Abstract:

In order to fully coordinate the relationship between yield potential and efficient utilization of climate resources, and investigate the light and temperature utilization efficiency of spring rapeseed under plateau climate in Tibet, 3 spring rapeseed （Brassica napus L.） lines （with different maturity） were selected as materials, and 4 sowing dates were set in field experiments. The lines were analyzed on growth and yield formation under different sowing dates. Results showed that, with the delay of sowing date, the temperature during rapeseed growth period increased, thus it took fewer periods to reach the effective accumulated temperature. Meanwhile, growth period of the lines was shortened, among which seedling stage, bolting stage and flowering stage were also earlier, resulting to a prolonged silique maturation period. Under the late sowing treatment, plants （at stem extension period） encountered more sufficient rainfall and more heat than those of early sowing, thus the plant height increased, and the stem diameter decreased. At the same time, late sowing resulted in insufficient vegetative growth in the early growth stage, and dry matter accumulation in mature stage was less than those of early sowing. Under the late sowing treatment, plants （at mature stage） encountered continuous rainfall which caused the reduction of branch number, silique number and seed weight, as a result, seed yield was significantly lower than that of early sowing. Sowing date changed the light-temperature utilization efficiency of the rapeseed. Early maturing line NY16 had higher light-temperature utilization efficiency at B2 sowing date （March 15, 2021）, as 0.081 g·MJ^-1 and 1.017 kg·hm^-2·℃^-1 respectively. The light-temperature utilization efficiency of medium maturing line NY28 and late maturing line NY52 were higher at B1 sowing date （March 8, 2021）, as 0.1 g·MJ^-1, 1.282 kg·hm^-2·℃^-1, 0.134 g·MJ^-1 and 1.712 kg·hm^-2·℃^-1, respectively. Under the same sowing date, the light-temperature utilization efficiency of medium- and late-maturing lines was higher than that of early-maturing lines. Therefore, timely （and early） sowing could improve the light-temperature utilization efficiency and promote rapeseed yield. Suitable sowing date was from March 15 to March 22 for early-maturing rapeseed, and March 8 to March 15 for medium- and late-maturing lines. Moreover, for the single-cropping system in Tibet, medium- and late-maturing rapeseed breeding might improve the yield of spring rapeseed.

Key words: Tibetan plateau, spring rapeseed （Brassica napus L.）, sowing date, light-temperature resource use efficiency, differing in maturities