Abstract:Two varieties of super rice,Peizataifeng and Yuxiangyouzhan,were used to study the effects of different planting density on grain production of mechanical precision hill-drop drilling rice.The results showed that different planting density of precision hill-drop drilling rice produced high valid panicles,high population total number of spilelets and high yield compared with manual boardcasting(controls); but it had no significant effect on 1 000-grain weight of both varieties.The yields of Peizataifeng with four densities (P1-P4) was increased significantly by 69.07%,40.73%,34.34% and 35.09%,respectively.The yields of Yuxiangyouzhan (Y1-Y4) was increased significantly by 109.97%,45.14%,84.86% and 46.32%,respectively.The highest grain yield and highest harvest index were observed in both rice varieties with row spacing of 20 cm,followed by row spacing of 25 cm wide-narrow(35 +15) cm and 30 cm,but the difference between wide-narrow(35 +15) cm and 30 cm was not significant in the variety of Peizataifeng.For the grain yields of Yuxiangyouzhan,followed by the same levels of wide-narrow and 30 cm,and then followed by row spacing of 25 cm,indicating that appropriate row spacing could improve the harvest index of precision hill-drop drilling rice.The row spacing of 30 cm and wide-narrow achieved the highest individuals biological yield while 20 cm achieved the highest population biological yields,indicating that increasing the row spacing could improve the individuals biological yield.Improving population biological yields of precision hill-drop drilling rice should be on the basis of appropriate row spacing.The results also showed that higher net photosynthetic rate,but the significance levels of the transpiration rate,stomatal conductance (Cond) and intercellular carbon dioxide concentration in leaves(flag leaves) varied with the varieties of precision hill-drop drilling rice.The suitable row spacing could improve the population photosynthesis capacity of precision hill-drop drilling rice.Therefore,the main pathway to improve grain yield of precise hill-drop drilling rice is to guarantee grain number per panicle on the basis of certain population valid panicles,to highlight the production superiority of deepen fertilization and mechanical hill-lined characteristics,to coordinate the contradictions between individuals-and-population and yield and its components,to improve population photosynthesis capacity,and therefore to culminate in a performance of high yields of precise hill-drop drilling rice.