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Plantations play a vital role in the global nutrient cycle because they have large stocks of soil macronutrients. However, the impacts of plantations on soil macronutrient stocks combined with stand age and soil physicochemical properties have not been well quantified. We compared soil macronutrient stocks at soil depths of 0−20 and 20−40 cm across a 7-, 14-, 25-, and 30-year chronosequence of Masson pine (Pinus massoniana Lamb.) plantations. The results showed that the nitrogen (N), phosphorus (P), and potassium (K) stocks first increased and then decreased with stand age. The highest N and P stocks were observed in the 14-year-old plantation, and the 25-year-old plantation displayed the highest K stock. The C, N, and P stocks declined with increasing soil depth across all sites, whereas the reverse trend was found in the K stock. Carbon stocks were highest for all plantations, followed by the K, N, and P stocks. Plantation soils exhibited a higher C:P ratio and a lower P:K ratio at various soil depths. The dominant controlling factors for the soil macronutrient stocks varied significantly at different stand ages and soil depths according to statistical analysis. For the total soil system, the C stock was affected by the available nutrients, organic matter, and stoichiometry; the available nutrients and organic matter were the determinant factors of the N and P stocks. Aggregate stability could be the primary parameter affecting the K stock. Organic matter explained most of the variation in soil macronutrient stocks, followed by the P:K ratio and available K. Collectively, our results suggest that the response of soil macronutrient stocks to stand age and soil depth will be dependent on different soil physicochemical properties, and P and K may be important limiting factors in Masson pine plantation ecosystems.

A high calcium level is an important ecological factor in karst regions. Studying the adaptation mechanism of karst plants to high-calcium environments can provide a theoretical support for revealing biodiversity maintenance mechanisms and for the comprehensive management of rocky desertification. Based on a field investigation, 59 common epilithic moss species were selected for the determination of the calcium content of the plants and soils. By chemical measurement and biostatistical analysing the calcium contents in the soil and epilithic mosses. It was found that the average calcium content of the epilithic mosses was 19.03 mg/g and the average calcium content of the soil was 14.41 ± 8.41 g/kg. The effect of soil calcium content on plant calcium content is not significant, indicating that soil is not the main source of calcium in mosses. There were significant differences in the calcium contents of different families and genus. The average calcium content of Pottiaceae was highest in different regions and habitats than that of other families, and the average calcium content of Brachytheciaceae was loweret. Based on the relationship between the calcium content in epilithic mosses and soil to classify the adaptation methods of the epilithic mosses to the high-calcium environment in karst. The strategies of epilithic mosses adapting to high-calcium environment can be categorised into 3 types: 1) Random, in which the calcium content in plants varies widely with the change in the soil calcium content, which does not significantly affect the growth of the plant; 2) High-calcium, in which the calcium content in the plant remains high at different soil calcium levels; and 3) Low-calcium, in which the calcium content in the plant remains low at different soil calcium levels.

The forest soil humus carbon pool is a significant part of the global carbon cycle. However, there are currently few reports on the pattern of distribution of latitude and altitude and influencing factors on humus carbon in forest soils, although it is highly important to explore the decomposition, mechanism of transformation and storage of soil carbon in forests. We measured the contents of surface soil organic carbon (SOC), humic acid carbon (HAC), fulvic acid carbon (FAC) and humin carbon(HMC) in forest soils of low-latitude and high-altitude and clarified the characteristics and influencing factors of the changes in humus at different latitudes and altitudes. The results showed that the composition of SOC and HAC increased with the increase in latitude and altitude. The influence of altitude on the composition of humus carbon was significant at latitudes of 23°N ~ 25°N but not at other latitudes. The soil moisture content and the C/N were the primary factors that affected the soil SOC and HMC in high latitude and altitude areas. The soil HAC and FAC at low latitudes and altitudes are primarily affected by the mean annual temperature, pH and amount of silt. Therefore, when assessing forest soil carbon sequestration, the focus on should be on carbon sequestration in high-latitude and high-altitude areas. This study revealed the characteristics and influencing factors of soil humus carbon composition in low-latitude and high-altitude regions of China and provide a reference for the evaluation of soil carbon storage in complex terrain and climatic regions of the world.

Rocky desertification has become one of the global ecological environmental problems. Karst rocky desertification area of southwest China is suffering from ecosystem degradation, and the combination of water and soil resources determines the stability of their ecosystems. In recent years, soil leakage has attracted attention because it was that under the development of carbonate shallow fissures, the water and soil along the such pipes as shallow fissures leaks underground, resulting in the allocation of soil and water underground, affecting the integrity of the overlying ecosystem. This study aimed to reveal the leakage loss process, characteristic and mechanism of soil in fissures on sloping lands in the karst area, taking fissures on sloping lands in karst plateau of Guizhou province as the research object, combined with the methods of paint marking and soil particle analysis was conducted to study the leakage loss process of soils in fissures. The result showed that rainstorm or downpour is the key factor of soil fissure leakage loss, and its leakage form is mainly soil creep. Soil creep displacements of different fissure at 104.5 mm rainfall event between 1.0 cm and 2.5 cm, accounting for more than 62.5% of the displacement at 332.7 mm rainfall event, while the soil creep displacement of fissures just range from 0.2 cm to 0.3 cm at the larger rainfall of 181.5; the particle content with different particle sizes in rock-soil interfaces and soils of six fissures selected under 3 precipitation events (104.5, 151.2 and 332.7 mm) showed that the fissure soil does not leak down uniformly, but some particles at the soil layers or rock-soil interfaces leak to the lower layer at random in the process of creep leakage loss. In other words, the occurrence of soil layers and particles are accidental, and the soil particles in the rock-soil interfaces and the soil layers of fissures have the possibility to leak down. Facts proved that the soil creep leakage loss in fissures is a complex process which is determined by the internal factors such as fissure structure, fillings characteristics and bottom connectivity, and such external factors as rainfall etc.Key words: underground leakage loss; soil; karst fissure; sloping land; karst plateau

Vegetation restoration is one of the effective means to control soil erosion and an essential method of eco-environmental restoration in fragile karst rocky desertification areas. The shallow karst fissure (SKF) filled with soil has become one of the most important root habitats in this area. It is essential to scientifically evaluate the soil quality of SKF and to provide a basis for matching species with sites. Here, we explore and gain insight into the characteristics of the response of the physicochemical properties of SKF soil to different stages of vegetation succession. Additionally, we develop a synthetical assessment system to determine soil quality. The key results were as follows. Significant differences were found in the soil properties between the surface and the SKF. Compared with the surface, the SKF soil structural property was poor, but the water conditions were better. The soil nutrient content of the SKF was significantly (p

Soil water deficits have presented challenges to vegetation restoration in rocky desertification areas. In the field, small volumes of soil resources are present only in near-surface crevices, fissures, and other similar features. Water stored in the soil in near-surface fissures can help plants grow in such areas. The goals of this study are to discuss the soil water retention functions of near-surface fissures in terms of soil structure, water infiltration and water storage capacity and to define the role of fissure water in the growth of plants in rocky desertification areas. Several near-surface fissures with four types of vegetation (i.e., crops, grass, shrubs and trees) within a rocky karst desertification area on the Karst Plateau in Guizhou Province, China, were examined. Soil physicochemical property analysis and stable isotope techniques were applied. Fissures with shrubs and trees present high levels of soil porosity, while fissures with crops and grasses present low levels of soil porosity. The water infiltration rates of the soil in all of the examined fissures are higher than the rainfall intensity of the maximum daily rainfall for this province. Consequently, most rainwater infiltrates through the fissure soils. Compared to the other fissures, fissures with crops present higher levels of usable soil storage capacity in the surface soils (0–20 cm), which are affected by tillage (ploughing), but exhibit lower capacities in the bottom soil layer. Additionally, tree and shrub fissures present higher usable soil storage capacities in bottom soil layer than other types of fissures. The main source of water for Ligustrum and Pyracantha in the dry season is fissure water, which accounts for 44.7% and 58.2% of all the water utilized by these species, respectively. Fissure water may represent the most important source of water for plants growing in near-surface karst fissures.

Serious soil erosion and an extremely low rate of soil formation leads to a thin layer of surface soil that makes tree growth difficult in areas of karst. Meanwhile, surface soil, driven by runoff, enters shallow karst fissures (SKFs); these SKFs filled with soil have become the major habitat type in the area. Here, we explore the morphological characteristics of shallow karst fissures as well as the soil physical and chemical properties of the SKFs and comprehensively analyse the factors that influence the soil properties. Three key results are presented. First, a high heterogeneity of morphological characteristics exists for shallow karst fissures. According to the different characteristics of the vertical section, the SKFs can be divided into 5 types. These types are Rectangle-type, Pyramid-type, Funnel-type, Net-type and Diamond-type. In addition, the SKF dip angles were mainly between 60° and 90° (76.39%), the width of the top aperture was mainly between 20 and 40 cm (51.39%), and the trace lengths were mainly between 80 and 160 cm (76.39%). Second, compared with their characteristics of surface soil, the bulk density and fractal dimension of soil particles of the SKFs were both large, and the main composition of the SKF soil was clay. Third, the soil nutrients of the SKFs (the organic matter, total nitrogen and total phosphorus) were lower than the surface soil nutrients but not significantly so. The total potassium (TK) of the SKFs was greater than that observed for the surface and increased as the depth of the SKF increased. The soil nutrients of the SKFs were significantly affected by the fissure morphology. The poorly connected fissures had better soil fertility. When the morphological characteristics and soil properties of the SKFs were comprehensively considered, the vegetation types that were determined to be the best for use in the ecological restoration of areas of karst rocky desertification were deep-rooted plants with especially strong root penetration. The result of this study can supply some reference for future studies of karst rocky desertification control and vegetation restoration in the karst area of Southwest China; in the South Claw Silicon Island in Yogyakarta Province, Indonesia; and in other karst regions with the same ecological background.

Ground fissures (GF), appearing in front of dumps, are one of the most obvious and harmful geological hazards in coal mining areas. Studying preferential flow and its influencing factors in the ground fissures of dumps may provide basic scientific support for understanding the rapid movement of water and vegetation restoration and reconstruction in mining areas. Based on field surveys of ground fissures, three typical ground fissures were selected in the studied dump. The morphological characteristics of preferential flow for ground fissures were determined through field dye tracing, laboratory experiments, and image processing technology. The results indicated that the lengths of the three ground fissures ranged from 104.84 cm to 120.83 cm, and the widths ranged from 2.86 cm to 9.85 cm. All of the ground fissure area densities were less than 10%, and the proportion of ground fissure surface area was small in the dump. The maximum fissure depth was 47 cm, and the minimum was 16 cm. The ground fissure widths ranged from 0 cm to 14.98 cm, and the fissure width and fissure width-to-depth ratios decreased with increasing soil depth. The stained area was greater than 90% in the 0–5 cm soil layers of the three fissures, and water movement was dominated by matrix flow. The stained width decreased from 90 cm to 20 cm with increasing soil depth. The preferential flow was mainly concentrated on both sides of the fissure, which was distributed as a “T” shape. The preferential flow stained area ratios were 27.23%, 31.97%, and 30.73%, respectively, and these values decreased with increasing soil depth. The maximum stained depths of the preferential flow among the three fissures were different, and the maximum stained depth of GF II was significantly larger than that of GF I and GF III (P < 0.05). The stained path numbers of the three fissures ranged from 0 to 49. With increasing soil depth, the stained path number first increased and then decreased. The stained path widths of the three fissures ranged from 0 cm to 90 cm. With the increase in soil depth, the stained path width decreased. The stained area ratio was significantly positively correlated with ground fissure width, the ground fissure width-to-depth ratio, soil saturated hydraulic conductivity, soil organic matter, and sand content and was significantly negatively correlated with soil water content and clay content. The stained path number was significantly positively correlated with ground fissure width, the ground fissure width-to-depth ratio, soil saturated hydraulic conductivity and soil organic matter. The stained path width was significantly positively correlated with the ground fissure width-to-depth ratio, soil saturated hydraulic conductivity, soil organic matter and sand content and was significantly negatively correlated with clay content. Plant roots could significantly increase the stained area ratio, stained path number, and width and promote the formation and development of preferential flow.

Nutrient losses from sloping farmland in karst areas lead to the decline in land productivity and nonpoint source pollution. A specially tailored steel channel with an adjustable slope and underground hole fissures was used to simulate the microenvironment of the "dual structure" of the surface and underground of sloping farmland in a karst area. The artificial rainfall simulation method was used to explore the surface and underground runoff characteristics and nutrient losses from sloping farmland under different rainfall intensities. The effect of rainfall intensity on the nutrient loss of farmland on karst sloping land was clarified. The results showed that the surface was the main route of runoff and nutrient loss during the rainy season on sloping farmland in karst areas. The influence of rainfall intensity on the nutrients in surface runoff was more substantial than that on underground runoff nutrients. Nutrient loss was more likely to occur underground than on the surface. The losses of total nitrogen, total phosphorus, and total potassium in surface and underground runoff initially increased and then gradually stabilized with the extension of rainfall duration and increased with increasing rainfall intensity and the amount of nutrient runoff. The output of nutrients through surface runoff accounted for a high proportion of the total, and underground runoff was responsible for a low proportion. Although the amount of nutrients output by underground runoff was small, it could directly cause groundwater pollution. The research results provide a theoretical reference for controlling land source pollution from sloping farming in karst areas.

Background Bryophytes have an important ecological function in maintaining ecological diversity, material transformation, and energy cycles in ecosystems. In this study, bryophytes in a typical karst area were the research objects. The coverage and abundance of rocky bryophytes in established plots were recorded. The composition and distribution characteristics of the karst epilithic mosses were analyzed by importance values, a dissimilarity index and ggplot2 in R. Results The karst epilithic moss communities included 207 species in 93 genera and 37 families, including 185 species in 27 families and 80 genera of mosses and 22 species in 10 families and 13 genera of liverworts. The dominant families were Pottiaceae, Brachytheciaceae, Thuidiaceae, Bryaceae, Hypnaceae, Mniaceae, Entodontaceae, and Lichenaceae. The dominant species were Thuidium kanedae, Pseudosymblepharis angustata, Trichostomum involutum, Racopilum cuspidigerum, Brachythecium helminthocladum, Eurohypnum leptothallum, Hyophila involuta, Anomodon rugelii, Taxiphyllum taxirameum, and Bryohaplocladium angustifolium. Epilithic mosses in karst habitats have five life forms: turf, weft, cushion, slanting, and pendant. The main life forms we observed were turf and weft. Conclusions The distribution of the epilithic moss communities is closely related to their habitats. The diversity of bryophytes in areas with high forest coverage, high humidity, and abundant water and heat conditions is higher than that of bryophytes in rocky desertification habitats.

The ecological environment of karst mountainous areas is fragile, and soil erosion has become an important factor restricting the social and economic development of these regions. How can the degree of soil erosion be scientifically assessed with a reasonable evaluation method? What is effect of the ecological environmental control measures? This study used extenics to assess the degree of soil erosion in karst mountainous areas. The typical karst mountainous area of Guizhou Province was used as the research object. In this study, a soil erosion monitoring indicator system for karst mountainous areas was developed, an evaluation model based on extenics was established, and an index correlation function and comprehensive correlation function were designed to assess the soil erosion of the karst mountainous areas. The key results were as follows. In the soil erosion monitoring index system, the soil nutrient indexes, soil erosion modulus, rock exposure, diversity index, flood season rainfall, population density and natural population growth rate had significant effects on soil erosion in the karst mountainous area. Additionally, we determined the grading standards for soil erosion intensity in typical karst mountains. Finally, the evaluation model was applied to a case study. The status of water and soil conservation was as follows: XW > ML > SB > ZS. These results provide new insights into the evaluation method, namely, extenics, which is helpful for conveniently, quickly and scientifically assessing soil erosion.

Due to the impacts of global warming, extreme precipitation events are increasing in frequency and are accelerating the process of rocky desertification in the karst area in southwestern China. In this study, the dual structure of a karst system was simulated in a steel tank, and a rainfall simulation was employed to determine the intensity threshold of erosive rainfall at the surface and the effects of extreme rainfall on runoff generation and sediment yield on karst hillslopes. The results showed the following. i) In order of importance, the factors contributing to runoff were rainfall intensity, slope angle and underground pore fissure degree (UPD), and the factors contributing to sediment yield were rainfall intensity, UPD and slope angle. To cause surface soil erosion, the rainfall intensity had to be >0.8 mm/min. ii) Under light (0.5 mm/min) and moderate rainfall (0.8 and 1.2 mm/min), underground pore fissures are the main pathway for runoff and sediment loss. iii) Under extreme rainfall (1.5 mm/min), surface runoff (and the associated sediment yield) represents the main part of soil erosion on the slope. During such events, the underground erosion proportion is lower, but the underground sediment yield is greater. Because underground pore fissures are the main pathway for underground soil loss, reducing the UPD is an immediate way to prevent and control underground leakage. Engineering measures have the fastest effect, but plant-based measures are more effective and worth popularizing to prevent and control underground soil loss in karst areas. These results provide information significant for controlling rocky desertification and preventing soil erosion in the karst area of southwestern China.

Near-surface karst fissures are filled with soils. These soils are often derived from the erosion and transport of surface soil but have different properties than the surface soil in karst rocky desertification regions. This study was undertaken to determine the soil structure and nutrient contents in underground fissures with different grades of rocky desertification (no, potential, mild, moderate and severe). Based on field surveys, near-surface karst fissures were selected in a typical karst plateau area. Soil particle compositions, particularly nutrient characteristics, were determined through field sampling and laboratory experiments. The results indicated that the higher the rock desertification grade was, the higher the soil sand (0.02–2 mm) content and the lower the clay (

Surface erosion and underground leakage loss simultaneously exist on slopes with a double‐layered structure (surface and underground) and have caused rocky desertification in karst regions. Because of the great difficulty of directly determining the underground leakage loss of soil and water, soil erosion processes in this region remain unclear, especially underground leakage loss. The aim of this study was to reveal the plot‐scale characteristics of surface soil erosion and underground leakage loss of yellow soils on karst slopes. Simulated rainfall tests and field runoff plot monitoring were conducted to achieve this aim. We found that surface erosion formed on steep slopes (30°) or at greater rainfall intensities (over 50 mm hr⁻¹) and that surface runoff and surface soil loss dominated the total runoff and soil loss on karst slopes at greater rainfall intensities. However, underground leakage loss always occurred at different slopes and rainfall intensities. For small rainfall intensity cases (lower than 80 mm hr⁻¹), underground runoff and underground soil leakage loss dominated the total runoff and soil loss and showed an underground runoff ratio of over 90% and an underground soil leakage ratio of over 44%. Rainfall intensity had significant effects on surface runoff depth and surface soil loss rates but an insignificant influence on underground leakage loss. Slope gradient and slope length influenced the runoff yield, and slope degree had a greater effect on the surface soil loss than had slope length. This study improves our understanding of surface erosion and underground leakage loss in karst rocky desertification regions.

Underground pore fissure is one of common ways of soil leakage, and the soil loss in underground pore fissure would aggravate the development of rocky desertification in karst areas. A designed steel tank with varied underground pore fissure degrees was used to measure how underground pore fissure affected soil erosion and sediment yield on karst bare slope. We found that sediment yield rates and its distribution ratios obviously differed between the surface and underground. Surface sediment yield rate greatly responded to rainfall intensity conditions, while underground sediment yield rate rarely changed. Both bed rock bareness and underground pore fissure degree had an insignificant effect on both surface and underground sediment yield rate, but the former greatly influenced sediment distribution between the surface and underground. With increasing of bed rock bareness rate, both the average surface and underground sediment yield rates first increased and then decreased. The later posed an effect on underground sediment yield rate, which increased with increase of underground pore fissure degree. With increase of underground pore fissure degree, critical rainfall intensity for producing surface sediment would increase from 0.8–1.3 mm min−1 to 1.3–2.0 mm min−1. The results provide a mechanistic understanding of how underground pore fissure affects soil erosion and sediment production. Copyright © 2017 John Wiley & Sons, Ltd.

Underground pore fissure and bedrock bareness are the main factors that lead to complicated mechanisms of soil erosion in karst regions. The objectives of this study were as follows: a) to measure runoff and sediment generated from the surface and underground in the karst bare slope; and b) to analyse the impacts of underground pore fissures and bedrock bareness rates on soil erosion. To achieve these objectives, we designed an experiment in which underground pore fissure degrees and bedrock bareness rates were varied, and their impacts on soil erosion were measured. The results showed that і) runoff and sediment yields from the surface and underground increased with increasing rainfall intensity, and the surface runoff was much more easily generated when the rainfall intensity was greater; ii) surface runoff yield first increased and then decreased with increasing bedrock bareness rates, while the runoff yield in underground pore fissures increased with increasing bedrock bareness rates; thus, sediment production on the surface and in underground pore fissures showed the same pattern, i.e., first decreased and then increased; iii) the surface runoff and sediment generally decreased with increasing degrees of underground pore fissures, while that of underground pore fissures presented a different pattern; and iv) rainfall intensity, bedrock bareness rates and underground pore fissure degrees were the important factors affecting soil erosion processes in karst bare slopes because the bedrock bareness rates and underground pore fissure degrees were the main factors causing the uneven distribution of runoff and sediment on soil surfaces and underground. Therefore, soil and water loss in underground pore fissures was the special pattern and main difference in soil erosion processes in the karst region compared with other regions. These results have theoretical and practical significance for understanding soil erosion mechanisms and controlling soil and water loss in karst regions.

In karst regions, shallow karst fissure (SKF) soil has proven to be an important plant habitat and soil resource. However, how plants affect the microbial abundance and community composition of SKF soil remains poorly studied. We explored the soil microbial community structure differences in fractured soil-plant systems by determining phospholipid fatty acid (PLFA) profiles under three vegetation types (herbs, shrubs and trees) in SKF and used a bare SKF without vegetation as the control in a karst rocky desertification area. The total microbial biomass and microbial community composition differed between surface soil and SKF soil. The total microbial biomass in surface soil was higher than that in SKF soil. In addition, in contrast to surface soil, the microbial communities in SKF soil were more vulnerable to the effects of environmental variables. Furthermore, plants had a significant positive effect on the accumulation of microbial biomass in surface and SKF soil: shrubs had the strongest effect, followed by trees. Vegetation types significantly affected the ratios of saturated PLFAs to monounsaturated PLFAs (SAT/MONO ratio) and cyclopropyl PLFAs to precursors (cy/pre ratio). In contrast to the SKF without vegetation, the SAT/MONO ratio and cy/pre ratio under grasslands, shrublands and trees were low. Herbs and shrubs had the greatest capacity to enhance the ability of soil to respond to environmental stress compared to trees. Our results suggest that, as an important plant habitat in karst regions, the condition of SKF soil should be urgently improved. The stereoscopic collocation of shrub-grass vegetation may be the preferred measure for vegetation restoration. Deep-rooted shrubs and grasses are best at improving soil and plant growth. Our study can be useful for developing strategies for vegetation rehabilitation in karst regions.

Karst rocky desertification and vegetation restoration have become major environmental and social problems throughout the world. In regions facing rocky karst desertification, any form of residual soil is pivotal to vegetation growth and the restoration of rocky desertification. The goals of this study were to discover the impact of vegetation restoration on soil properties in near-surface fissures of karst rocky desertification regions, and analyses of the physical and chemical properties of soil and stable isotope techniques were used to achieve these goals. We found that the morphological structures of karst near-surface fissures are diverse. Fissures with grass and shrubs exhibit improved soil bulk density and more fine soil particles than those with other vegetation. Fissures with shrubs have higher soil field capacity, an increased capillary water content and a greater field capacity, whereas fissures with grass display greater fertility, particularly with respect to hydrolysable nitrogen, and greater available phosphorus and potassium contents, which create conditions that are superior to those found in areas with other crops, shrubs and even trees. Karst near-surface fissures are the optimal locations for vegetation restoration in areas of karst rocky desertification. Fissures with grass have a better soil structure, a higher water content and improved fertility compared with other fissure with growing crops, shrub grasses and forests with certain soil degradation. The use of grasses should be prioritized to improve soil conditions and to advance sustainable land use during the implementation of vegetation restoration projects in karst rocky desertification regions, particularly in highly fissured areas.

Nitrogen loss in karst sloping farmland will lead to declining land productivity and environmental pollution, in which the nitrogen loss through underground pore fissures will directly lead to groundwater pollution. The characteristics of total nitrogen (TN) production were studied by simulating the “dual structure” microenvironment of sloping farmland in a karst region using an artificial rainfall simulation method. The results show that rainfall was the main driving factor of TN loss in karst sloping farmland. TN was mainly lost through underground pore fissures when the rainfall intensity was ≤ 30 mm · h−1. TN was lost at the surface and underground when the rainfall intensity was ≥ 50 mm · h−1, TN loss on the surface accounted for a large proportion, and the surface flow was the main carrier of TN loss. The TN loss underground is easily ignored because it is hidden underground. Therefore, TN loss belowground in karst sloping farmland should receive increased attention. It would be interesting to explore the influences of connectivity and type of underground pore fissure system on TN loss in karst sloping farmland. The prevention and control of TN loss in karst sloping farmland should be considered both at the surface and underground. Reducing the formation of slope flows and slowing rainwater filtration by increasing slope vegetation coverage can be considered to reduce TN loss. The results of this study provide a theoretical reference for agricultural non-point source pollution control in a karst region.

The influence on soil erosion by different bedrock bareness ratios, different rainfall intensities, different underground pore fissure degrees and rainfall duration are researched through manual simulation of microrelief characteristics of karst bare slopes and underground karst crack construction in combination with artificial simulation of rainfall experiment. The results show that firstly, when the rainfall intensity is small (30 and 50 mm h−1), no bottom load loss is produced on the surface, and surface and underground runoff and sediment production is increased with the increasing of rainfall intensity; secondly, surface runoff and sediment production reduced with increased underground pore fissure degree, while underground runoff and sediment production increased; thirdly, raindrops hit the surface, forming a crust with rainfall duration. The formation of crusts increases surface runoff erosion and reduces soil infiltration rate. Increasing of surface runoff erosion damaged crust and increased soil seepage rate. Raindrops continued to hit the surface, leading the formation of crust. Soil permeability showed volatility which were from reduction to increases and reduction, and so on. Surface and subsurface runoff were volatility with rainfall duration; fourthly, when rock bareness ratio is 50% and rainfall intensities are 30 and 50 mm h−1, runoff is not produced on the surface, and the slope runoff and sediment production presents a fluctuating change with increased rock bareness ratio; fifthly, the correlation degree between the slope runoff and sediment production and all factors are as follows: rainfall intensity > rainfall duration > underground pore fissure degree > bed rock bareness ratio.