Role of nitrogen regulation in sink and source formation of high-yielding rice cultivars

By applying nitrogen (N) and phosphorus (P) fertilizers at different rates and times to high-yielding rice cultivars, we analyzed the absorption of N at different stages in relation to the formation of the source and sink as well as grain yield. The results showed that, the grain yield increased alo ng with the enlargement of the sink size. N absorption from 30 d before hea ding (DBH) to heading was more important for enlarging the yield sink than that at other stages. N absorption during this period was even more importa nt for panicle weight type cultivars (line 9004 and Yangdao 4) than that fo r a panicle number type cultivar (Suweon 258), N absorption before 30 DBH l ed to a higher increase of the leaf area index (LAI) compared to that after wards. And faster decrease of LAI after heading was correlated more closely with the LAI at 30 DBH than with the LAI increase from 30 DBH to heading. A larger N absorption from 30 DBH to heading enabled to maintain a higher L AI after heading, Dry matter accumulation after heading contributed more to grain yield than that at heading in the panicle weight type cultivars, whe reas it was equally important in the panicle number type cultivar, Regulati on of N absorption at different growth stages of high-yielding rice cultiva rs was also examined.