锡林河流域羊草草原暗栗钙土矿质氮动态变化

Mineral nitrogen dynamics in Dark Chestnut soil of Leymus chinensis grassland in the Xilin River Basin, China

通过野外采样,分析了内蒙古锡林河流域三个不同放牧强度羊草草原0~30cm表层土壤中矿质氮(NH4+-N+NO3--N)的浓度特征,研究了它们在生长季期间的含量变化情况。结果表明:羊草草原暗栗钙土中矿质氮主要以NH4+-N形式存在,矿质氮含量仅占土壤全氮的0·20%~0·92%;土壤矿质氮含量随草地放牧强度升高而降低,围封禁牧多年的羊草样地矿质氮含量高于轮牧地和自由放牧地;生长季期间0~10cm、10~20cm和20~30cm各层次土壤NH4+-N和NO3--N含量随土壤温度、水分和植物生长吸收的变化而波动明显,不同深度土壤矿质氮的季节变化趋势基本一致,表层0~10cm土壤矿质氮含量波动幅度最大:在4月和7、8月份,NO3--N和NH4+-N浓度分别出现峰值;NH4+-N和NO3--N含量随采样深度增加而降低,各采样点0~30cm土壤中NH4+-N含量均高于NO3--N。

In the paper, the dynamic features of mineral nitrogen (SMN, NH^+_4-N+NO^-_3-N) of the 0-30cm Dark Chestnut soil were studied, its seasonal variations during growing season and the SMN content differences among different research points were analyzed. All the samples were taken randomly from three different managed Leymus chinensis grasslands of Xilin River Basin in Inner Mongolia of China. The results showed that in Dark Chestnut soil the prevailing form of SMN was NH^+_4-N,the plant available nitrogen only takes a very small part of the soil total nitrogen, always below 1%(0.20%～0.92%).With the increase of grassland grazing intensity, the SMN content changed oppositely. The sequence of SMN content from high to low was: fenced grassland﹥rotational grazing grassland﹥random grazed grassland. During the growing season, the contents of NH^+_4-N and NO^-_3-N in different soil layers of three different managed grasslands changed evidently with the changes of soil temperature, moisture and plant absorbance, the trends of seasonal change were similar in different soil layers. The mineral nitrogen content of 0-10cm surface soils fluctuated most significantly, the content of NO^-_3-N was the highest in April and that of NH^+_4-N was higher in July and August. The content of NH^+_4-N was higher than that of NO^-_3-N in three different soil layers, and their contents decreased with the increase of sampling depth. The SMN content changed just the same order as the soil total nitrogen, organic carbon and soil water content with the increase of the depth, but there were no significant correlations between SMN content and anyone of them.