In 2006, daily mean soil temperature under mulch was 2–9 °C higher than without mulch, especially during early growth (Fig. 2). As plant canopy enlarged, more soil surface was shaded and the soil temperature difference (soil temperature under mulch minus soil temperature without mulch) between mulched and non-mulched beds decreased. By the 10th day of July, the temperature difference at 25 cm soil depth even became negative. At the end of the season as the plant stems and leaves senesced, the temperature difference became positive again. In 2007, similar soil temperature differences between mulched and non-mulch potato beds were found. These soil temperature patterns are comparable to those described by other researchers in both potato (Ma and Li, 1996 and Cheng and Zhang, 2000) and spring wheat (Li et al., 1999 and Li et al., 2004a) fields during the whole growing season.