Soil Organic Matter Properties Research Articles

The Use of Spectroscopic Methods to Study Organic Matter in Virgin and Arable Soils: A Scoping Review

The use of modern spectroscopic methods of analysis, which provide extensive information on the chemical nature of substances, significantly expands our understanding of the molecular composition and properties of soil organic matter (SOM) and its transformation and stabilization processes in various ecosystems and geochemical conditions. The aim of this review is to identify and analyze studies related to the application of nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy techniques to study the molecular composition and transformation of organic matter in virgin and arable soils. This article is mainly based on three research questions: (1) Which NMR spectroscopy techniques are used to study SOM, and what are their disadvantages and advantages? (2) How is the NMR spectroscopy technique used to study the molecular structure of different pools of SOM? (3) How is ESR spectroscopy used in SOM chemistry, and what are its advantages and limitations? Relevant studies published between 1996 and 2024 were searched in four databases: eLIBRARY, MDPI, ScienceDirect and Springer. We excluded non-English-language articles, review articles, non-peer-reviewed articles and other non-article publications, as well as publications that were not available according to the search protocols. Exclusion criteria for articles were studies that used NMR and EPR techniques to study non-SOM and where these techniques were not the primary methods. Our scoping review found that both solid-state and solution-state NMR spectroscopy are commonly used to study the structure of soil organic matter (SOM). Solution-phase NMR is particularly useful for studying soluble SOM components of a low molecular weight, whereas solid-phase NMR offers advantages such as higher 13C atom concentration for stronger signals and faster analysis time. However, solution-phase NMR has limitations including sample insolubility, potential signal aggregation and reduced sensitivity and resolution. Solid-state NMR is better at detecting non-protonated carbon atoms and identifying heterogeneous regions within structures. EPR spectroscopy, on the other hand, offers significant advantages in experimental biochemistry due to its high sensitivity and ability to provide detailed information about substances containing free radicals (FRs), aiding in the assessment of their reactivity and transformations. Understanding the FR structure in biopolymers can help to study the formation and transformation of SOM. The integration of two- and three-dimensional NMR spectroscopy with other analytical methods, such as chromatography, mass spectrometry, etc., provides a more comprehensive approach to deciphering the complex composition of SOM than one-dimensional techniques alone.

The Impact of the Elemental Interactions on Soil Fertility and Toxicity in the Presence of Wastewater and Biosolids: A Quantitative Evaluation

A field experiment was conducted in Mesologgi, Greece, for the study of the elemental contribution to the soil under the following treatments in four replications i.e.,: a—Wastewater (TMWW), b—Biosolid (BSD), c—(TMWW + BSD) and d—CONTROL (fresh irrigation water). Similarly, the data of a greenhouse experiment conducted in four replications in Agrinion, under the effect of wastewater and biosolids was also taken into account for reasons of comparison. The soil analytical data of these two experiments were chosen to study the elemental interactions under two different experimental conditions The actual scope was the use of the elemental interactions as a tool for the evaluation of their contribution in terms of plant nutrients, and heavy metals to soil fertility and of heavy metals to soil toxicity. Based on the results of elemental contributions obtained for both of the above experimental soils, the key role of elemental interactions as a tool in evaluating the contributed heavy metals, and essential nutrients, as well as in producing quantitative changes in the physical and chemical properties of soil (pH, organic matter, calcium carbonate, and electrical conductivity), was also, studied. According to the obtained results, it was shown that the elemental interactions have shown approximately the same quantitative trend between some of the results obtained, differing in some others, showing higher concentrations. In other words, it was shown that the elemental interactions could be used as an effective tool for the quantitative evaluation of the elemental interactions’ contribution in terms of nutrients to soil fertility, and of heavy metals to soil toxicity, under the reuse of wastewater and biosolids, as well as in terms of changes of the soil physical and chemical properties. However, due to the complex nature of this subject, more detailed research must be conducted on the elemental contributions, so that the plant nutrients, or the heavy metals, eventually be managed effectively to the benefit of the agricultural economy and environmental quality.

Soil management effects on soil organic matter properties and carbon sequestration (SOMPACS)

SOMPACS is a project recommended by EJP SOIL for funding under the 1st External Call "Towards Healthy, Resilient and Sustainable Agricultural Soils". The goal of this project is to assess management practices that enrich organic matter pools that are resilient to rapid microbial decomposition. The project started in 2022 as a consortium of 12 research institutions from Poland, Germany, Ireland, Lithuania, UK, Italy and USA for a period of three years. Soil and vegetation samples from eight long-term experiments that differ in soil management practices (i.e., conventional vs. no-tillage; mineral vs. organic fertilization; with and without catch crop; and arable land vs. undisturbed grassland) are investigated. Study sites include: 22- and 54-year long experiments in Lithuania; 26-year long experiment in Italy; 30- and 40-year long experiments in Ireland; 30- and 46- and 100-year long experiments in Poland; and 178-year long Broadbalk experiment in Great Britain. Additional experimentation includes assessing the impact of root growth promoting amendments (commercially available humic substances, biochar and biogas digestate) on stable organic matter pools. In parallel with soil sampling, plant productivity are measured in all field experiments. This investigation is couples fields studies with small-scale experimental plots and laboratory incubations under controlled conditions. In addition to assessing basic soil properties, the following state-of-the-art analyses are conducted: SOM composition and stability by Py-GC-MS; fractionation of aggregate size classes and C pools of increasing physicochemical protection; isotopic analysis of δ13C and δ15N performed on different SOM pools; microbiological properties (community-level physiological profiling, selected functional genes involved in C and N cycles, microbiome and mycobiome analyses by next-generation sequencing, genetic diversity using terminal restriction fragment length polymorphism); enzymatic activity; soil water retention and soil water repellency; mineral composition of clay fraction; (8) soil structure stability. SOM composition and stability by Py-GC-MS; fractionation of aggregate size classes and C pools of increasing physicochemical protection; isotopic analysis of δ13C and δ15N performed on different SOM pools; microbiological properties (community-level physiological profiling, selected functional genes involved in C and N cycles, microbiome and mycobiome analyses by next-generation sequencing, genetic diversity using terminal restriction fragment length polymorphism); enzymatic activity; soil water retention and soil water repellency; mineral composition of clay fraction; (8) soil structure stability. The most resistant SOM pool (humin) are isolated by different methods (isolation vs. extraction) and examined for chemical composition and structure, using spectrometric and spectroscopic techniques (mass spectrometry, NMR, FTIR, EPR, UV-Vis-NIR, fluorescence). The carbon stocks in the soil profile will be evaluated and the carbon extractable in cold water will be determined to assess the potential carbon leaching and microbial availability. Additionally, in-field soil carbon dioxide (CO2) fluxes from selected experiments is monitored. Thus far, soil samples (0-100 cm depth) were collected and the humin fraction from surface A horizon was isolated for spectroscopic studies. Crop yield and vegetation productivity was also assessed. The research was financed by NCBR (EJPSOIL/I/78/SOMPACS/2022).

Linking above and belowground carbon sequestration, soil organic matter properties, and soil health in Brazilian Atlantic Forest restoration

Forest restoration mitigates climate change by removing CO2 and storing C in terrestrial ecosystems. However, incomplete information on C storage in restored tropical forests often fails to capture the ecosystem's holistic C dynamics. This study provides an integrated assessment of C storage in above to belowground subsystems, its consequences for greenhouse gas (GHG) fluxes, and the quantity, quality, and origin of soil organic matter (SOM) in restored Atlantic forests in Brazil. Relations between SOM properties and soil health indicators were also explored. We examined two restorations using tree planting (‘active restoration’): an 8-year-old forest with green manure and native trees planted in two rounds, and a 15-year-old forest with native-planted trees in one round without green manure. Restorations were compared to reformed pasture and primary forest sites. We measured C storage in soil layers (0–10, 10–20, and 20–30 cm), litter, and plants. GHG emissions were assessed using CH4 and CO2 fluxes. SOM quantity was evaluated using C and N, quality using humification index (HLIFS), and origin using δ13C and δ15N. Nine soil health indicators were interrelated with SOM attributes. The primary forest presented the highest C stocks (107.7 Mg C ha−1), followed by 15- and 8-year-old restorations and pasture with 69.8, 55.5, and 41.8 Mg C ha−1, respectively. Soil C stocks from restorations and pasture were 20% lower than primary forest. However, 8- and 15-year-old restorations stored 12.3 and 28.3 Mg ha−1 more aboveground C than pasture. The younger forest had δ13C and δ15N values of 2.1 and 1.7‰, respectively, lower than the 15-year-old forest, indicating more C derived from C3 plants and biological N fixation. Both restorations and pasture had at least 34% higher HLIFS in deeper soil layers (10–30 cm) than primary forest, indicating a lack of labile SOM. Native and 15-year-old forests exhibited higher soil methane influx (141.1 and 61.9 μg m−2 h−1). Forests outperformed pasture in most soil health indicators, with 69% of their variance explained by SOM properties. However, SOM quantity and quality regeneration in both restorations approached the pristine forest state only in the top 10 cm layer, while deeper soil retained agricultural degradation legacies. In conclusion, active restoration of the Atlantic Forest is a superior approach compared to pasture reform for GHG mitigation. Nonetheless, the development of restoration techniques to facilitate labile C input into deeper soil layers (>10 cm) is needed to further improve soil multifunctionality and long-term C storage.

Evaluation of calcium, phosphorus and soil organic matter effects on lead accumulation in Cenchrus ciliaris L. grown near a cement factory in Jazan region, Saudi Arabia

Heavy metals associated with cement production and their environmental impacts have received much attention recently. Lead (Pb) is the second most hazardous element after arsenic (As). However, information about its availability and uptake by plants in polluted soil as influenced by soil properties has shown some contradictions. We evaluated the influence of soil calcium (Ca), soil phosphorus (P), and soil organic matter (SOM) on Pb uptake by Cenchrus ciliaris L. based on distance from cement dust polluted soil near a cement factory in Jazan region, Saudi Arabia. We also evaluated the potential of Cenchrus ciliaris L. as a hyperaccumulator of Pb. Soil and plant samples were collected in triplicates from three zones based on distance from the fence of the factory: 10 – 100, 100 – 350, and 350 – 700 m. Concentrations of total Pb, total Ca, and total P in soil and plant tissues were detected using ICP-AES. SOM and other soil properties were also analyzed. Bioconcentration and translocation factors (BF&TF) of Pb were also calculated. Results showed that Pb concentration in Cenchrus ciliaris roots had a strong negative relationship with SOM (R2 = 0.93) and P concentration in soil (R2 = 0.97) but a moderate negative relationship with Ca concentration in soil (R2 = 0.69). The highest TF value was 1.87. It can be concluded that SOM, Ca, and P concentrations in soil negatively affected Pb availability and uptake by Cenchrus ciliaris. Also, based on the highest TF value, Cenchrus ciliaris could be used as a hyperaccumulator in Pb-contaminated soils.

Evolution of terminology in the sphere of organic matter of soil and humus

Goal. To analyze the existing concepts in de­termining the organic matter of the soil and humus and to separate the modern ideas that have developed as a result of a long study of the nature of these substances. Method. Theoretical and analytical. Results. The reasoning of prominent scientists of the 20th century is given, as well as modern researchers regarding the origin, composition, and properties of soil and humus organic matter. Based on an analytical review of scientific publications, the basic terminology of soil organic matter, humus, humus substances, and humification, which has changed over time, is given, and the definition of unified formulations is discussed. The concept of loss (dehumification, dehumus), preservation, and accumulation (sequestration, deposition) of organic matter in soils are considered, and the formulation of separate terms is proposed. Conclusions. At the beginning of the XXI century scientists understand soil organic matter as a system of organic particles of various sizes and biomolecules of plant, animal, and microbiological origin, which consists of plant residues (2–10 mm), solid particles of semi-decomposed organic material (0.053–2 mm), humus (≤0.053 mm) in the form of biomolecules chemically bound to mineral particles, humic and dissolved substances (≤0.45 µm). Humus is a part of the soil organic matter, which in modern literature is called “mineral-associated organic matter”, contained in fractions of dust and clay with a size of ≤0.053 mm.

Diversity and Assembly of Bacteria Community in Lime Soil under Different Karst Land-Use Types

Bacteria play an important role as decomposers in karst ecosystems, which can be associated with karst soil and plants, promoting the cycling of nutrients between plants and soil. To reveal the diversity and structure of soil bacterial communities in some karst land-use types after the Grain for Green pattern, soil samples were collected from different land-use types (crops, grasses, and plantations) for analysis. Changes in the structure and assembly of karst soil bacteria were examined using 16S rRNA Illumina sequencing and soil chemical properties. We found that 18 years after the Grain for Green program, the soil chemical properties of available nitrogen (AN), total phosphorus (TP), total nitrogen (TN), and soil organic matter (SOM) of grassland were significantly different from those of farmland. The soil chemical properties in plantations were also significantly lower than those in farmlands. Different land-use types did not significantly affect the soil bacterial community structure. Actinobacteria, Proteobacteria, Chloroflexi, and Acidobacteria were the dominant phyla in all the plots. The relative abundance of Proteobacteria was higher in grasslands and plantations than in farmlands, whereas that of Actinobacteria was lower in grasslands. Furthermore, no significant correlations were observed between the soil chemical factors and soil bacterial groups at the genus level. The null model analysis indicated that dispersal limitations in stochastic processes predominated for the different land-use systems. Combined with previous analyses of the factors driving bacterial core species diversity in karst soils, we speculated that stochastic processes play a more important role in the construction of core bacterial species in restored karst soils at the plot scale.

Thermodynamic characterization of LF, H, and mineral soil layers from oak forest ecosystems: Exploring the role of proximate analysis

Studying the thermodynamic properties of soil organic matter is a developing field that involves the measurement of the energy stored by the soil. Quantifying soil energy content is still challenging despite different methodological approaches are available to calculate that value. One of the options is the proximate analysis following the guidelines for the energetic characterization of biomass. However, proximate analyses are still unexplored for soils. In this paper, we investigate the potential of this analysis to contribute to study soil from a thermodynamic perspective. With that goal, 31 soil samples collected in mature oak forests following a depth transect were used for elemental, thermal and proximate analysis. Proximate analyses and energetic characterization were performed by simultaneous thermogravimetry and differential scanning calorimetry.These methods allowed fragmentation of the soil organic matter in water content, volatile matter, fixed carbon, and ash, as well as the quantification of the soil organic matter and energy content. Pearson's correlation showed significant relations among the proximate, the elemental components of soils and the energy. The equations relating all of these variables were calculated for soils from oak forests by partial least squares analysis. Equations representing the relationship between energy and the proximate fractions provide an additional alternative to calculate the heat of combustion of the soil organic matter. This value is the essential step for the thermodynamic characterization of soils.

Aerification Strategies Affecting Golf Green Subsurface Properties

Golf greens often become compacted due to: 1. Construction of less-than-ideal soil containing high percentages of silt and clay. 2. Extensive traffic not only from daily play but continuous maintenance often with heavy machinery. 3. Traffic not being sufficiently curtailed during periods of excessive soil moisture. A two-year field experiment was conducted on a 14-year-old U.S. Golf Association (USGA)-specified Crenshaw creeping bentgrass [Agrostis stolonifera L. var palustris (Huds.)] research putting green in Clemson, SC, to evaluate the effects of varying spring HTA size and timing on turfgrass rooting, soil organic matter (OM) and soil properties. Spring HTA treatments included 1.2-cm i.d. tines spaced at 5.1 cm x 5.1 cm in March and May (standard); 1.2-cm i.d. tines spaced at 3.8 cm x 3.4 cm in March only (2x); 0.9-cm i.d. tines spaced at 3.8 cm x 3.4 cm in March and May; and 0.6-cm i.d. tines spaced at 3.8 cm x 3.4 cm in March, April, May and June. All aerification was to a depth of 7.6 cm, with cores removed. Plots aerified with 0.6-cm tines had the least 2-year reduction in dry root weight (DRW). Plots aerified with 1.2-cm tines in March only (2x) had the greatest reduction in DRW and had the deepest thatch mat depth (TMD) across both years. This “doubling up” treatment would not be advisable on greens where low root mass or thatch accumulation is a concern. Plots aerified with 1.2-cm tines had higher thatch OM content in Year 2. Plots aerified with 0.6-cm tines had higher soil OM content across both years. Repetitive equal depth aerification did not create a layer of increased compaction. Turf managers can vary their spring HTA size and timing to increase TQ during periods where this is important (e.g., for a tournament) with manageable effects on surface, OM, and soil properties.

Biochemical composition of soil organic matter physical fractions under 32-year fertilization in Ferralic Cambisol

Biochemical properties of soil organic matter (SOM) are fundamental for soil fertility and health. However, it is unclear how fertilization regime influences the biochemical compositions and oxidation states of SOM and physical fractions. In this study, this issue was studied under four 32-year amendment regimes: unfertilized control, urea (N), N + calcium dihydrogen phosphate + potassium chloride (NPK), and NPK plus manure (NPKM). Three physical fractions: coarse particulate (> 250 μm, cPOM), fine particulate (53–250 μm, fPOM) and mineral-associated OM (< 53 μm, MAOM) were separated and measured by pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). Compared with the background in 1986, the SOM increased by 10.6%, 14.2%, 23% and 52% in unfertilized control, N, NPK, and NPKM, respectively. The red soil here had not reached carbon saturation, because of the low conversion efficiency (6.8%) from input-carbon to soil organic carbon (SOC). Physical size but not amendment type primarily regulated the SOM molecular composition, with relative selective retention of aromatics and lignin in both the cPOM and fPOM, whereas N-containing compounds (particularly amino-N) were enriched in MAOM due to their high abilities to adsorb soil minerals. The C oxidation state was also mainly dependent on physical size, with the highest value in fPOM. The sources of SOM and its fractions, dominated by microbial-derived compounds (60–90%), were independent of physical size and fertilization. In conclusion, physical size arrangement (proxy of microbial decomposition degree) played a more important role in regulating the SOM biochemical features than initial quality of various amendments.Graphical

Reclamation of ancient agricultural terraces in the Negev Highlands; soil, archeological, hydrological, and topographical perspectives

AbstractAncient terraced lands are considered badlands without profitable utilization except for urbanization. Nevertheless, this attitude prevents further agricultural utilization in addition to the loss of archaeological data. The study hypothesizes that the main influencing part in these systems is the retaining walls (RW). An analysis of their current influence on soil fertility, stability, and hydrology will indicate their adequate reclamation strategy. The objectives are to gather the influences and correlate them to the RW constructional state. In the Yeroham Hills, three parallel located terraced systems (one on the Wadi Shualim channel and the other, which is located on its banks) were studied. Their ancient agricultural utilization was dated, after in‐site excavations, to the Roman until early Islamic eras. Ten representative RWs were chosen, five from each terraced system. Their influences on the soil fertility, hydrology, and physical properties of the adjacent soil and 2 m ahead (the terrace) were studied. The finding indicates that the RW serves as a physical ecosystem engineer with positive influences on soil organic matter (0.5% higher content compared to the terrace) and land stability properties (maturated soil biocrust and higher aggregate stability). Comparison of the finding from both terraced irrigation systems, which differ in their conservation state, enables to determine the agricultural utilization and land stabilization after an adequate reclamation strategy, which is based on the RWs constructional parameters analyzed in‐site, and adaption to the current floodwater paths. The study's principles and analysis scheme enable the study and conservation of similar areas worldwide for increased utilization and profitability.

Dry–wet seasonal variations of microbially mediated carbon metabolism in soils of a floodplain lake

AbstractSeasonal water level fluctuations in floodplain lakes are known to alter carbon transport, yet it is unclear how such changes affect microbially mediated carbon metabolism. Poyang Lake is a typical floodplain lake linked to the Yangtze River and is significantly affected by water level fluctuations. In this study, we examined the differences of soil organic matter (SOM) properties, bacterial communities and carbon metabolic functions between dry (March) and wet (August) seasons in lake centre, delta and floodplain from Poyang Lake. Generally, the SOM properties (quantity and quality) and microbially mediated carbon metabolism in the three types of sampling areas have undergone greater changes from dry to wet season than bacterial community. Structural equation modelling and variation partition analysis indicated that SOM properties contributed more in shaping the carbon metabolism of microorganisms than bacterial community structures, especially in lake centre. Dry–wet seasonal changes of microbially mediated carbon metabolism in lake centre were mainly affected by amide C=O1650 and aliphatic C‐H2850, 2924, while the delta and floodplain were mainly affected by aromatic C‐O1234. Furthermore, we also found that bacterial community composition could better explain the effects of seasonal hydrology on carbon metabolism, rather than the diversity and assembly processes. We highlight that studies on tightly coupled changes in SOM and microbially mediated carbon metabolism can enhance the understanding of soil carbon dynamics across the floodplain lake.

Improving models to predict holocellulose and Klason lignin contents for peat soil organic matter with mid-infrared spectra

Abstract. To understand global soil organic matter (SOM) chemistry and its dynamics, we need tools to efficiently quantify SOM properties, for example, prediction models using mid-infrared spectra. However, the advantages of such models rely on their validity and accuracy. Recently, Hodgkins et al. (2018) developed models to quantitatively predict peat holocellulose and Klason lignin contents, two indicators of SOM stability and major fractions of organic matter. The models may help to understand large-scale SOM gradients and have been used in various studies. A research gap to fill is that these models have not been validated in detail yet. What are their limitations and how can we improve them? This study provides a validation with the aim to identify concrete steps to improve these models. As a first step, we provide several improvements using the original training data. The major limitation we identified is that the original training data are not representative for a range of diverse peat samples. This causes both biased estimates and extrapolation uncertainty under the original models. In addition, the original models can in practice produce unrealistic predictions (negative values or values &gt;100 mass-%). Our improved models partly reduce the observed bias, have a better predictive performance for the training data, and avoid such unrealistic predictions. Finally, we provide a proof of concept that holocellulose contents can also be predicted for mineral-rich samples (e.g., peat with mineral admixtures or potentially mineral soils). A key step to improve the models will be to collect training data that are representative for SOM formed under various conditions. This study opens directions to develop operational models to predict SOM holocellulose and Klason lignin contents from mid-infrared spectra.

Albic Podzols of Boreal Pine Forests of Russia: Soil Organic Matter, Physicochemical and Microbiological Properties across Pyrogenic History

Albic podzols under pine forests are more prone to fires on the planet. The influence of fire extends to all soil components, including chemical properties, microbiological characteristics, and the composition and structure of soil organic matter, which persists for a long time. Here, we present the results of a study of the morphological, physicochemical, and microbiological properties and features of soil organic matter (SOM) in the albic podzols of pine forests (Pinus sylvestris L.) not exposed to fires for a long time (from 45 to 131 years). The study areas are characterized by different numbers of old fires (from four to five) that occurred over the previous several centuries in various territories of the Russian Federation such as Central Siberia (CS) and the European North (EN). In general, the albic podzols developing in CS and EN are characterized by similar morphological and physicochemical properties, with high acidity and poor mineral horizons. In terms of the lower vegetation layer and stand parameters, forest communities at the CS sites have a lower density and species diversity than those in EN. The ground cover is almost completely restored 45 years after the surface fire. The upper mineral horizon of albic podzols in EN contains higher PAHs in comparison with similar horizons of the CS sites. In the soil of EN pine forests, the MB content in the mineral horizons is, on average, three times higher than those in CS. Differences were also found in the qualitative composition of the studied soils’ microbiomes. The EN soil communities are represented by a wide variety of bacteria and fungi. The presented soil parameters can be used as a reference in assessing the increasing impact of fires on pine forests and podzols.

Advances in Molecular and Microscale Characterization of Soil Organic Matter: Current Limitations and Future Prospects.

Soil organic matter (SOM) comprises a continuum of organic materials from granular organic debris to small organic molecules and contains more organic carbon than global vegetation and the atmosphere combined. It has remarkable effects on soil ecological functions and the global carbon cycle as well as the fate of pollutants in the terrestrial ecosystem. Therefore, characterization of SOM is an important topic in soil science, ecology, and environmental science. Chemical complexity and spatial heterogeneity are by far the two biggest challenges to our understanding of SOM. Recent developments in analytical techniques and methods provide the opportunity to reveal SOM composition at the molecular level and to observe its distribution in soils at micro- and nanoscales, which have greatly improved our understanding of SOM. This paper reviews the outstanding advances in SOM characterization regarding these two issues from target and nontarget analyses comprising molecular marker analysis, ultrahigh-resolution mass spectrometry analysis, and in situ microscopic imaging techniques such as synchrotron-based spectromicroscopy, nanoscale secondary ion mass spectrometry, and emerging electron and optical microscopic imaging techniques. However, current techniques and methods remain far from unlocking the unknown properties of SOM. We systematically point out the limitations of the current technologies and outline the future prospects for comprehensive characterization of SOM at the molecular level and micro- and nanoscales, paying particular attention to issues of environmental concern.

Biodegradable and biobased mulch residues had limited impacts on soil properties but reduced yield of the following crop in a low fertility soil

AbstractBiodegradable and biobased mulch films and fabrics (BDMs) are potentially sustainable alternatives to polyethylene plastic mulch film (PE) in vegetable production because BDMs can be incorporated into the soil by tillage at the end of the growing season for decomposition. However, grower adoption has been limited in part by concerns about slow degradation rates and possible adverse effects on soil health and productivity. The objective of this study was to measure the effects of soil incorporated residues from two BDMs and compost on soil chemical and physical properties and vegetable crop yield across two diverse locations [Lincoln (LNK) and Scottsbluff (SBF), NE, USA] during a 2-yr study. The BDMs, including a polylactic acid biofabric with embedded wood particles (PLA; 1.14 mm thick and 298 g m−2), and a starch-polyester bioplastic mulch film (STP; 0.015 mm thick and 20 g m−2), were applied in May 2017 for vegetable production. Mulches were incorporated in soil by tillage in September 2017 in half of the experimental plots and removed in the other half as a control. Compost was applied in fall 2017 and 2018 at rates between 42 and 60 Mg ha−1 to establish high and low (no compost) fertility soil environments within each location. Sweet corn (Zea mays) was grown in 2018 and cabbage (Brassica oleraceae) in 2019, and yield data were collected. The soil was sampled at ~6 month intervals for two years. The BDM residues had little effect on soil pH, organic matter or physical properties, but the incorporation of PLA in the soil at SBF reduced soil nitrate 6 months after the incorporation of residues. Nitrogen immobilization likely contributed to the 16% ± 5% reduction in sweet corn yield observed at SBF in plots without compost where BDM residues were incorporated compared to removed. No additional yield differences were detected in sweet corn (2018) or cabbage (2019) across locations or treatments, which suggests that BDM residues are less likely to immobilize nitrogen and reduce yield in high fertility soil environments. Given the potential environmental benefits of BDMs as an alternative to PE, future research should seek to mitigate the negative effects of BDM residues on crop yield, particularly in lower fertility soils.

Influence of Poly-3-hydroxybutyrate Micro-Bioplastics and Polyethylene Terephthalate Microplastics on the Soil Organic Matter Structure and Soil Water Properties.

Adverse effects of microplastics on soil abiotic properties have been attributed to changes in the soil structure. Notably, however, the effects on the supramolecular structure of soil organic matter (SOM) have been overlooked, despite their key role in most soil properties. This work accordingly investigated the influence of plastic residues at various concentrations on the SOM supramolecular structure and soil water properties. To model plastic residues of micro-bioplastics, spherical or spherical-like poly-3-hydroxybutyrate (PHB) was used, while polyethylene terephthalate (PET) was used as a model of conventional microplastics. The results suggest that both types of plastic residues affect SOM properties, including physical stability (represented by water molecule bridges), water binding (represented by decreased desorption enthalpy or faster desorption), and the stability of SOM aliphatic crystallites. The results further showed that the polyester-based microplastics and micro-bioplastics affected the SOM abiotic characteristics and that therefore the observed effects cannot be attributed solely to changes in the whole soil structure. Notably, similar adverse effects on SOM were observed for both tested plastic residues, although the effect of PHB was less pronounced compared to that of PET.

Holocene and recent fires influence on soil organic matter, microbiological and physico-chemical properties of peats in the European North-East of Russia

The influence of fires on the development and chemical composition of two Rheic Hemic Histosols in the native territory of the middle taiga of the Komi Republic was estimated. The development of peat on site I (SI) located in the south boarder of the middle taiga began in the Boreal period (about nine ths. years ago14C yr BP). The growth of peat on site II (SII) located at the foothills of the Northern Urals started in the middle of the Atlantic Holocene period (about 6.7 ths. years ago14C yr BP). This work shows that during the time of development, peatlands experienced various pyrogenic events. The organic horizons were burned out and often led to a change in the dominant ground cover plants. Also, the charcoal particles formed during the fire at the forest surrounding the bogs were transported by air and accumulated in the peat. The pyrogenic history of the studied peats is different, the SI was subjected to intense fires at least twice: at the beginning of formation and in the modern period (140 years ago). The Histosol on SII experienced only low-intensity and indirect fire effect. The highest burning activity of nearest forests in both sites estimated based on charcoal content occurred at the end of the Atlantic, middle of the Subboreal periods. It was shown that an increase in the aromatic compounds occurs in horizons with pyrogenic features; in some cases, an increase in the concentration of polycyclic aromatic hydrocarbons (PAHs) was revealed. The aromatic compounds content in the SOM is determined by the content of macroscopic charcoal particles with significant correlation (CAr-H(C), R = 0.49, p < 0.05, CAr-O,N, R = 0.68, p < 0.05). It is shown that a high frequency of fires leads to an increase in carbon stocks at Histosols.

Half-a-century effects of a slow-release nitrogen fertilizer, ureaformaldehyde, on stand growth and soil processes in a Scots pine stand

Slow-release nitrogen fertilizers have received little attention as alternatives to conventional fast-release fertilizers in N-limited boreal forests. Slow-release fertilizers better match the rate at which trees can uptake nutrients from the soil solution and are less likely to be vulnerable to losses to the environment. Ureaformaldehyde is a polymer that is synthesized from formaldehyde and urea and mainly used as a nitrogen fertilizer in lawns and greenhouse cultivations. Our goal was to assess ureaformaldehyde (UF) as a forest fertilizer. We aimed to determine its long-term effects on tree ring widths and stand basal area growth and how the effects differ from those of a conventional fast-release N fertilizer, ammonium nitrate (AN). We also attempted to determine whether the fertilizer additions changed soil organic matter properties in the long term. The study site was an unfertile Scots pine (Pinus sylvestris L.) stand with study plots with both fertilizer treatments that were performed 47 years ago and unfertilized control plots. As expected, AN addition resulted in a sharp increase in tree ring widths and the annual basal area increment that lasted for approximately seven years. UF addition caused a slower increase that lasted much longer, approximately 17 years. In addition, the UF addition showed indications that it slightly enhanced the growth even during the last decade. Our results also suggested that different fertilization treatments resulted in differences in tree size distribution. After almost a half century, some signs of UF-induced effects were still visible in soil organic matter; for instance, the humus layer in the UF treatment had a lower C-to-N ratio by 7 units than that in the humus layer of the AN treatment. In conclusion, slow-release ureaformaldehyde has a considerably longer effect on tree growth than conventional ammonium-nitrate fertilizer and, after almost a half century, there were signs that it still increased nitrogen availability for trees.

Modified Biochars and Their Effects on Soil Quality: A Review

Biochar (BC) has attracted attention due to its impacts on soil quality by enhancing soil fertility, carbon storage and contaminants immobilization. BC also induces changes in microbial community structure and enhances crop productivity in long term scenarios compared to many other organic amendments. However, information related to the role of modified BCs in altering the soil quality is still scarce. BC can be modified by using physical, chemical and microbial methods. Modified BC can change the functional groups, pore size, pore structure, surface area and chemical properties of soil, which plays a key role in changing the soil quality. The addition of modified BCs as soil amendment increased soil CEC (cation exchange capacity), EC (electron conductivity), pH, organic matter, hydraulic conductivity, soil porosity, infiltration rate, microbial activities (enzymes and community), nutrient profile and gas exchange properties, but it varies according to the soil structure and pervading environmental conditions. This study provides a basis for effective practical approaches to modifying BCs for improving soil quality.