【Objective】This study aims to reveale the law of soil quality variation caused by water erosion provides scientific data support for soil erosion control and low-efficiency forest transformation in hilly red soil region of southern china.【Method】The small watershed of Qingyuan Mountain in Ji ’an City, Jiangxi Province was selected as a typical area of red soil hilly area in southern China. According to the typicality and representativeness, the small watershed was divided into slope positions, and three sections were set up to collect soil repeatedly. The composition of soil aggregates was analyzed, and the correlation analysis was used to explore the relationship between various indicators in the process of water erosion.【Result】Water erosion changed the spatial distribution pattern of bulk density and soil porosity, resulting in weaker soil anti-erodibility in erosion area and less influence in deposition area, which accelerated the occurrence of soil erosion. Soil bulk density increased after long-term erosion. Compared with other slope positions, soil bulk density at slope toe increased significantly by 0.16 g/cm3 (P < 0.05), while saturated water holding capacity and capillary porosity decreased significantly (P < 0.05). After water erosion, the composition of soil texture also changed, soil sand content increased significantly, clay and silt content decreased significantly (P < 0.05). The water erosion process had different effects on soil nutrients at different slope positions. The soil total nitrogen, available phosphorus, organic carbon content and carbon-nitrogen ratio decreased on the upper, middle and lower slopes, and the content on the slope decreased significantly (P < 0.05). Compared with other slope positions, the nutrient content at the toe of the slope increased, and the available phosphorus increased significantly by 39.31% (P < 0.05). After water erosion, the mass fraction (R0.25), mean mass diameter (MWD) and geometric mean diameter (GMD) of water-stable aggregates at different slope positions showed a decreasing trend, and the change at the foot of the slope was not obvious, and the stability of soil structure was the highest.【Conclusion】The ecosystem of red soil hilly area in southern China is fragile. Long-term water erosion can reduce the stability of red soil aggregates. The water erosion process causes spatial differentiation of soil physical and chemical properties in erosion-deposition sites. Vegetation coverage and litter thickness are the main environmental factors.
【Objective】 This study aims to explore the characteristics of surface runoff and sediment yield of economic forest land with different planting and management measures in the hilly region of Southern Jiangsu. 【Method】 Analyzing the process of runoff and sediment yield on the slope based on the observation data of runoff plots in Wuxi Yixing City in 2021. 【Result】 ① In the hilly region of Southern Jiangsu, the runoff and sediment yield of economic forest mainly occurred from May to August, in which the runoff and soil erosion yield of different runoff plots accounted for more than 72.5% and 68.7%, respectively. ② The comparison of slope runoff and erosion in different runoff plots is as follows: Ⅰ-peach forest (with grass) <Ⅱ-peach forest (weeding), and compared with Ⅱ, the annual runoff reduction of Ⅰwas 156.3% and the annual soil erosion reduction was 122.9%; Ⅴ-tea garden (cross slope) < Ⅳ-tea garden (along slope), and compared with Ⅳ, Ⅴ had an annual runoff reduction of 57.0% and erosion reduction of 41.5%. In addition to it, the annual runoff of different economic forest slopes was reduced by 50.6%-380.4%, and the annual soil erosion was reduced by 155.3%-513.1% compared with Ⅲ-bare slope (blank). ③ The maximum runoff and erosion of the Ⅰ-Ⅴ plots accounted for 15.3%, 14.5%, 10.8%, 12.5%, 14.4% and 7.9%, 6.3%, 4.5%, 7.1%, 8.0% of the total, respectively. It can be seen that high-intensity rainfall has an important impact on slope soil erosion. 【Conclusion】 Soil erosion in runoff plots of different economic forests was significantly positively correlated with rainfall, average rainfall intensity, I30 and runoff depth, and the correlation with soil water content before rainfall was complex, in which soil erosion had the closest relationship with runoff depth (R2=0.553).
【Objective】 This study explored the influence of sampling interval on the measurement accuracy of urban soil magnetic susceptibility. 【Method】 Taking typical forest land in Nanjing and its suburbs as the research object, four representative sample plots (suburban forest farms, urban forest farms, undisturbed land and disturbed road green belts) were selected, and 0-30 cm topsoil samples were collected. Taking soil magnetic susceptibility as the main index, five topsoil sampling intervals (2, 5, 10, 15 and 30 cm) were set. The profile variation characteristics of surface soil mass susceptibility and percentage frequency susceptibility at different sampling intervals were analyzed. 【Result】Soil low frequency mass susceptibility (χlf) of the four sample plots ranged from 59.2 × 10-8 to 1 210.0 × 10-8 m3/kg, with a peak value of 5-7 cm. Low frequency magnetic susceptibility of soil profiles in all plots basically followed the pattern of first increasing and then decreasing and fluctuating. Fine sampling intervals (such as 2 cm) better captured the peak value and abnormal values of soil magnetic susceptibility; the 5 and 10 cm soil sampling intervals reflected the general variation trend of soil magnetic susceptibility; the soil sampling interval of 15 cm showed no detail in the soil magnetic susceptibility changes. Mixed soil samples at 0-30 cm soil sampling intervals only indicated the mean value of magnetic susceptibility of various surface soils. 【Conclusion】 During the sampling process, appropriate sampling intervals should be set according to the research purpose in order to improve the accuracy of experimental data.
【Objective】The Black Soil Region is an important food base, which has a vital strategic position to ensure the food security in China. However, due to the long-term unreasonable utilization, the black soil resources suffered from serious water erosion. The objective is to clarify the spatio-temporal characteristic of soil loss on cropland and discuss the feasibility of evaluating soil erosion by magnetic susceptibility. 【Method】Magnetic susceptibility (MS) had been proved to be a rapid, reliable, economic and nondestructive method in estimating hillslope soil redistribution. In this paper, three typical black soil slope transects were selected in Heshan Farm, Heilongjiang Province, and collected soil profile samples from surface to 60-100 cm depth, measured soil magnetic susceptibility. The MS was used as a tracer to analyze the spatio-temporal heterogeneity of soil susceptibility at slope scale and discussed the soil erosion patterns in Black Soil Region. 【Result】The results showed that MS of topsoils on all the slope were generally high, and decreased with the increasing of soil depth. MS at parent layers become stable, which was in line with the MS characteristics of temperate soil developed from weak magnetic parent materials. The average MS at upperslopes and middleslopes were less than that of reference sites, which were 24.1×10-8 m3/kg and 24.8×10-8 m3/kg, respectively, the average MS of lowerslopes were greater than that of reference sites, for 39.71×10-8 m3/kg. It conformed to the general soil erosion pattern on hillslope that soil material deposited from its original position to the lower position. The whole slope were divided into erosion area and deposition area according to the topsoil MS of reference sites. The topsoil MS at the erosion area was lower than that of reference sites, while the topsoil MS at the deposition area was higher than that of reference sites. The topsoil particles were removed and transported at upperslopes and middleslopes, deposited at lowerslopes. With the increasing of cultivation periods, the MS between upperslopes and lowerslopes varied significantly which showed strong slope heterogeneity, and the cultivation periods were positively correlated to the soil redistribution. The range of MS on cropland reclaimed for 110 years was 1.7×10-8-88.7×10-8 m3/kg, which was about 1.4 and 1.9 times of cultivated for 60 and 30 a, respectively. 【Conclusion】The MS at topsoils of the black soil slope presented heterogeneity, that is, upperslopes and middleslopes located in the erosion area while lowerslopes were located in the deposition area. The longer the cultivation period, the higher the degree of soil redistribution on slope. Soil erosion was the most intense on the slope reclaimed 110 years ago. In view of the soil erosion in Black Soil Region, we should vigorously carry out the quality protection and improvement of cultivated land, encourage contour farming and strengthen the monitoring and investigation of soil conservation of black soil under a longer spatio-temporal series. The results can provide a theoretical basis for the prediction and prevention of water conservation and controlling soil erosion in Northeast China, which is conducive to the sustainable development of regional agriculture and ecological environmental protection.
