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Soil Syst., Volume 4, Issue 3 (September 2020) – 21 articles

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Article
Soil Organic Carbon Stabilization: Influence of Tillage on Mineralogical and Chemical Parameters
Soil Syst. 2020, 4(3), 58; https://doi.org/10.3390/soilsystems4030058 - 22 Sep 2020
Cited by 4 | Viewed by 1185
Abstract
The interaction of organic carbon (OC) with clay minerals and amorphous iron and aluminum oxides, especially in the finest soil fractions (<20 μm), represents a good method for its stabilization, and different tillage practices can improve or reduce the persistence of OC in [...] Read more.
The interaction of organic carbon (OC) with clay minerals and amorphous iron and aluminum oxides, especially in the finest soil fractions (<20 μm), represents a good method for its stabilization, and different tillage practices can improve or reduce the persistence of OC in soils. This study investigates the effects of conventional (CT) and no (NT) tillage and soil depth (0–30, 30–60, and 60–90 cm) on the soil organic carbon (SOC) in four soil size fractions and its interactions with clay minerals and amorphous oxides. To identify the mineralogical composition of the four soil size fractions isolated from each soil, the X-ray powder diffraction (XRPD) technique was used with near infrared (NIR) spectroscopy, while the X-ray fluorescence (XRF) technique was used to determine the chemical composition of soil fractions. The higher OC content found in the finest soil fraction is related to its higher content of clay minerals and amorphous oxides. The SOC content is similar among CT and NT treatments as well as the mineralogical composition and the amount of amorphous oxides, suggesting that more than ten years of different tillage did not influence those parameters. Full article
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Review
Selenium and Nano-Selenium Biofortification for Human Health: Opportunities and Challenges
Soil Syst. 2020, 4(3), 57; https://doi.org/10.3390/soilsystems4030057 - 09 Sep 2020
Cited by 15 | Viewed by 1703
Abstract
Selenium is an essential micronutrient required for the health of humans and lower plants, but its importance for higher plants is still being investigated. The biological functions of Se related to human health revolve around its presence in 25 known selenoproteins (e.g., selenocysteine [...] Read more.
Selenium is an essential micronutrient required for the health of humans and lower plants, but its importance for higher plants is still being investigated. The biological functions of Se related to human health revolve around its presence in 25 known selenoproteins (e.g., selenocysteine or the 21st amino acid). Humans may receive their required Se through plant uptake of soil Se, foods enriched in Se, or Se dietary supplements. Selenium nanoparticles (Se-NPs) have been applied to biofortified foods and feeds. Due to low toxicity and high efficiency, Se-NPs are used in applications such as cancer therapy and nano-medicines. Selenium and nano-selenium may be able to support and enhance the productivity of cultivated plants and animals under stressful conditions because they are antimicrobial and anti-carcinogenic agents, with antioxidant capacity and immune-modulatory efficacy. Thus, nano-selenium could be inserted in the feeds of fish and livestock to improvise stress resilience and productivity. This review offers new insights in Se and Se-NPs biofortification for edible plants and farm animals under stressful environments. Further, extensive research on Se-NPs is required to identify possible adverse effects on humans and their cytotoxicity. Full article
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Article
Finding Suitable Transect Spacing and Sampling Designs for Accurate Soil ECa Mapping from EM38-MK2
Soil Syst. 2020, 4(3), 56; https://doi.org/10.3390/soilsystems4030056 - 07 Sep 2020
Cited by 3 | Viewed by 1182
Abstract
Finding an ideal sampling design is a crucial stage in detailed soil mapping to assure reasonable accuracy of resulting soil property maps. This study aimed to evaluate the influence of sampling designs and sample sizes on the quality of soil apparent electrical conductivity [...] Read more.
Finding an ideal sampling design is a crucial stage in detailed soil mapping to assure reasonable accuracy of resulting soil property maps. This study aimed to evaluate the influence of sampling designs and sample sizes on the quality of soil apparent electrical conductivity (ECa) maps from an electromagnetic sensor survey. Twenty-six (26) parallel transects were gathered in a 72-ha plot in Southeastern Brazil. Soil ECa measurements using an on-the-go electromagnetic induction sensor were taken every second using sensor vertical orientation. Two approaches were used to reduce the sample size and simulate kriging interpolations of soil ECa. Firstly, the number of transect lines was reduced by increasing the distance between them; thus, 26 transects with 40 m spacing; 13 with 80 m; 7 with 150 m; and 4 with 300 m. Secondly, random point selection and Douglas-Peucker algorithms were used to derive four reduced datasets by removing 25, 50, 75, and 95% of the points from the ECa survey dataset. Soil ECa was interpolated at 5 m output spatial resolution using ordinary kriging and the four datasets from each simulation (a total of twelve datasets). Map uncertainty was assessed by root mean square error and mean error metrics from 400 random samples previously selected for external map validation. Maps were evaluated on their uncertainty and spatial structure of variation. The transect elimination approach showed that maps produced with transect spacing up to 150 m could preserve the spatial structure of ECa variations. Douglas-Peucker results showed lower nugget values than random point simulations for all selected sample densities, except for a 95% point reduction. The soil ECa maps derived from the 75% reduced dataset (by random sampling or Douglas-Peucker) or from 13 transect lines (80 m spacing) showed reasonable accuracy (RMSE of validation circa 0.7) relative to the map interpolated from all survey points (RMSE of 0.5), suggesting that transect spacing of 80 m and reading intervals greater than one second can be used for improving the efficiency of on-the-go soil ECa surveys. Full article
(This article belongs to the Special Issue Proximal Soil Sensing Applications)
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Article
Investigating the Potential Impact of Louisiana Coastal Restoration on the Trace Metal Geochemistry of Constructed Marshlands
Soil Syst. 2020, 4(3), 55; https://doi.org/10.3390/soilsystems4030055 - 05 Sep 2020
Cited by 1 | Viewed by 1366
Abstract
Coastal restoration through diversion of suspended sediments from the Lower Mississippi River (LMR) into hydrologically isolated marshlands of Mid-Barataria Bay and Mid-Breton Sounds in southern Louisiana has the potential to mobilize lead (Pb), and other trace elements. We investigate the potential impact(s) of [...] Read more.
Coastal restoration through diversion of suspended sediments from the Lower Mississippi River (LMR) into hydrologically isolated marshlands of Mid-Barataria Bay and Mid-Breton Sounds in southern Louisiana has the potential to mobilize lead (Pb), and other trace elements. We investigate the potential impact(s) of the diversion on marsh porewater through analysis of modern riverbank and suspended sediments, compared to sediments from pre-industrial deltaic deposits of LMR. Sequential extraction methods were used to evaluate Pb, cobalt (Co), copper (Cu), nickel (Ni), and zinc (Zn) in the sediments. Our results show that metal contents are higher (e.g., 8- to 10-fold for Pb) in the modern sediments relative to pre-industrial deposits. Also, the reducible fraction, presumably iron/manganese (Fe/Mn) oxides/oxyhydroxides, is the chief reservoir of environmentally available metals. The substantially higher trace metal contents of the modern relative to pre-industrial sediments suggest that the modern sediments contain a sizeable amount of anthropogenic contributions. Furthermore, the concentration of the trace metals in the reducible fraction suggests bioavailability to marsh organisms upon reductive dissolution within the planned, constructed coastal marshes. Still, additional sediment samples from the marshlands during the diversion implementation phase will be necessary to support the preliminary findings in this contribution as it affects coastal marshes and vital local fisheries. Full article
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Article
Reversal of Forest Soil Acidification in the Northeastern United States and Eastern Canada: Site and Soil Factors Contributing to Recovery
Soil Syst. 2020, 4(3), 54; https://doi.org/10.3390/soilsystems4030054 - 27 Aug 2020
Cited by 12 | Viewed by 1305
Abstract
As acidic deposition has decreased across Eastern North America, forest soils at some sites are beginning to show reversal of soil acidification. However, the degree of recovery appears to vary and is not fully explained by deposition declines alone. To assess if other [...] Read more.
As acidic deposition has decreased across Eastern North America, forest soils at some sites are beginning to show reversal of soil acidification. However, the degree of recovery appears to vary and is not fully explained by deposition declines alone. To assess if other site and soil factors can help to explain degree of recovery from acid deposition, soil resampling chemistry data (8- to 24-year time interval) from 23 sites in the United States and Canada, located across 25° longitude from Eastern Maine to Western Ontario, were explored. Site and soil factors included recovery years, sulfate (SO42−) deposition history, SO42− reduction rate, C horizon pH and exchangeable calcium (Ca), O and B horizon pH, base saturation, and exchangeable Ca and aluminum (Al) at the time of the initial sampling. We found that O and B horizons that were initially acidified to a greater degree showed greater recovery and B horizon recovery was further associated with an increase in recovery years and lower initial SO42− deposition. Forest soils that seemingly have low buffering capacity and a reduced potential for recovery have the resilience to recover from the effects of previous high levels of acidic deposition. This suggests, that predictions of where forest soils acidification reversal will occur across the landscape should be refined to acknowledge the importance of upper soil profile horizon chemistry rather than the more traditional approach using only parent material characteristics. Full article
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Article
Adsorption, Desorption and Bioavailability of Tungstate in Mediterranean Soils
Soil Syst. 2020, 4(3), 53; https://doi.org/10.3390/soilsystems4030053 - 22 Aug 2020
Cited by 3 | Viewed by 1033
Abstract
The adsorption and desorption process of the tungstate ion was studied in three soils characteristic of the Mediterranean area, with particularly reference to bioavailability pathways. In the three soils examined, the tungstate adsorption was described by a Langmuir-type equation, while the desorption process [...] Read more.
The adsorption and desorption process of the tungstate ion was studied in three soils characteristic of the Mediterranean area, with particularly reference to bioavailability pathways. In the three soils examined, the tungstate adsorption was described by a Langmuir-type equation, while the desorption process showed that not all the adsorbed tungstate was released, probably due to the formation of different bonds with the adsorbing soil surfaces. The pH was found to be the main soil property that regulates the adsorption/desorption: The maximum adsorption occurred in the soil with the acidic pH, and the maximum desorption in the most basic soil. In addition, the organic matter content played a fundamental role in the adsorption of tungstate by soils, being positively correlated with the maximum of adsorption. These results indicate that the lowest bioavailability should be expected in the acidic soil characterized by the highest adsorption capacity. This is confirmed by the trend of the maximum buffer capacity (MBC) of soils which is inversely related to bioavailability, and was the highest in the acidic soil and the lowest in the most basic soil. Our data could contribute in drafting environmental regulations for tungsten that are currently lacking for Mediterranean soils. Full article
(This article belongs to the Special Issue Sorption Processes in Soils and Sediments)
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Article
Field Proximal Soil Sensor Fusion for Improving High-Resolution Soil Property Maps
Soil Syst. 2020, 4(3), 52; https://doi.org/10.3390/soilsystems4030052 - 21 Aug 2020
Cited by 7 | Viewed by 1184
Abstract
Mapping soil properties, using geostatistical methods in support of precision agriculture and related activities, requires a large number of samples. To reduce soil sampling and measurement time and cost, a combination of field proximal soil sensors was used to predict and map laboratory-measured [...] Read more.
Mapping soil properties, using geostatistical methods in support of precision agriculture and related activities, requires a large number of samples. To reduce soil sampling and measurement time and cost, a combination of field proximal soil sensors was used to predict and map laboratory-measured soil properties in a 3.4-ha pasture field in southeastern Brazil. Sensor soil properties were measured in situ on a 10 × 10-m dense grid (377 samples) using apparent electrical conductivity meters, apparent magnetic susceptibility meter, gamma-ray spectrometer, water content reflectometer, cone penetrometer, and portable X-ray fluorescence spectrometer (pXRF). Soil samples were collected on a 20 × 20-m thin grid (105 samples) and analyzed in the laboratory for organic C, sum of bases, cation exchange capacity, clay content, soil volumetric moisture, and bulk density. Another 25 samples collected throughout the area were also analyzed for the same soil properties and used for independent validation of models and maps. To test whether the combination of sensors enhances soil property predictions, stepwise multiple linear regression (MLR) models of the laboratory soil properties were derived using individual sensor covariate data versus combined sensor data—except for the pXRF data, which were evaluated separately. Then, to test whether a denser grid sample boosted by sensor-based soil property predictions enhances soil property maps, ordinary kriging of the laboratory-measured soil properties from the thin grid was compared to ordinary kriging of the sensor-based predictions from the dense grid, and ordinary cokriging of the laboratory properties aided by sensor covariate data. The combination of multiple soil sensors improved the MLR predictions for all soil properties relative to single sensors. The pXRF data produced the best MLR predictions for organic C content, clay content, and bulk density, standing out as the best single sensor for soil property prediction, whereas the other sensors combined outperformed the pXRF sensor for the sum of bases, cation exchange capacity, and soil volumetric moisture, based on independent validation. Ordinary kriging of sensor-based predictions outperformed the other interpolation approaches for all soil properties, except organic C content, based on validation results. Thus, combining soil sensors, and using sensor-based soil property predictions to increase the sample size and spatial coverage, leads to more detailed and accurate soil property maps. Full article
(This article belongs to the Special Issue Proximal Soil Sensing Applications)
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Article
Speciation of Phosphorus from Suspended Sediment Studied by Bulk and Micro-XANES
Soil Syst. 2020, 4(3), 51; https://doi.org/10.3390/soilsystems4030051 - 18 Aug 2020
Cited by 1 | Viewed by 1018
Abstract
Mobilization, transformation, and bioavailability of fluvial suspended sediment-associated particulate phosphorus (PP) plays a key role in governing the surface water quality of agricultural catchment streams. Knowledge on the molecular P speciation of suspended sediment is valuable in understanding in-stream PP cycling processes. Such [...] Read more.
Mobilization, transformation, and bioavailability of fluvial suspended sediment-associated particulate phosphorus (PP) plays a key role in governing the surface water quality of agricultural catchment streams. Knowledge on the molecular P speciation of suspended sediment is valuable in understanding in-stream PP cycling processes. Such information enables the design of appropriate catchment management strategies in order to protect surface water quality and mitigate eutrophication. In this study, we investigated P speciation associated with fluvial suspended sediments from two geologically contrasting agricultural catchments. Sequential chemical P extractions revealed the operationally defined P fractions for the fluvial suspended sediments, with Tintern Abbey (TA) dominated by redox-sensitive P (PCBD), Al, and Fe oxyhydroxides P (PNaOH) and organic P (POrg) while Ballyboughal (BB) primarily composed of acid soluble P (PDetr), redox-sensitive P (PCBD), and loosely sorbed P (PNH4Cl). The dominant calcareous (Ca) elemental characteristic of BB suspended sediment with some concurrent iron (Fe) influences was confirmed by XRF which is consistent with the catchment soil types. Ca-P sedimentary compounds were not detected using bulk P K-edge XANES, and only P K-edge µ-XANES could confirm their presence in BB sediment. Bulk P K-edge XANES is only capable of probing the average speciation and unable to resolve Ca-P as BB spectra is dominated by organic P, which may suggest the underestimation of this P fraction by sequential chemical P extractions. Notably, µ-XANES of Ca K-edge showed consistent results with P K-edge and soil geochemical characteristics of both catchments where Ca-P bonds were detected, together with calcite in BB, while in TA, Ca-P bonds were detected but mostly as organic complexed Ca. For the TA site, Fe-P is detected using bulk P K-edge, which corresponds with its soil geochemical characteristics and sequential chemical P extraction data. Overall, P concentrations were generally lower in TA, which led to difficulties in Fe-P compound detection using µ-XANES of TA. Overall, our study showed that coupling sequential chemical P extractions with progressively more advanced spectroscopic techniques provided more detailed information on P speciation, which can play a role in mobilization, transformation, and bioavailability of fluvial sediment-associated P. Full article
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Article
Landscape Influence on the Browning of a Lake Watershed in the Adirondack Region of New York, USA
Soil Syst. 2020, 4(3), 50; https://doi.org/10.3390/soilsystems4030050 - 12 Aug 2020
Cited by 5 | Viewed by 1191
Abstract
Watershed recovery from long-term acidification in the northeastern U.S. has been characterized by an increase in the influx of dissolved organic matter (DOM) into surface waters. Increases in carbon quantity and shifts to more aromatic and “colored” OM has impacted downstream lakes by [...] Read more.
Watershed recovery from long-term acidification in the northeastern U.S. has been characterized by an increase in the influx of dissolved organic matter (DOM) into surface waters. Increases in carbon quantity and shifts to more aromatic and “colored” OM has impacted downstream lakes by altering thermal stratification, nutrient cycling and food web dynamics. Here, we used fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC) to model predominant carbon quality fractions and their seasonal changes within surface waters along landscape positions of Arbutus Lake watershed in the Adirondack region of NY, USA. All DOM components were terrestrial in origin, however their relative fractions varied throughout the watershed. DOM in headwater streams contained high fractions of recalcitrant (~43%) and microbial reprocessed humic-like OM (~33%), sourced from upland forest soils. Wetlands above the lake inlet contributed higher fractions of high molecular weight, plant-like organic matter (~30%), increasing dissolved organic carbon (DOC) concentrations observed at the lake inlet (492.5 mg L−1). At the lake outlet, these terrestrial fractions decreased significantly during summer months leading to a subsequent increase in reprocessed OM likely through increased microbial metabolism and photolysis. Comparisons of specific ultraviolet absorbance between this study and previous studies at Arbutus Lake show that OM draining upland streams (3.1 L·mg C−1 m−1) and wetland (4.1 L·mg C−1 m−1) is now more aromatic and thus more highly colored than conditions a decade ago. These findings provide insight into the emerging role that watersheds recovering from acidification play on downstream water quality. Full article
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Article
Manganese (Mn) Concentrations and the Mn-Fe Relationship in Shallow Groundwater: Implications for Groundwater Monitoring
Soil Syst. 2020, 4(3), 49; https://doi.org/10.3390/soilsystems4030049 - 05 Aug 2020
Cited by 4 | Viewed by 1363
Abstract
Manganese (Mn) concentrations in approximately 32,000 groundwater analyses from more than 4800 monitoring wells in northern Germany were evaluated. This region was considered well suited to study Mn in shallow groundwater in unconsolidated sediments. Spearman rank correlation was used to correlate between redox-sensitive [...] Read more.
Manganese (Mn) concentrations in approximately 32,000 groundwater analyses from more than 4800 monitoring wells in northern Germany were evaluated. This region was considered well suited to study Mn in shallow groundwater in unconsolidated sediments. Spearman rank correlation was used to correlate between redox-sensitive parameters and the Mann–Kendall test for an evaluation of temporal trends. Manganese concentrations varied over two orders of magnitude and more than 40% of the wells had concentrations above 0.3 mg/L. Median Mn concentrations in the major hydrogeological units, the Geesten, tidal wetlands, and fluviatile lowlands were 0.12 mg/L, 0.46 mg/L, and 0.27 mg/L, respectively. Separating the data by land use, the median concentrations were 0.20 mg/L for arable land, 0.15 mg/L for forests, and 0.24 for grassland. Calculated background concentrations of Mn varied from <0.25 mg/L to 4.79 mg/L. A new parameter, ∆Mn-Fe, defined as the concentration difference between Mn and Fe in mg/L together with nitrate concentrations exceeding 50 mg/L was used to identify the fertilizer-borne input of nitrate. However, the factor controlling Mn occurrence seemingly was the depth of monitoring wells and the screen-length. Elevated concentrations of Mn and a high ∆Mn-Fe were generally found in shallow wells and wells with short screen-lengths. Full article
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Article
Short-Term Effects of Sewage Sludge Compost Amendment on Semiarid Soil
Soil Syst. 2020, 4(3), 48; https://doi.org/10.3390/soilsystems4030048 - 05 Aug 2020
Cited by 8 | Viewed by 1456
Abstract
The adoption of sewage sludge as an agricultural management strategy to improve soil properties and crop production is attracting great interest. Despite many positive effects on soil inorganic and organic components reported for different soil types, little information is available on sewage sludge [...] Read more.
The adoption of sewage sludge as an agricultural management strategy to improve soil properties and crop production is attracting great interest. Despite many positive effects on soil inorganic and organic components reported for different soil types, little information is available on sewage sludge application on Mediterranean soils, as well as on its use at different dose rates. The objectives of the present research was to evaluate, through an integrated approach, the effects of sewage sludge compost from urban wastewater on physicochemical, hydrological, biochemical parameters, and microbiota composition in soil pots under a three-year crop rotation system. Four different doses of sewage sludge compost (C3, C6, C9, C12) from municipal wastewater and a dose of them in combination with mineral fertilizer (C6N) were used. We have used 3-6-9-12 Mg/ha of sewage sludge compost for the treatments C3, C6, C9 and C12, respectively, and 6 Mg/ha of sewage sludge compost in combination with 60 kg/ha of ammonium nitrate for the treatment C6N.The effects were compared to non-fertilized (C0) and mineral fertilized (Min) sets of controls. The electrical conductivity, soil pH, stability of soil aggregates, percent of moisture of the dry soil both at the field capacity and at the wilting point, available P, and exchangeable K were all positively affected by increasing the amounts of composted sludge. The organic carbon and total N increased up to 66% and 39%, respectively. Increased enzymatic activities and microbial biomass were also observed in soil after the application of sewage sludge compost when compared to un-amended control. A higher richness and evenness among the soil plots amended with sewage sludge compost was observed, with no significant differences among the application dose rates, when compared to the un-amended soil control and soil treated with a mineral fertilizer. A three-year amendment was able to separate soil plots amended with high doses of sewage sludge compost from the low dose amended and control samples. Among the microbial groups responsible for such marked separation, bacteria belonging to Actinobacteria, Acidobacteria, Cyanobacteria and Bacteroidetes contribute the most, with a shift from oligotrophic to copiotrophic taxa. Significant changes in bacterial composition and taxonomic structure should be considered in order to properly balance agronomic and economic advantages with environmental concerns. After all, our results have evidenced the effects of sewage sludge amendment on different soil properties, microbial activity, and composition already after a short period of application. The findings are particularly relevant in semiarid soils, where an immediate restoration of soil fertility by short-term compost application is needed. Full article
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Article
Effect of Cathode Material and Its Size on the Abundance of Nitrogen Removal Functional Genes in Microcosms of Integrated Bioelectrochemical-Wetland Systems
Soil Syst. 2020, 4(3), 47; https://doi.org/10.3390/soilsystems4030047 - 03 Aug 2020
Cited by 1 | Viewed by 1613
Abstract
Constructed wetland-microbial electrochemical snorkel (CW-MES) systems, which are short-circuited microbial fuel cells (MFC), have emerged as a novel tool for wastewater management, although the system mechanisms are insufficiently studied in process-based or environmental contexts. Based on quantitative polymerase chain reaction assays, we assessed [...] Read more.
Constructed wetland-microbial electrochemical snorkel (CW-MES) systems, which are short-circuited microbial fuel cells (MFC), have emerged as a novel tool for wastewater management, although the system mechanisms are insufficiently studied in process-based or environmental contexts. Based on quantitative polymerase chain reaction assays, we assessed the prevalence of different nitrogen removal processes for treating nitrate-rich waters with varying cathode materials (stainless steel, graphite felt, and copper) and sizes in the CW-MES systems and correlated them to the changes of N2O emissions. The nitrate and nitrite removal efficiencies were in range of 40% to 75% and over 98%, respectively. In response to the electrochemical manipulation, the abundances of most of the nitrogen-transforming microbial groups decreased in general. Graphite felt cathodes supported nitrifiers, but nirK-type denitrifiers were inhibited. Anaerobic ammonium oxidation (ANAMMOX) bacteria were less abundant in the electrochemically manipulated treatments compared to the controls. ANAMMOX and denitrification are the main nitrogen reducers in CW-MES systems. The treatments with 1:1 graphite felt, copper, plastic, and stainless-steel cathodes showed higher N2O emissions. nirS- and nosZI-type denitrifiers are mainly responsible for producing and reducing N2O emissions, respectively. Hence, electrochemical manipulation supported dissimilatory nitrate reduction to ammonium (DNRA) microbes may play a crucial role in producing N2O in CW-MES systems. Full article
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Review
Managing Soils for Recovering from the COVID-19 Pandemic
Soil Syst. 2020, 4(3), 46; https://doi.org/10.3390/soilsystems4030046 - 28 Jul 2020
Cited by 22 | Viewed by 6526
Abstract
The COVID-19 pandemic has disrupted the global food supply chain and exacerbated the problem of food and nutritional insecurity. Here we outline soil strategies to strengthen local food production systems, enhance their resilience, and create a circular economy focused on soil restoration through [...] Read more.
The COVID-19 pandemic has disrupted the global food supply chain and exacerbated the problem of food and nutritional insecurity. Here we outline soil strategies to strengthen local food production systems, enhance their resilience, and create a circular economy focused on soil restoration through carbon sequestration, on-farm cycling of nutrients, minimizing environmental pollution, and contamination of food. Smart web-based geospatial decision support systems (S-DSSs) for land use planning and management is a useful tool for sustainable development. Forensic soil science can also contribute to cold case investigations, both in providing intelligence and evidence in court and in ascertaining the provenance and safety of food products. Soil can be used for the safe disposal of medical waste, but increased understanding is needed on the transfer of virus through pedosphere processes. Strengthening communication between soil scientists and policy makers and improving distance learning techniques are critical for the post-COVID restoration. Full article
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Comment
Current Estimates of Soil Organic Carbon Stocks Are Not Four to Six Times Underestimated. Comment on “Non-Flat Earth Recalibrated for Terrain and Topsoil. Soil Syst. 2018, 2, 64”
Soil Syst. 2020, 4(3), 45; https://doi.org/10.3390/soilsystems4030045 - 27 Jul 2020
Viewed by 1354
Abstract
In the interesting paper “Non-Flat Earth Recalibrated for Terrain and Topsoil” published in Soil Systems [...] Full article
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Article
Subsoil Microbial Diversity and Stability in Rotational Cotton Systems
Soil Syst. 2020, 4(3), 44; https://doi.org/10.3390/soilsystems4030044 - 25 Jul 2020
Cited by 2 | Viewed by 1554
Abstract
Microbial diversity has been well documented for the top 0–0.30 m of agricultural soils. However, spatio-temporal research into subsoil microbial diversity and the effects of agricultural management remains limited. Soil type may influence subsoil microbial diversity, particularly Vertosols. These soils lack distinct horizons [...] Read more.
Microbial diversity has been well documented for the top 0–0.30 m of agricultural soils. However, spatio-temporal research into subsoil microbial diversity and the effects of agricultural management remains limited. Soil type may influence subsoil microbial diversity, particularly Vertosols. These soils lack distinct horizons and are known to facilitate the downward movement of organic matter, potentially supporting subsoil microbiota, removed from the crop root system (i.e., bulk soils). Our research used the MiSeq Illumina Platform to investigate microbial diversity down the profile of an agricultural Australian Vertosol to 1.0 m in bulk soils, as influenced by crop system (continuous cotton and cotton–maize) and sample time (pre- and in-crop samples collected over two seasons). Overall, both alpha- (Chao1, Gini–Simpson Diversity and Evenness indices) and beta-diversity (nMDS and Sørensen’s Index of Similarity) metrics indicated that both bacterial (16S) diversity and fungal (ITS) diversity decreased with increasing soil depth. The addition of a maize rotation did not significantly influence alpha-diversity metrics until 0.70–1.0 m depth in the soil, where bacterial diversity was significantly higher in this system, with beta-diversity measures indicating this is likely due to root system differences influencing dissolved organic carbon. Sample time did not significantly affect bacterial or fungal diversity over the two seasons, regardless of the crop type and status (i.e., crop in ground and post crop). The relatively stable subsoil fungal and overall microbial diversity in bulk soils over two crop seasons suggests that these microbiota have developed a tolerance to prolonged agricultural management. Full article
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Article
Soil Carbon Change Due to Land Conversion to Grassland in a Semi-Arid Environment
Soil Syst. 2020, 4(3), 43; https://doi.org/10.3390/soilsystems4030043 - 16 Jul 2020
Viewed by 1022
Abstract
A 5-year study evaluated the change in the quantity of soil total C (STC), soil organic C (SOC), and soil inorganic C (SIC) stored in the surface 60 cm of the soil profile on two adjacent blocks of land with a long-term history [...] Read more.
A 5-year study evaluated the change in the quantity of soil total C (STC), soil organic C (SOC), and soil inorganic C (SIC) stored in the surface 60 cm of the soil profile on two adjacent blocks of land with a long-term history of cropping (CH) or undisturbed grassland (NH) on similar soil types between 1999 and 2004. The NH area was tilled and a grass-legume species mix was seeded into plots on both the NH and the CH areas. Selected plots of restored grass were established so they could be grazed (GG) by livestock while other plots were left ungrazed (UG). Original undisturbed (and ungrazed) grassland plots within the NH area were used as a control treatment. Initially, STC and SOC in CH were lower than NH when compared under the semi-arid environmental conditions found in southwestern North Dakota. Over the study period, the undisturbed grass control plots had increases in STC and SOC levels in the soil profile of 3.90 kg·m−2 and 3.34 kg·m−2, respectively. Restored grass on the NH area with grazing showed increases in STC and SOC values of 2.11 and 1.26 kg·m−2, respectively, while without grazing, profile STC and SOC had values of 3.80 and 3.28 kg·m−2, respectively. Restored grass on the CH area showed increases in profile STC and SOC values of 0.55 and 1.96 kg·m−2, respectively, for the grazed plots and 0.78 and 2.11 kg·m−2, respectively, when left ungrazed. Soil inorganic C, though present in the soils, did not significantly change during the study. The lower C accumulation in the CH plots may be due to a lag time in the establishment of mycorrhizal associations with the seeded species, the inoculums of which were already present in the NH soils. Changes in STC were likely due to changes in water relationships in the soil profile where management changes affected water infiltration and its movement causing leaching of SIC below the 60 cm depth evaluated. Soils under undisturbed grassland continue to accumulate carbon while soils of the disturbed grassland or cropped prior to re-establishing grass showed losses that occurred due to either accumulating C at a lower rate or perhaps to C loss during the initial establishment period (1–2 years). Full article
Article
Visible Near-Infrared Reflectance and Laser-Induced Breakdown Spectroscopy for Estimating Soil Quality in Arid and Semiarid Agroecosystems
Soil Syst. 2020, 4(3), 42; https://doi.org/10.3390/soilsystems4030042 - 09 Jul 2020
Cited by 2 | Viewed by 1185
Abstract
Visible near-infrared reflectance spectroscopy (VNIRS) and laser-induced breakdown spectroscopy (LIBS) are potential methods for the rapid and less expensive assessment of soil quality indicators (SQIs). The specific objective of this study was to compare VNIRS and LIBS for assessing SQIs. Data was collected [...] Read more.
Visible near-infrared reflectance spectroscopy (VNIRS) and laser-induced breakdown spectroscopy (LIBS) are potential methods for the rapid and less expensive assessment of soil quality indicators (SQIs). The specific objective of this study was to compare VNIRS and LIBS for assessing SQIs. Data was collected from over 140 soil samples taken from multiple agricultural management systems in New Mexico, belonging to arid and semiarid agroecosystems. Sampled sites included New Mexico State University Agricultural Science Center research fields and several commercial farm fields in New Mexico. Partial least squares regression (PLSR) was used to establish predictive relationships between spectral data and SQIs. Fifteen soil measurements were modeled including the soil organic matter (SOM), permanganate oxidizable carbon (POXC), total microbial biomass (TMB), total bacteria biomass (TBB), total fungi biomass (TFB), mean weight diameter of dry aggregates (MWD), aggregates 2–4 mm (AGG > 2 mm), aggregates < 0.25 mm (AGG < 0.25 mm), wet aggregate stability (WAS), electrical conductivity (EC), calcium (Ca), magnesium (Mg), sodium (Na), and iron (Fe). Overall, calibrations based on measurements irrespective of locations performed better for LIBS and combined VNIRS-LIBS. Measurements separated according to locations highly improved the quality of prediction for VNIRS as compared to combined locations. For example, the prediction R2 values for regression of VNIRS were 0.19 for SOM, 0.30 for POXC, 0.24 for MWD, 0.15 for AGG > 2 mm, and 0.13 for EC in combined datasets irrespective of location. When separated according to locations, for one of the locations, the predictive R2 values for VNIRS were 0.48 for SOM, 0.70 for POXC, 0.67 for MWD, 0.60 for AGG > 2 mm, and 0.51 for EC. The prediction values varied with the sampling time for both LIBS and VNIRS. For example, the prediction values of some SQIs using VNIRS were higher in samples collected in winter for measurements, including SOM (0.90), MWD (0.96), WAS (0.66), and EC (0.94). Using the VNIRS, the corresponding predictive values for the same SQIs were lower for samples collected in the fall (SOM (0.61), MWD (0.45), WAS (0.46), and EC (0.65)). While this study illustrates the prospects of VNIRS and LIBS for estimating SQIs, a more comprehensive evaluation, using a larger regional dataset, is required to understand how the site and soil factors affect VNIRS and LIBS, in order to enhance the utility of these methods for soil quality assessment in arid and semiarid agroecosystems. Full article
(This article belongs to the Special Issue Proximal Soil Sensing Applications)
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Article
Microbe Biomass in Relation to Organic Carbon and Clay in Soil
Soil Syst. 2020, 4(3), 41; https://doi.org/10.3390/soilsystems4030041 - 08 Jul 2020
Cited by 7 | Viewed by 1523
Abstract
Soil microbes are key to nutrient cycling and soil formation, yet the impact of soil properties on microbe biomass remains unclear. Using 240 soil cores of 0–15 cm depth, taken at random points across six cattle-grazed pastures on an undulating landscape, we evaluated [...] Read more.
Soil microbes are key to nutrient cycling and soil formation, yet the impact of soil properties on microbe biomass remains unclear. Using 240 soil cores of 0–15 cm depth, taken at random points across six cattle-grazed pastures on an undulating landscape, we evaluated the biomass of microbes in soil as affected by naturally occurring variation in soil organic carbon (SOC), clay content, and local topography. The study pastures varied in historic land-use for crops or forage seeding. SOC was found to be greater in topographically low areas. In contrast, clay content was not related to topography, and clay deposition possibly varies with glaciation legacy. Microbial biomass carbon (MBC) was correlated positively with SOC, increasing from 700 mg kg−1 MBC at 25 g kg−1 SOC to 2240 mg kg−1 MBC at 90 g kg−1 SOC. Most likely, SOC promotes MBC through the release of water-soluble organic carbon. However, the response of MBC to clay content was negative, decreasing from 1340 mg kg−1 MBC at 5% clay to 880 mg kg−1 MBC at 30% clay. Small voids in association with clay particles likely restrict the access of microbes to SOC. The relationship between SOC and MBC illustrates the important role of SOC for soil function, in terms of nutrient availability and development of soil structure via the contribution of microbes. Lastly, there was considerable spatial variability in MBC across the 65 ha site, highlighting the importance of land-use histories and gradients in environmental variables, to determine the biomass of microbes in soil. Full article
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Article
Mobile Proximal Sensing with Visible and Near Infrared Spectroscopy for Digital Soil Mapping
Soil Syst. 2020, 4(3), 40; https://doi.org/10.3390/soilsystems4030040 - 07 Jul 2020
Cited by 2 | Viewed by 1282
Abstract
The objective of this study was to estimate multiple soil property local regression models, confirm the accuracy of the predicted values using visible near-infrared subsurface diffuse reflectance spectra collected by a mobile proximal soil sensor, and show that digital soil maps predicted by [...] Read more.
The objective of this study was to estimate multiple soil property local regression models, confirm the accuracy of the predicted values using visible near-infrared subsurface diffuse reflectance spectra collected by a mobile proximal soil sensor, and show that digital soil maps predicted by multiple soil property local regression models are able to visualize empirical knowledge of the grower. The parent materials in the experimental fields were light clay, clay loam, and sandy clay loam. The study was conducted in Saitama Prefecture, Japan. To develop local regression models for the 30 chemical and 4 physical properties, a total of 231 samples were collected; to evaluate accuracy of prediction, 65 samples were collected. The local regression models were developed using 2nd derivative pretreatment by the Savitzky–Golay algorithm and partial least squares regression. The local regression models were evaluated using the coefficient of determination (R2), residual prediction deviation (RPD), range error ratio (RER), and the ratio of prediction error to interquartile range (RPIQ). The R2 accuracy of the 34 local regression models was 0.81 or higher. In the predicted values for 65 unknown samples, the local regression models could ‘distinguish between high and low’ for 3 of the 34 soil properties, but were ‘not useful’ as absolute quantitative values for the other 31 soil properties. However, it was confirmed that the predicted values followed the transition in measured values, and thus that the developed 34 regression models could be used for generating digital soil maps based on relative quantitative values. The grower changed the ridge direction in the field from east–west to north–south just looking at the digital soil maps. Full article
(This article belongs to the Special Issue Proximal Soil Sensing Applications)
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Article
The Change of pH Value and Octolasion cyaneum Savigny Earthworms’ Activity under Stubble Crops after Spring Triticale Continuous Cultivation
Soil Syst. 2020, 4(3), 39; https://doi.org/10.3390/soilsystems4030039 - 04 Jul 2020
Viewed by 1041
Abstract
The changes of pH value followed by various agricultural practices are crucial for biotic components of soil, along with other environmental factors, like temperature and moisture content. In this paper, the earthworms population in triticale continuous cultivation was monitored. Their presence associated with [...] Read more.
The changes of pH value followed by various agricultural practices are crucial for biotic components of soil, along with other environmental factors, like temperature and moisture content. In this paper, the earthworms population in triticale continuous cultivation was monitored. Their presence associated with various agrotechnical methods (e.g., stubble crops maintained as mulch, mineral fertilization without pesticides) were assessed twice by the handsorting method, and their presence during the triticale vegetation season (occurrence of coprolites) were monitored too. The aim of the study was to analyse the distribution of earthworm populations in cereal continuous cultivation fields, and whether they prefer any of the stubble crop species (Sinapis alba L., Phacelia tanacetifolia Benth., Fagopyrum esculentum Moench.), which were sown after triticale harvest. The results reveal the most abundant earthworms occurence in the F. esculentum objects (43.1% of all sampled earthworms, which consists of 42% and 47.2% of all sampled matured and juveniles individuals, respectively), and species homogeneity (dominate Octolasion cyaneum Savigny, 1826). The changes of pH varied through the triticale vegetation season, but didn’t exhibit severe variation between sampling sites. Using earthworm services in cropping systems after having enticed them to the field through stubble crop has the potential to boost agricultural sustainability. Their ecological preferences, along with their trophic behaviour, have already been put in place to complete a case study of the autecology of the O. cyaneum Savigny 1826 species. Full article
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Article
Natural Recovery and Liming Effects in Acidified Forest Soils in SW-Germany
Soil Syst. 2020, 4(3), 38; https://doi.org/10.3390/soilsystems4030038 - 30 Jun 2020
Cited by 3 | Viewed by 1313
Abstract
In the state of Baden-Wuerttemberg, Southwest-Germany, a large-scale forest liming trial was government-funded in 1983 and a lime treatment was carried out in autumn 1983 until early winter 1984. Repeated liming was applied in 2003. The limed sites and adjacent control plots were [...] Read more.
In the state of Baden-Wuerttemberg, Southwest-Germany, a large-scale forest liming trial was government-funded in 1983 and a lime treatment was carried out in autumn 1983 until early winter 1984. Repeated liming was applied in 2003. The limed sites and adjacent control plots were surveyed repeatedly: in 2003 before the second lime application and again in 2010 and 2015. Research of this scope presents a rare opportunity to evaluate firstly the long-term development of acidified soils with their potential for natural recovery on established control plots, and secondly the long-term effects of repeated lime application—at a collective of study sites of various growth regions and soil properties. A natural recovery in soil pH was observed since 2003, on average limited to an increase of 0.2–0.4 pH units in the forest floor and 0.1–0.3 pH units in the mineral soil until 2015. The majority of the organic layers still show very strong or extreme acidity with a pH value 3.9 on average and in the mineral soil with pH values between 3.8 and 4.6 on average. The exchangeable cations calcium and magnesium slightly increased also, although the base saturation remained <20% by 2015. The exchangeable acid cation concentrations indicated no significant changes and thus no recovery. The lime treatment greatly accelerated the rise in pH by 1.2–1.3 units and base saturation by 40–70% in the organic layer, as well as 0.3–1.2 pH units and base saturation by 7–50% in mineral soil. These effects were decreasing (yet still significant) with depth in the measured soil profile as well as with time since last treatment. Changes in soil cation exchange capacity after liming were significant in 0–5 cm mineral soil, below that they were negligible as the significant increase in base cations were accompanied by decreasing acid cations aluminum and iron (III) especially in the upper soil profile. Additionally, a decrease of forest floor and an enrichment of organic carbon and nitrogen in the mineral topsoil tended to follow liming at some sites. Overall the liming effects had a high variability among the study sites, and were more pronounced in the more acidic and coarser textured sites. Liming of acidified forest soils significantly adds to natural recovery and therefore helps to establish greater buffering capacities and stabilize forest nutrition for the future. Full article
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