1玉米产生空秆的原因1.1种植密度辽宁省无霜期差异很大。南部沿海,年平均无霜期接近200d;北部内陆,年平均无霜期超过130d;中部150～180d,因地域差异,应选择不同生育期的玉米品种,且种植密度不同,南部3.75万株/hm2,北部5.25万株 1 maize to produce empty stalks 1.1 planting density Liaoning frost-free period vary widely. In the southern part of China, the average annual frost-free period is nearly 200 days. In the northern inland, the annual average frost-free period is more than 130 days. For the middle part of 150 ~ 180 days, maize varieties with different growth stages should be selected due to their regional differences. The southern part has 37,500 plants / hm2, 5.25 million