measurement of leaf water potential (LWP) were also made. The effect of drought was least on the traditional variety Kinandang Patong and most on the modern variety IR 20. Increasing nitrogen levels from 0 (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 levels of nitrogen, Kinandang Patong had significantly higher LWP than IR 20. There was a curvilinear decrease in the number of days to heading and a linear increase in plant height and dry matter production with increase in total water applied. The yield-water-fertilizer relationships of the four cultivars revealed different production surfaces. The early-maturing IR 52 rice gave the highest grain yield at 120 kg N/ha and with maximum water application of 850 mm. Without nitrogen fertilizer application, Kinandang Patong gave the highest predicted yield with 550 mm of water applied. At 120 kg N/ha and 550 mm of water, IR 36 was superior in yield to other rices tested. Results suggest that in areas of uncertain moisture supply, nitrogen application rate should be reduced from that normally used for irrigated rice.