Growth, yield and nitrogen allocation in two rice cultivars under field conditions in venezuela

a field experiment was set out to evaluate the differences in biomass production, nitrogen economy and grain production between two rice cultivars araure 4 (a4) and fonaiap 2000 (f2000), which differ in yield potential. aboveground biomass and n distribution within the plant were determined at different growth stages and their relation to grain yield analyzed. a4 produced more biomass than f2000. however, yield and harvest index of a4 were 13 and 27% lower, respectively, than those of f2000. spikelets per m2 and the weight of 1000 grains were higher in f2000, but the percentage of filled grains was the same, resulting in a greater grain sink capacity in f2000. a4 maintained higher rates of biomass production than f2000 until anthesis; the opposite occurred during grain filling. organ n concentrations were similar between cultivars, although leaves of a4 showed slightly larger values than leaves of f2000. a4 accumulated 15% more n than f2000 during the growth cycle. most of the accumulated n (92%) in a4 was taken up between transplant and anthesis, whereas f2000 took up over 30% of total n between flowering and maturity, most of it for grain development. in f2000 60% of total n accumulated in the plant was in the grain whereas in a4 grains accounted for only 44%. consequently, n harvest index and n use efficiency for grain production were much larger in f2000. the higher yield in f2000 compared to a4 can be partly attributed to greater sink capacity, larger rates of post-anthesis growth, n uptake and remobilization. these traits can compensate for a smaller plant size in f2000.