Abstract: To achieve high yield with high quality of mechanically transplanted rice, suitable sowing date is a key factor. The effect of sowing date on the formation of quality characteristics of Japonica- super rice and IndicaJaponica- hybrid rice under mechanical transplanting were studied, to provide basis for the production of mechanically transplanted rice with high yield and high quality. The results showed that, with delayed sowing date, the brown rice percentage, milled rice percentage and head rice percentage were increased, improving the milling quality, but the yield of brown rice, milled rice and head rice was significantly higher on early sowing date than on late sowing date (P<0.05). The chalky grain percentage and chalkiness degree varied greatly among different sowing dates, and decreased with the delayed sowing date; the difference of these two parameters were significant between early sowing and late sowing date (P<0.05). The appearance quality was ameliorated when the sowing date was postponed. The postponement of sowing date reduced the amylase content, shortened the gel consistency, debased the peak viscosity, trough viscosity, final viscosity and breakdown, increased the setback, and had little effect on pasting temperature, worsened the RVA profile, and deteriorated the cooking and eating quality. With the delayed sowing date, both the protein content and protein yield were decreased (P<0.05), worsening the nutritional quality. It is concluded that suitable early sowing date for mechanically transplanted rice can easily obtain high yields of brown rice, milled rice, head rice and protein, lift the nutrition quality and cooking and eating quality, improve the characteristics of RVA profile, but deteriorate milling quality and appearance quality. Sowing date during May 26-31 is a best period for mechanically transplanted rice in ricewheat cropping areas to maintain high yield with high quality of rice.

Key words: ionic homeostasis, NaCl stress., magnetic effect