THE STUDY ON CROP YIELD UNDER POPLAR-CROP INTERCROPPING SYSTEM

The results of 6 years of studies showed that the relationship between the crop yield and the intercropping years was of the parabola form under the poplar-crop intercrpping system,and the year when the highest yield achieved was relative to tree spacing.In the reasonable bound, the more tree spacing between-rows was wider,the more the year to get the highest yield was later.It also demonstrated that proper intercropping years and tree spacing between-rows would effectively increase crop yield.For example,the total crop yield was 8 0% higher than that of control land from the second year to the sixth year when the tree spacing between-rows was 18m but the per year wheat yield was 22 6% higher over the third year to the ninth year when it was 30 m. The crop yield distributed between-rows had the same pattern when the tree rows were different, i.e. higher in middle and lower near the tree rows. That means the poplar, besides its protection effect to crop, strive for resources from crop as well. When it makes crop yield to decrease seriously, poplar thinning will obviously increase crop yield. It is proposal that the spacing between-rows should maintain 40～60 m when poplars get to mature stage(10～15 years).