民勤绿洲不同年限退耕地土壤养分变化及其相关性分析
Woodland soil nutrient changes and correlation analysis of different fixed numbers of abandoned lands in Minqin oasis

以石羊河下游的典型区—民勤退耕地为研究对象，对石羊河下游地区不同恢复年限退耕地土壤养分变化情况及其养分与退耕时间之间相关性进行分析，结果表明：① 土壤中N肥含量随退耕年限的增加呈波动式上升趋势，但在同一年限退耕地中随土层的加深而逐渐减小，退耕后1～10 a，N含量变化的幅度较小；15～30 a，N含量变化的幅度相对较大；50 a后，趋于稳定；P含量在各个演替阶段土壤层次上均呈A（0～10 cm）>B（10～20 cm）>C（20～30 cm）>D（30～40 cm）规律性分布，退耕后1～10 a，A、B两层P含量的差异较大，C、D两层受退耕时间的影响较小；15～50 a间，A、B、C、D四个土层P含量变化的幅度相对较小；K的含量表现出和P同样的规律性；有机质含量在退耕后1～7 a间变化幅度较大，10～50 a间变化幅度较小。1～5 a间，A、B、C、D四层含量变化呈逐层递减的趋势；7～50 a间，A层变化较大，B、C、D三层趋于稳定。② 养分与退耕年限相关性分析表明：退耕1 a,速效磷、有机质含量与退耕时间呈显著负相关；5～10 a间，各养分与退耕时间均呈显著正相关且差异不显著；15～20 a间，各养分与退耕时间之间存在显著差异，30～50 a间，速效钾、速效磷、有机质含量与退耕时间差异不显著，50 a时差异显著。
The typical region of Shiyang River in Minqin cultivated land was selected to analyze different restorations of soil distribution, changes of soil nutrient and community structure of recovery process in vegetation land of Shiyang River, and their correlations were also investigated. The results showed that N fertilizer had a fluctuant trend to become increased in farmland soil. However, during the same period, it was gradually decreased with the increase of soil depth. 1～10 a after abandonment, N level showed small variations, whereas 15～30 a after abandonment, the variations became large. It went stabilized after 50 a. Additionally, levels of P content in soil depths followed the order as the follow: A (0～10 cm)＞B(10～20 cm)＞C(20～30 cm)＞D(30～40 cm). 1～10 a after abandonment, P level difference between A and B layers varied largely. However, it in C and D layers were affected subtly by the time of abandonment. During 15～50 a, P levels in A, B, C and D layers showed small variations. K level exhibited similar variation trends as P level. Organic matter content varied largely during 1～7 a after abandonment, whereas it varied little during 10～50 a. During 1～5 a, it became decreased with the increase of soil depths in A, B, C and D layers. During 7～50 a, it resulted in large change in A layer, while it reached stabilization in B, C and D layers. In addition, the correlation analysis about nutrients showed that the 1a after abandonment, contents of available phosphorous and organic matters were significantly negatively correlated with the time. During 5～10 a, all nutrients were positively correlated with the time at an insignificant level. Between 15～20 a, significant differences were found between all nutrients and the time. During 30～50 a, available potassium, available phosphorous, and contents of organic matters did not have a significant deviation from the time, while in 50 a, they did.