Determination of Optimum Growing Degree-Days (GDD) Range Before Winter for Wheat Cultivars with Different Growth Characteristics in North China Plain

To provide base for adjusting the sowing date, achieving the yield potential of wheat cultivars with different growth characteristics, and improving the utilization rate of natural resource in the North China Plain (NCP), a 4-yr field experiment of growing degree-days (GDD) before winter (realized through different sowing dates) with three wheat (Triticum aestivum L.) cultivars of each type of semi-winterness and weak springness was carried out at 20 test experimental sites (32°4′N-36′1′N) of Henan Province in the NCP. The results showed that: (i) yield of semi-winterness wheat was significantly higher than weak springness wheat (**P<0.01); (ii) there was a quadratic regression between the yield and GDD before winter. According to the regression equation, the optimum GDD range with high yield of semi-winterness and weak springness wheats was 750-770 and 570-590°C d, respectively; (iii) under the optimum GDD condition, the foliar age on the main stem of semi-winterness and weak springness wheats was 7.67–7.91 and 6.36–6.86 leaves, respectively, calculated by the linear regression equation between foliar age and GDD before winter; (iv) both semi-winterness and weak springness wheats were in the double ridge stage of spike differentiation under the condition of the optimum GDD range, and at this time, the foliar age on the main stem of semi-winterness and weak springness wheats was about 7.80 and 6.07 leaves, respectively, which was consistent with the results calculated by the liner regression equation. Therefore, we could consider that the sowing date is appropriate if the foliar age is about 7.8 and 6.3 leaves for semi-winterness and weak springness wheats, respectively. According to the results of this study, choosing semi-winterness wheat and planting 7-10 d earlier would improve yield and natural resource utilization in NCP.