Rock Fragment Content Research Articles

Rainfall-simulated quantification of initial soil erosion processes in sloping and poorly maintained terraced vineyards - Key issues for sustainable management systems

In the context of the Sustainable Development Goals (SDG), understanding landscape evolution is essential to design long-term management plans. In agricultural fields, such as the vineyards on steep slopes, the terraces offer one of the most important morphological changes. However, it is not clear if the poorly managed agricultural terraces are optimal to reduce soil erosion and overland flow, although the trafficability is improved. Therefore, the main aim of this research is to compare the differences between initial soil erosion processes on poorly managed terraced vineyards and sloping vineyards at the pedon scale, considering the key role of the SSC (Soil Surface Components). To achieve this goal, twenty-six rainfall simulations were performed, considering the inclination, vegetation and stone covers, and surface roughness. Our research was carried out in the sloping vineyards (>20°) of the Almáchar municipality, in the Montes de Málaga (Spain). Those vineyards are characterized by bare soils, low organic matter and high rock fragment contents. Our results showed that higher soil losses (42.2 g m−2vs 9.4 g m−2) and runoff (4.9 l m−2vs 1.6 l m−2) were detected in the plots of the poorly managed terraced vineyard than in the sloping one. Moreover, the time to runoff generation was lower in the poorly conserved terraces (232 s) than in the sloping vineyard (679 s), showing a faster saturation capacity. The SSC considered as the key factors were the reduction of the stone cover and an increase of roughness. As a conclusion, we confirm that the imminent transformation from sloping vineyards into terraced fields could lead several land degradation processes if a poor management is carried out, and no control measures are applied during the process, such as the conservation of stone walls or vegetation cover above the embankment, which is not in compliance with the SDG.

Effect of rock fragment content on erosion processes of disturbed soil accumulation under field scouring conditions

Soil and water erosion from high rock fragment content disturbed soil accumulation severely threatens ecological security. Evaluation of the quantitative influence of rock fragment content on soil erosion processes was the basic research for soil and water conservation. Field simulation scouring experiments were conducted on the disturbed soil accumulation experimental plot. A 10 × 1-m2 plot with 28 gradients was established on Changwu Experimental Station in the Loess Plateau, China. Tap water was applied at the top of the plot with the four different flow discharge rates of 1.3 × 10−4, 1.7 × 10−4, 2.1 × 10−4 and 2.5 × 10−4 m3 s−1 to simulate surface runoff processes. The experimental plots underlying surfaces were filled with different rock fragment content of 20%, 40% and 0%. The soil used in these experimental plots was a silty loam from the disturbed soil accumulation formed by expressway construction in the loess plateau areas. The disturbed soil accumulation site was located near the G70 Fujian–Yinchuan expressway and the vegetation cover was very low. The mean diameter of rock fragments was 22 mm in these experiments, and the rock fragments were unsmooth, angular crushed stone taken from the quarry in the Changwu County. The results showed that rock fragment content of 20% and 40% could significantly decreased runoff and sediment (P < 0.05), although there was no significantly different between 20 and 40%. The rock fragments decreased mean flow velocity by 43 to 55% in mean flow velocity compared to the pure soil. Furthermore, the flow was laminar flow in the rock fragments slope. The rock fragments significantly decreased flow shear stress (52–89%), stream power (63–89%), unit stream power (41–59%), runoff kinetic energy (67–88%) and unit energy of the water-carrying section (81–89%) compared with the pure soil. With increased rock fragment content, the rill erodibility decreased. The rill erodibility was estimated to be 1.4 × 10−3 s m−1, 0.7 × 10−3 s m−1 and 0.5 × 10−3 s m−1, under the condition of pure soil, rock fragment content of 20% and 40%, respectively. Low rock fragment content (< 40%) in disturbed soil accumulation significantly decreased runoff and sediment. With the rock fragment content increased, the rill erodibility was decreased. Appropriate rock fragment content could be used to control soil erosion on disturbed soil accumulation in practice. The important parameters from this study will be helpful for disturbed soil accumulation erosion prediction model establishment.

The effects of rock fragment content on the erosion processes of spoil heaps: a laboratory scouring experiment with two soils

Spoil heaps on newly engineered landforms create extensive artificially accelerated erosion, especially when there are catchment areas above spoil heaps, erosion caused by runoff will be much greater than that induced by rainfall. This study investigated the erosional characteristics of clay loam and sandy loam spoil heaps and proposed an appropriate hydraulic parameter to simulate the variation in erosion rate. A laboratory scouring experiment was conducted using a soil pan (dimensions 5 m × 1 m × 0.5 m deep) with a discharging arrangement to test four samples of clay loam and sandy loam containing rock fragments (0%, 10%, 20%, and 30%) by mass. The slope of simulated spoil heaps was 53.2% with a discharging inflow rate of 15 L min−1. The rock fragments used were those commonly used in construction works, having a diameter of 2–3 cm and irregular shape. Twenty-four scouring tests for eight treatments with duplication were accomplished in total. Average erosion rates showed a negative linear correlation with rock fragment content in clay spoil heaps (R2 = 0.94) and a positive linear correlation in sandy loam spoil heaps (R2 = 0.92). Rill width evolution of clay loam spoil heaps mainly developed at the early scouring stage (0–15 min), and rills developed even more rapidly during later scouring times (30–60 min) in sandy loam spoil heaps. Grey relational analysis showed that sheer stress and stream power both had higher Grey relational degrees with erosion rate for both soils, regression analysis showed that stream power can efficiently describe the erosional process of clay loam and sandy loam for each rock fragment content, but sheer stress only did well in sandy loam heaps. Adding rock fragments to spoil heaps resulted in significantly opposite effects in the different soils; great attention should be paid to sandy loam spoil heaps due to their more severe erosion with increasing rock fragment content; stream power is an appropriate hydraulic parameter to simulate the soil erosion process of spoil heaps for both soil types.

Determining hot moments/spots of hillslope soil moisture variations based on high-resolution spatiotemporal soil moisture data

Characterizing soil moisture variation has critical implications for various ecosystem processes and the hydrological cycle. In this study, we identified the hot moments (times with high temporal variation rates) and hot spots (areas with high temporal variation rates) of the soil moisture variation and investigated their controlling factors on a tea garden hillslope in Taihu Lake Basin, China. Daily soil moisture data were calculated for 39 sites, and then, daily soil moisture maps were generated from March 1, 2014 to February 28, 2015. The soil moisture temporal variation rates (VR) at different locations and during different time periods were calculated based on these maps. We found that because soil water content at the subsurface was more spatially varied than that at the surface on this hillslope, spatial heterogeneity of VR was also greater at 0.3-m depth than that at 0.1-m depth. Elevation, sand content and rock fragment content were positively correlated (p < 0.05) with this spatial heterogeneity, while slope and clay content were negatively correlated (p < 0.05) with it. June and July 2014 were the hot moments with high VR at both depths of 0.1- and 0.3-m, while December 2014 was the cold moment with the lowest VR at both depths on this study hillslope. Meteorological factors (precipitation and temperature) explained 59.9% and 56.9% of the total variance in the time series of spatial mean VR at the depths of 0.1- and 0.3-m, respectively. Stronger variations in spatial mean VR were found during representative medium and large rainfall events than during representative small rainfall events. In addition, the response of spatial mean VR to rainfall at 0.3-m depth was delayed compared to that at 0.1-m depth. The findings and methodologies of this study can be useful in determining the hot spots and hot moments of soil moisture variations, which could be potentially useful for investigating various hydrological, ecological, environmental, and agronomic processes.

High‐Frequency Sequence Stratigraphy and Fine‐Scale Reservoir Characterization of the Devonian Sandstone, Donghe Formation, North Uplift of the Tarim Basin

AbstractThe Devonian Donghe Sandstone complex in North Uplift of the Tarim Basin comprises of a series of diachronous sandy intervals deposited from the Late Devonian to Early Mississippian. They are constrained by a Late Devonian to Early Pennsylvanian 2nd‐order supersequence and can be subdivided into five 3rd‐order sequences, namely, S1, S2, S3, S4, and S5, from the oldest to youngest. Cores from four wells, 40 wireline logs, 410 thin sections, and porosity and permeability data from 639 spots from four wells were used to study the sediment provenance, build up the sequence‐stratigraphic model of S5, and characterize the reservoirs at a feet scale. Detrital modes of sandstone from point counting indicate that Donghe Sandstone is directly sourced from recycled orogeny. The low content of feldspar and volcanic rock fragments suggests that Donghe Sandstone is recycled from sediment with a cratonic ultimate source. 1D and 2D chronostratigraphic correlation shows that at least 12 4th‐order high‐frequency sequences (HFSs), from the oldest HFS1 to the youngest HFS12, can be recognized in S5. Each HFS is characterized by a general trend of shallowing‐upward facies assemblage. Sequence boundaries were defined at where regionally correlatable deep‐water facies overlaying shallow‐water facies. There is a general shallowing‐upward trend in the S5 3rd‐order sequence, characterized by a systematically increasing proportion of shallow‐water facies (foreshore and upper shoreface), and a decreasing proportion of deep facies (offshore transition and lower shoreface). The shallowing‐upward trend within both 3rd‐ and 4th‐order sequences is resulted from a combined effect of eustatic sea‐level change, tectonic activity, and sediment supply. The sequence‐stratigraphic model of Donghe Sandstone S5 is similar to the rift‐basin sequence‐stratigraphic model. Sweet spots were defined as porosity &gt;15% and permeability &gt;100md intervals, and their distribution and lateral continuity were investigated. HFS is one of the primary controls on the distribution of sweet spots distribution and can be used to guide hydrocarbon exploration.

Effects of rock fragment content, size and cover on soil erosion dynamics of spoil heaps through multiple rainfall events

Spoil heaps are the main sources of soil erosion on disturbed land surfaces as an artificial accelerated erosion form, and rock fragments are an important component of spoil heaps. This study examined different fragment contents (0, 20, 40, 60 mass percentage) and sizes (1–4, 4–7, 7–10 cm) on hydrological processes, sediment yielding processes and rock fragment cover evolution through three sequential simulated rainfalls with a constant intensity of 1.5 mm min−1. The rock fragments in spoil heaps were found to reduce the soil loss amount by 35.23–76.84% through effects on runoff production and rock fragment cover. Runoff rates decreased with increasing rock fragment content, and size class 4–7 cm had the strongest reduction effect, but for a definite treatment runoff rates have little change in three rainfall events. The expanding rock fragment cover with cumulative rainfall in the multiple rainfall events, which increased fastest during the first rainfall period led to a significant decreasing soil detachment rate. Multiple regression analysis shows that the average detachment rate under each rainfall event could be estimated using a power function of average runoff rate and median rock fragment cover. These findings indicated that the presence of rock fragments in spoil heaps has an obvious mitigating effect on soil erosion, with the rock fragment content making a larger percentage contribution than rock fragment size.

Rock fabric and pore structure of the Shahejie sandy conglomerates from the Dongying depression in the Bohai Bay Basin, East China

The pore structure of sandy conglomerates, which is primarily controlled by the rock fabric, is a key topic in the microscopic physical study of reservoirs and is also of great significance for sandy conglomerate reservoir evaluation. This study focuses on the rock fabric and pore structure characteristics of sandy conglomerates of the upper submember of the fourth member of the Eocene Shahejie Formation (Es4U) in the Dongying depression, Bohai Bay Basin, East China. This study incorporates integrated approaches of casting thin-sections, scanning electron microscopy (SEM), X-ray diffraction, high-resolution core scanning image acquisition, grain size analysis, physical property tests and mercury injection. The sandy conglomerates mainly consist of pebbly sandstone and gravel sandstone; feldspar and rock fragments are dominant rock components, followed by quartz, with ranging from 25.8% to 37.7% (averaged 31.8%), 21.8% to 46.9% (averaged 31.1%) and 17.0% to 34.4% (averaged 28.0%), respectively. The pore types mainly include primary pores, secondary interparticle (interP) pores and secondary intraparticle (intraP) pores, in addition to some microcracks and intercrystalline pores. Rock textures are divided into two types according to sorting features and roundness: uniform and uneven. Porosity values are between 2.2% and 16.5% and exhibit positive correlations with quartz content and grain size and negative correlations with the content of rock fragments, interstitial material, gravel distribution uniformity, sorting coefficient and maximum particle size. In contrast, the relationships between displacement pressure and these rock fabric parameters show very different trends. The different relationships suggest that rock fabric is closely related to pore structure. In particular, sandy conglomerate samples have a relatively high compositional maturity and uniform rock texture and exhibit a better pore structure. Four typical samples were chosen to verify the relationship between rock fabric and pore structure in the logging profile of Well YN22-22. The results strongly suggest that the rock fabric can be used to indicate the effectiveness of the reservoir in the study area.

Rock fragment and spatial variation of soil hydraulic parameters are necessary on soil water simulation on the stony-soil hillslope

Whether the spatial variation and influence of rock fragment contents (RFCs) on soil hydraulic parameters (SHPs) should be jointly considered in the soil water simulation have been less investigated in previous studies. In this study, we tested whether considering these factors were necessary in the soil water simulation on a representative stony-soil hillslope located in Taihu Lake Basin, China. Five schemes of SHPs in HYDRUS-3D model were established. They were (i) MultiRFHet: spatially varied SHPs extracted from Durner’s multimodal retention function based on the observed soil water retention data; (ii) RosHom: spatially uniformed SHPs derived from ROSETTA; (iii) RosHet: spatially varied SHPs derived from ROSETTA; (iv) RosRFCHom: spatially uniformed SHPs derived from ROSETTA and adjusted by RFCs; (v) RosRFCHet: spatially varied SHPs derived from ROSETTA and adjusted by RFCs. Results indicated when the spatial variation and influence of RFCs on SHPs were both considered (MultiRFHet and RosRFCHet), acceptable accuracies (Nash-Sutcliffe efficiency or NSE ≥ 0.58 for MultiRFHet and > 0.17 for RosRFCHet) were achieved in simulating the soil water storage (SWS) variation. Since the MultiRFHet required the calibration by the observed soil water retention data, RosRFCHet was a good alternative in the simulation. On the contrary, the SHPs acquired without considering neither the RFCs nor the spatial variation yielded unacceptable simulation results (NSE general < 0). This demonstrated that spatial variation and influence of RFCs on SHPs should be included in the SWS simulation on this stony-soil hillslope, although it had limited effect in subsurface flow simulation.

Effect of embedded-rock fragments on slope soil erosion during rainfall events under simulated laboratory conditions

Quantifying the role of embedded-rock fragments in soil-water processes on a slope is crucial for the application of rock fragments in soil and water conservation practice. In this study, a laboratory runoff and erosion experiment was conducted in the soils embedded with rock fragments (including five rock fragment contents (RC) of 0, 0.1, 0.2, 0.3, and 0.4 kg kg−1) in a metal flume under three slopes (5°, 10°, and 15°). Results showed that the mean steady infiltration rate in the soil without rock fragment (NULL) was lower than that in the soils containing rock fragments (low rock fragment contents of 0.1–0.2 kg kg−1 and high rock fragment contents of 0.3–0.4 kg kg−1, labelled as LOW and HIGH, respectively) as slope gradient = 5°, but was higher than the latter two soils as slope gradients = 10° and 15°. Initial infiltration rate significantly increased with RC (P < 0.05). Runoff discharge was negatively related to RC as slope gradient = 5° and was positively related to it as slope gradients = 10° and 15°. There was a steady sediment concentration (SC) after runoff generated as slope gradient = 5°. Sediment discharge and soil erosion modulus for the treatment of HIGH significantly increased with slope gradient (P < 0.05). Reynolds number (Re) decreased with RC and the other hydraulic parameters of friction coefficient (f), shear stress (τ), and stream power (ω) increase with RC. In general, the embedded-rock fragment in the soil can accelerate soil erosion by changing the ratio of infiltration/runoff, surface roughness, and related hydraulic parameters, especially under higher slope gradients. Our findings suggest that using rock fragments to control soil erosion is workable only under the conditions of lower slope gradients and rock fragment contents.

Comment on “Soil organic stocks are systematically overestimated by misuse of the parameters bulk density and rock fragment content” by Poeplau et al. (2017)

Comment on “Soil organic stocks are systematically overestimated by misuse of the parameters bulk density and rock fragment content” by Poeplau et al. (2017)

The Upper Oligocene of Montgat (Catalan Coastal Ranges, Spain) : new age constrains to the western Mediterranean Basin opening.

The Oligocene deposits of Montgat are integrated in a small outcrop made up of Cenozoic and Mesozoic rocks located in the Garraf-Montnegre horst, close to the major Barcelona fault. The Oligocene of Montgat consists of detrital sediments of continental origin mainly deposited in alluvial fan environments; these deposits are folded and affected by thrusts and strike-slip faults. They can be divided in two lithostratigraphic units separated by a minor southwest-directed thrust: (i) the Turo de Montgat Unit composed of litharenites and lithorudites with high contents of quartz, feldspar, plutonic and limestone rock fragments; and (ii) the Pla de la Concordia Unit composed of calcilitharenites and calcilithorudites with high contents of dolosparite and dolomicrite rock fragments. The petrological composition of both units indicates that sediments were derived from the erosion of Triassic (Buntsandstein, Muschelkalk and Keuper facies), Jurassic and Lower Cretaceous rocks (Barremian to Aptian in age). Stratigraphic and petrological data suggest that these units correspond to two coalescent alluvial fans with a source area located northwestwards in the adjoining Collserola and Montnegre inner areas. Micromammal fossils (Archaeomys sp.) found in a mudstone layer of the Pla de la Concordia Unit assign a Chattian age (Late Oligocene) to the studied materials. Thus, the Montgat deposits are the youngest dated deposits affected by the contractional deformation that led to the development of the Catalan Intraplate Chain. Taking into account that the oldest syn-rift deposits in the Catalan Coastal Ranges are Aquitanian in age, this allows to precise that the change from a compressive to an extensional regime in this area took place during latest Oligocene-earliest Aquitanian times. This age indicates that the onset of crustal extension related to the opening of the western Mediterranean Basin started in southern France during latest Eocene-early Oligocene and propagated southwestward, affecting the Catalan Coastal Ranges and the northeastern part of the Valencia trough during the latest Chattian-earliest Aquitanian times.

Diagenetic controls on reservoir quality of tight sandstone: A case study of the Upper Triassic Yanchang formation Chang 7 sandstones, Ordos Basin, China

Through a range of petrological techniques, the petrology, diagenesis, pore characteristics, and controlling factors on the regional variations of reservoir quality of the Chang 7 sandstones were studied. These sandstones, mainly arkoses, lithic arkoses, and feldspathic litharenites, were deposited in a delta front and turbidites in semi-deep to deep lacustrine. The detrital constituents were controlled by the provenance and sedimentary condition, which resulted in a spatially variable composition; e.g., high biotite and feldspar contents in the northeast (NE) of the study area, and high contents of rock fragments, especially dolomite, matrix, and quartz in the southwest (SW). Diagenesis includes intense mechanical compaction, cementation, and dissolution of unstable minerals. Diagenetic minerals which were derived internally include quartz, ankerite, ferrous calcite, albite, illite, kaolinite, and chlorite. Thus the original sandstone composition hadfirm control over the development and distribution of cement. Mechanical compaction and late-stage cementations contribute to the porosity loss of sandstones of Chang7 member. The dissolution porosity in major sandstone, slightly higher than primary porosity is principally dependent on the accessibility of acid fluid. The high content of plastic component facilitated the reduction of primary porosity and limited the mineral dissolution. The best reservoir sandstones are found in W, and partly from NE, M districts, with porosity are primary. The relatively high textural maturity of these sandstones reduces the impact of compaction on primary pores, and commonly existed chlorite rims limited the precipitation of pore filling quartz and carbonate cementation in late stage.

Characteristics of rock fragments in different forest stony soil and its relationship with macropore characteristics in mountain area, northern China

Rock fragments have major effect on soil macropores and water movement. However, the characteristics of rock fragments and their relationship with macropore characteristics remain elusive in forest stony soils in northern mountainous area of China. The objectives of this study are to (1) use Industrial Computed Tomography (CT) scanning to quantitatively analyze rock fragment characteristics in intact soil columns in different forest lands and (2) identify the relationship between characteristics of rock fragments and that of the macropores. Intact soil columns that were 100 mm in diameter and 300 mm long were randomly taken from six local forest stony soils in Wuzuolou Forest Station in Miyun, Beijing. Industrial CT was used to scan all soil column samples, and then the scanned images were utilized to obtain the three-dimensional (3D) images of rock fragments and macropore structures. Next, the parameters of the rock fragments and macropore structure were measured, including the volume, diameter, surface area, and number of rock fragments, as well as the volume, diameter, surface area, length, angle, tortuosity and number of macropores. The results showed that no significant difference was found in soil rock fragments content in the 10-30 cm layer between mixed forest and pure forest, but in the 0-10 cm soil layer, the rock fragments in mixed forest were significantly less than in pure forest. The number density of macropores has significant negative correlation with the number of rock fragments in the 0-10 cm soil layer, whereas this correlation is not significant in 10-20 cm and 20-30 cm soil layers. The volume density of macropore was not correlated with the volume density of rock fragments, and there is no correlation between the density of macropore surface area and the density of rock fragment surface area. Industrial CT scanning combined with image processing technology can provide a better way to explore 3D distribution of rock fragments in soil. The content of rock fragments in soil is mainly determined by parent rocks. The surface soil (0-10 cm) of forest contains fewer rock fragments and more macropores, which may be caused by bioturbation, root systems, gravitational settling and faunal undermining.

Implications of Rock Fragments for Soil Quality Evaluation: Assessing Changes in a Gravelly Irrigated Soil Following No Till Adoption

ABSTRACTStony soils are increasingly being converted to intensive agricultural use, including irrigation. Conservation tillage can be adopted in these soils for soil protection and quality enhancement, but its assessment can be troublesome. Crop yields and the implications of rock fragments for soil quality indicators and for calculating C and N stocks were monitored under conventional and no-tillage in an experimental field recently converted to irrigation, on a soil with 40% rock fragments. Gains of up to 10 Mg C ha−1 were observed in the tilled layer (0–30 cm) only with two years of irrigation, with no differences between treatments, although the vertical distribution of carbon (C) and nitrogen (N) was affected by the correction of the rock fragment content. The labile organic fraction stood as a sensitive indicator to management changes, even after rock fragment correction. Different methodologies used for rock fragment correction led to overestimations of 20% of organic C stocks.

Solubility of phosphorus in subtropical forest soils as influenced by low-molecular organic acids and key soil properties

Low phosphorus (P) solubility in soil limits primary productivity in terrestrial ecosystems worldwide. However, our understanding about drivers of soil P solubility is still incomplete. This study examined the levels of water soluble inorganic P (Pi) and organic P (Po) in soils under mature subtropical forests in China, and how they can be influenced by three low-molecular organic acids (LOAs, i.e. citric, malic and oxalic acids) and key soil properties (e.g. organic C concentration). Water soluble Pi (mean 0.05mgkg−1) and Po (0.32mgkg−1) in the soils studied were generally low, compared to in many other areas of the world. While all three LOAs significantly solubilized P from the soils studied as a whole, the solubilized amount varied greatly among soils and also varied largely with the type of LOA and P forms. Solubilized Po by the three LOAs were >2.5 times of the solubilized Pi. Soluble total P (Pi+Po) increased in the order of oxalic acid<malic acid<citric acid and was positively related to the soluble aluminum and iron. Rock fragment (4–50mm) content explained 69%, 51%, and 31%, respectively, of the variations in water, oxalic acid, and malic acid soluble Pi. Efficiencies of the three LOAs in solubilizing Pi, but not Po, generally increased with soil organic C, total N, total P, and microbial biomass C concentrations. Our results suggest that interplay among P forms, LOAs, and soil properties control soil P solubility.

Reservoir quality, natural fractures, and gas productivity of upper Triassic Xujiahe tight gas sandstones in western Sichuan Basin, China

The main target for hydrocarbon exploration in the western Sichuan Basin in China is the tight gas sandstone reservoir of the Upper Triassic Xujiahe Formation. Sandstones of the Xujiahe Formation are characterized as tight with ultralow porosity, ultralow permeability, and intensive heterogeneity. In this study, various techniques, such as scanning electron microscopy, X-ray diffraction, cathodoluminescence microscopy, casting thin-section, and fluid inclusion thermometry, were employed to investigate the composition, sedimentary facies, diagenesis history, diagenetic intensity, natural fracture characteristics, and their impact on reservoir quality. The results showed that subaqueous distributary channels and mouth bars with low rock fragment content are favorable for pore preservation and secondary pore development. Except for the medium to strong dissolution intensity, chlorite rim growth is also important for the development of high quality reservoirs. Intraformational shear fractures and horizontal shear fractures associated with tectonic movement increase pore space and improve the capability of transmitting fluids. Differences in gas productivity could be attributed to differences in reservoir quality, which were controlled by the sedimentary environment, diagenetic intensity, and fracture characteristics. A significantly positive correlation was found between total porosity and gas productivity of the tight sandstones. The high density fracture distribution was found owing to the fault system and structural deformation zone, which resulted in high gas productivity. The research results were successfully applied to improve production efficiency in the Xujiahe tight gas sandstones, and could be applicable to other similar fields involving tight gas.

Embedded rock fragments affect alpine steppe plant growth, soil carbon and nitrogen in the northern Tibetan Plateau

Rock fragments within topsoil have important effects on soil properties and plant growth. This study mainly aimed to investigate the relationships between rock fragments, soil carbon (C) and nitrogen (N) densities and vegetation biomass in an alpine steppe. Rock fragments, plant and soil samples were collected from four topographic positions (top, upper, lower, and bottom) on a hillslope. Volumetric rock fragment content within the 0–30 cm soil profile varied from 17.8 to 30.5%, the upper position value was significantly greater (P < 0.05) than those at other positions. The highest aboveground biomass was observed at the lower position (921 kg ha−1), while the highest belowground biomass within the 0–30 cm profile was found at the upper position (4460 kg ha−1). More fine earth and plant litter input accompanied by lower C and N losses induced by rainfall erosion resulted in higher soil organic C and total N densities (28.6 Mg C ha−1 and 2.87 Mg N ha−1) at the lower position. Rock fragments may promote root growth but limit aboveground biomass production, and can therefore change the biomass distribution pattern. Our findings provide more evidence for scientifically assessing alpine steppe productivity.

Assessment of soil group, site and climatic effects on soil organic carbon stocks of topsoil in Japanese forests

The aim of this study was to assess the factors that account for the geographical variation in soil organic carbon stocks at the 0–30‐cm depth (SOC30) of forests in Japan. Boosted regression tree analysis was applied to 2157 points throughout Japan and to four regional geographical subdivisions with 16 environmental variables. The rank of predictor variables was different for Japan as a whole and among the regions. For Japan as a whole, soil group, air temperature, slope inclination, altitude and organic carbon stocks of litter were the most important factors that affected SOC30 stocks. Overall, SOC30 stocks decreased with air temperature, which was attributed to the decomposability of organic carbon. In addition, SOC30 stocks decreased with slope inclination because of instability of the topsoil on slopes, which, in turn, is related to the increase in rock fragment content and decrease in soil bulk density. The distribution of volcanic soil resulted in larger SOC30 stocks than was expected from climatic conditions. Precipitation was not important because of conflicting effects between the increase in soil organic carbon content with increasing net primary production and the decrease in mineral soil mass by the loss in topsoil. The regional analyses provide insight into the factors that cause variation in SOC30 stocks, which were obscured by the macroscale analysis of Japan as a whole, thereby illustrating the power of regional geographical analyses. Our results provide an improved basis for soil, forestry and biogeochemical models that require accurate estimates of SOC30 stocks.HighlightsWe assessed factors that account for geographic variation in soil organic carbon (SOC) stocks. Effect and dependence of factors were estimated by a machine learning approach. SOC stocks were affected by soil type, climate, site‐specific location and organic matter input. Volcanic soil distribution, climate, slope steepness and historical overuse of forest affected SOC stocks.

Impact of landslides on soil characteristics: Implications for estimating their age

The slopes of Mount Elgon, a complex volcano at the border between Uganda and Kenya, are frequently affected by landslides with disastrous effects on the livelihood of its population. Since local people greatly depend on the land for crop production, this paper examines if and how fast physico-chemical characteristics in landslide scars recover. A chronosequence of 18 landslides covering a period of 103years was sampled in order to explore differences between topsoil inside and outside landslide scars. For each landslide, two topsoil samples were taken within the landslide and two in nearby undisturbed soils to compare their physico-chemical characteristics. Samples inside the landslides were located at the transition zone between the depletion and accumulation zone, which is situated at the contact line between the plan concave and plan convex section of the landslide. No differences were found for available phosphorus, Ca2+, Mg2+ content or for the fine earth texture. Recent landslides had however lower content of soil organic carbon (OC) and K+, and higher content of rock fragments and Na+ than the adjacent soils. Soil OC content increased significantly with age and reached levels of the corresponding undisturbed soils after ca. 60years. Older landslides had even higher OC contents than soils adjacent to the landslide. Hence landslide scars act as local carbon sink. We suggest that the occurrence of rock fragments in the topsoil is a useful indicator for mapping past landslides. Moreover, the difference in soil OC content between landslide scars and adjacent soil could be used for estimating the age of landslides in data-poor regions.

Influence of rock fragments on hydraulic properties of Ultisols in Ratchaburi Province, Thailand

In Thailand, stony soils are mainly located in hillside areas. Even though they have physical limitations for agricultural use and they are exposed to a risk for soil erosion, they continue to be used for crop production. A good understanding of the hydraulic characteristics of soils containing an important fraction of rock fragments is crucial for soil and water management in these areas. The objective of this study was to investigate the influence of different rock fragment contents on effective hydraulic properties of skeletal soil with a clay content lower than 35% using measurements of the water retention curve and the hydraulic conductivity. A tension infiltrometer was used to determine the field hydraulic conductivity at four pressure heads (h) of 0, −30, −60 and −120mm. Soil water retention was determined on a pressure plate between −33 and −1500kPa. Finally, the Hydrus-1D was used to predict soil moisture dynamics using the obtained effective hydraulic parameters. The results show a decreasing water retention capacity with increasing rock fragment content. The saturated hydraulic conductivity decreased with increasing stone contents from 0 to 20%, but then increased for increasing stone content. Contradicting behavior can be observed using field and lab measurements, clearly exposing the need for a better understanding of the functioning of stony soils.