Content In Topsoil Research Articles

Natural and Anthropogenic Factors Affecting the Development of Two Highland Agricultural Soils of Bukidnon, Philippines

This research was conducted in two highland areas of Bukidnon, Philippines: Miarayon, a sub-catchment of the upper Cagayan de Oro River; and Bendum, a sub-catchment of the upper Pulangui River. Due to their pyroclastic parent rock materials, soils in the upper Cagayan de Oro are classified as Andic Cambisol in open and convex positions, and Andic Umbrisol in concave and depressed positions. Soils in the upper Pulangui are classified as Pisoplinthic Acrisol, Ferralic Nitisol, and Acric Nitisol in areas with ultramafic rock parent materials, and Haplic Cambisol with pyroclastic deposits. Element contents in rocks were congruent to the total soil element content analysis results except for the total calcium which was higher in Miarayon. This is attributed to the parent rocks and soil management. Total magnesium and iron were highlighted in upper Pulangui soils because of their ultramafic rock parent materials. Soil management practices and length of cultivation were identified as anthropogenic factors affecting soil development. The constant application of organic fertilizers from chicken manure had caused the build-up of organic carbon and calcium in the topsoil of Miarayon soils. The differences in total organic carbon, total nitrogen, and potassium were highly significant, particularly in soil pH and total calcium between two sites in Miarayon. In Bendum, traces of phosphate fertilizers and lime application were evidenced by the relatively higher phosphorus and calcium content in topsoil. Tillage influenced the water conductivity in soils. Organic matter content increased the water-holding capacities of soil.

Habitat suitability evaluation of invasive plant species Datura stramonium in Liaoning Province: Based on Biomod2 combination model.

Datura stramonium, as a major invasive plant in Liaoning Province, is difficult to be removed after its successful invasion, and is a great threat to ecological environment and biodiversity. To evaluate the habitat suitabi-lity of D. stramonium, we collected its geographic distribution data in Liaoning Province through field investigation and database query, and using the Biomod2 combination model, and investigated its potential and suitable distribution areas and main influencing environmental variables at present and under future climate change scenarios, respectively. The results showed that the combined model which composed of GLM (generalized linear model), GBM (generalized boosting regression model), RF (random forest model), and MaxEnt (maximum entropy model) had a good performance. By classifying the habitat suitability of D. stramonium into four categories: high-, medium-, low- and un-suitable habitats, we found that the high-suitable habitats were generally distributed in the northwest and south of Liaoning Province, with an area of about 3.81×104 km2, accounting for 25.8% of the total area. The medium-suitable habitats were mostly distributed in the northwest and central parts of Liaoning Province, with an area of about 4.19×104 km2, accounting for 28.3% of the total area. Slope and clay content of topsoil (0-30 cm) were the two main variables explaining the habitat suitability of D. stramonium, and the total suitability of D. stramonium first increased and then decreased with the increasing slope and clay content of topsoil in this region. Under future climate change scenarios, the total suitability of D. stramonium showed an expanding trend, and its suitability would be obviously increased in Jinzhou, Panjin, Huludao, and Dandong.

Modeling Topsoil Phosphorus—From Observation-Based Statistical Approach to Land-Use and Soil-Based High-Resolution Mapping

Phosphorus (P) is a macronutrient that often limits the productivity and growth of terrestrial ecosystems, but it is also one of the main causes of eutrophication in aquatic systems at both local and global levels. P content in soils can vary largely, but usually, only a small fraction is plant-available or in an organic form for biological utilization because it is bound in incompletely weathered mineral particles or adsorbed on mineral surfaces. Furthermore, in agricultural ecosystems, plant-available P content in topsoil is mainly controlled by fertilization and land management. To understand, model, and predict P dynamics at the landscape level, the availability of detailed observation-based P data is extremely valuable. We used more than 388,000 topsoil plant-available P samples from the period 2005 to 2021 to study spatial and temporal variability and land-use effect on soil P. We developed a mapping approach based on existing databases of soil, land-use, and fragmentary soil P measurements by land-use classes to provide spatially explicit high-resolution estimates of topsoil P at the national level. The modeled spatially detailed (1:10,000 scale) GIS dataset of topsoil P is useful for precision farming to optimize nutrient application and to increase productivity; it can also be used as input for biogeochemical models and to assess P load in inland waters and sea.

Microbial gradual shifts during the process of species replacement in Taihang Mountain.

Understanding microbial gradual shifts along species replacement can help elucidate the mechanisms driving secondary succession, and predict microbial responses to changing environments. However, how climate-induced species replacement alters microbial processes, and whether microbial shifts follow predictable assembly trajectories remain unclear. Using space-for-time substitution approach, we studied shifts in bacterial and fungal communities in the succession from Leptodermis oblonga to Vitex negundo var. heterophylla shrubland in Taihang Mountain. Species replacement, induced by climate related environmental change, significantly increased the above-ground biomass of shrublands, and TP and TK contents in topsoil. The succession from L. oblonga to V. negundo var. heterophylla communities resulted in the gradually replacement of cold-tolerant microbes with warm-affinity ones, and alterations of microbial communities involved in soil biogeochemical processes. Soil and plant variables, such as above-ground biomass, soil pH, total phosphorus, and total potassium, well explained the variations in microbial communities, indicating that the coordinated changes in plant communities and soil properties during secondary succession caused accompanied shifts in microbial diversity and composition.

Mapping Topsoil Total Nitrogen Using Random Forest and Modified Regression Kriging in Agricultural Areas of Central China

Accurate understanding of spatial distribution and variability of soil total nitrogen (TN) is critical for the site-specific nitrogen management. Based on 4337 newly obtained soil observations and 33 covariates, this study applied the random forest (RF) algorithm and modified regression kriging (RF combined with residual kriging: RFK, hereafter) model to spatially predict and map topsoil TN content in agricultural areas of Henan Province, central China. According to the RFK prediction, topsoil TN content ranged from 0.52 to 1.81 g kg-1, and the farmland with the topsoil TN contents of 1.00-1.23 g kg-1 and 0.80-1.23 g kg-1 accounted for 48.2% and 81.2% of the total farmland area, respectively. Spatially, the topsoil TN in the study area was generally higher in the west and lower in the east. By using the Boruta variable selection algorithm, soil organic matter (SOM) and available potassium contents in topsoil, nitrogen deposition, average annual precipitation, livestock discharges, and topsoil pH were identified as the main factors driving the spatial distribution and variation of soil TN in the study area. The RF and RFK models used showed the expected performance and achieved acceptable TN prediction accuracy. In comparison, RFK performed slightly better than the RF model. The R2 and RMSE achieved by the RFK model were improved by 4.5% and 4.5%, respectively, compared with that by the RF model. However, the results suggest that RFK was inferior to the RF model in quantifying prediction uncertainty and thus may have a slight disadvantage in model reliability.

Differences in available phosphorus in temperate and subtropical forest soils

Soil P availability is influenced by the acid phosphomonoesterase (ACP) activity, microbial biomass P (MBP), pH, and other soil properties. To date, there is no clear understanding about how the enzyme catalytic efficiency (Vmax/Km) and the abundance of the phoC and phoD genes that encode ACP and alkaline phosphomonoesterase (ALP) influence the available P contents at different depths in temperate and subtropical forest soils. We investigated how the soil enzyme kinetic parameters, phoC and phoD gene abundance, pH, total P contents, and other soil properties influenced the P availability in soils from a temperate forest (ChangBai Mountain) and a subtropical forest (QianYanZhou Plantation). The results showed that the DNA contents and the ACP and ALP activities were positively correlated with the available P contents in the temperate forest soil. The phoC and phoD gene abundance and the ALP activity were positively correlated with the available P contents in the subtropical forest soil. The ACP-Vmax/Km and DNA contents were positively correlated with the available P contents in topsoil (0–10 cm). The total P contents, pH, MBP, and ACP-Vmax/Km in subsoil (10–30 cm) were positively correlated with the available P contents. A structural equation model showed that DNA content had the greatest effect on the soil available P in temperate forest soil, and phoC and phoD gene abundance had the greatest effect on the soil available P in subtropical forest soil. The mechanism of H+ dissolution affected the P availability through low pH in the topsoil and weathering in the subsoil. Overall, these findings provided an improved understanding about how the catalytic efficiencies of ACP and ALP and the phoC and phoD gene abundance, influenced the P availability in temperate and subtropical forest soils at different depths. We also gained insights into how the P availability was affected by H+ dissolution and the parent material in topsoil and subsoil, respectively.

PHYTOACCUMULATION OF MERCURY INTO VASCULAR PLANTS AT AREA OF ABANDONED Hg-ORE DEPOSIT MALACHOV (CENTRAL SLOVAKIA)

The study is focused on Hg content in topsoil of dump-field Veľká Studňa, nearby former mining area Malachov and its accumulation by selected plants, which consisted of the local representatives of grass, herb, and wood species. The study area was divided into several parcels, based on physiognomic features of plant communities. In the order to predict the Hg distribution for the whole study area, the interpolation methods were used in GIS. The plant material consists of 4 plant species: Calamagrostis epigejos, Lotus corniculatus, Leontodon hispidus and Picea abies. The samples were dried, grained, dissolved in HNO3 and HCl solution and consequently measured by inductively coupled plasma mass-spectrometry (ICP-MS) for Hg content. The results show a mass contamination of the dump top-soil horizon by mercury. The values in soil variable from 16 to 910 mg kg-1. The bioaccumulation potential of some investigated plant species can be considered as significant as well. The highest concentration of Hg was found in Picea abies ─ 24 mg kg-1. With the regard to presented data, the dump-field could be assigned as the risk enclave for the local environment and therefore its study is demanding. Applying proper techniques for investigations of bioavailable forms of mercury in the topsoil samples should be also considered.

Soil Moisture Retrieval from Multi-GNSS Reflectometry on FY-3E GNOS-II by Land Cover Classification

The reflected GNSS signals at the L-band is significantly advantageous in soil moisture monitoring as they are sensitive to the dielectric properties determined by the volumetric water content of topsoil, and they can penetrate vegetation, except in very dense forests. The Global Navigation satellite system Occultation Sounder (GNOS-II) with a reflectometry technique onboard the Fengyun-3E (FY-3E) satellite, launched on 5 July 2021, is the first mission that can receive reflected Global Navigation Satellite System (GNSS) signals from GPS, BeiDou and Galileo systems. This paper presents the soil moisture retrieval results from the FY-3E GNOS-II mission using 16 months of data. In this study, the reflectivity observations from different GNSS systems were firstly intercalibrated with some differences analyzed. Observations were also corrected by considering vegetation attenuation for 16 different land cover classifications. Finally, an empirical model was constructed for volumetric soil moisture (VSM) estimation, where the reflectivity of GNOS-II was linearly related to the SMAP reference soil moisture for each 36 km ease grid. The overall root-mean-square error of the retrieved soil moisture is 0.049 compared with the SMAP product, and 0.054 compared with the in situ data. The results of the three GNSS systems show similar levels of accuracy. This paper, for the first time, demonstrates the feasibility of global soil moisture retrieval using multiple GNSS signals.

Geochemical characteristics of soil selenium and evaluation of selenium-rich land resources in Guiyang area

Selenium concentration in soil is of great importance for the production of selenium-rich crops. In this article, we studied the geochemical characteristics of soil selenium and evaluated selenium-rich land resources in the Guiyang city area using results from a Guizhou multi-purpose regional geochemical survey. The results indicate that 1) the selenium content in topsoil in the Guiyang area ranges from 0.11 to 4.12 mg kg−1, with an average value of 0.70 mg kg−1, which is 2.4 times and 3.5 times the national and world soil background values, respectively, while the selenium content in deep soil ranges from 0.11 to 4.10 mg kg−1, with an average value of 0.42 mg kg−1, which is 1.4 and 2.1 times the national and world soil background values, respectively; in the vertical profile, the selenium content in soil decreases with the increase in soil depth. 2) The main factors affecting the distribution of selenium in soil include soil parent material, soil physical and chemical properties, and other components, such as soil type and land use, among which the soil parent material (rock) plays a decisive role. The selenium in soil mainly comes from the soil parent rock, increasing accordingly with the increase of the selenium background value of the parent rock; the physical and chemical properties of the soil and other components impose certain influences on the selenium content. Selenium presents a significant linear positive correlation with sulfur and organic carbon, while it has a negative correlation with the pH value; there is no significant difference in the selenium content in different soil types, following the distribution order of paddy soil >yellow soil> skeletal soil> lime soil> purple soil; land use has a certain effect on selenium in soil, following the distribution order of garden land > construction land > grassland > farmland > rocky hills > forest land. 3) The area of selenium-enriched soil in the study region is 11,408 km2, with 91.76% of selenium-enriched soil and 8.24% of general soil or extremely little excess-selenium soil. Therefore, the vast majority of soil in Guiyang is selenium-enriched. The city has large and abundant selenium-enriched areas, which are domestically and internationally rare and provides particularly favorable resource conditions for developing selenium-enriched efficient mountain agriculture to expedite rural revitalization.

Microbial activity and hard red spring wheat growth improvement following biostimulant application

AbstractReclamation of oil and gas disturbed soils is challenging due to diminished function (i.e., soil physical, chemical, and biological properties) from the loss of soil organic carbon (SOC) and potential mixing of topsoil and subsoil. Biostimulants are agro‐products applied to soil to improve SOC formation, microbial nutrient cycling, and crop yields, suggesting their potential use in reclaiming oil and gas disturbed soils. However, studies on the ability of biostimulants to enhance reclamation in disturbed soils are limited. Therefore, research was conducted to determine if biological properties were affected by biostimulant products in soil collected from an active pipeline installation project. The study was conducted in a greenhouse using pots consisting of the following soil treatments: TS100 (100% topsoil), TS50 (1:1 by‐weight subsoil/topsoil), TS25 (3:1 subsoil/topsoil), TS12.5 (7:1 subsoil/topsoil), and TS0 (100% subsoil). Blended soil either received a liquid inoculant or biotic mulch biostimulant and were planted with hard red spring wheat (Triticum aestivum) later on. Soil biological properties were generally influenced by topsoil concentration where TS50 consistently produced similar results to TS100, however, nitrogen (N) and phosphorus (P) were also influenced by biostimulant treatment. Additionally, wheat biomass was significantly greater in the liquid treatment, whereas the biotic mulch stimulated greater microbial abundance and activity. Overall, increased topsoil improved biological recovery in the short term, and the addition of biostimulants in blended soils can also enhance recovery regardless of topsoil content. However, it is unclear whether the recovery is sustained into the long‐term without additional biostimulant application.

Особенности проявления эрозии в пределах овражно-балочного водосбора

Purpose: to determine patterns of formation of hydrographic network elements depending on the melt-and rainwater runoff and soil losses. Materials and methods. The studies were carried out in the upper reaches of the Bolshoy Log gully system, which is a part of the land use of the experimental farm “Polevoy” of the Federal Rostov Agrarian Research Center, with an area of 2070 hectares, of which more than 70 % is arable land. Soils are ordinary chernozems of varying degrees of erosion. The standard methods of research and the method of pins were used on runoff plots. Results. Within the catchment area, the amount of runoff and hydraulic indicators of water courses are greatly influenced by the agricultural background and the soil surface condition from which meltwater flows, and the intensity of erosion processes is influenced by the depth of soil freezing, the moisture content of topsoil, water storage in snow, snowmelt intensity. The water sprays are concentrated along the gullies, where the soil is washed out over time, and they pass into the category of hollows, then into ravines and gullies, forming a hydrographic network in the gully-ravine catchment area. The most intensive meltwater runoff was observed over the years: in 1988 – 33.8 mm, 2003 – 63.9 mm, 2006 – 24.6 mm, 2014 – 14.3 mm, 2017 – 19.3 mm, 2023 – 10–14 mm. In the variants with reclamation protective forest plantations and hydraulic structures, the runoff was 5–12 mm less than in the control and it retained in the forest belt. The mathematical data analysis made it possible to determine the relationship between the runoff rate and soil loss in the gully-ravine catchment, depending on the distance from the watershed. Conclusions. On the gully-ravine catchment, the sheet wash smoothly turns into a linear one and forms hollows and valleys. The final link of the catchment area are ravines and gullies. During the peak periods of meltwaters, the water flow velocity on flat sections of the slope is 0.33–0.46 m/s, and along the hollows – 0.57–0.83 m/s.

Vanadium Contamination in Soil and Atmospheric Deposition in Albania

By examining and evaluating the vanadium content in topsoil and moss samples, this study sought to better understand vanadium contamination in soil and atmospheric deposition. In the research area, Hypnium cupressiforme sps. moss is used. According to different distribution patterns and the lack of a link between vanadium in moss and soil samples studied by correlation analysis, no interactions between substrate soil and moss samples were investigated. Maximum vanadium concentrations (13.2mg/kg and 250mg/kg, respectively) were found in both moss and soil samples near the Cu mineral-rich Gjegjan area. Using lithium-normalized data on vanadium, the effect of anthropogenic activity on the vanadium in moss and soil samples is examined. There were no relationships between concentration and normalized data in moss and soil samples, showing the simultaneous effects of natural and anthropogenic sources of vanadium in the research area. Country-specific trends revealed no change for vanadium since 2010 in Albania.

Exploring the safe utilization strategy of calcareous agricultural land irrigated with wastewater for over 50 years

The trace element (TE) contamination of farmland caused by wastewater irrigation threatens food security and food safety. We selected a typical calcareous soil area in western China that has been irrigated with wastewater for >50 years to explore safe use strategies for flax farmland contaminated by cadmium (Cd) and arsenic (As). We found that Cd and As were mainly accumulated in flax roots rather than seeds. However, regardless of the type of TE and acceptor, direct ingestion of the flaxseed would seriously endanger human health (hazard quotient >1). According to the results of redundancy analysis and Pearson correlation analysis, the concentration of Cd and As in flaxseed depended on the concentration of soil total TE, Olsen phosphorus, dissolved organic carbon, soil organic matter, and active calcium carbonate (CaCO3). This was largely because the pH and total CaCO3 content in topsoil of flax farmland decreased by 1.05 units and 37 %, respectively, compared with their background levels before wastewater irrigation. Interestingly, after pressing, Cd and As in flaxseed transferred to flaxseed oil were 3.87–10.55 % and 17.21–30.48 %, respectively, which led to an acceptable risk of adults and children (hazard quotient <1) consuming flaxseed oil. Our results suggest that with the production of flaxseed oil as the goal, the long-term wastewater-irrigated calcareous land can be safely utilized while obtaining income.

Increased nutrient availability speeds up permafrost development, while goose grazing slows it down in a Canadian High Arctic wetland

Abstract It is of prime importance to understand feedbacks due to the release of carbon (C) stored in permafrost soils (permafrost‐climate feedback) and direct impacts of climatic variations on permafrost dynamics therefore received considerable attention. However, indirect effects of global change, such as the variation in soil nutrient availability and grazing pressure, can alter soil and surface properties of the Arctic tundra, with the potential to modify soil heat transfers toward the permafrost and impact resilience of Arctic ecosystems. We determined the potential of nutrient availability and grazing to alter soil energy balance using a 16‐year split‐plot experiment crossing fertilization at different doses of nitrogen (N) and phosphorus (P) with protection from goose grazing. Moss biomass and some determinants of the surface energy budget (leaf area index (LAI), dead vascular plant biomass and albedo) were quantified and active layer thaw depth repeatedly measured during three growing seasons. We measured soil physical properties and thermal conductivity and used a physical model to link topsoil organic accumulation processes to heat transfer. Fertilization increased LAI and albedo, whereas grazing decreased dead vascular plant biomass and albedo. Fertilization increased organic accumulation at the top of the soil leading to drier and more porous topsoil, whereas grazing increased water content of topsoil. As a result, topsoil thermal conductivity was higher in grazed plots than in ungrazed ones. Including these properties into a simulation model, we showed that, after 16 years, nutrient addition tended to shallow the active layer whereas grazing deepened mean July active layer by 3.3 cm relative to ungrazed subplots. As a result of OM accumulation at the surface, fertilization increased permafrost vertical aggradation rate by almost an order of magnitude (up to 5 mm year−1 instead of 0.7 mm year−1), whereas grazing slowed down permafrost aggradation by reducing surface uprising and deepening thaw depth. Synthesis. We demonstrated that long‐term grazing and N and P addition, through their impact on vegetation and soil properties have the potential to impact permafrost dynamics to the same extent as contemporary temperature increase in High Arctic polygonal wetlands.

Digital soil mapping with adaptive consideration of the applicability of environmental covariates over large areas

• Adaptively considering covariate applicability can improve soil prediction. • Terrain conditions well indicate spatial variation of soil–environment relations. • Prediction uncertainty considers both similarity and covariate applicability. • Parameters for covariate applicability are insensitivity in this large study area. The effective use of environmental covariates in characterizing soil–environment relationships is key to successful digital soil mapping. The typical way to use environmental covariates in digital soil mapping is by selecting diverse environmental covariates considering the overall geographical characteristics of the study area and considering these covariates to have consistent applicability across the whole area. However, this practice ignores the fact that the applicability of each environmental covariate in characterizing soil–environment relationships varies over complex environmental conditions, especially in large areas. This study proposed a method to adaptively consider covariate applicability in large-area digital soil mapping using soil–environment relationships. The applicability of each covariate at each location was quantified from the terrain conditions using the newly designed fuzzy functions in the study. Then the covariate applicability was regarded as the importance weight and integrated into an existing representative method, iPSM (individual predictive soil mapping). The integration was separately performed at the similarity calculation and soil estimation stages of iPSM to generate two new methods: iPSM weighting on the applicability of all covariates (iPSM_WCovar_all), and iPSM weighting on the applicability of the limiting covariate (i.e., the covariate with the minimum similarity between two locations that constrains the overall similarity) (iPSM_WCovar_limit). Experiments were carried in Anhui Province, China. The two new methods were used to predict the soil organic matter content of topsoil and outperformed the original iPSM and random forest kriging methods. The root mean square error of the iPSM_WCovar_all, iPSM_WCovar_limit, iPSM and random forest kriging methods were 8.14, 8.00, 8.88 and 9.65 g/kg, respectively, while the mean absolute error of those methods were 6.48, 6.31, 6.61 and 6.82 g/kg. Both proposed methods outperformed the iPSM method and the other commonly used method, i.e., random forest kriging. Moreover, the performance was stable under different parameter settings. Experimental results indicate that the idea of adaptively considering covariate applicability in digital soil mapping is feasible and effective.

Long-Term Effect of Tamarisk Plantation on Soil Physical Properties and Soil Salt Distribution in Coastal Saline Land

Ecological restoration of coastal land by planting salt-tolerant plants has been widely used to construct vegetation. The aim of this study was to evaluate the changes induced by tamarisk (Tamarix chinensis) shrub on coastal soil physical quality and as well as the corresponding impact on salt distribution in the soil. A field study was conducted on coastal saline land, North China, where tamarisk plantation was established 5-year-old (T-5yr) and 11-year-old (T-11yr), and compared with barren land as control (CK). Quantitative soil physical properties, soil physical quality index, soil salt distribution, and salt leaching were examined. The results indicated that planting tamarisk improved the coastal soil properties at higher degree in topsoil than in deep soil layers. Tamarisk plantation significantly increased soil organic carbon content and pH. It also enhanced the formation of soil large aggregates and porosity; however, reduction soil bulk density and salt content in topsoil were recorded. Soil physical quality index was positively correlated with root weight density of tamarisk, and soil of T-11 yr plantation exhibited the highest soil physical quality index, with promoted soil physical functions of supporting root growth and the resistance to soil degradation. In addition, tamarisk induced soil physical changes which enhanced the salt-leaching in rainy season and contributed to the homogeneous salt distribution in soil profile. Consequently, the ecological benefits of tamarisk vegetation turned coastal saline land into a fertile land by plant–soil interaction and the soil structure improvement, therefore, it prevented the natural soil accumulation by accelerating the salt leaching after tamarisk was restored. This study provides some insights into the mechanism of tamarisk on coastal soil restoration and its regulation of soil salt distribution.

Soil matrix infiltration characteristics in differently aged eucalyptus plantations in a southern subtropical area in China

In this study, we improved the method for measuring soil matrix infiltration by using a surface-positioned double-ring infiltrometer. The soil matrix infiltration processes of four differently aged (1, 3, 5, and 7 years) eucalyptus plantations were measured in situ in a southern subtropical area in China. Soil matrix infiltration characteristics (SMICs), including initial infiltration rate (IIR), stable infiltration rate (SIR), and cumulative infiltration (CI), were calculated using the experimental data of the soil matrix infiltration process. The physical and chemical properties of layered soil (0–60 cm with an interval of 20 cm), including soil textures, buck density (BD), soil organic matter (SOM), and soil water stable macroaggregate (WSMA) closely related to infiltration, were analyzed. Results showed that the IIR (140.33–233.14 mm h−1), SIR (116.24–194.04 mm h−1), and CI (118.42–217.20 mm) decreased with increasing forest age. In addition, the SIR and CI of the 1-year-old eucalyptus plantation were significantly higher than those of the other plantations. The decrease trend of SMICs with forest age was attributed to the soil properties changing in the eucalyptus plantations. The clay content, BD, SOM, and WSMA increased and sand content decreased with increasing forest age, thus inhibiting the SMICs. The results of stepwise regression analysis showed that the sand content of topsoil (0–20 cm) was the main factor affecting IIR, and the clay content of deep subsoil (40–60 cm) was the dominant factor affecting SIR and CI. The in situ soil matrix infiltration measurement in eucalyptus plantations was achieved with the improved method, and the main influencing factors were clarified. The results enhance understanding of soil matrix infiltration and its effect on precipitation redistribution and are helpful in quantifying the water storage capacity of plantation soil.

Spatial heterogeneity and source apportionment of soil metal(loid)s in an abandoned lead/zinc smelter

Metal smelting have brought severe metal(loid)s contamination to the soil. Spatial distribution and pollution source analysis for soil metal(loid)s in an abandoned lead/zinc smelter were studied. The results showed that soil was contaminated heavily with metal(loid)s. The mean of lead (Pb), arsenic (As), cadmium (Cd), mercury (Hg) and antimony (Sb) content in topsoil is 9.7, 8.2, 5.0, 2.3, and 1.2 times higher than the risk screening value for soil contamination of development land of China (GB36600-2018), respectively. Cd is mainly enriched in the 0–6 m depth of site soil while As and Pb mainly deposited in the 0–4 m layer. The spatial distribution of soil metal(loid)s is significantly correlated with the pollution source in the different functional areas of smelter. As, Hg, Sb, Pb and copper (Cu) were mainly distributed in pyrometallurgical area, while Cd, thallium (Tl) and zinc (Zn) was mainly existed in both hydrometallurgical area and raw material storage area. Soil metal(loid)s pollution sources in the abandoned smelter are mainly contributed to the anthropogenic sources, accounting for 84.5%. Specifically, Pb, Tl, As, Hg, Sb and Cu mainly from atmospheric deposition (55.9%), Cd and Zn mainly from surface runoff (28.6%), While nickel (Ni) mainly comes from parent material (15.5%). The results clarified the spatial distribution and their sources in different functional areas of the smelter, providing a new thought for the risk prevention and control of metal(loid)s in polluted site soil.

Impact of Long-term and Intensive Rice Cultivation on Heavy Metal Accumulation in Soil: An Observation from Mae La River Basin, Central Thailand

Intensive rice cultivation relies greatly on chemical fertilizers and pesticides, some of which contain heavy metals as impurities. Application of these agrochemicals can result in heavy metal accumulation in soil. This research discusses the current concentrations and migration pathways of heavy metals (Cu, Pb and Zn) in paddy soil subjected to long-term use of chemical fertilizers and pesticides. The study of soil pH and metal concentrations in 60 surface and subsurface samples from a relatively small river basin revealed that although highly varied, pH values and metal concentrations in topsoil were significantly different from values in subsurface soil. The soil pH as low as 5.4 was observed in topsoil. Although the observed levels in topsoil were in within safe limits according to the Dutch standard, they were significantly elevated above the subsurface concentrations. Evidence on the differences between their concentrations in paddy soil and river sediments suggests that considerable amount of metals in paddy fields have been transported into the river. A detailed study of input inventory, fluxes and migration pathways of these metals in the river basin can provide a better understanding of their mobility and measures that might needed to safeguard aquatic habitats, especially the well-known striped snakehead fish in Mae La River.&#x0D; HIGHLIGHTS&#x0D; &#x0D; Agrochemicals such as chemical fertilizers and pesticides contain heavy metals as impurities&#x0D; Long-term and continuous use of agrochemicals in rice production has resulted in lower pH and higher heavy metal contents in topsoil&#x0D; Low pH in topsoil can enhance metal mobility, suggesting that some of the heavy metals from agrochemical inputs are likely to be transported from paddy fields to their surrounding environments&#x0D; This study demonstrates that the effects of agrochemical use extend beyond agricultural soil. Impact assessment of their application, thus, should cover all major compartments/systems in the basin&#x0D; &#x0D; GRAPHICAL ABSTRACT

Novel Methodology for the Assessment of Organic Carbon Stocks in German Arable Soils

There is currently a significant focus on oil organic carbon, as interest in mitigating climate change by increasing soil carbon stocks is leading to efforts to include this within carbon farming and the trade of CO2 certificates. In addition, soil organic carbon controls many other soil functions, such as soil productivity. However, results from long-term field experiments suggest that an ever-increasing carbon content in soil, at some point, will no longer increase productivity, but will cause environmental risks, especially from excess nitrogen. In Germany, the most widely recognized soil organic matter (SOM) balance method, VDLUFA (Association of German Agricultural Investigation and Research Institutions), addresses soil management only, without a relation to the soil carbon stock. To close this gap, a methodology is developed based on results from European long-term field experiments that allows for an assessment of agricultural management both in terms of the carbon input to soil and the amount of carbon stored in soil. Due to the transformation of carbon stock into carbon flux, it is possible to apply the classification scheme of the VDLUFA balance to the carbon content of topsoils. This provides information to qualify further decisions about fostering carbon accumulation. This was demonstrated on experimental results from Bad Lauchstädt, as well as on data from the German Agricultural Soil Inventory (BZE-LW) for arable soils on a regional scale.