黑河中游典型土地利用方式下土壤粒径分布及与有机碳的关系

土地利用方式是影响土壤粒径分布、土壤有机碳及其组成含量的重要因素。研究显示:黑河中游典型土地利用类型下,不同土壤粒径分布和土壤总有机碳(TOC)、活性有机碳(AOC)、非活性有机碳(NOC)的含量存在差异。剖面上TOC、AOC、NOC含量较高的旱地、水田、中覆盖度草地与含量较低的戈壁、裸土地、沙地、盐碱地相比,<1μm、1—5μm、5—10μm、10—50μm的粒径含量较高,而50—250μm、250—1000μm的含量较低,这种变化以50μm为分界,分析表明<50μm的粉粒和粘粒可起到固碳作用,而50—250μm、250—1000μm的砂粒起碳损失作用。统计结果表明,以50μm为分界,水田、戈壁、中覆盖度草地剖面上TOC、AOC、NOC与1—5μm、5—10μm、10—50μm呈正相关,与50—250μm、250—1000μm呈负相关。分析发现,粉粒和粘粒与土壤TOC、AOC、NOC的关系较显著,是影响和控制团聚体形成和稳定的重要因素。增加地表植被覆盖度、退化生态系统的植被恢复、农田耕种、防风固沙措施是提高土壤有机碳、粘粒和粉粒含量的方式,也为土壤团聚体的形成和稳定提供基础。

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

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 silt— and 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.