【摘要】 为探究黄土丘陵区退耕还林后土壤可溶性氮养分积累的季节动态变化特征,以志丹县永宁镇沙棘和山杏林地为研究对象,采集0—10,10—20,20—30 cm土壤样品,分析土壤可溶性氮组分含量和比例的季节动态变化。结果表明:退耕还林可显著增加土壤硝态氮、铵态氮和可溶性有机氮含量,尤其是0—10 cm土层增加明显。0—10,10—20,20—30 cm土层间差异显著,沙棘林和山杏林间也达到显著差异水平。总体来看,硝态氮含量随季节变化明显,3月最高,3—6月下降,6—9月上升,9—11月又下降,11月最低。各样地间0—30 cm土层铵态氮含量变化幅度较小。可溶性有机氮含量随季节变化明显,6月最高,11月最低,3—6月上升,6—9月下降,9—11月又上升。可溶性有机氮含量季节变化规律与硝态氮变化规律相反。沙棘林地土壤可溶性氮含量较杏树林地高,且阳坡高于阴坡。0—30 cm土层可溶性氮组分以可溶性有机氮为主,占73.3%～99.0%,其次是硝态氮,占0.9%～24.3%;铵态氮所占比例最少,在2%以下。退耕还林措施可显著增加0—10 cm土层土壤可溶性氮含量,不同林分土壤可溶性氮含量增加不同,沙棘林地高于杏树林地。更多还原

【Abstract】 In order to investigate the seasonal dynamics of soil soluble nitrogen after returning farmland to forest in loess hilly region, the Hippophae rhamnoides forestland and Armeniaca vulgaris Lam. forestland in Yongning Town of Zhidan County were taken as the research object. Soil samples were collected in 0—10 cm, 10—20 cm and 20—30 cm soil layers, and seasonal dynamic variation of the density and proportion of soil soluble nitrogen component were analyzed. The results showed that the measures of returning farmland to forest significantly increased the density of soil nitrate nitrogen, ammonium nitrogen and soluble organic nitrogen, especially in the 0—10 cm soil layer. There were significant differences in the above indexes among different soil layers and between H. rhamnoides forestland and A. vulgaris Lam. forestland. On the whole, nitrate nitrogen density varied significantly with seasons, the value was the highest in March, declined from March to June, increased from June to September, declined from September to November, and was the lowest in November. The ammonium nitrogen content in 0—30 cm soil layer varied little. The soluble organic nitrogen content varied significantly with seasons, and the highest and lowest value was found in June and November, respectively, and the content increased from March to June, declined from June to September and rised from September to November. The seasonal variation of soluble organic nitrogen density was opposite to that of nitrate nitrogen. The content of soluble nitrogen in H. rhamnoides forestland was higher than that in A. vulgaris Lam. forestland. The soluble nitrogen content of sunny slope was higher than that of shady slope. In 0—30 cm soil layer, the soluble nitrogen was mainly soluble organic nitrogen, accounting for 73.3%～99.0%, followed by nitrate nitrogen accounted for 0.9%～24.3%, and the proportion of ammonium nitrogen was the least, which was below 2%. The conversion of farmland to forest significantly increased the density of soluble nitrogen in 0—10 cm soil layer. The soluble nitrogen density increased differently in different forestlands, the value in H. rhamnoides forestland was higher than that in A. vulgaris Lam. forestland.更多还原