A field experiment was conducted using two summer maize cultivars, Zhengdan 958 (ZD, shallow root type) and Denghai 661 (DH, deep root type). At the V12 stage, we cut roots vertically at different horizontal distance of 10 cm, 20 cm and 30 cm from maize plant in 60 cm soil depth, with no roots cutting as contrast check, which were referred to as ZDCK, ZD10, ZD20, ZD30 and DHCK, DH10, DH20, DH30 respectively. Roots of ZD10 and ZD20 decreased 24.81%, 11.69% and those of DH10, DH20 decreased 16.82%, 7.52% after cutting roots, respectively. Grain yield of summer maize decreased significantly after cutting roots, with a decrease of 13.09%, 9.10% for ZD10 and ZD20, respectively, and 9.81%, 4.64% for DH10 and DH20. After cutting roots, grains per ear and 1000-grain weight of ZD20, ZD10, DH20, and DH10 declined 4.90%, 5.60%, 4.37%, 7.88%, and 3.38%, 5.15%, 1.15%, 4.97%, respectively, which is the important factors resulting in lower grain yield. Grain sink and setting rate were also decreased to a different extent after cutting roots. Cutting roots decreased days to the maximum grain filling rate (Tmax), weight at the time up to the maximum grain filling rate (Wmax), maximum grain filling rate (Gmax), the phase of active grain filling, and average grain filling rate of two cultivars, with more decrease in Zhengdan 958 than in Denghai661.
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