Abstract:

In August 2018， 200 samples were surveyed in Longxi County. Using correlation analysis， analysis of variance， principal component analysis， and geostatistical analysis， we analyze sampling point data explored the spatial distribution characteristics of soil organic carbon density and reserves in Longxi County， and the relationship with climate， topography， and land use. The results showed that： （1） the total amount of organic carbon in soil from 0 to 50 cm was 6.29±2.41 Tg， and the SOCD was 2.67±1.02 kg·m^-2. The SOCD in the 0-10 cm， 10-30 cm soil layers and 30-50 cm were 0.63±0.17， 1.10±0.38 and 0.93±0.48 kg·m^-2， the organic carbon storagewere 1.49±0.41， 2.58±0.90 and 2.21±1.11 Tg， respectively. （2） Significant correlatios were observed between temperature， precipitation， elevation and Stream Power Index with SOCD in each soil layer. With the increase of soil depth， the correlations between slope， topographic relief and surface roughness with SOCD were gradually decreased， and no significant correlation was found in 30-50 cm soil layer. The correlation between topographic wetness index and SOCD was gradually increased and showed a significant negative correlation 30-50 cm soil layer. （3） The spatial distribution of SOCD as follows： the SOCD ratchet up from the central plains of the Wei River to the northern foothills and southern mountain areas with the rising of altitude. SOCD of Northern Mountain was higher than that of the Southern Mountain. The river valley plain formed by Wei River Basin has a lower organic carbon density. The distribution of soil organic carbon density in different soil layers and grades was markedly different. Due to the influence of human activities， the SOCD of the townships with large per capita cultivated land area was relatively low； the SOCD of the towns with large planted area of cash crops was relatively high； and SOCD of the towns with large per-mu investment in Chinese medicinal planting areas was relatively high. The SOCD was lower in the towns with larger arable land area per capita， higher in the towns where the planting area of cash crops was larger， higher in the towns with higher input per mu.

Key words: organic carbon density, organic carbon storage, principle component regression Kriging Model, composite terrain factor