中文摘要：

以江苏省泗洪县陈圩林场不同林分密度的‘南林95’杨（Populus＆#215;euramericana cv． Nanlin－95）人工林为试验林，利用原位离子交换树脂法对不同季节的外源无机氮输入量以及土壤0-20 cm的无机氮库进行测定。结果表明：外源无机氮输入量随着季节的变化均呈现出一定的变化规律，硝态氮在8-10月输入量较大，铵态氮2-4月输入量较高；高密度林分在5-10月之间的无机氮输入量比低密度林分的高。杨树人工林无机氮含量和无机氮库的变化趋势也呈现出季节变化规律，硝态氮含量在生长季节（5-10月）较高，铵态氮含量在11月较高，无机氮库总量在2月时最低；低密度林分无机氮库总量要低于高密度林分的无机氮库总量，8月时，两种密度林分的无机氮库有差异。

英文摘要：

The seasonal soil nitrogen input was monitored using ionexchange resin method, and the soil inorganic N pool （ 0-20 cm） was also determined in poplar plantations with different planting spacing in Chenwei Forestry Farm, Sihong County, Jiangsu Province. The results showed that the external inorganic nitrogen input had a seasonal pattern and the input of nitrate was the highest from August to October 2012 and the input of ammonium was the highest from February to April 2013. The gross input of inorganic nitrogen from May to October under high density stand was higher than those under low density stand. Inorganic nitrogen concentration and total inorganic nitrogen had a seasonal pattern. The concentration of NO-3-N was higher in growing season than other periods and the concentration of NH＋4-N was higher in November. However, total inorganic nitrogen concentration of different stand structures had the minimum in February 2013. The total inorganic nitrogen was lower in low density stand than high density stand, which could be displayed obviously in August.