Effects of tree-crop intercropping on young plantations of Populus tomentosa

In order to study the effects of tree-crop intercropping on young plantations of Populus tomentosa in the plain along the Yellow River,field experiments have been conducted by observing the growth of forests,nutrient contents in leaves,nutrient contents and water contents in soil and the output of crops.The relationship between forests growth and nutrient contents in tree leaves and soil has been analyzed.Resultsshowed that tree-crop intercropping in young plantations could not only improve the soil water contents,but also enhance the contents of organic matters,available nitrogen,phosphorus and potassium in the soil,which resulted in the vigorous growth of the individual tree.Diameter at breast height(DBH) was positively relative to the contents of organic matters in the soil and contents of N,P and K in tree leaves,and the correlation coefficient was 0.967,0.955,0.988 and 0.972.Whole-tree leaf area,crown width,branch number and the mean length of branches in the intercropped plantations(intercropped with watermelon and vegetable,peanut and winter wheat,and soybean) were 1.70-3.0 times,2.22-2.47 times,1.0-1.41 times and 1.70-2.32 times of those of CK(without intercropping).DBH and tree height in the intercropped plantations were 50.5%-136.7% and 27%-59.5% higher than those of the CK.The study also showed that intercropping with the watermelon and vegetables was proved to have the highest economic return among the treatments adopted.Tree-crop intercropping in young plantations is an effective measure for the increase of forest growth and economic benefit.