开垦和弃耕对黑河上游亚高山草甸土壤氮库的影响

Effects of cultivation and subsequent abandonment on soil nitrogen pools of the Sub-Alpine Meadow in the headwater area of Heihe River

通过分析天然放牧草地、20年燕麦耕地、3年燕麦弃耕地、10年燕麦弃耕地的土壤全氮、微生物量氮含量的差异,旨在探讨改变土地利用方式对黑河上游亚高山草甸土壤氮库的影响。结果表明:开垦和弃耕对黑河上游地区草地土壤氮库有显著影响。亚高山草甸被开垦为燕麦耕地20年后,土壤全氮含量(0-30cm)减少了21-35%,微生物量氮含量减少了20-70%。燕麦耕地弃耕后,土壤全氮和微生物量氮含量均显著提高。弃耕3年,土壤全氮和微生物量氮含量分别增加了4-9%,27-35%;弃耕10年,二者分别增加了9-20%,35-38%,说明随弃耕年限的增长,土壤氮库含量在增加。在四种草地利用方式下,土壤全氮、微生物量氮、微生物量氮占全氮比例三者之间均呈现极显著正相关关系(P<0.01)。土壤微生物量氮与全氮比值变化在1.96-4.29%之间,其中天然放牧草地最高为4.29%,燕麦耕地最低为1.96%。因此,弃耕可提高黑河上游地区开垦草地的土壤氮库含量,是实现该区草地恢复的有效措施,但需要的时间比较长。

Measurement of soil total nitrogen（TN） and microbial biomass nitrogen（MBN） contents on four typical land-use types including native meadow for grazing,oats cultivation for 20 years,oats abandonment for 3 years and oats abandonment for 10 years were carried out to detect the effect of land-use change on soil nitrogen pools of the sub-alpine meadow in the headwater area of Heihe River.The results showed that there was a significant influence of cultivation and subsequent abandonment on soil nitrogen pools.After the native sub-alpine meadow was cultivated for 20 years,TN concentration decreased by 21-35% and MBN declined by 20-70% along soil profile（0-30cm）,respectively.TN concentration accumulated significantly when the oats cultivation was abandoned.Abandonment for three years,TN and MBN contents increased by 4-9% and 27-35%,respectively.Ten years later,they increased by 9-20% and 35-38%,which indicated soil nitrogen pools improved with the year increasing.Under the four land-use types,there was a positively correlation among TN,MBN concentration and the ratio of MBN in TN（P0.01）.The ratio of MBN in TN was changing between 1.96-4.29%,with the maximum value in the soil of native meadow and the minimum value in the oats cultivation.Therefore,to the cultivated land in the headwater area of Heihe River,abandonment can improve soil nitrogen pools,which will be an effective measure to realize grassland recovery,but a long time is needed.