Daily mean soil temperatures under mulch was 2–9 °C higher than without mulch, especially during the early growing period (Fig. 2). As the plant canopy enlarged, more soil surface was shaded and the soil temperature difference between mulching and non-mulching became less. When it came to the mid-July, the difference at 25 cm soil depth even became negative. Finally, as the plant stems and leaves became senescent, the difference became positive again. Similar soil temperature variations under plastic mulch were found for potatoes