Variation In Bulk Density Research Articles

Quantitative contributions of climate change, new cultivars adoption, and management practices to yield and global warming potential in rice-winter wheat rotation ecosystems

ContextWith the growing demand for food and the threat from climate change, increasing grain yields with lower greenhouse gas (GHG) emissions is an important target. Yet, the quantitative effects of climate change and management practices on yield and global warming potential (GWP) of rice-winter wheat rotations are still uncertain. ObjectiveTo investigate the key factors influencing the tradeoffs between yield and GHG of rice-winter wheat ecosystems in mid-eastern China over the two periods. MethodsIn this study, the DeNitrification-DeComposition (DNDC) model was used to examine the spatio-temporal county-scale variations in yields of rice-winter wheat rotations and associated GHG (CH4, N2O) and GHG intensity (GHGI) over two periods (1980–1989, 2010–2019) in mid-eastern China. The DNDC model is driven by a county-scale database, consisting of meteorological data (79 stations), soil properties, management practice, and crop parameters for 213 counties. Eight scenarios were defined to isolate the individual and combined impacts of climate change, new cultivars adoption, and management practices on yields, GWP, and GHGI. Results and conclusionsResults revealed that the total yield increased by 48.7% over the two periods but stagnated in the 2010s; the average emission rate of CH4 and N2O in the two periods were 250.7, 196, 0.63 and 2.83 kg ha−1, respectively, while GWP and GHGI declined by 12.8% and 38.3%. The individual contributions of climate change, new cultivars adoption, and management practices to the GHGI of the rice-winter wheat rotations were 37%, −42.5%, and 16.4%, respectively. Adoption of new cultivars was a decisive factor for improving yields and mitigating GHG, while climate change and management practices had a minor influence on yields. The negative responses of yield to improved management practices (i.e., high N fertilization, mid-season drainage) were mainly attributed to soil organic carbon (SOC) and bulk density variations and different fertilization patterns. The combination of new cultivars adoption and management practices decreased GHGI by 46.6%. These findings demonstrate the importance of high-yield crop varieties to low carbon agriculture, and that management practices should be adapted to local conditions and specific crop varieties. SignificanceGiven that the crop harvest index is approaching its theoretical upper limit and that promoting new varieties presents many challenges, future innovations should focus on introducing optimal strategies that balance the tradeoffs between yield and GHG emissions to mitigate the negative effects of climate change on agriculture.

Within-Field Spatial Variations in Subsoil Bulk Density Related to Crop Yield and CO2 and N2O Emissions

Subsoil compaction is an increasing problem in modern agriculture, but is not easily recognized in practice, also because of possible within-field spatial variations. This paper addresses the question of how within-field spatial variations in soil bulk density and other soil characteristics relate to within-field spatial variations in crop yield and CO2 and N2O emissions from soil. Four fields (5 to 20 ha each) were selected at the suggestion of crop farmers, and sampled using a random soil sampling design (100 samples per field). Undisturbed soil samples were taken at depth of 5-10, 30-35, and 50-55 cm and soil bulk density and CO2 and N2O emissions measured under controlled conditions. At each sampling point, also top soil (0-20 cm) samples were taken for determination of pH, texture, SOM, and (micro)nutrients, and soil penetration resistance measurements and visual assessments of soil structure were made. Wheat yields were recorded with harvesters equipped with GPS and yield recorders. Mean soil bulk density in the sub-soil (30-35 cm) ranged between fields from 1.36±0.08 to 1.60±0.11 g cm-3. Mean wheat yields ranged between fields and years from 7.6±0.6 and 11.3±2.4 Mg ha-1. Semi-variogram analyses showed that crop yields and soil properties were mostly spatially dependent; nugget-to-sill ratios were < 25% with ranges of 137 to 773 m. The ratio of CO2 emissions to N2O emissions was negatively related to soil bulk density, especially following N application.In conclusion, within-field spatial variations in subsoil bulk density were successfully related to spatial variations in crop yield and in CO2 and N2O emissions. The ratio of CO2 emissions to N2O emissions had a much greater response to spatial variations in soil bulk density than wheat yield. Our study suggests that N2O emission factors may depend on (sub)soil bulk density.

Spatial heterogeneity of soil water physical properties in coal gangue pile in arid desert area

Based on grid sample method (20 m×20 m), spatial heterogeneity and distribution of soil water physical properties from 0 to 5 cm of the coal gangue pile in arid desert area were explored by using classical statistics and geostatistics methods. The results showed that the variation of soil bulk density, capillary porosity, capillary maximum moisture capacity, total porosity and saturated moisture contents were weak, while water content showed a moderate variation. The best fitting model of soil bulk density was Gaussian model, and exponential model was the best fitting model for other indices. The C0/(C0+C) values of soil bulk density and water content were low and had strong spatial autocorrelation. The capillary porosity, capillary maximum moisture capacity, total porosity and soil saturated moisture showed moderate spatial autocorrelation. Soil bulk density was negatively correlated with capillary porosity, capillary maximum moisture capacity, total porosity and water content, whereas there was no significant correlation between soil moisture content and other indices. Soil capillary porosity, capillary maximum moisture capacity, total porosity, and saturated water content showed a significant synergistic effect between each other. On Kriging contour maps, capillary porosity, capillary maximum moisture capacity, total porosity and saturated moisture had a similar spatial pattern, with high values on the middle and the left side of the lower slope, whereas soil bulk density showed an opposite pattern. Soil water content was mainly affected by the slope position and increased from the upper slope to the lower slope. Our results suggested that land preparation measures should be taken to loosen the soil in root area over the coal gangue pile in arid desert area during vegetation restoration. Moreover, irrigation amount should be properly increased on the upper slope during the initial stage of vegetation restoration, which could improve soil moisture status in the overlying soil area of coal gangue and create uniform and suitable soil water physical conditions for vegetation restoration.

Quantifying blue carbon and nitrogen stocks in surface soils of temperate coastal wetlands

Coastal wetlands are carbon and nutrient sinks that capture large amounts of atmospheric CO2 and runoff of nutrients. ‘Blue carbon’ refers to carbon stored within resident vegetation (e.g. mangroves, tidal marshes and seagrasses) and soil of coastal wetlands. This study aimed to quantify the impact of vegetation type on soil carbon stocks (organic and inorganic) and nitrogen in the surface soils (0–10 cm) of mangroves and tidal marsh habitats within nine temperate coastal blue carbon wetlands in South Australia. Results showed differences in surface soil organic carbon stocks (18.4 Mg OC ha–1 for mangroves; 17.6 Mg OC ha–1 for tidal marshes), inorganic carbon (31.9 Mg IC ha–1 for mangroves; 35.1 Mg IC ha–1 for tidal marshes), and total nitrogen (1.8 Mg TN ha–1 for both) were not consistently driven by vegetation type. However, mangrove soils at two sites (Clinton and Port Augusta) and tidal marsh soils at one site (Torrens Island) had larger soil organic carbon (SOC) stocks. These results highlighted site-specific differences in blue carbon stocks between the vegetation types and spatial variability within sites. Further, differences in spatial distribution of SOC within sites corresponded with variations in soil bulk density (BD). Results highlighted a link between SOC and BD in blue carbon soils. Understanding the drivers of carbon and nitrogen storage across different blue carbon environments and capturing its spatial variability will help improve predictions of the contribution these ecosystems to climate change mitigation.

Evaluation of installation procedures of volumetric water content and matric potential probes: fundamentals for obtaining field and laboratory accordance

The current paper aims to analyze the influence of installation procedures when it comes to the accordance of the Soil Water Retention Curve and field monitoring data. The method comprises testing three different installation procedures: with driving the rod into the soil; with the application of mud inside the auger hole; and with a hardened steel gauge. Further, is evaluated the influence of the variation of Bulk density on volumetric water content values by using the Proctor and a double ring hydraulic equipment. To analyze the soil-rod coupling, a microtomography imaging routine was performed. The results point out that the probe’s data are connected to the Bulk density of the material, producing higher volumetric water content values with the increase of Bulk density. Comparing results of different installation methods with laboratory results, it is possible to conclude that driving the rod directly into the soil is the best way to install the equipment since the probe underestimates the volumetric water content data by 2,5%, while the mud application by 4%, and the gauge method by 5%.

Effect of Various Vegetable Oils and Edible Salts on Popping Quality of Corn Variety-Azad Uttam

Grains of maize for enhancing the popping quality were soaked/dipped with/without various vegetable oils as well as also by the use of various dry edible salts such as common salt, black salt and sendhasalt (rock salt). The range of variability of bulk density, popping percentage, loss in weight of grains during popping and expansion volume were 0.68–0.89 g/ml, 85–96%, 0.2–2.2% and 337–494 ml, respectively. The popping percentage was positively and significantly correlated with grains soaked/dipped in various vegetable oils alongwith the use of sendha salt. Grains soaked/dipped with soybean oil alongwith the application of sendha salt in corn variety-Azad Uttam was found most superior from popping point of view as it showed significantly highest values of volume expansion and popping percentage.

Spartina alterniflorainvasion alters soil bulk density in coastal wetlands of China

AbstractAlthough empirical studies show that invasiveSpartina alternifloraLoisel. (S. alterniflora) has reduced soil bulk density (BD), the mechanisms that underpin this response are still unclear. To explore this pattern, we used a space‐for‐time substitution approach and collected soil samples from the eastern coast of China, whereS. alternifloraecosystems were established a short period of time after initial invasion. We used structural equation modelling to test the hypothesis thatS. alterniflorainvasion has an indirect influence on BD through the interacting effects of soil and plant variables, including plant productivity, soil organic carbon (SOC), total nitrogen (TN), pH, salinity, sand, and clay content. These variables, which are associated withS. alterniflorainvasion, were assumed to represent multiple physicochemical and biological processes. The model showed that these processes explain 82% of the BD variation in response toS. alterniflorainvasion. We observed that SOC had the most direct influence on BD, followed by salinity and soil sand content. We also found thatS. alterniflorainvasion had an important direct influence on the measured variables. Although plant productivity was not directly related to BD, it was indirectly associated with the impacts of plant productivity on salinity. Our results highlight the occurrence of BD variability within an interacting system of soil and plants whereinS. alterniflorainvasion leads to a decrease in BD. This work also highlights that identifying the mechanisms driving BD variability in response toS. alterniflorainvasion would help to improve our understanding of soil development inS. alternifloramarshes.

Predicting bulk density in deep unsaturated soils based on multiple scale decomposition

Information on bulk density (BD) in the unsaturated zone (USZ) is critical to the development of Earth’s critical zone science. However, models for predicting deep soil BD are limited due to poor understanding of the variability of deep soil BD. This study aimed to examine the dominant scales of variations in BD, identifying the scale-specific controls of BD and developing a new multi-scale physically based conceptual model for predicting BD in the deep USZ. Three undisturbed soil cores (90.0, 47.6, and 59.2 m in depth) were collected from the Changwu, Haiyuan, and Weinan regions within the Chinese Loess Plateau and a range of soil properties were measured at 0.2 m intervals. Scale specific variations were identified using empirical mode decomposition and the multi-scale model was compared against traditional pedo-transfer functions. The USZ BD distribution with depth exhibited two types of dominant variations: (a) large-scale logarithmic growth, due mainly to compaction and (b) medium-scale oscillations from variation of soil inherent properties. A multi-scale model accounted for 82% of the total variation in BD, from soil depth, magnetic susceptibility, and clay content. Compared with conventional pedo-transfer functions at the measurement scale, the multi-scale model improved prediction (adjusted R2) of BD by around 15% and provided an interpretable and rational form. This study provided new insights and a model to predict USZ BD, which are valuable for improving our understanding of the deep USZ.

Study on fabric compression under seam vis a vis quantitative measurement of seam boldness and thread consumption for lockstitch 301

Purpose This paper aims to develop at sewing thread during the seam formation may lead to the compression of fabric under seam. In the present study, the model has been proposed to predict the seam compression and calculation of seam boldness, as well as thread consumption by considering seam compression. Design/methodology/approach The effect of sewing parameters on the fabric compression at the seam (Cf) for fabrics of varying bulk density was studied by the Taguchi method and also the multilinear regression equation is obtained to predict seam compression by considering these parameters. The framework has been set as per the single view metrology approach to measuring structural seam boldness (Bs). One of the basic geometrical models (Ghosh and Chavhan, 2014) for the prediction of thread consumption at lock stitch has been modified by considering fabric compression at the seam (Cf). Findings The multilinear regression model has been proposed which can predict the compression under seam using easily measurable fabric parameters and stitch density. The seam boldness is successfully calculated quantitatively using the proposed formula with a good correlation with the seam boldness rated subjectively. The thread consumption estimation from the proposed approach was found to be more accurate. Originality/value The compression under seam is found out using easily measurable parameters; fabric thickness, fabric weight and stitch density from the proposed model. The attempt has been made to calculate seam boldness quantitatively and the new approach to find out thread consumption by considering the seam compression has been proposed.

Seasonal changes in bulk density-based waste identification and its dominant controlling subcomponents in food waste

Bulk density is an effective evaluation criterion for food and residual household solid waste (HSW) source separation accuracy, but the effect of seasonal components on its variation is unknown. The objective was to accurately determine seasonal variation in bulk-density based waste identification and to ascertain the dominant controlling subcomponents in food waste leading to seasonal variation. A total of 540 bagged wastes were collected in Beijing in August and December representing summer and winter half year. Low-valued food and residual waste were the primary categories, accounting for 60% and 35% of HSW, respectively. Average residual waste threshold was <114 kg/m3, irrespective of season, with good homogeneity (p=1.000). For food waste, winter thresholds were all lower than summer in investigated communities, appearing relatively seasonal difference (p=0.102), so they were divided into two: >193 kg/m3 in winter and >211 kg/m3 in summer. Mixed waste thresholds were 114-193 and 114-211 kg/m3 in winter and summer, respectively. Moreover, the pericarp moisture remarkably changes with season (p<0.005) while other subcomponents remain unaffected. Frequency distribution of pericarp species further indicate a higher frequency of watermelon pericarp in summer leads to greater food waste moisture than in winter, and therefore significant bulk density threshold differences between seasons. Understanding seasonal change in bulk density identification provides a theoretical basis for ‘intelligent supervision trashcan’ application in various climate areas across China, further realizing more efficient residual and food waste resource recovery.

The effect of permeability on the erosion threshold of fine-grained sediments

The erosion of marine sediments, although difficult to predict, can lead to important implications in offshore engineering, sedimentology and coastal management. Continued research is, therefore, warranted to compile high-quality erosion data from which to develop models to better predict the erosion resistance of different types of marine sediments. In this paper, dimensional analysis is performed to express the threshold shear stress as a function of a selection of soil properties that are commonly linked to the erosion process of sediments. To identify the dominant dimensionless group, an experimental investigation on the erosion threshold was carried out using fine-grained sediments that were systematically prepared to ensure variations in (i) particle size distribution (i.e. fines content), (ii) bulk density, and (iii) hydraulic permeability. The samples included silica, carbonate and marine sediments, each of which are expected to have limited or no clay-mineral content.The measurements were analysed and compared with existing literature and predictive models. It was found that marine sediment samples with limited fines content showed good agreement with the empirical Shields curve, irrespective of particle size distribution, bulk density and permeability. In contrast, for finer marine sediment it was found that variations in these soil properties modify the threshold shear stress away from the Shields curve. Across each of these parameters only permeability appeared to independently correlate with the observed range of threshold measurements. Motivated by this finding, a model is introduced to predict the threshold shear stress as a function of permeability and the reference erosion rate that is used to define when the threshold is reached. The resulting expression is shown to quantitatively explain the experimental data and is found to also agree with existing data from the literature for quartz sediments with a wide range in fines content. An apparent advantage of the new model is that it is consistent with existing studies that identify variations in threshold shear stress due to changes in bulk soil parameters – including fines content and bulk density – since each of these parameters also affect permeability.

Spatial distribution of soil bulk density and its relationship with slope and vegetation allocation model in rehabilitation of dumping site in loess open-pit mine area.

Studies of soil bulk density (BD) spatial variations of land reclaimed after mining have become a focus of land reclamation and ecological restoration research. However, there have been few studies on the relationship among the reconstructed BD, terrain conditions, and vegetation growth. We examined the southern dumping site of the Pingshuo Antaibao open-pit coal mine located in a loess area in China. Field sampling data, digital elevation models (DEMs), and high-definition images were obtained, and indoor testing, geostatistics, and inverse distance weighting (IDW) were applied. This paper aims to analyze the spatial distribution law of the reconstructed BD and focus on its relationship with slope and vegetation allocation models. We demonstrated that (1) BD increased with soil depth and varied moderately within each layer. (2) The BD variation amplitude of the top 0-20-cm soil layer in both the east-west and south-north directions was small and more similar in the east-west direction than in the south-north direction, which was affected by herbaceous root systems. In the next four layers from 20 to 60 cm, the variation in BD in the east-west direction was far larger than that in the south-north direction, which was affected by vegetation classification. (3) On the whole, BD decreased with increasing slope, but when the slope was between 0° and 21°, BD exhibited a specific change law. (4) From the perspective of vegetation classification, the orders of magnitude of BD in the 0-20-cm and 20-60-cm layers differed. Overall, BD in areas vegetated with Korshinsk Peashrub was the lowest, and BD was moderate in areas with mixed vegetation, while BD was the highest in areas without vegetation or only vegetated with Black Locust. The mixed grass-bush-tree or bush-tree mode attained the best effect in regulating BD. These results can improve the basic principles of land reclamation in mining areas and provide a basis for further optimizing land reclamation technology in practice.

Soilphysics: An R package for simulation of soil compaction induced by agricultural field traffic

Agricultural traffic is the main mechanism responsible for the increase in compacted fields. Strategies to minimize the impact of field traffic on the soil includes knowledge of stress-strain relationships, which involve the use of soil compaction models; however, one of the challenges for dissemination of these models among researchers and academics is its availability as computational tools, easily and freely accessible. In this work, we present a computational tool for simulation of compaction induced by agricultural field traffic based on soil physical and soil mechanics principles, which includes the calculation of contact stress, stress propagation in the soil profile, simulation of bulk density variation in response to the applied stress and assessment of the risk of compaction through readily available soil properties and machinery parameters. Furthermore, the soil inputs of the model is facilitated by a set of pedo-transfer functions for estimation of the required soil properties. The model was computationally implemented as a set of R functions (R software), as well as on an interactive web page, named PredComp, both available in the R package soilphysics (available from https://arsilva87.github.io/soilphysics/ or http://cran.r-project.org/web/packages/soilphysics/index.html).

New pedotransfer functions for soil water retention curves that better account for bulk density effects

Pedotransfer functions (PTFs) describing soil water retention curves (WRCs) have been widely used in crop, soil, and land surface models. A limitation of the available PTFs is that they fail to account for shape changes in WRCs due to bulk density variations caused by soil tillage, compaction, and other processes. This study develops new PTFs that include bulk density effects on the WRC shape. A new framework is introduced to build the bulk density-associated PTFs based on a widely-used WRC dataset. The new PTFs were validated by comparing the performance with two common PTFs from the literature using two independent datasets. The results show that the newly developed PTFs provide reliable WRC estimates for the validation datasets, with mean RMSE values of 0.055 and 0.059 m3 m-3, respectively. The accuracy of the new PTFs is comparable or in some cases better than the common PTFs. While the literature PTFs investigated do not always properly describe bulk density effects on WRC changes, the new PTFs effectively account for such effects on the WRC shape, thus have the potential to be integrated into crop and soil management models to represent bulk density impacts on WRCs due to anthropogenic (e.g., plowing and compaction) and natural (e.g., wetting/drying) processes.

Quantitative Evaluation of the Spatial Variation of Surface Soil Properties in a Typical Alluvial Plain of the Lower Yellow River Using Classical Statistics, Geostatistics and Single Fractal and Multifractal Methods

The spatial variability of soil properties has always been a significant research field in geoscience. The types of soil properties cover a wide range, but most studies have focused on the spatial variability of soil physicochemical properties over the past decades. Studies on soil hydraulic characteristics are limited, and most of them are limited to the farmland scale. However, the spatial variability of regional soil properties (soil texture and hydraulic properties) is valuable for the study of sedimentation processes and soil water transport. Therefore, here, the spatial variation of six soil properties (sand, silt, clay content, bulk density, saturated water content and saturated hydraulic conductivity) in the typical alluvial plain area of the lower Yellow River is quantitatively studied, by using classical statistics, geostatistics and single fractal and multifractal methods. This study mainly quantitatively analysed the spatial variability of different soil properties and compared four research methods. Although the coefficient of variation, nugget coefficient, single fractal dimension and multifractal spectral width can reflect spatial variability, diverse conclusions are drawn (on variability) if different methods are used, and the different soil properties show large disparities. These four methods show a different variation order of soil properties, but there are some common conclusions based on analysis and judgment. In general, the silt content in the study area is stable, mainly originating from loess transported by Yellow River erosion, which is also reflected in the Kriging interpolation maps under the geostatistical models. The variation in bulk density and saturated water content is weak, and the spatial variability of sand and clay content is moderate. In addition, the saturated hydraulic conductivity fluctuates violently. This may be related to the differences in local topography, human activity and the content of sand and clay, each of which significantly affects the saturated hydraulic conductivity. Classical statistics has a limitation because it fails to corelate with spatial location. Due to the small sample capacity and calculation error of lag distance, the accuracy of geostatistics and single fractal dimensions needs to be improved. Multifractal spectral analysis does not need to consider the normality of data and can quantitatively represent local characteristics; therefore, its results have high reliability.

Physical-chemical predictors of soil pollution in the megapolis

The problem of quantitative assessment of soil pollution of the capital metropolis by controlling physical-chemical factors of solid and liquid phases of soil is investigated. The metals were used as an integral indicator of pollution taking into account the mass fraction and the variation of soil bulk density. Multiple regression (R2=0.91-0.95) of layered heavy metals, as well as accumulation of biophilic elements of the exchange fund from two main predictors – dispersion (effective specific surface area of solid phase, determined by the original thermal desorption method) and pH of salt extract was revealed.

Thermoelectric Power, Electrical Resistivity and Magnetic Properties of Ni-Sm Nano-particles

Nanocrystalline Samarium doped Nickel ferrites having compositional formula NiSmXFe2-XO4 (0.00≤X≥0.10) were prepared by the citrate-gel auto combustion method and sintered at 5000C. The structural characteristics such as XRD analysis were shown cubic spinel structure, and the structural parameters like lattice parameter, X-ray density, bulk density, and porosity variations with Sm doping were studied. The surface morphology of prepared samples was observed by Scanning Electron Microscopy (SEM). The magnetic parameters were studied at room temperature with VSM, and the observed results are discussed with composition. The DC electrical properties were studied using a two-probe method in the temperature range from room temperature to well beyond Curie temperature. Thermoelectric power studies were carried out from room temperature to well beyond transition temperature with a differential method. The Seebeck coefficient variation with temperature was studied, and it shows the prepared samples are classified as n-type semiconductors. The observed results can be explained on the basis of the conduction mechanism.

Yarı Humid Ekolojik Koşullar Altında Oluşmuş Bazı Vertisol Alt Grup Toprakların Profillerinde Isı Akışının Belirlenmesi

The evaluation of heat flow in soil is necessary for the management of soil temperature regime, determining the amount of heat stored in soil, and modeling soil temperature. In this study, the volumetric heat capacity values calculated for horizons of different soil profiles (Typic Calciustert, Chromic Hapluster, Typic Haplustert) belong to Vertisol order varied between 2.173∙106 J m-3 oC-1 and 2.307∙106 J m-3 oC-1, and the thermal conductivity coefficient values varied between 12.412watt m-1 oC-1 and 21.404 watt m-1 oC-1. The volumetric heat capacity changed in a narrow range due to small variation in bulk density and volumetric moisture content values in soil horizons. Heat flow values were determined as 43.892 watt m-2, 26.424 watt m-2, 10.284 watt m-2 in Ap, Bss 2C horizons of Typical Calciustert profile; 43,910 watt m-2, 22,665 watt m-2, 7,629 watt m-2 in A, Bss1, Bss2 horizons of Chromic Hapluster profile and 35.958 watt m-2, 14.770 watt m-2, 7.530 watt m-2 in Ap, Bss1, Bss2 horizons of Typic Haplustert profile, respectively. The positive difference between the average and the maximum temperature values in the horizons causes downward heat flow in the soil profiles. Although the heat diffusivity coefficients increased towards the lower horizons of soils, it was determined that the heat flow values decreased. Increase in the total porosity due to increase in clay accumulation causes to decreases in volumetric heat capacity and heat flow values.

Effects of Tree Forest Plantations on Soil Physicochemical Properties in the Arboretumof Ruhande,Southern Province of Rwanda

Different tree speciesare blamed to have negative effects on soil ecosystems by changing soil physicochemical properties, and hence soil quality. However, few researches to verify this statement were done in Rwanda. This study provides prior information on the effects of planted forest tree species on soil physicochemical properties. It was conducted in the Arboretum of Ruhande, in southern Rwanda. Soil cores were collected in plots of exotic, native and agroforestry tree species. Collected soils were analysed for soil pH, total nitrogen, organic carbon, available phosphorus, aggregate stability, bulk density, soil humidity, cation exchange capacity, and soil texture. Soils sampled under exotic tree species were acidic, richin soil organic carbon, and in soil available phosphorus. Native and agroforestry tree species offer better conditions in soil pH, soil water content, cation exchange capacity, clay and silt. Less variations in soil total nitrogen and soil bulk density were found in soils sampled under all studied forest types. Research concluded that studiedtree species have different effects on soil physicochemical parameters. It recommended further studies to generalize these findings.&#x0D; Key words: soil, exotic, native, agroforestry, soil properties

Impact of grazing on shaping abundance and composition of active methanotrophs and methane oxidation activity in a grassland soil

The effect of grazing on the abundance, composition, and methane (CH4) uptake of methanotrophs in grasslands has been well documented in the past few decades, but the dominant communities of active methanotrophs responsible for CH4 oxidation activity in grazed soils are still poorly understood. In this study, we characterized the metabolically active, aerobic methanotrophs in grasslands with three different levels of grazing (light, medium, and heavy) by combining DNA-stable isotope probing (SIP) and quantitative PCR (qPCR) for methane monooxygenase (pmoA) gene– and 16S rRNA gene–based amplicon sequencing. The CH4 oxidation potential was as low as 0.51 μmol g dry weight−1 day−1 in the ungrazed control, while it decreased as grazing intensity increased in grazed fields, ranging from 2.25 μmol g dry weight−1 day−1 in light grazed fields to 1.59 in heavily grazed fields. Increased CH4 oxidation activity was paralleled by twofold increases in abundance of pmoA genes and relative abundance of methanotroph-affiliated 16S rRNA genes in the total microbial community in grazed soils. SIP and sequencing revealed that the genera Methylobacter and Methylosarcina (type I; Gammaproteobacteria) and Methylocystis (type II; Alphaproteobacteria) were active methanotrophs responsible for CH4 oxidation in grazed soils. Light and intermediate grazing stimulated the growth and activity of methanotrophs, while heavy grazing decreased the abundance and diversity of the active methanotrophs in the typical steppe. Redundancy and correlation analysis further indicated that the variation of bulk density and soil C and N induced by grazing determined the abundance, diversity of active methanotrophs, and methane oxidation activity in the long-term grazed grassland soil.