Soil particle size distribution and its relationship with soil organic carbons under different land uses in the middle of Heihe river

Abstract

Land use plays an important role in soil particle size distribution, soil organic carbon (SOC) and its components. Based on the methods of field sampling, laboratory analysis and statistical analysis, soil particle size distribution and its relationship with SOC under different land uses are researched in the middle of Heihe river, which locates in Hexi corridor, Gansu province. We sampled the soil down to 100 cm in depth with interval of 0-20 cm, 20-40 cm, 40-60 cm, 60- 80 cm and 80-100 cm. Distribution of particle size under different land uses shows that percentage of the particle size <1, 1-5, 5-10 and 10-50 μm for paddy field, dry land, nakedness land and middle density grassland are higher than those of the saline-alkali field, sandlot and desert, but percentage of the size 50-250, 250 -1000 and 1000-3000 μm are inverse. In soil profile, average total organic carbon (TOC), active organic carbon (AOC) and nonactive organic carbon (NOC) contents for different land uses vary respectively with a range of 0. 11% -2. 46%, 0. 06% -0. 78% and 0.05% -1. 68%, it is higher in the topsoil (0-20 cm) compared to that in the low depths (20-100 cm), also TOC, AOC and NOC content gradually decline with the incremental depth. Results show soil particle size distribution and content of TOC, AOC and NOC have difference under different land uses. In the soil profile, average TOC, AOC and NOC contents are higher in dry land, paddy field and middle density grassland than in the desert, nakedness land, sandlot and saline-alkali field. The trends of soil particle size and SOC (TOC, AOC and NOC) have the similarities and differences, the similarities is percentage of particles <1, 1-5, 5-10 and 10-50 in dry land, paddy field and middle density grassland that have high SOC (TOC, AOC and NOC) are higher than that in desert, nakedness land, sandlot and saline-alkali field that have low SOC, but the situation is opposite for particles 50-250 and 250-1000, the dividing point is 50. It is found that soil particle size under 50 μm play a role in carbon sequestration and soil particle size surpass 50 μm play a role in carbon loss. Statistics analysis show that SOC (TOC, AOC and NOC) in paddy field, desert and the middle density grassland have significant positive (P<0. 01 or P<0. 05) correlation with soil silt- and clay-size fractions under 50 μm size and significant negative relation (P<0. 01 or P<0. 05) with sand fractions surpass 50 μm size. The result show siltand clay-size fractions play a major role in the formation and stabilization of soil aggregates. Measures of increasing vegetation coverage, vegetation restoration of degraded ecosystems, tillage, wind-break and sand-fixing can enhance content of SOC, silt- and clay-size fractions, and further provide foundation and stability for soil aggregates formation.