Long Term Water-Nitrogen Coupling Effect on Stand Volume of Different Clones of Populus tomentosa

【Objective】 In Wei County nursery of Hebei province, we applied different irrigation and nitrogen addition treatments to study the long-term water-nitrogen coupling effect on stand volume of Populus tomentosa. 【Method】 A split plot experiment design was used to study effects of different water-nitrogen coupling treatments in forest land on stand volume of different clones of P. tomentosa.【Result】 Results showed that: 1) different irrigation and nitrogen application had significantly different effects on stand volume of different clones. Clone S86 had better response mechanism under high water and fertilizer treatment, but it was opposite to clone 1316. 2) during irrigation to poplar plantation, the field capacity of more than 75% should be set as the critical value of irrigation, and the afforestation region of the environmental conditions, such as planting density, forests age and other factors, should be taken into account. 3) It is suggested that the range of nitrogen fertilizer to poplar plantation should