小流域土壤矿质氮与地形因子的关系及其空间变异性研究

Spatial Variability and the Relationships of Soil Mineral N and Topographic Factors in a Small Watershed

为掌握小流域土壤特性与地形因子的关系及其空间变异规律,采用经典统计学与地统计学相结合的方法,对黄土高原水蚀风蚀交错带小流域土壤矿质氮与地形因子的关系及其空间变异性进行了系统研究,结果表明:①硝态氮的变异程度为强变异性,铵态氮、坡度、坡向则为中等变异性,土壤类型、土地利用对矿质氮的变异程度有极显著影响;②各研究特性在采样尺度内表现出不同程度的空间依赖性,铵态氮、海拔为强烈的空间依赖性,而硝态氮、坡度及坡向则为中等的空间依赖性;③分维数与空间异质比所揭示的结果具有一致性,各变量的分维数从大到小依次为:硝态氮(1.9826)>坡向(1.9767)>坡度(1.9420)>铵态氮(1.8791)>海拔(1.7461);④硝态氮在0°与90°,45°与135°方向上具有各向同性结构,而海拔为各向异性结构,其余的研究特性则表现出微弱的各向异性;⑤海拔、铵态氮具有很强的空间自相关性,硝态氮则为空间不相关;硝态氮与铵态氮、坡度与坡向之间具有极显著的正相关性,而铵态氮与海拔、坡度与海拔之间则为显著的负相关,表明在水蚀风蚀交错带铵态氮和坡度的空间分布具有海拔梯度性.

Objective of this study was to understand the spatial pattern of soil properties and topographic factors and their relationships in a small watershed. We used classical statistical coupling with geo-statistieal theory to characterize and compare the spatial variability of soil mineral N and topographic factors in the wind-water erosion crisscross region on the Loess Plateau. The results show that： ① The nitrate＇s variable extent is strong while other properties are moderate variability, and the impacts of soil types, land uses on variable extent are significant. ②All properties have different spatial dependence extent in the study area. Ammonium and elevation are strong spatial dependence while nitrate, slope gradient and slope aspect are moderate spatial dependence. ③The analysis results of fraetal dimension and spatial heterogeneity proportion are coherent, and the decreased sequence is： nitrate （1.982 6） 〉 slope aspect （1.976 7） 〉 slope angle （1.942 0） 〉 ammonium （1.879 1）〉 elevation （1.746 1）. ④In 0°/90°, 45°/135° aspects, nitrate is isotropy while elevation is anisotropy, and others are weak anisotropy. ⑤ Ammonium and elevation have strong spatial autoeorrelation while nitrate has not. There exist extremely notable positive correlations between nitrate and ammonium, slope gradient and aspect, and the negative correlations between ammonium, slope aspect and elevation, which indicate that the distribution of ammonium and slope gradient have elevation gradients.