Effect of Plant Type and Nitrogen Level on the Growth Characteristics and Grain Yield of Indica Rice in the Tropics1

Abstract
Of the various factors affecting nitrogen response in rice, plant form or plant type is particularly significant. Experiments were conducted during two crop seasons to study the N response and the growth characteristics of some traditional leafy tropical indica varieties and two dwarf indicas of improved plant type. Most of the traditional tall varieties lodged at certain growth stages, and yielded the best when 30 to 60 kg/ha N was applied. One of the dwarf varieties developed by the Institute produced progressively higher yields (the highest being 9,477 kg/ha) up to 120 kg/ha N in the sunny dry season. The increase in dry matter production from panicle initiation to harvest was significantly correlated with grain yield.During the cloudy wet season when the grain yield response to fertilizer N is lower than during the dry season, the dwarf indica variety, IR8, produced 3,480 kg/ha more rough rice than the tall, weak‐strawed variety, Peta, indicating the importance of short stature and culm strength in obtaining high yields.
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