Changes In Soil Bulk Density Research Articles

Monitoring of Soil Bulk Density in Context with Its Small-Scale Spatial Heterogeneity

The main aim of soil monitoring system is to obtain the knowledge of the most current state and development of soil properties according to concrete threats to soil. To determine the significant changes of soil properties in time, it is important to know spatial variability of concrete soil parameter for concrete site. Only those time changes of the soil parameter are significant, which exceed its spatial variability at the site. The main aim of the study has been focused on the evaluation of small-scale site heterogeneity of equilibrium soil bulk density and the integration of impact of this heterogeneity in evaluation of degradation process of soil compaction in time. As site variation coefficients have considerably varied at standard sampling with five repetitions during monitoring period, one-time detail spatial variability mapping of soil bulk density was realized at 17 repetitions on five selected monitoring sites with different soil type, texture and use. This increase in the number of sampling points helped us to specify and stabilize the values of variation coefficients (between minimum and maximum by standard sampling) as well as the extent of confidence intervals. Standard deviations at the chosen monitoring sites moved from 0.039 to 0.118 g·cm-3 in topsoil and from 0.031 to 0.067 g·cm-3 in subsoil and expressed as variation coefficient 2.9% - 9.2% and 2.0% - 4.9%, respectively. The intervals of significant time changes of soil bulk density for the sites and depths were determined on the base of its site confidence interval (95%) and uncertainty rate of its measure methodology. The time changes of bulk density values between single year-to-year sampling were overlapped by this interval of significant changes to obtain significant bulk density changes in time. This method allowed us to distinguish significant time changes in soil bulk density from insignificant ones. The bulk density value changes on the monitoring sites were significant in the range of six to nine years within observed period 2002-2014 in both depths.

Variations in soil organic carbon content with chronosequence, soil depth and aggregate size under shifting cultivation

Shifting cultivation is a globally important form of agriculture covering over 280 million hectares in the tropics, but it has often been blamed for deforestation and forest degradation. In North East India (NEI) it has been practiced for millennia and it is an important element of the cultural identity of indigenous communities. It is often practiced on slopping lands with fragile soils (mostly Acrisols), which are prone to rapid degradation with cultivation. The shortened fallow cycle as practised currently is ecologically unsustainable and economically not viable. This study aimed to quantify (i) changes in soil bulk density, aggregate stability and compaction in relation to chronosequence and soil depth, (ii) changes in the proportion of macro, meso, and micro aggregates and associated soil organic carbon (SOC) content in relation to soil depth and fallow chronosequence, and (iii) determine the minimum fallow length that achieves SOC stocks comparable with adjacent intact forest land. The proportion of soil macro-aggregates and meso-aggregates significantly varied with land-use and soil depth as well as their interactive effects. Across all soil depths, forest land had the highest proportion of macro-aggregates (75.6%), while the currently cultivated land had the least proportion (51.1%). The SOC contents in macro-aggregates increased with fallow age and decreased with soil depth; the highest (1.95%) being in the top 10 cm soil of 20 years old fallows and the lowest (0.39%) in 21–30 cm depth of 5 years old fallows. Multivariate analysis identified bulk density and porosity as the most important variables to discriminate between land use practices. The analysis provided evidence for significant changes in soil compaction, aggregate stability and SOC content with the transition from undisturbed forest to slash-and-burn cultivation and fallow phases. It is concluded that a minimum of 20 years of fallow period is required to achieve SOC content and C stocks comparable with intact forest land.

Effects of biochar amendments on soil water retention characteristics of red soil at south China

Biochar has been extensively used for the improvement of soil water retention. However, the effects of various biochars were not well determined. The objectives of this study were to investigate the effects of three biochars [biochars made from bamboo (Bambusaceae), rice straw (Oryza sativa), and tobacco stem (Nicotiana L.)] on soil physical properties and the water retention characteristics of red soil at southeast China. The air-dried soil samples were mixed with ratios of 2%, 5%, and 10% (w w−1) BC (bamboo biochar), RC (rice straw biochar), and TC (tobacco biochar), respectively, and evaluated for changes in soil bulk density (BD), soil saturated water content, field capacity, capillary porosity and soil hygroscopic coefficient. The results showed that BD decreased significantly with the application of the three types of biochar, total soil porosity and capillary porosity increased with the increase of the biochar ratio. The soil hygroscopic coefficient, wilting moisture capacity, saturated water content, and field capacity were significantly affected by the application of the three types of biochar. Compared with the other two treatments, the BC showed the best effects on soil water characteristics. BC treatments with addition ratios of 2%, 5%, and 10% significantly decreased BD by 6.55%, 18.03%, and 36.07%, respectively. Moreover, saturated water content and field capacity were increased by BC. BC treatments significantly increased the readily available water by 32.65%, 42.49%, and 50.01%, respectively. However, the increased non-readily available water induced by the high ratio of biochar addition was not easily utilized by plants. Our results suggested that the biochar amendment can improve soil structure, decrease soil BD, boost soil porosity and capillary porosity, and increase soil moisture constant, and 2–5% of BC was recommended in the field condition.

Estimating soil water retention for wide ranges of pressure head and bulk density based on a fractional bulk density concept

Soil water retention determines plant water availability and contaminant transport processes in the subsurface environment. However, it is usually difficult to measure soil water retention characteristics. In this study, an analytical model based on a fractional bulk density (FBD) concept was presented for estimating soil water retention curves. The concept allows partitioning of soil pore space according to the relative contribution of certain size fractions of particles to the change in total pore space. The input parameters of the model are particle size distribution (PSD), bulk density, and residual water content at water pressure head of 15,000 cm. The model was tested on 30 sets of water retention data obtained from various types of soils that cover wide ranges of soil texture from clay to sand and soil bulk density from 0.33 g/cm3 to 1.65 g/cm3. Results showed that the FBD model was effective for all soil textures and bulk densities. The estimation was more sensitive to the changes in soil bulk density and residual water content than PSD parameters. The proposed model provides an easy way to evaluate the impacts of soil bulk density on water conservation in soils that are manipulated by mechanical operation.

A Bayesian approach toward the use of qualitative information to inform on-farm decision making: The example of soil compaction

As the development of predictive tools to aid decision making in agriculture increases, it must be acknowledged that the ability to incorporate management decisions as input data is limited. The data is either not recorded, or highly inadequate in terms of the volume, variety or relevance. Some circumstances are further hampered by the lack of benchmark data for comparison, and soil compaction is an example of this. The premise of this work was to take a probability based approach to decision making, utilising both qualitative and quantitative data to provide a probability distribution of risk against decisions made, in the context of grains production systems as an example of an agricultural enterprise. A Bayesian Belief Network (BBN) was constructed for soil compaction risk, as an exemplar. The BBN conditional probability tables for nodes were populated via a combination of biophysical model output (namely SoilFlex for soil stress distribution, and the APSIM package for soil-water and crop parameters) and expert opinion. Input nodes were parameterised with measured soil data, and the risk of soil compaction, given the soil stress at the wheel of a particular vehicle, was provided as the output. Potential effect on yield was subsequently calculated on the basis of percent change in soil bulk density, which was determined using literature based information (expert opinion). The tool broadly estimated yield impacts due to various agricultural traffic scenarios, providing means to highlight the financial consequences of failing to adopt controlled traffic farming management for a particular agricultural enterprise. Of significance, the BBN approach was determined useful for data limiting environments where empirical models struggle, thus providing a pragmatic and novel approach to on farm decision making incorporating management nuance.

Effects of long-term fertiliser regime on soil organic carbon and its labile fractions under double cropping rice system of southern China

ABSTRACT This study was designed to explore changes in soil bulk density, soil organic carbon content, soil organic carbon stock and soil labile organic carbon fractions under 34 years fertilizer regime in the double-cropping rice system of southern China. The experiment including five fertilizer treatments: chemical fertilizer alone (MF), rice straw residue and chemical fertilizer (RF), 30% organic manure and 70% chemical fertilizer (LOM), 60% organic manure and 40% chemical fertilizer (HOM), and without fertilizer input as control (CK). The results showed that soil bulk density in the 0-20 cm soil layer with long-term fertilizer treatments were significantly decreased compared to CK treatment. The soil organic carbon content and stock with RF, LOM and HOM treatments were significantly higher than that of MF and CK treatments. These results confirmed by the soil carbon management index which were significantly increased with RF, LOM and HOM treatments. As a result, combined application of organic manure with chemical fertilizer is a benefit nutrient management for improving soil organic carbon content and stock, soil carbon management index in paddy field of southern China.

Soil Compaction Study Due to 4 Wheel Tractor Track in PTPN II Kulmpang Sugar Cane Plantation

Soil compaction can occur due to repeated tractor trajectories in the tillage process. Changes in soil physical and mechanical properties that occur can be seen with changes in soil bulk density, soil porosity, ground pressure and soil penetration resistance. Soil compaction can cause disruption of plant root growth that will reduce crop production. The purpose of this study was to evaluate changes in soil physical and mechanical properties due to soil compaction caused by repeated tractor trajectories. The study was carried out at 20.05% moisture content, bulk density 1.06 gr / cm3 porosity 53.9% and an average penetration resistance of 1.32 kgf/cm2 (0.13 MPa) with an average tractor ground pressure value of 0.88 kg/cm2 crossing the ground as much as 1-8 times the track. The results showed that the number of tractor trajectories affected the value of bulk density, soil porosity and soil penetration resistance. The increasing number of trajectories, causing an increase in the level of soil density which can be seen by increasing the bulk density value by 1.31gr / cm3, decreasing porosity value by 26.63% while the average penetration resistance increases by 6.88 kgf/cm2 (0.67 MPa).

Effect of biochar on soil properties on the Loess Plateau: Results from field experiments

Soil erosion on the Loess Plateau has been partly controlled, but soil nutrients remain limited throughout the region. Biochar amendments are an efficient method of improving availability of soil nutrients due to their strong adsorptive capacity; however, the effects of biochar amendments on different soil types on the Loess Plateau are not well understood. In this paper, we compared the effects of biochar on soil bulk density, soil organic carbon, and soil nitrogen and phosphorus contents among four soil types on the Loess Plateau. An eight-year field study was conducted in Loessal soil, Dark Loessial soil, Lou soil, and Aeolian sandy soil to investigate changes in soil bulk density and nutrient retention caused by biochar amendment at rates of 0 g/kg (control), 4 g/kg, 8 g/kg and 16 g/kg. Soil organic carbon, total nitrogen, total phosphorus, ammonium nitrogen, and nitrate nitrogen concentrations were measured eight years after biochar application. The biochar amendments significantly increased the soil organic carbon and nitrate nitrogen concentrations in the 0–40 cm layer of all soils. The nitrate nitrogen concentration in the Lou soil and Dark Loessial soil decreased with 4 g/kg biochar application and increased significantly with 8 g/kg and 16 g/kg biochar application, but it did not significantly change in the Loessal soil. In contrast, the nitrate nitrogen concentration in the Aeolian sandy soil decreased with increasing biochar application. Biochar amendments did not significantly influence soil ammonium nitrogen in the 0–20 cm soil layer. However, the soil phosphorus content in the 0–20 cm layer decreased with increasing biochar application, except in the Lou soil and Aeolian sandy soil. These data suggest that biochar-soil interactions on the Loess Plateau have the potential to enhance soil organic carbon and soil nitrogen storage. Moreover, using an appropriate biochar amendment rate according to soil type might help optimise the use of fertilizer on the Loess Plateau.

Consolidation effects on relationships among soil erosion properties and soil physical quality indicators

Consolidation of soil by wetting and drying cycles following tillage rapidly changes the soil physical properties but little is known about how these changes impact soil erosion. The objective of this study was to develop equations to predict soil erodibility (Kd) and critical shear stress (τc) in response to consolidation based upon changes in soil bulk density, saturated hydraulic conductivity, water content, soil penetration strength and surface shear strength following a series of wetting and drying cycles. Air-dried soil from four contrasting soil series was loosely filled into 20 soil cylinders (80 total) to simulate freshly tilled conditions. Soil physical and erosion properties were determined at six time periods (0, 1, 3, 5, 7, 10 days) following daily simulated rainfall of 33 mm h−1 for 1 h and 24 h of drainage/drying. The Jet Test device was used to determine Kd, and τc. The bulk density increased with time due to consolidation following the simulated precipitation events with the largest increase (50–100 % of the total) occurring after the first wetting/drying cycle. The Onstad consolidation model tended to over-predict this initial surface bulk density increase, whereas, an exponential model better represented the surface and depth-averaged bulk density changes for the four soils tested. The shear strength and soil penetration resistance increased dramatically after the first wetting/drying cycle then decreased to a fairly stable value in response to subsequent wetting/drying cycles. The saturated hydraulic conductivity, Ks, decreased so rapidly with accumulated rainfall that an exponential decay model could not match the decrease in Ks as the soil consolidated. The best indicators of erodibility response to consolidation were accumulated rain, surface bulk density, saturated hydraulic conductivity and soil penetration resistance at the 1.3 cm depth. The best indicators of critical shear stress were accumulated rainfall, soil penetration resistance at 1.3 cm and saturated hydraulic conductivity. Because these erosion parameters had intercepts that were dependent upon the soil series, prediction of changes in soil erosion with time following tillage will be soil-specific.

Soil compaction from cut-to-length thinning operations in young redwood forests in northern California

In northern California, United States, a cut-to-length (CTL) system was recently used for the first time to harvest young redwood (Sequoia sempervirens (Lamb. ex D. Don) Endl.) forests. Landowners and public agencies in this region have been concerned about the potential negative impacts of CTL on soils during wet-season harvest operations. To determine soil impacts, we measured changes in soil bulk density (BD) and hydraulic conductivity (HC) after CTL operations in May and August. Soil samples were collected at two locations (track and center) along forwarder trails and at a reference point at three soil depths (0–5, 10–15, and 20–25 cm), and HC samples were collected only at the 0–5 cm soil depth from the same sample points. We found a significant difference in BD between the reference point and track at 0–5 cm, which decreased as soil depth increased. There was a negative correlation between initial BD values and percent increase of BD, supporting the fact that the percent increase in BD was high at the soil surface (25%–30%), but BD did not exceed 1.13 Mg·m–3 at the 0–5 cm depth. However, our HC results were different from what we expected and were not as consistent as the BD results, as the HC data had much higher variability.

Effects of subsoiling stage on summer maize water use efficiency and yield in North China Plains

Aiming at the problems of shallow effective soil layering and low utilization rate of precipitation in the North China Plain. The effects of different subsoiling stages on soil physical properties and water use in winter wheat/summer maize fields were studied. Three kinds of tillage treatments were studied: rotary tillage to a depth of 15 cm in October and no-tillage in June (RT), rotary tillage to a depth of 15 cm in October and subsoiling to 35 cm in June (ST-J), subsoiling to a depth of 35 cm in October and no-tillage in June (ST-O). Changes in soil bulk density and soil compaction were consistent over two seasons. Compared to RT, in the 10–50 cm soil layer, ST-J and ST-O decreased the average soil bulk density by 6.18% and 5.66%, respectively, and the soil compaction in the 10–60 cm layer was reduced by 17.89% and 20.50%. ST was improved soil structure and increased the water content of deep soil. The water use efficiency (WUE) of ST-J and ST-O increased by 4.73% and 14.83%, respectively, and the maize yields by 2.90% and 11.35%, respectively. Considering the WUE and maize yields, it was considered that ST-O is more suitable for tillage in the North China Plain.

Measurements and simulations of compaction effects on the least limiting water range of a no-till Oxisol

No-till has many environmental advantages, but concerns are growing about vehicle-induced topsoil compaction limiting crop growth. We performed a wheeling experiment in a long-term no-till field on an Oxisol with sandy loam texture. The objectives were to measure changes in soil bulk density and corresponding impacts on the least limiting water range (LLWR) due to passage of a maize harvester, and to compare bulk density and LLWR measurements with values simulated using the SoilFlex-LLWR soil compaction model. Soil cores were sampled before and after wheeling, for bulk density measurements and to determine LLWR. Simulated increase in bulk density due to vehicle wheeling agreed well with measurements. However, simulated LLWR and its decrease with compaction were inaccurate. This was ascribed to the pedo-transfer function used in SoilFlex-LLWR to estimate LLWR parameters, which was developed based on data from conventionally tilled sugarcane fields, whereas our site was a long-term no-till soil under a wheat/soybean–maize/black oats rotation. Our measurements showed that LLWR was strongly restricted by soil penetration resistance, which was not captured by the pedo-transfer function incorporated in SoilFlex-LLWR. For better prediction of LLWR, we recommend development of specific pedo-transfer functions or of mechanistic models that can be incorporated in SoilFlex-LLWR.

Comparing the Biogeochemistry of Storm Surge Sediments and Pre-storm Soils in Coastal Wetlands: Hurricane Irma and the Florida Everglades

Hurricanes can alter the rates and trajectories of biogeochemical cycling in coastal wetlands. Defoliation and vegetation death can lead to increased soil temperatures, and storm surge can variously cause erosion or deposition of sediment leading to changes in soil bulk density, nutrient composition, and redox characteristics. The objective of this study was to compare the biogeochemistry of pre-storm soils and a carbonate-rich sediment layer deposited by Hurricane Irma that made landfall in southwest Florida as a category 3 storm in September 2017. We predicted that indicators of biogeochemical activity (e.g., potential soil respiration rates, microbial biomass (MBC), and extracellular enzyme activities) would be lower in the storm sediment layer because of its lower organic matter content relative to pre-storm soils. There were few differences between the storm sediment and pre-storm soils at two of the sites closest to the Gulf of Mexico (GOM). This suggests that marine deposition regularly influences soil formation at these sites and is not something that occurs only during hurricanes. At a third site, 8 km from the GOM, the pre-storm soils had much greater concentrations of organic matter, total N, total P, MBC, and higher potential respiration rates than the storm layer. At this same site, CO2 fluxes from intact soil cores containing a layer of storm sediment were 30% lower than those without it. This suggests that sediment deposition from storm surge has the potential to preserve historically sequestered carbon in coastal soils through reduced respiratory losses.

沙质草地营造樟子松林后土壤容重的变化及其影响因子

PDF HTML阅读 XML下载 导出引用 引用提醒 沙质草地营造樟子松林后土壤容重的变化及其影响因子 DOI: 10.5846/stxb201808161750 作者: 作者单位: 辽宁工程技术大学,辽宁工程技术大学,辽宁工程技术大学,辽宁工程技术大学,辽宁工程技术大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金面上项目（31570709） Changes in soil bulk density and its influencing factors after sandy grassland afforestation with Pinus sylvestris var. mongolica Author: Affiliation: Liaoning Technical University,Liaoning Technical University,Liaoning Technical University,Liaoning Technical University,Liaoning Technical University Fund Project: The National Natural Science Foundation of China (General Program, Key Program, Major Research Plan) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:采用野外调查和室内试验相结合，以辽宁省章古台地区不同生长阶段（包括幼龄林、中龄林、成熟林和过熟林）的20块樟子松人工固沙林样地（以临近的7块天然草地为对照）为研究对象，研究了沙质草地营造樟子松人工林后不同生长阶段0-100 cm土层土壤容重的变化及其影响因子。结果表明：天然沙质草地营造樟子松人工固沙林后，不同生长阶段樟子松林在0-10 cm土层土壤容重变化的变异系数为78%，其他土层变异系数范围为1.08%-4.35%。随着樟子松人工林林龄的增加，土壤容重变化量在0-20 cm和60-100 cm层逐渐降低，在20-60 cm层先降低，到37年左右后逐渐升高，过熟林较成熟林显著增大。林龄对不同土层容重变化的决定系数由大到小依次为40-60、60-80、20-40、10-20、0-10、80-100 cm层。土壤容重变化在60-80 cm层与土壤粗颗粒（粒径>0.05 mm）含量、在0-10、20-40 cm和60-80 cm层与土壤全氮含量、在0-10、20-60 cm和80-100 cm层与土壤全磷含量、在20-40 cm和80-100 cm层与土壤全钾含量显著负相关，且土壤全氮和全磷含量对土壤容重的影响效果随土层深度的增加逐渐降低，土壤容重变化在10-20 cm层与土壤含水率、在20-40 cm层与土壤有机碳含量呈显著的正相关。总体上，沙质草地营造樟子松人工林可以改善土壤结构，提高土壤质量，建议采取封育禁牧等营林措施增加樟子松林下枯落物积累，提高土壤养分含量，同时对37年樟子松人工林逐渐进行更新。 Abstract:Using a combination of field surveys and laboratory analysis, in the Zhanggutai area of Liaoning province, 20 forest plantations of Pinus sylvestris var. mongolica in different growth stages (including young forests, mid-aged forests, mature forests, and over-mature forests) and 7 neighboring control grasslands were selected. In this paper, the changes in soil bulk density and its influencing factors were studied in the 0-100 cm soil layer of different growth stages after sandy grassland afforestation with P. sylvestris var. mongolica. The results showed that after sandy grassland afforestation, the variance coefficient of soil bulk density was 78% in the 0-10 cm soil layer and the variance coefficient in other soil layers ranged from 1.08% to 4.35%. As the stand age increased, the magnitude of soil bulk density decreased gradually in 0-20 and 60-100 cm soil layers, however, the magnitude decreased firstly and then increased after 37 years in 20-60 cm soil layers, and the magnitude in over-mature forests was significantly higher than that in mature forests. In different soil layers, the coefficients of determination of stand ages for the magnitude of soil bulk density in decreasing order were 40-60, 60-80, 20-40, 10-20, 0-10, and 80-100 cm soil layers. The coarse-textured soil (particle size>0.05 mm) in the 60-80 cm soil layer; soil total nitrogen content in 0-10, 20-40, and 60-80 cm soil layers; soil total phosphorus content in 0-10, 20-60, and 80-100 cm soil layers; and soil total potassium content in 20-40 and 80-100 cm soil layers were significantly negatively correlated with soil bulk density, and the impact of soil total nitrogen and soil total phosphorus content on soil bulk density changes gradually decreased as the soil layer depth increased. However, soil moisture in the 10-20 cm soil layer and soil organic carbon content in the 20-40 cm soil layer were significantly positively correlated with soil bulk density. On the whole, sandy grassland afforestation with P. sylvestris var. mongolica can improve soil structure and quality. It is suggested that enclosure and grazing prohibition are effective to increase leaf litter accumulation and improve soil nutrient content in P. sylvestris var. mongolica plantations. In addition, 37 year old P. sylvestris var. mongolica plantations need to be regenerated gradually. 参考文献 相似文献 引证文献

The soil structural cost of traffic from heavy machinery in Vertisols

The agricultural industry has a strong and continuing trend for the incorporation of heavy machinery into the farming system, in order to create operational efficiencies. It is therefore important to understand the soil structural cost of such machinery, which was the objective of this work. Using the John Deere 7760 (JD7760) cotton picker (soil surface stress at the rear wheel ≈0.5 MPa), as a case study, seven randomly allocated experimental sites within the Australian cotton industry were investigated for changes in soil bulk density after traffic with the JD7760. The modified Proctor test optimum moisture content (OMC) for compaction was measured, based upon the JD7760 imposed surface stress, and compared to the field results for compaction. Soil water deficits, calculated for the modified Proctor test OMC, were determined and used to discuss the soil structural implications of heavy machinery, as well as threshold soil water content for safe traffic. All sites underwent significant soil compaction within the 0.3 m depth. More than 50% of sites exhibited compaction to the limit of investigation (0.8 m depth), with the remaining sites having significant reduction in spatial heterogeneity of Vertisol cracks and macropores for the same depth. General equations for OMC and plastic limit, based on clay content and OMC, respectively, were developed. These were used to facilitate extrapolation of experimental data to an open-database of 116 Vertisol sites. For these data, it was determined that safe traffic thresholds did not exist above to the lower limit (soil matric potential −1.5 MPa). Implications for soil structural relations and soil-water movement are discussed.

Impact of poplar shelterbelt plantations on surface soil properties in northeastern China

The Three-North Shelterbelt Program in China is one of the largest ecological rehabilitation programs in the world, but its impact on soil properties has not been thoroughly investigated. We collected 144 soil samples from soil depths of 0–20 cm in farmlands and neighbouring shelterbelts in Songnen Plain, northeastern China. The sample plots covered six locations in the study area. The analysis of variance (ANOVA) showed that there were significant location-related differences (P < 0.05) among 9 of 10 parameters, while the land use effects were much weaker and smaller. The pooled data statistics showed that shelterbelt establishment caused a 3.5% decrease in soil bulk density, a 10.6% decrease in soil total phosphorus (P), and a 63.1% increase in available potassium (K). To exclude the location effects, forest–farmland ratios were used to find possible associations to climatic conditions and forest characteristics. The poplar-induced changes in soil bulk density, soil moisture, total K, and total P were closely related to mean annual temperature, while the larger variations in available nutrients could be explained by height, diameter at breast height, and tree density. Our findings can help explain soil changes in poplar shelterbelt plantations in degraded farmland in China, especially in the black-soil region in northeastern China.

Impact of Extensive Grazing on Supporting and Regulating Ecosystem Services of Mountain Soils

Consejo Nacional de Ciencia y Tecnologia A.C. a traves de proyecto Ciencia Basica 219696. Universidad Autonoma del Estado de Mexico; project 3770/2014/CID.

Correction: Developmental morphology of cover crop species exhibit contrasting behaviour to changes in soil bulk density, revealed by X-ray computed tomography.

[This corrects the article DOI: 10.1371/journal.pone.0181872.].

Soil labile organic carbon fractions and soil organic carbon stocks as affected by long-term organic and mineral fertilization regimes in the North China Plain

To improve C sequestration in soils and mitigate climate change, it is essential to understand how nutrient management strategies impact on soil organic carbon (SOC) stocks and labile fractions. This study was designed to explore changes in soil bulk density (BD), SOC concentrations, SOC stocks and soil labile organic C fractions (mineralizableC (Cmin), microbial biomass C (MBC), dissolved organic C (DOC), particulate organic C (POC), light fraction organic C (LFOC) and permanganate oxidizable C (KMnO4-C)) under 26-year fertilization regimes in a wheat-maize rotation system in the North China Plain. Soil from the following six treatments was analyzed: (1) Control with no amendment addition (CK); (2) Standard rate of mineral fertilizer treatment (SMF) reflecting local farmers' practice; (3) Standard rate of organic manure treatment (SMA) with total N input equal to SMF; (4) Half the standard rate of mineral fertilizer plus half the standard rate of organic manure treatment (1/2 SMF+1/2 SMA); (5) Double standard rate of mineral fertilizer treatment (DMF); (6) Double standard rate of organic manure treatment (DMA). Results showed that all long-term fertilization regimes significantly decreased BD in topsoil compared to CK except for SMF, with treatments that included organic manure resulting in the lowest BDs. Treatments that included organic manure had significantly higher SOC concentrations and stocks than mineral or unfertilized treatments. The organic manure treatments also had higher concentrations of non-labile C but at the same time a higher proportion of labile C than the mineral or unfertilized treatments. This was confirmed by the carbon management index (CMI) which was significantly increased by organic manure addition. Control and mineral fertilized treatments had higher efficiencies of C retention (RE) from added inputs (crop residues only). Differences in Cmin, POC and KMnO4-C were affected by differences in MA-C, however, changes in rhizodeposition-C, stubble-C and root-C significantly affected DOC, MBC and LFOC. This study demonstrates that fertilization strategies that include organic manure can increase the pool of stable C in the surface soil layer, while at the same time increasing concentrations and proportions of labile C. Organic manure use can therefore contribute to improved nutrient cycling services and higher soil quality in the North China Plain.

Developmental morphology of cover crop species exhibit contrasting behaviour to changes in soil bulk density, revealed by X-ray computed tomography.

Plant roots growing through soil typically encounter considerable structural heterogeneity, and local variations in soil dry bulk density. The way the in situ architecture of root systems of different species respond to such heterogeneity is poorly understood due to challenges in visualising roots growing in soil. The objective of this study was to visualise and quantify the impact of abrupt changes in soil bulk density on the roots of three cover crop species with contrasting inherent root morphologies, viz. tillage radish (Raphanus sativus), vetch (Vicia sativa) and black oat (Avena strigosa). The species were grown in soil columns containing a two-layer compaction treatment featuring a 1.2 g cm-3 (uncompacted) zone overlaying a 1.4 g cm-3 (compacted) zone. Three-dimensional visualisations of the root architecture were generated via X-ray computed tomography, and an automated root-segmentation imaging algorithm. Three classes of behaviour were manifest as a result of roots encountering the compacted interface, directly related to the species. For radish, there was switch from a single tap-root to multiple perpendicular roots which penetrated the compacted zone, whilst for vetch primary roots were diverted more horizontally with limited lateral growth at less acute angles. Black oat roots penetrated the compacted zone with no apparent deviation. Smaller root volume, surface area and lateral growth were consistently observed in the compacted zone in comparison to the uncompacted zone across all species. The rapid transition in soil bulk density had a large effect on root morphology that differed greatly between species, with major implications for how these cover crops will modify and interact with soil structure.