PLANT-POPULATION EFFECTS ON GROWTH AND YIELD IN WATER-SEEDED RICE

Initial management strategies, such as established plant stand, significantly affect rice (Oryza sativa L.) crop development, grain yield, and final profits. Critical rice plant population for optimum yield differs greatly among various cultural systems. The objectives of this study were to: (i) characterize effects of increasing plant population on tillering, yield components, yield, and phytomass development in continuously flooded, direct water-seeded rice culture; and (ii) identify which crop development parameters are associated with optimum grain yield in this cultural system. Two cultivars, S-201 and M-201, were seeded at rates ranging from 120 to 840 seeds m-2 on Stockton clays (fine, montmorillonite, thermic, Typic Pelloxererts) in Butte and Colusa counties, California, in 1984 and 1985. Plant populations ranged from 122 to 458 plants m-2. Initial rapid tillering resulted in a maximum tiller density within 37 to 63 d after seeding (DAS). Total above-ground phytomass (TAGPM) was not significantly different among the plant populations, either during or at the end of the growing season. Although final vegetative above-ground phytomass (VAGPM) increased as a function of tiller density, VAGPM above 850 g m-2 did not result in further yield increases. Grain yields were dependent on final tiller density (FTD) rather than plant population, with yields increasing as FTD increased to 700 tillers m-2. Panicles m-2, a direct result of FTD, was the most important component of yield accounting for 89% of the variation in yield. Final tiller density or the tillering capacity of the rice crop is determined by the environmental limitations and favorability of the growing conditions. Under continuously flooded, direct water-seeded culture, the rice crop functioned more as a population of tillers than a population of plants.