温带草原土地利用变化对土壤碳氮含量的影响

Effect of Land-use Change on the Contents of C & N in Temperate Grassland Soils.

2001年6月,分别对内蒙古锡林河流域典型温带草原中贝加尔针茅草原(Stipabaicalensis)、羊草草原(Leymuschinensis)、大针茅草原(Stipagrandis)及其相应的农垦和放牧地等0～100cm土体不同层次的土壤全氮和有机碳含量分别进行了测定。结果显示:温带草原土地利用方式的改变对草原土壤全氮和有机碳含量变化影响明显,其中贝加尔针茅草原经28年农垦,使0～100cm土体中土壤全氮和有机碳含量相对于未开垦的草原分别减少8.8%和14.8%,平均每年分别减少0.31%和0.53%;0～10cm的表层土壤平均减少速率分别为0～100cm土体的2.9倍和1.9倍。11年围栏轮牧使羊草草原0～100cm土体的土壤全氮和有机碳分别增加了50.0%和47.4%,平均每年分别增加4.55%和4.31%;30cm以下土层增加异常显著。自由放牧使大针茅草原土壤0～100cm土体中土壤全氮和有机碳含量减少了4.88%和2.22%,平均每年分别减少0.24%和0.11%;0～10cm土壤全氮和有机碳分别为0～100cm土体平均减少速率的3倍和1.7倍,10cm以下各土层的土壤全氮和有机碳含量变化较小,说明自由放牧地对土壤表层全氮和有机碳含量的影响尤为明显。另外,选择适当的放牧强度可以维持草原生态系统的碳氮平衡,促进系统内的碳氮良性循环。

The contents of total nitrogen and organic carbon in soils of typical temperate grasslands such as Stipa baicalensis,Leymus chinensis and Stipa grandis grasslands(including the corresponding cropland and grazing field)in 0～100cm soil profile were measured respectively during June 22～23,2001.The results showed that the average contents of total nitrogen and organic carbon 0～100cm soil profile decreased by 8.8%and 14.8% after 28-year tillage,at the rate of 0.31%and 0.53%per year respectively,compared with Stipa baicalensis grassland;the rates of the decrease in total nitrogen and organic carbon in the 10cm of the profile were 2.9 and 1.9 times of those in 0～100cm of the soil profile respectively.In the past11years,pasture rotation resulted in the increase in the average contents of total nitrogen and organic carbon by 50.0%and 47.4%,at the rates of 4.55%and 4.35%per year,respectively;and they were significantly increased below the 30cm soil in depth.Overgrazing reduced the contents of total nitrogen and organic carbon in 0～100cm layer at the rates of 0.24%and 0.11%per year respectively,especially in the 0～10cm soil layer,in which the contents of total nitrogen and organic carbon were 3 and 1.7 times of the average rate in the 0～100cm layer respectively;however they were relatively stable with in 10～100cm soil profile.Moreover,properly grazing could maintain the balance of N and C and improve their cycling in grassland ecosystems.