The shading and its effect on crop yield under poplar-crop intercropping system

The poplar(Populus tomentosaCarr．)shading on farm field is reported under poplar-crop intercropping systam in Northern China farm region．The results show that the young poplar with a space of 3m×2m×18m brings a shading index of 1．3％～67．8％ and a shading degree of 0．3％ ～ 16．5％ on farm field when the stand ages are 1～7 years，and middle-mature poplar with a space of 4m ×30m results in a shading index of 51．3％～ 76．0％ and a shading degree of 22．8％～28．1％ when the stand ages 10～14 years as wel1．The study shows that the shading degree of 10％ is the maximum shading degree that can be accepted in farm field，and the trees with a space of 30m between rows can keep the crop yield stea dy when poplar is entering mature stage．