Nitrogen response of IR8 rice at Coastal Plains Research Station in northern Australia

Abstract

An initial evaluation of the yield potential of IR8 rice in northern Australia was carried out in the 1968 dry season, in the form of a nitrogen trial. The mechanically harvested grain yields (oven dry) varied from 1700 kg/ha with no nitrogen to a calculated maximum of 7335 kg/ha with a nitrogen application of 216 � 11.3 kg N/ha. The highest rate of application (269 kg N/ha) caused a small but significant reduction in mechanically harvested yields. Hand-harvested quadrat yields were closely related to machine-harvested yields (r = 0.90) ; they were some 20 per cent higher, and were not significantly reduced by the highest rate of nitrogen application. The yield response to nitrogen was mainly due to increased panicle numbers per unit area and secondarily to increased numbers of grains per panicle. Mean individual grain weight was only slightly, though significantly, affected by the treatments. The highest calculated yield was recorded with LA1 at flowering of 12.3 � 1.05. With an increase in LA1 to the highest value of 13.5 there was no significant decline in hand-harvested yield. Nitrogen uptake was linearly related to rates of nitrogen application throughout the range of treatments. Apparent nitrogen recovery was 103 per cent at flowering and 71 per cent at maturity in all treatments.