Search Results (4)

Agroforestry systems can fully exploit the ecological benefits of an ecosystem’s component plants, and improve the ecological environment, soil quality, and land use efficiency, all of which have recently attracted the attention of many scholars. Southwest China’s karst graben basins have barren soil that needs immediate improvement. The karst graben basin in southwest China was used for this study to examine the impacts of several forest–grass composite systems of Bingtang orange–alfalfa–ryegrass on soil improvement, which is located in Jianshui County, Honghe Prefecture, Yunnan Province. The experiment had four treatments, Bingtang orange–alfalfa sowing (B2), Bingtang orange–ryegrass × alfalfa mixed sowing (A), Bingtang orange–ryegrass × alfalfa intercropping (R), and Bingtang orange monocropping (CK). The results showed that different forest–grass composite patterns had noticeable effects on improving the soil’s organic carbon (SOC), total nutrients, and available nutrients, especially in the rainy season when plants grew vigorously. Forage grass intercropping under forest exerted the best effect on soil improvement in the surface layer, and the effect decreased with the increase in soil depth. Alfalfa intercropping under Bingtang orange forest had the strongest effect on improving SOC, total N, ammonia nitrogen, and nitrate nitrogen, whose content increased by 30.7%, 27.3%, 35%, and 36.3%, respectively, in the dry season and 38%, 46.7%, 48.7%, and 55.3%, in the rainy season. However, the effect of alfalfa–ryegrass intercropping under the Bingtang orange forest on soil total P, total K, and available P was better than that of the Bingtang orange–alfalfa intercropping system. The C:N ratio is more suitable in the Bingtang orange–ryegrass-alfalfa composite system. Forage grass intercropping under the Bingtang orange forest effectively improved the soil NPK and C status, and the results of this study provided a basis for the selection of forest–grass composite patterns for soil improvement. Full article

Dodonaea viscosa is widely cultivated in the karst graben basin and is crucial for recovering land after rocky desertification. However, the effect of long–time D. viscosa afforestation on changes in the quality of soil remains unclear. Soil nutrients and aggregate composition can be used to evaluate the beneficial effects of afforestation of D. viscosa in improving soil functional stability. In this study, soil nutrients and aggregate stability were investigated using cropland, 10–year, 20–year, and 40–year D. viscosa afforestation and secondary succession shrub. Compared to the cropland, D. viscosa afforestation significantly increased the soil water content (WC), soil organic carbon (SOC), and total nitrogen (TN) contents, with an enhanced effect observed with prolonged afforestation. Soil nutrient contents under D. viscosa afforestation rapidly reached the level of the shrub. Dodonaea viscosa afforestation promoted the formation of >2 mm aggregates and decreased the ratio of 0.053–0.25 mm aggregates, which varied with afforestation years. Compared to the cropland, the content of >0.25 mm water–stable aggregates (R_>0.25), mean weight diameter (MWD), and geometric mean weight diameter (GMD) of soil increased exponentially. However, soil erodibility factor (K) and unstable aggregates index (E_It) decreased exponentially with prolonged D. viscosa afforestation, and the latter two indicators did not reach the level of the shrub. These results indicated that soil nutrients, aggregate stability, and erosion resistance increased with prolonged D. viscosa afforestation. However, the aggregate stability and erosion resistance exhibited by D. viscosa could not reach the level of secondary shrub for a long time. Full article

Land use patterns can change the structure of soil bacterial communities. However, there are few studies on the effects of land use patterns coupled with soil depth on soil bacterial communities in the karst graben basin of Yunnan province, China. Consequently, to reveal the structure of the soil bacterial community at different soil depths across land use changes in the graben basins of the Yunnan plateau, the relationship between soil bacterial communities and soil physicochemical properties was investigated for a given area containing woodland, shrubland, and grassland in Yunnan province by using next-generation sequencing technologies coupled with soil physicochemical analysis. Our results indicated that the total phosphorus (TP), available potassium (AK), exchangeable magnesium (E-Mg), and electrical conductivity (EC) in the grassland were significantly higher than those in the woodland and shrubland, yet the total nitrogen (TN) and soil organic carbon (SOC) in the woodland were higher than those in the shrubland and grassland. Proteobacteria, Verrucomicrobia, and Acidobacteria were the dominant bacteria, and their relative abundances were different in the three land use types. SOC, TN, and AK were the most important factors affecting soil bacterial communities. Land use exerts strong effects on the soil bacterial community structure in the soil’s surface layer, and the effects of land use attenuation decrease with soil depth. The nutrient content of the soil surface layer was higher than that of the deep layer, which was more suitable for the survival and reproduction of bacteria in the surface layer. Full article

Understanding ecological stoichiometric characteristics of soil nutrient elements is crucial to guide ecological restoration and agricultural cultivation in karst rocky desertification region, but the information about the effect of the geological background on ecological stoichiometric ratios remains unknown. Soils from different landforms, including a basin, slope, and plateau, were sampled to investigate the spatial variance of the ecological stoichiometric characteristics of soil carbon (C), nitrogen (N), and phosphorus (P) under different rocky desertification grades (LRD: light rocky desertification; MRD: moderate rocky desertification; and SRD: severe rocky desertification) in a karst graben basin of Southwest China. Soil C:N ratio was not significantly influenced by rocky desertification grade, which was at a relatively stable level in the same landform, but soil C:P and N:P ratios increased with increasing rocky desertification grade. This change was consistent with increased soil organic carbon (SOC) and total nitrogen (TN) concentrations in the same geomorphic location along with the intensification of rocky desertification, but soil P concentration remained at a relatively stable level, indicating that P may be the limiting macronutrient for plant growth during vegetation restoration in a karst graben area. The soil C:N ratio of slope land was larger than that of the basin and plateau, while the soil C:P ratio and N:P ratio of the slope and plateau were significantly larger than that of the basin. The correlations between pH and C, N, and P stoichiometry decreased significantly when Ca was used as a control variable. In sharp contrast, the correlations between Ca and C, N, and P stoichiometry were highly significant no matter whether pH was used as a control variable, suggesting the important role of Ca in soil C, N, and P stoichiometry in karst graben basins. Full article