En los últimos 150 años la humanidad incrementó la emisión de CO2, acelerando el calentamiento atmosférico global. La retención de carbono orgánico en los suelos (COS) mitiga dicho efecto y contribuye a mejorar la calidad del recurso. Los factores que regulan el COS pueden analizarse desde la perspectiva pedológica utilizando la ecuación de estado, que postula que modificaciones en los factores formadores (FF) producirán variaciones en los procesos pedogenéticos (PP) y cambios en las propiedades de los suelos. Los objetivos de la presente tesis fueron: i) Cuantificar los niveles de COS en regiones geográficas homogéneas y establecer su variación a través del paisaje; ii) Evaluar efectos por cambio en la condición climática sobre COS en suelos de granulométrica homogénea y similar relieve; iii) Establecer efectos sobre COS por cambios en los materiales parentales (MP) en condiciones análogas de relieve y clima; iiii) Determinar la acción antrópica por diferentes usos de la tierra e intensidades de uso agrícola. El área de estudio se ubicó en la Pampa Austral, abarcando 110 perfiles en los que se evaluaron 15 variables de sitio, morfológicas, físicas, químicas, biológicas y taxonómicas. Los resultados indicaron que el relieve fue el FF de mayor influencia sobre COS y que la incidencia del resto de los FF varió en función del mismo. Las llanuras de inundación presentaron los más altos contenidos de COS, superando a los valles interserranos y paleocauces, seguidos de planos normales o cóncavos, lomadas y laderas. El análisis jerárquico permitió una mayor comprensión de los FF, PP y mejor predicción del COS. El clima ejerce una acción positiva afectada por el relieve y el MP. En suelos de sedimentos loéssicos y en planos normales la precipitación media anual y la profundidad efectiva en conjunto explicaron un 49 % de la variabilidad del COS (P <0,01). Los MP ejercieron influencia regional sobre COS (r= 0,28, P <0,05, N= 110), aún con la interferencia de otros FF. Los sedimentos aluviales presentaron elevados niveles de COS (171 Mg ha-1), seguido por los sedimentos loéssicos (108 Mg ha-1) y sedimentos eólicos recientes (81 Mg ha-1). El uso produjo cambios en el carbono de 0-25 cm y en el carbono orgánico de 0-1 m. El uso forestal mostró los más altos contenidos de CO0-25 en todos los materiales parentales. La intensidad del uso impactó de manera diferencial sobre el COS en función de la granulometría. Bajo agricultura extractiva los suelos de texturas gruesas presentaron mermas del 60 % en CO. La inclusión de siembra directa y pasturas puede lograr retenciones de 0,7 Mg ha-1 año-1. Se ha demostrado que el relieve es el FF que regula los niveles de COS de la región, modificando el balance de los PP. COS mostró respuesta a la intensidad de la melanización. Los PP modificaron su relación en función de la profundidad efectiva: los suelos someros presentaron melanización intensa, mientras que los suelos profundos redujeron la misma a favor de la iluviación o la alcalinización. La clasificación taxonómica a nivel de familia reflejó claramente los principales FF y PP que ocurren en la Pampa Austral. Las taxas de suelos segregadas y los contenidos de carbono orgánico presentaron una fuerte asociación, lográndose a partir de ellas una mayor certidumbre en la explicación de la variabilidad del COS. Palabras claves: Carbono orgánico del suelo, factores formadores, procesos pedogenéticos, usos del suelo, retención de carbono, Pampa Austral. / Human activity increased CO2 emissions in the last 150 years, accelerating global atmospheric warming. Soil organic carbon storage (SOC) mitigates warming and helps to improving soil quality. Factors that regulate SOC can be analyzed from the pedological approach using the equation of state factors, says changes in the soil forming factors (FF) and their interactions produce variations in pedogenic processes (PP) and changes in soil properties. The objectives of this thesis were: i) measure SOC levels in homogeneous geographic region and analyzing variability across landscape; ii) measure effects of change climatic condition of SOC in soils with similar parent material (PM) and relief; iii) quantify effects on SOC for changes in PM to similar conditions of relief and climate; iiii) determine antropic effects by different land uses and management practices. The study area was located in Austral Pampa, using 110 soil profiles in which 15 site, morphological, physical, chemical, biological and taxonomic variables were evaluated. Results indicated that relief was the most influential FF on SOC, and the incidence of the remaining FF varied according to the same. Flood-plains showed the highest SOC level, followed by saw-valleys and paleo-valleys, normal flats, concave flats, hills and slopes. Hierarchical analysis showed greater understanding of the FF, PP and better prediction of SOC. The climate has a positive effect modified by relief and PM. In soils of loess sediments located in normal flats annual average rainfall and the effective depth explained 49% of the SOC variability (P <0.01). PM presented a regional effect on COS (r = 0.28, P <0.05, N= 110), despite the interference from other FF. Alluvial sediments showed high COS levels (171 Mg ha-1) followed by loess sediments (108 Mg ha-1) and recent aeolian sediments (81 Mg ha-1). Land use produced changes in 0-25 cm and 0-1 m organic carbon. Forest use showed the highest organic carbon content in 0-25 cm on all parent materials. Tillage systems and management practices impacted differently on the SOC in relation to soil texture. Intensive farming in coarse soils showed declines of 60% in CO. No-tillage and pasture showed retention rates of 0.7 Mg ha-1 yr-1. Relief is the main FF regulating COS levels in the region and the balance of the PP, and responded to intensity of melanization. PP changed their relationship as a function of effective depth: shallow soils showed intense melanization, whereas deep soils reduced melanization in favor of illuviation or alkalinization. Soil Taxonomy family level reflected clearly the main FF and PP occurring in the Austral Pampa. Soil taxas segregated and organic carbon contents showed a strong association, improving the explanation of SOC variability. Keywords: Soil organic carbon, soil forming factors, pedogenetic processes, land use, carbon retention, Austral Pampa.

Soil organic matter (SOM) is a well known indicator of soil quality due to its direct influence on soil properties such as structure, soil stability, water availability, cation exchange capacity, nutrient cycling, and pH buffering and amelioration. Study sites were selected in the Valley region of Virginia with the study objectives to: i) compare the efficiency of density solutions used in recovering free-light fraction (FLF) organic matter; ii) compare different soil organic fractions as sensitive indices of short-term changes in SOM due to management practices; iii) investigate on-farm effects of tillage management on soil organic carbon (SOC) and soil organic nitrogen (SON) stocks; and iv) evaluate the role of SOM in controlling soil available nitrogen (N) for corn uptake. The efficiency of the density solutions sodium iodide (NaI) and sodium polytungstate (SPT) in recovering FLF was the same at densities of 1.6 and 1.8 g cm⁻³, with both chemicals presenting less variability at 1.8 g cm⁻³. The sensitivity of SOM fractions in response to crop and soil management depended on the variable tested with particulate organic matter (POM) being the most sensitive when only tillage was tested, and FLF being the most sensitive when crop rotation and cover crop management were added. The on-farm investigation of tillage management on stocks of SOC and total soil N (TSN) indicated significant increases at 0–15 cm depth by increasing the duration (0 to 10 years) of no-tillage (NT) management (0.59 ± 0.14 Mg C ha⁻¹ yr⁻¹ and 0.05 ± 0.02 Mg N ha⁻¹ yr⁻¹). However, duration of NT had no significant effect on SOC and TSN stocks at 0–60 cm depth. Soil available N as controlled by SOM was modeled using corn (<i>Zea mays</i> L.) plant uptake as response and several soil N fractions as explanatory variables. The final model developed for 0–30 cm depth had 6 regressors representing the different SOM pools (active, intermediate, and stable) and a 𝑅² value of 65%. In summary, this study provides information about on-farm management affects on SOM levels; measurement of such effects in the short-term; and estimation of soil available N as related to different soil organic fractions. / Ph. D.

This research investigated the long-term effects of transitioning from intensive tillage to no-till (NT) practices with cover crop (CC) incorporation on soil quality, agronomic performance, and economic returns in Virginia's Coastal Plain. Nine years after integrating NT practices and CCs, improvements in soil physical and chemical properties were observed, including a 22% to 65% increase in soil organic matter (SOM) in the top 5 cm, a 4% reduction in bulk density, and enhanced soil moisture retention in corn production. Timing of CC termination played a crucial role in optimizing biomass production and nutrient accumulation. Overall accumulation rates were 44.4 kg dry biomass ha-1 d-1, 1.22 kg N ha-1 d-1, 0.16 kg P ha-1 d-1, 1.36 kg K ha-1 d-1, and 0.08 kg S ha-1 d-1 of delayed termination between March 15 and April 30. Each additional day of cover crop growth contributed to a fertilizer value of $3.91 ha-1, highlighting the economic advantage of extending CC growth during this critical period. In 2023, CC effects on corn N fertilizer demand and yields were assessed by applying variable N rates of 0, 56, 112, and 168 kg N ha-1 at sidedressing. Greatest corn yields at each N rate were observed following hairy vetch and a vetch-dominant CC mix, which had low C:N ratios (≤12:1) and accumulated 134 to 186 kg N ha-1 in their aboveground biomass. Corn yields after these CCs were 8.5 to 9.3 Mg ha-1 at the zero N sidedressing rate, increasing to 10.8 to 11.3 Mg ha-1 at the 168 kg N ha-1 rate. However, increasing the N rate yielded minimal economic benefits for these treatments. Vetch treatments produced the highest net returns, with greater returns at lower N rates, as vetch generated an additional US$1,012 ha-1 at the zero N sidedressing rate compared to the no CC control. Conversely, cereal rye produced a negative net return across all N rates, with positive returns achievable only with state cost-share payments. The findings underscore the importance of adaptive N management strategies and policy adjustments to support environmentally and economically sustainable cover crop practices in corn production. / Doctor of Philosophy / This research examines long-term benefits of switching from intensive tillage to no-till (NT) farming with cover crops (CC) on soil health, crop performance, and economic returns in Virginia's Coastal Plain. After nine years of using NT and CCs, we saw significant improvements in soil quality: soil organic matter in the top 5 cm increased by 22% to 65%, bulk density decreased by 4%, and soil moisture retention improved in corn crops. The timing of cover crop termination was crucial for maximizing biomass and nutrient benefits. Delaying termination from March 15 to April 30 resulted in additional dry biomass and nutrients, translating into a fertilizer value of $3.91 per hectare for every day of extra growth. In 2023, we assessed how different nitrogen (N) rates affected corn yields and fertilizer needs. Best yields were achieved with hairy vetch and vetch-dominant cover crops, which had low carbon-to-nitrogen (C:N) ratios and accumulated significant N in their biomass. Although these cover crops improved yields, increasing N rates returned minimal economic gains. Vetch treatments provided the highest net returns, especially at lower N rates, generating an additional $1,012 per hectare compared to no cover crop. In contrast, cereal rye resulted in negative returns across all N rates, unless state cost-share payments were applied. These results highlight the need for flexible N management strategies and policy changes to support effective and profitable cover crop practices in corn farming.

Global urbanization has resulted in rapidly increased urban land. Soils are the foundation that supports plant growth and human activities in urban areas. Furthermore, urban soils have potential to provide a carbon sink to mitigate greenhouse gas emission and climate change. However, typical urban land development practices including vegetation clearing, topsoil removal, stockpiling, compaction, grading and building result in degraded soils. In this work, we evaluated an urban soil rehabilitation technique that includes compost incorporation to a 60-cm depth via deep tillage followed by more typical topsoil replacement. Our objectives were to assess the change in soil physical characteristics, soil carbon sequestration, greenhouse gas emissions, and stormwater mitigation after both typical urban land development practices and post-development rehabilitation. We found typical urban land development practices altered soil properties dramatically including increasing bulk density, decreasing aggregation and decreasing soil permeability. In the surface soils, construction activities broke macroaggregates into smaller fractions leading to carbon loss, even in the most stable mineral-bound carbon pool. We evaluated the effects of the soil rehabilitation technique under study, profile rebuilding, on soils exposed to these typical land development practices. Profile rebuilding incorporates compost amendment and deep tillage to address subsoil compaction. In the subsurface soils, profile rebuilding increased carbon storage in available and aggregate-protected carbon pools and microbial biomass which could partially offset soil carbon loss resulting from land development. Yet, urban soil rehabilitation increased greenhouse gas emissions while typical land development resulted in similar greenhouse gas emissions compared to undisturbed soils. Additionally, rehabilitated soils had higher saturated soil hydraulic conductivity in subsurface soils compared to other practices which could help mitigate stormwater runoff in urban areas. In our study, we found urban soil management practices can have a significant impact on urban ecosystem service provision. However, broader study integrating urban soil management practices with other ecosystem elements, such as vegetation, will help further develop effective strategies for sustainable cities. / Ph. D.

Much of Haitian agriculture is characterized by subsistence farming systems on eroded and nutrient-poor soils. Implementation of Conservation Agriculture systems has proven effective at improving soil quality and crop yield in many areas of the world, including areas similar to those in Haiti. While most Haitian smallholder farmers are highly resource-limited and adoption of new technologies is limited, these farmers are known to adopt new crops and practices if benefits that outweigh risks are demonstrated. Cover crops that help provide soil cover and increase nutrient mineralization are one of the most potentially beneficial changes that could be made on most smallholder farms. However, before specific cover crop recommendations can be made, their potential benefits need to be quantified. One field experiment in the summer of 2013 assessed decomposition rates and nutrient mineralization from common cash crops and two potential cover crops either on the soil surface or buried at 15 cm. The relative difficulty and expense of conducting these types of field trials led to the development and assessment of a laboratory-based system that could be used to simulate plant residue decomposition and nutrient release under controlled conditions. Additional benefits of a laboratory-based study include the ability to test significantly more treatment combinations than would likely be possible under field conditions and to control nearly all other experimental variables, other than the desired treatment comparisons. / Master of Science

Soil organic carbon represents the largest constituent of the global C pool and carbon budgets are studied by researchers and modelers in C cycling, global climate change, and soil quality studies. Pedon and soil interpretation record databases are used with soil and ecological maps to estimate regional SOC even though these databases are rarely complete for surface litter and mineral subsurface horizons. The first main objective of the project is to improve the ability to produce soil organic carbon estimates from existing spatial soils datasets, such as STATSGO. All records in the STATSGO Layer table that were incomplete or appeared to be incorrectly filled with a null or zero value were considered invalid. Data sorting procedures and texture lookup tables were used to identify exiting correct (valid) data entries that were used to substitute invalid records. STATSGO soil property data were grouped by soil order, MLRA, layer number, and texture to produce replacement values for all invalid data used to calculate mass SOC. Grouping criteria was specific to each variable and was based on texture designations. The resulting filled and unfilled tables were used with procedures assuming Normal and Lognormal distribution of parameters in order to analyze variation of mass SOC estimates caused by using different computation techniques. We estimated mass SOC to 2 m in Maine and Minnesota using filled and unfilled STATSGO data tables. Up to 54% of the records in Maine and up to 80% of the records in Minnesota contained null or zero values (mostly in fields related to rock fragments) that were replaced. After filling, the database resulted in 1.5 times higher area-weighted SOC. SOC calculated using the Normal distribution assumption were 1.2 to 1.5 times higher than those using the Lognormal transformation. SOC maps using the filled tables had more logical geographic SOC distribution than those using unfilled tables. The USDA Forest Service collects and maintains detailed inventory data for the condition and trends of all forested lands in the United States. A wide range of researchers and landowners use the resulting Forest Inventory and Analysis (FIA) database for analytical and decision making tasks. FIA data is available to the public in transformed or aggregate format in order to ensure confidentiality of data suppliers. The second main objective of this project was to compute SOC (kg m-2) results by FIA forest type and forest type group for three depth categories (25 cm, 1 m, and 2 m) at a regional scale for the 48 contiguous United States. There were four sets of results derived from the filled STATSGO and FIA datasets for each depth class by region: (1) SOC computed by the Lognormal distribution approach for (1a) all soil orders, (1b) without Histosols; and (2) SOC computed by the Normal distribution approach for (2a) all soil orders, (2b) without Histosols. Two spatial forest cover datasets were relevant to this project, FIA and AVHRR. We investigated the effects of FIA inventory data masking for Maine and Minnesota, such as plot coordinates rounding to the nearest 100 arc-second, and the use of 1 km resolution satellite-derived forest cover classes from AVHRR data, on SOC estimates to 2 m by forest type group. SOC estimates by soil mapping unit were derived from fixed STATSGO database tables and were computed by the Lognormal distribution approach including all soil orders. The methods in this study can be used for a variety of ecological and resource inventory assessments and the automated procedures can be easily updated and improved for future uses. The procedures in this study point out areas that could benefit the most during future revisions of STATSGO. The resulting SOC maps are dynamic and can be rapidly redrawn using GIS whenever STATSGO spatial or tabular data undergo updating. Use of pedon data to define representative values for all properties in all STATSGO layers and correlation of STATSGO layers to soil horizons will lead to vast improvement of the STATSGO Layer table and promote its use for mass SOC estimation over large regions. / Master of Science

Current Virginia nitrogen (N) fertilizer recommendations do not include site-specific estimates of N supply from cover crops (CCs) or soil organic matter (SOM). Recent research successfully predicted the contribution of N from SOM and CCs to corn (Zea mays L.) in Pennsylvania. The objective of this work was to validate the biophysical model developed in Pennsylvania under Virginia conditions and to evaluate the decomposition rates of different surface-applied CC residues and the relationship between their chemical composition and decomposition rate. For the first objective, 83 N response trials were conducted in different regions of Virginia across 9 years using a randomized complete block design with four replications. The model was able to explain 47% and 15% of variability in unfertilized corn yield (RMSE = 1.6 Mg ha-1) and economical optimum N rate (EONR) (RMSE = 30 kg N ha-1) respectively. Efforts to improve the model by adding economically unresponsive sites improved the model performance to explain 45% of the variability in EONR. For the second objective, a lab incubation was performed to compare carbon (C) and N mineralization from four different CCs {Cereal Rye (CR), Hairy vetch (HV), Crimson clover (Cc) and Rapeseed (R)} on a sandy loam soil. Destructive sampling was performed at 6 different sampling dates – 3, 7, 14, 28, 56 and 112 days. ANOVA test revealed that the effects of CC species, incubation days and their interaction had a significant effect on mass decomposed, plant biochemical composition and net N mineralization. Variation in mass loss was positively related to lignin content for all the CCs while it was moderately correlated to C:N ratio for CR and R and weakly to HV and Cc. Biomass loss and N release was highest in HV followed by Cc, R and CR. Net N mineralization was highest in HV followed by R, Cc and CR amended soils. / Master of Science / Current Virginia nitrogen (N) fertilizer recommendations do not include site-specific estimates of N supply from cover crops or soil organic matter, both of which can influence crop N need. Recent research successfully predicted the contribution of N from cover crops and soil to corn (Zea mays L.) in Pennsylvania. The objectives of this work were to validate the biophysical model developed in Pennsylvania under Virginia conditions and to evaluate the decomposition rates of different surface-applied cover crop residues and the relationship between their chemical composition and decomposition rate. The Pennsylvania-developed model was able to successfully estimate the economical optimum N rate for corn and predict the yield of unfertilized corn. Corn yield did not increase with increasing N rates in some fields. When these sites were omitted, the accuracy of the model improved. For the second objective, a lab incubation study was performed comparing C and N released from Cereal Rye (CR), Hairy vetch (HV), Crimson clover (Cc) and Rapeseed (R)} on a sandy loam soil. Destructive sampling was performed at 6 different sampling dates – 3, 7, 14, 28, 56 and 112 days. Variation in mass loss was positively related to lignin content for all the cover crops while it was moderately correlated to C:N ratio for CR and R and weakly to HV and Cc. Biomass loss and N release was highest in HV followed by Cc, R and CR.

Mineral-associated organic carbon (MAOC) is a vital component of soil health and ecosystem productivity, playing a key role in carbon (C) sequestration and nutrient cycling. This dissertation investigates how plant root traits, nitrogen (N) fertilization, and cover cropping influence soil organic carbon (SOC) and MAOC. In the first chapter, a greenhouse experiment with 30 herbaceous plant species found that non-N-fixing plants exhibited stronger positive correlations with MAOC compared to N-fixing species, which were more closely linked to SOC. Root biomass contributed to decreases in MAOC, while specific root length (SRL), and coarse root traits were found to significantly contribute to increases in MAOC, highlighting the importance of plant root architecture in stabilizing C. In the second chapter which focused on relationships among N-fertilization, root traits, and MAOC, moderate N fertilization (56 and 112 kg N/ha) was found to enhance total SOC (∆SOC) and MAOC (∆MAOC) accumulation in the system, while higher N inputs (168 kg/ha) reduced C gains. Notably, the use of stable isotopes allowed for the quantification of fresh C additions, with results that indicate plant-added MAOC (PA-MAOC) was influenced more by plant species and root traits, such as coarse root length and aboveground biomass, rather than N fertilization. In the third chapter, a long-term field study demonstrated the effectiveness of cover cropping in increasing both SOC and MAOC by 43–59% and 27–36%, respectively, compared to conventional and no-till systems without cover crops. Despite triennial additions of N fertilizer over nine years, no significant increases in SOC or MAOC was observed. Additionally, root biomass exhibited positive trends with MAOC. These findings suggest that cover cropping, combined with no till practices, plays a pivotal role in enhancing MAOC by minimizing soil disturbance and promoting root-driven C inputs. This research highlights the importance of integrating plant species selection, root morphological traits, N management, and conservation practices to optimize long-term C storage (i.e., MAOC) and support sustainable soil management. Future studies should continue to include MAOC and particulate organic carbon fractions as these functional C sub pools may respond differently than bulk SOC pool. Including further studies on the interactions between root morphology, environmental factors, and C/N dynamics is necessary to develop more resilient agroecosystems capable of mitigating C losses and improving long-term soil health. / Doctor of Philosophy / This dissertation explores soil organic carbon, an important component of soil organic matter, which is vital for soil health and fertility. Soil organic matter promotes plant growth and agricultural productivity, and is critical for mitigating climate change by acting as a carbon sink, absorbing carbon dioxide from the atmosphere, which is why maintaining and building soil carbon is important. Soil carbon that is bound to minerals such as clays, is referred to as mineral-associated carbon (MAOC), which holds the largest pool of carbon on land and is often believed to persist over longer time-scales. Cover crops, their plant roots, and nitrogen fertilizer may have different relationships with MAOC when compared to total soil carbon, and these responses are not well understood. To address some of these knowledge gaps, this dissertation measured MAOC, plant root traits such as root size and structure, among different types of plants commonly used in agriculture and land reclamation practices. Results from this work show that root traits play an important role in increasing MAOC during short-term plant growth, with different effects depending on whether the plants can fix nitrogen from the air. Nitrogen fertilization was found to strongly impact MAOC, with moderate levels increasing amounts of MAOC, but low or too much nitrogen caused losses. Additionally, plant traits like root and stem biomass had a stronger influence on fresh carbon inputs from plants to the soil versus nitrogen alone. Cover crops proved to be a highly effective strategy for improving MAOC storage over 9 years, while additional nitrogen fertilizer had little long-term effect. These findings highlight the importance of balancing plant selection, fertilization, and sustainable practices to maintain healthy, carbon-rich soils.

<p>Ово истраживање има за циљ да процени резерве органског угљеника у земљишту и представи његову просторну дистрибуцију у земљиштима Републике Србије, као и да утврди зависност садржаја органског угљеника у земљишту од типа земљишта, температуре, падавина, надморске висине, начина коришћења земљишта и морфогенетских карактеристика рељефа. Резерве органског угљеника у земљишту процењене су за слој 0-30 cm и 0-100 cm дубине на основу резултата из базе података уз коришћење педолошке карте и карте коришћења земљишта. За потребе утврђивања зависности садржаја органског угљеника и типа земљишта педолошка карта Србије је прилагођена WRB класификацији и садржи 15.437 полигона. Примењена методологија за процену резерве органског угљеника за дату дубину је базирана на сумирању резерве органског угљеника по слојевима земљишта која се добија на основу запреминске масе, вредности садржаја органског угљеника и дебљине слоја. Прорачун је урађен за сваки профил посебно, затим је урађена калкулација за сваку референтну групу земљишта на основу резултата средњих вредности садржаја органског угљеника до 30 cm и 100 cm дубине за главне референтне групе и њихових површина. На основу површина референтних група земљишта, површине Републике Србије и вредности садржаја за сваку референтну групу, добијене су укупне резерве органског угљеника до 30 cm дубине које износе 0,71 Pg. Резултати анализе резерве органског угљеника до 100 cm дубине показују вредност 1,16 Pg.<br />На основу Corine Land Cover (CLC) базе података за 2006. годину издвојене су површине главних категорија начина коришћења земљишта. На основу резултата средњих вредности садржаја органског угљеника до 30 и 100 cm дубине и површине коју заузима Corine Land Cover категорија начина коришћења земљишта израчуната је укупна вредност резерве органског угљеника за пољопривредна земљишта, шуме и полуприродна подручја и вештачке површине.<br />Резултати показују да су резерве органског угљеника у оквиру категорије пољопривредних површина 303,22 x 1012g (Tg) до 30 cm дубине и 600,25 x 1012g (Tg) до 100 cm дубине. Категорије шуме и полуприродна подручја имају резерве од основних климатских елемената температуре и падавина и надморске висине показује да постоји средње јака до јака статистичка зависност у оквиру испитивања реализованих до 30 и 100 cm дубине.</p><p>органског угљеника 345,26 x 1012g (Tg) угљеника до 30 cm и 457,55 x 1012g (Tg) до 100 cm дубине. Резултати показују вредности резерве органског угљеника у категорији вештачке површине која углавном обухватају локалитете у оквиру зелених урбаних подручја и рекреационих површина 19,21 x 1012g (Tg) до 30 cm и 41,50 x 1012g (Tg) до 100 cm дубине.<br />Анализа садржаја резерве органског угљеника према начину коришћења земљишта показује да су вредности садржаја органског угљеника веће у шумама и полуприродним подручјима у односу на пољопривредне површине и то за 40,71 % до 30 cm, односно за 11,43 % до 100 cm дубине. Прорачун губитка резерве органског угљеника у земљишту на подручјима где је извршена пренамена пољопривредних површина, шума и полуприродних подручја у урбано земљиште, без категорије зелена урбана подручја, у периоду 1990-2006. године показује укупну вредности од 0,92 Mt С, односно 1,49 Mt С за дубинe до 30 cm, односно до 100 cm.<br />Утврђивање статистичке зависности садржаја органског угљеника у земљиштуод основних климатских елемената температуре и падавина и надморске висине показује да постоји средње јака до јака статистичка зависност у оквиру испитивања реализованих до 30 и 100 cm дубине.</p><p>Прорачун садржаја резерве органског угљеника у земљишту у зависности од морфометријских карактеристика рељефа показујe да резерва садржаја органског угљеника у земљишту расте са порастом надморске висине. Највеће средње вредности садржаја измерене су на терену који обухвата планине са надморским висинама од 1.000-2.000 m и који обухвата 11,5 % територије Републике Србије</p> / <p>Ovo istraživanje ima za cilj da proceni rezerve organskog ugljenika u zemljištu i predstavi njegovu prostornu distribuciju u zemljištima Republike Srbije, kao i da utvrdi zavisnost sadržaja organskog ugljenika u zemljištu od tipa zemljišta, temperature, padavina, nadmorske visine, načina korišćenja zemljišta i morfogenetskih karakteristika reljefa. Rezerve organskog ugljenika u zemljištu procenjene su za sloj 0-30 cm i 0-100 cm dubine na osnovu rezultata iz baze podataka uz korišćenje pedološke karte i karte korišćenja zemljišta. Za potrebe utvrđivanja zavisnosti sadržaja organskog ugljenika i tipa zemljišta pedološka karta Srbije je prilagođena WRB klasifikaciji i sadrži 15.437 poligona. Primenjena metodologija za procenu rezerve organskog ugljenika za datu dubinu je bazirana na sumiranju rezerve organskog ugljenika po slojevima zemljišta koja se dobija na osnovu zapreminske mase, vrednosti sadržaja organskog ugljenika i debljine sloja. Proračun je urađen za svaki profil posebno, zatim je urađena kalkulacija za svaku referentnu grupu zemljišta na osnovu rezultata srednjih vrednosti sadržaja organskog ugljenika do 30 cm i 100 cm dubine za glavne referentne grupe i njihovih površina. Na osnovu površina referentnih grupa zemljišta, površine Republike Srbije i vrednosti sadržaja za svaku referentnu grupu, dobijene su ukupne rezerve organskog ugljenika do 30 cm dubine koje iznose 0,71 Pg. Rezultati analize rezerve organskog ugljenika do 100 cm dubine pokazuju vrednost 1,16 Pg.<br />Na osnovu Corine Land Cover (CLC) baze podataka za 2006. godinu izdvojene su površine glavnih kategorija načina korišćenja zemljišta. Na osnovu rezultata srednjih vrednosti sadržaja organskog ugljenika do 30 i 100 cm dubine i površine koju zauzima Corine Land Cover kategorija načina korišćenja zemljišta izračunata je ukupna vrednost rezerve organskog ugljenika za poljoprivredna zemljišta, šume i poluprirodna područja i veštačke površine.<br />Rezultati pokazuju da su rezerve organskog ugljenika u okviru kategorije poljoprivrednih površina 303,22 x 1012g (Tg) do 30 cm dubine i 600,25 x 1012g (Tg) do 100 cm dubine. Kategorije šume i poluprirodna područja imaju rezerve od osnovnih klimatskih elemenata temperature i padavina i nadmorske visine pokazuje da postoji srednje jaka do jaka statistička zavisnost u okviru ispitivanja realizovanih do 30 i 100 cm dubine.</p><p>organskog ugljenika 345,26 x 1012g (Tg) ugljenika do 30 cm i 457,55 x 1012g (Tg) do 100 cm dubine. Rezultati pokazuju vrednosti rezerve organskog ugljenika u kategoriji veštačke površine koja uglavnom obuhvataju lokalitete u okviru zelenih urbanih područja i rekreacionih površina 19,21 x 1012g (Tg) do 30 cm i 41,50 x 1012g (Tg) do 100 cm dubine.<br />Analiza sadržaja rezerve organskog ugljenika prema načinu korišćenja zemljišta pokazuje da su vrednosti sadržaja organskog ugljenika veće u šumama i poluprirodnim područjima u odnosu na poljoprivredne površine i to za 40,71 % do 30 cm, odnosno za 11,43 % do 100 cm dubine. Proračun gubitka rezerve organskog ugljenika u zemljištu na područjima gde je izvršena prenamena poljoprivrednih površina, šuma i poluprirodnih područja u urbano zemljište, bez kategorije zelena urbana područja, u periodu 1990-2006. godine pokazuje ukupnu vrednosti od 0,92 Mt S, odnosno 1,49 Mt S za dubine do 30 cm, odnosno do 100 cm.<br />Utvrđivanje statističke zavisnosti sadržaja organskog ugljenika u zemljištuod osnovnih klimatskih elemenata temperature i padavina i nadmorske visine pokazuje da postoji srednje jaka do jaka statistička zavisnost u okviru ispitivanja realizovanih do 30 i 100 cm dubine.</p><p>Proračun sadržaja rezerve organskog ugljenika u zemljištu u zavisnosti od morfometrijskih karakteristika reljefa pokazuje da rezerva sadržaja organskog ugljenika u zemljištu raste sa porastom nadmorske visine. Najveće srednje vrednosti sadržaja izmerene su na terenu koji obuhvata planine sa nadmorskim visinama od 1.000-2.000 m i koji obuhvata 11,5 % teritorije Republike Srbije</p> / <p>The aim of this study was to quantify current SOC stocks and present the spatial distribution of organic carbon (SOC) in the soils of Republic of Serbia. The relation of SOC content to soil type, temperature, precipitation, altitude, land use and topography was investigated. Organic carbon stocks were estimated for soil layers 0-30 cm and 0-100 cm based on the results from a database and using soil and land use maps.<br />To establish the relationship between organic carbon content and soil type, a soil map of Serbia was adapted to the WRB classification and divided into 15,437 polygons (map units). The methodology for SOC stocks estimation was based on bulk density, organic carbon content and thickness of the analyzed soil layers. We calculated the values for each reference soil group based on mean values of SOC at 0-30 and 0-100 cm in the main reference groups and their areas. Based on the size of the reference groups, total area of Republic of Serbia, and the SOC values for each reference group, we calculated the total SOC stocks. The obtained values for the soil layers 0-30 cm and 0-100 cm amounted to 0,71 Pg and 1,16 Pg respectively.<br />Using Corine Land Cover (CLC) database for 2006, we defined areas of the major categories of land use. Based on the obtained mean values of organic carbon content at 0-30 and 0-100 cm and the areas indicated by Corine Land Cover categories of land use, we calculated the organic carbon stocks in agricultural land, forest land, semi-natural areas, and artificial areas. The results showed that the organic carbon stocks in the category of agricultural land were 303.22 x 1012 g (Tg) and 600.25 x 1012 g (Tg) at 0-30 cm and 0-100 cm, respectively. In the category of forests and semi-natural areas, the organic carbon stocks were 345.26 x 1012 g (Tg) and 457.55 x 1012 g (Tg) at 0-30 cm and 0-100 cm, respectively. In the category of artificial areas, which mainly included sites within urban green areas and recreational areas, the organic carbon stocks were 19.21 x 1012 g (Tg) and 41.50 x 1012 g (Tg) at 0-30 cm and 0-100 cm, respectively. The map of organic carbon distribution depending on land use method indicated that organic carbon stocks were higher in forests and semi-natural areas than in agricultural land, up to 40.71% and 11.43% at 0-30 cm and 0-100 cm, respectively.<br />SOC loss amount to 0,92 Mt С at 0-30 cm layer and 1,49 Mt С at 0-100 cm layer in the period 1990-2006 as a results of conversion from agricultural land, forestland and semi-natural areas to artificial areas.<br />For soil layers 0-30 and 0-100 cm, a medium to strong statistical relationship between temperature, precipitation and altitude and amount of organic carbon in soil is indicated. The soil organic carbon density was significantly affected by altitude. SOC content increased with increasing altitude.<br />The highest mean values of organic carbon content were found in the mountainous areas within the elevation of 1000-2000 m, which covers 11,5 % of the territory of the Republic of Serbia.</p>

Soils are the largest pool of carbon (C) in terrestrial ecosystems and store 1500 Gt of C in their soil organic matter (SOM). SOM is a dynamic, complex and heterogeneous mixture, which influences soil quality through a wide range of soil properties. Labile SOM comprises a small fraction of total SOM (approximately 5%), but due to its rapid turnover has been suggested to be most vulnerable to loss following soil disturbance. This research was undertaken to examine the consequences of soil disturbance on labile SOM, its availability and protection in soils using the isotopic analysis of soil-respired CO₂ (δ¹³CO₂). A range of soils were incubated in both the short- (minutes) and long-term (months) to assess changes in labile SOM. Shifts in soil-respired δ¹³CO₂ over the course of soil incubations were found to reflect changes in labile substrate utilisation. There was a rapid depletion of δ¹³CO₂ (from a starting range between -22.5 and -23.9‰, to between -25.8 and -27.5‰) immediately after soil sampling. These initial changes in δ¹³CO₂ indicated an increased availability of labile SOM following the disturbance of coring the soil and starting the incubations. Subsequently δ¹³CO₂ reverted back to the initial, relatively enriched starting values, but this took several months and was due to labile SOM pools becoming exhausted. A subsequent study was undertaken to test if soil-respired δ¹³CO₂ values are a direct function of the amount of labile SOM and soil physical conditions. A range of pasture soils were incubated in the short-term (300 minutes), and changes in soil-respired δ¹³CO₂ were measured along with physical and chemical soil properties. Equilibrium soil-respired δ¹³CO₂, observed after the initial rapid depletion and stabilisation, was a function of the amount of labile SOM (measured as hot water extractable C, HWEC), total soil C and soil protection capacity (measured as specific soil surface area, SSA). An independent experimental approach to assess the effect of SSA, where labile SOM was immobilised onto allophane – a clay mineral with large, active surface area – indicated limited availability of labile SOM through more enriched δ¹³CO₂ (in a range between -20.5 and -20.6 ‰) and a significant (up to three times) reduction in HWEC. In the third study, isotopic measurements were coupled with CO₂ evolution rates to directly test whether equilibrium soil-respired δ¹³CO₂ can reflect labile SOM vulnerability to loss. Soils were sampled from an experimental tillage trial with different management treatments (chemical fallow, arable cropping and permanent pasture) with a range of C inputs and soil disturbance regimes. Soils were incubated in the short- (300 minutes) and long-term (600 days) and changes in δ¹³CO₂ and respiration rates measured. Physical and chemical fractionation methods were used to quantify the amount of labile SOM. Pasture soils were characterised by higher labile SOM estimates (HWEC; sand-sized C; labile C respired during long-term incubations) than the other soils. Long-term absence of plant inputs in fallow soils resulted in a significant depletion of labile SOM (close to 50% based on sand-sized C and HWEC estimates) compared with pasture soils. The values of δ¹³CO₂ became more depleted in 13C from fallow to pasture soils (from -26.3 ‰ to -28.1 ‰) and, when standardised (against the isotopic composition of the solid soil material), Δ¹³CO₂ values also showed a decrease from fallow to pasture soils (from -0.3 ‰ to -1.1 ‰). Moreover, these patterns in isotopic measures were in strong agreement with the amount of labile SOM and its availability across the soils, and were best explained by the isotopic values of the labile HWEC fraction. Collectively, these results confirm that labile SOM availability and utilisation change immediately after soil disturbance. Moreover, isotopic analysis of soil-respired CO₂ is a powerful technique, which enables us to probe mechanisms and examine the consequences of soil disturbance on labile SOM by reflecting its availability and the degree of SOM protection.