Variability Of Soil Bulk Density Research Articles

Topography Dominates the Spatial and Temporal Variability of Soil Bulk Density in Typical Arid Zones

Soil bulk density is a crucial indicator for assessing soil matter storage and soil quality. Due to the complexity of sampling soil bulk density, particularly in deeper layers, it is essential to study the spatial distribution patterns of soil bulk density and their influencing factors. To address the gap in large-scale studies of vertical (from surface to deeper layers) and horizontal (across a broad area) variations in soil bulk density in arid regions, this study focuses on Changji Prefecture, located in the central northern slope of the Tianshan Mountains and characterized by typical vertical zonation. By integrating classical statistics, geostatistics, and geographic information systems (GISs), this study investigates the spatial distribution patterns and driving factors of soil bulk density. The results indicate that soil bulk density in Changji Prefecture increases with soil depth, with significantly lower values in the surface layer than in deeper layers. Spatially, despite minimal variation in latitude, there is considerable elevation difference within the study area, with the lowest elevations in the central region. Soil bulk density exhibits a spatial distribution pattern of higher values in the northeast (desert areas) and lower values in the southwest (forest areas). The nugget effect in the surface layer (0–20 cm) is substantial at 44.9%, while the deeper layers (20–100 cm) show nugget effects below 25%, suggesting that the influence of both natural and anthropogenic factors on deep soil bulk density is limited and mainly affects the surface layer. Stepwise regression analysis indicates that among topographic factors, slope and elevation are the primary controls of spatial variability in soil bulk density across layers. This research demonstrates that, in arid regions, soil bulk density is influenced primarily by natural factors, with limited impact from human activities. These findings provide valuable data support and theoretical guidance for soil management, agricultural planning, and sustainable ecosystem development in arid regions.

Mangrove species found in contrasting environments show differing phytohormonal responses to variation in soil bulk density

Background and aimsMangrove species respond to variation in soil bulk density (BD). However, very little is known about the regulatory mechanisms that trigger these responses.MethodsEndogenous concentrations of different phytohormones were measured in the roots of two mangrove species (Avicennia marina and Rhizophora stylosa) grown in low and high BD soils. The potential involvement of ethylene in regulating plant growth responses was tested by applying the ethylene biosynthesis inhibitors cobalt chloride (CoCl2) and aminoisobutyric acid (AIB).ResultsThe two mangrove species responded differently to variation in soil BD. High BD decreased root growth of R. stylosa, but not A. marina. Soil BD had no effect on root phytohormone levels in R. stylosa, but loose soils increased 1-aminocyclopropane-1-carboxylic acid whilst decreasing salicylic acid and gibberellin in A. marina. Applying ethylene inhibitors enhanced R. stylosa root growth, while increasing indole-3-acetic acid but decreasing isopentenyl adenine levels. In contrast, AIB inhibited A. marina root growth, while increasing trans-zeatin levels. Ethylene inhibitors affected salicylic acid levels in both species.ConclusionSalicylic acid is central to root growth responses to variation in BD in A. marina. Conversely, the interaction of ethylene and gibberellin drives responses in R. stylosa. Hormonal interactions involving ethylene potentially reflect the adaptations of the two species to differing conditions within the intertidal zone, with A. marina behaving like an aquatic species and R. stylosa behaving like a terrestrial species.

Variations in soil physico-chemical properties, soil stocks, and soil stoichiometry under different soil layers, the major forest region Liupan Mountains of Northwest China.

Liupan Mountains are an important region in China in the context of forest cover and vegetation due to huge afforestation and plantation practices, which brought changes in soil physio-chemical properties, soil stocks, and soil stoichiometries are rarely been understood. The study aims to explore the distribution of soil nutrients at 1-m soil depth in the plantation forest region. The soil samples at five depth increments (0-20, 20-40, 40-60, 60-80, and 80-100 cm) were collected and analyzed for different soil physio-chemical characteristics. The results showed a significant variation in soil bulk density (BD), soil porosity, pH, cation exchange capacity (CEC), and electric conductivity (EC) values. More soil BD (1.41 g cm-3) and pH (6.97) were noticed in the deep soil layer (80-100 cm), while the highest values of porosity (60.6%), EC (0.09 mS cm-1), and CEC (32.9 c mol kg-1) were reflected in the uppermost soil layer (0-20 cm). Similarly, the highest contents of soil organic carbon (SOC), total phosphorus (TP), available phosphorus (AP), total nitrogen (TN), and available potassium (AK) were calculated in the surface soil layer (0-20 cm). With increasing soil depth increment a decreasing trend in the SOC and other nutrient concentration were found, whereas the soil total potassium (TK) produced a negative correlation with soil layer depth. The entire results produced the distribution of SOCs and TNs (stocks) at various soil depths in forestland patterns were 0→20cm > 20→40cm > 40→60cm ≥ 60→80cm ≥ 80→100 cm. Furthermore, the stoichiometric ratios of C, N, and P, the C/P, and N/P ratios showed maximum values (66.49 and 5.46) in 0-20 cm and lowest values (23.78 and 1.91) in 80-100 cm soil layer depth. Though the C/N ratio was statistically similar across the whole soil profile (0-100 cm). These results highlighted that the soil depth increments might largely be attributed to fluctuations in soil physio-chemical properties, soil stocks, and soil stoichiometries. Further study is needed to draw more conclusions on nutrient dynamics, soil stocks, and soil stoichiometry in these forests.

Different plant species exhibit contrasting root traits and penetration to variation in soil bulk density of clayey red soil

AbstractHigh bulk density reduces yields in almost every soil and management system worldwide. Using pioneer plants was one of the practical solutions to remediate the adverse effects from high bulk density. The objectives of this research were to investigate the effect of soil bulk density on root traits and penetration of different pioneer plants (rape [Brassica napus L. cv. Huashuang 4]; deep rape [Brassica napus L. cv. Xinan 28]; lucerne [Medicago sativa L. cv. Ladino]; vetiver [Chrysopogon zizanioides L. cv. Wild]) under controlled and field conditions. Replicated field and laboratory studies were conducted in a soil composition of high clay percentage, high oxides content, and low organic matter content. Seedling and matured root traits of four plants under contrasting bulk density in controlled study and field were analyzed. Under controlled situations, soil with a bulk density of 1.4 g cm–3 had thicker roots (higher diameter) than soil with a bulk density of 1.2 g cm–3, whereas soil with a bulk density of 1.6 g cm–3 had reduced root lengths (RL), branch number, root tip angle, and root elongation rate than soil with a bulk density of 1.4 g cm–3. Similar changes of root diameter (RD) and root length density (RLD) with bulk density also appeared in the field. Generally, the penetration ability of plant species displayed in the order of vetiver > lucerne > deep rape > rape. Vetiver showed the highest penetrating ability due to its high RD (0.7 mm in field), percentage of medium roots (20–50%) and RLD, and small root tip angle to ensure penetration through hard layers. The results demonstrated that vetiver will be an effective pioneer plant for red soil management.

PERFORMANCE EVALUATION OF THE POPULAR SWRC MODELS AT DIFFERENT SOIL BULK DENSITY RANGES

Soil bulk density is an important soil property which influences the hydraulic properties of soil. Soil bulk density has never been a fixed soil property, but it varies spatially due to soil changes and temporally due to human activities, soil management and effects of climate change. This changes in soil bulk density affects the characterization of hydraulic properties of soil especially when mathematical soil retention models are used. Since the measurement of the soil water retention characteristics in the field is expensive, labor intensive and time consuming, mathematical models have been developed to predict these properties. Therefore, it is important to establish the impact of the soil bulk density on the performance of these mathematical models especially their accuracy to fit measured data using measured data. The aim of this study was performance evaluation of the water retention models at different soil bulk density ranges. The study used the dataset downloaded from the global database (ISRIC). The study used Residual Standard Error (RSE) and R2 to measure the accuracy of the model in predicting or quantify the goodness of fit to the experimental data. The low values of RSE shows that experimental data are close to the model predictions. This paper discussed the popular Soil Water Retention Characteristic (SWRC) models then it assessed their performance on varying soil bulk density ranges. The results from the study showed that the performance of the models improved with increase in values of field bulk density. It was established that Gardner and Bi-exponential models were better suited to describe SWRC irrespective of the variation of soil bulk density because they displayed consistent best performance (R2 greater than 0.98) at low and high soil bulk density. From the study, the soil scientist can choose these models to apply especially when the soil bulk density varies greatily.

Spatial and temporal variation in soil bulk density and saturated hydraulic conductivity and its influencing factors along a 500 km transect

Soil bulk density (BD) and saturated hydraulic conductivity (Ks) are two critical soil physical parameters that affect soil water holding capacity, infiltration, carbon stocks, and many land and surface processes. Although variations in spatial and temporal BD and Ks are widely recognized and known to differ at different scales, little large-scale data is available. This study explores changes in spatial and temporal BD and Ks along a 500 km transect on the Chinese Loess Plateau (CLP). On seven different occasions, we took BD and Ks measurements in undisturbed soil samples within the surface (0–10 cm) and subsurface (10–20 cm) soil layers from August 2015 to October 2018 along this long transect. This transect covers two climate zones (subhumid and semiarid) and mainly includes five land-use types. BD and log10-transformed Ks (LogKs) exhibited weak and moderate spatial variations during different sampling periods along the long transect, respectively. The highest LogKs values of the two soil layers were observed in summer. Only BD (LogKs) in the surface soil layer of semiarid zone was significantly higher (lower). Grassland had slightly lower BD and higher Ks compared to the other land-use types. Climate had no significant effect on BD and Ks variability. Land-use type and season separately had a significant impact on BD and Ks variability, while sampling time significantly influenced both BD and Ks variability. Ks was negatively correlated with soil water content in spring, summer and autumn. In this long transect, spatial and temporal variations in BD and Ks are determined by land-use types, seasonal changes, sampling time and soil water condition. Understanding temporal BD and Ks variations and their dominant factors will help in the selection of soil physical parameters to optimize hydrological models more accurately at a regional scale.

Decomposition of mangrove roots depends on the bulk density they grew in

Mangroves hold large organic carbon (C) stocks in their soils. These C stocks are mainly attributed to the high productivity and slow decomposition of the below-ground biomass. Rates of decomposition are strongly influenced by edaphic factors including soil bulk density (BD). Hence, this study assessed the influence of soil BD on mangrove root material and its effect on decomposition. To determine the effect of the BD in which the plants were grown on decomposition rates (i.e. mass loss), four mangrove species were grown in soils of six different BD. The root material was then placed in litterbags and incubated in mangrove forest soil for three months. Additionally, the root material was analysed for nitrogen (N) and phosphorus (P), as well as lignin and cellulose content. The soil BD experienced during root growth strongly affected mass loss, which decreased with increasing soil BD of the growth media. Decomposition also differed among species. Variation in mass loss was likely influenced by N levels, C:N ratios and lignin content of the root tissue. Variation in soil BD influences the C sequestration potential of mangroves, as BD affects the decomposability of mangrove root tissues.

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.

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.

Variation in soil bulk density and hydraulic conductivity within a quasi-circular vegetation patch and bare soil area

Soil bulk density and hydraulic conductivity are two of many key factors for vegetation establishment and the other way around. Variations in them may cause patchy vegetation distribution in arid and semiarid areas. Characterizing their spatial variations in relation to quasi-circular vegetation patches (QVPs) is important for the effective revegetation of wetlands in the Yellow River Delta (YRD), China. This study investigated the variations of soil bulk density and hydraulic conductivity based on 86 soil bulk density and 63 hydraulic conductivity samples within a quasi-circular vegetation patch area in the YRD. The nonparametric Mann-Whitney U and Kruskal-Wallis H tests, respectively, were used to evaluate the differences in soil bulk density and hydraulic conductivity between the QVPs and bare soil areas. There were significant differences in soil bulk density and hydraulic conductivity between QVPs and bare soil areas. Conversely, there were no significant differences in the two parameters among different QVPs. The average QVP bulk density and hydraulic conductivity (2.0 cm suction) were 12.4% lower and 191.8% higher, respectively, than those of bare soil areas. Plant species communities within QVPs did not significantly differ in terms of their influences on hydraulic conductivity but did differ in terms of their impacts on soil bulk density. Soil bulk density increased from the QVP centers to their edges whereas the opposite was observed for hydraulic conductivity. This finding indicated that QVPs drastically increase soil hydraulic conductivity, and soil bulk density influenced the spatial distribution of plant species communities within QVPs. This study expanded our understanding of occurrence and encroachment of QVPs in the YRD, may help understand spontaneous plant colonization and succession mechanism and lay the foundation for developing adaptive wetland restoration strategies in the YRD.

Plasticity in the Above- and Below-Ground Development of Mangrove Seedlings in Response to Variation in Soil Bulk Density

Mangroves store large amounts of organic carbon (C) in their soils and are important in the global C cycle. These C stocks have been attributed to the below-ground productivity of mangroves, yet there is limited knowledge about the environmental factors that influence mangrove root growth. Thus, this study aimed to assess the role of variation in soil bulk density (BD) on the early development of mangroves. Seedlings of four mangrove species were grown in a pot-experiment in soils with a BD ranging from 0.2 to 1.2 g cm−3. Nine functional above- and below-ground plant traits were measured. Above- and below-ground traits of mangrove seedlings were influenced by variation in soil BD, but the effect was species specific. The reaction norms for most plant traits of Bruguiera gymnorrhiza and Rhizophora stylosa suggested a growth optimum at a specific soil BD (0.6 and 0.4 g cm−3, respectively), whilst the reaction norm of Avicennia marina was highly variable among traits, and Ceriops australis showed a very limited response. Moreover, A. marina was the most plastic species above-ground, while R. stylosa was the most plastic species below-ground. Ceriops australis was the least plastic species. Hence, soil BD is an environmental factor that influences mangrove root traits and seedling establishment, and may therefore affect mangrove species distributions and ecosystem C stocks.

Estimates of Tillage and Rainfall Effects on Unsaturated Hydraulic Conductivity in a Small Central European Agricultural Catchment

In arable land, topsoil is exposed to structural changes during each growing season due to agricultural management, climate, the kinetic energy of rainfall, crop and root growth. The shape, size, and spatial distributions of soil aggregates are considerably altered during the season and thus affect water infiltration and the soil moisture regime. Agricultural topsoils are prone to soil compaction and surface sealing which result in soil structure degradation and disconnection of preferential pathways. To study topsoil infiltration properties over time, near-saturated hydraulic conductivity of topsoil was repeatedly assessed in a catchment in central Bohemia (Czech Republic) during three consecutive growing seasons, using a recently developed automated tension minidisk infiltrometer (MultiDisk). Seasonal variability of soil bulk density and saturated water content was observed as topsoil consolidated between seedbed preparations. Topsoil unsaturated hydraulic conductivity was lower in spring and increased in the summer months during two seasons, and the opposite trend was observed during one season. Temporal unsaturated hydraulic conductivity variability was higher than spatial variability. Cumulative kinetic energy of rainfall, causing a seasonal decrease in soil macroporosity and unsaturated hydraulic conductivity, was not a statistically significant predictor.

The roots of blue carbon: responses of mangrove stilt roots to variation in soil bulk density.

Mangroves harbour large soil organic carbon (C) pools. These C stocks are attributed to the production and slow decomposition of the below-ground biomass. Novel in-growth containers were used to assess the effect of soil bulk density (BD: 0.4, 0.8 and 1.2 g cm-3) on morphological, anatomical and chemical traits of the below-ground fraction of aerial roots of the mangrove Rhizophora stylosa. Dense soils increased total root biomass and primary root diameter, while the primary root length decreased. Furthermore, high soil BD reduced aerenchyma lacunae and led to the formation of structural features such as fibrous strands. These morphological and anatomical changes were not reflected in tissue chemistry, with lignin levels averaging 17.0 ± 0.6%, although roots grown in high BD had higher nitrogen levels. This likely affects decomposition rates. Thus, variation in soil BD has major implications for C sequestration in Rhizophora-dominated mangroves.

Spatial variability of soil bulk density and its controlling factors in an agricultural intensive area of Chengdu Plain, Southwest China

Soil bulk density is a basic but important physic soil property related to soil porosity, soil moisture and hydraulic conductivity, which is crucial to soil quality assessment and land use management. In this study, we evaluated the spatial variability of soil bulk density in the 0–20, 20–40, 40–60 and 60–100 cm layers as well as its affecting factors in Southwest China's agricultural intensive area. Results indicated the mean value of surface soil bulk density (0–20 cm) was 1.26 g cm−3, significantly lower than that of subsoil (20–100 cm). No statistical difference existed among the subsoil with a mean soil bulk density of 1.54 g cm−3. Spatially, soil bulk density played a similar spatial pattern in soil profile, whereas obvious differences were found in details. The nugget effects for soil bulk density in the 0–20 and 20–40 cm layers were 27.22 and 27.02% while 12.06 and 3.46% in the 40–60 and 60–100 cm layers, respectively, gradually decreasing in the soil profile, indicating that the spatial variability of soil bulk density above 40 cm was affected by structural and random factors while dominated by structural factors under 40 cm. Soil organic matter was the controlling factor on the spatial variability of soil bulk density in each layer. Land use and elevation were another two dominated factor controlling the spatial variability of soil bulk density in the 0–20 and 40–60 cm layers, respectively. Soil genus was one of the dominated factors controlling the spatial variability of soil bulk below 40 cm.

Predicting Spatial Variability of Soil Bulk Density in Gravel-Mulched Fields

AbstractInformation about soil bulk density (SBD) is important for soil-water conservation, carbon content, and nutrient reserves. The authors studied the spatial variability of SBD in gravel-mulch...

Soil Physical Quality Indicators and Refinement of the Evaluation Method through the Srelative

This study aimed to verify the efficiency of indicators of measure of physical attributes’ alterations and to refine the Srelative determination method in order to increase its sensitivity to soil physical alterations. Soils under Ficus carica L. cultivation (with 0, 20, 40 and 60% of liquid bovine biofertilizer in the irrigation depth) and under forest were used. Parameters evaluated included soil granulometry, soil bulk and particle density, soil water retention curve (SWRC), porosity and the indices S and Srelative. The experimental design was completely randomized with four replicates. For Srelative refinement, with the SWRC containing only textural porosity, the soil was dispersed in water and with the addition of 1 N sodium hydroxide (with and without removal of sodium through washing). An ANOVA was performed for 0, 20, 40 and 60% of biofertilizer in 0-10, 10-20 and 20-30 layers; Dunnett test was used to compare the mean values of S-index and Srelative-index. With respect to four methods to obtain the Srelative-index the means were compared by Tukey test. Tests of line parallelism and intercept were performed for the regressions between each of the soil physical variables and Srelative-index obtained. It was found that S and Srelative indices were sensitive to soil physical alterations caused by the application of the biofertilizer; Srelative-index was sensitive to variation in soil bulk density and total porosity and the Srelative-index obtained from the method of soil dispersion in water is more sensitive to soil physical alterations in comparison to Srelative-index obtained through ADFE.

Temporal Variation of Hydro‐Physical Properties of Paddy Clay Soil under Different Rice‐Based Cropping Systems

AbstractSpatial variability of hydro‐physical properties has long been observed, whereas temporal variation is much less documented and considered in studies and applications, particularly of paddy clay soils under different cropping systems. The objective of this study was therefore to assess the seasonal‐ and inter‐seasonal variation of selected hydro‐physical properties of a paddy clay soil under different rice‐based cropping systems with contrasting tillage. In a long‐term experiment, plots were arranged in a randomized complete block design with four treatments and four replications: (i) rice–rice–rice; (ii) rice–maize–rice; (iii) rice–mung bean–rice; and (iv) rice–mung bean–maize. Soil samples were collected at three depths (0–10, 10–20 and 20–30 cm) at three times during two cropping seasons, i.e., 15 days after soil preparation (DASP), 45 DASP and 90 DASP during the winter–spring and spring–summer seasons. Results show that temporal variability of soil bulk density, macro‐porosity (MacP) and matrix‐porosity within both seasons and between seasons was limited for cropping systems with upland crop rotations, whereas within season variation was significant for rice monoculture system. Observed variation in bulk density, matrix‐porosity and MacP was mainly associated with cropping system and soil depth. Field saturated hydraulic conductivity of topsoil showed great temporal variability, both seasonal and inter‐seasonal, in correspondence with MacP (r = 0·58). These results highlight the need of depth differentiated soil sampling and time consideration when evaluating management practices on soil physical properties and modeling the hydrological behavior of paddy soil. Copyright © 2017 John Wiley & Sons, Ltd.

Variation in soil properties under different land use types managed by smallholder farmers along the toposequence in southern Ethiopia

Understanding soil properties under different land use types along toposequences is vital in determining the types of soil management practices that could be implemented by smallholder farmers for improving the soil health as well as soil productivity. It is also important in addressing the issues of agricultural sustainability. With the objectives of investigating variation in soil properties under different land use types managed by smallholder farmers along the toposequences, three land use types: agroforestry land (AG), cultivated land (CL) and grazing land (GL) under three slope categories (upper, middle and lower slope) were selected in southern Ethiopia, Deko watershed. A total of 108 composite soil samples [3 treatments (land use types)−3 replications−3 slope categories (upper, middle and lower)−4 soil depth layers: 0–20cm, 20–40cm, 40–60cm and >60cm] were collected for laboratory analyses. In addition, undisturbed soil samples were taken using core sampler from each soil depth for the determination of soil bulk density. To infer the biological properties of the soils naked eye soil macro-fauna (NEMF) was counted. The results showed that among the soil properties sand (p<0.001), clay (p=0.002), soil bulk density (p<0.001), soil reactio (pH, p<0.001), Electrical conductivity (EC, p<0.001), Soil organic carbon (SOC %, p<0.001), Total nitrogen (TN %, p=0.001) and NEMF (p<0.001) have shown a significant variation among the land use types while sand (p=0.027), silt (p=0.001), clay (p<0.001), SOC (p<0.001) and TN (p=0.002) exhibiting significant variation among the slope categories. Similarly, variation of soil bulk density (p<0.001), soil pH (p<0.001), SOC (p<0.001), TN (p=0.002) and NNEMF (p<0.001) were also statistically significant along the soil depth. Clay was the dominant soil textural fraction showing an increasing trend along the toposequence. Agroforestry land use type has the higher SOC, TN, pH values and EC while cultivated land use type having relatively low amount of SOC, TN, pH and EC. The lower values on cultivated land use types were due to the effects of continuous tillage practices by the smallholder farmers in the area. Slope had minimum effect on soil pH, EC, soil bulk density and the number of observable macro-faunas in the area. Moreover, SOC and TN were increased down the slope on the cultivated land use types of the area. The role of erosion is magnificent in removing SOC and TN from upper slope to lower slope as the area is more vulnerable to erosion due rugged topography. Thus, applying soil and water conservation measures on cultivated land use types play a vital role in minimizing the removal of soils down the slope.

Sensing of soil bulk density for more accurate carbon accounting

SummaryMeasurements of soil bulk density can aid our understanding of soil functions and the effects of land use and climate change on soil organic carbon (C) stocks. Current methods for measuring bulk density are laborious and expensive, subject to errors and complicated by the need to measure below the soil surface. These shortcomings are emphasized when there is need to characterize the spatial (lateral and vertical) and temporal variation of soil bulk density and related properties. We developed a technique that combines gamma‐ray attenuation and visible–near infrared (vis–NIR) spectroscopy to measure ex situ the bulk density of 1‐m soil cores that are sampled freshly, wet and under field conditions. We found that the accuracy of the sensor measurements was similar to that of the conventional single‐ring method, but sensing is rapid, inexpensive, non‐destructive and practical. Sensing can be used to measure many soil cores efficiently at fine depth resolutions (e.g. every 2 cm along the core), thereby allowing effective characterization of spatial variation in both lateral and vertical directions. The measurements can be made in the field, on wet soil cores, which reduces the costs and errors associated with transport, handling, oven‐drying and laboratory measurements. We show that sensing of bulk density can be used to measure organic C stocks on either a fixed‐depth (FD) or cumulative soil mass (CSM) basis. Our sensing approach to measure bulk density meets all the requirements for inclusion in a well‐designed soil organic C accounting system; it provides accurate and verifiable data on the spatial variation of soil bulk density so that changes in C stocks might be attributed more accurately to changes in either bulk density or in C content.Highlights Proximal soil sensors enable practical, accurate, verifiable and inexpensive measurements of bulk density for C accounting. We describe a new sensing approach for measuring soil bulk density. Measurements are rapid, accurate, verifiable and can be made on wet soil under field conditions and to depth. Sensing enables measurements of C stocks using both fixed‐depth or cumulative soil mass.

Warm‐season Grazing Benefits Species Diversity Conservation and Topsoil Nutrient Sequestration in Alpine Meadow

AbstractSeasonal grazing is one way of the moderate grazing regimes, but little information is available on compared study of seasonal grazing in alpine meadow. We studied the aboveground and belowground properties among warm‐seasonal grazing meadows and cold‐seasonal grazing meadows on the Qinghai–Tibetan Plateau. Results showed that the warm‐seasonal grazing increased forb functional group proportion, plant density and evenness index but decreased root biomass, plant height and graminoid functional group proportions. Grazing seasons affected variation in soil bulk density, soil water content, pH and soil nutrient content, and the variations caused the various of soil carbon and nitrogen density. The highest values of soil carbon and nitrogen contents and densities in the warm‐season grazing meadow occurred at the top 10‐cm soil, while the highest values in the cold‐season grazing meadow occurred at the depth of 30‐ to 50‐cm soil. Our results indicated that the warm‐season grazing is suitable for the species diversity conservation and the nutrient sequestration at the topsoil. However, the cold‐season grazing is suitable for the nutrient sequestration at the deep soil. This study implied that the warm‐season and cold‐season grazing might be exchanged regularly to practice continuous carbon and nitrogen sequestration. Periodic cold‐season and warm‐season grazing would be the suitable grazing regime to keep alpine meadow sustainability. Copyright © 2016 John Wiley &amp; Sons, Ltd.