Activation energy (Ea) of (bio)chemical reactions – the fundamental parameter, defining the reaction rates – has never been critically evaluated and generalized for processes of organic matter transformations in soil. Based on the database of Ea for a broad range of i) oxidative and hydrolytic exoenzyme activities, ii) CO2 production and iii) heat release during soil incubation, as well as iv) thermal decomposition of soil organic matter (SOM), we assessed the Ea for processes of SOM transformation. After a short description of the four approaches to assess Ea of SOM transformation – all based on the Arrhenius equation – we present the Ea of chemical (79 kJ mol-1) and microbial (67 kJ mol-1) mineralization, microbial decomposition (40 kJ mol-1), and exoenzyme-catalyzed depolymerization (33 kJ mol-1) of SOM. The catalyzing effects of exoenzymes reduce the energy barrier of SOM decomposition by more than twice that of its chemical oxidation (from 79 to 33 kJ mol-1). The Ea of exoenzymatic hydrolysis of N-, P-, and S-containing organic compounds is about 9 kJ mol-1 lower (40-fold faster reactions) than that of other (N-, P-, and S-free) organic substances. Under real soil conditions (not in suspension as in enzyme activity analysis), where organic substrates are physically protected and exoenzymes are partly deactivated, microbial mineralization of SOM is 140-fold faster compared to its chemical oxidation. The Ea of microbial mineralization of SOM increases from biochemically labile to stable pools. This is one of the reasons for the decrease in the CO2 efflux from soil during long-term incubations.
Since processes with higher Ea are more sensitive to temperature increase, global warming will stimulate faster decomposition of stable organic compounds and accelerate the C cycle much stronger than the cycling of the nutrients N, P, and S. The consequence will be a shift in the stoichiometric ratios of microbially utilized substrates. Overall, Ea is an easily measurable crucial parameter of (bio)chemical transformations of organic matter in soil, enabling the assessment of process rates and the inherent stability of SOM pools, as well as their responses to global warming.
How to cite: Kuzyakov, Y. and Filimonenko, E.: Activation energy of soil organic matter decomposition, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4580, https://doi.org/10.5194/egusphere-egu25-4580, 2025.
Underlying mechanisms via phosphorus (P) fertilization driving soil organic matter (SOM) formation and stabilization remain largely unclear. In this study, we employed a suite of biomarkers (i.e., free and bound lipids, lignin phenols, PLFAs, neutral and amino sugars), 13C NMR techniques, and soil extracellular enzyme activities to investigate SOM characteristics in response to an 18-year P fertilizer gradient (i.e., 0, 50, 190 kg P ha−1 yr−1, defined as P0, PL, and PH) down to 60 cm depth in Northeast China. Despite limited changes in soil organic C, P fertilization distinctly modified the SOM signatures (e.g., molecular composition, degradation, and source) across soil profile (particularly within 20 cm of topsoil). On average, P additions increased plant-derived free lipids by 10.5–48.6% and microbial-derived free lipids by 39.8–49.0% in this topsoil compared to P0. P enrichment increased cutin compounds by 21.9–44.7% while decreased suberin compounds by 21.3–35.1% as compared to control in the topsoil. PL enhanced lignin phenols by 53.1% relative to P0 in the topsoil due to high plant C input. Compared to control, P fertilization reduced microbial-derived neutral sugars by 20.0–30.6% and the plant-derived neutral sugars by 36.6-37.0% in the topsoil relative to P0. Moreover, bacterial necromass carbon decreased by 10.8–23.8% and fungal necromass carbon by 7.9–27.9% under P fertilization, driven by enhanced microbial residue decomposition via elevated residue-decomposing enzyme activities. Using stoichiometric theory, we estimated that P fertilization reduced microbial carbon use efficiency by 4.3–8.6% and energy use efficiency by 4.7–9.5%. Overall, P fertilization marked by more reduced compounds (e.g., lipids, lignin phenols) and fewer oxidized ones (e.g., microbial necromass, neutral sugars), reduced the nominal oxidation state of C for SOM by 5.6–15.6%, which corresponded to lower microbial energy and carbon use efficiency. These findings suggest that P fertilization alters SOC composition by modulating plant- and microbial- derived C contributions and their turnover. Such findings are critical for advancing our understanding of SOM stabilization and microbial-driven SOC dynamics in P-fertilized agroecosystems.
How to cite: Wang, X. and Du, Z.: Long-term phosphorus fertilization alters soil organic matter molecular composition via lowers microbial carbon and energy use efficiency in a temperate cropland , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9603, https://doi.org/10.5194/egusphere-egu25-9603, 2025.
Climate change, marked by rising atmospheric CO₂ levels and temperature, can strongly influence soil processes such as nutrient cycling and microbial dynamics. Metals can negatively impact soil functionality, and modify microbial community composition and activity, introducing additional complexity to nutrient cycling under shifting environmental conditions. In addition, metals can disrupt plant growth and nutrient uptake, affect root development and activity, and trigger stress responses, ultimately compromising plant productivity. On the other hand, elevated CO₂ and temperature stimulate plant primary productivity, increasing carbon inputs to the soil through root exudates, litter, and rhizodeposition. Climate-altered root activities influence soil microbial processes, which are critical in regulating nutrient dynamics. While the responses of microbial communities and nutrient cycling processes to climate change are often scenario-dependent, the interplay between soil metal backgrounds and climate drivers remains underexplored.
This study investigates the susceptibility of agricultural soils with varying natural metal levels to climate change, focusing on nutrient cycling processes in both bulk and rhizosphere compartments. By exploring how metal backgrounds influence nutrient availability and transformations, this work aims to shed light on the resilience and vulnerability of these soils under changing environmental conditions. A greenhouse pot study was set up with the plant Arabidopsis halleri, using three agricultural soils with natural contents of cadmium (Cd): low-Cd (0.2 ppm), mid-Cd (1 ppm), and high-Cd (14 ppm). Soils and plants were exposed to today’s and future climatic conditions (according to IPCC SSP3-7: +3.5 ºC and +400 ppmv CO2 predicted to 2100 vs. preindustrial times). Soil microbial processes were analyzed by combining stable isotope analysis for tracking N transformations and carbon use efficiency (CUE) with qPCR N functional genes, potential hydrolytic enzyme activities (C, N, P), and the nutrients pools (C, N, P) assessment by colorimetric methods.
Future climatic conditions enhanced plant growth and triggered changes in soil processes in the rhizosphere with minimal fluctuations in bulk soil responses. Under future climatic conditions, rhizosphere nutrient cycling was accelerated by higher organic matter decomposition (boosted enzyme activities and ammonification) at low-Cd soil. The future climate also impacted the rhizosphere response in the mid-Cd soil by reducing CUE and shifting N transformation processes such as nitrate production and consumption rates, ammonification, and denitrification, highlighting higher microbial N demand and stress. High-Cd soils, however, showed resilience to climate change, but this stability was primarily due to the overriding effects of metal toxicity, which impaired microbial responses. Here we demonstrate that the rhizosphere exhibited higher susceptibility to future climatic conditions compared to bulk soil, which can be related to enhanced plant growth demanding more nutrients. Our findings suggest that soil metal contents modulate the resilience and adaptability of soils to climate drivers, with distinct outcomes for nutrient cycling and microbial functionality.
How to cite: Vergara Cid, C., Hamm, J., Sánchez, N., Kümmel, S., Knöller, K., Jurburg, S., Blagodatskaya, E., and Muehe, E. M.: How varying natural metal concentrations shape climate change impacts on nutrient cycling in bulk and rhizosphere agricultural soils, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9327, https://doi.org/10.5194/egusphere-egu25-9327, 2025.
In recent decades, large areas of temperate grasslands in arid regions worldwide have been increasingly encroached upon by shrubs. This encroachment has intensified the competition for resources, particularly nitrogen (N), a critical element for plant growth, between the newly established shrubs and the surrounding grasses in temperate grasslands. Despite this, it remains unclear whether shrubs and grasses adopt distinct strategies for N acquisition and how these strategies may contribute to competition between them. Additionally, the role of soil microbes in regulating the N competition between shrubs and grasses also remains unclear. To address these gaps, we conducted an in situ 15N labeling experiment in a shrub-encroached temperate grassland with significant slope variations of North China. The study aimed to investigate the competition for N acquisition among shrubs, grasses, and soil microbes. The results revealed that both shrubs and grasses preferred to absorb NO3- across soil depths. However, in the subsoil (10–30 cm) at the upper slope, shrubs displayed significantly higher total N uptake compared to grasses. The ratio of N uptake by shrubs to grasses (RS/G) for different N forms was consistently higher in the subsoil, and that for total N uptake of subsoil was only greater at both upper and lower slopes. Moreover, the RS/G in the subsoil or overall soil depth was markedly higher at the upper than lower slope.
The competition for N between shrubs and grasses also regulated by soil microbes, with higher 15N recovery in soil microbes (RM) than plants (RS or RG). The ratio of N uptake by grasses to soil microbes (RG/M) was higher in the topsoil, and varied across N forms and slope locations. Structural equation model (SEM) reveals that location changes strongly affect plant-soil interactions, influencing the RS/G. Increased soil depth lowered soil organic matter (SOM), soil microbial biomass N (MBN), and soil water content (SWC), but increased shrub root biomass (SRB). Lower slopes have associated higher MBN and SWC, but less SRB. SWC enhanced MBN, which reduced SRB. SOM lowered RS/G, whereas SRB increased it. The competition for nitrogen (N) between shrubs and grasses was more intense in the subsoil and particularly pronounced at the upper slope. These findings provided valuable insights into the competitions between shrubs and grasses for N, as well as the role of soil microbial regulation in temperate grasslands of North China undergoing shrub encroachment, highlighting the influence of soil depths and slope locations.
How to cite: Tian, Y. and Li, Z.: Competition between shrubs and grasses in a shrub-encroached temperate grassland of North China: implications from the nitrogen acquisition, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5347, https://doi.org/10.5194/egusphere-egu25-5347, 2025.
Despite advancements in fertilizer management practices, such as applying crop-specific doses, splitting fertilizer applications throughout the growing season, and selecting appropriate types of fertilizers, global estimates suggest that agroecosystems lose approximately half of the applied nitrogen fertilizer. This inefficiency arises partly because the potential for spatial precision application is not fully utilized. Additionally, research on further strategies to improve nitrogen use efficiency remains limited. The environmental consequences of these nitrogen losses, including gaseous emissions and leaching, are a significant concern, contributing to ecosystem degradation and climate change. Soil nitrogen losses can be mitigated through practices that increase organic carbon inputs, enhance native soil organic carbon, and, most importantly, boost soil microbial biomass levels. However, there is a limited understanding of how soil-plant interactions influence nitrogen immobilization and plant uptake across gradients of organic carbon inputs, native soil organic carbon levels, and microbial biomass. To address this knowledge gap, our study aims to determine the fate of fertilizer nitrogen within a plant-soil system under varying organic matter quantity and quality. To this end, we conducted a field experiment within a long-term organic amendment trial spanning over 45 years. This trial is characterized by a gradient in soil organic carbon and microbial biomass, induced by differing rates of repeated manure amendments. To introduce short-term organic carbon input variability, we further established a gradient in fresh organic carbon using harvest residues. Microplots were installed along these gradients and fertilized with 140 kg N/ha of nitrogen-15-enriched ammonium nitrate, applied in three split doses, to trace the fate of fertilizer-derived nitrogen. We are assessing its incorporation into wheat grain, straw, root biomass, and soil pools, including the microbial and organic nitrogen pools. Preliminary data indicate that neither microbial biomass nor soil organic carbon directly affected the uptake of fertilizer nitrogen into the aboveground plant biomass (grain and straw). However, we hypothesize that, at the plant-soil level, fertilizer recovery and, therefore, nitrogen use efficiency will improve with higher organic carbon inputs, greater native soil organic carbon, and more abundant microbial biomass. This improvement primarily being driven by enhanced nitrogen immobilization within the soil. Through this research, we aim to elucidate the connections between carbon and nitrogen cycling, with a particular focus on the role of soil carbon-to-nitrogen stoichiometry in determining the fate of fertilized nitrogen in agricultural systems. Ultimately, our findings will contribute to the development of optimized residue management strategies to increase nitrogen use efficiency at the agroecosystem level without compromising yields and food security.
How to cite: Steiner, S., Keiluweit, M., Oberson, A., Rathnayake, D., and Guillaume, T.: Nitrogen use efficiency of agroecosystems along a gradient of organic matter quality and quantity using stable nitrogen isotope tracing, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20062, https://doi.org/10.5194/egusphere-egu25-20062, 2025.
Improving soil organic carbon (SOC) and total nitrogen (TN) stocks in croplands is crucial to mitigate climate change and ensuring food security. Soil microbes are important engines driving terrestrial biogeochemical cycles. Their C use efficiency (CUE) and N use efficiency (NUE), defined as the proportion of metabolized organic C and N allocated to microbial biomass, is a key regulator controlling the fate of soil C and N. It is assumed that microbial CUE and NUE will increase with higher organic fertilizers application rates, however, any empirical evidence is scare. Microbial necromass is a large and persistent component of SOC and TN especially under croplands. It is still unclear how the simultaneous cycling of C and N in soils would be affected under longer-term organic fertilizer addition.
Here, we studied soil microbial CUE and NUE simultaneously using 18O-H2O tracer approach in a 13-year winter wheat-summer maize cropping rotation field trial in the North China Plain.Here organic fertilizers (i.e. straw, manure, compost, biogas residue and biochar) are annually applied with (optimal N input, Nopt) or without N (zero N input, N0) addition. We found straw, manure, compost, and biogas residue additions increased microbial CUE by 42-80% in N0 and 40-77% in Nopt, and NUE by 25-65% and 33-127% in both N0 and Nopt, respectively. Organic matter addition increased the SOC by 36-150% and 31-137% in both N0 and Nopt, while the TN increased by 21-55% and 21-70% in both N0 and Nopt, respectively. Additionally, organic material additions increased the total microbial necromass C and N by 50-83%, 60-97% and 38-80%, 52-93% under N0 and Nopt, which contributed 14-43% and 33-58% to the SOC and TN, respectively. We concluded that these C-induced enhancements in microbial growth and CUE or NUE and necromass accumulation were mainly owing to an increased C availability (Easily oxidizable organic C, EOC), and fungal fast-growth strategists. Composting most effectively facilitated microbial C and N cycling, promoting SOC and TN accumulation in cropland.
How to cite: Wang, C., Kuzyakov, Y., Bol, R., Chen, H., and Fan, M.: Thirteen years of applying maize-derived organic materials and N fertilizers in North China Plain increased microbial CUE and NUE while increasing SOC and TN through necromass inputs., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5128, https://doi.org/10.5194/egusphere-egu25-5128, 2025.
Rice paddy has been regarded as a unique ecosystem compared to other crops as rice is cultivated under highly saturated conditions for most growth stages. Its unique ecosystem selects for distinct microbial composition and abundance in response to the oxic-anoxic interface. Rice paddy is also known to be a significant source for greenhouse gas emissions (GHG) including CO2, CH4, and N2O, the deleterious gases causing global warming. This study investigated the effects of N fertilization on the changes of soil microbial biomass and the changes of GHG in organic rice ecosystem. Soil microbial biomass C and N were significantly affected by N application rates of organic soil amendments at heading stage and before harvest. The use of soil amendment at 150 kg N ha-1was observed to promote higher total microbial biomass C and N than any other treatments. CO2, CH4, and N2O weekly fluxes were significantly influenced by different N rates of organic soil amendments at 44, 54, and 70 days after planting. Higher global warming potential was stimulated by highest N fertilization (150 kg N ha-1). The smallest GHG index was estimated in rice paddy receiving soil amendment at 150 kg N ha-1.
How to cite: Dou, F., Lasar, H., and Gentry, T.: Soil microbial biomass and greenhouse gas emission dynamics response to nitrogen rates under organically amended paddy soil, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2891, https://doi.org/10.5194/egusphere-egu25-2891, 2025.
The unique geological structure combined with human activities cause serious rocky desertification in fragile karst regions, which restricts regional social and economic developments. Vegetation restoration is the key practice of comprehensive administration of rocky desertification, but this process is extremely slow, especially in some special karst geomorphic units. Nitrogen (N) element has been suggested to be a critical limiting factor for vegetation growth, but the characteristics of soil N supply and plant N acquisition remain largely unknown in karst regions. This hinders our better understanding of vegetation restoration of karst rocky desertification as well as its restoration effects. We chose natural succession sequences with different vegetation restoration stages in karst peak-cluster depression and faulted basin regions. Vegetation survey and data collection were conducted, and the N/phosphorus (P) ratio, N content and δ15N values of plant leaf were used to reflect the degree of plant N limitation. In addition, 15N labeling techniques were employed to investigate soil gross N transformation rates, available N supply capacity and N acquisition characteristics of the dominate plant species during vegetation succession. We found that plants were severely limited by N in the early stages of vegetation restoration, which was more seriously in the karst fault basin. As vegetation recovered, plants were no longer limited by N but by P. This difference was mainly attributed to the changes in soil N supply capacity and plant N utilization strategies. In the early stages of vegetation restoration, the rates of soil N supply processes including mineralization and nitrification was weak and inorganic N was mainly ammonium. In the later stages, soil inorganic N supply capacity increased significantly, resulting in higher inorganic N content dominated by nitrate. In such N condition, plants can adjust their own root functional traits to develop different N utilization strategies. Plants develop larger specific root length and specific surface area in the early stages to increase ammonium utilization, but plants improve nitrate utilization in the later stages. Overall, our results unraveled the mechanism underlying reduced plant N limitation following vegetation restoration through increasing soil inorganic N supply and adjusting plant N utilization strategy. The present study provided a scientific basis for ecological restoration and reconstruction of karst rocky desertification.
Keywords: Rocky desertification; Nitrogen availability; Plant N limitation; Plant N utilization strategy; Gross N transformation rates
How to cite: Wen, D. and Zhu, T.: The mechanism underlying plant nitrogen limitation following vegetation restoration in karst regions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4930, https://doi.org/10.5194/egusphere-egu25-4930, 2025.
Phosphorus is one of the main plant nutrient and plants can obtain this nutrient only from soil. The total P content in soil ranges from 1.5 to more than 9000 mg kg⁻¹, with the global average being approximately 550–600 mg kg⁻¹. Phosphorus exists in soil in many different forms. Most phosphorus compounds in soil are insoluble in water. Plants can uptake only the soluble form of phosphorus, which constitutes approximately 0.5% of the total phosphorus in the soil.
To determine the plant-available or so-called soluble P, numerous extraction methods have been developed over more than a century. In Europe alone, more than ten different methods are used for determining plant-available P content. Typically, these are simple extraction methods using low-concentration salts, mineral acids, water solutions, or their mixtures. Depending on the solution composition, the amount of extractable P may vary significantly. Not only does the solution composition influence the amount of P extracted from soil, but the soil's chemical and physical properties also play a significant role.
Many studies have explored the relationship between different methods and the impact of soil chemical properties (such as pH and organic matter) and physical properties (like clay content) on soil P analysis results. All these methods are extraction methods, and the extracted P represents only part of the soluble P fraction in soil.
The amount of P in soil extract is in equilibrium with P in solid form. This equilibrium is determined by both the properties of the solution and the properties of the solid phase (soil). The aim of our work was to investigate how the amount of extracted P changes over three consecutive extractions and what soil chemical and physical properties affect this process. For the extraction, the Mehlich 3 method was used. Our results indicate the influence of soil carbon, calcium, magnesium, and clay content on the relative quantities of sequentially extracted P using the Mehlich 3 method.
How to cite: Tõnutare, T., Tõnutare, T., Krebstein, K., Kõlli, R., and Hindreko, H.: The Impact of Soil Chemical and Physical Properties on the Amount of Sequentially Extracted P by the Mehlich 3 Method, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13531, https://doi.org/10.5194/egusphere-egu25-13531, 2025.
Nitrogen (N) uptake by plant roots from soil is the largest flux within the terrestrial N cycle. Despite its significance, a comprehensive analysis of plant uptake for inorganic and organic N forms across grasslands is lacking. Here we measured in-situ plant uptake of 13 inorganic and organic N forms by dominant species along a 3,000 km transect spanning temperate and alpine grasslands. To generalize our experimental findings, we synthesized data on N uptake from 60 studies encompassing 148 plant species worldwide. Our analysis revealed that alpine grasslands had faster NH4+ uptake than temperate grasslands. Most plants preferred NO3– (65%) over NH4+ (24%), and then over amino acids (11%). The uptake preferences and uptake rates were modulated by soil N availability that was defined by climate, soil properties, and intrinsic characteristics of the N form. These findings pave the way towards more fully understanding of N cycling in terrestrial ecosystems, provide novel insights into the N form-specific mechanisms of plant N uptake, and highlight ecological consequences of chemical niche differentiation to reduce competition in co-existing plant species.
How to cite: Liu, M. and Xu, X.: Nitrogen availability in soil controls uptake of different nitrogen forms by plants, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2247, https://doi.org/10.5194/egusphere-egu25-2247, 2025.
Rice root aerenchyma (RA) and irrigation practices play critical roles in key physiological processes in rice paddies, influencing both grain yield and methane (CH₄) emissions. However, the interaction between RA and irrigation practices, as well as its implications for CH₄ mitigation, remains poorly understood, complicating efforts to identify rice cultivars suited for reducing CH₄ emissions. To address this, we conducted field and pot experiments to investigate how RA impacts rice yield and CH₄ emissions under two common irrigation methods: continuous flooding (CF) and alternate wetting and drying (AWD). Our findings reveal that the interaction between RA and irrigation regime significantly affects both yield and CH₄ emissions. Under CF, cultivars with enhanced RA formation exhibited higher yields and lower CH₄ emissions, likely due to increased root oxygen loss, which promotes CH₄ oxidation and enhances nitrogen availability for plant growth. In contrast, under AWD, no significant differences in yield, methanogenesis, or methanotrophy were observed among cultivars with varying RA development. However, cultivars with well-developed RA increased CH₄ emissions by 28%–32% compared to those with less-developed RA, likely due to enhanced CH₄ transport from anaerobic soil layers to the atmosphere. Consistent with these observations, inhibiting RA development through root irrigation with brassinosteroids reduced CH₄ emissions under AWD conditions. In summary, our study demonstrates that AWD can reverse the effects of RA on CH₄ emissions, emphasizing the importance of integrating irrigation practices into CH₄ mitigation strategies and accounting for cultivar-specific variations.
How to cite: van Groenigen, K. J., Li, S., Chen, Y., and Liu, L.: Aerenchyma Development and Irrigation Practices Shape Methane Emissions and Yield in Rice Paddies, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10912, https://doi.org/10.5194/egusphere-egu25-10912, 2025.
The soil CO2 efflux is the largest terrestrial source of CO2 to the atmosphere, primarily driven by the metabolic activity of soil organisms. Consequently, it has often been considered low to negligible in desert soils. However, the contribution of abiotic factors to the soil CO2 flux could be significant in desert soil, particularly during dry periods when observed diel patterns of CO2 exchange appear to contradict conventional expectations. I will show evidence that atmospheric water vapor, adsorbed to soil particles at night, supplies the water to dissolve gaseous CO2. This process reduces CO2 concentrations in the soil pore space and can explain the diel pattern of CO2 exchange reported in dry periods. To show this, I used various field and laboratory methods during two field experiments in the Sahara Desert, Morocco, and the Negev Desert, Israel. Finally, I will discuss the relative contribution of dry and wet periods to the total yearly carbon balance and show how summer heat waves, which increase the daily minimum air temperature, may intensify carbon losses from the soil.
How to cite: Bekin, N. and Agam, N.: An inter-seasonal analysis of abiotic factors involved in the surface and subsurface fluxes of CO2 in desert soils, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15343, https://doi.org/10.5194/egusphere-egu25-15343, 2025.
Soil is a significant part of the global terrestrial carbon and nitrogen biogeochemical cycles. Recently those cycles have been intensively altered by anthropogenic activities. That leads to a massive imbalance that enriches the atmosphere with additional Greenhouse gases (GHG). Organic farming practices are considered a form of sustainability that can enhance soil quality and reduce GHG emissions. Little research has focused on the impact of crop rotation and compost addition in the enhancement of organic carbon soil (SOC) and reducing GHG emissions from the soil on arid lands. Thus, this research aimed to investigate the impact of annual crop rotation (Sweet corn, Sunflower, and Eggplant) and unique alkaline compost addition on improving (SOC) stock and reducing GHG emissions in arid soils. This research was conducted on a field scale for two years. Unique alkaline compost was used as a treatment with two different application doses (dose1 and dose2) based on soil exchangeable primary macronutrient calculation with an equivalent dose of NPK for both application doses. The closed static chamber method was used to measure the CO2, CH4, and N2O efflux from the plots. Randomized complete block design (RCBD) experimental design was followed. Soil samples were collected at the beginning and the end of each growing season from each plot to measure the change in soil organic matter and SOC. The primary results of this study showed there was a significant increase of SOC from sweetcorn to eggplant season in both compost application doses. SOC stock in the second application dose at eggplant season was the highest among all the other treatments in all growing seasons. Similarly, organic matter (O.M) content increased steadily from sweetcorn to eggplant seasons. Regarding the GHG effluxes, dose1 of the compost contributes to lower N2O and CH4 efflux compared to dose2 in all the growing seasons. Dose 2 of the compost in sweet corn season contributed to the highest CH4 and N2O effluxes. The primary results from this research confirmed that utilizing organic farming practices can enhance the organic carbon stock in arid land and lower GHG emissions from the soil.
How to cite: Al-Majrafi, A., Al Wardy, M., Blackburn, D., Janke, R., Al-Hadhrami, A., Al Sabahi, J., and Al Shukaili, M.: Assessing the Impact of Organic Farming Practices on the Soil Organic Carbon Stock and the Efflux of Greenhouse Gases of Calcareous Arid Soils , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14205, https://doi.org/10.5194/egusphere-egu25-14205, 2025.
The long-term stability of biochar is valuable for carbon sequestration in soil. Biochar’s aromatic structure inhibits microbial decomposition and prolongs the mean residence time of this organic soil amendment. During residence in soil, biochar particles do not remain rigidly in place but experience several dissipation processes, including vertical and lateral transport. However, the quantitative dissipation of biochar under field conditions remains unclear due to lacking long-term field observations.
Uncertainties concerning decreasing topsoil biochar stocks were inspected in a long-term field experiment located on a loamy soil and under humid temperate conditions in Bayreuth, Southern Germany. Industrially produced biochar was applied 14 years ago. Four differing amendments were arranged in a Latin rectangle experimental design: unamended control, pristine biochar (31.5 Mg ha⁻¹), biochar mixed with compost (31.5 Mg ha⁻¹ and 70.0 Mg ha⁻¹, respectively), and co-composted biochar with addition before composting (31.5 Mg ha⁻¹ and 70.0 Mg ha⁻¹, respectively). Soil samples were retrieved in 30 cm intervals to a depth of 90 cm. Benzene polycarboxylic acids (BPCA) were analyzed as a molecular marker for biochar. Our results indicate vertical biochar transport exceeding mechanical influence by agricultural practices. While treatments differed, all amendments containing biochar showed a trend of particle transport. The highest amounts were found in soil treated with pristine biochar, while the difference between treatments decreased with increasing soil depth. Furthermore, the contribution of individual BPCAs differed between depths. Relatively, higher condensed BPCA tended to decrease vertically. This indicates a preferential vertical transport of less condensed BPCA.
This study proves vertical particle transport of biochar in soil. This valuable insight partially explains decreasing biochar stocks near the surface with increasing time. Downward movement can be beneficial for carbon sequestration in soil due to generally reduced microbial activity at lower depths. However, hereby provided and associated organic matter may alter microbial abundance and must be studied further, as must the apparent effect of different amendments and selective transport of different BPCA. This future research bears implications on biochar’s mechanisms as a carbon sequestration technology in mitigating climate change.
Keywords: Biochar aging, biochar transport, carbon sequestration, climate change mitigation, molecular marker, organic soil amendment, pyrogenic carbon, soil organic carbon
Funding information: EU grant no. 101059546-TwinSubDyn
How to cite: Pearson, R., Gross, A., Bromm, T., and Glaser, B.: Vertical biochar transport in soil in a long-term field experiment in Germany, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18297, https://doi.org/10.5194/egusphere-egu25-18297, 2025.
Biochar undergoes significant transformations in soil as a result of chemical, physical, and biological processes. These alterations can impact its initial properties, influencing both its agronomic effectiveness and its capacity for carbon sequestration. Long-term observations of biochar aging effects in soil are limited but highly relevant, as they provide a more realistic picture of the agronomic and societal benefits of biochar than short-term studies with relatively “fresh” biochar. This study aimed to describe the aging effects of biochar and their impact on a range of soil properties at a long-term biochar experiment in Bayreuth, Germany. For this purpose, soil and biochar samples were taken 13 years after application (two variants: 1. co-composted and 2. pristine biochar) and compared with a fresh variant in which the same unaged biochar was freshly mixed with the control soil.
The soil quality parameters, pH and electrical conductivity, decreased significantly (p < 0.05) during biochar aging. Specifically, the pH dropped from 7.4 in freshly biochar-amended soil to 6.8 in the pristine aged biochar variant and 6.9 in the co-composted aged biochar variant. Electrical conductivity decreased from 217.0 µS cm⁻¹ in the freshly amended soil to 81.1 µS cm⁻¹ in the pristine aged variant and 87.6 µS cm⁻¹ in the co-composted aged variant. Nitrogen retention was enhanced in the soil amended with co-composted aged biochar compared to the pristine aged biochar soil. Total nitrogen (TN) was higher at 1.94 g kg⁻¹ versus 1.57 g kg⁻¹ (p < 0.05), and ammonium-N (NH₄⁺-N) was slightly elevated at 35.7 mg kg⁻¹ versus 33.0 mg kg⁻¹, although the difference was not statistically significant. The nitrate-N (NO₃⁻-N) content was significantly lower in all biochar-amended soil variants compared to the control soil. Total carbon (TC) levels decreased during biochar aging in all soil variants. However, the reduction was significantly lower in the co-composted aged biochar soil (25.0 g kg⁻¹) compared to the pristine aged biochar soil 20.5 g kg⁻¹, p < 0.05).
This study identified multiple aging effects on biochar following 13 years of exposure in loamy soil. Importantly, the results showed that compared to the amendment of pristine biochar, co-composting did not diminish TC of the treated soil, and more N could be retained, 13 years after amendment. In fact, co-composting prior to soil application is recommended to fully realize the potential agronomic benefits.
How to cite: Gross, A., Apostolovic, T., García Rodríguez, Á. F., de la Rosa, J. M., Glaser, B., Knicker, H., and Maletic, S.: Impact of Biochar Aging on Soil Physicochemical Properties, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10162, https://doi.org/10.5194/egusphere-egu25-10162, 2025.
Hydrochar (HC), as an organic soil amendment, has the potential to improve soil fertility and crop yield. However, only recent studies have focused on its impact on soil microorganisms. At present, the effects of HC application on the abundance, activity, and taxonomic composition of distinct bacterial and fungal communities are still not fully understood. Therefore, we conducted a greenhouse pot experiment with five treatments under two different irrigation conditions (well-irrigated and water-deficit). We investigated the responses of sunflower (Helianthus annuus L.) yield, as well as soil chemical and biological properties, to two application rates of HC (3.25 and 6.5 t ha⁻¹) prepared from chicken manure. Mineral fertilizer treatments with equivalent total nitrogen contributions to those of the HC treatments were included for comparison. After 77 days of cultivation, the plants were harvested, and soil samples were collected from the topsoil (0-15 cm) for metagenomic analysis and to assess the abundance and activity of microorganisms.
At the onset of the experiment, HC application did not cause a significant change in the composition of most soil nutrients. However, in comparison to non-amended soils, HC application, particularly at elevated doses, improved plant productivity and induced changes of the soil nutrient concentrations under both irrigation conditions at the end of the experiment. Our primary hypothesis to explain our observation posits that the presence of HC in soils, can play a significant role in the development and activity of their microbial communities, which may indirectly enhance nutrient availability and affect other soil biogeochemical processes. Through microbial abundance analyses, including Colony Forming Unit (CFU) counts and qPCR (16S rRNA and ITS), soils treated with 6.5 t ha⁻¹ HC exhibited higher bacterial and fungal populations compared to untreated soils. Likewise, results from basal and substrate-induced (glucose, alpha-ketoglutarate, N-acetylglucosamine, and L-cysteine) micro-respiration (MicroResp) indicated greater microbial CO₂ production in HC-amended soils. Furthermore, soils treated with HC under well-irrigated conditions displayed a distinct microbial community-level physiological profile from that of untreated soils. These differences in microbial functional diversity suggest changes in the relative abundance of soil microbial communities in HC-treated soils, as it was confirmed by metagenomic analysis.
Our results underscore that the effects of HC amendments on soil systems should not be regarded as a straightforward linear process. Rather, it requires evaluation within the framework of the complex interplay of climatic conditions, application rate, plant physiology, and microbial composition and activity.
Acknowledgements: This work was supported by a PhD scholarship (PREDOC_00339) granted by the Junta de Andalucía, as well as by the “SequestCarb” project (PY20_01065, funded by the Junta de Andalucía) and the MarshSOIL project (PID2020-119220GB-I00, funded by the Agencia Estatal de Investigación).
How to cite: Moreno Racero, F. J., Velasco-Molina, M., López-Núñez, R., Martínez-Force, E., Rosales, M. Á., and Knicker, H.: Hydrochar as a Modulator of Soil Microbial Communities: Abundance, Activity, and Shifts in Bacterial and Fungal Composition, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-202, https://doi.org/10.5194/egusphere-egu25-202, 2025.
Research into methods for carbon dioxide removing (CDR) is experiencing strong growth worldwide. To protect the climate, not only greenhouse gas emissions need to be reduced, but in addition, carbon sinks have to be created. At the same time, we need measures to adapt to climate change, especially in agriculture. The PyMiCCS project (Pyrolysis and Mineral Weathering for Carbon Capture and Storage) consortium under the umbrella of the CDRterra research line investigate the CDR potential and synergies of a combination of the CDR methods “biochar” and “enhanced weathering” (EW) as soil amendments. Biochar is the solid product of biomass pyrolysis and contains persistent carbonaceous compounds whereas the weathering of rock powder in agricultural soil results in the transfer of atmospheric CO2 into dissolved bicarbonate. It is known that biochar has the potential to positively influence agronomically relevant parameters and to reduce soil-borne nitrous oxide (N2O) emissions, while rock powder shows neutral to positive agronomical effects.
To identify synergistic effects of biochar and EW, cabbage turnip (Brassica oleracea L.) was grown in sandy soil in pseudo-lysimeters enriched with four different amendments in two application rates and compared with an untreated control variant: 1) application of wood biochar or 2) rock powder, 3) co-application of both and 4) rock-enriched biochar, produced by co-pyrolysis of wood and rock powder. Nitrate leaching and greenhouse gas emissions were measured over the cultivation period. At harvest, the yield was determined and soil samples were analyzed for enzyme kinetics from project partners.
Depending on the application rate, either no significant effects on yield were found or a significant yield increase was observed in all variants involving wood biochar, with no difference between the sole application of biochar, its co-application with rock powder, and the rock-enriched co-pyrolysis variant. Likewise, no significant differences were observed between these variants in the amount of nitrate leached, whereas the difference to the control was always clear: the biochar variants significantly reduced nitrate leaching. A similar pattern was also observed for N2O. Our results indicate that biochar and EW can be combined without adverse interactions on the parameters studied and that rock enhancement did not negate biochar’s positive environmental effects, but synergistic effects have not yet been demonstrated.
How to cite: Hamburger, S. E., Seedtke, M., Becker, J. N., Eschenbach, A., Hagemann, N., Meyer zu Drewer, J., Görres, C.-M., and Kammann, C.: Impact of combined application of biochar and basanite powder on soil-borne greenhouse gas emissions and nitrate leaching, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14808, https://doi.org/10.5194/egusphere-egu25-14808, 2025.
Soil microbes are major regulators of soil ecosystem services and play a crucial role for carbon and nutrient cycling. Soil microbial activity can be altered by the application of biochar and of rock powder for enhanced weathering – two promising carbon dioxide removal (CDR) techniques. While most recent research considered both CDR methods separately, their co-application could offer additional benefits for CDR, soil health, and crop yield. Here, we compare the influence of pure wood biochar and pure basanite powder with the product of pre-pyrolytic combination of woody biomass and basanite powder (referred to as PyMiCCS). To determine the influence of joint pyrolysis, we also include a post-pyrolysis-combination (PPC) equivalent to PyMiCCS. The aim of this study was to determine the influence of co-applied biochar and basanite powder on enzyme kinetics. Therefore, we grew cabbage turnip (Brassica oleracea) in lysimeters filled with a sandy agricultural topsoil (control) and an amendment (biochar, basanite powder, PyMiCCS, PPC) over a period of nine weeks. Afterwards, the soil samples were analyzed for enzyme kinetics of ß-glucosidase, chitinase, leucine-aminopeptidase, and acid phosphatase.
Preliminary results show significantly enhanced Vmax (maximum rate of soil enzyme activity) of acid phosphatase in all treatments compared to the other studied enzymes, implying a relatively high demand for P. Furthermore, we found that treatments containing biochar, PyMiCCS, and PCC had up to 50% lower Vmax values for ß-glucosidase, chitinase, and acid phosphatase relative to control and basanite treatments. In contrast to this, leucine-aminopeptidase showed an increase in Vmax of up to 40% in biochar, PyMiCCS, and PCC treatments compared to control and basanite treatments. This could be interpreted as a shift of nutrient demand towards N due to the addition of biochar, PyMiCCS, and PCC, resulting in an increased production of the N-cycle-related leucine-aminopeptidase. This increased N demand could be caused by the fixation of N-rich molecules by the amendments, or by the release of other nutrients, such as P or C. Consistently with the latter, we observed a significant increase in C content of up to 50% following the application of biochar, PyMiCCS, and PPC, whereas the N content showed little to no increase. Our results so far indicate that the co-application of biochar and basanite powder affects soil microbial activity by shifting nutrient availability. However, the interactive effect of the co-applied amendments on mineral N and microbial biomass is still subject to further analyses.
How to cite: Seedtke, M., Stock, S. C., Dippold, M., Hamburger, S. E., Kammann, C., Hagemann, N., Eschenbach, A., and Becker, J. N.: Influence of co-applied biochar and enhanced basanite weathering on soil enzyme kinetics in an agricultural soil, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18855, https://doi.org/10.5194/egusphere-egu25-18855, 2025.
Posters on site: Tue, 29 Apr, 10:45–12:30 | Hall X4
The intensifying wildfire regimes under climate change, as expressed, for example, in the recent fire seasons in the boreal zones, call for an improved understanding of the impacts of forest fires on air, water and soil quality. One group of compounds released during wildfires are the polycyclic aromatic hydrocarbons (PAHs), of which many are considered toxic for organisms, including human health.
This study investigated 13 sites along a transect across five boreal forest and tundra biomes for the abundance and composition of 16 USEPA listed PAHs in soil organic and mineral horizons. Accelerated solvent extraction in a combination with organic solvents (MeOH:DCM and n-hexane:DCM) was used for PAHs extraction and subsequently analyzing them using an Agilent 7890A gas chromatograph coupled to an Agilent 5975C mass spectrometer. We tested how far distance to the nearest fire event (<1 km up to 73 km), years since the fire event (1989 to a recent burn that extinguished few weeks before sampling in August 2022) and fire intensities calculated using MODIS Thermal Anomalies/Fire Location Collection 6.1 (MCD14DL) and LANDSAT based dNBR indices affected PAHs concentrations and composition across sites and in organic and mineral horizons, respectively.
Our results revealed significantly higher PAHs concentrations in freshly burnt sites, with litter samples showing values up to 17181 ng/g, surpassing the strict regulatory thresholds set by Canadian government. Phenanthrene was the only PAH significantly more abundant in organic compared to mineral horizons. At older fire sites (>15 years), total PAH concentrations declined significantly (range: 0.7 to 1806.7 ng/g) in comparison to recent fire sites, likely due to degradation and wash-out processes. Litter horizons generally exhibited higher PAH levels than organic and mineral horizons, with high molecular weight (HMW) PAHs dominating (~30% LMW vs. ~70% high molecular weight). Apparently, the distance to the fire source had no significant effect on PAHs abundance. However, fire intensity, as indicated by fire radiative power (FRP) and dNBR, correlated with PAHs levels in the litter horizon, suggesting that temperature and combustion conditions are critical determinants of PAHs formation and persistence. Diagnostic PAHs ratios also confirmed the predominance of pyrogenic sources. These initial findings highlight the post-fire loss of PAHs via degradation and wash-out, reducing soil toxicity over time. More research might focus on a high-resolution soil and water monitoring shortly after wildfires to better understand how far degradation and wash-out dominates PAHs loss that could shift burning residues from soil to water biomes.
How to cite: Voitz, P., Kruse, S., Yadav, A., and Dietze, E.: The impact of wildfires on the abundance of polycyclic aromatic hydrocarbons (PAH) in soils of Northwestern Canada, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5622, https://doi.org/10.5194/egusphere-egu25-5622, 2025.
Assessment of soil response to climate-smart agriculture practices may assist in better management decisions in sensitive ecosystems. Despite the approved role of sole biochar or microalgae application in yield stability and climate resilience, their synergistic effects have not been well discovered, especially in fragile saline-alkali land. Here, in a three-year agricultural field by three doses of microalgae application (0, 30, 60 L ha-1) combined with two biochar application rates (0, 30 t ha-1), we explored the individual and combined effects on sunflower yield, soil carbon (C), greenhouse gas (GHG) emissions, and carbon footprint (CF). As expected, solely microalgae fertilizer application caused minimal changes in SOC storage, while biochar application had a more predominant effect on SOC storage, indicating that biochar was a key contributor to SOC storage. Notably, the synergistic effects of biochar and microalgae on yield enhancement, SOC storage, and emission reduction were stronger than each factor separately, confirming the positive complementarity effects of such dual application. Combined biochar with high-dose microalgae achieved an average increased yield and SOC storage by 58% and 24%, respectively, and reduced GHG emissions and CF by 18%-31% and 101%, respectively. Therefore, our findings shed new light on the essential roles of biochar and microalgae’ synergistic effects on enhancing crop yield and mitigating climate change in saline-alkali land.
How to cite: Ma, C., Xu, Z., yang, W., Liu, Q., Prasanna, P., and Qu, Z.: Co-application of microalgae and biochar to achieve yield enhancement and climate change mitigation in saline-alkali soil, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6644, https://doi.org/10.5194/egusphere-egu25-6644, 2025.
With the global emphasis on carbon reduction, biochar production has emerged as a promising carbon sequestration technology. While high-tech biochar production has matured, artisanal methods, widely used in developing countries, face challenges due to emissions of CH₄ during pyrolysis which is estimated at 30 kg per ton of biochar under Carbon Standards International (CSI) methodologies, can significantly reduce the carbon sequestration potential of artisanal biochar. However, previous studies use twig and leaves as biomass and suggest that optimizing feedstock moisture could have minimal CH₄ emissions even zero CH₄ emission.
This study investigates the relationship between pyrolysis conditions—specifically feedstock moisture levels and kiln temperatures—and methane emissions in Kon-Tiki soil pit kilns, a widely adopted low-cost solution in developing regions. Experiments will include agricultural residues such as bamboo and Lantana camara, under varying moisture levels, to calculate the emission factor of biochar production and assess their impact on CH₄ emissions through carbon balance method. Additionally, we will analyze emissions of CO, CO₂, and kiln temperature throughout the production process to provide a comprehensive understanding of the environmental implications of artisanal biochar production. By exploring the factors influencing emissions, this research aims to enhance the sustainability of biochar production in developing countries.
How to cite: Lin, C. E., Preaux, P., and Cortes, J.: Impact of Bamboo Feedstock Moisture Levels on Methane Emissions and biochar quality in kon-tiki Biochar Production , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14624, https://doi.org/10.5194/egusphere-egu25-14624, 2025.
Diffusion is the primary driver of limiting nutrient transfer in terrestrial ecosystems, a process that is controlled by dynamic interactions between soil chemical, biological, and physical properties. These properties interact through complex mechanisms, and their impacts on diffusive fluxes vary significantly due to the inherent heterogeneity of soil environments. Building on Fick’s first law of diffusion, this study seeks to unravel the underlying relationships among key driving factors of nutrient diffusion in soil and to quantify their contributions using a mathematical approach.
Fick’s first law defines diffusion as the product of the diffusion coefficient times the concentration gradient, divided by the diffusive path length. Among these factors, the diffusion coefficient is therefore positively related with nutrient diffusion rates and is primarily influenced by soil chemical properties, such as pH, texture, and mineral type, and nutrient properties, such as molecular size and charge, driving nutrient sorption and immobilization reactions. Similarly, the concentration gradient between the diffusion source and sink acts as another positive driver, which is shaped by (i) dynamic source processes like organic matter mineralization, microbial turnover, and nutrient addition by fertilization and (ii) sink processes governed by biological uptake and sorption. In contrast, diffusive path length is negatively related to the diffusive flux, with longer path lengths reducing nutrient fluxes. Path length is largely determined by soil porosity and soil water content, highlighting the importance of physical soil properties and hydrology in regulating nutrient diffusion.
Through theoretical analysis, a comprehensive review of the existing literature and new measurements, we explore how these factors influence nutrient diffusion under varying land management types, across soils varying in soil pH and texture, and in biological activity. The ultimate goal of this study is to identify the primary drivers of soil nutrient diffusion, to quantify their relative contributions, and to establish a generalized mathematical model to describe their interrelationships. By adopting an integrative approach, this work aims to provide a comprehensive understanding of nutrient diffusion mechanisms across diverse soil environments, offering insights beyond single-factor and single-species studies.
How to cite: Wen, M. and Wanek, W.: Biotic and Abiotic Factors on Soil Nutrient Diffusion Flux Based on Microdialysis: A Meta-Analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13145, https://doi.org/10.5194/egusphere-egu25-13145, 2025.
Organic fertilizers can enhance soil health and multifunctionality in agroecosystems, but their impact on nitrate reduction processes and associated soil-borne greenhouse gas emissions remains insufficiently understood. Our research found that organic fertilizer amendment in upland arable soils enhanced the contribution of fungal denitrification to N2O emissions, while decreasing N2O/(N2O+N2) ratio, primarily by enhancing fungal-bacterial denitrifier mutualism. This effect on the magnitude and pattern of N2O and N2 emissions were also depended on soil nitrate content In paddy soils, biochar application significantly reduced N2O fluxes and N2O/(N2O+N2) ratios, which was mainly attributed to the changes in the abundance and composition of nitrate reducing microorganisms. Specifically, biochar simultaneously increased denitrification and dissimilatory nitrate reduction to ammonium (DNRA) rates, and shifted more NO3– partitioning toward DNRA process. These promoting effects were primarily due to the increased carbon availability and the altered nitrate reducer communities. Collectively, our study suggests that organic fertilizer amendment in arable soils is helpful for alleviating the environmental effect of N fertilizer, which deepens our understanding of how organic fertilization regulates N cycling in the agroecosystem.
How to cite: Wei, Z.: Organic fertilizer amendment regulated the pattern and product characteristics of nitrate reduction processes in arable soils, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11804, https://doi.org/10.5194/egusphere-egu25-11804, 2025.
Tile drainage, a common agricultural practice in the Midwest USA, improves soil aeration and crop yields but also contributes to environmental challenges, such as nitrate (NO₃) loss and nitrous oxide (N₂O) emissions. To address these issues, ecohydrological models are essential for understanding the intricate hydrological and biogeochemical processes in tile-drained watersheds and for evaluating management strategies. Recent enhancements to the Soil and Water Assessment Tool (SWAT) have incorporated Century-based soil carbon and nitrogen cycling processes, along with N₂O emission algorithms, improving its ability to simulate nitrogen cycling and greenhouse gas emissions at the watershed scale. In this study, the Century-based soil carbon and nitrogen cycling module was integrated with two tile drainage modules within SWAT to enhance its simulation capabilities. The enhanced model was first evaluated at the Kelley experimental site, using observed data on drainage discharge, NO₃ loss, and N₂O emissions influenced by cover crops, corn-soybean rotation, and fertilization. Subsequently, the model was applied to simulate NO₃ loss and N₂O emissions in Iowa’s South Fork Watershed (SFW) using an ensemble modeling approach. This approach tested eight scenarios combining the two nitrogen modules, the two tile drainage modules, and calibration variations. Results showed that all eight scenarios effectively simulated daily stream flow but underestimated daily NO₃ load due to the underrepresentation of peak flows. Most models performed well at the monthly scale for both stream flow and NO₃ load. The ensemble modeling results aligned with prior studies, suggesting that ensemble approaches can reduce prediction uncertainties and address equifinality issues. However, the study emphasizes the need for additional data collection to improve the accuracy of denitrification and N₂O emissions simulations, especially in tile-drained systems. This research advances ecohydrological modeling for tile-drained watersheds, offering insights into improving water quality and reducing greenhouse gas emissions under agricultural management practices.
How to cite: Qi, J., Malone, R., Liang, K., Cole, K., Emmett, B., Moriasi, D., Shahid, M. R., and Castellano, M.: Assessing Nitrate Loss and Nitrous Oxide Emissions in a Typical Tile-Drained Field and Watershed in the Midwest USA, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14932, https://doi.org/10.5194/egusphere-egu25-14932, 2025.
The turnover and content of carbon (C) and nitrogen (N) in soil aggregates are influenced by land use and soil texture, with fractionation methods further contributing to differences between macro- and microaggregates by altering their composition and microbial activity. Our work investigated total and available C and N pools, alongside enzyme activities related to C and N cycling, in aggregates separated by wet and optimal moisture sieving from grassland and cropland Luvisol soils with sandy and loamy textures. The following incubation, with and without the 14C-glucose addition during 30 d, aimed to reveal the differences in the utilization strategies of soil organic matter by microorganisms inhabiting macro- and microaggregates. Optimal moisture sieving preserved higher dissolved N and peroxidase activity in macroaggregates, and 2.14 times higher microbial biomass N in microaggregates compared to wet sieving. Grasslands had higher C and N pools and associated enzyme activities than croplands, while loamy soils outperformed sandy soils in nutrient retention and microbial activity support. Wet sieving altered the relative content of -C=O and C-H bonds, especially in sandy soils. Sandy and loamy soils differed in the intensity of CO3²⁻, SiO2, and Al-OH bonds of clay minerals; still, they showed no differences in the functional groups of organic compounds. Optimal moisture sieving was more effective in preserving the available N pool inside. Loamy soils and grasslands demonstrated higher N and biological activity levels than sandy soils and croplands. This study underscores the critical role of fractionation methods, particularly optimal moisture sieving, in preserving soil nutrients and microbial activity, which is essential for understanding nutrient cycling in different ecosystems.
How to cite: Gunina, A., Qiang, W., Chen, J., and Dorodnikov, M.: Comparing wet and optimal moisture sieving for soil aggregate fractionation: impacts on C and N pools and microbial activity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12765, https://doi.org/10.5194/egusphere-egu25-12765, 2025.
Interelement relations in extracts simulating mobilizable soil fractions
Whereas many standardized soil extracts target only at a few parameters, ICP multielement determinations enable to trace interelement effects, respective correlations and possibly data simulations of amounts leached by other extractants. Ammonium salts and dilute organic acids are most favorable for the plasma torch, but salt solutions like LiCl, BaCl2, or CAL (Ca-acetate-lactate) need specially matrix matched standards. Sr blanks in CAL and Ni blanks in LiCl have to be considered anyway.
Mobilizable amounts of nutrient and trace elements from soil and related non-polluted substrates, have been compiled from monitoring and research projects of organic farming, obtained within the last 8 years. Up to 22 elements have been measured in the extracts, but some of them may remain below detection limits. As weakest extractants, water and LiCl are only suitable to release alkali, alkaline earths, P and S. Dilute acetic and formic acid act by mobilizing more due to their acidity, whereas acid complexants like CAL, oxalate pH3 and NH4-citrate attack pedogenic oxides in addition, and 0,5M HCl releases even more. Expectable concentration ranges versus aqua regia data will be given.
The samples will be grouped according to their carbonate, humics and nitrogen contents, in order to detect different concentration ranges and interelement effect, particularly for P and S.
How to cite: Sager, M. and Bonell, M.: Interelement relations in extracts simulating mobilizable soil fractions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15972, https://doi.org/10.5194/egusphere-egu25-15972, 2025.
Posters virtual: Fri, 2 May, 14:00–15:45 | vPoster spot 3
EGU25-14128 | Posters virtual | VPS15
The Impact of Nitrogen Management and Winter Wheat as A Double Crop on Nitrous Oxide Emissions in A Wheat-Soybean Crop Rotation.Fri, 02 May, 14:00–15:45 (CEST) | vP3.7
Optimizing nitrogen (N) management in agricultural cropping systems is important for reducing nitrous oxide (N₂O) emissions. This study examined the effect of managing N application in a winter wheat (Triticum aestivum L.) double-cropped with soybean (Glycine max L.) on biomass, grain yield, and N₂O emissions. The experiment was conducted at the Agronomy Research Center (ARC), Carbondale in Southern Illinois University, IL using a Randomized Complete Block Design (RCBD). The treatments include N timing and rate, creating three N management intensities of low, medium, and high. Low-intensity treatment received 120 kg N ha-1 in fall and spring, medium-intensity treatment received 186 kg N ha-1 all in spring and high intensity treatment received 186 kg N ha-1 in fall and spring. Results revealed that the treatment with medium-intensity input of N application did not have a significant effect on winter wheat biomass, grain yield, and N₂O cumulative fluxes in comparison to the high-intensity N management treatment. The results for average soybean grain yield under the various fertilizer inputs (3,087 kg ha-1) were significantly different when compared to the no-cover crop (NOCC) (3,527 kg ha-1) The cumulative N₂O fluxes were similar under all treatments for soybean and winter wheat. The summed cumulative N₂O fluxes were similar in both the medium and high N-intensity treatments during the soybean and winter wheat phases but higher than those of low intensity. Since the wheat yield was similar among all treatments, reduction in N2O during wheat-soybean rotation suggests that low-intensity treatment ensures farm profit while reducing N2O emissions.
How to cite: Ola, O., Guzel, O., Gage, K., Williard, K., Schoonover, J., Mueller, S., Brevik, E., and Sadeghpour, A.: The Impact of Nitrogen Management and Winter Wheat as A Double Crop on Nitrous Oxide Emissions in A Wheat-Soybean Crop Rotation., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14128, https://doi.org/10.5194/egusphere-egu25-14128, 2025.
EGU25-13616 | ECS | Posters virtual | VPS15
Nitrate Leaching and Nitrous Oxide Emissions from Fall Applied Manure and Phosphorous Fertilizers in Southern IllinoisFri, 02 May, 14:00–15:45 (CEST) | vP3.8
Illinois nutrient loss reduction strategy is questing to reduce nitrate-N (NO3-N) and phosphorus (P) loss by 25 and 15% by 2025. Fall applied ammonium-based P fertilizers could result in both NO3-N and phosphate loss during the fallow period. Two ways to minimize these losses are by utilizing nitrification inhibitors and also assessing other sources of P including triple superphosphate (TSP) and dissolved air flotation (DAF) that separates solids from liquid manure. A four-times replicated experiment was initiated in fall 2023 with Randomized Complete Block Design and five treatments in Agronomy Research Center, Carbondale, IL. Treatments were fertilizers [Control, TSP, DAF (Dissolved Air Flotation), MAP, & MAPI (MAP + urease and nitrification Inhibitor)], timing (fall & spring) and application type (surface & tilled). Data on nitrous oxide emissions, moisture, temperature, NO3-N leaching, and soil N were recorded during fall and spring prior to planting of corn (Zea mays L.) and agronomic observations (plant height, LAI & NDVI) were recorded on corn in fall. Soil N2O-N emissions were higher in MAPI and DAF during early February and late April dates, which can be explained by N availability along with high moisture and high temperatures, respectively during those sampling dates. Over winter and spring, MAPI had consistently higher NO3-N, NH4-N and total N especially in the late sampling dates and leaching losses were less under DAF (23% and 34%, respectively) and TSP (56% and 63%, respectively) compared to MAP or MAPI, suggesting that nitrification inhibitor did not reduce leaching from MAP source when applied in fall. Corn growth was slightly higher under DAF compared to other fertility treatments indicating it can be a potential replacement to the synthetic P fertilizers.
How to cite: Koduru, S., Keshavarz Afshar, R., Javid, M., Brevik, E., and Sadeghpour, A.: Nitrate Leaching and Nitrous Oxide Emissions from Fall Applied Manure and Phosphorous Fertilizers in Southern Illinois, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13616, https://doi.org/10.5194/egusphere-egu25-13616, 2025.
EGU25-14393 | ECS | Posters virtual | VPS15
Assessing the Impacts of Tillage and Crop Rotation on Nitrous Oxide Emissions in Poorly Drained Alfisols.Fri, 02 May, 14:00–15:45 (CEST) | vP3.9
Shifting from reduced tillage (RT) to no-till (NT) often reduces phosphorus (P) runoff by minimizing soil erosion. However, it might increase nitrous oxide (N2O) emissions or nitrate-N (NO3-N) leaching. Including a legume cover crop such as hairy vetch (Vicia villosa L.) before corn (Zea mays L.) is a common practice among growers in the Midwest USA. However, the effects of hairy vetch following soybean (Glycine max L.) harvest on NO3-N leaching and N2O emissions during the following corn season in soil with clay and fragipans are less assessed. This study evaluated the influence of cover crop (hairy vetch vs. no-CC control) and tillage systems (NT vs. RT) when 179 kg ha−1 nitrogen (N) was applied at planting on (i) corn yield, N uptake, removal, and balance; (ii) N2O emissions and NO3-N leaching; (iii) yield-scaled N2O emissions and NO3-N leaching during two corn growing seasons. We also evaluated factors influencing N2O emissions and NO3-N leaching via principal component analysis. Corn grain yield was higher in RT (8.4 Mg ha−1) than NT (6.2 Mg ha−1), reflecting more available N in the soil in RT than NT, possibly due to the favorable aeration and increased soil temperature in deeper soil layers resulting from tillage. Hairy vetch increased corn grain yield and soil N. However, it led to higher losses of both N2O-N and NO3-N, indicating that increased corn grain yield, due to the hairy vetch’s N contribution, also resulted in higher N losses. Yield-scaled N2O-N emissions in NT-2019 (3696.4 g N2O-N Mg−1) were twofold higher than RT-2019 (1872.7 g N2O-N Mg−1) and almost fourfold higher than NT-2021 and RT-2021 indicating in a wet year like 2019, yield-scaled N2O-N emissions were higher in NT than RT. Principal component analysis indicated that NO3-N leaching was most correlated with soil N availability and corn grain yield (both positive correlations). In contrast, due to the continued presence of soil N, soil N2O-N fluxes were more driven by soil volumetric water content (VWC) with a positive correlation. We conclude that in soils with claypan and fragipans in humid climates, NT is not an effective strategy to decrease N2O-N fluxes. Hairy vetch benefits corn grain yield and supplements N but increases N loss through NO3-N leaching and N2O-N emissions.
How to cite: Adeyemi, F., Thilakaranthne, A., Tiwari, M., Adeyemi, O., Singh, G., Williard, K., Schoonover, J., Brevik, E., and Sadeghpour, A.: Assessing the Impacts of Tillage and Crop Rotation on Nitrous Oxide Emissions in Poorly Drained Alfisols., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14393, https://doi.org/10.5194/egusphere-egu25-14393, 2025.
