Humification Of Soil Organic Matter Research Articles

Thermodegradation of organic matter in soils of different mineral composition in Brazil

Thermodegradation is an analytical tool that quantifies the loss of organic carbon under increasing temperatures. The degradation process is related to chemical functions and provides data on the stability of soil organic matter (SOM). There needs to be more information about SOM stability in different Brazilian ecosystems. This study aimed to evaluate SOM stability under three tropical environments: Dry Forest, Brazilian Savanna, and Atlantic Forest. Thus, we related thermal stability to soil mineral composition and SOM quality and quantity. We analyzed samples of the surface horizon of four illitic soil profiles sampled in Dry Forest (P1 to P4), three soil profiles in Cerrado (Brazilian Savanna), with predominant 2:1 clay (P5), iron oxide (P6), and gibbsite (P7), and a kaolinite profile from Atlantic Forest (Rainforest) (P8). Mineralogical, chemical, and physical analyses of the soils were studied to better comprehend soils' behavior under thermodegradation. The thermic treatment was performed by heating air-dried fine earth (ADFE) samples at 100, 200, 300, 400, and 500 °C for 2 h. The results were submitted to sigmoidal regression with four points and presented a good curve fit (r2 > 0.99). Dry Forest soils with the most humified SOM presented greater resistance to loss of SOM by the thermic process. However, P7 (gibbsitic clayey soil) stood out and was the most resistant to thermodegradation. P4 was the sandiest soil and showed the curve most affected by the thermal process, indicating the importance of clay content to SOM stability. The results suggest that the TOC (content and quality), calcium content, and clay (content and type) play essential roles in determining the thermostability of SOM in different ecosystems.

Addition of Biochar and Fertiliser Drives Changes in Soil Organic Matter and Humic Substance Content in Haplic Luvisol

Humic substances (HSs) constitute a primary component of soil organic matter (SOM) and play a crucial role in soil formation and fertility. However, comprehensive information regarding quantitative and qualitative changes in HS following biochar’s application to soil still needs to be improved. This study reports on the impact of biochar application at rates of 0, 10, and 20 t ha⁻1 (B0, B10, B20), both with and without nitrogen fertilisation at varying levels (N0, N1, N2), on SOM and HS contents throughout the cropping seasons between 2014 and 2019. The findings reveal changes in SOM and HS contents due to biochar addition and fertilisation. Notably, the most substantial increase in soil organic carbon content was observed in the B20N1 and B10N1 treatments, in stark contrast with the reference B0N0 treatment. A decrease in humification of SOM was noted across all treatments involving biochar, whether alone or combined with different N fertilisation levels. An interesting positive change in HS contents was observed in B10N2, where an increase in humic acids and a decrease in fulvic acids enhanced HS stability and improved HS quality. These findings shed light on the intricate dynamics of SOM and HSs in response to biochar application and nitrogen fertilisation over multiple vegetation seasons of crops on loamy Haplic Luvisols in Central Europe.

Tillage Long-Term Effects on Soil Organic Matter Humification and Humic Acids Structural Changes in Regosol Profiles Typical of an Arid Region

Tillage Long-Term Effects on Soil Organic Matter Humification and Humic Acids Structural Changes in Regosol Profiles Typical of an Arid Region

Soil organic mater management – a decisive measure in climate change mitigation and adaptation

Global warming requires the implementation of both immediate and long-term mitigation and adaptation measures in agriculture, which is affected by greenhouse gas emissions through the use of practices from the industrial model arsenal of agricultural intensification (oversaturation of planting areas with arable crops and lack of crop rotations with a greater diversity of arable and successive crops; excessive tillage; irrigation; application of mineral fertilizers, especially nitrogen etc.). Data from the long-term field experiments at Research Institute of Field Crops ”Selecția” (Bălți, Republic of Moldova) are proving the dominance of mineralization over humification of soil organic matter with the emissions of CO2 and oxides of nitrogen in the atmosphere. Chernozem soils have a high potential for carbon sequestration and consequently for mitigation and adaptation to climate change. Sustainable and resilient management of soil organic matter is one of the key issues for the transition to a more sustainable agriculture, capable to supply ecosystem and social services.

First assessment of soil mesofauna, microbiota, and humic substances associations in a minesoil revegetated with four grasses in Brazil: An 18-year field study

Moving away from coal protects our environment and soil. However, coal use in 2022 exceeded all previous years, systematically generating minesoils. The reestablishment of vegetation and organisms in minesoils is jeopardized by excessive soil compaction, eventual acidity, and depletion of soil organic matter (SOM), fauna, and microbial communities. Therefore, monitoring the recovery of soil attributes and functions as influenced by revegetation species is crucial to understanding the processes and time of ecological restoration. We aimed to verify if 18 years of revegetation with perennial grasses (Hemarthria altissima, Paspalum notatum, Cynodon dactylon, Urochloa brizantha) transformed the minesoil a habitat for mites, springtails and other invertebrates as well as for soil microorganisms. Moreover, we investigated associations between these biological indicators with soil humic substances (HS) content. The minesoil is located in Candiota (Brazil), and was constructed in 2003, when revegetation with the grasses started. In 2021, soil samples (0.10 m depth) were collected to determine mites and springtails abundance, microbial respiration, carbon and metabolic quotient, soil, HS content, pH, bases, and aluminum saturation. In order to monitor the soil attributes recovery by the perennial grasses, the means of treatments were compared to the control using percentage differences (positive or negative), as the control was not part of the experimental design. The relationship between the biological variables and the soil variables was assessed using Spearman correlation, and the Canonical Correspondence Analysis was used to identify the performance of each grass in relation to the dataset. The associations observed confirm that the minesoil recovery process is still in its initial, mainly between soil biological functions with SOM humification. Positive associations occurred between mites and microbial respiration and accumulation of humin, especially with Urochloa brizantha revegetation.

Quantitative Approaches in Assessing Soil Organic Matter Dynamics for Sustainable Management

The aim of this study was to provide an overview of the approaches and methods used to assess the dynamics of soil organic matter (SOM). This included identifying relevant processes that describe and estimate SOM decomposition, lability, and humification for the purpose of sustainable management. Various existing techniques and models for the qualitative and quantitative assessment of SOM were evaluated to gain a better understanding of advances in organic matter transformation. This evaluation aimed to identify the strengths, limitations, and applications of these techniques and models, and to highlight new research directions in the field. Quantitative analysis of SOM can be performed using various parameters, including oxidation kinetics, lability, carbon management index, humification degree, humification index, and humification ratio. On the other hand, qualitative evaluation of SOM can involve techniques such as oxidizability, high-performance size-exclusion chromatography, electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry, visual examination, smell, assessment of microorganism content, plant growth, cation exchange capacity, type of organic material, and decomposition. These techniques and parameters provide valuable insights into the characteristics and transformation of SOM, enabling a comprehensive understanding of its dynamics. Evaluating SOM dynamics is of utmost importance as it is a determining factor for soil health, fertility, organic matter stability, and sustainability. Therefore, developing SOM models and other assessment techniques based on soil properties, environmental factors, and management practices can serve as a tool for sustainable management. Long-term or extensive short-term experimental data should be used for modeling to obtain reliable results, especially for quantitative SOM transformation analysis, and changes in the quality and quantity of SOM should be considered when developing sustainable soil management strategies.

Disentangling drivers of soil organic carbon storage in deltaic rice paddies from the Ebro Delta

Paddy farming can potentially sequester carbon. However, agricultural practices may alter the stability of the soil organic carbon (SOC) stocks and thereby increase carbon mobilization in the topsoil and subsoil. We hypothesize that both agricultural practices and soil physical–chemical characteristics, mostly those related to the type of the parental soil where the paddy is established, play an important role in SOC stabilization and sequestration. To test this, we profiled the biochemical characteristics of soil organic matter (SOM) and the SOC concentrations in sediment cores of 10 rice fields from the Ebro Delta (Northeast Spain) representing former reclaimed habitats (i.e., peatlands, meadows, coastal lagoons, riverbanks and salt marshes). The effects of physical–chemical soil properties on SOM content were tested with Generalized Linear Models and the best models were selected using information-theoretic approach. The optical characteristics of SOM extracts were analyzed by UV–Visible and fluorescence spectrophotometry, and six fluorescence components were identified by Parallel Factor Analysis (PARAFAC). Higher clay and lower sand content explained the greater SOM presence in topsoil while higher clay content and salinity prevailed as the main explanatory factors in the subsoil showing a positive correlation with SOM content. The results revealed a correlated gradient of SOM quantity and quality where in SOM-rich soils both the aromaticity and the humification degree were higher while in soils with lower SOM content it was fresher and more microbially derived. Current agricultural practices favored SOM humification in the topsoil while the variability in SOM quality in subsoil is attributed to the combination of soil physical–chemical characteristics (pH, conductivity and clay content) and the previous habitat’s influence. This study represents a comprehensive empirical analysis on the carbon stocks in rice fields and the identification of soil physical–chemical factors, related to prior land uses, favoring soil carbon accumulation. These results may have major implications in decision-making process for climate change mitigation in vulnerable Mediterranean coastal paddies.

Impact of Urea-Intercalated-Biochar on N-Release in Soil and Humified Soil Organic Matter

This research investigated the impact of urea-intercalated-biochar (ICB) on nitrogen release as well as on humified soil organic matter (SOM) distribution in highly weathered soil. Incubation studies were performed with a typical dystrophic red Ultisol and with 10 treatments: soil without amendment (control, CON), soil with three doses of biochar (BC75, BC145, and BC 290), and soil with ICB doses (ICB75, ICB145 and ICB 290). BC and ICB were characterized by 13C Nuclear Magnetic Resonance 13C-NMR CP/MAS spectroscopy and elemental analyses. N-extractable forms were periodically determined by Kjeldahl method and humic substances (HS) distribution was analyzed on the 28th day after incubation begins (DAI). Intercalation of urea in BC increased sample N content from 2.7 to 22 %, whereas that of C decreased from 40 % to 28 %. As a consequence, C: N decreased from 14.9 to 1.3. The 13C NMR spectra of BC and ICB were similar but relative abundance of major organic functional groups differs, for example, ICB presented a greater proportion of C=O groups due to the carbonyl group of urea and a greater proportion of N/O alkyl C, O-alkyl C, and anomeric C groups due to the addition of starch. There was a significant increase in the concentration of extractable N-NH4+ by addition of urea from the onset of incubation down late period and a significant difference (P > 0.05) was obtained between the ICB and BC over time. This could be as a result of the less accessible form of N in the biochar materials due to the pyrolysis process. There was no evidence of extractable N-NO3- ion until 14 DAI, significant difference in N-NH4+ concentrations at 28 DAI between the ICB and control was observed over time and the highest value recorded from ICB treated pots at 145 and 290 kg N ha-1.

The long-term effects of intensive grazing and silvopastoral systems on soil physicochemical properties, enzymatic activity, and microbial biomass

Brazil is the largest exporter and the second-largest beef producer in the world. The country's biggest challenge has been to increase the production capacity of soils in an environmentally sustainable way. In this context, agricultural practices that preserve the environment have demonstrated high productivity and sustainability by emphasizing intensive grazing management and silvopastoral systems. In this study, the effects of the conversion of a native forest (FO) into different pasture-based cattle production systems were assessed in long-term field experiments using microbiological and physicochemical measurements. Five pasture systems were evaluated: i) irrigated high stocking rate pasture (IHS); ii) rainfed high stocking rate pasture (RHS); iii) rainfed moderate stocking rate pasture (RMS); iv) silvopastoral system with moderate stocking rate (SPS); and v) degraded pasture (DP), the latter used as a reference for conventional pasture management, extensively used by farmers. Soil samples (0–10 cm) were analyzed for bulk density (BD), total carbon content (TC), soil organic matter humification index (HLIFS), activities of soil enzymes β-glucosidase (BG) and arylsulfatase (ARYL), microbial biomass carbon (MBC), and basal respiration (BR). The results showed that all managed pastures presented higher soil carbon content than DP (16.2 ± 1.7 g kg−1), especially the RMS system, which presented the highest carbon content (32.9 ± 0.9 g kg−1). Activities of BG and ARYL were more sensitive to detecting management changes than MBC and BR. Increased activities of BG and ARYL were observed in the RMS system, possibly due to the higher amount of biomass input, while this effect was less expressive in the other management systems. The results indicated that soil enzymatic activities are sensitive to land use and management and could be used as soil quality indicators in pasture-based beef cattle production for different systems in tropical soils.

Changes in Relationships between Humic Substances and Soil Structure following Different Mineral Fertilization of Vitis vinifera L. in Slovakia

The quantity and quality of soil organic matter (SOM) depending on many edaphic and environmental factors may change in response to agriculture-related practices. The SOM humification process can be supported by the application of mineral fertilizers, but in the production vineyards, such information is lacking. NPK fertilizer alters the soil quality, and therefore, the aim of this study was to: (1) assess the extent and dynamics of different NPK (control—no fertilization; 1st NPK; and 3rd NPK levels) rates to the soil with grass sward cover in a productive vineyard on changes in SOM, humic substances (HS), and soil structure, and (2) identify relationships between SOM, HS, and soil structure. Results showed that the share of humic acids in soil organic carbon decreased only in NPK1 compared to control and NPK3 treatments. The color quotient of humic substance values in NPK1 and NPK3 increased by 4 and 5%, respectively, compared to control. Over a period of 14 years, the content of soil organic carbon increased by 0.71, 0.69, and 0.53 g kg−1 year−1 in the control, NPK1, and NPK3, respectively. The content of HS increased linearly with slight differences due to NPK application. The vulnerability of the soil structure decreased due to fertilization—more at the higher NPK level. The rate of formed soil crust was decreasing in the following order: control > NPK1 > NPK3. In the control treatment, the relations between SOM, HS, and soil structure were most abundant and with the greatest significance, while with the increasing level of NPK, these relations lost their significance.

Plant-microbial linkages underpin carbon sequestration in contrasting mountain tundra vegetation types

Tundra ecosystems hold large stocks of soil organic matter (SOM), likely due to low temperatures limiting rates of microbial SOM decomposition more than those of SOM accumulation from plant primary productivity and microbial necromass inputs. Here we test the hypotheses that distinct tundra vegetation types and their carbon supply to characteristic rhizosphere microbes determine SOM cycling independent of temperature. In the subarctic Scandes, we used a three-way factorial design with paired heath and meadow vegetation at each of two elevations, and with each combination of vegetation type and elevation subjected during one growing season to either ambient light (i.e., ambient plant productivity), or 95% shading (i.e., reduced plant productivity). We assessed potential above- and belowground ecosystem linkages by uni- and multivariate analyses of variance, and structural equation modelling. We observed direct coupling between tundra vegetation type and microbial community composition and function, which underpinned the ecosystem's potential for SOM storage. Greater primary productivity at low elevation and ambient light supported higher microbial biomass and nitrogen immobilisation, with lower microbial mass-specific enzymatic activity and SOM humification. Congruently, larger SOM at lower elevation and in heath sustained fungal-dominated microbial communities, which were less substrate-limited, and invested less into enzymatic SOM mineralisation, owing to a greater carbon-use efficiency (CUE). Our results highlight the importance of tundra plant community characteristics (i.e., productivity and vegetation type), via their effects on soil microbial community size, structure and physiology, as essential drivers of SOM turnover. The here documented concerted patterns in above- and belowground ecosystem functioning is strongly supportive of using plant community characteristics as surrogates for assessing tundra carbon storage potential and its evolution under climate and vegetation changes.

Impact of siltation on the stability of organic matter in drained peatlands

Peatlands are unique ecosystems but when they are drained for agriculture or peat mining, stored carbon is released to the atmosphere as CO2. The aim of the study was to assess the influence of siltation on secondary humification basing on humification indicators (C/N ratio, humification degree, humification index, E4/E6 ratio). It is essential to examine to what extent siltation hampers soil organic matter (SOM) oxidation. The study revealed that after drainage the amount of humus fractions, both acid and alkali soluble, were increasing at the expense of non-soluble carbon pool (residuum). Siltation hampered the transformation of organic matter and the quantities of OC and N in humus fractions were lower in silted soil samples than in not silted ones. The carbon extracted in acid-soluble fraction was not related to the state of siltation and was associated with the depth. The nitrogen content in this fraction did not change after drainage or siltation. The siltation did not affect C/N ratios. In unaltered peats these ratios were typical for fen soils (lowland peats) but in other studied soil samples the values of the C/N ratios suggested secondary transformation. The humification indicators (HI, HD and E4/E6) also revealed that secondary humification was more advanced in strongly silted soils, i.e. the stability of SOM in these soils is lower and the values of these indicators were dependent on the state of siltation. The study revealed that both drainage and siltation of soils changed the relations in SOM fractions. Drainage of peatlands resulted in initiation of the secondary humification of SOM and increase of chemically extractable humus fractions as well as increase of the humification degree. Stable SOM, which can have a mean residence time of centuries, became a potential source of CO2. However, siltation which led to a 50% decrease in SOM, hampered oxidation of SOM and had a stabilizing effect on SOM quality. These findings provide new insights into possibilities of mitigation of C losses from agricultural areas and may serve as a guidance for soil C management.

Evaluation of soil organic matter from integrated production systems using laser-induced fluorescence spectroscopy

Agricultural areas under integrated production systems, such as Integrated Crop-Livestock-Forest System (CLFS), have the potential to sequestrate carbon (C) since both Soil Organic Matter (SOM) content and trees biomass increase thus mitigating the emission of greenhouse gases (GHGs) from agriculture. Regarding soil aspects, the C content stands out as the main indicator, but the structural aspect of SOM is also relevant since it plays a key role in the chemical stability of C compounds and the soil lifetime of C compounds. Laser-Induced Fluorescence Spectroscopy (LIFS) is an effective technique to evaluate the SOM humification index (HLIFS) from practically intact whole soil samples under different agricultural systems. Thus, the objective of this study was to analyze the SOM humification index in different integrated systems, such as Integrated Crop-Livestock-Forest System (CLFS), Integrated Livestock-Forest System (LFS), Integrated Crop-Livestock System (CLS), and in references areas, such as Intensive Pasture (INT), Extensive Pasture (EXT) and Native Forest (NF). For this purpose, samples of Red-yellow Latosol (Haplorthox by Soil taxonomy) from the experimental site located at Embrapa Pecuária Sudeste (Southeast of Brazil) were collected five years after the establishment of the integrated systems. Samples were collected at soil depths of 0–5, 5–10, 10–20, 20–30, 30–40, 40–60, 60–80, and 80–100 cm. Pellets of the whole soil samples were prepared for LIFS analysis. In these areas, SOM humification indices (HLIFS) presented the following descending order: CLS > EXT > INT > LFS > CLFS > NF. Previous results have shown a greater soil organic carbon stock in these integrated production systems than in the NF area, suggesting C sequestration in agricultural soil. In the present study, SOM was classified by LIFS as more chemically stable in integrated production systems than in native vegetation. Higher amounts of fluorescent compounds were identified from LIFS data, probably resulting from condensed aromatic groups. SOM with more recalcitrant groups normally has a longer lifetime in the soil, indicating a long-term contribution to mitigating climate change by avoiding fast SOM decomposition and CO2 return to the atmosphere. Also, for the first time, this study was able to identify a positive correlation (R = 0.79) between the SOM humification index (HLIFS) and the Cation Exchange Capacity (CEC)/C content ratio of whole soil samples, another innovative contribution from soil LIFS analyses.

Forest Soil Cation Dynamics and Increases in Carbon on the Allegheny Plateau, PA, USA Following a Period of Strongly Declining Acid Deposition

Reductions in exchangeable calcium and magnesium and increase in exchangeable aluminum concentrations have been shown in soils impacted by acid deposition, including at four sites on the Allegheny Plateau, PA, USA, sampled in 1967 and 1997 during a period of peak deposition. We repeated sampling at these sites in 2017 to evaluate changes in soils during the more recent period when there has been a strong decline in acid deposition. The uppermost horizons, including the Oa and A horizons where humified organic matter transitions to mineral soil, were thicker, had higher concentrations of organic carbon and exchangeable calcium and magnesium, and lower concentrations of exchangeable aluminum in 2017 compared to 1997, approximating values measured in 1967. Below the Oa/A horizons, 2017 soil chemistry was more similar to the 1997 results, with some reduction of Ca in the recent measurements. These results suggest recovery of base cation–aluminum balance in surface horizons and may indicate a reduction of aluminum mobilization and increased efficiency of vegetation recycling of nutrients with decreased acid anion concentrations. These changes are consistent with a partial recovery from acid deposition. However, the increase in humified soil organic matter may also be affected by coincident increases in temperature and soil moisture.

Fire effects on C and H isotopic composition in plant biomass and soil: Bulk and particle size fractions

This work studies carbon (C) and hydrogen (H) isotope composition of plant biomass and soil organic matter (SOM) in an attempt to assess both, changes exerted by fire and possible inputs of charred materials to the soil after a wildfire. Isotope composition of bulk soil, soil particle size fractions and biomass of the dominant standing vegetation in the area (Quercus suber) from Doñana National Park (SW-Spain) were studied by isotope ratio mass spectrometry (IRMS). SOM C isotope composition indicates the occurrence of two SOM pools with different degree of alteration. Coarse soil fractions (>0.5 mm) were found 13C depleted with δ13C values close to those in leaf biomass, pointing to a predominance of poorly transformed SOM. Conversely, fine fractions (<0.1 mm) were found enriched in 13C as corresponds to a more humified SOM. The fire produced no changes in this trend, although a consistent 13C enrichment (c. 1‰) was observed in all soil fractions with decreasing size. Concerning H isotopes, the coarse fractions (>0.5 mm) displayed significant lower δ2H values than the intermediate and fine ones (<0.5 mm), again similar to those in leaf biomass (c. -80‰), whereas the fine fractions were found deuterium (2H)-enriched with significant higher δ2H values (c. 50‰), suggesting physical speciation of H depending on soil particle size. The fire produced a significant 2H depletion (Δ2H c. -10‰) in the finer fractions (<0.1 mm). The study of stable isotope analysis added new information and complements the results obtained by other proxies to better understand the effect of fire on SOM.

Change and spatial variability of soil organic matter humification after long-term tillage and olive mill wastewater application in arid regions

The changes of soil organic matter (SOM) humification induced by long-term combination of tillage and olive mill wastewater (OMW) application compared to natural and cultivated soil have been little investigated. This study aimed to compare effects of no cultivation with natural vegetation soil (NC), tillage (CT1) for 80 years and combination of tillage with OMW application (CT2) for 20 years on SOM humification degree. Fluorescence spectroscopy and UV-visible ratios (E4/E6 and CHA/CFA) were used to study soil humic acids (HAs). The SOM and humification distribution was determined for the whole field area using the Inverse Distance Weighting method. Results showed that SOM content, fluorescence emission area and E4/E6 and CHA/CFA ratios were higher in NC. Tillage reduced SOM amount, molecular size, aromatic condensation and humification degree as shown by the strong correlation between fluorescence area and CHA/CFA ratio in CT1 conversely to E4/E6. Contradictory results between fluorescence emission area and E4/E6 ratio found in NC and CT1 indicated that E4/E6 ratio was not a reliable indicator of SOM humification degree. The SOM amount, CHA/CFA ratio and emission fluorescence area increased conversely to E4/E6 ratio in CT2. This revealed a greatly humified organic matter and aromatic structure condensation with tillage and OMW application. Spatial distribution showed a progressive increase of SOM and CHA/CFA from north-west to south-east linked to the positive relationship between CHA/CFA ratio and SOM amount independent of soil management practices. Soil amended with OMW provided a favourable environment for the development of HAs which improved soil quality. The UV-visible ratio CHA/CFA with fluorescence emission area can be used as parameters to investigate SOM humification degree.

Nitrogen fertilization changes the molecular composition of soil organic matter in a subtropical plantation forest

AbstractThe biochemical mechanisms responsible for soil organic C (SOC) accumulation under N enrichment are not well understood. By examining two N types (NH4Cl and NaNO3) and three rates (0, 40, and 120 kg N ha−1 yr−1), we investigated the concentration and distribution of SOC by using soil aggregate separation and physical fractionation of soil organic matter (SOM). The molecular composition of SOM within bulk soil and each physical fraction was determined by pyrolysis–gas chromatography‐mass spectrometry. Nitrogen fertilization led to soil NO3−–N accumulation and intensified soil acidification. Four years of N fertilization did not change total SOC concentrations in the 0‐ to 20‐cm depth but a high rate of NaNO3 addition increased the concentrations of fine particulate organic C and microaggregate‐associated organic C by 133 and 83.4%, respectively. The change in SOC concentration was positively correlated with the change in fine particulate organic C and mineral‐associated organic C concentrations. Four years of N fertilization significantly changed the molecular composition of SOM, with an increase in the relative abundance of furfural and acetic acid and a decrease in pyrrole in the mineral‐associated organic matter (MAOM) fraction. Fertilization increased the furfural/pyrrole and aliphatic/aromatic ratios in the SOM and MAOM fractions, suggesting decreased stability of the passive SOM fraction. The SOC concentration was negatively correlated with the benzene/toluene ratio in both bulk soil and the MAOM fraction. Overall, exogenous N input to this subtropical plantation forest decreased the mineralization and humification of SOM, which could be detrimental to soil C accumulation.

Response of Humic Acids and Soil Organic Matter to Vegetation Replacement in Subtropical High Mountain Forests

AbstractReforestation can alter the chemical composition of soil organic matter (SOM) and humification; however, information on how specific plant types impact SOM lability and humification is not well documented. In this study, we used solid‐state 13C nuclear magnetic resonance spectroscopy, photometric analysis, and chemical fractionation to examine carbon (C) components and lability of SOM in a Japanese cedar (Cryptomeria japonica) forest and bamboo (Phyllostachys edulis) plantation that reforested a cutover primary broadleaf forest. The ∆logK value of soil humic acids, the inverse index of SOM humification, was lowest in the bamboo plantation, suggesting a higher SOM humification stage in the bamboo plantation. The soil labile C/Total C ratio was highest in the bamboo plantation, and this can be attributed to low aromaticity and alkyl‐C/O‐alkyl‐C ratio (A/O‐A) in the bamboo litter. Intensive cultivation of the bamboo plantation accelerated litter breakdown in the strongly acidic soil, resulting in the depletion of SOM. Cedar coniferous leaves, with their high recalcitrant substances and slow decomposition, only slightly lowered SOM humification due to the substantial broadleaf understory. Our results suggest that the type of plants involved in reforestation and understory reestablishment is critical to how SOM humification and lability change during the reforestation through the control of litter C components. Further research into the interaction between microclimate change and forest type in forest conversion will be useful for increasing understanding on the impact of forest conversion on SOM lability and humification in subtropical high mountain forest ecosystems.

Late Vistulian and Holocene development of litho-morpho-pedogenic processes in the southern Baltic coastal zone: A case study from Dębina, northern Poland

The study aimed to reconstruct major phases of the litho-morpho-pedogenic processes in the southern Baltic coastal zone near Dębina in northern Poland. Five profiles of fossil soils in the coastal cliff were described, sampled and analysed using standard procedures. The studied outcrop covers a sequence of deposits, including the basal till of the Świecie Stadial (MIS 4) of the Vistula Glaciation, the ablation till of the Pomeranian Phase (MIS 2) of the Vistula Glaciation, the thin cover of glacilimnic sand, the lacustrine sediments filling the palaeolake basin, and aeolian deposits of varied age. A sequence of paleosols developed successively within these deposits during the Late Vistulian and Holocene (MIS 1). The initialization of soil-forming processes occurred under the influence of periglacial environment and pioneer tundra vegetation. Endostagnic Podzols (Abruptic, Epiarenic, Endoloamic, Endodensic) developed within the plateau, and they have some features typical for periglacial environments (e.g. the presence of a cryoilluvial horizon, the poor humification of soil organic matter, the low abundance in N and P, and the vertical displacement of P). The basin of a small lake has been filled successively with sediments and Dystric Endocalcaric Katostagnic Fluvisols (Arenic, Humic, Endolimnic) developed from these sediments during the Late Vistulian and Early Holocene. The previously mentioned soils were buried by sandy cover in the Early Subatlantic due to intensification of aeolian processes. Ortsteinic Podzols (Pantoarenic) developed within a newly formed sandy cover. A fossil fireplace preserved in the top of these soils constitutes evidence of human activity dating back almost 2000 years. Ortsteinic Podzol (Pantoarenic) are dissected by a dry valley that developed as a result of some fluvial episode, perhaps induced by human activity. It was subsequently filled with aeolian sands, and Dystric Arenosols (Aeolic, Ochric) developed within them. Ortsteinic Podzol (Pantoarenic) and Dystric Arenosols (Aeolic, Ochric) were buried approximately five centuries ago. Our findings for the studied cliff section correlate well with results of other authors concerning the postglacial dynamics of morphogenetic processes. The studies provide significantly enriched geomorphological knowledge related to the formation of relief in the study area, with pedological aspects.

Revisiting the Nature of Phosphorus Pools in Chilean Volcanic Soils as a Basis for Arbuscular Mycorrhizal Management in Plant P Acquisition

This review covers the nature, characteristics, and reactivity of soil organic matter (SOM) in volcanic soils and the phosphorus (P) accumulation mainly via the formation of stable complexes with organic and inorganic constituents to form P-containing macromolecules derived from both pedogenesis and fertilization. With the time, P accumulates as organic and inorganic compounds with differing lability, but the bulk appears to be recalcitrant. Chilean volcanic soils follow this same trend, subsequently having detrimental characteristics for plant growth, like the highly humified SOM and high P-sorption capacity. In addition, certain Chilean volcanic soils have high acidity, concomitant with a high exchangeable Al. As a result of the continuous application of P fertilizers, together with a low P efficiency of plant root acquisition, a “P reservoir” has built up, giving rise to the so-called residual P. This residual P consists of the inorganic and organic P, as macromolecular structures representing the cumulative average of several decades worth of agronomic P usage. Root modifications are an essential biological intervention to deal with this P accumulation. The general root modifications that are required to mobilize the residual P are discussed in the context of biochemical modifications (root exudations) and the symbiotic alterations by arbuscular mycorrhizal (AM) fungi. For a more efficient utilization of this accumulated P, however, it is essential to investigate the chemical nature and lability of these P forms in order to determine their capacity for plant acquisition and utilization. In this context, attention is focused on P fractionation and on some 31P-NMR analysis of residual P constituents in Andisols. The major root trait evaluated and discussed here is the AM association, which is able to be extensively modified by management practices. Finally, some potential practices to avoid the excessive application of P fertilizers in volcanic soils by using technologies of P recycling, management of AM fungal populations, or agricultural management for mobilizing the accumulated residual P are outlined.