渭北旱塬土地利用方式对土壤团聚体稳定性及其有机碳的影响

揭示果园、农耕地两种土地利用方式对土壤团聚体分布、稳定性及有机碳含量的影响,为渭北旱塬乃至黄土高原区土壤碳库的优化管理提供科学依据.通过同步采样及湿筛法将果园和农耕地这2种土地利用方式进行土壤粒径分组,得到大团聚体( 2 mm)、中间团聚体(0. 25～2 mm)、微团聚体(0. 053～0. 25 mm)及粉黏粒(0. 053 mm)组分质量分数,测定各组分团聚体有机碳含量,并计算出0～40 cm土层各组分有机碳储量.结果表明,在0～20 cm土层,农业土地利用方式对土壤团聚体含量分布、稳定性具有显著影响.果园不同粒级团聚体( 2、0. 25～2、0. 053～0. 25和0. 053 mm)含量均值分别为12. 9%、51. 3%、28. 8%和7. 0%,农耕地土壤各粒级团聚体含量分别为8. 3%、49. 7%、33. 6%和8. 4%, 0. 25 mm团聚体含量显著高于农耕地.在0～40 cm土层,农耕地土壤平均重量直径(MWD)和几何平均直径(GMD)均显著低于果园(P 0. 05).不同土地利用方式对土壤各团聚体内有机碳含量影响主要在0～10 cm土层,与农耕地相比,果园大团聚体、中间团聚体、微团聚体和粉黏粒内有机碳含量分别提高了56. 0%(P 0. 05)、57. 1%(P 0. 05)、40. 8%(P 0. 05)、13. 0%(P0. 05).各粒径团聚体内有机碳(粉黏粒除外)储量均为果园高于农耕地.果园增加了 0. 25 mm大团聚体及其有机碳含量,缓解了农耕地对土壤团聚体的破坏,并提高了有机碳的稳定性.因此,与农耕地相比,果园土壤团聚体稳定性及有机碳含量较高,提高了团聚体对土壤有机碳的物理保护作用,有利于土壤有机碳积累,促进了土壤固碳.

Impact of Land Use Type on the Stability and Organic Carbon Content of Soil Aggregates in the Weibei Dryland

Soil aggregates are important indicators of soil quality and sustainable land utilization, and impact the retention abilities of water and fertilizers and the release of nutrients in soil. This study aimed to understand the effects of two land use types (an orchard and farmland) on the distribution, stability, and organic carbon content of soil aggregates, and provides a theoretical basis for the optimal management of the soil carbon pool in the Weibei Dryland of the Loess Plateau. We examined the soils from an orchard and from farmland by simultaneous sampling and wet sieving; the proportions of large macroaggregates (>2 mm), small macroaggregates (0.25-2 mm), microaggregates (0.053-0.25 mm), and silt and clay (<0.053 mm) were then determined; the content of organic carbon in each aggregate fraction at soil depths of 0-40 cm were also measured, and the total organic carbon content of all aggregates fractions was determined for each soil. The results showed that the type of agricultural land use had a significant effect on the distribution and stability of soil aggregates in the 0-20 cm soil layer, with the relative proportions of the different sized aggregates (>2, 0.25-2, 0.053-0.25, and<0.053 mm) being 12.9%, 51.3%, 28.8%, and 7.0% in the orchards, respectively, and 8.3%, 49.7%, 33.6%, and 8.4% on the farmland, respectively. The proportion of macro-aggregates (>0.25 mm) was significantly higher in the orchard soils than in the farmland soils. Mean weight diameter (MWD) and geometric mean diameter (GMD) are important indicators of the soil aggregate stability; the MWD and GWD of the farmland soils were significantly lower than the orchard soils in the 0-40 cm depth zone (P<0.05). The effects of different land use types on the organic carbon content of soil aggregates was most marked in the 0-10 cm layer. Compared with farmland, the organic carbon content in the large aggregates, intermediate aggregates, micro-aggregates, and the silt and clay fraction of orchard soils were relatively increased by 56.0% (P<0.05), 57.1% (P<0.05), 40.8% (P>0.05), and 13.0% (P>0.05), respectively. Organic carbon storage in each aggregate class (excluding the<0.053 mm fraction) in the orchard soils was higher than in the farmland soils. In the orchard soils, the proportion of soil macro-aggregates (>0.25 mm) and the associated organic carbon content was elevated, damage to aggregates was reduced, and the organic carbon stability was enhanced. In general, the soil aggregate stability and organic carbon content of orchard soils were higher than for the farmland soils. Orchards appear to enhance the physical stability of aggregates with respect to soil organic carbon, contribute to soil organic carbon accumulation, and thus promote soil carbon sequestration.