Abstract: Thermal time before winter and soil moisture before sowing are the important basis for the selection of sowing date in dry-land wheat area. It is of great significance to use the decision system to select the optimal sowing date of wheat under different precipitation years. The wheat decision system was calibrated and validated by using field test data of winter wheat in Wenxi county of Shanxi province from 2009 to 2014 years (2009, 2010 and 2012 were dry year, 2011 and 2013 were wet year). The modified decision system was used to simulate and analyze the change of the optimal sowing date of winter wheat and the change of sowing date with yield under different precipitation years in recent 36 years (1980−2015) in Wenxi area. The results showed that, (1) the optimal sowing date was mainly around September 25 in 1980−1984, the optimal sowing date was around September 30 in 1985−1995, the optimal sowing date was around October 5 in 1995−2015. (2) The average yield of wheat reached the highest value when sown around September 30 in wet year and normal year, which were 4293.1kg·ha−1 and 4055.2kg·ha−1, respectively; the average yield of wheat reached the highest value (3334.5kg·ha−1) when sown around October 5 in dry year. Therefore, with the increase of atmospheric temperature, the historical optimal sowing date of winter wheat was delaying; it was appropriate to sow around September 30 in wet year and normal year, and around October 5 in dry year.

Key words: Dry-land wheat, Wheat decision system, Simulation, Optimal sowing date, Precipitation pattern