Relationships between ripening-phase productivity and crop duration, canopy photosynthesis and senescence in transplanted and direct-seeded lowland rice
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A field experiment was conducted to analyze the effect of crop duration on growth and the yield-formation process in tropical lowland rice. Three semidwarf rices (IR58, IR64, and IR29723-143-3-2-1) of different growth durations were either transplanted or broadcast-seeded, and grown under different nitrogen fertilizer regimes. Dry-matter accumulation and N concentration of various plant organs, leaf-area index (L), tissue death, tiller number, plant height, and canopy photosynthesis were recorded periodically. Crop duration increased plant biomass but did not significantly affect grain-yield. Plant N uptake was not affected by crop duration. Direct seeding gave grain yields superior to those of transplanted rice using short-duration IR58, but equal or lower grain-yield using the medium-and long-duration varieties. Growth and development were delayed, and tillering and foliage growth were reduced in transplanted rice due to transplant shock. Tiller production and abortion were a function of relative growth rate. Tissue death occurred during the reproductive phase and depended on L and foliage N concentration. IR58 had the highest L (up to 11.6) and IR64 the lowest. Direct-seeded rice had higher L and dry-matter during vegetative and reproductive growth, but lower foliage N concentration, than had transplanted rice. Growth during ripening was negatively affected by high biomass and L at flowering but enhanced by high foliage N concentration. It is concluded that grain-yield is impeded by high biomass at flowering in direct-seeded rice, particularly in long-duration varieties. High biomass at flowering, however, may enable further yield improvement if N partioning and foliage expansion patterns are modified.
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