Abstract: 【Objective】In order to solve the practical productive problems that sowing only to wait for the rain decreased the yield of dryland wheat conventionally cultivated as a single crop per year in the Loess Plateau in most of the year, the study of effects of subsoiling during the fallow period (SS) with great soil water storage and timely sowing on yield and its component was implemented to improve the precipitation use efficiency, and to build the rational community structure for achieving high yield and efficiency.【Method】The field experiments were conducted in a two-factor split-block design with SS or traditional farming (CK) in the main plots and three sowing dates (Sep 20^th, early sowing date, T₁; Oct 1^st, timely sowing, T₂; Oct 10^th, late sowing date, T₃) in the subplots at Qiujialing village, Wenxi county, Shanxi province from 2012 to 2014, to study the effects of SS on yield formation of dryland wheat and the adjusting effects of sowing dates. 【Result】 The soil water storage in the 0-300 cm soil profile was increased by 59-71 mm and 34-52 mm under SS compared with CK in 2012-2013 and 2013-2014 at sowing stage, respectively. Adoption of SS obviously improved the group tillers before wintering stage and plant dry matter at different growth stages, which increased by 8%-18% and 8%-15% of the number of spike, 19%-36% and 17%-22% of yield, 6%-21% and 10%-12% of water use efficiency compared with CK during 2012-2013 and 2013-2014, respectively. Soil water storage in T₂ treatments was the highest from wintering to booting stage under SS treatments. The highest tiller number before wintering stage and plant dry matter before anthesis stage were obtained in T₂ treatment, however, no significant difference was observed with T₁ treatment. The largest post-anthesis plant dry matter was attained in T₃ treatment under SS, no significant difference was observed with T₂ treatment. The significant highest spike number, grain number per spike and yield were observed in T₂ treatment, while 1000-grain weight increased with the delay of sowing date. Under traditional farming in the dry year (2012-2013), the highest soil water storage from wintering to booting stage, spike number, grain number per spike and yield were attained in T₁ treatment. In addition, in three sowing dates and SS treatments, spike number, grain number per spike, plant dry matter at mature stage and yield were more significantly correlated with soil water storage of different soil layers before anthesis than post-anthesis, especially with soil water moisture in deeper layers before anthesis. Wheat yield was increased by 17 and 23 kg·hm^-2 with an increase of 1 mm soil water storage at sowing stage under SS matched with T₂ treatment during 2012-2013 and 2013-2014, respectively. 【Conclusion】 Subsoiling during the fallow period was conducive to store precipitation during the fallow period into the soil resulting in the increase of soil water storage before sowing. Adoption of early sowing and timely sowing in SS treatments were favor to build the strong seedling before wintering, however, the number of spike, grain yield and water use efficiency were the highest under timely sowing. In conclusion, adoption of subsoiling during the fallow period matching sowing on October 1^st could optimize the yield composition and increase yield and efficiency of dryland wheat.

Key words: dryland wheat, subsoiling during fallow period, sowing date, soil water moisture, yield