Abstract: We carried out an experiment with two sowing dates \[early sowing (September 20, EB) and late sowing (October 10, LB)\] and three sowing rates \[low sowing rate (67.5 kg·hm^-2, LD), medium sowing rate (90 kg·hm^-2, MD) and high sowing rate (112.5 kg·hm^-2, HD). According to the number of tillers at the jointing stage of wheat, the populations were divided into three levels: class I (> 12 million plants·hm^-2, G1), class II (9-12 million plants·hm^-2, G2) and class Ш (< 9 million plants·hm^-2, G3). We examined water consumption, dry matter accumulation and transportation, yield and its components, and water use efficiency under different population levels. The results showed that compared with class II and Ш, soil water consumption under class I after anthesis was increased by 3-11 and 16-32 mm respectively, while the dry matter mass at maturity was increased by 664-1122 and 2072-2300 kg·hm^-2 respectively. Dry matter accumulation was the highest in each growth stage of class I, with the dry matter transport before flowering being increased by 42-60 and 17-179 kg·hm^-2 respectively. The contribution of dry matter allocation to grain after anthesis was increased by 306-403 and 681-926 kg·hm^-2, with a growth rate of 7.45%-8.40% and 18.97%-20.83%, respectively. Water use efficiency was increased by 7.93%-10.94% and 14.69%-18.94%, respectively. Under class I, soil water consumption (especially after anthesis) was significantly correlated with dry matter mass and yield at maturity. Early sowing with low sowing rate (EB+LD) was important for the formation of class I population. When population density reached class I at jointing stage, soil water consumption after anthesis, dry matter accumulation during growth period, dry matter transport before flowering, yield and water use efficiency were significantly increased. In conclusion, the class I population formed under a sowing rate of 67.5 kg·hm^-2 and sowing date on September 20 could increase the absorption and utilization of soil water by grain filling after anthesis as well as dry matter accumulation, which is conducive to its transport and contribution to grain and finally increased the yield and water use efficiency of dryland wheat in the southern Shanxi Province.

Key words: dryland wheat, population density, water consumption, dry matter, yield.