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Net soil CO2 emissions are not independent of topography but tend to decline with increasing slope gradients. Such decline has been attributed to increased runoff and greater soil loss on steep slopes, leaving the soil less habitable for microorganisms. However, the specific variations of slope gradients and thus the associated soil properties relevant for CO2 emissions, especially from terraced slopes, are often disguised by the coarse resolution of digital terrain models (DTMs) based on commonly available open-source data. Such misrepresentation of the relationship between topography and soil CO2 emissions carries the risk of a wrong assessment of soil-atmosphere interaction. By applying a slope dependent soil CO2 emission model developed from erosion plots to nearby sloping and partially terraced cropland using two DTMs of different spatial resolutions, this study tested the significance of these resolution-induced errors on CO2 emission estimates. The results show that the coarser-resolution Shuttle Radar Topography Mission (SRTM) underestimated CO2-C emission by 27% compared to the higher-resolution DTM derived from Unmanned Aerial Vehicles (UAV) imagery. Such difference can be mostly attributed to a better representation of the proportion of flat slopes in the high-resolution DTM. Although the observations from erosion plots cannot be directly extrapolated to a larger scale, the 27% underestimation using the coarser-resolution SRTM DTM emphasizes that it is essential to represent microreliefs and their impact on runoff and erosion-induced soil heterogeneity at an appropriate scale. The widespread impact of topography on erosion and deposition on cropland, and the associated slope-dependent heterogeneity of soil properties, may lead to even greater differences than those observed in this study. The greatly improved estimation on CO2 emissions by the UAV-derived DTM also demonstrates that UAVs have a great potential to fill the gap between conventional field investigations and commonly applied coarse-resolution remote sensing when assessing the impact of soil erosion on global soil-atmosphere interaction.
Yaxian Hu; Vincent Schneider; Brigitte Kuhn; Shengli Guo; Nikolaus J. Kuhn. Capturing the Scale Dependency of Erosion-Induced Variation in CO2 Emissions on Terraced Slopes. Frontiers in Environmental Science 2021, 9, 1 .
AMA StyleYaxian Hu, Vincent Schneider, Brigitte Kuhn, Shengli Guo, Nikolaus J. Kuhn. Capturing the Scale Dependency of Erosion-Induced Variation in CO2 Emissions on Terraced Slopes. Frontiers in Environmental Science. 2021; 9 ():1.
Chicago/Turabian StyleYaxian Hu; Vincent Schneider; Brigitte Kuhn; Shengli Guo; Nikolaus J. Kuhn. 2021. "Capturing the Scale Dependency of Erosion-Induced Variation in CO2 Emissions on Terraced Slopes." Frontiers in Environmental Science 9, no. : 1.
Soil C-acquiring enzymes are good indicators for the biological mechanism of soil nutrients and organic matter cycles. However, they have been used less frequently to assess the ecological stability and soil C cycle in eroding landscapes due to a lack of knowledge of the responses of C-acquiring enzyme activities to soil erosion and deposition. In the present study, a 3-year field simulation experiment was conducted to examine the variations in the activities of C-acquiring enzymes (β-1,4-xylosidase (βX), β-1,4-glucosidase (βG) and β-D-cellobiohydrolase (CBH)) from erosion-deposition plots with different slope gradients (5°, 10° and 20°) on the Loess Plateau in China (2016–2018). The activities of βX, βG and CBH were higher in the depositional plots than in the erosional plots, and those differences were enlarged with increasing slope gradients. Compared to the 5°-erosional plot, the activities of βX, βG and CBH respectively declined by 3.2–4.5%, 14.3–37.5% and 12.7–29.1% in the 10°-and 20°-erosional plots. The βX, βG and CBH activities were 2.2–18.1%, 17.3–32.1% and 14.8–86.2% higher in the 10°- and 20°-depositional plots than in the 5°-depositional plot. Moreover, the total soil CO2 emissions from the whole erosion-deposition plots decreased as slopes steepened. The displaced runoff and sediment depleted soil moisture, SOC, clay and microbial biomass in the erosional plots but enhanced these resources in the depositional plots, which can account for the changes in C-acquiring enzyme activities. The spatial distribution of enzyme activities affected soil CO2 emissions in a positive linear function. The sensitive responses of the C-acquiring enzyme activities and the controlling effects of C-acquiring enzyme activities on soil CO2 emissions during erosion and deposition processes, should be properly considered in assessing the biological mechanism for nutrition cycling in regions predominated with fragmented eroding landscapes.
Lanlan Du; Rui Wang; Yaxian Hu; Xiaogang Li; Sheng Gao; Xihui Wu; Xin Gao; Lunguang Yao; Shengli Guo. Contrasting responses of soil C-acquiring enzyme activities to soil erosion and deposition. CATENA 2020, 198, 105047 .
AMA StyleLanlan Du, Rui Wang, Yaxian Hu, Xiaogang Li, Sheng Gao, Xihui Wu, Xin Gao, Lunguang Yao, Shengli Guo. Contrasting responses of soil C-acquiring enzyme activities to soil erosion and deposition. CATENA. 2020; 198 ():105047.
Chicago/Turabian StyleLanlan Du; Rui Wang; Yaxian Hu; Xiaogang Li; Sheng Gao; Xihui Wu; Xin Gao; Lunguang Yao; Shengli Guo. 2020. "Contrasting responses of soil C-acquiring enzyme activities to soil erosion and deposition." CATENA 198, no. : 105047.
Rill erosion is a small-scale but universally occurring phenomenon. Given its potential to concentrate into larger-scale erosion and its non-negligible contributions to soil loss, substantial research has been dedicated to understanding its processes. In this article, we conducted a holistic review of the major achievements in rill erosion research over the past few decades, mainly from the following perspectives: 1) Hydraulic parameters to describe rill development; 2) morphological indicators to represent rill morphology; 3) commonly used measuring methods for rill morphology and rill flow; and 4) advantages and limitations of rill erosion modelling. In each of the perspectives, we also identified the challenges faced by current rill erosion research. Concrete suggestions on the pressing needs to help advance rill erosion research in the future are further presented.
Xiaojing Ou; Yaxian Hu; Xianwen Li; Shengli Guo; BaoYuan Liu. Advancements and challenges in rill formation, morphology, measurement and modeling. CATENA 2020, 196, 104932 .
AMA StyleXiaojing Ou, Yaxian Hu, Xianwen Li, Shengli Guo, BaoYuan Liu. Advancements and challenges in rill formation, morphology, measurement and modeling. CATENA. 2020; 196 ():104932.
Chicago/Turabian StyleXiaojing Ou; Yaxian Hu; Xianwen Li; Shengli Guo; BaoYuan Liu. 2020. "Advancements and challenges in rill formation, morphology, measurement and modeling." CATENA 196, no. : 104932.
Soil redistribution is an important movement process of surface material that drastically affects the dynamic cycling of essential elements and soil productivity in the terrestrial ecosystem. Although a number of studies have focused on the soil organic carbon (SOC) pool under soil redistribution, few studies have comprehensively assessed the effects of soil redistribution on the ecosystem carbon pool. A five-year experiment of simulated topsoil redistribution (removal and addition, R-A) was conducted to explore the effects of soil redistribution on soil CO2 emissions, the SOC pool and the plant C pool in the semi-arid Loess Plateau of China. The soil properties, soil CO2 emissions, and crop parameters were measured after the topsoil removal (R20) treatment and topsoil addition (A20) treatment and in the undisturbed control (CK). Our results showed that 1) compared with the undisturbed control, the mean soil CO2 emissions of the R-A treatment decreased by 8% while the mean SOC pool increased by 3.0%; 2) the plant C pool was significantly reduced by 53.8% in 2015 and 5.8% in 2019 compared with the undisturbed control; 3) the ecosystem C pool (the sum of the SOC pool and plant C pool) of the R-A treatment was reduced by 10.3%, 3.7% and 1.1% compared with the ecosystem C pool of the undisturbed CK for 2015, 2016 and 2017, respectively, but increased by 0.6% and 1.9% from 2018 to 2019. During the first three experimental years, the decrease in the ecosystem C pool of the R-A treatment was caused by the reduced plant C pool in R20 exceeding the elevated plant C pool in A20. Over time, the soil bulk density (BD) decreased in R20 and the SOC, microbial biomass carbon (SMBC) and total nitrogen (TN) increased, which jointly improved the plant C pool in R20 and the ecosystem C pool by 2019. The gradual recovering pattern of the ecosystem C pool in the later years highlights the key role of plants in restoring soil properties and stabilizing ecosystem C cycling. Overall, our findings highlight that any attempt to assess the net impacts of soil redistribution, whether as a sink or source for atmospheric CO2, should comprehensively consider the changes in the SOC pool and plant C pool.
Weijia Li; Xin Gao; Rui Wang; Lanlan Du; Fangbin Hou; Yao He; Yaxian Hu; Lunguang Yao; Shengli Guo. Soil redistribution reduces integrated C sequestration in soil-plant ecosystems: Evidence from a five-year topsoil removal and addition experiment. Geoderma 2020, 377, 114593 .
AMA StyleWeijia Li, Xin Gao, Rui Wang, Lanlan Du, Fangbin Hou, Yao He, Yaxian Hu, Lunguang Yao, Shengli Guo. Soil redistribution reduces integrated C sequestration in soil-plant ecosystems: Evidence from a five-year topsoil removal and addition experiment. Geoderma. 2020; 377 ():114593.
Chicago/Turabian StyleWeijia Li; Xin Gao; Rui Wang; Lanlan Du; Fangbin Hou; Yao He; Yaxian Hu; Lunguang Yao; Shengli Guo. 2020. "Soil redistribution reduces integrated C sequestration in soil-plant ecosystems: Evidence from a five-year topsoil removal and addition experiment." Geoderma 377, no. : 114593.
Erosion-induced land degradation in the northeastern China, the Chinese breadbasket, has become one of the biggest risks to national food security. Apart from depleting topsoil, incising gullies, and waterlogging depositional sites, slope-scale erosion also spatially redistributes soil nutrients and introduces localized soil degradation. This requires to systematically understanding topography-specific spatial distribution patterns of eroded soil compositions and the relative abundance of each nutrient at different topographic settings. In this study, topsoil at predetermined space intervals were collected from two adjacent but differently curved segments (convex vs. concave) on a sloped cropland in northeastern China. The spatial distributions of topsoil soil organic carbon (SOC), total nitrogen (TN), total phosphorous (TP), and the variations of their atomic ratios were compared. Our results show that: (1) Compared with the nearby undisturbed tree rows, the SOC and TN was halved on the investigated slope, demonstrating great degradation since the land use conversion. (2) The spatial distribution of topsoil nutrients were evidently topography specific, with the SOC being comparable at slope summit, but declining from 27.57 to 4.72 g kg−1 (depletion ratio of 0.17) at the convex segment meanwhile accumulating up to 34.71 g kg−1 (enrichment ratio of 1.26) at the concave segment. Similar but more deviated spatial patterns were also observed on the TN and TP. (3) The atomic ratios of C:N:P also differed as the slope curvatures diverted, by being more variable from 51:3:1 to 105:6:1 along the convex segment but rather stable between 74:5:1 and 89:5:1 along the concave segment. (4) The lower content of SOC and the heavier δ13C along the convex segment suggest more advanced mineralization of C and thus greater susceptibility of C-limitation. Meanwhile, the slightly lower C:N ratios and the greater δ15N along the concave segment indicate greater stability of C, more advanced mineralization of N and thus likely a N-limited process. Overall, our findings demonstrate the controlling influences of minor geomorphic features to on-site soil dislocation and localized degradation at slope scale. Apart from general soil conservation measures, topography-specific practices must also be integrated to local land use policy to effectively target localized land degradation.
Yaxian Hu; Xianwen Li; Shengli Guo; Xin Gao; Xiaojing Ou; BaoYuan Liu. On-site soil dislocation and localized CNP degradation: the real erosion risk faced by sloped cropland in northeastern China. Agriculture, Ecosystems & Environment 2020, 302, 107088 .
AMA StyleYaxian Hu, Xianwen Li, Shengli Guo, Xin Gao, Xiaojing Ou, BaoYuan Liu. On-site soil dislocation and localized CNP degradation: the real erosion risk faced by sloped cropland in northeastern China. Agriculture, Ecosystems & Environment. 2020; 302 ():107088.
Chicago/Turabian StyleYaxian Hu; Xianwen Li; Shengli Guo; Xin Gao; Xiaojing Ou; BaoYuan Liu. 2020. "On-site soil dislocation and localized CNP degradation: the real erosion risk faced by sloped cropland in northeastern China." Agriculture, Ecosystems & Environment 302, no. : 107088.
Slope induced runoff and erosion processes redistribute water, soil and nutrients, thus potentially influence soil CO2 emissions and perturb the carbon balances on sloping land. However, most of the previous studies on soil CO2 emissions were conducted on flat land. In regions with complex terrains and fragmented fields with terraces, such as the Chinese Loess Plateau, it is particularly important to understand slope dependent soil CO2 emissions. This requires investigations to unravel the relationship between soil erosional responses and CO2 emissions on different slopes. In this study, erosion plots, set at angles of 0.5°, 5°, 10°, and 20°, were refilled with loess soils from local farmland on the Chinese Loess Plateau. Changes of soil properties and CO2 emission rates were measured at three positions (upper, middle, lower) on each plot from October 2014 to September 2015. Our results show that greater runoff from the steeper slopes evidently depleted soil water and nutrients, directly responsible for the less soil CO2 emissions. Furthermore, the average yearly soil CO2 emissions decreased exponentially with slope gradients, from approximately 832.7 g m−2 yr−1 on the 0.5° slope, to 380.9 g m−2 yr−1 when the slope gradient was 20°. This not only proves the dependency of soil CO2 emission to slope gradients, but also provides the fundamental dataset to develop an empirical model between slope gradients and soil CO2 emissions. A coefficient βhas been parameterized for the first time in this study to represent the sensitivity of soil CO2 emissions to slope gradients. The model of slope-dependent CO2 emissions identified in this study tentatively demonstrate non-negligible implications for global carbon fluxes from sloped and terraced field to the atmosphere. Further investigations on slope-scale carbon balances should test and integrate topography specific CO2 emissions.
Yaxian Hu; Zhiqi Wang; Rui Wang; Lunguang Yao; Shengli Guo. Slope sensitivity: A coefficient to represent the dependency of soil CO2 emissions to slope gradients. CATENA 2020, 193, 104659 .
AMA StyleYaxian Hu, Zhiqi Wang, Rui Wang, Lunguang Yao, Shengli Guo. Slope sensitivity: A coefficient to represent the dependency of soil CO2 emissions to slope gradients. CATENA. 2020; 193 ():104659.
Chicago/Turabian StyleYaxian Hu; Zhiqi Wang; Rui Wang; Lunguang Yao; Shengli Guo. 2020. "Slope sensitivity: A coefficient to represent the dependency of soil CO2 emissions to slope gradients." CATENA 193, no. : 104659.
Erosion processes spatially redistribute soil particles and the associated carbon across landscapes. Their spatial redistribution pattern is governed by the transport distances of individual displaced soil particles, which is not only dependent on their settling velocity, but also affected by slope topography. However, the potential impacts of fine-scale variation of slope topography on the erosion-induced lateral and carbon fluxes are often over-generalized by coarse digital elevation models. In this study, two topo-sequences, convex and concave, over a long gentle slope in the northeast China were investigated. Surface soils were sampled at predetermined space intervals from upslope to downslope along the two toposequences, and then fractionated by the settling velocity of individual fractions into four classes: > 250, 63 – 250, 20 – 63 and < 20 μm. The soil organic carbon (SOC) and δ13 C of the unfractionated soils and all the settling classes were measured, and their CO2 emission rates were also determined at six temperature gradients: 5°C, 10°C, 15°C, 20°C, 25°C and 30°C. Our results show that: 1) The soil fractions along the upper lying convex segment showed a coarsening effect toward the knee point and then a fining trend at the slope toe, whilst the soil compositions along the lower lying concave segment stayed fairly comparable as the slope descended. 2) The net loss of surface soil along the eroding convex segment resulted in depleted SOC and more positive δ13 C signatures than that along the depositional concave segment. 3) The CO2 emission rates of almost all the settling fractions were enhanced compared with that of the unfractionated soil, and the settling class-specific CO2 emission rates and their temperature sensitivity (Q10 ) also differed along the two topo-sequences. This demonstrates that fine scale topographic variations had a strong control over the lateral and vertical carbon fluxes, which has been often disguised by coarse grid size in digital elevation models or average sediment delivery ratios. Topography-dependency must be properly accounted for when calculating slope-scale carbon balances.
Yao He; Yaxian Hu; Xin Gao; Rui Wang; Shengli Guo; Xianwen Li. Minor topography governing erosional distribution of SOC and temperature sensitivity of CO2 emissions: comparisons between concave and convex toposequence. Journal of Soils and Sediments 2020, 20, 1906 -1919.
AMA StyleYao He, Yaxian Hu, Xin Gao, Rui Wang, Shengli Guo, Xianwen Li. Minor topography governing erosional distribution of SOC and temperature sensitivity of CO2 emissions: comparisons between concave and convex toposequence. Journal of Soils and Sediments. 2020; 20 (4):1906-1919.
Chicago/Turabian StyleYao He; Yaxian Hu; Xin Gao; Rui Wang; Shengli Guo; Xianwen Li. 2020. "Minor topography governing erosional distribution of SOC and temperature sensitivity of CO2 emissions: comparisons between concave and convex toposequence." Journal of Soils and Sediments 20, no. 4: 1906-1919.
Crust formation affects soil erosion by raindrop impacted flow through changing particle size and cohesion between particles on the soil surface, as well as surface microtopography. Therefore, changes in soil microtopography can, in theory, be employed as a proxy to reflect the complex and dynamic interactions between crust formation and erosion caused by raindrop-impacted flow. However, it is unclear whether minor variations of soil microtopography can actually be detected with tools mapping the crust surface, often leaving the interpretation of interrill runoff and erosion dynamics qualitative or even speculative. In this study, we used a laser scanner to measure the changes of the microtopography of two soils placed under simulated rainfall in experimental flumes and crusting at different rates. The two soils were of the same texture, but under different land management, and thus organic matter content and aggregate stability. To limit the amount of scanning and data analysis in this exploratory study, two transects and four subplots on each experimental flume were scanned with a laser in one-millimeter interval before and after rainfall simulations. While both soils experienced a flattening, they displayed different temporal patterns of crust development and associated erosional responses. The laser scanning data also allowed to distinguish the different rates of developments of surface features for replicates with extreme erosional responses. The use of the laser data improved the understanding of crusting effects on soil erosional responses, illustrating that even limited laser scanning provides essential information for quantitatively exploring interrill erosion processes.
Yaxian Hu; Wolfgang Fister; Yao He; Nikolaus J. Kuhn. Assessment of crusting effects on interrill erosion by laser scanning. PeerJ 2020, 8, e8487 .
AMA StyleYaxian Hu, Wolfgang Fister, Yao He, Nikolaus J. Kuhn. Assessment of crusting effects on interrill erosion by laser scanning. PeerJ. 2020; 8 ():e8487.
Chicago/Turabian StyleYaxian Hu; Wolfgang Fister; Yao He; Nikolaus J. Kuhn. 2020. "Assessment of crusting effects on interrill erosion by laser scanning." PeerJ 8, no. : e8487.
The availability and precision of topographic data determines the reliability of the calculated slope length and slope gradient (LS) factor, which limits the use of the universal soil loss equation (USLE) and its adapted versions in region-scale soil erosion risk assessment. One of the common complications is the effectiveness of topographic data with different resolutions or the compatibility of topographic data originated from different sources. In this study, the topographic data from five common sources, 5-m digital elevation model (DEM) based on 1:10,000 topographic maps (5-m topo DEM of 1:10,000), 25-m DEM derived from 1:50,000 topographic maps (25-m topo DEM of 1:50,000), 30-m ASTER GDEM, 30-m and 90-m SRTM DEMs, were individually applied to calculate the LS factors of five catchments with distinct terrain characteristics. Our results show that the computation accuracy of the LS factors in the five study catchments decreased with greater grid sizes derived from the five topographic data sources. Compared to the most precision 5-m topo DEM of 1:10,000, the relative computation error of the mean LS factors was less than 10% when calculated from the 25-m topo DEM of 1:50,000, and that was less than 25% from the 30-m ASTER and 30-m SRTM DEMs. For scenarios in gently rolling areas, the 90-m SRTM DEM with the relative computation error less than 15% could be recommended when there are noises on the open sources DEMs surface. Therefore, depending on the requirements of data accuracy, different data sources can be applied individually or in combined to obtain the optimal predictions of the LS factors. However, such recommendations on data sources proposed in this study appeared to be more applicable for regions with complex terrains. Further studies over a range of terrain features and spatial scales are required to validate the effectiveness of different topographic data sources in calculating the LS factor.
Shaojuan Lu; BaoYuan Liu; Yaxian Hu; Suhua Fu; Qi Cao; Yandong Shi; Tingting Huang. Soil erosion topographic factor (LS): Accuracy calculated from different data sources. CATENA 2019, 187, 104334 .
AMA StyleShaojuan Lu, BaoYuan Liu, Yaxian Hu, Suhua Fu, Qi Cao, Yandong Shi, Tingting Huang. Soil erosion topographic factor (LS): Accuracy calculated from different data sources. CATENA. 2019; 187 ():104334.
Chicago/Turabian StyleShaojuan Lu; BaoYuan Liu; Yaxian Hu; Suhua Fu; Qi Cao; Yandong Shi; Tingting Huang. 2019. "Soil erosion topographic factor (LS): Accuracy calculated from different data sources." CATENA 187, no. : 104334.
Soil redistribution by terrace construction, as one of the most evident anthropogenic imprints on hill-slopes, may influence soil organic carbon (SOC) dynamics through re-shaping topography and altering water and oxygen availability. However, the fundamental role and mechanisms by which terrace construction affects in situ soil CO2 emissions and its temperature sensitivity (Q10) remain poorly understood. In this study, topsoil removal-addition approach was used to simulate topsoil redistribution during terrace construction. Compared with the nearby undisturbed soil, the average annual soil CO2 emission over two years was reduced by 24% in the topsoil removed field but enhanced by 33% in the topsoil added field. The decreased soil CO2 emission at the topsoil removed field was largely associated with the depletion of SOC stocks and microbial biomass carbon, while the increments of SOC available for decomposition at the topsoil added field contributed to its increased soil CO2 emissions. However, the average Q10 value in the topsoil removed field was 23% greater at seasonal scale and 28% greater at diurnal scale than that in the undisturbed soil. The increased Q10 in the topsoil removed field is mainly due to higher aromaticity of water-extractable organic carbon (WEOC) and the domination of Actinobacteria in keystone taxa. Overall, our results show that changes in both aromaticity of WEOC and soil microbial community composition induced by soil redistribution during terrace construction may alter the response of soil CO2 emission to elevated temperature. Our study indicates that the impact of man-made soil redistribution should not be neglected when studying regional carbon cycling.
Xin Gao; Weijia Li; Ali Salman; Rui Wang; Lanlan Du; Lunguang Yao; Yaxian Hu; Shengli Guo. Impact of topsoil removal on soil CO2 emission and temperature sensitivity in Chinese Loess Plateau. Science of The Total Environment 2019, 708, 135102 .
AMA StyleXin Gao, Weijia Li, Ali Salman, Rui Wang, Lanlan Du, Lunguang Yao, Yaxian Hu, Shengli Guo. Impact of topsoil removal on soil CO2 emission and temperature sensitivity in Chinese Loess Plateau. Science of The Total Environment. 2019; 708 ():135102.
Chicago/Turabian StyleXin Gao; Weijia Li; Ali Salman; Rui Wang; Lanlan Du; Lunguang Yao; Yaxian Hu; Shengli Guo. 2019. "Impact of topsoil removal on soil CO2 emission and temperature sensitivity in Chinese Loess Plateau." Science of The Total Environment 708, no. : 135102.
Two-dimensional (2-D) numerical models have been widely used to predict soil water-salt transport under mulched drip irrigation. However, conventional 2-D models often neglect the spatial variation of soil water-salt transport along drip lines and over-simplifies it by averaging values. This calls for a more robust model to better reflect the actual spatial and temporal variation of soil water-salt distribution in the field, especially in arid regions using brackish water with additional salt. In this study, mulched drip irrigation with brackish water was applied to a cotton field with loam soil in an arid region of southern Xinjiang, northwest China. The changes of soil water potential and total dissolved solid (TDS) of soil water over two irrigation events were intensively measured on hourly base to establish and calibrate a 3-D model, and another five irrigation cycles were monitored on daily base to validate the 3-D model. The mean absolute relative errors between measured and calculated soil water potential and TDS of soil water were 13.7% and 10.7% during hourly-based model calibration, even though there might be bias inevitably introduced by pre-determined sampling intervals and volumes. The calculated values during model validation were reasonably in line with the temporal patterns of soil moisture and TDS before and after irrigation at different irrigation cycles. This 3-D model was then applied to predict the spatial and temporal variations of soil water-salt transport during and after irrigation. Our results show that (1) the 3-D model with additional consideration on point-source discharge from individual drippers effectively reflected the wet front interferences along the drip lines. (2) A semi-elliptic cylindrical wet bulb together with relatively low salinity was formed along the drip lines, which matched well with the cotton layout (one mulch, two drip lines and four rows). However, the uneven overlapping of wet front interferences among individual drippers required to optimize the design of dripper intervals and irrigation regime to provide desirable soil water-salt conditions for cotton growth in this loam soil. (3) During the 96 h after irrigation, the TDS of soil water was always greatest in the dense root zone, increasing from approximately 3.8 g L−1 to 7.0 g L−1 as a result of root water uptake. Such localized re-salinization patterns demand repeated leaching in continued irrigation cycles to ensure cotton growth. Our study suggests that a smaller interspace between drippers with short but more frequent irrigation cycles would be much more helpful to timely and spatial-precisely meet plant water demanding.
Xianwen Li; Menggui Jin; Nianqing Zhou; Simin Jiang; Yaxian Hu. Inter-dripper variation of soil water and salt in a mulched drip irrigated cotton field: Advantages of 3-D modelling. Soil and Tillage Research 2018, 184, 186 -194.
AMA StyleXianwen Li, Menggui Jin, Nianqing Zhou, Simin Jiang, Yaxian Hu. Inter-dripper variation of soil water and salt in a mulched drip irrigated cotton field: Advantages of 3-D modelling. Soil and Tillage Research. 2018; 184 ():186-194.
Chicago/Turabian StyleXianwen Li; Menggui Jin; Nianqing Zhou; Simin Jiang; Yaxian Hu. 2018. "Inter-dripper variation of soil water and salt in a mulched drip irrigated cotton field: Advantages of 3-D modelling." Soil and Tillage Research 184, no. : 186-194.
Soil erosion influences both lateral soil organic carbon (SOC) re-distribution and vertical soil CO2 emissions. While potential SOC mineralization during transport and the burial effects of SOC at depositional sites have been addressed in previous reports, erosion induced on-site CO2 emissions are still under-studied. In this study, two soils (Loess soil and Black soil) with similar texture but contrasting aggregate structure and SOC content were subject to a set of 60-min long simulated rainfall events. There were two different rainfall intensities (30 and 90 mm h−1) at three slope gradients (5°, 15° and 25°). Runoff and sediment from erosion plot were collected at 10-min intervals over 60 min. Soil CO2 emissions from eroding slopes, SOC and particle size distribution of the eroding soil were measured after the erosion events. The results show that the runoff rates from the two soils were comparable, but the sediment rates from the Loess soil roughly three times that from the Black soil. In general, the SOC erosion from the Loess soil was 1.8 times that from the Black soil, even though the SOC concentration in the original Black soil was 56% higher than the Loess soil. The cumulative soil CO2 emissions from the eroding slopes of the Loess soil ranged from 15.4 to 19.7 g C m−2, which was doubled on the Black soil (from 28.1 to 59.6 g C m−2). When the rainfall intensity raised from 30 mm h−1 to 90 mm h−1, the cumulative soil CO2 emissions from the Black soil decreased by 38.2%, but only declined by 10.0% on the Loess soil. When the slope gradient increased from 5° to 25°, the cumulative soil CO2 emissions decreased by 23.8% on the Black soil but by 12.6% on the Loess soil. Therefore, our observations suggest that the soil CO2 emissions on the Black soil was much more sensitive to the variations of rainfall intensity and slope gradients than the Loess soil. Greater SOC erosion should not be directly translated to less on-site soil CO2 emissions. The selective depletion/enrichment of SOC and the lability of individual components must be fully understood when accounting for slope-scale carbon balances.
Xin Gao; Yaxian Hu; QiQi Sun; Lanlan Du; Pengfei Duan; Lunguang Yao; Shengli Guo. Erosion-induced carbon losses and CO2 emissions from Loess and Black soil in China. CATENA 2018, 171, 533 -540.
AMA StyleXin Gao, Yaxian Hu, QiQi Sun, Lanlan Du, Pengfei Duan, Lunguang Yao, Shengli Guo. Erosion-induced carbon losses and CO2 emissions from Loess and Black soil in China. CATENA. 2018; 171 ():533-540.
Chicago/Turabian StyleXin Gao; Yaxian Hu; QiQi Sun; Lanlan Du; Pengfei Duan; Lunguang Yao; Shengli Guo. 2018. "Erosion-induced carbon losses and CO2 emissions from Loess and Black soil in China." CATENA 171, no. : 533-540.
Biomass as a renewable energy source has become increasingly prevalent in Europe to comply with greenhouse gas emission targets. As one of the most efficient perennial bioenergy crops, there is great potential in the Upper Rhine Region to explore biomass utilization of Miscanthus to confront climate change and land use demand in the future. Yet, the impacts of Miscanthus cultivation on soil quality have not been adequately explored. This study investigated the soil profiles of five- and 20-year-old Miscanthus fields (1 m depth) as well as grassland for reference in eastern France and Switzerland. The soil organic carbon (SOC) concentrations and δ13C compositions of four soil layers (0–10 cm, 10–40 cm, 40–70 cm and 70–100 cm) were determined. The CO2 emission rates of the topsoil were monitored for 42 days. Our results showed that Miscanthus, in general, could increase the SOC stocks compared to grassland, but the benefits of SOC sequestration were constrained to the surface soil. Isotopically, the Miscanthus-derived SOC ranged from 69% in the top 10 cm of soil down to only 7% in the 70 cm to 100 cm layer. This result raises the risk of overestimating the total net benefits of Miscanthus cultivation, when simply using the greater SOC stocks near the surface soil to represent the SOC-depleted deep soil layers. The Miscanthus fields had greater CO2 emissions, implying that the Miscanthus fields generated greater ecosystem respiration, rather than larger net ecosystem exchanges. Compared to the grassland soils, the surface soils of the Miscanthus fields tended to have a risk of acidification while having higher concentrations of phosphorus and potassium, calling for the inclusion of soil characteristics and SOC stability when evaluating the impacts of long-term Miscanthus cultivation on both current and future land use changes.
Yaxian Hu; Gerhard Schäfer; Joëlle Duplay; Nikolaus J. Kuhn. Bioenergy crop induced changes in soil properties: A case study on Miscanthus fields in the Upper Rhine Region. PLoS ONE 2018, 13, e0200901 .
AMA StyleYaxian Hu, Gerhard Schäfer, Joëlle Duplay, Nikolaus J. Kuhn. Bioenergy crop induced changes in soil properties: A case study on Miscanthus fields in the Upper Rhine Region. PLoS ONE. 2018; 13 (7):e0200901.
Chicago/Turabian StyleYaxian Hu; Gerhard Schäfer; Joëlle Duplay; Nikolaus J. Kuhn. 2018. "Bioenergy crop induced changes in soil properties: A case study on Miscanthus fields in the Upper Rhine Region." PLoS ONE 13, no. 7: e0200901.
The validity of soil erosion data is often questioned because of the variation between replicates. This paper aims to evaluate the relevance of interreplicate variability to soil and soil organic carbon (SOC) erosion over prolonged rainfall. Two silty loams were subjected to simulated rainfall of 30 mm h−1 for 360 min. The entire rainfall event was repeated ten times to enable statistical analysis of the variability of the runoff and soil erosion rates. The results show that, as selective removal of depositional particles and crust formation progressively stabilized the soil surface, the interreplicate variability of runoff and soil erosion rates declined considerably over rainfall time. Yet, even after the maximum runoff and erosion rates were reached, the interreplicate variability still remained between 15 and 39 %, indicating the existence of significant inherent variability in soil erosion experiments. Great caution must be paid when applying soil and SOC erosion data after averaging from a small number of replicates. While not readily applicable to other soil types or rainfall conditions, the great interreplicate variability observed in this study suggests that a large number of replicates is highly recommended to ensure the validity of average values, especially when extrapolating them to assess soil and SOC erosion risk in the field.
Yaxian Hu; Wolfgang Fister; Nikolaus J. Kuhn. Inherent interreplicate variability during small-scale rainfall simulations. Journal of Soils and Sediments 2016, 16, 1809 -1814.
AMA StyleYaxian Hu, Wolfgang Fister, Nikolaus J. Kuhn. Inherent interreplicate variability during small-scale rainfall simulations. Journal of Soils and Sediments. 2016; 16 (6):1809-1814.
Chicago/Turabian StyleYaxian Hu; Wolfgang Fister; Nikolaus J. Kuhn. 2016. "Inherent interreplicate variability during small-scale rainfall simulations." Journal of Soils and Sediments 16, no. 6: 1809-1814.
During slope-scale erosion events, re-distribution of eroded soil and the associated soil organic carbon (SOC) is not always uniform, but very often affected by preferential transport and deposition. Under given flow conditions, the site of SOC deposition depends on the transport distances of sediment particles containing the SOC. Very often, soil and SOC erosion risk are assessed by applying mineral particle specific SOC distributions to erosion models. However, soil is not always eroded as individual mineral particles, but mostly in a form of aggregates. Aggregates are likely to increase settling velocities of individual mineral particles, which may considerably reduce the transport distance of sediment fractions and the associated SOC, skewing SOC redistribution and its subsequent fate. Yet, little is known about the potential effects of aggregation on the movement and fate of eroded SOC.\ud \ud To assess the effect of preferential deposition, a simulated rainfall was applied to two soils in this study, with the Movelier silty clay having greater SOC content and aggregate stability than the Möhlin silty loam. The eroded sediments of the two soils were fractionated by a settling tube apparatus according to their potential transport distances. The CO2 emissions of the fractionated and incubated sediments were then measured for 50 days enabling the assessment of the bioactivity of eroded SOC for weeks after deposition. Our results show that: 1) the re-deposition of eroded SOC into terrestrial systems increased by 64% if considering the actual aggregate specific rather than the mineral particle specific SOC distribution. 2) The CO2 emission rates differed across settling fractions, with the most pronounced rates in the finest fractions from the Möhlin silty loam sediment and in the medium-size fractions from the Movelier silty clay sediment. 3) Over 50-day incubation, the CO2 emissions from the Möhlin silty loam sediment was 114% greater than that from the non-eroded Möhlin soil, whereas CO2 emissions were roughly equivalent for the Movelier sediment and non-eroded Movelier silty clay. These data demonstrate that erosion and preferential deposition of SOC-enriched aggregates can enhance terrestrial SOC deposition. This can further result in greater CO2 efflux than commonly applied mineral particle size specific SOC distribution would suggest. The different performances of deposition and CO2 emissions between the two soils also suggest that these effects can vary with soil type. Our observations certainly illustrate that sediment aggregation requires further investigation to assess the redistribution and subsequent fate of eroded SOC appropriately
Yaxian Hu; Nikolaus Kuhn. Erosion-induced exposure of SOC to mineralization in aggregated sediment. CATENA 2016, 137, 517 -525.
AMA StyleYaxian Hu, Nikolaus Kuhn. Erosion-induced exposure of SOC to mineralization in aggregated sediment. CATENA. 2016; 137 ():517-525.
Chicago/Turabian StyleYaxian Hu; Nikolaus Kuhn. 2016. "Erosion-induced exposure of SOC to mineralization in aggregated sediment." CATENA 137, no. : 517-525.
Climate change is expected to affect both the amount of global crop production, and annual variability in food supply. Agriculture is a major source of greenhouse gas emissions, but also considered to mitigate climate change. Conservation tillage, as a climate-smart agricultural practice, is repeatedly reported to mitigate net greenhouse gas emissions by increasing soil organic carbon (SOC). However, with reduced tillage, less litter is moved from the surface deeper into the soil profile, so SOC increase is very likely constrained to topsoil layers. Further adaptation benefits, such as increasing crop yield and resilience to famine, have recently been questioned after averaging yields from field studies. However, such global averaging masks the geographic extent individual studies apply to. This paper attempts a holistic regional analysis on the benefits of conservation tillage, in particular its fundamental principle no-tillage (NT), on the Chinese Loess Plateau. Based on a review of almost 20 years of conservation tillage plot experiments, the potential of NT to increase SOC stocks and to adapt to lower but more variable rainfall in the future has been assessed. The results show that the difference of total SOC stocks between NT and CT decreased with soil depth, confirming that the SOC benefits of NT are concentrated to the immediate topsoil still subject to direct seeding. The topsoil achieved maximum SOC stocks after about 10 years of NT. Crop yields from NT increased by up to 20% for years with average and below average precipitation, demonstrating the advantages of NT in stabilizing crop yields in dry years. However, the results in previous reports are not weighted by the actual spatial extent of drylands and humid regions after counting individual plot studies. As a consequence of such global and unweighted averaging, the benefits from NT to increase SOC stocks are likely to misrepresent the actual impact. Therefore, given the size of the Loess Plateau and its relevance for food security in China, our analysis illustrates the need to assess the benefits of a tillage and residue management system for each combination of eco-region and farming practice, weighted by their area and the affected population, rather than just using a global average for policy development on sustainable productivity.
Nikolaus Kuhn; Yaxian Hu; Lena Bloemertz; Jin He; Hongwen Li; Philip Greenwood. Conservation tillage and sustainable intensification of agriculture: regional vs. global benefit analysis. Agriculture, Ecosystems & Environment 2016, 216, 155 -165.
AMA StyleNikolaus Kuhn, Yaxian Hu, Lena Bloemertz, Jin He, Hongwen Li, Philip Greenwood. Conservation tillage and sustainable intensification of agriculture: regional vs. global benefit analysis. Agriculture, Ecosystems & Environment. 2016; 216 ():155-165.
Chicago/Turabian StyleNikolaus Kuhn; Yaxian Hu; Lena Bloemertz; Jin He; Hongwen Li; Philip Greenwood. 2016. "Conservation tillage and sustainable intensification of agriculture: regional vs. global benefit analysis." Agriculture, Ecosystems & Environment 216, no. : 155-165.
The use of sediment settling velocity based on mineral grain size distribution in erosion models ignores the effects of aggregation on settling velocity. The alternative approach, wet-sieved aggregate size distribution, on the other hand, cannot represent all destructive processes that eroded soils may experience under impacting raindrops. Therefore, without considering raindrop impact, both methods may lead to biased predictions of the redistribution of sediment and associated substances across landscapes. Rainfall simulation is an effective way to simulate natural raindrop impact under controlled laboratory conditions. However, very few methods have been developed to integrate rainfall simulation with the settling velocity of eroded sediment. This study aims to develop a new proxy, based on rainfall simulation, in order to identify the actual settling velocity distribution of aggregated sediment. A combined Raindrop Aggregate Destruction Test-Settling Tube (RADT-ST) approach was developed to (1) simulate aggregate destruction under a series of simulated rainfalls; and (2) measure the actual settling velocity distribution of destroyed aggregates. Mean Weight Settling Velocity (MWSV) of aggregates was used to investigate settling behaviors of different soils as rainfall kinetic energy increased. The results show the settling velocity of silt-rich raindrop impacted aggregates is likely to be underestimated by at least six times if based on mineral grain size distribution. The RADT-ST designed in this study effectively captures the effects of aggregation on settling behavior. The settling velocity distribution should be regarded as an evolving, rather than steady state parameter during erosion events. The combined RADT-ST approach is able to generate the quasi-natural sediment under controlled simulated rainfall conditions and is adequately sensitive to measure actual settling velocities of differently aggregated soils. This combined approach provides an effective tool to improve the parameterization of settling velocity input for erosion models.
Liangang Xiao; Yaxian Hu; Philip Greenwood; Nikolaus J. Kuhn. A Combined Raindrop Aggregate Destruction Test-Settling Tube (RADT-ST) Approach to Identify the Settling Velocity of Sediment. Hydrology 2015, 2, 176 -192.
AMA StyleLiangang Xiao, Yaxian Hu, Philip Greenwood, Nikolaus J. Kuhn. A Combined Raindrop Aggregate Destruction Test-Settling Tube (RADT-ST) Approach to Identify the Settling Velocity of Sediment. Hydrology. 2015; 2 (4):176-192.
Chicago/Turabian StyleLiangang Xiao; Yaxian Hu; Philip Greenwood; Nikolaus J. Kuhn. 2015. "A Combined Raindrop Aggregate Destruction Test-Settling Tube (RADT-ST) Approach to Identify the Settling Velocity of Sediment." Hydrology 2, no. 4: 176-192.
The effect of soil erosion on global carbon cycling, especially as a source or sink for greenhouse gases, has been the subject of intense debate. The controversy arises mostly from the lack of information on the fate of eroded soil organic carbon (SOC) whilst in-transit from the site of erosion to the site of longer-term deposition. Solving this controversy requires an improved understanding of the transport distance of eroded SOC, which is principally related to the settling velocity of sediment fractions that carry the eroded SOC. Although settling velocity has already been included in some erosion models, it is often based on mineral particle size distribution. For aggregated soils, settling velocities are affected by their actual aggregate size rather than by mineral particle size distribution. Aggregate stability is, in turn, strongly influenced by SOC. In order to identify the effect of aggregation of source soil on the transport distance of eroded SOC, and its susceptibility to mineralization after transport and temporary deposition, a rainfall simulation was carried out on a silty loam. Both the eroded sediments and undisturbed soils were fractionated into six different size classes using a settling tube apparatus according to their settling velocities: > 250, 125 to 250, 63 to 125, 32 to 63, 20 to 32 and < 20 μm. Weight, SOC content and instantaneous respiration rates were measured for each of the six class fractions. Our results indicate that (1) 41% of the eroded SOC was transported with coarse aggregates that would be likely re-deposited down eroding hillslopes, rather than with fine particles likely transferred to water courses; (2) erosion was prone to accelerate the mineralization of eroded SOC, and thus might contribute more CO2 to the atmosphere than current estimates which often ignore potential effects of aggregation; (3) preferential deposition of SOC-rich coarse aggregates potentially causes an increase of SOC remaining in the colluvial system and a reduction of SOC flux to the alluvial or aquatic system. These findings identify a potential error of overestimating net erosion-induced carbon sink effects, and thus add an additional factor to consider when improving our current understanding of SOC erosion and deposition on hillslopes.
Y. Hu; Nikolaus Kuhn. Aggregates reduce transport distance of soil organic carbon: are our balances correct? Biogeosciences 2014, 11, 6209 -6219.
AMA StyleY. Hu, Nikolaus Kuhn. Aggregates reduce transport distance of soil organic carbon: are our balances correct? Biogeosciences. 2014; 11 (22):6209-6219.
Chicago/Turabian StyleY. Hu; Nikolaus Kuhn. 2014. "Aggregates reduce transport distance of soil organic carbon: are our balances correct?" Biogeosciences 11, no. 22: 6209-6219.
Sediment generated by interrill erosion is commonly assumed to be enriched in soil organic carbon (SOC) compared to the source soil. However, the reported SOC enrichment ratios (ERSOC) vary widely. It is also noteworthy that most studies reported that the ERSOC is greater than unity, while conservation of mass dictates that the ERSOC of sediment must be balanced over time by a decline of SOC in the source area material. Although the effects of crusting on SOC erosion have been recognized, a systematic study on complete crust formation and interrill SOC erosion has not been conducted so far. The aim of this study was to analyze the effect of prolonged crust formation and its variability on the ERSOC of sediment. Two silty loams were simultaneously exposed to a rainfall simulation for 6 h. The ERSOC in sediment from both soils increased at first, peaked around the point when steady-state runoff was achieved and declined afterwards. The results show that crusting plays a crucial role in the ERSOC development over time and, in particular, that the conservation of mass applies to the ERSOC of sediment as a consequence of crusting. A “constant” ERSOC of sediment is therefore possibly biased, leading to an overestimation of SOC erosion. The results illustrate that the potential off-site effects of selective interrill erosion require considering the crusting effects on sediment properties in the specific context of the interaction between soil management, rainfall and erosion.
Yaxian Hu; Wolfgang Fister; Nikolaus J. Kuhn. Temporal Variation of SOC Enrichment from Interrill Erosion over Prolonged Rainfall Simulations. Agriculture 2013, 3, 726 -740.
AMA StyleYaxian Hu, Wolfgang Fister, Nikolaus J. Kuhn. Temporal Variation of SOC Enrichment from Interrill Erosion over Prolonged Rainfall Simulations. Agriculture. 2013; 3 (4):726-740.
Chicago/Turabian StyleYaxian Hu; Wolfgang Fister; Nikolaus J. Kuhn. 2013. "Temporal Variation of SOC Enrichment from Interrill Erosion over Prolonged Rainfall Simulations." Agriculture 3, no. 4: 726-740.