Agricultural Land Use and Management Practice Influence on Efflux and Influx of Carbon between Soil and the Atmosphere: A Review

Organic Matter Budgets for Streams: A Synthesis

Large-Scale Trends for Stream Benthic Respiration

Previous articleNext article No AccessStream Organic Matter BudgetsOrganic Matter Dynamics in the West Fork of Walker Branch, Tennessee, USAP. J. MulhollandP. J. Mulholland Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Volume 16, Number 1Mar., 1997 Article DOIhttps://doi.org/10.2307/1468235 Views: 7Total views on this site Citations: 17Citations are reported from Crossref Journal History This article was published in the Journal of the North American Benthological Society (1986-2011), which is continued by Freshwater Science (2012-present). Copyright 1997 The North American Benthological SocietyPDF download Crossref reports the following articles citing this article:J. David Allan, Maria M. Castillo, Krista A. Capps Detrital Energy and the Decomposition of Organic Matter, (Mar 2021): 177–224.https://doi.org/10.1007/978-3-030-61286-3_7Florian Caillon, Jakob Schelker Dynamic transfer of soil bacteria and dissolved organic carbon into small streams during hydrological events, Aquatic Sciences 82, no.22 (Mar 2020).https://doi.org/10.1007/s00027-020-0714-4Jesús Pozo, Arturo Elosegi Coarse Benthic Organic Matter, (Jul 2020): 29–35.https://doi.org/10.1007/978-3-030-30515-4_4Astrid Harjung, Elisabet Ejarque, Tom Battin, Andrea Butturini, Francesc Sabater, Masumi Stadler, Jakob Schelker Experimental evidence reveals impact of drought periods on dissolved organic matter quality and ecosystem metabolism in subalpine streams, Limnology and Oceanography 64, no.11 (Aug 2018): 46–60.https://doi.org/10.1002/lno.11018Ryan A. McManamay, Matthew J. Troia, Christopher R. DeRolph, Arlene Olivero Sheldon, Analie R. Barnett, Shih-Chieh Kao, Mark G. Anderson, Steven Arthur Loiselle A stream classification system to explore the physical habitat diversity and anthropogenic impacts in riverscapes of the eastern United States, PLOS ONE 13, no.66 (Jun 2018): e0198439.https://doi.org/10.1371/journal.pone.0198439Jeremy M. Alberts, Jake J. Beaulieu, Ishi Buffam Watershed Land Use and Seasonal Variation Constrain the Influence of Riparian Canopy Cover on Stream Ecosystem Metabolism, Ecosystems 20, no.33 (Sep 2016): 553–567.https://doi.org/10.1007/s10021-016-0040-9Scott C. Brooks, Craig C. Brandt, Natalie A. Griffiths Estimating uncertainty in ambient and saturation nutrient uptake metrics from nutrient pulse releases in stream ecosystems, Limnology and Oceanography: Methods 15, no.11 (Oct 2016): 22–37.https://doi.org/10.1002/lom3.10139Natalie A. Griffiths and Scott D. Tiegs Organic-matter decomposition along a temperature gradient in a forested headwater stream, Freshwater Science 35, no.22 (Feb 2016): 518–533.https://doi.org/10.1086/685657Natalie A. Griffiths, Jennifer L. Tank, Todd V. Royer, Thomas J. Warrner, Therese C. Frauendorf, Emma J. Rosi-Marshall, Matt R. Whiles Temporal variation in organic carbon spiraling in Midwestern agricultural streams, Biogeochemistry 108, no.1-31-3 (Mar 2011): 149–169.https://doi.org/10.1007/s10533-011-9585-zE. S. Kane, E. F. Betts, A. J. Burgin, H. M. Clilverd, C. L. Crenshaw, J. B. Fellman, I. H. Myers-Smith, J. A. O'Donnell, D. J. Sobota, W. J. Van Verseveld, J. B. Jones Precipitation control over inorganic nitrogen import-export budgets across watersheds: a synthesis of long-term ecological research, Ecohydrology 1, no.22 (Jan 2008): 105–117.https://doi.org/10.1002/eco.10HOLLY L. MENNINGER, MARGARET A. PALMER Herbs and grasses as an allochthonous resource in open-canopy headwater streams, Freshwater Biology 52, no.99 (Sep 2007): 1689–1699.https://doi.org/10.1111/j.1365-2427.2007.01797.xVicenç Acuña,* Adonis Giorgi,† Isabel Muñoz,‡ Francesc Sabater,§ and Sergi Sabater∥ Meteorological and riparian influences on organic matter dynamics in a forested Mediterranean stream, Journal of the North American Benthological Society 26, no.11 (Jul 2015): 54–69.https://doi.org/10.1899/0887-3593(2007)26[54:MARIOO]2.0.CO;2Salvador Mollá, Santiago Robles, Carmen Casado Seasonal Variability of Particulate Organic Matter in a Mountain Stream in Central Spain, International Review of Hydrobiology 91, no.55 (Oct 2006): 406–422.https://doi.org/10.1002/iroh.200510857Mark S. Johnson, Johannes Lehmann, Evandro Carlos Selva, Mara Abdo, Susan Riha, Eduardo Guimarães Couto Organic carbon fluxes within and streamwater exports from headwater catchments in the southern Amazon, Hydrological Processes 20, no.1212 (Jan 2006): 2599–2614.https://doi.org/10.1002/hyp.6218Jon Molinero, Jesus Pozo Impact of a eucalyptus (Eucalyptus globulus Labill.) plantation on the nutrient content and dynamics of coarse particulate organic matter (CPOM) in a small stream, Hydrobiologia 528, no.1-31-3 (Oct 2004): 143–165.https://doi.org/10.1007/s10750-004-2338-4Lara A. Martin,* Patrick J. Mulholland, Jackson R. Webster, and H. Maurice Valett Denitrification potential in sediments of headwater streams in the southern Appalachian Mountains, USA, Journal of the North American Benthological Society 20, no.44 (Jul 2015): 505–519.https://doi.org/10.2307/1468084John F. McCarthy, George R. Southworth, Kenneth D. Ham, Jennifer A. Palmer Time-integrated, flux-based monitoring using semipermeable membrane devices to estimate the contribution of industrial facilities to regional polychlorinated biphenyl budgets, Environmental Toxicology and Chemistry 19, no.22 (Feb 2000): 352–359.https://doi.org/10.1002/etc.5620190215

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 %).

In Kenya, less than 10% of the land is arable, out of which 30% suffers severe soil degradation. This study investigates impact of various agricultural land use management practices (on the concentration and distribution of essential nutrients in different soil particle size fractions (SPSF) within Oroba Valley, Nandi County. Two agricultural plots were selected: Plot 1 (non-terraced) and Plot 2 (terraced cultivation), with topsoil (0–20 cm) sampled using a stratified method. Soil particles were separated by sieving (2000–500 µm, 500–100 µm, 100–50 µm, 50–25 µm) and sedimentation (25–10 µm and < 10 µm). Organic matter (OM), soil pH, and nutrient concentrations were quantified using loss on ignition (LOI), a pH meter in CaCl2, and ICP-QQQ analysis, respectively. Median soil pH was 5.6 for Plot 1 and 5.9 for Plot 2, with OM concentrated at 40% in smaller particles (< 25 µm) and 24% in larger particles (100–2000 µm). Nutrients such as I, Se, Zn, Mg, P, Al, Mn, Fe, Co, Mo, and Cu were concentrated in SPSF of < 10 µm, while Na, K, and Ca were concentrated in medium particle sizes (25 µm–100 µm). Terraced plot (Plot 2) experience greater nutrient loss down the slope compared to Plot 1, that showed nutrient accumulation at lower elevations. Principal component analysis (PCA) revealed that soil pH did not significantly influence element adsorption within SPSFs. Differences in land use management between plots directly impacted nutrient distribution. Optimising agricultural land management can improve soil health, contributing to attaining the United Nations sustainable development goals 1, 2, 6, and 8.

Agroforestry is recognized as a multifunctional land use system that provides numerous benefits, including improved soil quality, enhanced agricultural productivity, and reduced climate change impacts. This article explores the mechanisms behind the underground storage of soil organic carbon (SOC) in agroforestry systems, emphasizing its link to soil health and climate resilience. Trees contribute to SOC through processes such as the addition of organic matter from falling leaves and dying roots, which enhances carbon storage and initiates essential soil functions like humification, mineral association, and aggregate formation that protect against microbial decay. The organic matter's quality, particularly its lignin and nitrogen content, influences decomposition rates, affecting nutrient cycling and long-term carbon stability. Research illustrates significant increases in SOC across various agroforestry practices involving crops, livestock, and trees, with tree systems demonstrating the most substantial daily carbon deposition and biological enrichment. A global synthesis indicates that even a modest increase in agroforestry (up to 30 percent) could sequester between 12 to 19 petagrams of carbon dioxide, notably in regions like South America, sub-Saharan Africa, and Southeast Asia, which exhibit high potential. Besides carbon sequestration, agroforestry positively influences soil structure, nutrient cycling, and microbial diversity, thereby promoting ecologically resilient and productive farming. However, outcomes vary by context, influenced by climate, soil properties, species diversity, and management practices. The article concludes that agroforestry is a scientifically valid natural climate solution and sustainable agriculture alternative, with its effectiveness hinging on intentional policy support and its inclusion in climate mitigation strategies.

&amp;lt;p&amp;gt;The incorporation of a comprehensive crop module in land surface models offers the possibility to study the effect of agricultural land use and land management changes on the terrestrial water, energy and biogeochemical cycles. It may help to improve the simulation of biogeophysical and biogeochemical processes on regional and global scales in the framework of climate and land use change. In this study, the performance of the crop module of the Community Land Model version 5 (CLM5) was evaluated at point scale with site specific field data focussing on the simulation of seasonal and inter-annual variations in crop growth, planting and harvesting cycles, and crop yields as well as water, energy and carbon fluxes. In order to better represent agricultural sites, the model was modified by (1) implementing the winter wheat subroutines after Lu et al. (2017) in CLM5; (2) implementing plant specific parameters for sugar beet, potatoes and winter wheat, thereby adding the two crop functional types (CFT) for sugar beet and potatoes to the list of actively managed crops in CLM5; (3) introducing a cover cropping subroutine that allows multiple crop types on the same column within one year. The latter modification allows the simulation of cropping during winter months before usual cash crop planting begins in spring, which is an agricultural management technique with a long history that is regaining popularity to reduce erosion and improve soil health and carbon storage and is commonly used in the regions evaluated in this study. We compared simulation results with field data and found that both the new crop specific parameterization, as well as the winter wheat subroutines, led to a significant simulation improvement in terms of energy fluxes (RMSE reduction for latent and sensible heat by up to 57 % and 59 %, respectively), leaf area index (LAI), net ecosystem exchange and crop yield (up to 87 % improvement in winter wheat yield prediction) compared with default model results. The cover cropping subroutine yielded a substantial improvement in representation of field conditions after harvest of the main cash crop (winter season) in terms of LAI magnitudes and seasonal cycle of LAI, and latent heat flux (reduction of winter time RMSE for latent heat flux by 42 %). Our modifications significantly improved model simulations and should therefore be applied in future studies with CLM5 to improve regional yield predictions and to better understand large-scale impacts of agricultural management on carbon, water and energy fluxes.&amp;lt;/p&amp;gt;

Soil organic carbon (SOC) is an important soil parameter of agricultural soils, ensuring food security and agricultural sustainability. It plays a critical role in the global carbon budget and carbon sequestration. Spatial mapping of SOC can help develop sustainable management approaches to enhance soil carbon sequestration and mitigate greenhouse gas emissions and adverse environmental effects. However, quantifying Spatio-temporal distributions of SOC at the global level is complex because of high land heterogeneity and several climatic and hydrologic influential parameters. The main goal of this study was to quantify the annual global SOC change focusing on cropland using daily soil moisture active passive (SMAP) satellite SOC data. The specific objectives of this study were to assess annual SOC change globally, quantify the annual SOC distribution before and during the COVID-19 pandemic, and evaluate change in SOC on cropland during the study period. Results showed an increase of annual SOC on cropland in several countries in 2020 compared to 2019, which can be attributed to the direct and indirect impact of partial and complete lockdowns due to the COVID-19 pandemic. The change in SOC between 2015 and 2019 was considerably different from the SOC change between 2019 and 2020. For example, between 2019 and 2015, 45.6% of the global area showed a decrease in SOC 0 to 25 g C m−2 and 30.4% area showed an increase in SOC 0 to 25 g C m−2. However, between 2020 and 2019, 11.4% of the global area showed a decrease in SOC 0 to 25 g C m−2, and 55.4% area showed an increase in SOC 0 to 25 g C m−2. There is a good relationship between lockdown measures and improvement in SOC, as 48 out of 50 highly infected countries showed increased SOC in 2020 than in 2019. This study suggests better land use management practices can help enhance carbon sequestration and improve soil health.

Summary Stream ecosystem metabolism integrates production and respiration of organic matter and plays a fundamental role in the global carbon (C) cycle. Several studies have identified distal and proximal physical controls, for example, land use and transient storage, or the effects of water chemistry, that is, organic matter and nutrient availability, on stream metabolism. In parallel, research on organic matter quality has identified conspicuous gradients of chemical composition, yet mostly without demonstrating any functional implications. We hypothesise that organic matter holds a key position in a more comprehensive causal framework of stream ecosystem metabolism, and that a concurrent study can improve mechanistic understanding. Specifically, we here postulate that dissolved organic matter (DOM) quality, that is, its chemical composition, acts as a control of ecosystem respiration (ER) as much as it is a result of gross primary production (GPP). As such, DOM quality likely forms a central link between land use and stream metabolism, besides known physical controls including transient storage and light availability. To examine these hypotheses, we studied 33 streams in north‐eastern Austria, a region with diverse land use ranging from semi‐natural, forested areas to agricultural areas and settlements. We analysed DOM composition by absorbance and fluorescence spectroscopy, including modelling excitation–emission matrices with parallel factor analysis. We then opposed these data to GPP and ER estimated by fitting a metabolism model to single‐station diurnal oxygen records. Structural equation modelling revealed land use as a control on light conditions, DOM composition and concentration and nutrient concentrations, which together ultimately shaped GPP and ER. In particular, humified, coloured and aromatic DOM of predominantly terrestrial origin was prevalent in coniferous forest catchments and increased stream ER. Agricultural and urban areas enriched streams with phosphorous and nitrogen, which increased ER and GPP. Besides nutrients, GPP seemed to be weakly correlated with light availability and – in contrast to our hypothesis – left only a weak imprint on DOM composition. Land‐use change is rated as the most pervasive human influence on natural ecosystems and our results highlight its impact on aquatic GPP and ER in streams. To understand the role of inland waters in the global C cycle will require mechanistic understanding of ecosystem metabolism, which notably includes organic matter quality as a hitherto underappreciated key player.

&amp;lt;p&amp;gt;In order to mitigate climate change and reduce the anthropogenic greenhouse gas (GHG) emissions, the Kyoto protocol has been adopted in 1997 and the Paris Agreement entered into force in 2016. The Paris Agreement have ratified 190 out of 197 Parties of the United Nations Framework Convention on Climate Change (UNFCCC) and Croatia is one of them as well. Each Party has obliged regularly to submit the national inventory report (NIR) providing the information on the national anthropogenic GHG emissions by sources and removals by sinks to the UNFCCC. Reporting under the NIR is divided into six categories / sectors, and one of them is land use, land use change and forestry (LULUCF) sector, where an issue of uncertainty estimates on carbon emissions and removals occurs. As soil respiration represents the second-largest terrestrial carbon flux, the national studies on soil respiration can reduce the uncertainty and improve the estimation of country-level carbon fluxes. Due to the omission of national data, the members of the University of Zagreb Faculty of Agriculture, Department of General Agronomy have started to study soil respiration rates in 2012, and since then many different studies on soil respiration under different agricultural land uses (i.e. annual crops, energy crop and vineyard), management practices (i.e. tillage and fertilization) and climate conditions (i.e. continental and mediterranean) in Croatia have been conducted. The obtained site specific results on field measurements of soil carbon dioxide concentrations by &amp;lt;em&amp;gt;in situ&amp;lt;/em&amp;gt; closed static chamber method will be presented in this paper.&amp;lt;/p&amp;gt;

Purpose. The aim of the article is determining the conditions of rational use of agricultural land conditions and substantiation of measures to optimize the distribution and rational use of agricultural land. Methodology of research. General scientific and special methods are used to achieve this goal: the dialectical method of scientific knowledge – to consider the essence of the rational use of land and its protection; synthesis – to clarify the relationship between the subjects of land relations; analysis – to assess the constituent elements of agricultural land; graphic – for visual display of the obtained results; abstract and logical method – for the formation of conclusions and research proposals. Findings. The state and rational use of land in the region and the state are studied. The structure of agricultural lands in Ivano-Frankivsk region and Ukraine is analysed. The main ecological and economic aspects of land tenure and land use in agriculture are described, including changes in land relations. The main reasons that caused the negative trends of rational use and protection of land in agriculture are identified. Measures have been developed for the rational use of land in the economic activity of land and its protection. Originality. Approaches to the interpretation of the concept of “rational use of land” are systematized and generalized. Measures on rational use of agricultural lands in economic activity are offered, namely: creation and realization of innovative scientific and technical programs in the field of rational use of lands and their protection; improving the regulatory framework in the field of land relations; development of a mechanism for financing programs; introduction of environmentally friendly ways of agricultural production, etc. Practical value. The expediency of studying and forming the conditions of rational use of agricultural lands is proved. The results of the study can be used by agricultural enterprises in conducting business activities. Key words: agricultural lands, rational use of lands, land protection, land tenure, land use, land fund, agricultural enterprises.

Scenarios for Australian agricultural production and land use to 2050

Stream ecosystems form an active component of the carbon (C) cycle, and are identified as “hotspots” for carbon dioxide (CO2) emissions. However, the mechanisms driving CO2 emissions from streams are not completely understood. Beside the input of C in the form of CO2 from groundwater, streams receive organic matter from aquatic and terrestrial origins which is partly mineralized to inorganic nutrients and CO2. Future predictions suggest enhanced input of terrestrial organic matter into streams. As such, surrounding land use may highly influence dissolved organic matter (DOM) composition and turnover in streams. The quality, i.e. bioavailability or lability, of aquatic and terrestrial organic matter, as well as which quality feature provides which bioavailability, is controversially discussed and the research is still in its infancy. Thus, the main goal of my thesis is to enhance the understanding of the role of organic matter quality as a potential driver for organic matter turnover in stream ecosystems. A further goal is to shed light on C dynamics with main focus on CO2 of streams surrounded by different land use. The presented work is based on an experimental approach in the laboratory, supported by seasonal field studies and a developed model in order to explore C dynamics and the corresponding drivers in stream ecosystems. The underlying mechanisms and the importance of DOM quality as a main driver was assessed on the small scale in laboratory experiments. The C emissions from streams were quantified and the influence of DOM quality was examined on a stream reach scale by investigating two stream types with different organic matter quality inputs. By developing a process-based model, the understanding of the daily and seasonal scale of C turnover in stream ecosystems was amplified. The results from the experiment under controlled conditions demonstrate that DOM quality governs microbial metabolism (i.e. respiration and bacterial protein production). Moreover, I revealed significant quality differences between two terrestrial DOM sources, while respiration and bacterial protein production increased with the available proportion of the labile DOM source. The molecular weight of DOM was the strongest predictor of bacterial protein production and respiration, while among others, the concentration of low molecular weight substances was another highly influential predictor. The importance of molecular size/weight and DOM quality for microbial metabolism was further confirmed on the stream reach scale where we demonstrated among others a significant linkage between molecular size of DOM and pCO2 across agricultural and forest streams. Moreover, agricultural streams contained significantly higher pCO2 compared to forest streams during all seasons. However, CO2 emissions measured with the powerful drifting chamber method were not significantly different between the stream types. Modeled dissolved oxygen (O2) and CO2 dynamics calibrated with field data resulted in respiratory quotients (RQ = mole of CO2 produced per mole of O2 consumed), which are intimately linked to the elemental composition of the respired compounds across four seasons and two stream types. RQ values were not related to adjacent land use or season. Nevertheless, I found significant relationships between RQ values and DOM quality indicators, such as fluorescing component characteristic for higher plant material and molecule size of DOM in agricultural streams. In conclusion, this thesis demonstrates that DOM quality is an important driver for organic matter turnover in streams. Consequently, my results indicate that ongoing and future land use change and enhanced terrestrial DOM input into streams may influence CO2 emissions, and underline the status of streams as C turnover “hotspots”. Thus, my thesis contributes to the mechanistic understanding of organic matter cycling in stream ecosystems and their role in the regional and global C cycle. Therefore, organic matter quality should be considered in future models and studies with respect to C cycling.

Impacts on ecosystem services that are related to agricultural land use greatly differ depending on management practices employed. This study aimed to reveal issues associated with evaluating ecosystem services related to land use at the management level during life cycle assessment (LCA) and to consider future challenges. Firstly, a relationship between agricultural ecosystem services and management practices was outlined. Then, a survey was performed to disclose the current status of assessment of impact of land use in agricultural LCA case studies that compared between different management practices. In addition, this study also investigated how management practices have been differently considered by factors that characterize ecosystem services that are related to land use. The results show that the number of agricultural LCA cases where land use impacts instead of land areas were assessed was still small. The results of limited LCA case studies, which using factors could differentiate between various management practices, suggest that although organic farming methods have been employed over large land areas, lower impact may be caused by agricultural land use. For factors developed in existing research, services related to soil quality, and some of the regulatory services were considered, those unique to agriculture were missing. Although most of factors were calculated at levels of intensity or land use type, some of them were based on a process-based model that could consider management practices. In the future, factors that characterize the impacts of land use on ecosystem services, such as carbon storage and erosion prevention, will need to be calculated at the management level. For ecosystem services, such as habitat conservation and pollination, further efforts in accumulating evaluation case studies that collect and accumulate foreground data are important.

Soil organic carbon (SOC) is important to soil nutrient status in agroecosystems. Some of the soils of the Northeast of China, noted for their high SOC content, suffer from serious soil erosion to the point of having the parent material exposed or near the surface, which has raised concerns for food security. The Chinese Mollisols were derived from loamy Quaternary loess that developed from parent material. To effectively restore parent material to productive soils, information on the effects of land use/management practices on SOC concentration and C fractions in loess parent material of Chinese Mollisols is needed. The main objective of this study was to investigate the changes in C sequestration and C density fractions by physical and chemical fractionation (humic substances) occurring in the process of soil development from parent material under different management practices and land use. Six treatments were imposed in plots of loess parent material in a 5-year experiment: (1) natural fallow without weed control; (2) alfalfa; (3) soybean-maize rotation (S-M), straw of unfertilized maize removed; (4) S-M, straw of chemically fertilized maize removed; (5) S-M, straw of chemically fertilized maize and dried soybean powder incorporated; (6) S-M, biomass, including grain, of chemically fertilized maize incorporated. The SOC content increased by 15% to 77% depending on treatments. In the process of soil development, the C fractions of the parent material changed rapidly. The heavy fraction C pool accounted for a larger proportion of total SOC (78%–89%) than both the free light fraction (2.1%–10.2%) and the occluded light fraction (1.3%–12.9%) pools. The occluded light fraction was more sensitive than the free light fraction as indicator of soil C changes because of different land use and management practices. Humin accounted for a larger proportion (29.9%–54.7%) of SOC than fulvic acid (18.0%–34.4%), which was larger than the humic acid fraction (11.8%–14.8%). Our results indicate that SOC increase in loess parent material depends on types and amounts of organic matter inputs. The treatments, in which aboveground crop biomass and grain were incorporated, contributed more to C sequestration, distributions of density fraction, and humic substances than the treatments without organic matter. Management practices maximizing biomass inputs are recommended to restore SOC in degraded Chinese Mollisols in order to restore their fertility.