In order to investigate the most suitable sowing period and the optimum planting density of new com variety ‘Yudan 30＇ In Chongqing region, using split plot experiment design, the effect of sowing date and planting density on main a- gronomic characters and yield of maize in the field was studied. The results showed that in Chongqing, the delay of sowing date could shorten the fertility peri- od, and reduce 100-grain Weight and yield, but could increase plant height and ear height, panicle traits did not change significantly. With the density increasing, plant height and ear height also increased, while ear length, ear diameter, stem diameter, row number and kernel number also decreased. 100-grain weight and yield also in- creased with the increase of density, but to a certain threshold, yield and 100-grain weight decreased with the increase of density. The yield of 3 sowing periods pre- sented as AI〉A2〉A3, the yield of 4 kinds of density presented as B3〉EH〉B2〉B1, and the yield under sowing time and density interaction presented as AIB3〉A1B4〉 A2.B3〉A2.B4〉A3B3〉 A3B4〉A2.B2〉A1BI〉A2BI〉A3BI. So proper eady sowing and increase of planting density could raise the yield of maize per unit area, and AIB3 was the optimum planting configuration in Chongqing area.
The general combining ability（GCA）, special combining ability（SCA） and genetic parameter of ten characters of 22 maize inbred lines including plant height and ear height were analyzed using 10×12 through incomplete diallel cross（NC Ⅱ）.The results showed that：（1） Among the 22 maize inbred lines, the yield GCAs of11 HN 097, 11 HN 099, 11 HN 105 and 11 HN 110 were high, which were elite inbred lines to collocate hybridized combinations with strong heterosis. The yield of11 HN110 × 11 HN097, 11 HN110 × 11 HN105, 11 HN112 × 11 HN 097 and 11 HN 106 × 11 HN 104 were in the first four place. The yielding abilities, adaptabilities and yielding stabilities of the four combinations can be further identified by experiment. The heredities of the ten characters were mainly controlled by additive gene effect whereas the influence of non-addictive gene effect was small. The narrow heritabilities of plant height, ear height, ear rows, ear length, kernels per row,100-grain weight and seed-producing percentage were more than 50%. The variances were mainly caused by heredity and early-generation selection should be conducted. The narrow heritabilities of ear diameter, bare tip length and yield was low, which should not be selected in early-generation.
