Soil Region Of Southern China Research Articles

Effects of Rainfall Variability and Land Cover Type on Soil Organic Carbon Loss in a Hilly Red Soil Region of Southern China

Rainfall intensity (RI) and land cover type are two important factors that affect soil erosion and thus the transfer and loss of soil organic carbon (SOC). However, the in situ quantitative monitoring of SOC loss under natural rainfall and various land cover types restored on eroded lands has not been thoroughly examined. In order to further study the effects of rainfall changes and vegetation types on SOC loss in the red soil region of Southern China, the Jiangxi Eco-Science Park of Soil and Water Conservation in De’an County, Jiangxi Province, was taken as the research object. Considering natural rainfall and based on the long-term field in situ monitoring of rainfall and runoff and sediment data, we studied the effects of three land cover types (bare land, orchards, and grass cover) on surface runoff, sediment production, and SOC loss in relation to 1 hour of RI during natural rainfall in the red soil region of Southern China during rainy seasons of 2020 and 2021 (March to August). Compared with bare land plots, the orchard and grass cover plots had surface runoff reductions of 67% and 98%, respectively, and sediment reductions of 79% and 99% over the two rainy seasons, respectively. With an increasing RI over 1 hour, total SOC loss increased for each of the three land cover types. More SOC loss was associated with sediments, and the enrichment ratio of SOC in the sediments (ERoc) decreased significantly. The ERoc values decreased in the following order: bare land (1.23) > orchard (1.08) > grass cover (0.81). Bare land exhibited the highest proportion of SOC associated with sediment in the total SOC loss (Ps), at 68.69%, followed by the orchard plots, at 55.02%, and then the grass cover plots at 49.24%. With the transfer of land cover type from bare land to orchard and to grass cover (decreased soil loss intensity, SLI), more SOC was lost associated with runoff in the form of dissolved organic carbon (DOC); the values of ERoc and organic carbon loss intensity (CLI) also decreased significantly. These findings are crucial to improving our understanding of the regulatory mechanisms of rainfall changes and land cover types on SOC loss during soil erosion.

Evaluation of Spatial–Temporal Variations in Ecological Environment Quality in the Red Soil Region of Southern China: A Case Study of Changting County

Evaluation of Spatial–Temporal Variations in Ecological Environment Quality in the Red Soil Region of Southern China: A Case Study of Changting County

Runoff and sediment reduction effects of different Paspalum wettsteinii‐planting measures on the slopes of Masson pine plantation in the red soil region of southern China

AbstractGrass‐planting measure is a crucial vegetation approach to mitigate understory soil erosion and improve ecological environment in the red soil region of southern China. This study aimed to quantify the effects of grass (Paspalum wettsteinii Hackel.)‐planting measures on runoff and sediment reduction on slopes of Masson pine plantations under rainstorm conditions. We conducted a rainfall simulation experiment at a rainfall intensity of 2.0 mm/min, comparing single strip (MT1, strip spacing: 145 cm), double strips (MT2, strip spacing: 70 cm), and triple strips (MT3, strip spacing: 45 cm) grass‐planting measures on slope surface runoff generation and soil erosion processes of the young Masson pine (MT0, no grass strip) plantation, and the bare slope (CK) was selected as the control. Results revealed that grass‐planting measures significantly decreased slope erosion parameters compared to CK and MT0. As the average grass coverage increased (MT1 from 10% to 25%, MT2 from 7.5% to 22.5%, MT3 from 7.3% to 25%), the slope surface erosion parameters under the grass‐planting measures decreased, resulting in significantly improved runoff and sediment reduction benefits. The runoff reduction effect could reach 32%, while the sediment reduction effect could reach 88%. Moreover, MT3 demonstrated superior performance over MT2 and MT1, with minimal runoff and sediment reduction effects observed for the MT0. Overall, this study suggests that grass‐planting measures, coupled with the increasing of grass coverage rates, significantly improve runoff and sediment reduction benefits on slopes in regions experiencing heavy rainfall. Among the tested configurations, MT3 emerged as most effective measure for controlling understory soil erosion in Masson pine plantations, especially when its average grass coverage rate reached 25%. These findings provide valuable insights for selecting appropriate grass‐planting strategies, as well as for understanding the underlying mechanisms of how these measures mitigate soil erosion. This scientific reference will aid in the design and implementation of soil and water conservation measures in the region.

Effects of tillage practices on runoff and soil losses in response to different crop growth stages in the red soil region of southern China

Effects of tillage practices on runoff and soil losses in response to different crop growth stages in the red soil region of southern China

Water Erosion Response to Rainfall Type on Typical Land Use Slopes in the Red Soil Region of Southern China

Land use and rainfall are two important factors affecting soil erosion processes. The red soil region of southern China is a representative region with high rainfall amounts and rapidly changing land use patterns where the water erosion process is sensitive to changes in land use and rainfall. To comprehensively understand the water erosion response to land use and rainfall in this region, a 6-year in situ experiment based on eight plots (bare land and seven typical land uses) was conducted from 2015 to 2020. The 320 rainfall events were divided into 4 types, and there were 3 main rainfall types. The runoff of different rainfall types was primarily determined by the rainfall amount, while the soil erosion of different rainfall types was primarily determined by the rainfall intensity. High-intensity rainfall contributed the most to both total runoff and soil erosion. Compared with bare land, the seven typical land uses reduced runoff and soil erosion by more than 75%. Grassland, cropland, and forest with low vegetation coverage experienced high runoff and soil erosion, while shrubland most effectively reduced runoff and soil erosion. The combination of land use and rainfall type significantly affected the annual average runoff depth, soil erosion modulus, and soil loss coefficient. Rainfall types can change the relationship between runoff and soil erosion for different land uses. The runoff and soil erosion of bare land were highly correlated with rainfall characteristics, while vegetation weakened this relationship under short- or moderate-duration rainfall. To effectively reduce water erosion, high-intensity rainfall should receive special attention, and all land uses should ensure that vegetation is well developed, especially understory vegetation.

Erosion processes and sediment source tracing on heterogeneous slopes in the red soil region of southern China

AbstractUnderstanding erosion, sediment sources and the spatial distribution along heterogeneous slopes is essential for soil and water conservation. In this study, soils derived from nodular limestone, mud‐like limestone and limestone breccia (abbreviated as SMTL, SMDL and SLBC, respectively) were utilized to establish artificial homogeneous and heterogeneous slopes. The homogeneous slopes MTL, MDL and LBC represent SMTL‐, SMDL‐ and SLBC‐filled‐ slopes, respectively. The heterogeneous slopes were abbreviated as MTL/MDL, MDL/LBC and LBC/MTL. Rare earth elements (REEs; lanthanide, cerium and ytterbium) were used to tag soils on the upper and lower slope sections to track sediment transport and deposition. The results showed that for homogeneous slopes, the LBC slope was the most severely eroded, followed by the MDL and MTL slopes. For heterogeneous slopes, the order of erosion was LBC/MTL > MTL/MDL > MDL/LBC. Upslope sections contributed a sizable portion of the total sediment yield, ranging from 51% to 79%. Over time, the difference in the sediment contribution between the upslope and downslope regions decreased and reached equilibrium. Runoff rates on heterogeneous slopes demonstrated an inverse function (R2 > 0.75) in contrast to a logarithmic distribution (R2 > 0.87) on homogeneous slopes. Heterogeneous slopes displayed minimal intersegment variation and the absence of a consistent ordering of the magnitude of hydraulic parameters. Conversely, the hydraulic parameters of homogeneous slopes were consistently ordered across the slope sections. For sediment transport, all slopes exhibited suspension‐dominated flow with percentages greater than 89%. However, the particle size distribution of the sediment of heterogeneous slopes exhibited greater diversity and complexity because of the coexistence of distinct soils. These findings underscore the importance of customized strategies for soil and water conservation in environments characterized by diverse soil parent materials.

Evolutionary patterns and influencing factors of relationships among ecosystem services in the hilly red soil region of Southern China.

As a crucial ecological protection area in China, the Southern hilly red soil region is characterized by uneven spatial and temporal distribution of ecological landscape elements, unpredictable and changeable interrelationships between them, diversified driving factors, and lack of comprehensive consideration of ecosystem services. In order to better understand the interaction between ecosystem services, restore regional ecology, and promote sustainable development, the evolution law and influencing mechanism of ecosystem services and their driving factors are quantitatively analyzed in the study. Based on simulations of different ecosystem services from 2000 to 2020, their spatial and temporal changes and the contributions of main drivers are quantified, their trade-offs and synergies are analyzed, and the changing rules under the influence of natural factors and socioeconomic factors are explored. The results show that (1) the crop production significantly increases in the southwest and north regions, the habitat quality decreases in urban and coastal areas, and the soil retention and water yield show an increasing trend from west to east. (2) Land use/cover is the main driver of carbon storage and habitat quality variation, and precipitation is an important driver of water yield spatial variation. (3) The crop production and the other four ecosystem services show a trade-offs relationship, and the relationship between supporting services and regulating services is the synergetic. (4) The altitude weakens the synergistic relationship between soil retention and habitat quality/carbon storage, while it enhances the synergistic relationship between soil retention and water yield. Driven by precipitation factors, ecosystem services related to water yield have significant differences in the change. The population density enhances the trade-offs of crop production and soil retention, as well as the synergistic relationship between soil retention and habitat quality/carbon storage. In different land use/cover (LULC), the influence of urban land on ecosystem services relationship change is more obvious. Overall, this study can provide scientific bases and policy suggestions for ecosystem protection/restoration in the red soil region of Southern China, which has an important theoretical and practical significance.

Rice planting acceleration of the activation and loss of soil iron in the red soil region of southern China

Rice planting acceleration of the activation and loss of soil iron in the red soil region of southern China

Impacts of the soil pore structure on infiltration characteristics at the profile scale in the red soil region

The complexity and uncertainty of pore structures, hinder the understanding of the water infiltration process along a soil profile. In this study, soil pore structures quantified by X-ray computed tomography (CT) scanning and infiltration processes traced using stable hydrogen and oxygen isotopes were linked under three land uses (forestland, citrus land, and rainfed cropland) in the red soil region of southern China. Our results showed that 95% of the soil pore diameters in the surface layer (0–20 cm) in forestland, citrus land, and rainfed cropland were concentrated in the ranges of 0.05–2.46, 0.05–2.24 and 0.05–1.04 mm, respectively. Rainfed cropland had the most soil micropores, along with a high porosity and poor connectivity, while there were more large, well-connected tubular pore channels in the forestland and citrus land. Hydrogen and oxygen stable isotopes were effective in tracing soil water infiltration processes under saturated and near-saturated conditions. The soil infiltration depths of citrus land, forestland, and rainfed cropland were 45, 40, and 25 cm, with "new water" volumes of 37.2, 26.4, and 22.3 mm, respectively. CT-based porosity and the soil texture were considered crucial indicators in the evaluation of the exchange between “old water” and “new water” during infiltration processes. More specifically, the soil structure of the limiting layer not only controlled the infiltration rate but also played an extremely important role in the infiltration mechanism, reflected by the different ratios of “new water”. The soil pore characteristics mainly affected soil water transport, while other soil properties played more important roles in soil water retention.

Runoff and sediment characteristics of a typical watershed after continuous soil erosion control in the red soil region of Southern China

To investigate the runoff and sediment characteristics of the watershed after continuous soil erosion control in the red soil region of southern China, hydrological data were collected from 2013 to 2020 in the Zhuxi watershed, which is located in the southeast of the red soil region. The results showed that the monthly suspended sediment concentration and annual sediment yield have significantly decreased since 2017. At the event scale, 180 floods were classified into four flood patterns (A, B, C and D) by the K-medoids clustering method based on the flood duration, runoff depth and peak discharge. Each flood pattern resulted in differing levels of the event sediment yield (D > C > B > A), and Pattern C contributed the most to runoff and sediment yield. The study period was divided into two stages according to the annual sediment yield. Compared with 2013–2016, the total runoff and sediment yield of the 3 major flood patterns (A, B and C) in 2017–2020 decreased by 17.88%∼25.12% and 78.92%∼90.34%, respectively. These flood patterns decreased not only in frequency but also in suspended sediment concentration, which was caused by the changes in the runoff-sediment relationships of flood events. Six types of suspended sediment concentration and discharge (SSC-Q) relations appeared in the flood events, indicating that the sediment sources and sediment transport processes were complex and dynamic. In 2017–2020, the single-valued relation became the dominant type of SSC-Q relations for all flood patterns, which suggests that the sediment supply was inhibited. The results provide a more comprehensive understanding of the runoff and sediment processes of a watershed after continuous soil erosion control, which is beneficial for revealing the development of soil erosion in the red soil region of southern China.

Divergent soil health responses to long-term inorganic and organic fertilization management on subtropical upland red soil in China

To optimize soil health, land use, and soil management decisions need to be guided by an understanding of the underlying soil health. Although widely used fertilizers guarantee crop production, they ultimately damage agricultural soil environmental quality and threaten the overall food chain safety. Thus, an integrative assessment considering both environmental safety and soil fertility is required for the sustainable development of long-term fertilization systems. In this study, we conducted a comprehensive assessment of soil health using 20 soil physical, chemical, and biological indicators and assessed them according to four heavy metals—copper, zinc, cadmium, and lead. This experiment was conducted in an area where there is an ongoing, 23-year-long fertilization experiment in a typical red soil region of southern China, including four treatments of common inorganic chemical fertilizer (CF), CF mixed with micronutrients (CF + T), CF mixed with pig manure (PM), and PM mixed with micronutrients (PM + T). To assess the soil fertility quality, we selected a minimum data set consisting of soil water-stable aggregates mean weight diameter, available phosphorus, total nitrogen, microbial biomass carbon, and dehydrogenase activity. The results revealed that soil fertility quality followed the order of PM + T ≈ PM > CF + T > CF. We also used a modified potential ecological risk index to assess the soil environmental quality. This approach considered the acid-soluble and exchangeable fraction of heavy metals as the bioavailability component. Both PM and PM + T treated soils were significantly contaminated by heavy metals, with particularly large amounts of Cd contamination. The soil health index escalated from CF, CF + T, PM to PM + T, which indicated that the use of pig manure allowed for more fertile soil relative to standard chemical fertilization. Moreover, applying additional micronutrients also had a significant influence on soil fertility. Therefore, our study revealed that long-term fertilization using organic pig manure was beneficial to overall soil fertility; however, these benefits were coupled with significant limitations regarding heavy metal contamination. Collectively, this study provides a better supporting method for soil health management and long-term fertilization strategies.

Climate-vegetation-erosion interactions revealed by the sediments of Huguangyan Maar Lake, southern China

Soil erosion is a serious environmental problem in the red soil region of southern China, yet little is known about the factors responsible and their specific effects on long-term soil erosion dynamics in this region. We addressed this issue via a study of the sediments of Huguangyan Maar Lake (HML), a crater lake in southern China. Our results confirm that the sediments in HML are mainly derived from the erosional input of weathering products of wall rocks, via catchment runoff. Having established the provenance of the HML sediments, the sediment accumulation rate, mass accumulation rate, and geochemical element fluxes were used to reconstruct soil erosion processes in the HML catchment over the past ∼1400 years. The potential drivers of soil erosion were explored, and regional comparisons were made to evaluate the representativeness of this study. The results show that: 1) Higher precipitation before ∼830 CE, coupled with a lower level of human activity, promoted increased vegetation coverage which reduced the rate of soil erosion. 2) Lower precipitation during 830 CE–1390 CE reduced the rate of soil loss. 3) Abundant precipitation was the main cause of the more intense soil erosion during 1390 CE–1878 CE, which may have been exacerbated by the reduced vegetation cover caused by intensive human activity. 4) During 1878 CE–2019 CE, the vegetation cover gradually recovered under the combined effects of vegetation restoration and higher precipitation, which reduced the rate of soil erosion within the HML catchment. Compared to the Chinese Loess Plateau, the erosion level in the HML catchment was relatively low during the period of intensive human activities. Overall, our results contribute to an improving understanding of the driving mechanisms of soil erosion, and they provide a guide for soil conservation measures in southern China.

Rare microbial communities drive ecosystem multifunctionality in acidic soils of southern China

Soil microbial communities are important for maintaining ecosystem multifunctionality, and abundant and rare sub-communities often have fundamentally different characteristics and ecological roles. However, little is known about the links between microbial sub-communities and soil multifunctionality in acidic soils across large spatial scales. Here, we collected 52 soil samples from four locations spanning 961.3 km in the acidic soil region of southern China and characterized bacterial and fungal sub-communities and their contributions to soil multifunctionality. Sub-community compositions of both rare bacteria and rare fungi significantly explained changes in soil multifunctionality, but abundant sub-communities were not significantly related to soil multifunctionality. This suggested that soil multifunctionality might be mainly controlled by rare microbes in acidic soils. Rare fungal α-diversity, rather than rare bacterial α-diversity, was significantly and positively correlated with multifunctionality. Deterministic processes were the primary drivers of the sub-community assembly of rare bacteria and rare fungi and thus might have an important effect on soil multifunctionality. Soil pH was the most dominant soil factor driving rare bacterial and fungal sub-community structures and affecting soil multifunctionality. In the co-occurrence networks of bacterial and fungal communities, most of the keystone taxa were rare species. The numbers of positive interactions of rare fungal taxa, but not rare bacterial taxa, were positively related to soil multifunctionality. Our results provided evidence that rare microbial sub-communities are important for maintaining ecosystem multifunctionality in acidic soils, and rare bacteria and fungi may display the potentially different mechanisms to drive ecosystem functions.

Soil and water conservation measures reduce erosion but result in carbon and nitrogen accumulation of red soil in Southern China

Soil erosion is continually overlooked in the hilly red soil region of southern China, and there is a substantial lack of knowledge about the effects of soil and water conservation measures (SWCMs) on erosion prevention and soil carbon and nitrogen accumulation for the eroded sloping arable land in this region. Herein, based on a long-term experiment in the red soil hilly region in China, we investigated the effects of 17 years of SWCMs on soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon and nitrogen (MBC and MBN, respectively) as well as soil erodibility (K factor) at soil depths of 0–100 cm in the top, middle and bottom parts of the slope. The SWCMs included straw mulching (SM), downslope ridge cultivation (DC), downslope ridge cultivation + contour hedgerow planting (DCH), and contour ridge cultivation tillage (CC). A bare land treatment without any crops was used as a control (CK). We found that SWCMs increased SOC, TN, MBC, and MBN by 8–57%, 1–14%, 25–68%, and 17–35%, respectively, with greater increases in these variables in the CC and SM treatments and smaller increase in the DC treatment. Additionally, the effects of the SWCMs were greater at the top and middle of the slope than at the bottom of the slope, and the effects varied with soil depth. Moreover, the SWCMs decreased soil erodibility, with a lower K factor in the SWCMs treatments (0.018–0.049 t ha h ha−1 MJ−1 mm−1) than in the CK (0.042–0.068 t ha h ha−1 MJ−1 mm−1) and a greater decrease in the CC treatment. The effects of the SWCMs on soil erodibility mainly occurred through the regulation of SOC according to structural equation modeling. Overall, this study suggested that straw mulching and contour ridge cultivation tillage were the most effective strategies for restoring soil carbon and nitrogen and preventing soil erosion.

Exploring the Impacts of Data Source, Model Types and Spatial Scales on the Soil Organic Carbon Prediction: A Case Study in the Red Soil Hilly Region of Southern China

Rapid and accurate mapping of soil organic carbon (SOC) is of great significance to understanding the spatial patterns of soil fertility and conducting soil carbon cycle research. Previous studies have dedicated considerable efforts to the spatial prediction of SOC content, but few have systematically quantified the effects of environmental covariates selection, the spatial scales and the model types on SOC prediction accuracy. Here, we spatially predicted SOC content through digital soil mapping (DSM) based on 186 topsoil (0–20 cm) samples in a typical hilly red soil region of southern China. Specifically, we first determined an optimal covariate set from different combinations of multiple environmental variables, including multi-sensor remote sensing images (Sentinel-1 and Sentinel-2), climate variables and DEM derivatives. Furthermore, we evaluated the impacts of spatial resolution (10 m, 30 m, 90 m, 250 m and 1000 m) of covariates and the model types (three linear and three non-linear machine learning techniques) on the SOC prediction. The results of the performance analysis showed that a combination of Sentinel-1/2-derived variables, climate and topographic predictors generated the best predictive performance. Among all variables, remote sensing covariates, especially Sentinel-2-derived predictors, were identified as the most important explanatory variables controlling the variability of SOC content. Moreover, the prediction accuracy declined significantly with the increased spatial scales and achieved the highest using the XGBoost model at 10 m resolution. Notably, non-linear machine learners yielded superior predictive capability in contrast with linear models in predicting SOC. Overall, our findings revealed that the optimal combination of predictor variables, spatial resolution and modeling techniques could considerably improve the prediction accuracy of the SOC content. Particularly, freely accessible Sentinel series satellites showed great potential in high-resolution digital mapping of soil properties.

Heavy Metal Pollution and Soil Quality Assessment under Different Land Uses in the Red Soil Region, Southern China.

The influences of different land uses associated with human activities on soil quality and the redistribution of heavy metal in soil have been widely concerned. Surface soil samples were obtained to assess comprehensive soil quality in a typical red soil region of southern China, combining the heavy metal pollution evaluation with fertility evaluation. It can be learned from the results that the overall level of soil fertility was at medium and lower level, and soil heavy metal pollution risk in the study area in a few regions had reached warning line and slight pollution line, and there was a risk of potential pollution. TOPSIS evaluation results showed that the comprehensive soil quality was mainly good quality and moderate quality, accounting for 31.7% and 29.0% of the total land area, respectively. Positive matrix factorization (PMF) model results showed that transportation source contributes a lot in terms of Cd and Pb. As for Cr, natural source contributes 53.8%. In terms of Cu and Zn, agriculture source contributes 50.7% and 38.7%, respectively. In a word, the comprehensive soil quality assessment in red soil region of southern China provides an important basis for the scientific management and sustainable utilization of soil resources.

Quantification of physical soil crust thickness and its effects on runoff and sediment yield

AbstractPhysical soil crusts will form on most soils during and after rainfall and it has important effects on the runoff and sediment on slopes. However, objective and effective methods for quantifying the characteristics of physical soil crusts (such as the thickness) are not currently available. A new method was used for determining the thickness of physical soil crusts based on X‐ray computed tomography (CT) in order to quantify the thickness of the structural crust (SC) and depositional crust (DC) for two typical erodible soils comprising granite red soil (GRS) and Quaternary red clay (QRC) in the red soil region of southern China. The pores in the GRS and QRC were characterized as finely and densely spatially distributed, with an average porosity of 15.47% and a range of 1.66–28.83%. The soil porosity increased rapidly in the 0‐to‐3‐mm depth, but the porosity of the SC and DC soil samples generally decreased or was stable in the 3‐to‐30‐mm depth. The average thickness of the soil crust was 1.31 mm, and the average thicknesses of SC and DC were 1.16 and 1.46 mm, respectively. The thickness of SC of GRS decreased with the slope, whereas the thickness of DC of QRC generally increased with the slope. The thickness of SC increased with runoff yield and its contribution rate to the runoff and sediment yield cannot be neglected. The study provides a method for the objective quantification of physical soil crust and can deepen the research on slope erosion process and influencing factors.

Effects of tillage-induced soil surface roughness on the generation of surface–subsurface flow and soil loss in the red soil sloping farmland of southern China

The role of tillage-induced soil surface roughness (SSR) in altering surface–subsurface flow and soil loss needs to be investigated in the red soil region of southern China. In this study, two different roughness conditions (smooth surface and rough surface), produced by plowing with and without flattening, were employed to assess the effects of surface roughness on rainfall redistribution, surface and subsurface flow generation, and soil loss. In-situ rainfall simulations with three different rainfall intensities (30, 60, and 90 mm h−1) during 180 min of rainfall were tested for a steep farmland sloped at 15°. The results showed that the rough surface had a higher capability for improving subsurface flow, whereby 34% of the rainfall changed into surface flow, and 24% changed into subsurface flow; whereas the proportions of surface and subsurface flow on the smooth surface were 40% and 16%, respectively. The rough surface exhibited a faster initial generation of surface flow and subsurface flow, and the progress of erosion from sheet erosion to rill erosion was more rapid than on the smooth surface, leading to a higher sediment yield from the rough surface under stronger rainfall events. However, the rough surface demonstrated enhanced infiltration behavior and prevention of soil loss under low-intensity rainfall events. The difference in soil crusts on smooth and rough surfaces was the dominant factor affecting surface–subsurface flow generation and soil loss from the red soil sloping farmland. The roughness decreased on the rough surface and increased on the smooth surface during rainfall events. The interactions between surface and subsurface flow should be considered to evaluate soil loss; hence, this research provides a comprehensive understanding of the impact of tillage activities on soil erosion.

赤红壤植蔗坡地坡面径流及溶解态氮磷流失特征

为探究南方高强度、高频次降雨下赤红壤区坡耕地土壤侵蚀及氮磷养分流失的特征，基于野外径流小区原位观测试验，通过测定自然降雨下赤红壤植蔗坡地坡面径流和溶解态氮磷流失量，探讨自然降雨下甘蔗种植对赤红壤坡面径流及溶解态氮磷流失的影响。结果表明：（1）2019年和2020年，径流量分别为1111.3 m³/hm²和3269.4 m³/hm²，硝态氮（NO₃^--N）流失量分别为1.39 kg/hm²和15.60 kg/hm²，铵态氮（NH₄⁺-N）流失量分别为0.37 kg/hm²和1.02 kg/hm²，可溶性磷流失量分别为0.20 kg/hm²和0.27 kg/hm²。2019年和2020年植蔗坡地径流及溶解态氮磷流失量均集中在6月份，占流失总量的45%以上，硝态氮（NO₃^--N）是径流氮素流失的主要形式，占79%以上。此外，2019年和2020年5月至8月，侵蚀性降雨场次分别为18次和23次，侵蚀性降雨量分别为407.8 mm和668.0 mm。（2）不同侵蚀性降雨条件下，植蔗坡地溶解态氮磷流失量及其浓度波动较大，甘蔗生长前期（5-6月）溶解态氮磷流失量及其浓度呈上升趋势，而生长后期（7-8月）则呈波动下降趋势。2019年和2020年观测期侵蚀性降雨的年内分布存在明显差异，均集中在6月份，占35%以上。（3）坡面径流量与降雨量和最大30 min降雨强度呈极显著的正相关关系，同时坡面径流量与径流中硝态氮、铵态氮及可溶性磷流失量均呈极显著正相关关系。研究结果有助于明晰南方赤红壤区蔗区坡面土壤侵蚀及养分流失特征。;The characteristics of soil loss and nutrient loss in sloping land are quitely different among different areas of China, and crop patterns also have significant impacts on these indicators. The objectives of this study were as follows:1) to explore the characteristics of soil erosion and nutrient loss in sloping land with planting sugarcane of lateritic soil; and 2) to analyze the impacts of sugarcane growing stage and natural rainfall characteristics on soil erosion and nitrogen and phosphorus loss characteristics. This research based on the in-situ observation test of runoff plot and measured the loss of runoff, dissolved nitrogen, and phosphorus in sloping land with planting sugarcane. The amounts and concentrations of nitrate nitrogen (NO₃^--N), ammonium nitrogen (NH₄⁺-N), and dissolved phosphorus (DP) under individual natural rainfall during May to August in 2019 and 2020 were observed. The results showed that:(1) in 2019 and 2020, the runoffs, nitrate nitrogen (NO₃^--N), ammonium nitrogen (NH₄⁺-N), and dissolved phosphorus (DP) loss were 1111.3 m³/hm² and 3269.4 m³/hm², 1.39 kg/hm² and 15.60 kg/hm², 0.37 kg/hm² and 1.02 kg/hm², 0.20 kg/hm² and 0.27 kg/hm², respectively. The runoff and its dissolved nitrogen and phosphorus loss in sloping land with planting sugarcane under 2019 and 2020 were both concentrated in June, which accounted for more than 45%, and NO₃^--N was the main form of nitrogen loss in runoff, which accounted for more than 79% of total nitrogen loss. Besides, the times of individual erosive rainfall were 18 and 23, and the erosive rainfall amounts were 407.8 and 668.0 mm from May to August in 2019 and 2020, respectively. (2) The amounts of dissolved nitrogen and phosphorus loss and their concentrations in sloping land with planting sugarcane showed great fluctuation under different erosive rainfalls and stages of sugarcane growth. There were obvious differences in the annual distribution of erosive rainfall between observation period of 2019 and 2020, which were both concentrated in June, which accounted for more than 35% of total rainfall. In the early stage of sugarcane growth (from May to June), the losses of dissolved nitrogen and phosphorus and their concentrations showed an upward trend, while in the late stage of sugarcane growth (from July to August), they showed a fluctuating downward trend. (3) There was a significantly positive correlation between runoff and rainfall and maximum 30 min rainfall intensity, meanwhile, there was a significantly positive correlation between runoff and the loss of nitrate nitrogen (NO₃^--N), ammonium nitrogen (NH₄⁺-N), and dissolved phosphorus (DP). The results can provide a theoretical basis for clarifying the soil erosion characteristics of sloping land with planting sugarcane in the lateritic soil region of southern China.

Integrating satellite-based passive microwave and optically sensed observations for evaluating spatio-temporal dynamics of vegetation health in the red soil region of southern China

Integrating satellite-based passive microwave and optically sensed observations for evaluating spatio-temporal dynamics of vegetation health in the red soil region of southern China