SSS5.7

Organic soil amendments are proposed to mitigate climate change and support soil fertility by introducing recalcitrant carbon into soil. However, the full impact of recycled biosolids on soil greenhouse gas (GHG) dynamics are still unknown. We conducted a laboratory incubation to assess the climatic effects of two biochars (willow and spruce) and two ligneous biosolids on GHG emissions in controlled moisture conditions. The soil used in the incubation was collected from a soil-amendment field experiment on a clay cropland in South-West of Finland. The soil was sieved, air-dried and then individual samples were adjusted to 25%, 50%, 80% and 120% of water filled pore space (WFPS) before being incubated for 32 days in laboratory conditions. Soil GHG fluxes were measured after 1, 5, 12, 20 and 33 days.  

The application of 20–40 Mg ha^-1 of ligneous amendments, two years prior to our experiment, had increased soil pH, soil organic carbon content and plant available water content. The carbon dioxide (CO₂) fluxes were unaffected by the amendment treatments and correlated mainly with soil moisture and microbial biomass. Nitrous oxide (N₂O) emissions were reduced by all amendments compared to the un-amended control. Methane (CH₄) exchange consisted mostly of slight uptake by the soil but played only a minor role in the total GHG budget overall. 

The sum of CO₂, N₂O and CH₄ emissions, calculated as CO₂-equivalents, exhibited a strong linear relationship with soil moisture. Where the GHG budget was dominated by CO₂, it was accompanied by significant N₂O emissions at 120% WFPS. The results indicate that soil moisture critically affects the GHG emissions and that while organic soil amendments may have persisting effects on GHG exchange, they primarily occur in water-saturated conditions through N₂O dynamics.

How to cite: Peltokangas, K., Heinonsalo, J., Karhu, K., Kulmala, L., Liski, J., and Pihlatie, M.: Effects of organic soil amendments on soil greenhouse gas exchange under controlled soil moisture conditions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16469, https://doi.org/10.5194/egusphere-egu21-16469, 2021.

In Senegal, a large part of women of childbearing age (over 35%) and children under 5 years of age (over 40%) suffer from malnutrition by iron and zinc deficiencies. These deficiencies result from low iron and zinc levels in crop products. The low solubilization and mobility of iron and zinc in Senegalese soils can contribute largely to this problem. Among the potential causes are high concentrations of calcium carbonates of iron oxides and zinc oxides, of low levels of moisture and of organic matter.

Agrobiofortification through agroecological systems using the application of organic soil amendments rich in micronutrients is now considered one of the best ways to transfer micronutrients from the soil to the plant.

This study aims to evaluate different agroecological systems established with a combination of: (i) existing agricultural practices that can improve the nutritional quality of crop products, (ii) organic residual products (ORPs) selected according to their availability in time and space and their micronutrient content, (iii) effective microorganisms (EM) according to their level of efficiency in the mineralization of the ORPs and the solubilization of iron and zinc, and (iv) crop species according to their natural richness in micronutrients.

Existing agricultural practices were selected by a territorial diagnosis. The study zone highlighted the good performance of monoculture and associated crops, with field application of cow dung and poultry manure.

ORP and EM were selected by incubation under controlled conditions for 28 days at 28°C of the soil-ORP-EM mixtures (collected in the study area). Poultry droppings and sewage sludge, and the EM designated as groundnut-South Groundnut Basin were selected.

Crop species were selected by crushing and chemical analysis of frequently consumed local harvest products. Two varieties of cowpea (Lisard and Yacine) and sweet potato (Cri Apomudem and Beauregard) with a natural richness in iron and zinc were selected.

The evaluation of the agronomic impact of the cropping systems established from the different components selected will be exemplified, together with the description of the elementary options. An assessment of the environmental impact of the ORPs will be outlined.

How to cite: Noumsi-Foamouhoue, E., Fernandes, P., Legros, S., Sarr, M. M., Diouf, D., Ndienor, M., and Médoc, J.-M.: Evaluation of cropping system prototypes combining naturally nutrient-rich crop species, organic residues, and effective microorganisms to agrobiofortify local foods in iron and zinc in Senegal, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14431, https://doi.org/10.5194/egusphere-egu21-14431, 2021.

There is a growing body of evidence that plants uptake a monumental amount of organic forms of nitrogen (N) like amino acids in addition to those in inorganic forms. An amino acid-based fertiliser has been shown to improve seedling development and commercialised. Boreal forests store a substantial amount of carbon (C) in the soil and this is widely known to be further enhanced by the addition of inorganic nitrogen fertiliser via hampered decomposition. However, very little is known about how amino acid-based fertiliser influences C/N cycling in the boreal soils. The organic forms of N supply not only nitrogen but also carbon. If the previously demonstrated suppression of SOM decomposition is owing to altered C:N ratios in substrates, the amino acid-based fertiliser may not have as pronounced effects on the soil as the inorganic fertiliser. 

 We have examined the impacts of the organic fertiliser (100 kg N and 130 kg C ha^-1 year^-1)—arginine—on the chemical composition of soil organic matter in a boreal forest in comparison to non-fertilised, inorganic fertilised (ammonium-nitrate) and C-controlled inorganic fertilised (sucrose + ammonium-nitrate) conditions. The soil organic matter was characterised using two metrics: pyrolysis GC/MS and 13C solid-state nuclear magnetic resonance (NMR), combined with enzymological and metagenomic analysis.

We will be presenting the results following 4-year of the fertiliser treatments. Preliminary results have shown that there is limited evidence that the fertiliser treatments alter soil C/N cycing in four years. Nevertheless, the chemical composition in SOM under the organic fertiliser condition was similar to that under C-controlled compared to inorganic fertiliser treatment. 

How to cite: Hasegawa, S., Näsholm, T., and Bonner, M.: The effects of organic fertiliser, arginine, on the chemical composition of soil organic matter in a boreal forest, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13275, https://doi.org/10.5194/egusphere-egu21-13275, 2021.

Nano-sized clay particles exhibit unique physicochemical properties within soil matrices relevant to several areas of applied environmental sciences. The amendment of soils with nano-clays in field, lab, and greenhouse settings has been increasingly studied over recent decades from various disciplinary perspectives. In general, nano-clay as a soil amendment is seen as a potentially effective and economically feasible method for managing soil resources. However, no comprehensive review and quantification of the impacts of nano-clay amendment on soil physical, chemical, and biological properties has been undertaken, which limits its uptake and application. Here, we provide a review of the impacts of nano-clay addition in soil, using a meta-analytical approach considering soil health parameters (e.g., organic carbon, water retention, cation exchange, pH, pollutant concentration). Preliminary results synthesizing field and lab experiments indicate a wide range of positive effect sizes across key soil properties, with only limited benefits occurring in specific cases. Our results highlight the significant potential of nano-clay as a soil amendment in diverse applications, especially when coupled with the economic and logistical suitability of nano-clay amendment globally.

How to cite: Maddox, G., Bell, S., and Barriocanal, C.: Impacts of nano-clay addition to soils: a meta-analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12868, https://doi.org/10.5194/egusphere-egu21-12868, 2021.

Biochar is charcoal obtained by thermal decomposition of biomass through pyrolysis. The amendment of biochar changes chemical, but also physical properties of soils such as aggregation and texture. Thus, it is assumed that it can also affect soil erosion and erosion-related processes like the movement of water within the soil. In this study, we investigated how biochar particles change erodibility by rain splash instantly after application, as well as the initial movement of soil water.

Therefore, we conducted a small-scale laboratory experiment with two sieved substrates and using hydrothermal carbonization (HTC)-char and Pyrochar. Soil erodibility was determined with Tübingen splash cups under simulated rainfall, soil hydraulic conductivity was calculated from texture and bulk soil density, and soil water retention was measured using the negative and the excess pressure methods.

Results showed that the addition of biochar significantly reduced initial soil erosion in coarse sand and silt loam immediately after biochar application. Furthermore, biochar particles were not preferentially removed from the substrate surface. Increasing biochar particle sizes partly showed decreasing erodibility of substrates. Moreover, biochar amendment led to improved hydraulic conductivity and soil water retention regarding soil erosion control, with increasing application rates. It became clear that these effects are already detectable in a very early stage, and without long-term incorporation of biochar into soils. We could further show that different biochar types have varying impacts on investigated parameters due to their chemical properties and sizes, and future research should include varying biochars produced with different production methods.

In conclusion, this study showed that biochar amendments have the potential to reduce soil erosion by water from a very early stage. This mechanism adds a further ecosystem service to the list of useful impacts of biochar application on agriculture.

How to cite: Seitz, S., Teuber, S., Geissler, C., Goebes, P., and Scholten, T.: Newly-amended biochar particles decrease erodibility and improve hydraulic soil properties, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3188, https://doi.org/10.5194/egusphere-egu21-3188, 2021.

Tropical soils are often deeply weathered and vulnerable to degradation. Biochar appears a promising means to improve soil quality while sequestering carbon into the soil. Yet, sustainable soil amelioration depends on stable soil organic matter (SOM) stocks for nutrient retention, water uptake and as habitat for soil life. In a literature meta-analysis, we investigated, if biochar amendment to tropical soils led to SOM increases additional to biochar C. We found a mean additional C accumulation (MAC) of 0.29% soil dry weight (% dw). MAC was independent of study duration, climate, and biochar addition rate, but strongly linked to soil type and nutrient status prior to the experiment: In Nitisols, MAC was highest (0.99% dw) and initial C and N contents were higher in these soils. MAC was slightly negative in Ferralsols and Oxisols (– 0.01% dw and –0.2% dw respectively). MAC as a percentage of initial C content was < 50% for most soil types, but –50% in Ferralsols, Oxisols and Ultisols. Changes to soil microbiomes were more conclusive and included elevated enzyme activities and shifts from bacterial to fungi dominated microbiomes. We conclude that soil nutrient status prior to amendment, which is often linked to microbial activity, determines if the alteration of soil conditions caused by the biochar can be buffered ecologically, so that fresh organic residues are transformed into SOM. Additionally, we remarked that research on biochar – SOM interactions in tropical soils largely depends on cooperations with institutions from North America and Europe for funding and analytical infrastructure. Researchers, institutions, and funding bodies need to be creative and cautious to realise equitable participation of all partners in international research projects designed to render added value for societies around the world.

How to cite: Schnee, L. S., Ngakou, A., and Filser, J.: Does biochar contribute to soil organic matter accumulation? – A tropical perspective, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11816, https://doi.org/10.5194/egusphere-egu21-11816, 2021.

Sewage sludge production from wastewater treatment plants (WWTP) progressively exceeds 60 Million m³ p.a. in the EU. Although it is rich in organic matter (OM) and essential nutrients for crop production, sewage sludge is mainly disposed in landfills. Under the framework of Cyclic Economy and EU Green Deal, sewage sludge represents an ideal soil amendment and fertilizer with a potential to increase soil OM, provide nutrients and reduce chemical fertilization. Nonetheless, its agronomic use comes with limitations due to the presence of heavy metals and pathogenic microorganisms. Several stabilization technologies, including composting, thermal treatment and liming, aim to produce safe sewage sludge products suitable for agronomic use.

This incubation study investigated the effects of municipal sewage sludge (stabilized by alternative and common methods) on nutrient and microbial dynamics in two soils; an acidic (pH 5) and an alkaline (pH 8). Stabilized sewage sludge (Thessaloniki WWTP, Greece) with clay minerals (bentonite and vermiculite), biochar (pine residues), Ca(OH)₂ and air-drying, was applied at 1% and 3% dw, in soil mesocosms (300 g). Non-amended soils were also included as control. Soils were incubated (15 days; 25^oC) and equilibrated with periodic wetting and air-drying. Then, chemical soil properties, heavy metal concentrations and microbial abundance were determined using standard methods.

Treated sewage sludge addition in the acidic soil, noticeably increased soil pH (pH 5.2 – 8.5), compared to the control treatment (pH 5.0). In the alkaline soil, pH remained at similar levels (pH 8.1 – 8.6). Interestingly, EC increased from 0.42 up to 4.10 and 0.80 up to 3.08 dS m-1 for the acidic and alkaline soils, respectively. The C/N ratio was approx. 10 for all treatments, except biochar (C/N=16). Higher NO₃^- concentrations were observed for (CaOH)₂, biochar and vermiculite stabilized sewage sludge treatments, and higher NH₄⁺ concentrations were observed for air-dried, bentonite and vermiculite stabilized sewage sludge treatments, in both soils, when compared to the control. Heavy metal concentration increased in all treatments, yet, it remained below legislative critical levels. Sewage sludge amendment increased total heterotroph abundance in all treatments (5.4 – 7.5 log₁₀ CFU g^-1) compared to the control. Antibiotic resistant prokaryote abundance ranged between 3.9 – 7.0 log₁₀ CFU g^-1 and no persistent pattern was found. Pathogens remained below legislative critical levels in all treatments.

Our preliminary results show that stabilized sewage sludge has the potential to be a safe soil conditioner and fertilizer under the framework of Cyclic Economy and EU Green Deal. A desirable increase in soil fertility and organic C was observed for both soils, and an advantageous pH increase for acidic soil. Though, care should be taken not to exceed EC>2 dS m^-1 when amending agricultural soils with sewage sludge products. Also, further experimentation is required to understand the effects of soil amendments on plant nutrition and productivity.

Funding Acknowledgement: The research work was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “First Call for H.F.R.I. Research Projects to support Faculty members and Researchers and the procurement of high-cost research equipment grant” (Project Number: HFRI-FM17-1907).

How to cite: Giannopoulos, G., Karagianni, A.-G., Balidakis, A., Ipsilantis, I., and Matsi, T.: Nutrient and microbial dynamics of soils amended with sewage sludge stabilized with clay minerals and biochar; a preliminary study., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-367, https://doi.org/10.5194/egusphere-egu21-367, 2021.

Climate change is already affecting moisture dynamics in wetlands and previously moist soils. Elongated and localized dry spells lead to more aerobic conditions in previously oxygen depleted soils, favourable for organic matter decomposition. The substrate quality of older organic matter might, on the other hand, limit decomposition rates. The persistence of organic material towards microbial degradation and its relation to physico-chemical characteristics as well as biomarkers is however still unclear.

We are investigating soil organic matter characteristics and comparing them to soil respiration rates to quantify the soil’s persistence towards aerobic decomposition. Lipid biomarkers together with physico-chemical characteristics will assess the source and quality of soil organic matter and be compared to 60 days of aerobic respiration rates. Soil samples were taken up to 1m along a moisture gradient from a peat bog, an intermediate bushy site, and the adjacent forest in Siikaneva, Finland.

We hypothesize that soil respiration in aerobic incubations can be predicted by soil characteristics. Thus, from this data set, estimates of soil carbon vulnerability could be inferred and help predict decomposition rates with progressing climate change.

How to cite: Schwarzer, J., van Delden, L., Strauss, J., and Treat, C.: Decomposability of Soil Samples along a Moisture Gradient in a Peat Bog in Siikaneva, Finland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-869, https://doi.org/10.5194/egusphere-egu21-869, 2021.

Microbial derivatives and necromass are dominant sources of soil organic matter (SOM), yet the specific microbiological and geochemical reactions leading to the persistence of microbial compounds in SOM remains to be discovered. Identification of the microbial taxa and classes of microbial-derived compounds that are selectively preserved may enhance our ability to manage SOM, particularly in agroecosystems. We examined how perennial and annual biofuel cropping systems influence the production and selective preservation of microbial residues. Our experiment was replicated on a sandy and a silty loam to test the relative importance of microbial (biotic) and mineral (abiotic) filters on necromass accumulation and persistence. Using a ¹³C-labeling incubation experiment, we tested the effects of cropping system and soil texture on the production and persistence of microbial-derived residues. Soils were collected from sandy loams at the Kellogg Biological Station (MI, USA) and silty loams at the Arlington Agricultural Research Station (WI, USA). These soils were amended with ¹³C-labeled glucose, which was rapidly incorporated into microbial biomass. After 2 months, ~50% of the added ¹³C remained in the bulk soil. Approximately 30% of the ¹³C remaining in the bulk soil was recovered in the lipid, protein, and metabolite pools. Lipids contained the most ¹³C (16%) and the contribution was similar in both soils. Both soils had similar protein pools, but protein from the sandy loam was significantly more enriched than protein from the silty loam. The pool of metabolites was small, but highly enriched, suggesting substantial recycling over the 2-month incubation. The majority (40%) of the whole soil ¹³C persisted in the SOM even after repeat extractions. The remaining ~30% of the whole soil ¹³C was recovered in a complex of remaining unknown debris that separates from the soil at the solvent interphase with the protein but could not be solubilized. We provide novel evidence of the carbon pools that contribute to persistent microbial residues in soil. Our results suggest that metabolites may be more important than was previously recognized. Ongoing work is identifying the labeled metabolites and characterizing the chemistry of the highly enriched protein residue fraction.

How to cite: Hofmockel, K., Bell, S., and Kasanke, C.: Isotopic evidence reveals  persistent microbial residues in soil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14108, https://doi.org/10.5194/egusphere-egu21-14108, 2021.

Lipid biomarker analysis is an efficient tool for tracing organic matter sources in diverse environments. The quantification of biomarkers facilitates the location of soil organic carbon (SOC) from different sources in a soil profile. According to their structure, biomarkers from total lipid extracts (TLE) would exhibit different degrees of susceptibility to degradation, affecting thus their preservation in soils. Hence, it is crucial to better identify these biomarkers according to diverse stability scales. The aim of this study is to assess SOC contributions from aboveground and to develop a wider approach based on the allocation of C to quantitatively assess the sources of organic matter in low SOM content, highly weathered Mediterranean soils, following a C3-C4 rotation experiment.

Soil samples were taken from three depth intervals (0-5, 5-20, 20-40 cm) from a Mediterranean agricultural soil at “La Hampa” experimental station used for a crop rotation experiment with wheat (C3 plant) and maize (C4 plant). Lipids were extracted and quantified as described in [1].

The total lipid extracts were dominated by a homologous series of n-alkanols (saturated alcohols), short-, mid- and long-chain fatty acid methyl ester (FAME), branched FAME, unsaturated (mono- and polyunsaturated) FAME and sterols. Short-chain FAME, monounsaturated FAME were the most abundant fractions of free lipids. Mono-unsaturated alkanoic acids (Cn:1 FA) were detected in considerable amounts in all samples, namely various isomers of C16:1, C18:1, C20:1 and C22:1; these are believed to be mainly synthesised by soil bacteria. A significant increase of these compounds in rotation plots leads to an effective microbial consumption of labile organic matter in the surface soil [2]. Regarding FAME, the observed chain lengths ranged from C13 to C32, showing a unimodal distribution maximising at C16 and C18. These compounds are attributed also to microbial products, supporting our findings from the high proportion of the monounsaturated compounds found. In general, and in relation with all compounds, the abundances increased up to 20% compared with the control plots representing the initial content.

These results indicate that, only after three years of crop rotation, a considerable contribution of soil organic carbon is inherited from bacterial activity. The combination of extractable lipids has been shown to validate the use of TLE as a proxy for source and other information on vegetation change and soil processes. This work will bring a discussion on the use of these compounds for tracing the impact of crop rotation on carbon storage.

Acknowledgement: Ministerio de Ciencia Innovación y Universidades (MICIU) for INTERCARBON project (CGL2016-78937-R). L. San Emeterio also thanks MICIU for funding FPI research grants (BES-2017-07968). Mrs Desiré Monis is acknowledged for technical assistance.

[1] M. San-Emeterio, L., Bull, I. D., Holtvoeth, J., and González-Pérez, J. A.: Compound-specific isotopic analysis of fatty acids in three soil profiles to estimate organic matter turnover in agricultural soils., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18526, https://doi.org/10.5194/egusphere-egu2020-18526, 2020.

[2] Tu, T. T. N., Egasse, C., Anquetil, C., Zanetti, F., Zeller, B., Huon, S., & Derenne, S. (2017). Leaf lipid degradation in soils and surface sediments: A litterbag experiment. Organic Geochemistry, 104, 35-41.

How to cite: M. San-Emeterio, L., Bull, I. D., Holtvoeth, J., López, R., González-Vila, F. J., and González-Pérez, J. A.: Quantification of biomarkers as an estimation of soil organic matter turnover and sources under a crop rotation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14822, https://doi.org/10.5194/egusphere-egu21-14822, 2021.

Soil organic matter (SOM) is composed of multiple components from the living material, such as phenolic compounds, organic acids, lipids, peptides, polyesters, etc. A relevant part of these compounds forms part of supramolecular structures or mineral associations. Non-exchangeable hydrogen in SOM compounds is worth of study as an approach to estimate dynamic processes such as stabilization, mineralization, or biodegradation. The determination of H isotopes in SOMs faces analytical challenges related with e.g., the strength of the H bond, its exchangeability with ambient H from water or the instability of the isotopic analysis [1]. Nonetheless, along with the study of C isotopes, the study of H isotopes may certainly result in a complementary to give some light in this complex system, estimate the fate of organic compounds, and to better understand the link between hydrogen and carbon cycles in SOM [2].

In this communication, we describe and validate a methodology based on analytical pyrolysis for the direct measure of compound-specific H isotope composition (δ²H) in soil samples. The technique combines Py-GC with a high-temperature conversion reactor and a continuous flow isotope ratio mass spectrometer (IRMS) (Py-GC-HTC-IRMS).

Composite dehesa surface (0-10 cm) soil samples (Pozoblanco, Córdoba, Spain) were taken from four forced climatic treatment plots representing warming (W), drought (D), its combination (W+D), and control (D), installed in two different habitats: under evergreen oak canopy and in the open pasture. The samples were analysed in triplicate by conventional analytical pyrolysis (Py-GC/MS) and in parallel for δ²H Py-CSIA using the same chromatographic conditions and separation column type.

Up to 32 compounds were identified by Py-GC/MS, which H isotope composition corresponded presumably to non-exchangeable H, and with origin mainly from lignin (G- and S- units) and lipids. The H isotope composition showed an estimated average of -55 ‰ ± 7.09 for G-lignin units, -64 ‰ ± 8.64 S-lignin units and lighter -112 ‰ ± 4.32 for fatty acids (-109 ‰ ± 3.65) and the n-alkane series (C-19 to C-31). Significant differences are reportedly driven by the differences in habitat: more depleted δ²H values were found in SOM produced in the open pasture than under the tree canopy. In addition, a δ²H enrichment is observed for lignin-derived compounds in SOM under the W+D treatment.

The technique used and tested is expected to bring novelty results in relation to the processes affecting the isotopic composition of non-exchangeable hydrogen exerted by climatic treatments on diverse SOM specific compounds. Besides presenting the analytical challenges that are faced, we will discuss the effects of canopy and climatic treatments to tackle potential harsh climatic conditions as predicted, especially in Mediterranean areas. 

Acknowledgement: INTERCARBON project (CGL2016-78937-R), DECAFUN (CGL2015-70123-R). MICIU for funding FPI research grants (BES-2017-07968). Mrs Desiré Monis, Mrs Alba M. Carmona & Mr Eduardo Gutiérrez González are acknowledged for technical assistance.

[1] Paul, A. et al (2016). Biogeosciences, 13, 6587–6598.

[2] Seki, O. et al (2010). Geochimica et Cosmochimica Acta, 74(2), 599-613.

How to cite: M. San-Emeterio, L., Pérez-Ramos, I., Domínguez-Núñez, M. T., González-Vila, F. J., and González-Pérez, J. A.: Compound-specific δ2H using analytical pyrolysis (Py-CSIA) for assessing source and processes of soil organic matter driven by climatic changes within a Mediterranean evergreen oak forest (dehesas), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14610, https://doi.org/10.5194/egusphere-egu21-14610, 2021.