Changes In Soil Organic Matter Research Articles

A field investigation on the soil management practices in a productive vineyard considering C sequestration and water resistance of soil structure

AbstractOptimal soil structure is linked to soil organic matter (SOM). Different soil management practice alternates SOM but the storing C to soil structure formation in vineyard soils is not sufficiently studied. In addition, understanding the impact of soil management practices in vineyard on changes in SOM and soil structure is crucial for sustainable viticulture. In this study conducted in a productive vineyard near Nitra city, Slovakia, we investigated the dynamics of individual size-fractions of water-stable aggregates (WSA) as results of changes in soil organic matter (SOM) under different soil management practices. Five distinct management practices – Intensive tillage system (T); Intensive tillage system with poultry manure (T + M); Strip grass (G); Fertilization in lower rates of NPK (NPK 1) to grass strips; and Fertilization in higher level of NPK (NPK 2) to grass strips were adopted to to be tested. The results have shown that the highest content of soil organic carbon (SOC) 20.3 ± 3.68 g kg−1, labile carbon (CL) 2.71 ± 0.78 g kg−1, and the most favor soil structure were identified in NPK 1, however, the most effectively improved soil structure and C sequestration (SOC: 19.9 ± 3.88 g kg−1; CL: 2.53 ± 0.83 g kg−1) was under G treatment. SOC had a more significant influence on the content of water-stable aggregates than CL. Intense changes in SOM took place in larger size-fractions of water-stable macroaggregates (WSAma) above 2 mm, while smaller WSAma below 2 mm and water-stable microaggregates were more stable.

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.

Interaction between ectomycorrhizal and ericoid mycorrhizal plants decelerates stable soil organic matter decomposition

Boreal forests are N-limited ecosystems storing globally significant amounts of carbon (C) belowground as soil organic matter (SOM). The significant role of mycorrhizal fungi, both ericoid (ERM) and ectomycorrhizal (ECM) in decomposition and building up SOM has been proposed, but it is still largely unknown how these two types of mycorrhiza interact in terms of SOM changes. Here we try to elucidate the combined effect of these mycorrhizal types on the SOM decomposition and accumulation in a pot study with ECM-pine (Pinus sylvestris L.) and ERM-heather (Calluna vulgaris L.). Experimental design included plants growing alone or in a mixture, and a non-planted control. In contrast to the mixture, heather growing alone exerted higher biomass, higher uptake of N from stable SOM pool, slightly higher microbial biomass C and fungal biomass. Moreover, heather soil had the highest dissolved organic carbon and nitrogen. On the contrary, mixed cultures showed lower growth of heather and stable SOM decomposition. Our results suggest that interaction between ERM and ECM plants may lead to stable SOM accumulation in boreal forest soils.

Treeline displacement may affect lake dissolved organic matter processing at high latitudes and altitudes

Climate change induced shifts in treeline position, both towards higher altitudes and latitudes induce changes in soil organic matter. Eventually, soil organic matter is transported to alpine and subarctic lakes with yet unknown consequences for dissolved organic matter (DOM) diversity and processing. Here, we experimentally investigate the consequences of treeline shifts by amending subarctic and temperate alpine lake water with soil-derived DOM from above and below the treeline. We use ultra-high resolution mass spectrometry (FT-ICR MS) to track molecular DOM diversity (i.e., chemodiversity), estimate DOM decay and measure bacterial growth efficiency. In both lakes, soil-derived DOM from below the treeline increases lake DOM chemodiversity mainly through the enrichment with polyphenolic and highly unsaturated compounds. These compositional changes are associated with reductions in bulk and compound-level DOM reactivity and reduced bacterial growth efficiency. Our results suggest that treeline advancement has the potential to enrich a large number of lake ecosystems with less biodegradable DOM, affecting bacterial community function and potentially altering the biogeochemical cycling of carbon in lakes at high latitudes and altitudes.

Correlation of soil magnetic susceptibility with heavy metals and physico-chemical profile

The present study was conducted to determine magnetic susceptibility and its correlation with the concentration of selected heavy metals, including arsenic, chromium, cadmium and lead, as well as the physico-chemical properties of topsoil samples collected from District 5 of Tehran Municipality, Iran. The specimens were collected from 13 stations (0–10 cm depth), and the location of the sampling points was recorded as well using the Global Positioning System. The specimens were then analysed for physico-chemical properties, heavy metal concentration (by atomic absorption spectrometry) and in situ magnetic susceptibility at low frequency (χ lf, using a Bartington MS2 dual-frequency sensor). According to the results, the highest and lowest χ lf values were 34.1 × 10−8 and 16.3 × 10−8 m3/kg at stations 3 (Azadi bus station) and 11 (Jannatabad neighbourhood), respectively. A significant correlation was found between χ lf and the concentration of lead and chromium (P < 0.05). Moreover, there was a positive and significant correlation between χ lf and the soil organic matter in the study area (P < 0.01). Based on the research findings, the magnetic susceptibility measure can be used to evaluate quickly the level of soil contamination with heavy metals and also to monitor the changes in soil organic matter.

Response of maize yield to changes in soil organic matter in a Swedish long‐term experiment

AbstractAgricultural practices that lead to soil carbon sequestration may be a win–win strategy for mitigating global warming and improving soil fertility and resource use efficiency. The mechanisms through which soil organic carbon (SOC) concentration affects crop yields are numerous but difficult to separate. The objective of this study was to disentangle these processes and estimate to what extent the yield response to SOC is mainly driven by changes in physical or biochemical properties and processes. This was achieved by analysing the response of yields in continuous maize to SOC concentrations during 20 years (2000–2019), which had evolved in 14 experimental treatments in a Swedish long‐term field experiment at Ultuna since 1956, ranging from 0.94% to 3.65% in the topsoil (0–20 cm). Average maize yields during this period varied between 1.9 and 8.4 Mg dry mass per hectare in the different treatments. The treatments comprise applications of different mineral nitrogen (N) fertilizers and organic amendments and combinations thereof. Our analysis showed that maize yield in the treatments that were not severely limited by nitrogen supply or soil acidity increased by 16% for each percentage unit increase in SOC. We applied the widely used concept of critical N concentration in plant biomass to diagnose the N status in maize in the different treatments (N nutrition index [NNI]) and parameterized a response function between yield and pH (RpH). Dry soil bulk density (BD) was used as a proxy for soil physical properties. These three variables NNI, RpH and BD explained 95% of the variation in maize yields among treatments. Further analysis of the relationship between BD, SOC and plant available water capacity revealed that about two thirds of the yield increases in response to SOC change could be ascribed to associated changes in soil physical properties. Our analysis suggests that the extra storage capacity of water, which increased by up to 15 mm in the topsoil for each unit percentage increase in SOC, was the main driver for the observed yield responses. We conclude that measures for increasing SOC in soils most likely are an effective adaptation strategy for reducing the risk of crop damage during dry spells, which probably are becoming more frequent in the future due to climate change, even in relatively humid climates as in Sweden.

[Effect of Microplastics and Phenanthrene on Soil Chemical Properties, Enzymatic Activities, and Microbial Communities].

Microplastic and polycyclic aromatic hydrocarbon (PAHs) pollution have received increasing attention due to their ubiquitous distribution and potential risks in soils. However, the effects of microplastics-PAHs combined pollution on soil ecosystems remain unclear. Polyethylene (PE)/polypropylene (PP) and phenanthrene (PHE) were selected as the representatives of microplastics and PAHs, respectively. A 300-day soil microcosm experiment was conducted to study the single and combined effects of PE/PP and PHE on soil chemical properties, enzymatic activities, and bacterial communities (i.e., quantity, composition, and function), using the soil agricultural chemical analysis method and 16S amplicon sequencing technology. The interactions of soil properties, enzyme activities, and flora in the presence of PE/PP and PHE were analyzed. The results showed that the addition of PE/PP and PHE slightly changed the pH, available phosphorus (AP), and microbial quantity (i.e., bacteria, actinomycetes, and mold) but considerably increased the fluorescein diacetate hydrolase (FDAse) activity. There was a significant enhancement of soil organic matter (SOM) and urease activity in PE, PP, PHE-PE, and PHE-PP amended systems. PHE, PHE-PE, and PHE-PP obviously increased the dehydrogenase/neutral phosphatase activities and available nitrogen (AN) content. PHE had little effect on the microbial community. The PE, PP, PHE-PE, and PHE-PP addition influenced the microbial community to some extent. PE/PP and PHE showed positive effects on the energy production, growth, and reproduction of soil microorganisms and then accelerated the metabolism/degradation of pollutants and membrane transport. The changes in AN and SOM induced by PE/PP and PHE were the key factors affecting soil enzyme activities. Alterations in AN, AP, and pH were mainly responsible for the increase in microbial population. The changes in the microbial community were related to soil chemical properties and enzyme activities, and SOM had a significant effect on the microbial community. The presence of different carbon sources (PE/PP and PHE) in the soil and the microbial interaction also affected the microbiota. In conclusion, the addition of single or combined pollutants of PE/PP and PHE influenced the soil chemical properties, enzymatic activities, bacterial communities, and their interaction processes, thus facilitating the adaptation of the microbial community to pollutant stress.

Response of the rhizosphere soil microbial diversity to different nitrogen and phosphorus application rates in a hulless barley and pea mixed-cropping system

The mixed-cropping mode of hulless barley (Hordeum vulgare L) and peas (Pisum sativum L) can optimize the planting system, effectively enhancing crop nitrogen and phosphorus utilization and increasing yield. This mode has been widely applied in Qinghai Province, China. In this study, a split-plot experimental design was employed to investigate the bacterial and fungal communities in the rhizosphere soil of monocropping and mixed-cropping treatments under different fertilization levels. The Illumina MiSeq sequencing technology was used for the research, and the physicochemical properties of the soil were measured. The results indicated that with the increase in the application of nitrogen and phosphorus, the bacterial α-diversity in the rhizosphere of the mixed-cropping system initially increased and then decreased after reaching a peak. The α-diversity index of soil bacteria was higher under the mixed-cropping mode than under the monocropping mode. For the rhizosphere soil fungi in the mixed-cropping system, the Shannon index initially increased and then decreased, while the Chao1 and ACE indices decreased initially and then increased. Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, Sphingomonas, and Pseudomonas comprised the predominant bacterial genera in the rhizosphere soil of the hulless barley–pea intercropping treatment, whereas Fusarium, Metarhizium, and Cladosporium dominated among the fungal genera across the 12 treatments. Under the same fertilization levels, the relative abundances of Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium in the rhizosphere soil of the mixed-cropping treatment increased by 8.4 %, 7.1 %, 5.7 %, and 5.6 %, respectively, compared to the monoculture of hulless barley, with a decreasing trend as nitrogen and phosphorus levels increased. Compared to the monoculture of hulless barley, the relative abundance of Fusarium in the mixed-cropping treatment decreased by 37.3 %, 43.8 %, 56.8 %, and 40.3 %, respectively. Redundancy and correlation analyses suggested that the variation in bacterial and fungal diversity and community composition in the mixed-cropping zone due to the interaction between hulless barley and peas under different nitrogen and phosphorus fertilizer application levels was significantly correlated with changes in soil organic matter, available phosphorus, and alkaline hydrolyzable nitrogen.

Three years of cover crops management increased soil organic matter and labile carbon pools in a subtropical vegetable agroecosystem

AbstractCover crops have been widely adopted to improve soil functions in agroecosystems, including providing carbon (C) inputs that can contribute to soil C sequestration. However, soil C changes may be slow after introducing cover crops in unfavorable environments for soil organic matter (SOM) accumulation, like the Southeast United States subtropical region characterized by a warm humid climate, and coarse‐textured soils. We examined labile C pools as potential early indicators of SOM changes after cover crop introduction in a sandy subtropical vegetable production system. We compared the effects of four cover crop monocultures namely two grasses [sorghum sudangrass, Sorghum bicolor × S bicolor var. Sudanese and pearl millet, Pennisetum glaucum (L.) R. Br.], two legumes (sunn hemp, Crotalaria juncea L., and cowpea, Vigna unguiculata Walp.), and one four‐species mixture on soil organic carbon pools for 3 years. Soil samples were collected at a 15‐cm depth before cover crop planting and post cover crop incorporation to assess changes in SOM, permanganate‐oxidizable carbon (POX‐C), mineralizable carbon (Cmin), and water extractable organic carbon (WEOC). The incorporation of cover crops increased concentrations of SOM, POX‐C, and Cmin in year 3 relative to their baseline values in year 1. Concentration of SOM increased by 0.24 ± 0.05% (mean ± standard error) after 3 years of cover crop management. However, concentrations of WEOC significantly decreased in years 2 and 3 relative to the baseline. Monocultures and the mixture had similar effects on measured C pools, likely due to comparable aboveground biomass production. Our findings highlight the potential of POX‐C and Cmin as early indicators of SOM accumulation driven by cover crops use, as well as the capacity of cover crops to build SOM in similar subtropical systems and coarser textured soils.

Effects of Long-Term Management on Soil Organic Carbon in Tropical Peatlands

Objective: The aim of this study was to evaluate the effects of Histosols management on soil organic matter (SOM) characteristics.   Theoretical framework: Histosols are soils that provide ecosystem services, especially carbon stocks. Among the environments in which these soils are formed, peatlands stand out. The conversion of these areas into agricultural systems requires soil drainage. This practice causes reductions in carbon content and changes in the structure of the SOM.   Methodology: The study was conducted in the municipality of Rio de Janeiro, Brazil. The soils were classified as Histosols. Three areas were selected: a) cassava (Manihot esculenta) cultivation for 80 years; b) forest fragment for 20 years; c) consortium of coconut palm (Cocos nucifera) and cassava for 20 years. Total organic carbon (TOC); particulate organic carbon (COP); organic carbon associated with minerals (COam); fulvic acid fraction carbon (CAF); humic acid fraction carbon (CAH) and; humin fraction carbon (CHUM) were determined. Solid-state spectroscopy (UV-vis, ATR-FTIR and 13C NMR CP/MAS) was carried out to characterize the structure of the SOM.   Results and conclusion: The results showed that management and drainage have an impact on the TOC content, fractions and chemical structure of the SOM. The management adopted in the cassava area had an impact on the labile and humified fractions of the SOM. Spectroscopy showed that labile structures were lost in the humic acids (HA), while in the forest area only recalcitrant structures were preserved.   Research implications: The conversion of Histosols to agricultural production using the drainage technique promotes quantitative and qualitative changes in SOM in the long term. In order to reduce greenhouse gas emissions, it is necessary to use techniques that promote carbon stocks in the soil.   Originality/value: This study uses spectroscopic and chemometric techniques to highlight the effects of long-term soil management on the chemical structure of the SOM and to quantify the total carbon content and SOM fractions.

Changes in Soil Organic Matter and Biological Parameters as a Result of Long-Term Strip-Till Cultivation

The aim of the study was to determine the impact that three cultivation systems—conventional till (CT), reduced till (RT), and strip-till one-pass (ST-OP)—had on the biological parameters of the soil and their relationships with organic matter properties in the row zone (R) and inter-row zone (IR). For this purpose, a long-term static field experiment was carried out, from which soil samples were taken from a depth of 0–20 cm and the following were determined: TOC; TN content and fractional composition of organic matter; activity of dehydrogenases (DEHs), catalase (CAT), alkaline (AlP), and acid phosphatase (AcP); and the abundances of heterotophic bacteria (B), filamentous fungi (F), actinobacteria (Ac), and cellulolytic microorganisms (Ce). Soil samples for biological parameter tests were collected in summer (July) and autumn (October). RT and ST-OP increase the content of TOC, TN, carbon, and nitrogen in the humic and fulvic acid fractions. For the studied groups of microorganisms, the conditions for development were least favourable under CT cultivation. The results show that in July, the activities of DEH and CAT were the highest in ST-OP, whereas in October, they were the highest under CT. AlP and AcP activity were markedly the highest under ST-OP in both months. Enzyme activity was significantly the highest in the IR zone. The results indicate that, of the calculated multiparametric indicators, (AlP/AcP, GMea, BIF, BA12, and TEI), BA12 is a sensitive biological indicator of soil quality.

Trends in soil organic matter and topsoil thickness under regenerative practices at the University of Washington student farm.

Conventional methods of agriculture, especially tillage, are often accompanied by soil degradation in the form of erosion and organic matter depletion. Regenerative agricultural methods seek to repair soil ecosystems by building topsoil and soil organic matter (SOM), decreasing reliance on chemical fertilizers and increasing both water retention capacity and the diversity and quantity of soil microbial and fungal communities. The University of Washington (UW) student farm is an organic and regeneratively managed site on the UW Seattle campus. Over the past 20 years the farm gradually expanded so locations on the farm encompass both unimproved topsoil and soils managed regeneratively for periods of 5 to 20 years. This arrangement allows a time-trend analysis of soil development under regenerative methods. Measurements of topsoil thickness (defined as the distance from the ground surface to the base of the soil A horizon) and organic matter content were collected across 14 distinct plots on the farm to quantify trends over time and estimate net change in SOM (and soil organic carbon, or SOC). While SOM content weakly increased by 0.5% per year, topsoil thickness exhibited a significant linear increase of 0.86 cm per year. Over a twenty-year period under the management practices of the UW Farm total organic carbon storage in soils, determined using topsoil thickness, density, and SOC content, increased by between 4 and 14 t ha-1 yr-1. The general increases in topsoil thickness, SOM content, and total soil carbon demonstrate the potential of soil-health-focused practices to help maintain a productive and efficient urban growing space.

Modeling Dynamics of Soil Erosion by Water Due to Soil Organic Matter Change (1980–2020) in the Steppe Zone of Russia

This research aims to evaluate the dynamics of soil loss through soil erosion by water in agricultural lands in steppe areas using a modification of the RUSLE2 model from the 1980s to the 2010s. The calculation was performed using a raster model of data that included a model of the slope angle, slope length, soil erodibility, rainfall and snowmelt erosivity factors, types of land use, and cover management factor. All data were taken from open sources. The average soil erosion in the territory studied amounted to 1.48 t ha−1 year−1 in the 1980s and 1.72 t ha−1 year−1 in the 2010s. The discrepancy with other studies was 12% for the level of the 1980s and 2–7% for the level of the 2010s. The main factor leading to an increase in soil loss was soil erodibility due to the loss of soil organic matter, which affected about 52% of the studied lands. The increase in the amount of soil loss occurred against a background of compensating processes: reduction in precipitation and climate change (getting drier), as well as the overgrowth of agricultural lands with natural steppe vegetation. Modified model RUSLE2 has shown good results correlated with other studies for the research area.

Forest swamp succession alters organic carbon composition and survival strategies of soil microbial communities

Forest swamp ecosystems plays crucial role in the global carbon cycle. However, the effects of forest swamp succession on soil organic matter (SOM) and microbial community structure remain unclear. To determine the drivers of SOM change and soil microbial communities in forest swamp succession, a ‘space instead of time’ approach was used. Soil samples from 0 to 40 cm were collected along forest swamp (early stage), dried-up forest swamp (middle stage), and forest (late stage) ecosystems. Our findings reveal that as succession progresses, the relative content of aromatics decreases and SOM undergoes a transition towards a more readily degradable form. These changes affect soil carbon sequestration and nutrient availability. Bacterial diversity was significantly influenced by succession and changes in soil depth, with fungi exhibiting higher resilience. Soil properties and environmental conditions exert influence over the structure and function of microorganisms. As succession occurred, microbial interactions shifted from cooperation to competition, with bacteria displaying a deterministic distribution pattern and fungi exhibiting a random distribution pattern. SOM quality plays a key role in shaping microbial communities and influencing their growth strategies. Microorganisms are the major drivers of soil respiration, with K-strategist dominated communities in early succession exhibiting slower degradation rates, whereas r-strategists dominated in later stages, leading to faster decomposition.

Analisis Kesuburan Tanah di Pertambangan Minyak Tradisional Desa Wonocolo Kecamatan Kedewan, Kabupaten Bojonegoro

Wonocolo Village is known as a traditional mining area. This study aims to determine the level of soil contamination in traditional oil mining activities by testing N, P, K, organic matter and lime content of the soil. The method used in this research is using a proposive random sampling method. The results of testing the quality of soil in mining activities were found not to contain N,P,K. This can be seen when testing using N,P,K solutions, there was no change in soil color, organic matter and soil lime content when testing on 7 soil samples. only 2 soil samples contained organic matter and soil lime content, namely the 3rd and 7th samples. This can be seen from the presence of foam on the soil samples when dripped with H2O2 and HCL solutions. So it can be concluded that the soil in the Wonocolo mining area is highly polluted, so it is necessary to carry out bioremediation and phytoremediation the quality of soil in mining activities were found not to contain N,P,K. This can be seen when testing using N,P,K solutions, there was no change in soil color, organic matter and soil lime content when testing on 7 soil samples. only 2 soil samples contained organic matter and soil lime content, namely the 3rd and 7th samples. This can be seen from the presence of foam on the soil samples when dripped with H2O2 and HCL solutions. So it can be concluded that the soil in the Wonocolo mining area is highly polluted, so it is necessary to carry out bioremediation and phytoremediation.

Tillage system and cover crop effects on organic carbon and available nutrient contents in light chestnut soil

Optimal use of management systems including tillage and cover crops are recommended to improve available nutrient contents in soils and sustain agricultural production. The effects on organic carbon and available nutrient contents of three tillage methods (conventional tillage, minimum tillage and no-tillage) and different cover crops such as flaxseed oil, buckwheat, soybean, pea, corn, sorghum, spring oilseed rape and sugar beet were evaluated in a short-term experiment on a light chestnut soil in Kazakhstan. Organic carbon and available nutrient contents were measured in the autumn of 2021. The field measurements included the yield of cover crops and input of organic matter into soils with root and other residues of cover crops. In the laboratory, total organic carbon, labile organic carbon, easily hydrolyzable nitrogen (NH4-N), NO3-N, available P and exchangeable K were measured. The results showed that one season of cover crop growth was not enough to find detectable changes in soil organic matter and available nutrient status in light chestnut soils. On the other hand, even in a short-term field experiment period of 3 months, the most labile organic carbon in soil organic carbon was obtained in conventional tillage. Overall, the results show that at least in the short term and under lower drip irrigation rate in summer for the study area, reduced tillage methods (no-tillage and minimum tillage) is suitable in the study area for soybean, corn and sugar beet production after intensive tillage in the previous year.

Do carbon farming practices build bioavailable nitrogen pools?

AbstractAgricultural soils contain large amounts of nitrogen (N), but only a small fraction is readily available to plants. Despite several methods developed to estimate the bioavailability of N, there is no consensus on which extraction methods to use, and which N pools are critically important. In this study, we measured six soil N pools from 20 farms, which were part of a multi‐year soil carbon sequestration on‐farm experiment (Carbon action, 2019–2023). The aim was to quantify the N pools and to evaluate if farming practices that aim to build soil carbon pools, also build bioavailable N pools. We also aimed to test if the smaller and rapidly changing N pools could serve as an indicator for the slower change in soil organic matter. The measured N pools decreased in size, when moving from total N (7700 ± 1500 kg/ha) to slowly cycling (Illinois Soil Nitrogen Test ISNT‐N: 1063 ± 220 kg/ha, autoclave citrate‐extracted ACE protein N: 633 ± 440 kg/ha), water‐soluble organic N (50 ± 17 kg/ha), potentially mineralizable N (33 ± 13 kg/ha) and finally readily plant available inorganic pools (nitrate and ammonium, total: 14 ± 8 kg/ha). In total, the measured pools covered only 18%–44% of total N, indicating a large unidentified N pool, which is either tightly bound to soil mineral fraction and not easily extractable or is bound to undecomposed plant residues and not hydrolysed by the methods. Of the large N pools (ISNT‐N, ACE protein and unidentified residual N), clay, carbon (C) and C:Clay ratios explained most of the variability (R2 = .90–.93), leaving a minor part of the variation to the management effect. A pairwise comparison of carbon farming and control plots concluded that farming practices had a small (3%–5%) but statistically significant (p < .05) effect on soil total N and ISNT‐N pools, and a moderate and significant effect (18%, p < .01) on potentially mineralizable N. The large variation in protein N, water‐soluble organic N and inorganic N reduced statistical significance, although individual C sequestration practices had large effects (−30% to +50%). In conclusion, carbon sequestration practices can build both slowly cycling N pools (ISNT) and increase the mineralisation rate of these pools to release plant available forms, resulting in an additional benefit to agriculture through reduced fertilizer application needs.

THE IMPORTANCE OF SOIL ORGANIC MATTER (SOM) ON SOIL PRODUCTIVITY AND PLANT GROWTH

Soil organic matter (SOM) is vital to soil health and plays a critical role in crop production. This review paper examines the impact of SOM on soil health, crop production, and the challenges and opportunities associated with managing SOM. The paper emphasizes the importance of interdisciplinary research, technological advancements, and supportive policies in addressing SOM dynamics and management complexities. The review highlights the role of SOM in nutrient supply, soil structure improvement, water-holding capacity, and microbial activity enhancement, which are fundamental for sustainable agricultural systems. Various management practices to enhance SOM, including organic amendments, cover cropping, conservation tillage, and crop rotation, are discussed. Despite the benefits of managing SOM, challenges such as slow formation rates, trade-offs with other agricultural objectives, and economic viability exist. Addressing these challenges requires further research, knowledge exchange, and integrating traditional knowledge with modern technologies. Future perspectives and research needs include advancing interdisciplinary collaboration, harnessing emerging technologies, understanding the interactions between SOM and climate change, exploring novel management practices, quantifying ecosystem services, addressing knowledge gaps, and providing policy support and incentives. Sustainable soil management strategies can be developed by embracing these perspectives and addressing the identified research needs. These strategies optimize SOM levels, promote soil health, enhance crop productivity, and contribute to global food security and environmental sustainability. Overall, this review provides valuable insights for researchers, policymakers, and stakeholders in their efforts to enhance SOM management and promote sustainable agriculture.

One thousand soils for molecular understanding of belowground carbon cycling

While significant progress has been made in understanding global carbon (C) cycling, the mechanisms regulating belowground C fluxes and storage are still uncertain. New molecular technologies have the power to elucidate these processes, yet we have no widespread standardized implementation of molecular techniques. To address this gap, we introduce the Molecular Observation Network (MONet), a decadal vision from the Environmental Molecular Sciences Laboratory (EMSL), to develop a national network for understanding the molecular composition, physical structure, and hydraulic and biological properties of soil and water. These data are essential for advancing the next generation of multiscale Earth systems models. In this paper, we discuss the 1000 Soils Pilot for MONet, including a description of standardized sampling materials and protocols and a use case to highlight the utility of molecular-level and microstructural measurements for assessing the impacts of wildfire on soil. While the 1000 Soils Pilot generated a plethora of data, we focus on assessments of soil organic matter (SOM) chemistry via Fourier-transform ion cyclotron resonance-mass spectrometry and microstructural properties via X-ray computed tomography to highlight the effects of recent fire history in forested ecosystems on belowground C cycling. We observed decreases in soil respiration, microbial biomass, and potential enzyme activity in soils with high frequency burns. Additionally, the nominal oxidation state of carbon in SOM increased with burn frequency in surface soils. This results in a quantifiable shift in the molecular signature of SOM and shows that wildfire may result in oxidation of SOM and structural changes to soil pore networks that persist into deeper soils.

Chronic Warming and Nitrogen-Addition Alter Soil Organic Matter Molecular Composition Distinctly in Tandem Compared to Individual Stressors

Forest soils are major reservoirs of carbon (C), but these stores are threatened by increasing global temperatures and atmospheric nitrogen (N) deposition. These environmental stressors can alter soil microbial communities and soil organic matter (SOM) biogeochemistry through a variety of mechanisms. To investigate the impact of chronic warming, N-addition, and simultaneous warming and N-addition (warming + N) on forest soils, soil samples from the Harvard Forest Soil Warming and Nitrogen Addition (SWaN) experiment were analyzed after 14 years. Elemental analysis, targeted compound analysis by gas chromatography–mass spectrometry, and 13C nuclear magnetic resonance (NMR) spectroscopy were used to analyze changes in SOM in both the organic and mineral (0–10 cm) soil layers. Overall, changes in the molecular composition and microbial biomass were observed, but the extent of differences was unique to warming, N-addition, and warming + N treatments. Specifically, N-addition slowed SOM decomposition as measured via solid-state 13C NMR, while warming and warming + N accelerated SOM decomposition. Continued SOM decomposition after 14 years with warming + N signified a pronounced change to observations made after 4 and 10 years of experimental treatment. This is also demonstrative of how a two-factor approach leads to a unique molecular-level response that cannot be predicted from experiments with individual stressors alone. This study emphasizes the need to observe environmental stressors in tandem using a combination of molecular-level approaches to obtain a comprehensive understanding of how persistent anthropogenic activity will fundamentally alter forest soil systems.