Macro-element absorption at maturity in relation to grain yield in high-yielding rice cultivars

By applying nitrogen (N) and phosphorus (P) fertilizers at different rates and times to high-yielding rice cultivars, we determined the absorption of N, P, and potassium (Ii) in relation to the grain yield. The results showed that, at a higher top-dressing rate of N, the grain yield increased and th e absorption of N, P, and K was stimulated, whereas top-dressing of P did n ot significantly increase the grain yield and nutrient absorption. The abso rption of N, P, and K differed markedly among the cultivars, even at the sa me level of grain yield in the same field (for Yangdao 4 and Suweon 258). N absorption in line 9004 was 29.2 g m(-2) for a paddy grain yield of 1,250 g m(-2) (brown rice: about 1,000 g m(-2)), being much higher than the value reported in the literature. The ratio of N : P : K absorption at different yield levels revealed that, with the increase of grain yield of the cultiv ars, the absorption of P and IE relative to the absorption of N decreased. The absorption amounts and ratios of N, P, and K depended on the cultivars, yield levels, and possibly, soils of the held.