青海省大通县脑山区退耕还林土壤质量演变评价

选取青海省大通县脑山区退耕还林地典型土壤类型———黑钙土,进行标准地调查及标准剖面采样,以空间代替时间序列的方式,利用主成分分析(PCA)等多元统计方法来定量化比较不同退耕年限(0,5,10,15,20,25,30 a)的综合土壤质量指数,揭示不同退耕年限土壤质量演变规律。结果表明,退耕还林后的30 a中,随退耕年限的增长,土壤质量指数均呈增长趋势,其过程基本分为3个阶段:(1)退耕初期(退耕5a),林分幼林期,为土壤质量指数相对增长期;(2)退耕中期(退耕5~20 a),针阔叶林林分速生期,为土壤质量指数大幅度升高并达到峰值期;(3)退耕后期,退耕20 a后,林分相对稳定期,林分郁闭度增大,土壤质量指数随之下降;退耕25 a后,林分进入自疏期,土壤质量指数略有升高并趋于稳定。

Soil Quality Evolution on Converted Farmland in High-mountain of Datong County in Qinghai Province

The research was conducted in high-mountain of Datong County in Qinghai Province,where is a demonstration site for Land Conversion Program(LCP).For the specific converted lands,the typical soil type-Chernozem was selected as the main research object.Using the idea of substituting space for time,statistic analysis method and Principal Component Analysis(PCA),the paper appraises and compares soil quality index quantitatively so as to further study soil quality evolution in the time series.Results indicate that soil quality index in the 30 year conversion fluctuates with time,showing a rising trend.The history of the conversion can be basically divided into three stages of the initial,middle and later periods.The initial period is the first 5 years after the conversion initiation,which is characterized by the sapling stage and a relative increase in soil quality index.The middle period ranges from 5 to 20 years after land conversion initiation.Conifer and broad-leaf forests grow rapidly in the period,and soil quality index increases greatly and reaches its peak.The later period is from 20 years after conversion initiation to current time.The period is the stable period characterized by the forest with dense canopy and a modest decline in soil quality index.After conversion for more than 25 years,forests will self-sparse,and soil quality index will rise to some extent and tend to be stable.