Determination Of The Optimum Sowing Rate Of Hybrid Rice Varieties In Dry Direct Seeded Rice System

Looming water crisis and labor shortage demand the shift from conventional transplanted rice(CTR) to dry direct seeded rice(DDSR). Compared with inbred rice varieties, hybrid rice varieties possess greater yield potential. But the combination of high sowing rate in DDSR and the high price of hybrid rice seeds limit the usage and extension of hybrid rice varieties in DDSR. Some researches reported hybrid rice varieties own greater early vigor in comparison with inbred rice varieties,which make it possible that they can perform well even at low sowing rate. Present study investigated the yield responses of three hybrid rice varieties to different sowing rates and explored the physiological basis for grain yield formation under DDSR system. A widely grown inbred rice variety Huanghuazhan was grown as control.Results showed that reducing sowing rates of hybrid rice varieties from 240 grains m-2 to 60 grains m-2 did not reduce grain yield, while that of inbred rice varieties declined with decreasing sowing rates. Decreased sowing rates of inbred rice varieties recorded insufficient tillers, and lower panicle number that decreased their yield. Contrarily, for hybrid rice varieties grain yield was maintained even at reduced sowing rate because of their enhanced tillering capacity to produce enough panicles, higher specific leaf weight(SLW) to enhance leaf assimilation capacity, and increased spikelet number per panicle(SPP) to form large panicle, which might have compensated the reduced sowing rate. Meanwhile, another reason may be the SLW of hybrid rice varieties were low to furnish fast leaf area expansion.Our results suggested that the sowing rate of hybrid rice varieties can be reduced to 60 grains m-2 without compensating yield of DDSR. However, in practice production,adversities like weeds and poor stand establishment should be overcome by proper increase in sowing rate to achieve maximum crop yield.