The nutrients of silicon,boron,zinc are crucially important for the growth of rice,while these and other trace elements are generally low in the red soil region of China.In this paper,the varieties of Zhongjiazao 17(earlyrice)and Hyou 518(laterice)were used as the experiment materials to study the effect of combined use of silicon,zinc and boron fertilizers on grain yield and population development of doublecropping rice in the red soil region of China.The results showed that compared with CK,grain yields of earlyrice were significantly increased by 8.6% for Si+Zn treatment and 126% for Si+Zn+B treatment,and the yields of laterice increased notably by 10.6% for Si+Zn+B treatment(P<0.05).The grain number per panicle,seed setting rate and 1 000grain weight for Si+Zn+B treatment were significantly higher than CK in earlyrice season(P<0.05),while only the grain number per panicle for Si+Zn and Si+Zn+B treatments were significantly increased in laterice season.Regression analysis with these treatments showed that the population spikelets per unit area were remarkably correlated with the grain yields(P<0.001).Compared with CK,the number of productive tillers,leaf area index,SPAD value,dry matter accumulation per area were increased after the using of silicon,zinc and boron fertilizers during the double rice growing periods,particularly in Si+Zn+B treatment.In addition,the nitrogen uptake was obviously higher in the treatments with silicon,zinc and boron fertilizers application than CK,except for Si treatment in earlyrice season.The results suggested that balanced use of medium trace elements should be considered,such as silicon,zinc,boron for doublecropping rice production,especially in earlyrice season under low temperature conditions in the red soil region of China.