Amount Of Soil Organic Matter Research Articles

Contribution of distinct components in divergent organic amendments to long-term accumulation of soil organic matter in agricultural soils: evidence from thermally assisted hydrolysis and methylation-GC/MS.

Although maintaining/improving soil organic matter (SOM) quantity through utilizing organic amendments (OAs) is a productive practice, information on OA components contributing to long-term SOM accumulation in agricultural soils remains meager. Hence, we examined soil samples from a long-term experiment with different fertilizer managements, including no fertilizer (NF), chemical fertilizer (CF) only (CF), bark compost plus CF (BC + CF), coffee residue compost plus CF (CRC + CF), cattle manure compost plus CF (CMC + CF), and cattle manure compost (CMC) or sewage sludge compost (SSC) alone at a higher application rate. SOM in those samples was physically fractionated into free particulate form (fSOM), free form occluded in aggregates (oSOM), weakly bound form (wSOM), and strongly bound form (sSOM). Analysis of structural components in OAs and SOM fractions using thermally assisted hydrolysis and methylation combined with gas chromatography/mass spectrometry (THM-GC/MS) revealed OA components that have contributed to long-term SOM accumulation in each treatment. The SSC was characterized by higher proportions of short-chain fatty acids (FAs; 50%) and other aliphatic compounds (22%). Correlation analysis suggested that these characteristics may be effective for greater C accumulation in the bulk soil and wSOM fraction. The proportion of lignin-derived phenols, e.g., 3,4-dimethoxybenzaldehyde (Vh) and 1,2-dimethoxy-4-(1,2,3-trimethoxypropyl)benzene, was high in CMC (43%), presumably vital for promoting C accumulations in the oSOM, wSOM, and sSOM fractions in the CMC treatment. The short-chain FAs in CRC and aromatic components in BC are likely important for contributing fSOM accumulation.

Soil Fertility Status of Paddy (Oryza Sativa L.) Growing Soils of Different Agro-climatic Zones, Telangana, India

The main occupation of Telangana State, India, is agriculture. Achieving food security requires intelligent management to increase land use productivity and production per unit area because of the expanding population and decreasing amount of agricultural land per capita. In this sense, assessing the productivity and fertility of the soil is a necessary step toward sustainable agricultural development. In the current study, paddy grown different soils in the districts of Telangana State were assessed for soil fertility using random sampling approach. This study was conducted to analyze the fertility characteristics of paddy cultivated soils in different districts of Telangana State. Collected 275 soil samples at 0-15cm depth under paddy crop grown during 2018-19 and 2019-20. The samples were found to be slightly acidic to alkaline in nature and low amount of soil organic matter. Soil nutrients such as available nitrogen (N), phosphorous (P) and potassium (K) ranged from 50-401 kg ha-1, 17-147 kg ha-1 and 60-842 kg ha-1 in red soil, 63-314 kg ha-1, 33-126 kg ha-1 and 95-460 kg ha-1 in black soil and 73-312 kg ha-1, 25-158 kg ha-1 and 153-458 kg ha-1 in alluvial soil, respectively. The paddy cultivated soil survey results conclusively indicate that the soil samples reveals normal soil reaction, electrical conductivity and low organic carbon (0.48% average) and widespread low nitrogen levels (91% of samples). Conversely, phosphorus availability is high (82% of samples) with an average content of 82 kg P2O5 ha-1, and potassium levels are notably elevated (57%).

Decrease in radiocesium adsorption of illite induced by soil organic matter: Quantity or quality?

Organic matter blocks highly selective frayed edge sites on clay minerals and reduces radiocaesium adsorption. The effects of different soil organic matter on Cs adsorption on illite have been investigated. The quantity and quality of soil organic matter was varied by extracting from three contrasting soils and varying extraction conditions. Extracted organic matter was quantified, and analysed using UV and fluorescent spectroscopy. Cs adsorption was markedly lower in soil aqueous extracts, than in simple electrolyte solution at the same ionic strength (IS). Part of the decrease was attributed to soluble soil potassium. After correction for ionic strength and potassium, the relative distribution coefficient of Cs, KdIS,K, decreased with increasing dissolved organic carbon (DOC) concentration. The correlation between KdIS,K and DOC was largely unchanged by taking into account any of the measured spectral parameters. We find no evidence that molecular size and composition of organic coatings determine their effect on the Cs adsorption properties of illite.

Environment and microbiome drive different microbial traits and functions in the macroscale soil organic carbon cycle.

Soil microbial traits and functions play a central role in soil organic carbon (SOC) dynamics. However, at the macroscale (regional to global) it is still unresolved whether (i) specific environmental attributes (e.g., climate, geology, soil types) or (ii) microbial community composition drive key microbial traits and functions directly. To address this knowledge gap, we used 33 grassland topsoils (0-10 cm) from a geoclimatic gradient in Chile. First, we incubated the soils for 1 week in favorable standardized conditions and quantified a wide range of soil microbial traits and functions such as microbial biomass carbon (MBC), enzyme kinetics, microbial respiration, growth rates as well as carbon use efficiency (CUE). Second, we characterized climatic and physicochemical properties as well as bacterial and fungal community composition of the soils. We then applied regression analysis to investigate how strongly the measured microbial traits and functions were linked with the environmental setting versus microbial community composition. We show that environmental attributes (predominantly the amount of soil organic matter) determined patterns of MBC along the gradient, which in turn explained microbial respiration and growth rates. However, respiration and growth normalized for MBC (i.e., specific respiration and growth) were more linked to microbial community composition than environmental attributes. Notably, both specific respiration and growth followed distinct trends and were related to different parts of the microbial community, which in turn resulted in strong effects on microbial CUE. We conclude that even at the macroscale, CUE is the result of physiologically decoupled aspects of microbial metabolism, which in turn is partially determined by microbial community composition. The environmental setting and microbial community composition affect different microbial traits and functions, and therefore both factors need to be considered in the context of macroscale SOC dynamics.

Soil organic carbon sequestration potential explained by mineralogical and microbiological activity using spectral transfer functions

The ability of soil to sequester carbon and reduce atmospheric CO2 concentrations is limited and depends on the soil minerals and their interaction with the microbiota. Microbial activities are closely associated with the types and amounts of soil organic matter (SOM) and clay minerals that have functional groups that interact with energy in Vis NIR-SWIR and Mid-IR wavelengths. The main objective of this research was to determine, based on these spectral ranges, the relation between mineralogical and organic compounds, as their sequestration and specialization in soils from Brazil. It was possible to map microbiological activity by spectral transfer functions and digital soil mapping reaching R2 from 0.77 to 0.85. Multiple regression equations were constructed to quantify enzymatic activity, microbial biomass carbon (MBC), particulate organic matter (POM), and resistant forms of carbon, and SOM associated with the mineral fraction (MAOM). All these properties were detected by specific bands obtained with the recursive feature elimination (RFE) algorithm, reaching correlations from 0.64 to 0.98 in specific ranges. The prediction model of the carbon sequestration potential was adjusted with microbiological and mineralogical variables from Vis-NIR-SWIR and the Mid-IR spectral range. A SARAR double autoregressive model was adjusted with r 0.61 and to a spatial error model (SEM) with r 0.7. The explanatory variables were associated with kaolinite, hematite, goethite, gibbsite, and the abundance of fungi, actinomycetes, vesico-arbuscular mycorrhizal fungi, enzymatic activity of beta-glucosidase, urease and phosphatase, and POM. Among the microbiological variables, the general abundance of fungi was the most important, in contrast to enzymatic activity that was the least important. The interaction between the different maps constructed and historical land use allowed the identification of areas that contribute to sequestering new carbon and could be the key to climate change mitigation strategies.

Waterline distance effects in the recovery of forest structure and soil organic matter 12 years after restoration

Efforts to restore tropical forests can result in large unpredictability in their trajectories, mainly due to spatial variation in abiotic conditions and plant resource availability. With the construction of a small hydroelectric power plant, a 70-ha forest restoration was conducted in 2008 within the boundaries of seasonal semideciduous forest in southeastern Brazil. This study described the spatial variation of the restored ecosystem after 12 years by simultaneously evaluating the direct influences of distance from the water body (waterline distance) and soil moisture, and the indirect influence of these factors mediated by the forest structure on accumulated litter and soil organic matter (SOM). These effects were estimated in the area under restoration and in forest remnants (considered as reference sites) (Model A), or in the area under restoration alone (Model B). Data on forest structure included density of individuals, total basal area, tree average diameter, average trunk volume index and stratification. Tree density decreased with increasing waterline distance both in the restoration area and in the forest remnants. Consequently, the sites closest to the reservoir formed denser and more stratified forests. Waterline distance and soil moisture content were correlated with each other, but each variable had independent effects of on the amount of litter and SOM. Wetter sites with denser and more stratified forest had greater amounts of accumulated litter and soil organic matter, but only in Model A, which included both the restored area and the forest remnants. In addition, higher basal area values contributed weakly to greater amounts of accumulated litter. Thus, our study suggests that the trajectory and speed of recovery of some ecosystem processes were determined by the waterline distance and soil moisture. Furthermore, the restoration implementation in the period of just 12 years was sufficient to detect the effect of these actions on the litter accumulation and a substantial increase in the amount of soil organic matter.

Nitrogen Supply from Soil Organic Matter: Predictors and Implications for Recommended Nitrogen Application Rates in Northern Highbush Blueberry

Nitrogen (N) management is a key component to maintaining high productivity of northern highbush blueberry (Vaccinium corymbosum L.) and nitrogen is often supplied by applying ammonium-based fertilizers. It can also be supplied through mineralization of soil organic matter (SOM), although the amount released by SOM is difficult to predict and not always considered in the development and implementation of N fertility programs. Laboratory and field experiments were conducted to estimate the timing and magnitude of net N mineralization from SOM throughout the growing season, identify soil properties that can be measured commercially and used to predict net N mineralization across a range of SOM, and determine whether N requirements for maximizing yield and fruit quality of blueberry vary across soils with different amounts of SOM. The laboratory experiment was conducted for 6 months using soil samples collected from 10 representative commercial blueberry fields in northwest Washington. The soils contained 2% to 42% soil organic carbon (SOC). The mean net N mineralization rates were fastest during the first 3 to 4 months of incubation, corresponding to the period during which N uptake reaches its maximum in blueberry. Results indicated that the soil total N may be a useful predictor of the N supply from SOM (6.34 ± 1.13 kg⋅ha−1 increase in net N mineralization with each 0.1% increase in total N), but there was substantial variability in the N supply that could not by explained by the total N (P < 0.001; r2 = 0.433). The field experiment was conducted from 2019 to 2021 and included four mature, regionally representative, commercial fields of ‘Duke’ blueberry. The fields contained 3% to 28% SOC and were each fertilized with low, medium (control), or high N rates, corresponding to 33 to 50, 67 to 84, or 102 to 118 kg⋅ha−1 N per year, respectively. Although soil inorganic N levels suggested that N mineralization was substantial at sites with higher SOM, sites with lower SOM did not require more fertilizer N than those with higher SOM. Under the conditions of this experiment, even the lowest N rates were sufficient to sustain production for at least 3 years at each site. The findings of this study indicate that SOM may be an important contributor to N fertility in managed blueberry systems, and that yield and fruit quality can be maintained across various N fertilizer rates, including at rates <50 kg⋅ha−1 N. However, the long-term impacts of reducing N application rates remain unclear, and future research should monitor long-term changes in plant health and soil fertility associated with reduced N applications across diverse soils and production systems.

Effect of Land Use Change on Molecular Composition and Concentration of Organic Matter in an Oxisol.

Land use change from native vegetation to cropping can significantly affect the quantity and quality of soil organic matter (SOM). However, it remains unclear how the chemical composition of SOM is affected by such changes. This study employed a sequential chemical extraction to partition SOM from an Oxisol into several distinct fractions: water-soluble fractions (ultrapure water (W)), organometal complexes (sodium pyrophosphate (PP)), short-range ordered (SRO) oxides (hydroxylamine-HCl (HH)), and well-crystalline oxides (dithionite-HCl (DH)). Coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), the impact of land use change on the molecular composition of different OM fractions was investigated. Greater amounts of OM were observed in the PP and HH fractions compared to other fractions, highlighting their importance in SOM stabilization. The composition of different OM fractions varied based on extracted phases, with lignin-like and tannin-like compounds being prevalent in the PP and HH fractions, while aliphatic-like compounds dominated in the DH fraction. Despite changes in the concentration of each OM fraction from native vegetation to cropping, there was little influence of land use change on the molecular composition of OM associated with different mineral phases. No significant selective loss or preservation of organic carbon compounds was observed, indicating the composition of SOM remained unchanged.

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.

Stock of Carbon and Soil Organic Fractions in No-Tillage and Crop–Livestock Integration Systems

Soil use and management practices influence the quantity and quality of soil organic matter (SOM). From this perspective, the objective of this work was to evaluate the carbon stock and SOM fractions in a no-tillage (NT) and crop–livestock integration (CL) system in the Cerrado biome. The treatments were divided into four areas, subdivided into an area under NT with 11 years of cultivation, two areas under CL with 5 or 10 years of cultivation, and an area of native vegetation (NV). Undisturbed and disturbed soil (Ferralsols) samples were collected in layers 0.0–0.1, 0.1–0.2, 0.2–0.4, and 0.4–0.6 m for the evaluations of soil properties, including bulk density, weighted mean diameter, clay content, carbon stock, carbon stock of light and mineral fractions, humification rate, and carbon management index. The results obtained suggest that the environments with the highest conservation of the physical properties of the soil are those that contain the highest levels of stable C. The main mechanism for C protection in the systems evaluated was mainly associated with physical protection, promoted by soil aggregates, capable of keeping C protected, and mitigation of C into the atmosphere. The values of the carbon management index in the agriculture areas were >100, indicating that these production systems could approach the soil quality of the native vegetation reference system.

No-tillage farming for two decades increases plant- and microbial-biomolecules in the topsoil rather than soil profile in temperate agroecosystem

The impact of conservation tillage on the composition, stability, and origin (plant- or microbial-derived) of soil organic matter (SOM) within soil profiles remains unclear. In this study, we characterized the impact of different tillage practices on the molecular composition and status of SOM. These tillage practices included conventional tillage (CT) and conservation tillage such as rotary tillage (RT) and no-tillage (NT). Our investigation spanned a two-decade period within a temperate agroecosystem. Soil samples were collected down to a 30 cm profile, and four biomarkers, namely free lipids, lignin phenols, neutral sugars, and amino sugars, in conjunction with 13C NMR techniques were used to quantify SOM characteristics. The results revealed that conservation tillage (especially NT) led to improvements in both the quantity and composition of SOM when compared to CT in the topsoil (0–5 cm), but not in deeper layers (5–30 cm). More precisely, the NT topsoil, as opposed to CT, exhibited enhancements in two categories: (1) an increase in plant-derived compounds such as long-chain lipids (≥ C20) and steroids by 51%, lignin phenols by 106%, and plant-derived neutral sugars by 61%, and (2) an augmentation in microbial-derived biomolecules, which includes microbial-derived neutral sugars by 49% and microbial necromass carbon (MNC) by 94%. Furthermore, NT, relative to CT, increased the contribution of MNC to soil organic carbon in topsoil (up to 64%, mainly fungal necromass). This highlighted the predominant role of microbial-derived biomolecules in SOM formation. Similarly, RT treatments enhanced the microbial-derived neutral sugars by 18%, plant-derived neutral sugars by 14%, and lignin phenols by 43% relative to CT in the topsoil. Collectively, our study suggests that NT practice could be considered an effective strategy for enhancing SOM accumulation and persistence by fostering the accrual of plant- and microbial-derived biomolecules in the topsoil.

Assessment of the Quality of Agricultural Soils in Manica Province (Mozambique)

Agriculture is the main economic activity of Mozambique and there is a lack of information about the quality of agricultural soils. In this paper, five soils from the Manica and Sussundenga districts (Manica province) sampled in the years 2021/2022 and 2022/2023 (before and after the rainy seasons) were subjected to an agronomical and environmental chemical analysis to assess their quality, from the fertility and environmental contamination points of view. Standard analytical methodologies from external certified laboratories and local X-ray fluorescence measurements were used. All the studied soils were acidic (pH ranging from 4.5 to 5.4), had no salinity problems (conductivity ranging from 4.2 to 11.8 mS/m), and had a low amount of soil organic matter (0.90% to 1.81%). Soils from the Sussundenga district had a very low cation exchange capacity (CEC) (average of 3.33 cmolc/kg), while that of those from the Manica district ranged from very low to average CEC (3.59 to 13.11 cmolc/kg). Sussundenga soils also had a phosphorous deficiency (values ranging from <20 to 38.5 mg/kg) and there were deficiencies and/or excesses of some macro and micronutrients in all soil samples. Manica soils were contaminated, apparently from geogenic origin, with Cr (280 to 1400 mg/kg), Co (80 mg/kg), Ni (78 to 680 mg/kg) and V (86 mg/kg). Agricultural soil monitoring must be fostered in Mozambique in order to improve food quality and quantity to ensure economic and environmental sustainability.

Contribution of the Soil Macro- and Microstructure to Organic Matter Stabilisation in Natural and Post-Mining/Industrial Soils under Temperate Climatic Conditions

The soil organic matter (SOM) content and stability in natural gypsum soils and mining/industrial soils were compared to check the effects of selected soil properties (mainly macro- and microstructure) on SOM stability and determine whether the old brownfield soils regardless of being highly polluted with trace metals could store high amounts of SOM. The mining/industrial soils were 50–400 years old and so had been left sufficiently long for full self-restoration. Despite having very different origins, both natural and brownfield soils stored similar amounts of SOM and had similar pH values, calcium carbonate contents, and textures but differed in SOM stabilisation, which was expressed by higher C/N ratios, lower aggregate water resistance index, lower dehydrogenase activity, and greater areas of undecomposed or slightly decomposed plant residues in mining/industrial soils compared to gypsum ones. However, the differences diminished with time, and in the oldest (150–400 years) brownfield soils, these parameters were similar to those in natural soils. Multiple regression analysis indicated that under the study conditions, SOM amounts, besides CaCO3 contents and dehydrogenase activity were also strongly affected by porosity and microaggregation. In the research we showed the role of degraded soils in the sustainable use of the environment.

Permafrost degradation and its consequences for carbon storage in soils of Interior Alaska

Permafrost soils in the northern hemisphere are known to harbor large amounts of soil organic matter (SOM). Global climate warming endangers this stable soil organic carbon (SOC) pool by triggering permafrost thaw and deepening the active layer, while at the same time progressing soil formation. But depending, e.g., on ice content or drainage, conditions in the degraded permafrost can range from water-saturated/anoxic to dry/oxic, with concomitant shifts in SOM stabilizing mechanisms. In this field study in Interior Alaska, we investigated two sites featuring degraded permafrost, one water-saturated and the other well-drained, alongside a third site with intact permafrost. Soil aggregate- and density fractions highlighted that permafrost thaw promoted macroaggregate formation, amplified by the incorporation of particulate organic matter, in topsoils of both degradation sites, thus potentially counteracting a decrease in topsoil SOC induced by the permafrost thawing. However, the subsoils were found to store notably less SOC than the intact permafrost in all fractions of both degradation sites. Our investigations revealed up to net 75% smaller SOC storage in the upper 100 cm of degraded permafrost soils as compared to the intact one, predominantly related to the subsoils, while differences between soils of wet and dry degraded landscapes were minor. This study provides evidence that the consideration of different permafrost degradation landscapes and the employment of soil fractionation techniques is a useful combination to investigate soil development and SOM stabilization processes in this sensitive ecosystem.

Partitioning the effects of coffee-Urochloa intercropping on soil microbial properties at a centimeter-scale

Conservation farming and crop diversity increase soil health, organic matter content, and soil microbial activity. However, the design and implementation of sustainable practices often lack a detailed understanding of their impacts on microbial communities in soil. Here, we studied the effects of an Arabica coffee (Coffea arabica) – Brachiaria (Urochloa spp.) intercropping system on soil microbial properties by partitioning at the centimeter-scale the topsoil layers. In particular, we collected and analyzed four soil layers in a vertical stratification gradient of 0–2.5 cm (layer 1), 2.5–5.0 cm (layer 2), 5–10 cm (layer 3), and 10–15 cm (layer 4). Soil samples were subjected to chemical analysis, bacterial community profiling, and quantification of microbial enzymatic activity for β-glucosidase and acid-phosphatase, in addition to the quantification of N-fixation and P-solubilization gene abundances. We found that intercropping increased acid-phosphatase activity at layer 1, β-glucosidase activity at layers 2 and 3, and the amount of soil organic matter and total magnesium at layers 2 and 3. Intercropping increased the relative abundance of the N-fixation gene at layer 3 and bacterial diversity at layers 1 and 3. Overall, intercropping significantly changed the soil bacterial community structure and resulted in a more interconnected co-occurrence network (i.e., greater node connectivity, network density, and lower edges average path length). Taken together, this study provides evidence for the positive impact of intercropping in the soil at a centimeter-scale vertical stratification. It corroborates the notion that plant diversity stimulates microbial activity and species interactions in soil.

Post-fire soil carbon emission rates along boreal forest fire chronosequences in northwest Canada show significantly higher emission potentials from permafrost soils compared to non-permafrost soils

Boreal forests are one of the most important biomes storing carbon (C). Wildfires burn yearly on average more than 1% of the boreal forest, and it is expected that the fire return intervals will shorten due to climate change. Fire is one of the most influential factors affecting soil organic matter quantity and quality, soil C pools, and presumably also the time C resides in the soil (soil C turnover time in years). We compared the potential effects of forest fire through post-fire succession on soil carbon dioxide (CO2) emission rates and soil C turnover time in two fire chronosequences, one with underlying permafrost soil and the other without permafrost. We found that fire had a significant effect on potential soil C turnover times, but surprisingly there was no significant difference in soil C turnover times between the permafrost and non-permafrost areas, although the soil CO2 emissions rates in permafrost areas are approximately three times higher compared to non-permafrost areas. In recently burned areas the potential soil C turnover times were two times longer compared to control areas located in forests burned more than 100 years ago. The longest potential soil C turnover times were recorded in mineral soil layers (30 cm) of permafrost soils, and the shortest potential soil C turnover times were recorded in humus layers of non-permafrost areas.

A new quality index based on soil-vegetation networks to determine the recovery of functionality in abandoned agrosystems

The development of indices of ecosystem quality makes it possible to obtain robust information with less human and material effort. These indices are especially useful for assessing the quality of ecosystems disturbed by anthropogenic impact since they can inform management decisions designed to recover their functionality. The abandonment of agricultural activity is a major environmental challenge, and it is important to understand its consequences on ecosystem functioning. The main objective of this work was to develop a robust quality index of abandoned agrosystems based on detailed information on soil properties and structure and the composition of the vegetation. A chronosequence was built of abandoned vineyards over the last 60 years. Seventeen soil physical-chemical properties and ten enzymatic activities related to the cycles of C, N, P and S were determined in 21 plots along the chronosequence. Total vegetation cover, cover of cryptograms and phanerogams and cover of plant functional groups was also recorded. The main factors involved in the quality of the ecosystem were detected by means of network analyses based on these variables. Models were then developed to calculate ecosystem quality indices. Our results showed how the evolution of soil properties occurred simultaneously with variations in the composition and structure of the vegetation. The major factors that determined the functionality of abandoned agrosystems were the quantity and quality of soil organic matter (high TOC and WHN) and the lesser abundance of sulphur accumulator plants. The ecosystem quality index model found to be the most robust was the index with integration by weights and non-linear scores, which followed a sigmoid pattern throughout the chronosequence. Our results highlight the importance of developing robust quality indices based on an interdisciplinary approach.

Impact of Diverse Agricultural Land Uses on Soil Organic Matter Fractions: A Comprehensive Evaluation

Organic matter is a crucial component of soil that influences various soil properties and functions, including nutrient cycling, soil structure, water holding capacity and microbial activity. Different agricultural land uses significantly influence the quantity and quality of soil organic matter (SOM) fractions. The primary constituent of SOM is humic substances, also known as humus. These are stable compounds originating from the decomposition of organic matter derived from plants, animals, and microorganisms. The soil humic fraction is categorized into humic acid (HA), fulvic acid (FA) and humin (HN) based on the solubility in acid and alkaline medium. The structural arrangement, chemical constitution and stability of the humic substances in soil are affected by various factors, including climate, parent material, altitude, vegetation and the management practices employed in the area. In this context the present study was proposed to assess the impact of various agricultural land use systems on humic acid, fulvic acid and humin fraction in soils of different agro-ecological units (AEUs) of southern Kerala. The study focused on specific AEUs in southern Kerala, including the southern coastal plain (AEU 1), Onattukara sandy plain (AEU 3), southern laterites (AEU 8), south central laterites (AEU 9) and southern and central foothills (AEU 12). Within each AEU, various agricultural land use categories such as, coconut, rice, rubber and uncultivated land were selected as specific focal points for this investigation. The HA, FA and HN content in soil exhibited varying ranges across different AEUs, ranging from 0.57 to 2.06, 0.73 to 2.33, and 0.62 to 1.59 per cent respectively. Among the various land uses, rubber exhibited significantly higher levels of HA (1.72%), FA (2.01%) and HN (1.44%) compared to coconut, rice and uncultivated land. Among the different organic matter fractions, FA (32.30-36.18 %) contributed more towards SOM than HA (29.40-32.51 %) and HN (26.43-29.25 %).

Ten-Year Impact of Cover Crops on Soil Organic Matter Quantity and Quality in Semi-Arid Vineyards

Soil organic matter depletion is a significant concern in agricultural soils, impacting crucial aspects of ecosystem health, especially soil properties such as fertility and soil moisture retention. Adopting sustainable soil management practices, such as cover crops, can mitigate this issue. In this study, we analyzed the soil organic carbon (SOC) content and quality in vineyards using two distinct management methods: permanent spontaneous cover crops and conventional tillage. Dissolved organic carbon (DOC) was quantified and chemically characterized using UV–visible spectroscopy. Our results showed an increase of 4.7 Mg C/ha in the carbon stock (50 cm depth) after 10 years of implementing vegetation covers compared with tilled soil. Additionally, cover crop management increased less humified soluble carbon in surface soil layers, while tillage transformed the solubilized carbon. This finding is important because tilled soil becomes more accessible to microbial degradation and leaching, which, in the long term, leads to a SOM content decrease. In conclusion, an increase in carbon stock was observed when using cover crops due to the incorporation of fresh organic matter, whereas tilled soils showed a depletion of carbon stock, including the mobilization of more stable carbon.

Earthworms facilitate stabilization of both more-available maize biomass and more-recalcitrant maize biochar on mineral particles in an agricultural soil

Agricultural soils have lost enormous amounts of soil organic matter (SOM) as the result of conventional agriculture. Nowadays, returning plant biomass in the form of crop residues is used as an efficient strategy to increase the amount of SOM. In addition, earthworms help increase the SOM content by transforming OM into stable forms. There is, however, limited information on how earthworms transform and stabilize various forms of crop residues and what the potential feedbacks on soil quality are. In a five-month laboratory manipulation experiment, we added maize biomass and/or biochar to a temperate agricultural soil both in the presence and absence of earthworms and carried out physical fractionation to analyse the stabilization of OM either as aggregate-occluded particulate OM (oPOM) or mineral-associated OM (MAOM).We show that the combination of maize biomass, maize biochar and earthworms proved to be highly efficient in increasing the OM content in agricultural soils and that earthworms can simultaneously enhance both OM decomposition and stabilization. In the absence of earthworms, the OM was stabilized more in the oPOM fraction, suggesting that both maize substrates acted as aggregation agents. In the presence of earthworms, however, maize substrates were stabilized more in the MAOM fraction, either through direct sorption as plant-derived substrates or as microbial necromass, suggesting that earthworms facilitate stabilization of both more-available maize biomass and more-recalcitrant maize biochar on mineral particles. We provide evidence that plant-derived rather than microbial-derived MAOM is present in the earthworm-affected agricultural soil and is thus important in increasing the SOM content and stability.