Data collection

The 216 weather stations provided daily records of sunshine hours; minimum, mean and maximum temperatures; precipitation; and wind speed from 1980–2009³⁴. Daily solar radiation was estimated using a previously published equation³⁵.

To assess how farmers have changed to longer-maturity varieties, we collected data on maize phenology (sowing, silking, and maturity dates) from both the 1980s and the 2000s from Agrometeorological Experimental Stations for each province in the CMB. Fifty agronomists at 50 experimental stations in the National Maize Production System in China were surveyed to verify the phenological information. The sowing, silking, and maturity dates for each province for varieties planted in the the 1980s and the 2000s are shown in Supplementary Table S2. The parameter growing degree-days (GDD, ≥10 °C) was used to characterize the varieties and for model simulation. At each station in both the 1980s and the 2000s, the GDD is the average of all collected varieties at that time. According to the average phenological data, the total GDD, pre-, and post-silking GDDs for varieties from both the 1980s and 2000s were calculated based on the average temperature in each province³⁶. Total, pre-, and post-silking GDDs for each province for varieties used in the 1980s and 2000s are shown in Supplementary Table S3. For each province, an average GDD was used for crop model simulation.

The soil data used in our study included soil texture, bulk density, initial soil moisture status, coverage of residues, and maximum root depth. These data were also obtained from the Agrometeorological Experimental Stations and the China Soil Scientific Database.