黄土丘陵区退耕地土壤养分变异特征

Heterogeneity of soil nutrients of cropland returning to forest on the loess hilly region

在延安、安塞和吴旗选择典型黄土丘陵不同植被类型区的不同年限退耕地为试点,通过S型方法采集土样,应用土壤养分系统研究法进行了养分分析,并应用传统统计学对土壤养分变异进行了研究。结果表明,不同植被类型区土壤养分性质均存在着空间变异。受传统农业影响的有机质、全N、有效N和速效K的变异较大;而全P和速效P的变异相对较小。不同退耕年限的土壤养分含量及其变异系数存在着明显差别。退耕初期,受耕作和施肥影响,土壤养分含量较高,植被特征指数呈显著上升趋势且变异性较大;随着耕作施肥活动的停止和植被恢复对土壤养分的消耗,使土壤养分含量有一个降低的过程,土壤养分的变异也较大;而随着植被恢复和群落演替的继续,植被枯落物逐步增多,土壤也逐步发育,植被指数与土壤养分均呈增长趋势,并在退耕地20年左右时达到稳定状态,但土壤的发育往往滞后于植被特征的变化。

Typical cropland returning to forest with different fixed number of years under different vegetation types in Yan＇an, Ansai and Wuqi on the loess hilly region were selected as experimental sites to study the heterogeneity of soil nutrient. Soil samples were collected using S shape method and analyzed using soil nutrient systematic approach. Soil nutrient variability was studied with traditional statistics method. The results showed that soil nutrient content manifested remarkable variability under different vegetation types. Soil organic matter, total N, available N and available K had a relatively greater variability, which were mainly attributed to the former agricultural fertilization system. However, total P and available P had a smaller variability. Except total P and available P, the content and variability of soil nutrients with different fixed number of years returning cropland to forest showed remarkable discrepancy. In the beginning of cropland returning to forest, the content and variability of soil organic matter, total N, available N and available K were higher caused by tillage and fertilization. Vegetation index showed an ascending tendency with a great variability. Thereafter, soil nutrients took on a declining process in company with the quit of cultivation and fertilization and the consumption of soil nutrients by vegetation restoration. Soil nutrients had a great variability as well. Along with further progress of vegetation restoration and continue of community succession, litter fall of vegetation successively increased and soil progressive developed too. Both vegetation index and soil nutrients showed an increasing tendency and got stable state around 20 years of cropland returning to forest. However, soil development lagged behind change of vegetation characteristics