INCREASING EFFICIENCY OF FERTILIZER NITROGEN IN WETLAND RICE BY MANIPULATION OF PLANT-DENSITY AND PLANT GEOMETRY

In a study of the effect of plant density and plant geometry on grain yield of rice grown under various levels of soil nitrogen and environmental regimes, the grain yield of IR36 (early maturing) and IR26 (intermediate maturing) rices grown during the 1976 wet season and the 1977 dry season in the Philippines increased by 0.6 t ha-1 as the plant density increased from 2.2 × 105 to 5.0 × 105 hills ha-1. The yield of two early maturing rices - IR36 and IR40 - grown during the 1977 wet season increased by 1.3 t ha-1 when the plant density increased from 0.67 × 105 to 106 hills ha-1. The rate of fertilizer application affected rice yield response to plant density with no fertilizer nitrogen applied or with low levels ({slanted equal to or less-than} 60 kg N ha-1) of applied fertilizer nitrogen. Grain yield increased either linearly or curvilinearly with increased plant density. At a high level of applied nitrogen (120 kg N ha-1, grain yield increased as the plant density was increased to a certain level beyond which the yield decreased with increased plant density. Plant geometry significantly affected the grain yield of rice. In the 1976 wet season, when the solar radiation was low and sunshine duration was short during the reproductive and ripening stages of rices, the yield of rice planted in a short-rectangular (20 cm × 10 cm) spacing pattern was significantly higher than that of rice planted in a long-rectangular (40 cm × 5 cm) spacing. During the 1977 dry season, however, with high solar radiation and long sunshine duration, the trend was reversed. © 1979.