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Scanning electron microscopy coupled with microanalysis (SEM-EDX) is an important analytical tool for the morphological and chemical characterization of different types of materials. In many applications, SEM-EDX elemental maps are usually used and processed as images, thus flattening and reducing the spectroscopic information contained in EDX hyperspectral data cubes. The exploitation of the full hyperspectral dataset could be indeed very useful for the study of complex matrices like soil. In order to maximize the information attainable by SEM-EDX data cubes analysis, the software package “Datamuncher Gamma” was implemented and applied to study soil aggregates. By using this approach, different phases (silicates, aluminosilicates, Ca-carbonates, Ca-phosphates, organic matter, iron oxides) inside soil aggregates were successfully identified and segmented. The advantages of this method over the common ROI imaging approach are presented. Finally, this method was used to compare different aggregates in a Cr-polluted soil and understand their possible pedological history. The present method can be used for the analysis of every type of SEM-EDX data cubes, allowing its application to different types of samples and fields of study.

Soil specific surface area (SA) reflects the quantity and quality of the soil mineral and organic fractions. For soil samples that have similar clay mineral types, clay content and or organic carbon (OC) contents are good predictors of SA. However, the magnitude of the OC contribution to SA for different soil types is unclear, particularly since SA varies depending on which method or probe molecule is used to measure it. Consequently, we set out to (i) quantify the contribution of soil OC to total SA for soils with varying clay mineralogy, and (ii) assess the effect of probe molecule (EGME or H2O) and water sorption direction on the contribution of OC to the total SA. We utilized 330 soil samples (clay = 1 to 89 %; silt = 2 to 78 %; OC = 0.03 to 34.9 %) that were grouped according to clay mineralogy and OC content. The total SA was measured using EGME adsorption (SAE) and water adsorption and desorption (SAH2O). The contribution of OC to SA was examined using regression and partial correlation analyses that combined clay, silt, and OC as explanatory variables. Results showed that SAE values were strongly correlated to SAH2O, except for OC-rich soils where SAE was significantly lower than SAH2O. Apart from montmorillonite-rich samples, OC contribution to SAE was smaller than for SAH2O. Organic carbon had a positive contribution to desorption SAH2O for all sample groups, except for montmorillonite-rich samples; OC contribution was 7.5, 10.7, and 13.9 m2/g per %C for illite-rich, kaolinite-rich and OC-rich samples, respectively. There was no significant effect of water sorption direction on the OC contribution to SAH2O. Partial correlation analyses that accounted for clay and silt contents confirmed a negative contribution of OC to SAE or SAH2O for soil samples dominated by montmorillonite clay minerals. We can conclude that for the soil types investigated here (except montmorillonitic soils), OC has a positive contribution to total SA, and the magnitude of the contribution depends on the clay type.

Nitrogen (N) input rapidly increases available N in natural and managed ecosystems, potentially altering key ecosystem processes like decomposition. The effect of N enrichment on decomposition rates may be affected by the chemical quality of organic matter (OM), and the extent of N increment. Manure decomposition is an important process in agricultural systems, releasing nutrients and contributing to carbon (C) cycling. However, its response to N fertilization is poorly understood. To help address this knowledge gap, we decomposed pig manure (PM) and chicken manure (CM) under two rates of N fertilization (N1, 75 kg N ha−1; N2, 112.5 kg N ha−1) in a cropland in northeast China. We used litterbags to determine the dynamics of manure decomposition, while monitoring changes in the molecular composition with solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. After one-year, the decomposition rate of PM was significantly greater than CM (0.516 vs. 0.483 year−1). Spectra of 13C NMR indicated that PM initially contained more O-alkyl C and di-O-alkyl C (representing cellulose). In contrast, the contents of alkyl C (representing lipids) and aromatic C (representing lignin) were less in PM than CM, such that PM was overall more easily degradable. There was no N rate effect on CM decomposition. However, the decomposition rate of PM was significantly lower under high N than low N (0.410 vs. 0.622 year−1), apparently related to suppressed degradation of O-alkyl C and di-O-alkyl C. This result was surprising, since N enrichment is generally expected to promote degradation of more labile compounds like cellulose. At the same time, the loss of syringyl monomer of lignin in PM was reduced by high N fertilization. Together, these results suggest that decreased losses of O-alkyl C and di-O-alkyl C may have resulted from physical association of cellulose with more resistant lignin compounds. Net N mineralization was observed from manure decomposition and was greater for CM than PM, and high N fertilization suppressed N release from PM. Overall, our findings suggest that high rate of N fertilization may slow the decomposition of otherwise labile manure, potentially promoting greater C retention in soils.

The main goal of this study was to assess if wetland restoration changes soil biogeochemistry, here measured as organic matter content (OM) and element concentrations of the soils, back to its original state. We selected nine sampling sites in the Sanjiang Plain, China, that had two or three of the wetland types ‘undisturbed/natural’, ‘restored’, and ‘paddy field’ close to each other. The paddy fields were originally established on natural wetlands, and the original wetland soils would therefore have been similar. We analyzed the soils for element composition, OM, as well as electrical conductivity (EC) and pH. Distinct differences between undisturbed wetlands, restored wetlands and paddy fields existed in terms of element composition, OM, and EC, with most values for restored wetlands in-between those of undisturbed wetlands and paddy fields. Ordination analysis of the element concentrations by RDA identified that OM explained most variance (23.9% of 34.4% of total). OM correlated positively with N and S, negatively with most metals. Disturbance of wetland soils by agricultural activities most likely depleted OM of the soils, which in turn altered the concentrations of most elements. Restoration, even if only a few years ago, recovered the OM and changed the element contents in the direction of a natural condition to some extent. This information is important for restoration of wetlands, because to be successful, not only hydrology and biodiversity need to be restored but also the soil composition and biogeochemistry. It further can be used for assessment of success of wetland restoration.

Ferrihydrite has been prevalently used in soil remediation as an effective amendment for in situ immobilization of arsenic (As). However, its poorly crystalline structure is unstable and can pose the risk of re-releasing As into soil. In this study, sequential extraction was coupled with a newly-established method, chelex-metsorb diffusive gradient in thin films (DGT), to study the ferrihydrite transformation/dissolution process and its effect on the mobility of arsenic in soil. Experiments in this work found that high soil moisture (70% SWHC) with a low soil redox potential (Eh) can significantly increase the rate of the ferrihydrite transformation/dissolution process compared to 30% SWHC. Soils with low pH and high available iron (Fe) content may also accelerate ferrihydrite transformation/dissolution, while soils with high clay fraction and high soil total organic matter (STOM) may inhibit the process. The amount of arsenic adsorption can also affect ferrihydrite transformation, even exceeding the effect of soil pH and dissolved Fe. Arsenic release was clearly observed in all three soils across all treatments, and it was also affected by changes in soil redox potential. More arsenic was released at high soil moisture (70% SWHC) roughly 7–15 d after the release of Fe. In addition, a partial arsenic fraction was transformed, along with ferrihydrite, from a combined As (F1 As) amorphous phase to combined As (F2 As) well-crystallized phase. These results suggested that ferrihydrite transformation/dissolution can affect the mobility of arsenic and that this phenomenon is more extreme at higher soil moisture levels.

Soil organic matter (SOM) is sensitive to land use and to physico-chemical soil properties as well soil microbial communities controlling SOM stabilization. Our study aimed at exploring how carbonates of Mediterranean soils – known to stabilize SOM by enhancing soil aggregation and binding SOM by calcium – are affecting SOM and microbial communities under different land uses. In soils with and without carbonates sampled in forests, cultivated and abandoned fields, we have fractionated SOM-pools according to particle sizes and determined C mineralization rates and polyvalent cations in these fractions. In agreement with larger scale assessments in the Mediterranean, our results show that SOM contents are greater in forest than in agricultural soils, but that the differences among land use types depend on carbonate contents. While SOM contents are greater in carbonated soils of forests, cultivated soils have low SOM levels independent of the carbonate content, presumably due to a reduced protection of particulate SOM by century-long intense tillage. Forest soils contain particularly large amounts of SOM associated with the coarser soil fraction. In this fraction, C mineralization was smallest in the carbonated forest soil, possibly due to a low SOM quality indicated by high C/N ratios and low δ15N values. Greater contents of Ca, Fe and Al in carbonated soils also suggests that stabilization through Ca and phyllosilicates was important. Mineralization of sand-associated SOM was highest in cultivated and abandoned soils, which is indicative for a small SOM stabilization, which in turn might restrict SOM accumulation after land abandonment. Microbial communities assessed by phospho-lipid fatty acid signatures and microbial carbon use efficiency were more closely associated with land use than with carbonate content – a pattern that reflects the distribution of C pools among size fractions which differed more strongly among land use types than between soils with and without carbonates.

Understanding and interpretation of soil quality is crucial to strategize land management practices for sustaining agricultural productivity while mitigating environmental degradation. A medium-term cover crop (CC) trial, established in 2007 and repeated in 2008, at Ridgetown, Ontario was used to evaluate the comprehensive assessment of soil health (CASH), to develop a weighted soil quality index (WSQI), and to compare scores of CASH, Haney soil health test (HSHT), and WSQI in surface soil (15 cm) in 2015 and 2016 (herein referred to as site-years). Out of 25 potential soil quality indicators, 19 soil indicators were responsive to CC treatments and represented a total dataset. Using principal component analysis (PCA) of the total dataset, a minimum dataset (five indicators; pH, organic matter (OM), Solvita labile amino N (SLAN), Solvita CO2-burst, and water extractable organic C (WEOC)) was identified to calculate a WSQI. The WSQI and CASH scores were equivalent in detecting CC treatment differences in site-year 2015, but CASH detected greater magnitude (12.1%) of treatment differences than WSQI (5.7%) in site-year 2016. Cereal rye and a mixture of oilseed radish and rye (OSR + Rye) led to greater soil quality values than other tested CCs. Our results indicate the potential of CCs in significantly improving soil quality in the medium-term (6 years). This study is the first independent evaluation of CASH in a horticultural system in a humid, temperate climate, and first study to compare WSQI with commercial soil quality tests. Even though CASH and WSQI differentiated between CC treatments for soil quality evaluation in both site-years, we recommend WSQI as a valuable and practical tool (lesser number of indicators; five vs. 15), for quantifying soil quality in similar production regions and climatic conditions.

Iron (Fe) is one of the most abundant elements in the earth's crust and intensively interferes with the biogeochemical cycles of carbon (C) and phosphorous (P), especially in highly weathered tropical and subtropical soils. The strong affinity of phosphate to Fe oxides and hydroxides limits the P availability in paddy soils. Reductive dissolution of Fe(III) can release occluded and adsorbed P into solution and make it available for plant uptake. Such effects remain elusive, especially in highly weathered subtropical paddy soils with oscillating redox (Eh) conditions. Under submerged conditions, incomplete litter decomposition occurs and rice roots release large amounts of labile organic compounds as exudates. We investigated the role of acetate, formate, oxalate, and propionate on Fe(III) reduction, P mobilization, and CO2 efflux in two paddy soils (i.e. oxisol and ultisol) of varying organic C (OC) and Fe(II) contents. Microbial mineralization of added labile C decreased soil Eh and increased the rates of Fe(III) reduction followed by P mobilization. This indicated that microbially-mediated Fe(III) reduction was intensified by labile OC compounds, which acted as energy sources and electron donors. The release of available P via Fe reduction was accompanied by peaks in Fe(II), dissolved OC, and pH and was followed by a decrease in iron-bound P (Fe P). This implied that Fe P was the main source of available P in the paddy soils. The faster release of available P in the oxisol than the ultisol indicated that the higher OC and Fe(II) contents in the oxisol allowed a fast Eh decrease, leading to rapid microbial oxygen (O2) consumption and consequently faster and more intensive Fe(III) to Fe(II) reduction. This conclusion is supported by a faster Eh decrease in the oxisol than the ultisol corresponding to early P mobilization after input of labile C, and it suggests that Eh-driven Fe transformations and P mobilization are strongly modulated by labile OC mineralization.

In this study, we applied coconut fiber-derived biochar (CFB) to a lead (Pb)-contaminated soil (at 600 mg kg−1) at 2% and 4% (w/w), in order to explore the efficacy and mechanism of CFB to immobilize Pb in soil during a 150-day incubation experiment. Our approach integrated various techniques namely micro-X-ray fluorescence, sequential extraction, X-ray absorption fine structure, scanning electron microscopy combined with energy dispersive X-ray spectroscopy to evaluate the Pb immobilization. Results indicated that the distribution of Pb in the studied soil was significantly affected by CFB application. The Pb content in organic matter bound fraction of the studied soil increased by 29.5% and 33.5% with 2% and 4% CFB, respectively, compared to control soil after 150-day of incubation. Lead-loaded humic acid (HA) and Pb3(PO4)2 were higher in the biochar-amended soil (2% CFB) as compared with the control soil. The CFB particles possibly offer more binding sites of PO43− and carboxylic functional groups than the binding sites of –FeO(OH), SiO32−, −Al2O3 and organic functional groups provided by the original soil particles alone (no biochar) for Pb. Overall, this study highlights that CFB can be a potential candidate to immobilize Pb for the restoration and remediation of Pb-contaminated soils.

The accumulation of soil organic matter (SOM), poorly crystalline Fe oxides and metal-humus complexes is a trait of non-allophanic Andosols. The process of andosolization, which may occur in ferrallitic soils with high organic matter content, can involve transformation from well crystallized Fe oxides to poorly crystallized Fe oxides and Fe-humus complexes. This study investigates such changes in pedogenic Fe mineral associations for a soil toposequence between 1500 and 2260 m altitude along the southern flank of the volcanic Bambouto Mountains, Western Cameroon. The soils consist of highly weathered material, dominated by kaolinite, gibbsite and Fe oxides, grading to Protoandic Umbrisols at high altitude, recording an increase in SOM content with increasing altitude. As revealed by selective extraction analysis, the relative amount of poorly crystalline Fe oxides is low in the Bt and Bo horizons of low-altitude pedons, as well as in deep subsurface horizons of the high-altitude pedons. In contrast, it is significantly higher in the A and Bw horizons of the high-altitude pedons, with a clear increase with increasing altitude. Mossbauer spectroscopy analysis of B horizon samples identifies goethite as the dominant Fe oxide phase in nearly all pedons, with higher hematite contents in a mid-altitude zone marked by lower annual rainfall than in other parts of the toposequence. The Mossbauer spectra also reveal the presence of dissolved organic matter (DOM)-ferrihydrite, whose abundance is greatest in the Bw horizon of the high-altitude pedons, with an increase in relative abundance with increasing altitude. The observed patterns are attributed to dissolution-reprecipitation of Fe oxides that initially formed through ferrallitic weathering of volcanic parent materials that were roughly uniform along the toposequence. At high altitude, coupled hematite dissolution and DOM-ferrihydrite formation are favoured by high organic matter contents and low pH, related to cool humid environmental conditions and their effect on the vegetation and organic matter cycling.

Mangroves are supreme agents in building blue carbon pools by capturing atmospheric carbon and storing them in biomass and soil. Anaerobic mangrove soils favour accumulation of partially decomposed organic matter that builds the carbon stocks over time. This study is an attempt to quantify the stock of total organic carbon (TOC) and to determine its spatial as well as vertical distribution in soils of mangrove ecosystems in Sri Lanka. Seven mangrove areas representing the wet, dry and intermediate climatic zones of Sri Lanka were chosen for this purpose. Samples were taken from three depths, (0–15 cm, 16–30 cm and 31–45 cm) of mangrove soils and TOC was determined by dichromate-oxidation method followed by colorimetry. Surface layers of soils (0–15 cm depth) in general contained high amounts of carbon, particularly in mangrove soils of the wet and intermediate climatic zones. In majority of mangrove areas TOC stocks increased with depth and across the water-land gradient. Estimated magnitude of the carbon pools in Sri Lankan mangrove soils ranged from 316.29 to 580.84 Mg ha−1(1 Mg = 1 t = 103 kg) (total sampling area 13600m2). Mangrove soils of Rekawa lagoon, located in the intermediate climatic zone was found to be the largest soil carbon sink (580.84 Mg ha−1), while that of Batticaloa lagoon in the dry zone, was the smallest (316.29 Mg ha−1). A statistically significant (p

Laboratory and field experiments were conducted on three Mediterranean agricultural soils in so as to investigate the effects of de-oiled two-phase olive mill waste (D) and two-phase olive mill waste (W) and their level of organic matter maturity on the environmental fate of the herbicide S‑metolachlor (SM). Three Mediterranean agricultural soils were amended with fresh (D and W) and composted W (CW) wastes under laboratory conditions. Furthermore, under field conditions, one of the soils was also amended with both wastes (D and W) over 9 years in order to assess the effects of the “aging” transformation (AD and AW treatments, respectively). Significant increases in SM adsorption were observed in all the amended soils, with no reduction in the herbicide's effectiveness. The adsorption process was more reversible with the fresh organic amendments (D or W) than with CW or (even more so) with AD or AW. The fresh amendments also increased the persistence of SM; however the field-aged and composted amendments enhanced its dissipation as a result increased soil microbial activity showed by high levels of soil dehydrogenase activity. The AD- and AW-amended soils, showed the greatest decrease in leaching loss of SM (from 51.9% in original soil to 9.33% in AD and 8.05% in AW), reflecting the strong influence of adsorption-desorption processes on SM leaching. This study has shown that the application of olive mill wastes as organic amendments may be considered a useful strategy to reduce leaching of SM in soils poor in organic matter, especially if those wastes have a high level of organic matter maturity.

Saturated acid sulfate soils with hypersulfidic material are productive wetland soils, but when they dry, they generate large amounts of sulfuric acid due to oxidation of pyrite to form sulfuric material (pH

Rhizosphere respiration (from roots and rhizosphere microbes utilizing root-derived carbon (C)) is a significant component of soil respiration, and rhizosphere priming effect (RPE, change in soil C decomposition by the presence of living roots in the rhizosphere) is crucial for regulating soil C decomposition. However, the relationships between rhizosphere respiration and RPE and root traits (such as biomass and nitrogen (N) concentration) across plant species and growing conditions are not fully resolved. In this study, we investigated rhizosphere respiration rate and RPE of three grassland species (a grass, a forb and a legume) using a continuous isotope-labeling technique. We found a significantly positive relationship between root-mass-specific rhizosphere respiration rate and root N concentration across the three species and two types of mesocosms (small pots and large buckets), and the scaling exponents were approximately one (indicating isometric scaling). Further, soil organic matter (SOM) decomposition rate was not statistically different between the planted treatments and the unplanted control, suggesting insignificant RPE at the early flowering stage (90 days after seeding) for these three species. Likely, respiration from rhizodeposition (root inputs to soil during the 90-day labeling period) was not included in SOM decomposition by the isotope labeling method, which underestimates SOM decomposition and may partly contribute to the lack of RPE of the three species. Overall, our results show that rhizosphere respiration rate is scalable with root N concentration across different plant species and growing conditions, while RPE of these grassland species at the early flowering stage was insignificant.

Freeze-thaw cycles strongly affect the transformation of soil phosphorus (P) and shape the composition of P pools. This study aimed to investigate the effects of successive freeze-thaw cycles on the transformation of soil labile P and enzymatically hydrolysable organic P (Po) fractions. Accordingly, five physico-chemically distinct soils were subjected to two, five, and ten freeze-thaw cycles, with each cycle including incubation at −10 °C (freeze) for 12 h and 5 °C (thaw) for 12 h. Control soils were maintained at 5 °C, and the bicarbonate-extractable P and hydrolysable Po fractions were analysed at the end of the incubation period (10 d). Freeze-thaw cycles increased the levels of bicarbonate-extractable inorganic P, bicarbonate-extractable Po, labile monoester P, and phytate-like P, but had no effect on the diester P and unknown Po contents. The interaction between soil type and freeze-thaw cycles significantly affected the NaHCO3-extractable Pi, and phytate-like P fractions, but did not affect the bicarbonate-extractable Po, and labile monoester P fractions. The extent of increase in NaHCO3-extractable Pi largely depended on the amount of organic matter in the soil. In most cases, bicarbonate-extractable P and hydrolysable Po fractions reached their maximum levels after two freeze-thaw cycles and declined or remained constant thereafter. Our results suggest that freeze-thaw cycles exacerbated the transformation of soil labile P fractions, including enzymatically hydrolysable Po species, especially in the earlier stages.

Made available in DSpace on 2019-10-06T17:05:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-07-01 U.S. Department of Agriculture The Brazilian Cerrado has undergone extensive land-use change in the past century with large areas converted to agriculture and silviculture. Eucalyptus is the dominant planted tree species in Brazil, but the short rotations (6–7 years) and the associated soil disturbances can reduce soil organic matter (SOM), particularly in subsurface soil over long timeframes. SOM is critical to the continued productivity of forests and may be particularly important in Oxisol soils, which underlie much of Brazil. These soils are low in cation exchange sites and rely upon SOM for nutrient and water retention. However, the mechanisms that drive SOM loss under Eucalyptus remain unclear. This study examines both bulk soil and water-soluble organic matter chemistry deep into the soil profile (1.3 m) in paired Eucalyptus and Cerrado forest stands to identify changes in biodegradability, radiocarbon age, and functional group composition that may explain long-term declines in SOM stocks. We hypothesize that changes in litter quality associated with the conversion of Cerrado forest to Eucalyptus plantations increases the content of aliphatic functional groups in water soluble organic matter (WSOM) more quickly than bulk SOM, which drives subsoil accumulation of aliphatic organic moieties through hydrophobic interactions with soil minerals. By utilizing a suite of spectroscopic techniques ( 1 H nuclear magnetic resonance and Fourier transform infrared spectroscopy) alongside isotopic and incubation techniques, this study found substantial shifts toward aliphatic functional group composition in WSOM in both Eucalyptus stands and deeper soil horizons. The radiocarbon age of WSOM was younger than bulk SOM at every depth but still substantially diverged from modern in B horizons. This observation is consistent with the theory that WSOM is in dynamic equilibrium with mineral adsorbed SOM, and that old organic matter replaced on mineral surfaces by fresh inputs may be leached or further degraded by microbes. Radiocarbon age of bulk SOM was younger under Eucalyptus compared to Cerrado forest and the difference between WSOM and bulk SOM radiocarbon age was much smaller in Eucalyptus soils, which together indicate that microbes may be preferentially consuming older SOM after land-use change. The presence of Cerrado understory in Eucalyptus may be important to maintaining SOM cycling; WSOM biodegradability and microbial biomass was greatly reduced in the Eucalyptus site without any understory. Ecotones with Cerrado understory provide diversity in litter types and rooting strategies, while monoculture Eucalyptus, which is commonly found in stand interiors, may reduce the ability for microbes to maintain active nutrient recycling of organic residues. University of Washington School of Environmental and Forest Sciences University of Alberta Edmonton Department of Renewable Resources University of California Berkeley Department of Environmental Science Policy and Management University of California Merced Life & Environmental Sciences São Paulo State University (UNESP) College of Agricultural Sciences University of Washington School of Engineering and Environmental Sciences São Paulo State University (UNESP) College of Agricultural Sciences U.S. Department of Agriculture: 2015-32100-06092

A screening part of this study examined soil enrichment in 7 potentially toxic elements: Cd, Cr, Cu, Ni, Pb, Sb and Zn, in two complexes of military shooting ranges situated in SW Poland. For those elements that pose a real threat to the environment, their release into pore water was examined more thoroughly. The highest values of geoaccumulation index Igeo, with the median values above 1.5, were found for Sb, Pb and Cu, therefore further release-oriented experiments focused on these three elements. Their maximum concentrations in soils were: 89.6, 48,400 and 1230 mg kg−1, respectively. A 140-day incubation experiment was carried out with 5 strongly enriched soils treated with acid, lime and commercial green-waste compost, to illustrate the effects of pH and exogenous organic matter on the release of Sb, Pb and Cu into soil pore water. The treatment with lime and/or compost is usually believed to immobilize metals, while various authors reported contradictory effects of soil amendment with organic matter on the solubility of Sb. The present work indicated that liming can induce a release of Sb and Cu into soil pore water, and the treatment with compost can result in increased Cu and Pb solubility in alkaline conditions. The effect of immobilization observed in acid- and lime-treated soils after a prolonged incubation, was in the case of Pb and Cu explained by simple buffering rather than by aging. Long incubation with compost ensured immobilization of Pb, but not necessarily of Sb and Cu. The overall effects of soil treatment with moderately mature compost on the release of Sb, Pb and Cu into pore water of shooting range soils are ambiguous, and for this reason, each case of planned application of compost to polluted soils should be preceded by a thorough experimental examination.

Plants have a large impact on the physical behaviour of soil, partly due to seed and root exudates that alter mineral:organic matter associations. In this study we explored how the decomposability of residues in soil interacts with seed or root exudate compounds to influence microbial respiration, mechanical behaviour and hydrological properties. Sandy loam and clay loam soils were amended at a rate of 40 t ha-1 with ground green barley (7.13 mg C g-1), barley straw (7.26 mg C g-1) or poultry manure (5.22 mg C g-1), and either chia seed exudate at 1.84 mg C g-1 soil or root exudate compounds at 14.4 mg C g-1 soil. On cores packed to 1.3 g cm-3, uniaxial compression, penetration resistance, water sorptivity, water retention and porosity were measured at time 0, after 14 days of incubation at 20 oC, and then after subjecting incubated soils to three cycles of wetting and drying to simulate weathering. These time increments and weathering were intended to simulate a newly germinated seed or tip of a root, through to a more mature system. Application of seed and root exudate increased carbon dioxide (CO2) emissions from 0.31 ± 0.01 to 15.11 ± 0.71 μg C-CO2 g soil-1 hour-1 for the sandy loam soil and from 0.171 ± 0.01 to 10.56 ± 0.78 C-CO2 g soil-1 hour-1 for the clay loam soil. There were large changes in soil physical properties caused by seed or root exudate amendment coupled with residues, their decomposition and weathering. After incubation and weathering, soils with added seed or root exudates and their interactions with organic residues were more mechanically stable, as measured by penetration resistance (22 to 58% increase) and compression index (25 to 43% decrease) compared to soils amended only with organic residue. Water sorptivity and porosity diminished with the addition of the exudate. Exudates in combination with organic residues better protected soils against structural destabilization by increasing particle cementation and decreasing rapid wetting and porosity.

Pollution of soils with As, Cd, Co, Cr, Cu, Ni, Pb and Zn, collectively termed heavy metals (HMs), can threaten human health and ecosystem functioning. Therefore, polluted soils must be remediated. Soil washing of strongly polluted soils and phytoextraction on moderately polluted sites seem currently the most attractive remediation methods. Both methods depend on HM solubility (extractability), which can be increased by addition of ligands such as EDTA, NTA and other aminopolycarboxylic acids. As an alternative to these synthetic and environmentally questionable chemicals, the possibility of using naturally occurring dissolved organic matter (DOM) to extract the HMs from anthropogenic polluted soils is evaluated in this review based on mainly recently published laboratory studies. DOM isolated or extracted from soils consists of fulvic acid (FA) with up to 10% low-molecular-weight-organic-acids (LMWOAs), e.g. citric, oxalic and salicylic acids. In addition to soil DOM, results with other soluble humic substances and organic waste materials have been included, e.g. food wastes that after composting give useful LMWOAs. Although generally less efficient than EDTA and NTA, the review clearly shows potential of DOM as HM extractant. Through its carboxylate and/or phenolate functional groups, DOM can form soluble complexes with Cd2+, Co2+, Cu2+, Ni2+, Pb2+ and Zn2+ (and other di- and trivalent cations). Extraction of anionic As(III), As(V) and Cr(VI) sorbed by soil solids, mainly amorphous Al and Fe oxides, is accomplished by DOM dissolution of the sorbents (oxides). In addition to the soil HM extraction potential, use of DOM will probably extract organic pollutants, stimulate microbial activity and improve soil structure. On the other hand, the efficiency of DOM to extract HMs (and other pollutants) seems to depend of numerous variables/factors including the specific HM, DOM and polluted soil as well as environmental (external) conditions such as pH, solution:soil ratio, extraction time and metal loading of the extractant. Furthermore, several different studies have shown conflicting (inconclusive) results, e.g. of pH and ageing effects on HM extractability. Therefore, much is still to be learnt about different DOM-HM-soil systems and their dependency of external factors. To create operational and safe guidelines for using DOM as HM extractant in relation to remediation of polluted field soils by phytoextraction or soil washing, considerably more precise knowledge is needed on influence of composition of different DOM samples and of characteristics of the polluted soils for extraction of the different HMs under various, clearly specified environmental conditions. If future investigations confirm the suitability of DOM in soil remediation, the next challenges will be upscaling to field conditions as well as to ensure availability of enough good quality DOM and to complete state-of-art economic analysis of using DOM in operational phytorextraction and soil washing.

Soil incubation studies commonly use archived, dry stored soil samples. Numerous studies have detected a profound impact of dry storage on soil microbial community composition and activity. However, comparatively few studies have explored the impact of storage on the short-term mineralisation of soil organic matter (SOM) after moistening dry soils to revive and stabilise microbial activity (“pre-incubation”). We examined whether pre-incubation of dry stored soil of contrasting texture (Alfisol and Vertisol) can recover native soil microbial functions in fresh soil or soil stored for 3 weeks, 3 or 36 years. The oldest samples had a delayed CO2 response after moistening, but matched CO2 production rates of younger samples within hours. The two soil types displayed contrasting CO2 emission responses after moistening; the Alfisols had a rapid but short-lived CO2 emission peak (the so-called “Birch Effect”) while the Vertisols demonstrated a long, sustained release of CO2 reflecting its higher abundance of microsite abundance and microaggregates which may protect SOM and microorganisms during adverse conditions like drying. After 10 days of pre-incubation, older Alfisol samples had higher protease activity and response to amino acid addition demonstrating altered microbial physiological responses relating to nitrogen (N) compared to fresher counterparts. However, such responses in Vertisols were unchanged suggesting high clay soils with high potential microsite abundance may improve preservation of soil N functions through dry storage or even drought. This work highlights both limitations and possibilities of incubating dry archived soils for SOM mineralisation studies.

Prescribed burning is used widely across Australia to reduce fuel load and associated wildfire hazard. However, prescribed burning can influence carbon (C) storage in affected ecosystems, potentially influencing C cycling. One important component of the C cycle is soluble C, which is available to microorganisms and therefore a key driver of nutrient cycling. However, studies of the effects of fire on soluble C in natural ecosystems are few. In this study, UV–Vis spectra of water extracts of soils from an Australian Eucalyptus forest were used to investigate soluble soil C characteristics to 30 cm depth after autumn burning every three or ten years for three decades contrasted with long non-burnt controls. A random forest prediction model was fit to the UV–VIS spectra and the wavelengths important to predicting soluble C investigated using conditional inference trees. The main absorbance of the UV–Vis spectra was in the aromatic region (~280 nm) indicating chemically complex soluble organic matter in both burnt and non-burnt soils. Water extractable organic carbon decreased significantly with depth and was reduced by 3-yearly burning in surface soils. Furthermore, burning, irrespective of treatment, led to significant shifts in the locations of soil spectra peaks, which were consistent with both lower quantities of non-aromatic substances and less substituted aromatic substances in the burnt than non-burnt sites. These results indicate that repeated prescribed fire over decades reduced the quantity of soluble C, and enhanced its aromaticity, potentially reducing biological availability and therefore nutrient cycling in the soils.

The development of spectral prediction models for soil attributes has been extensively studied in the last 10 years. However, one of the problems encountered during this period concerns the representativeness of the samples selected for model generation, which are often unable to capture the existing variability in agricultural areas, generating imprecise models. Thus, it is necessary to establish strategies for selecting soil samples, as well as for making them more representative within the model. Considering this, the aim of the present study was to evaluate strategies for soil sample selection and the recalibration of large models using samples from a smaller area, in a process called spiking, and its effect on soil attribute estimations. A total of 425 soil samples were used for the generation of the state models, as well as 200 soil samples from a target site for attribute recalibration and prediction. From these 200 samples, 10 (subset) were selected by different methods for state model recalibration (spiking), and 190 were used in the prediction. Another 5 and 10 copies of the subsets were also used as extra-weight to recalibrate the models. Models spiked with samples located in the center of the spectral space associated with extra-weight (10 copies) showed better accuracy in sand prediction (RPD = 2.20; r2 = 0.80; RMSEP = 71.6 g kg−1). For organic matter, the use of selected samples based on 5 clusters associated with extra-weight (10 copies) slightly improved the RMSEP and RPD in most cases, reaching a maximum value of 6.1 g dm−3 and 1.20, respectively. However, the subsets selected at the target site were not able to indicate the entire variability of the local samples concerning organic matter, damaging the expansion of the recalibrated state models.

Soil spectroscopy has proven efficient for providing quantitative properties of soil chromophores and soil classification. However, building generic/global models might bring to light some problems which stem from the false premise that each chromophore affects all soil types equally. The objective of this paper is to offer a new cluster-based approach for the assessment of soil properties and compensating issues that might rise from using heterogeneous soil dataset. For that purpose, 1480 soil samples from varying climate zones in Israel were used. All samples were air-dried, ground, and sieved to 2 mm, then CaCO3, organic matter (OM), clay and sand contents together with the spectral signature were measured according to laboratory protocols. The spectral analysis was performed using the Spectral Angle Mapper (SAM) algorithm, spectral gradient and k-means clusters to split the dataset into distinct clusters. Subsequently, cluster-based models were performed and compared with generic models. Later, we focused on the OM parameter and applied the OM detection limit approach for a more robust and accurate assessment. Our results show that soil property prediction improved significantly when using the cluster-based models compared to the generic models and therefore should be considered when dealing with large and heterogeneous databases.

Floodplain soils are important reservoirs of organic carbon (OC) in the terrestrial carbon cycle. Few rivers and floodplains in the world and particularly in central Europe are in a natural state. They are regulated, stabilised from erosion behind artificial levees, drained and used for agriculture. Fluvisols store high amounts of OC from the topsoil to the subsoil, but little is known about the soil organic matter (SOM) quality and its vulnerability to decomposition. In this study, two regulated floodplains originating from different parent materials under grassland use in Southern Germany (Alpine Foreland and the Bavarian Forest) were sampled and analysed for the quantity and quality of inherent SOM in the topsoil and two subsoil levels. We characterised bulk soil (pH, texture, inorganic carbon and total nitrogen) and applied a combined density and size fractionation scheme to obtain six fractions. The chemical composition of the fractions was further determined using solid-state 13C NMR spectroscopy (SOM composition), as well as X-ray diffraction (clay mineralogy) and N2-BET (specific surface area (SSA)). Contributions of light fractions and especially of occluded particulate organic matter (oPOMfine) to the total OC were remarkably high in the subsoils. Organo-mineral associations (OMFfine) highly contributed to total OC at both sites but only in the topsoils. The highest OC concentrations of OMFfine were found in calcareous parent material, which shows that polyvalent cations promote OC storage. However, the inter-site as well as intra-site heterogeneity of oPOMfine and OMFfine OC contribution was highly variable. In the Bavarian Forest, oPOMfine was enriched in lipids in the subsoil. This was most probably due to a limited supply of oxygen in the aggregates through fluctuating groundwater levels that retarded decomposition and selectively preserved aliphatic compounds. In the Alpine Foreland, soil biota had mixed fresh SOM into the subsoil. There, oPOMfine contained all the functional C-groups, particularly carbohydrates. A changing global climate jeopardises OC reservoirs in floodplains, due to increased flooding and associated river bank erosion. Such disturbances not only cause losses of productive land but also release OC stored in light fractions that could be oxidised to CO2, depending on its chemical composition, thus adding to global warming.

Coastal wetland submergence can occur when rates of relative sea-level rise exceed that of soil elevation gain or landward transgression. In highly organic soils, the collapse of the wetland platform into open water can cause disarticulation of the soil structure, exposing previously protected anaerobic microzones to oxygenated seawater, which may accelerate mineralization rates. Nine soil cores (1 m deep) were collected from three sites within Barataria Bay, LA (USA), a region known for high rates of wetland submergence. Both the biogeochemical properties of the soils with depth were determined, as well as the impacts of the introduction of oxygenated seawater on carbon mineralization rates. Both field enzyme activity (β‑glucosidase, N‑acetyl‑beta‑ d ‑glucosaminidase, alkaline phosphatase, β‑xylosidase, and β‑cellobiosidase) and microbial biomass carbon (MBC) did not significantly change with depth until 50 cm, where activity increased dramatically, then gradually decreased. Total carbon (C), total nitrogen, and percent organic matter were highest between 50 and 100 cm. Following initial biogeochemical characterization, soil microcosms were created for 11 depth segments under anaerobic conditions (mimicking an intact wetland) and aerobic conditions (mimicking a submerging wetland mixing with oxygenated water); carbon dioxide (CO2) production was measured within the bottles over 14 days. Carbon dioxide production averaged 66% greater in the aerobic treatment than the anaerobic treatment. Both treatments exhibited a general trend of increasing CO2 production with depth (particularly from 40 to 100 cm), with the difference in CO2 production between aerobic and anaerobic treatments being 4× greater at 90–100 cm than at the soil surface (0–5 cm). The increase in C mineralization rates observed at depth was positively correlated with indicators of greater microbial activity (i.e., higher enzyme activity and MBC) and greater nutrient availability. Study results indicate coastal wetland submergence into open water could significantly enhance CO2 emissions, even in deep (40+ cm) soils, contrary to the typically observed pattern of soil microbial activity and soil quality decreasing with depth. These findings underline the need to analyze deeper soil samples (1+ m) in order to fully understand the implications of sea level rise on C loss from submerging coastal wetland soils.

Microbial activity and functioning in soils are strongly limited by carbon (C) availability, of which a great proportion is released by living roots. Rhizodeposition and especially root exudates stimulate microbial activity and growth, and may shift the stoichiometric balance between C, N, and P. Thereby, exudates heighten microbial nutrient demand and acquisition of N and P from organic matter, leading to an increase in enzyme production. Aim of this study was to determine environmental controls of extracellular enzyme production, and hence on potential enzyme activities (Vmax) and substrate affinities (Km). To determine the controlling factors, we worked on four spatial scales from the microscale (i.e. rhizosphere) through the mesoscale (i.e. soil depth) and landscape scale (relief positions), and finally to the continental scale (1200 km transect within the Coastal Cordillera of Chile). Kinetics of seven hydrolyzing enzymes of the C, N, and P cycles (cellobiohydrolase, β‑glucosidase, β‑xylosidase, β‑N‑acetylglucosaminidase, leucine‑aminopeptidase, tyrosine‑aminopeptidase, and acid phosphatase) were related to soil texture, C and N contents, pH, and soil moisture via redundancy analysis (RDA). Potential activities of C, N, and P acquiring enzymes increased up to 7-times on the continental scale with rising humidity of sites and C and N contents, while substrate affinities simultaneously declined. On the landscape scale, neither Vmax nor Km of any enzyme differed between north and south slopes. From top- to subsoil (down to 120 cm depth) potential activities decreased (strongest of aminopeptidases under humid temperate conditions with up to 90%). Substrate affinities, however, increased with soil depth only for N and P acquiring enzymes. Affinities of cellobiohydrolase and β‑xylosidase, on the contrary, were 1.5- to 3-times higher in top- than in subsoil. Potential activities of N and P acquiring enzymes and β‑glucosidase increased form bulk to roots. Simultaneously, substrate affinities of N and P acquiring enzymes declined, whereas affinities of β‑glucosidase increased. These trends of activities and affinities in the rhizosphere were significant only for acid phosphatase. The RDA displayed a strong relation of potential activities of C and P acquiring enzymes and β‑N‑acetylglucosaminidase to C and N contents in soil as well as to the silt and clay contents. Aminopeptidase activity was mainly dependent on soil moisture and pH. We conclude that substrate availability for microorganisms mainly determined enzyme activity patterns on the continental scale by the humidity gradient. Patterns on the meso- and microscale are primarily controlled by nutrient limitation, which is induced by a shift of the stoichiometric balance due to input of easily available C by roots in the rhizosphere.

Playas are common natural occurrences in the Southern High Plains of Texas and act as sources of runoff in rural and urban settings and provide habitat for migratory waterfowl. Rural and urban playas in Lubbock County, TX were geochemically compared in order to optimize management for ecological functionality. Soil texture, specifically sand and clay, and organic matter concentration influenced geochemical properties such as trace element concentration, pH, and electrical conductivity. Rural playas contained more clay, organic matter, trace elements, and electrical conductivity than urban playas. Urban playas had a higher pH and roughly twice the sand content of rural playas. The prevalence of sand in urban playas likely influences groundwater recharge dynamics and potentially disqualifies these lakes as Vertisols owing to their sandy nature. The soil mineralogy between urban and rural playas were also different. Quartz and muscovite were the dominant minerals in urban and rural playas, respectively. The differing soil properties between rural and urban playas signify the necessity of unique management strategies.