Organic Matter Fractions Research Articles

Periodic membrane fractionation of freshwater organic matter reveals various reactivity patterns during chlorine/chloramine disinfection

Although drinking water disinfection has significantly reduced mortality from waterborne diseases, the formation of potentially harmful disinfection by-products (DBPs) remains a concern today. These DBPs emerge from the reaction of dissolved organic matter (DOM) with chlor(am)ine during disinfection. Identifying these DBP precursors from heterogeneous and complex DOM mixtures is challenging and to address this, a novel membrane fractionation protocol was developed to isolate and identify the organic DBP precursors from fresh water sources. A tight ultrafiltration and nanofiltration membrane were carefully selected to partition DOM into three molecular weight (MW) fractions: high (>20 kDa), medium (0.3–20 kDa) and low (<0.3 kDa) as defined by high performance-size exclusion chromatography- total organic carbon analysis. A mathematical tool was developed to optimize the fractionation protocol. Therefore, ultrafiltration was executed before nanofiltration and the concentration factor was maximized without inducing fouling to obtain the purest fractions. The mathematical tool was also set in place to predict the necessary diafiltration factor for each individual fractionation experiment based on the initial organic matter composition of the surface water allowing the fractionation protocol to be effective at all times. The protocol was applied to surface water samples collected six times across three seasons yielding a fraction enriched in high MW compounds (up to 50 %), a fraction having more than 80 % of medium MW compounds and a fraction only containing low MW compounds. Although the medium MW fraction showed the highest reactivity for the majority of the investigated DBPs, the low MW fraction showed high reactivity for iodinated trihalomethanes during chlorination and for haloacetonitriles during chloramination. The high MW fraction had the lowest reactivity towards DBPs, which can have important implications for a drinking water treatment since this fraction is generally the most effectively removed by e.g. coagulation, while the more important fractions for DBP formation such as the medium and low MW compounds remain in the water until the disinfection step.

Factors influencing mangrove carbon storage and its response to environmental stress

Mangrove forests serve as significant carbon sinks and play a crucial role in mitigating climate change. Currently, the response of mangroves to intensified climate change and human activities, and the factors that influence the magnitude of carbon storage in their sediments remain uncertain. To address these questions, two sediment cores were collected from the mangrove reserve in Pearl Bay, Guangxi, China. The activity of 210Pb in the sediment, grain size, bulk elemental composition, stable carbon isotopes, lignin, and different sediment organic matter (OM) fractions were investigated to determine the local mangrove’s response to climate change and human activities, as well as the factors influencing its carbon storage. The results showed mangrove forests with lower tidal ranges, slower sedimentation rates, and where OM predominantly originated locally tend to have larger carbon stocks. The mangrove OM (MOM) decreased progressively from the bottom to the top of the cores, indicating that the mangroves in Pearl Bay have possibly undergone degradation, which was further substantiated by the decrease in lignin content. Based on these results, the entire cores were divided into two stages: stable stage 1 (1963–2001) and degradation stage 2 (2001–2020). The cause of the mangrove degradation is likely due to the impact of human activities; however, these impacts are anticipated to gradually lessen in the future due to mangrove protection policies. Our results indicate that lignin can track and predict mangrove growth trends and provide guidance for the sustainable management of mangrove ecosystems.

Carbon and Nitrogen Stocks in Soil under Native Pastures in the Pantanal Wetland Biome, Brazil

The Pantanal has a high diversity of native pastures that provide food for many wild and domestic animals. Pantanal cattle raising is practiced in an extensive grazing-based system that varies according to the flood levels in the area. This study aimed to evaluate the fractions of soil organic matter in areas of native pastures under different uses and to quantify C and N stocks in sandy soils of the Pantanal. Soil samples from three native pastures differentiated by the predominance of Hymenachne amplexicaulis, Axonopus purpusii, and Mesosetum chaseae under different land use systems (continuous grazing and no grazing for five years) were collected and used to quantify the contents of carbon, nitrogen, and humic fractions. The dynamics of SOM are modified in grazed areas of the Pantanal, with influence on C and N, including their stocks. Native pastures of Axonopus purpusii and Hymenachne amplexicaulis showed an increase in organic matter after five years without grazing, while Mesosetum chaseae showed lower soil density and nitrogen levels. The highest C stock was observed in ungrazed areas of H. amplexicaulis (127.41 Mg ha−1 in the 0–40 cm layer). The dynamics of nitrogen in Pantanal pastures are influenced by the type of vegetation and land management, with higher nitrogen content in the surface layer (0–10 cm) and an increasing C/N ratio with soil depth, indicating lower nitrogen availability.

Pasture Recovery Period Affects Humic Substances and Oxidations of Organic Matter in Eastern Amazon

Land management practices that overlook soil limitations and potential have led to varying degrees of degradation. This study evaluates the carbon content in chemical and oxidisable soil fractions across different pasture recovery periods, comparing them to secondary forests. The management practices assessed include the following: secondary forest (SF), perennial pasture (PP), perennial pasture recovered five years ago (P5), and perennial pasture recovered eight years ago (P8), all on Plinthosols. We analysed carbon levels in oxidisable fractions and humic substances at depths of 0–0.10 m, 0.10–0.20 m, 0.20–0.30 m, and 0.30–0.40 m. The SF and P8 areas showed the highest organic matter content within the humic fractions, compared to the PP and P5 areas. Additionally, the P8 area demonstrated an increase in the labile and moderately recalcitrant fractions of organic matter, standing out among the different fractions evaluated. The multivariate principal component analysis indicated that P8 has the greatest impact on soil quality, followed by FS, P5, and PP. The pasture recovery over the past eight years has significantly improved soil carbon accumulation, highlighting the benefits of land restoration.

Nanofiltration membranes in asymmetric flow field-flow fractionation for improved organic matter size fractionation

Size fractionation of organic matter (OM) by asymmetric flow field-flow fractionation (FFFF) with ultrafiltration (UF) is limited by solute loss and peak resolution, particularly for low molecular weight fractions (<10 kDa). Nanofiltration (NF) with a molecular weight cut-off (MWCO) of ≤1 kDa can achieve significant OM retention and may improve OM fractionation. NF membranes with MWCOs ranging from 0.3 to 3 kDa were used to evaluate the retention and fractionation of nine OMs in the humic, polyphenol, biopolymer, and low molecular weight organic classes in stirred cell NF and FFFF. Membranes with an MWCO of 0.2–0.3 kDa (with a pure water permeability of 5–16 L.m−2.h−1.bar−1) with low OM interaction exhibited high peak recovery and resolution and hence improved OM fractionation. Loose NF (MWCO 3 kDa) exhibited a poor peak recovery because of a high OM loss due to both adhesion and permeation, particularly at high ionic strengths (>10 mM). A mixture of nine types of OM and natural organic matter samples from rivers, swamps and lakes achieved good fractionation with a 0.3 kDa (NF270) membrane at low ionic strength. The performance of NF for the analysis of OM and colloids in the smallest size range (≤1 kDa MW) could be further improved by optimizing the salt composition of the mobile phase and by overcoming the pressure limitations of FFFF channels.

Carbon in soil macroaggregates under coffee agroforestry systems: Modeling the effect of edaphic fauna and residue input

Crop diversification tends to favor the soil fauna community, soil aggregation, and consequently soil organic carbon (SOC) stock. Understanding the association between these attributes can help in understanding the dynamics of physical protection of soil organic matter. In this context, our study aimed to answer: (1) how does the edaphic macrofauna community and soil carbon and aggregate classes respond to two types of coffee agroforestry systems (coffee with Grevillea robusta and coffee with banana) and how these responses differ from native ecosystem; (2) how and to what extent are soil aggregation regulated by the complex structural interactions of plant residue input, SOC, and the soil faunal community? The work was conducted in the municipality of Planalto, state of Bahia, Brazil. Three systems were evaluated: agroforestry system of Coffee arabica L. with Grevillea robusta (CG); agroforestry system of Coffee arabica with Musa spp. (CB); and native forest (NF). Four plots were delimited in each system, in which dry fractionation of the soil was performed to obtain aggregates of classes >6, 6–4, 4–2 and < 2 mm. The macrofauna was sampled using the Tropical Soil Biology and Fertility Program method. The labile and total carbon of the soil and aggregates were determined and the carbon management indices were calculated. The CG and CB presented a greater amount of larger size aggregates (> 6, 6–4 and 4–2 mm) than the NF. The CB system provided more favorable conditions for the soil macrofauna. Despite this, both coffee agroforestry systems favored the occurrence of Oligochaeta. The CG was more favorable to maintain labile fractions of organic matter than the CB. The edaphic fauna show a close relationship with the formation of carbon aggregates and stabilization which was directly influenced by continuous input of plant residues in diverse coffee growing systems.

Precision and bias of carbon storage estimations in wetland and mangrove sediments.

Peaty sediments in coastal wetlands play an important role in the sequestration of atmospheric carbon dioxide and its belowground storage. Sediment cores are used to quantify organic matter (OM) density, estimated by multiplying the bulk density of a core segment by its OM fraction. This method can be imprecise, as repeated samples often differ widely. Recent studies have shown that sediment bulk density and OM fraction are not independent but tightly related by a function called the ideal-mixing model. Thus, the bulk density of the sediment can be directly estimated from its OM fraction. Statistical theory and simulations demonstrate that the high variance in the product estimation of OM density is the result of error propagation in the product of two functionally related variables with independent errors. Estimating OM density in wetland sediments using the ideal-mixing model is more precise than the traditionally used product estimate, especially in highly organic sediments.

Sediment organic matter predicts polycyclic aromatic hydrocarbon distribution in port sediments

We evaluated the influence of organic matter in polycyclic aromatic hydrocarbons (PAHs) in port sediments using multiple linear regression (MLR) and prediction models. Total sediment PAHs ranged between 45 and 3230 ng/g dw (average: 557 ± 962 ng/g dw), with PAHs primarily originating from river inputs, confined to areas near the estuaries. Coal/biomaterial combustion and petroleum mainly contribute to the presence of PAHs along estuaries, with medium-high to high ecological risks. MLR TPAHs prediction model included variables, namely, the marine-derived total organic carbon (TOCmar), terrestrial fraction of organic matter (Fterr), and carbon-to‑nitrogen ratio (CNR). Results indicate that mainly marine- followed by terrestrially-derived organic matter influenced sediment PAH distribution. Total organic nitrogen and CNR were variables in the toxic equivalent (TEQ) prediction model, demonstrating that terrestrial pollution sources primarily influenced TEQ. The study analyzes and predicts the impact of organic matter and its sources on the fate and transport of PAHs in port sediments.

Labile not stable SOC fractions constitute the manageable drivers of soil health advances in carbon farming

The assessment of soil health and the determination of carbon stability in soils are current challenges that have gained momentum through initiatives at national as well as international scales. However, inferring universally valid soil health parameters that are directly linked to carbon permanence remains challenging. Our aim was to evaluate the potential of simultaneous thermal analysis (STA) for an improved monitoring of soil health advances in the context of carbon farming strategies. For this purpose, an on-farm comparison of soil health in ten conservation agricultural systems with adjacent conventional farms was performed based on STA and thermal measures were related to key biological and physical indicators for monitoring soil functions. Using an autocorrelation-based approach, we identified independent thermal indicators, revealing that carbon farming efforts predominantly increased labile soil organic matter fractions in the range of 300–400 °C, while thermally more recalcitrant fractions did not respond to farming system transformation. Similarly, most soil health indicators revealed highest correlation with temperature ranges of mass loss of labile organic matter fractions. The relation of STA with commonly used soil health indicators was highest for soil organic carbon (SOC, r=0.971) and total nitrogen (TN, r=0.981). However, also inference on microbial activity parameters such as dimethylsulfoxid reduction, microbial biomass carbon and substrate-induced respiration could be demonstrated with r>0.663. The results thus highlight key temperature ranges of organic matter stability for future soil monitoring tasks of climate change mitigation potentials of carbon farming and related advances in soil health.

Model of U and 226Ra uptake by Spergularia rubra (L.) J. Presl & C. Presl in an area affected by Cu ore mining

Spergularia rubra (L.) J. Presl & C. Presl has a mycorrhizal resistance that leads to increased uranium uptake. The results show that 35% of the 238U is retained in the carbonate fraction and 59% in the residual or non-reactive fraction. 226Ra shows a different pattern with an average association of 19% in the organic matter fraction, 10% in the carbonate compounds and the remaining 71% in the residual fraction. The relationships between the activity concentrations of 238U and 226Ra in the soil fractions and in Spergularia were found to be statistically representative of the carbonate and organic matter fractions, respectively.

Efficient and sustained inhibition of ammonia nitrogen release from sediment in water by microbial self-aggregation zeolite layer.

Despite global efforts to manage water eutrophication, the continual release of ammonia nitrogen from sediments maintains the eutrophic state of water bodies, presenting serious challenges to the management. In order to find an efficient method for sediment remediation, the experiment of using signal molecules to enhance the adhesion of microorganisms on zeolite was carried out. Five different zeolitic ammonium adsorptions were examined using two different signal molecules, N-(3-oxohexanoyl)-L-homoserine lactone (OHHL) and N-(β-ketocaproyl)-DL-homoserine lactone (C6), to enhance microbial attachment on two types of zeolites. The results showed that the modified microbial attached Z1 zeolite reinforced with signal molecule C6 had the best effect. The effect was better in the case of high ammonium adsorption, and the TN removal could reach 7.99mg·L-1 with an inhibition rate of 90.08%. The ammonia nitrogen removal reached 4.75mg·L-1 with an inhibition rate of 87.64%, and the ammonia nitrogen and total nitrogen of the overlying water reached the surface III water quality standard. In addition, the addition of the signal molecule increased the zeta potential on the surface of the bacterial colloid. In addition, the amount of protein I in the dissolved organic matter (DOM) fraction increased, improving microbial adhesion ability and facilitating their attachment to the zeolite surface. The signal molecule C6 could increase the zeta potential of microbial surface and promote the production of protein I, thus strengthening the attachment of zeolite biofilm and improving the water quality.

Long-term integrated agronomic optimization maximizes soil quality and synergistically improves wheat yield and nitrogen use efficiency

Integrated agronomic optimization (IAO) adopts suitable crop varieties, sowing dates, planting density and advanced nutrient management to redesign the entire production system according to the local environment, which can achieve synergistic improvements in crop yields and resource utilization. However, the intensity and magnitude of the impacts of IAO on soil quality under long-term intensive production and high nitrogen use efficiency (NUE) require further clarification. Based on a 13-year field experiment conducted in Dawenkou, Tai'an, China, we investigated the effects of four cultivation modes on the grain yield, NUE, soil aggregate structure, as well as the fraction of organic matter (SOM) and soil quality, reflected by integrated fertility index (IFI) during the winter wheat maturation period in 2020–2022. The four cultivation modes were traditional local farming (T1), farmer-based improvement (T2), increased yield regardless of production cost (T3), and integrated soil–crop system management (T4). As IAO modes, T2 and T4 were characterized by denser planting, reduced nitrogen (N) fertilizer application rates, and delayed sowing compared to T1 and T3, respectively. In this long-term experiment, IAO was found to maintain aggregate stability, increase SOM content (by increasing organic carbon and total nitrogen of the light fraction (LF) and the particulate organic matter fraction (POM)), and improve SOM quality by increasing the proportions of LF and POM and the ratio of organic carbon to total nitrogen in SOM. Compared to T1, the IFI of T2, T3, and T4 increased by 10.91, 23.38, 25.55%, and by 17.78, 6.41, 28.94% in the 0–20 and 20–40 cm soil layers, respectively. The grain yield of T4 was 22.52% higher than that of T1, reaching 95.98% of that in T3. Furthermore, NUE of T4 was 35.61% higher than that of T1 and T3. In conclusion, our results suggest that T4 synergistically increases grain yield and NUE in winter wheat, while maximizing soil quality.

Enhanced silicate weathering accelerates forest carbon sequestration by stimulating the soil mineral carbon pump.

Enhanced silicate rock weathering (ERW) is an emerging strategy for carbon dioxide removal (CDR) from the atmosphere to mitigate anthropogenic climate change. ERW aims at promoting soil inorganic carbon sequestration by accelerating geochemical weathering processes. Theoretically, ERW may also impact soil organic carbon (SOC), the largest carbon pool in terrestrial ecosystems, but experimental evidence for this is largely lacking. Here, we conducted a 2-year field experiment in tropical rubber plantations in the southeast of China to evaluate the effects of wollastonite powder additions (0, 0.25, and 0.5 kg m-2) on both soil organic and inorganic carbon at 0-10 cm depth. We found that ERW significantly increased the concentration of SOC and HCO3 -, but the increases in SOC were four and eight times higher than that of HCO3 - with low- and high-level wollastonite applications. ERW had positive effects on the accrual of organic carbon in mineral-associated organic matter (MAOM) and macroaggregate fractions, but not on particulate organic matter. Path analysis suggested that ERW increased MAOM mainly by increasing the release of Ca, Si, and Fe, and to a lesser extent by stimulating root growth and microbial-derived carbon inputs. Our study indicates that ERW with wollastonite can promote SOC sequestration in stable MOAM in surface soils through both the soil mineral carbon pump and microbial carbon pump. These effects may have been larger than the inorganic CDR during our experiment. We argue it is essential to account for the responses of SOC in the assessments of CDR by ERW.

Temporal Variations in Fire Impacts on Characteristics and Composition of Soil-Derived Dissolved Organic Matter at Qipan Mountain, China.

Dissolved organic matter (DOM), the most reactive fraction of forest soil organic matter, is increasingly impacted by wildfires worldwide. However, few studies have quantified the temporal changes in soil DOM quantity and quality after fire. Here, soil samples were collected after the Qipan Mountain Fire (3-36 months) from pairs of burned and unburned sites. DOM contents and characteristics were analyzed using carbon quantification and various spectroscopic and spectrometric techniques. Compared with the unburned sites, burned sites showed higher contents of bulk DOM and most DOM components 3 months after the fire but lower contents of them 6-36 months after the fire. During the sharp drop of DOM from 3 to 6 months after the fire, carboxyl-rich alicyclic molecule-like and highly unsaturated compounds had greater losses than condensed aromatics. Notably, the burned sites had consistently higher abundances of oxygen-poor dissolved black nitrogen and fluorescent DOM 3-36 months after the fire, particularly the abundance of pyrogenic C2 (excitation/emission maxima of <250/∼400 nm) that increased by 150% before gradually declining. This study advances the understanding of temporal variations in the effects of fire on different soil DOM components, which is crucial for future postfire environmental management.

Improved Characterization of Soil Organic Matter by Integrating FT-ICR MS, Liquid Chromatography Tandem Mass Spectrometry, and Molecular Networking: A Case Study of Root Litter Decay under Drought Conditions.

Understanding of how soil organic matter (SOM) chemistry is altered in a changing climate has advanced considerably; however, most SOM components remain unidentified, impeding the ability to characterize a major fraction of organic matter and predict what types of molecules, and from which sources, will persist in soil. We present a novel approach to better characterize SOM extracts by integrating information from three types of analyses, and we deploy this method to characterize decaying root-detritus soil microcosms subjected to either drought or normal conditions. To observe broad differences in composition, we employed direct infusion Fourier-transform ion cyclotron resonance mass spectrometry (DI-FT-ICR MS). We complemented this with liquid chromatography tandem mass spectrometry (LC-MS/MS) to identify components by library matching. Since libraries contain only a small fraction of SOM components, we also used fragment spectral cosine similarity scores to relate unknowns and library matches through molecular networks. This integrated approach allowed us to corroborate DI-FT-ICR MS molecular formulas using library matches, which included fungal metabolites and related polyphenolic compounds. We also inferred structures of unknowns from molecular networks and improved LC-MS/MS annotation rates from ∼5 to 35% by considering DI-FT-ICR MS molecular formula assignments. Under drought conditions, we found greater relative amounts of lignin-like vs condensed aromatic polyphenol formulas and lower average nominal oxidation state of carbon, suggesting reduced decomposition of SOM and/or microbes under stress. Our integrated approach provides a framework for enhanced annotation of SOM components that is more comprehensive than performing individual data analyses in parallel.

Size and polarity fractions of mobile organic matter from manure affect the sorption of sulfadiazine, caffeine and atenolol in soil

Waste-derived organics introduced to soils along with pharmaceutical active compounds (PhAC) are a crude mixture of compounds occurring in various size and polarity fractions. They affect the sorption of PhACs to soil; however, the relevant knowledge is still insufficient. The effects of different size and polarity fractions of manure-derived mobile organic matter (<63 µm) on the sorption of sulfadiazine, caffeine and atenolol to five topsoils were investigated. Mobilization of the PhACs was strongest in the presence of dissolved organic matter (mDOM, <0.45 µm), with a reduction of Kd of sulfadiazine, caffeine and atenolol by mean factors of 0.66, 0.57 and 0.41, respectively. The mobilizing effects of colloidal organic matter (0.45–10 µm) were slightly smaller. Fine particulate organic matter (10–63 µm) reduced the sorption of the PhACs in slightly acidic soils (pH 6.0), but increased it in strongly acidic soil (pH 4.3). Furthermore, hydrophobic (HO-mDOM) and hydrophilic (HI-mDOM) fractions of mDOM reduced the sorption capacity but increased the sorption nonlinearity of PhACs in soils. Effects of HO-mDOM and HI-mDOM were PhAC specific. It is suggested to consider the varying impacts of mobile fractions in animal manure and/or treated wastewater in evaluating the fate and environmental relevance of associated PhACs.

Molecular features of uranium-binding natural organic matter in a riparian wetland determined by ultrahigh resolution mass spectrometry

Tims Branch riparian wetland located in South Carolina, USA has immobilized 94 % of the U released >50 years ago from a nuclear fuel fabrication facility. Sediment organic matter (OM) has been shown to play an important role in immobilizing U. Yet, uranium-OM-mineral interactions at the molecular scale have never been investigated at ambient concentrations. The objectives of this study were to extract, purify, and concentrate U-bound sediment OM along the stream water pathway and perform molecular characterization using Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). Out of 9614 identified formulas, 715 contained U. These U-containing formulas were enriched with Fe, N, and/or S compared to the total OM. Lignin-like and protein-like molecules accounted for 40 % and 19 % of the U-containing formulas, respectively. Phosphorus-containing formulas were found to exert an insignificant influence on complexing U. U-containing formulas in the ‘mobile’ (groundwater extractable) OM fraction had lower (reduced) nominal oxidation states of carbon (NOSC); and less aromatic moieties than OM recovered from the ‘immobile’ (sodium pyrophosphate extractable) OM fraction. U-containing formulas in the redox interfacial zones (stream banks) compared to those in nearby up-slope zones tended to have smaller molecular weights; lower NOSC; higher contents of COO and/or CONO functional groups; and higher abundance of Fe-containing formulas. Fe was present in 38 % of the U-containing formulas but only 20 % of the total OM formulas. It is postulated that Fe played an important role in stabilizing the structure of sedimentary OM, especially U-containing compounds. The identification for the first time of hundreds of Fe-U-OM formulas demonstrates the complexity of such system is much greater than commonly believed and numerically predicting U binding behavior in OM-rich systems may require greater use of statistical or artificial intelligence approaches rather than deterministic approaches limited to measuring metal complexation with well-defined individual analogue organic ligands.

Understanding Zinc Transport in Estuarine Environments: Insights from Sediment Composition

Sediments are sources and sinks of heavy metals in water, and estuaries are heavily influenced by human production and life. Therefore, it is of great significance to study the composition of estuarine sediments and the relationship between their components to understand the transport and transformation pathways of heavy metals in the environment. In this research, we investigated the characteristics and patterns of Zn adsorption by organic–inorganic composites, organic–clay mineral composites, and iron oxide–clay mineral composites in eight estuarine sediment samples from Dianchi Lake. The results show that both Langmuir and Freundlich isothermal models can describe the adsorption behaviour of the adsorbent better. The order of the adsorption capacity of the three groups of samples for zinc was organic–inorganic composites &gt; organic–clay mineral composites &gt; iron oxide–clay mineral composites. Through FTIR and XRD analyses, the adsorption of Zn2+ on the three groups of samples was dominated by electrostatic attraction and coordination adsorption, accompanied by the occurrence of ion exchange and co-precipitation. After FTIR semi-quantitative analysis, it was found that the source of the differences in the high and low Zn adsorption of the three types of samples may be mainly due to the content of phenolic functional groups in the organic matter. This may be related to the low redox site of the phenolic hydroxyl group, which, as an electron donor, is susceptible to electrostatic attraction and complexation with heavy metal cations. The organic–inorganic composite has a higher adsorption capacity for Zn when the ratio of the active fraction of organic matter to the free iron oxide content is 0.65–0.70. In this range, the organic matter can provide enough negative charge without making the sample surface too dense. Iron oxides can also activate the sample by providing sufficient contact between the clay minerals and the organic matter. When this ratio is too high or too low, it will be unfavourable for Zn adsorption.

Analysis of organic and mineral nitrogen, total organic carbon and humic fractions in Ferralsols: an approach using Vis-NIR-SWIR, MIR and X-ray fluorescence spectroscopy

This work aimed to develop suitable predictive models for ammonium, nitrate, total nitrogen, total organic carbon and soil humic fractions, for Ferralsols, using Vis-NIR-SWIR, MIR and X-ray fluorescence spectroscopic techniques in conjunction with machine learning algorithms, Cubist, PLSR, Random Forest and Support Vector Machine. Chemical analyzes were carried out to determine nitrate, total nitrogen, total organic carbon and chemical fractionation of soil organic matter, as well as spectral analyzes using Vis-NIR-SWIR spectroscopy, MIR and X-ray fluorescence. The spectroscopy results were processed using RStudio v. 4.1.3, applying Cusbist, PLSR, Random Forest and Support Vector Machine machine learning algorithms to create predictive models and describe spectral curves and Pearson correlation. Of the prediction models developed for nitrogen, total organic carbon and humic fractions, the PLSR and Support Vector Machine algorithms presented the best predictive performances. The descriptive analysis of the spectra identified the main absorption bands and the location of the bands sensitive to the attributes of interest. The correlation analysis proposed that the use of Vis-NIR-SWIR, MIR and XRF spectroscopic techniques were effective in predicting the contents of nitrogen, total organic carbon and humic fractions in soil with a medium sandy texture. However, it is important to highlight that each technique has its characteristic mechanism of action, Vis-NIR-SWIR and MIR detect the element based on overtones and fundamental tones, while XRF is based on the atomic number of the elements or elemental association.

Effect of soil management on carbon stock and soil aggregation in an area of natural regeneration and surrounding systems in the Atlantic Forest biome

This study aimed to quantify total organic carbon (TOC), carbon of humic substances (HS), and their stocks and evaluate the soil structural stability of areas with different uses under sandy loam soil texture. Soil samples were collected from managed areas and a reference area: Permanent Pasture (PP), No-Till (NT), Private Natural Heritage Reserve in the process of natural regeneration (PNHR) and Native Forest (FN). Dry mass analysis, carbon stock quantification, chemical fractionation of soil organic matter and soil aggregation were carried out. The NF area had the highest deposition of litter mass (ML). The PP and NT areas had the highest bulk density (Bd). TOC and Stock-C contents were higher in PNHR, followed by NF, and stratification index (STRATI) was also higher in the regeneration area. The NT, PNHR, and NF areas had a higher proportion of carbon fulvic acid fraction (C-FA) than carbon humic acid fraction (C-HA), but the fraction with the highest representation in all areas was carbon humin fraction (C-HUM). The PP, PNHR, and NF areas obtained the best aggregate stability indicators, as well as a higher proportion of macroaggregates, with the NT area having low aggregate stability. Recovery of C contents was observed in recent years in the area of PNHR, leading to a greater storage of C, which shows a quantitative recovery of C in the soil in this area after four years of natural regeneration. Furthermore, the PP and NT areas present a lower capacity for C sequestration, mainly due to the management conditions. Keywords: aggregate stability, climate change, crop production, soil quality.