Spatial variability of soil humus layer thickness at landscape scale in agro-pastoral transition zone

Soil humus constitutes the main part of soil organic matter, with ecological regulation effect, its content is an important index reflecting soil fertility． Soil humus layer thickness (HLT) indicates soil organic carbon storage and has important effects on soil water dynamics, nutrient storage, nutrient availability and land productivity． Climate changes could affect the soil humus layer in agro-pastoral transition zone． Field survey and observation data at landscape scale are used in this study to analyze the relationship between spatial distribution characteristics of HLT and environmental factors such as terrain and vegetation type in agro-pastoral transition zone, using geo-statistics and GIS． The average thickness of soil humus layer in the study area was 53.8 cm, ranging from 20 to 60 cm． The HLT exhibits medium spatial auto correlation, high spatial variability and obvious patch-like distribution． Elevation was the most significant factor affecting HLT (P < 0.05), mean value of HLT was different under different vegetation types, slope and slope-aspect, but overall difference was not significant (P > 0.05)． The soil humus layer becomes thinner as elevation increases． The average HLT of shady slope and half-shady slope is greater than sunny slope and half-sunny slope． HLT decreases with increasing slope． The spatial distribution of HLT is highly complex due to comprehensive effects of multiple environmental factors at landscape scale, its spatial heterogeneity should not be ignored, and should be fully considered in soil carbon storage estimation and related studies．