稻草覆盖和香根草篱对红壤水稳性团聚体组成及有机碳含量的影响

基于植物篱和秸秆覆盖控制红壤坡耕地水土流失的长期定位试验,研究香根草篱(H)、稻草覆盖(M)、香根草篱+稻草覆盖(HM)水保措施下红壤水稳性团聚体组成及有机碳分布特征。结果表明:与常规等高农作模式(CK)相比,草篱、稻草覆盖、草篱+稻草覆盖模式下土壤总有机碳含量提高0.07—2.42 g/kg。草篱对土壤团聚体组成及其结合有机碳的影响在篱内效果显著,随着与草篱距离增大影响减弱。草篱和稻草覆盖对土壤团聚体组成和结合有机碳含量的影响不同,草篱主要增加2 mm水稳性团聚体含量及其结合有机碳含量,稻草覆盖增加0.25 mm水稳性团聚体含量及其结合有机碳含量。综合来看,草篱和稻草覆盖相结合对改善坡面土壤结构作用稳定。土壤有机碳含量较高时,土壤总有机碳含量与粒径2mm的大团聚体有机碳含量呈显著正相关(r=0.659);随着有机碳含量降低,土壤总有机碳含量与土壤0.25—0.053 mm和0.053 mm微小团聚体碳含量相关性逐渐增大。

Effects of straw mulching and Vetiver grass hedgerows on the size distribution of the soil water stable aggregates and aggregate-associated organic carbon in red soil

The sloping fields of red soil are the main source of agricultural production in south China. A specific soil parent material, red soil helps decrease erosion resistance. Furthermore, the combination of population increase and reduction of cropland increases soil erosion significantly, which significantly restricts the region''s socio-economic development and ecological environment construction. Soil aggregates are the basic unit of soil structure, and their formation and stabilization have a direct impact on runoff and the loss of red soil in sloping farmland. The formation and stabilization of soil aggregates is a natural process influenced significantly by soil properties, soil organic carbon (SOC) in particular. Hedgerow and straw mulching, which are listed as important factors affecting the soil organic carbon and aggregate content by increasing the input of soil organic matter and improving soil water-stable aggregate (WSA) stability, are considered reasonable methods of restoring and reconstructing the fertility of eroded soil in red slope farmland. Compared to mulching, a hedgerow is a vegetative barrier preferably placed along a topographical contour perpendicular to the direction of water flow in the field, in order to trap sediments and reduce runoff velocity. The effect of trapping sediments and reducing runoff varies depending on the distance of the soil from the hedgerow. Most preliminary studies have focused on the effect of either hedgerow installation or mulching on soil and water conservation, soil nutrient condition, non-point pollution, composition and fractal features of soil micro-aggregates. Very few studies have investigated the effect of both hedgerows and mulching on the soil water stable aggregate size distribution and aggregate-associated organic carbon, especially the WSA distribution characteristics on the slope.Based on field soil and water conservation experiments we designed and carried out beginning in 2009, hedges of Vetiver Grass (H), rice straw mulching (M), and hedges of Vetiver Grass+rice straw mulching (HM) were applied to sampling plots to investigate the effect of biological metrics of water and soil conservation on soil water-stable aggregate stability (WSA) and aggregate-associated organic carbon content. Additionally, this study reports the area of influence of hedges on the soil structure and soil organic carbon, using Vetiver Grass hedges as an example. The soil was sampled at 0 m, 2 m, and 4 m uphill of the hedge. The results indicate that, compared to conventional cultivation (CK), the organic carbon content in the H, M, and HM treatments increased by 0.07-2.42 g/kg. The effect of Vetiver Grass on WSA size distribution and aggregate-associated organic carbon decreases gradually as the distance from hedge increases. H treatment increases the macro-aggregate (> 2 mm) content and the aggregate-associated organic carbon, whereas M treatment increases the micro-aggregate (< 0.25 mm) content. Overall, HM treatment is the best in terms of improving slope red soil structure. These results indicated a significant positive correlation between soil organic carbon and the organic carbon content of the macro-aggregates (>0.25 mm) in the soil. These results will play an important role in establishing reasonable measures of soil and water conservation measurement and determining good method of facilitating carbon accumulation in red slope farmland of southern China.