夏玉米播种以后25—30天开始拔节,进入玉米生育中期(拔节—抽雄),也叫穗期。这时玉米地下部分6—7层次生根基本形成,并向纵深发展,地上部展开叶8—9片,可见叶12—13片,叶面积和光合势已相当发达,雄穗和雌穗先后开始分化,经20— Summer corn sowing 25-30 days after the beginning of jointing, into the mid-maize growth (jointing - tasseling), also known as the spike. At this time, 6-7 layers of underground corn root basically formed, and to the depth of development, the ground to expand the leaves 8-9, 12-13 visible leaves, leaf area and photosynthetic potential has been quite developed, tassel and ear have started Differentiation, the 20-