Fertilization experiments provide insights into elemental imbalances in soil microbial communities and their consequences for soil nutrient cycling. By addition of selected nutrients, other nutrients become deficient and limiting for soil microorganisms as well as for plants. In this study we focused on microbial nitrogen (N) cycling in a long-term nutrient manipulation experiment. In many soils, the rate-limiting step in N cycling is depolymerization of high-molecular-weight nitrogen compounds (e.g., proteins) to oligomers (e.g., peptides) and monomers (e.g., amino acids) rather than the subsequent steps of mineralization (ammonification) and nitrification. The aim of our study was to determine whether nutrient deficiency directly or indirectly – via changes in plant carbon (C) inputs - affects soil microbial N processing.

We collected soil samples from a fertilization experiment, established in 1946 on a hay meadow close to Admont (Styria, Austria). The field experiment consisted of a full factorial combination of inorganic N, P, and K fertilization and a control with no fertilizers. Furthermore, liming (Ca-addition) and organic fertilizer application treatments (solid manure and liquid slurry) were established. In the experiment, plant biomass is harvested three times per year, inducing strong nutrient limitation in plots that have not received nutrient additions (fully deficient or deficient in a single element). We determined gross rates of microbial protein depolymerization, N-mineralization and nitrification via isotope pool dilution assays with ¹⁵N-labeled amino acids, NH₄⁺, and NO₃^-. We hypothesized that N deficiency (lack of N fertilization) would stimulate microbial N mining (depolymerization), and reduce subsequent N mineralization and nitrification. In contrast, we expected that organic fertilization would alleviate microbial C and N limitations, reducing N depolymerization rates and increasing mineralization and nitrification.

Our results show that organically fertilized and limed soils have significantly lower gross protein depolymerization rates than plots receiving inorganic N. No significant differences were found comparing gross N-mineralization and gross nitrification rates across the different treatments. Given the higher rates of protein depolymerization in inorganically fertilized soils as compared to organically fertilized and limed soils, microbial N processes seem to be controlled by plant C input and/or soil pH rather than by direct soil nutrient availability. However, depolymerization of macromolecular N does not only supply N to the soil microbial community but also organic C. Thus, the reduced plant C input compared to fully fertilized soils may have caused microorganisms to increase their mining for a C-containing energy source, thereby increasing protein depolymerization rates. In summary, this study suggests that long term nutrient deficiency or nutrient imbalances may affect soil nutrient cycling indirectly by changing plant C inputs (via reduced primary production) and/or changing soil pH, rather than directly, by nutrient availability. This further indicates that soil microbial communities are rather C than nutrient limited.

How to cite: Spiegel, F., Fuchslueger, L., Canarini, A., Schnecker, J., Schmidt, H., Martin, V., Wiesenbauer, J., Jenab, K., Watzka, M., Pötsch, E. M., Wanek, W., Kaiser, C., and Richter, A.: Controls of microbial N cycling in agricultural grassland soils, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12730, https://doi.org/10.5194/egusphere-egu21-12730, 2021.

The coupled cycles and interactions of soil carbon (C), nitrogen (N), and phosphorus (P) are fundamental for soil quality and soil organic matter (SOM) formation. Low C:N ratios through nitrogenous fertilizer addition may accelerate SOM cycling and promote C mineralization in soil, whereas P limitations may decline C storage by reducing plant and microbial biomass production. Deeper soil layers’ C-N-P stoichiometry has an important role in regulating SOM formation in subsoils. However, there is little information on soil C:N:P stoichiometry in deep soil layers of farmland. In this study, soil columns up to one meter were collected from 32 farms distributing across Finland with different soil texture and agricultural management history. The one-meter soil columns were cut into 10 cm deep slices and analyzed for the total organic carbon (TOC), total nitrogen (TN) by dry combustion method and total phosphorus (TP) contents by aqua regia digestion and ICP-OES method. Overall, the TOC, TN and TP contents all dropped sharply in 30-40 cm soil layers, but TP contents rose again in deep soil. The role of agricultural management practice (including crop rotation, crop cover, crop diversity and fertilization) on soil C:N:P stoichiometry as well as organic matter accumulation in the deep soil layers were explored. The preliminary results will be presented in the poster. The data deepens our understanding of soil C, N and P coupling and interaction related to soil C sequestration.

How to cite: Wang, S., Uhlgren, O., Salonen, A.-R., and Heinonsalo, J.: Soil contents and stoichiometry of carbon, nitrogen, and phosphorus in Finnish farmland and feedbacks on management patterns, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12350, https://doi.org/10.5194/egusphere-egu21-12350, 2021.

Elevated carbon dioxide in the atmosphere (eCO₂) has been found to influence soil C by altering the belowground balance between the decomposition of existing soil organic matter (SOM) and the accumulation of plant-derived C inputs. Even small changes in this balance can have a potentially large effect on future climate. The relative availability of soil nutrients, particularly N and P, are crucial mediators of both decomposition and new C accumulation, but both these two processes are rarely assessed simultaneously. We asked if the effect of eCO₂ on soil C decomposition was mediated by soil N and P availability, and if the effect of CO₂ and soil N and P availability on soil C decomposition was dependent on C pools (existing SOM C, newly added C). We grew Eucalyptus grandis and a C3 grass (Microlaena stipoides) from seed in an experimentally manipulated atmosphere with altered δ¹³C signature of CO₂, which allowed the separation of plant derived C, from the existing SOM C. Then we manipulated N and P relative abundance via nutrient additions. We evaluated how the existing SOM and the new plant-derived C pool, and their respiration responded to eCO₂ conditions and nutrient treatments. SOM respiration significantly increased in the eucalypts when N was added but was not affected by CO₂. In the grass the SOM respiration increased with eCO₂ and added N and SOM respiration per unit of SOM-derived microbial was significantly higher in both the added P and added N+P nutrient treatments. The rhizosphere priming of SOM was suppressed in both the added P and added N+P nutrient treatments. The heterotrophic respiration of plant-derived C was contingent on nutrient availability rather than eCO₂ and differed by species. The grass-derived respiration was significantly higher than the eucalypt and was higher in both added P and added N+P nutrient treatments. Thus, nutrient stoichiometry had similar effects on SOM and plant derived C, but e CO₂ only affected SOM and only for the Eucalyptus.  This study shows how species differences have large effects on rhizosphere C cycling responses to eCO2 and stoichiometric conditions.      

How to cite: Pihlblad, J., Andresen, L. C., Macdonald, C., Ellsworth, D., and Carrillo, Y.: Stochiometric control of SOM and plant derived soil C pools dynamics under elevated CO2  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14375, https://doi.org/10.5194/egusphere-egu21-14375, 2021.

Microbial processes are one of the key factors driving carbon (C) and nutrient cycling in terrestrial ecosystems, and are strongly controlled by the equilibrium between resource availability and demand. In deeply weathered tropical rainforest soils of Africa, it remains unclear whether patterns of microbial processes differ between soils developed from geochemically contrasting parent material. Here, we investigate patterns of soil microbial processes and their controls in tropical rainforests of Africa. We used soil developed from three geochemically distinct parent material (mafic, felsic, mixed sedimentary rocks) and three soil depths (0−70 cm). We measured microbial biomass C and enzyme activity at the beginning and end of a 120-day incubation experiment. We also conducted a vector analysis based on ecoenzymatic stoichiometry to assess microbial C and nutrient limitations. We found that microbial C limitation was highest in the mixed sedimentary region and lowest in the felsic region, which we propose was related to the strength of contrasting C stabilization mechanisms and varying C quality. None of the investigated regions and soil depths showed signs of nitrogen (N) limitation for microbial processes. Microbial phosphorus (P) limitation increased with soil depth, indicating that subsoils in the investigated soils were depleted in rock-derived nutrients and are therefore dependent on efficient nutrient recycling. Microbial C limitation was lowest in subsoils, indicating that subsoil microbes cannot significantly participate in C cycling and limit C storage if oxygen is not available, but can do so in our laboratory incubation experiment under well aerated conditions. Using multivariable regressions, we demonstrate that microbial biomass C normalized to soil organic C content (MBC_SOC) is controlled by soil geochemistry and substrate quality, while microbial biomass C normalized to soil weight (MBC_Soil) is predominantly driven by resource distribution (i.e., depth distribution of organic C). We conclude that due to differences in resource availability, microbial processes in deeply weathered tropical rainforest soils greatly vary across geochemical regions.

How to cite: Kidinda Kidinda, L., Kemi Ologoke, F., Vogel, C., Kalbitz, K., and Doetterl, S.: Parent material and organic matter control soil microbial processes in African tropical rainforests , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2982, https://doi.org/10.5194/egusphere-egu21-2982, 2021.

Human activity has caused imbalances in nitrogen (+N) and phosphorus (+P) loadings of ecosystems around the world, causing widespread P limitation of many biological processes. Soil phosphatases catalyze the hydrolysis of P from a range of organic compounds, representing an important P acquisition pathway. Therefore, a better understanding of soil phosphatase activity as well as the underlying mechanisms to individual and combined N and P loadings could provide fresh insights for wise P management. Here we show, using a meta-analysis of 188 published studies and 1277 observations that +N significantly increased soil phosphatase activity by 14%, +P significantly repressed it by 30%, and +N+P led to non-significant responses of soil phosphatase activity. Responses of soil phosphatase activity to +N were positively correlated with soil C and N content, whereas the reverse relationships were observed for +P and +N+P. Similarly, effects of +N on soil phosphatase activity were positively related to microbial biomass C, microbial biomass C:P, and microbial biomass N:P, whereas reverse relationships were observed for +P. Although we found no clear relationship between soil pH and soil phosphatase activity, +N-induced reductions in soil pH were positively correlated with soil phosphatase activity. Our results underscore the integrated control of soil and microbial C, N and P stoichiometry on the responses of soil phosphatase activity to +N, +P, and +N+P, which can be used to optimize future P management.

How to cite: Chen, J., Luo, Y., Cao, J., Jørgensen, U., Moorhead, D., and Sinsabaugh, R. L.: Contrasting responses of soil phosphatase activity to nitrogen and phosphorus loadings: Implications for phosphorus management, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1655, https://doi.org/10.5194/egusphere-egu21-1655, 2021.

Tropical forest ecosystems are important components of global carbon (C) and nutrient cycles. Many tropical rainforests grow on old and highly weathered soils depleted in phosphorus (P) and other rock-derived nutrients. While plants in such forests are usually P limited, it remains unclear if heterotrophic microbial communities are also limited by P or rather by C or energy. Elemental limitations of microorganisms in soil are often approached by measurements of changes in respiration rates or microbial biomass in response to additions of nutrients or carbon. However, it has been argued lately, that microbial growth rather than respiration or biomass should be used to assess microbial limitations.

In this study we asked the question whether the growth of heterotrophic microbial communities in tropical soil is limited by available P or by C. We sampled soils along a topographic gradient (plateau, slope, bottom) differing in soil texture and total and available P concentrations from a highly weathered site in French Guiana. We incubated these soils in the laboratory with cellulose as a C source, phosphate (pH adjusted) and with a combination of both. We determined microbial growth by measuring the incorporation of ¹⁸O from labelled water into microbial DNA.

In general, plateau soils were higher in microbial C, while bottom soils were higher in microbial P, leading to increased microbial C:P ratios in plateau soils compared to bottom soils. Microbial C, N and P did not respond to the addition of cellulose. Microbial P on the other hand was significantly increased by P additions, with no interactive effect between cellulose and P. Although microbial C was significantly higher in plateau soils, respiration rates were similar to those of bottom soils. This led to similar mass specific respiration rates in plateau and slope soils, with bottom soils being significantly higher. Moreover, we found that C and P addition increased mass specific respiration rates and both nutrient additions showed a positive interactive effect. Gross microbial growth rates were stimulated by P additions but were unresponsive to C additions alone. However, the addition of carbon further stimulated the effect of P on growth.

The observed interactive effect of C and P additions on gross microbial growth rates suggests a co-limitation of microorganisms by C and P in highly weathered soils. We argue that co-limitation bears significant ecological advantages for microorganisms as it minimizes the investments in acquiring nutrients for growth.We further conclude that microorganisms in tropical soils are highly efficient in taking up and storing P from the environment. In our experiment, microbial P almost doubled in the six days after P addition, while microbial C was not enhanced. This also means that the microbes were not homeostatic with regard to their C:P ratios. Finally, our study demonstrates the importance of investigating gross microbial growth rates, rather than respiration or biomass, for inferring nutrient limitations.

How to cite: Ranits, C., Fuchslueger, L., Van Langenhove, L., Verryckt, L. T., Verlinden, M., Vallicrosa, H., Ogaya, R., Llusià, J., Grau, O., Lugli, L. F., Janssens, I. A., Peñuelas, J., and Richter, A.: What controls microbial growth in tropical soils? The role of carbon and phosphorus., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10427, https://doi.org/10.5194/egusphere-egu21-10427, 2021.

Native forest substitution by intensively managed tree plantations can significantly alter carbon and nutrient biogeochemical cycling due to changes in forest dynamics and alterations on biogeochemical fluxes. To evaluate the magnitude of these alterations, we quantify the main C, N, and P pools and fluxes in paired plots established in secondary deciduous native forests and exotic pine plantation plots in five contrasting soils. Forest main fluxes were monitored for two years. We quantified total biomass and biomass C and nutrient pools, litterfall production, litter decomposition, soil CO₂ efflux, LAI, and annual root production. Besides, DOC, Nitrate, Ammonium, and DTP was determined on leachates.

Overall ecosystem C storage (soil and aboveground biomass) showed no differences between forest types across sites (p=0.07). However, two of the soil types displayed significantly higher C pools in the native forest sites. Besides, most native forest sites have higher total aboveground N and P stocks. Nitrate and ammonium leachate losses tend to be higher in native forests, but not significantly. On the contrary, phosphate losses were higher in plantations. Native forests and plantations differ on their annual C fluxes, particularly on their root and DOC productions. Native forests showed a significantly higher annual root production (1.76 ± 0.99 Mg ha^-1) than pine plantations (0.81 ±0.88 Mg ha^-1) (p=0.0001). Of the Measured variables, only root production showed a positive correlation (R² = 0.49) with soil total C (p=0.001). Exotic pine plantations display higher litterfall but a significantly lower root production modifying the main source of carbon to the system. Also, DOC losses increased considerably under plantations. Continuous monitoring of these pair plots will help to address the potential long term effect of this land-use change and the relative sensitivity of these systems to changes in environmental conditions.

How to cite: Aburto, F., Crovo, O., Albornoz, M. F., and Southard, R.: Effects of native forest replacement to exotic plantations on forest C, N, and P pools and dynamics in south-central Chile, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13749, https://doi.org/10.5194/egusphere-egu21-13749, 2021.

With climate change, much of the world will experience devastating shifts in weather patterns like increased flooding, intensifying periods of soil saturation. Soil carbon (C), nitrogen (N) and phosphorus (P) cycles are sensitive to changes in soil saturation, where exchange between the mineral-bound and the soluble bioavailable pools can occur with increases in moisture content. With soil saturation, C, N, and P may be mobilized either through greater diffusion or reduced conditions that cause desorption of mineral-bound C, N and P into their respective soluble pools. De-sorption, resorption and diffusion dynamics of C, N, and P may or may not reflect the stoichiometry of the mineral bound pool. Changes in bioavailable soluble C, N and P that could occur with soil saturation and drying may cause unknown consequences for microbial biomass C:N:P. With increases in soil moisture, simultaneous changes in both substrate stoichiometry and microbial growth may occur that impact microbial biomass stoichiometry.  Such changes in microbial stoichiometry and microbial retention of C, N, and P may affect the post-flood fate of soluble C, N, and P. Understanding how releases in mineral bound C, N and P alter the bioavailable C:N:P and how this in turn impacts microbial activity and accumulation of these substrates can inform predictions of retention or losses of C, N and P following soil saturation events.

To determine if mineral-bound, soluble and microbial biomass stoichiometry is maintained or altered during and after soil saturation events, we used a laboratory incubation approach with manipulated soil saturation and duration. Soil incubations were maintained at three water-holding capacity (WHC) levels: 20% (control), 50%, (moderate) and 100% (severe). We maintained the moderate and severe water-logging treatments for  0.5 h, 24 h, 1 week, followed by air-drying to 20% WHC to examine the influence of flood duration. To understand the exchanges of C, N and P between different pools during flooding, we compared changes in soluble and mineral bound soil C, N and P and impacts on microbial C, N, and P exo-cellular enzymes, and microbial biomass C:N:P. Preliminary results indicate that greater soil moisture content increases soluble P and that the 24 hour flood period captures shifts in the mineral bound P pool that do not remain for the longer flood period (1 week). Enzyme activity similarly reflects an increase in microbial activity in the soil held at 50% and 100% moisture content for 24 hours. We also discuss how soil moisture levels and flood duration impact soluble and mineral bound C relative to P, and how microbial biomass C:N:P tracks these fractions. By exploring the combined response of mineral-bound and soluble C, N, and P to variation in soil saturation, we can better understand how different flood scenarios will impact soil C, N and P retention.

How to cite: Lieberman, H., von Sperber, C., Rothman, M., and Kallenbach, C.: Understanding the interdependent cycles of soil carbon, nitrogen and phosphorus during soil saturation events , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6703, https://doi.org/10.5194/egusphere-egu21-6703, 2021.

Tree species capable of forming a symbiosis with N-fixing bacteria may affect P availability in reclaimed technosols. The objective of this study was to compare the effect of N-fixing tree species and non-N-fixing species on phosphorus forms in technosols developing from various materials. Soil samples were taken under black locust (Robinia pseudoaccaccia), black alder (Alnus glutinosa), silver birch (Betula pendula) and Scots pine (Pinus sylvestris) from two depths (0-5 cm and 5 – 20 cm). The soil substrates were fly ashes, sands and clays. In the soil samples measured were concentrations of total P (P_t),  water soluble P (P_H2O),  dilute salt-extractable P (P_ex), microbial biomass P (P_mic) and total labile P (P_labil). Multifactor ANOVA revealed that tree species did not influence contents of P_t, P_ex and P_H20. However, there was a statistically significant effect of soil substrate and soil horizon on these forms of P. The factors tree species, soil substrate and soil horizon had statistically significant effect on P_mic content whereas content of P_labil was affected by tree species and soil horizon. Multiple Range Tests by tree species showed that soils under Scots pine contained significantly less P_mic than soils under other tree species studied. There were no significant differences in P_mic between the soils under silver birch, black alder and black locust. The soils under Scots pine contained also significantly less P_labil than the soils under black locust and silver birch. Our study included P forms that are considered labile (except P_t). The obtained results indicated that the effect of N-fixing trees on these forms of P was weak. Instead we noticed that Scots pine had negative effect on some forms of labile P. 

The study was financed by The National Science Centre, Poland, grant No. 2018/31/B/ST10/01626.

How to cite: Sroka, K., Chodak, M., and Pietrzykowski, M.: Phosphorus forms in technosols afforested with N-fixing and non-N-fixing tree species , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7375, https://doi.org/10.5194/egusphere-egu21-7375, 2021.

Biochar is the solid residue produced by pyrolysis (thermal treatment under absence of oxygen) of biomass [1]. This material has been widely proposed for remediation of degraded soils [2]. Soil degradation comprises loss of chemical, physical and biological properties of soil, declining soil health. Soils that are polluted with high concentrations of trace elements present serious functional problems. It is estimated that 37 % of the degraded soils in Europe are polluted with trace elements [2]. This study aimed to determine the effects of biochar application into degraded acidic Fluvisols [3], that were polluted in April 1998 by the massive dumping of mine sludge contaminated with heavy metals, called the Aznalcóllar disaster. The studied soils were amended with 8 t ha^-1 of olive pit and rice husk biochars. After 6, 12 and 20 months under field conditions, both amended and un-amended soils were sampled for determining microbial diversity using the Illumina Miseq technology of the 16S rRNA gene. Soil properties, soil composition, enzymatic activities and plant development were also analysed. Physical properties of the degraded soils were improved by the application of biochars. Soil pH strongly influenced dehydrogenase and β–glucosidase activities. Biochars enhanced plant diversity and, more specifically, olive pit biochar increased plant yield in the more acidic soil. Differences in microbial communities were found between both soils and sampling campaigns. Moderately acidic soil showed greater alpha diversity comparing to the most acidic soil. In fact, after 6 months of biochar application, Bacteroidetes, Gemmatimonadetes and Verrucomicrobia were solely found in the moderately acidic soil. However, Shanon and Simpson index values showed that the application of biochars enhanced bacterial diversity in the most acidic soil after 6 months, which control sample was almost exclusively composed of Ktedonobacteria, belonging to the phylum Chloroflexi. Correlation coefficients explained that biochar amendment increased bacterial diversity by increasing soil pH. The effect of biochar on microbial communities was dissipated over time [4].

References:

[1] IBI, 2015. IBI-STD-2.1. International Biochar Initiative.

[2] European Environment Agency, 2020. https://www.eea.europa.eu/themes/soil/soil-threats.

[3] Campos, P., De la Rosa, J.M., 2020. Sustainability 12, 6025.

[4] Campos, P., Miller, A.Z., Prats, S.A., Knicker, H., Hagemann, N., 2020. Soil Biol. Biochem. 150, 108014.

Acknowledgements:

The former Spanish Ministry of Economy, Industry and Competitiveness (MINEICO) and AEI/FEDER are acknowledge for funding the project CGL2016-76498-R. J.M. De la Rosa thanks MINEICO for funding his “Ramón y Cajal” contract. “Fundación Tatiana Pérez de Guzmán el Bueno” for funding the PhD contract of P. Campos. A.Z. Miller thanks “Fundação para a Ciência e a Tecnologia” for its support.

How to cite: Campos, P., Miller, A. Z., Knicker, H., and De la Rosa, J. M.: Biochar potential in reclaiming degraded soils, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-788, https://doi.org/10.5194/egusphere-egu21-788, 2021.

It is estimated that over 37 % of degraded soils in the European Union are polluted by heavy metals [1], which are non-biodegradable and persistent pollutants in soils. The application of organic amendments to soils for their remediation has been worldwide used [2]. Several studies have shown that biochar, the carbonaceous material produced by pyrolysis of organic residues, has a high potential to stabilize trace elements in soils [3]. Biochars usually have an alkaline pH and high water holding capacity (WHC), large specific surface area and cation exchange capacity, which are appropriate characteristics to reduce the availability of heavy metals in the environment [4]. Nevertheless, recent studies exhibited that biochar recalcitrance could be much lower than assumed [5].  Beside this, the effects of the addition of biochar as a soil amendment on the composition of soil organic matter (SOM) are largely unknown. Thus, the aim of this study is to investigate the effects of the application of biochars from rice husk (RHB) and olive pit (OPB) in a Typic Xerofluvent polluted with trace-elements after 24 months at field in 12 plots installed at the surroundings of the Guadiamar Green Corridor (37° 23' 7.152"N, 6° 13' 43.175"; Southwest Spain). Specifically, for this study the effects of biochar amendment on soil physical properties (pH, water holding capacity-WHC, moisture, etc), elemental composition, total SOM, the content of oxidizable SOM as well as the content and composition of humic acids (HAs) have been assessed.

Biochar application caused an increase in soil pH (around 0.4 units), soil moisture (from 6-7% to 10-18 %) and WHC. In addition, the total organic carbon and HAs content increased slightly. Preliminary results show that biochar could become part of the humified SOM in a shorter time than initially expected. Nevertheless, the spectroscopic analyses (FT-IR and ¹³C NMR spectroscopy) documented that the qualitative composition of soil HAs was not altered due to the biochar amendment.

References:

[1] EEA; 2007. CSI 015. Copenhagen, Denmark: European Environmental Agency.

[2] Madejón, E.; Pérez de Mora, A.; Burgos, P.; Cabrera, F.; 2006. Environ. Pollut. 139, 40-52.

[3] Campos, P., De la Rosa, J.M., 2020. Sustainability 12, 6025.Uchimiya, M.; Klasson, K.T.; Wartelle, L.H.; Lima, I.M.; 2011. Chemosphere 82, 1438-1447.

[4] Campos, P., Miller, A.Z., Knicker, H., Costa-Pereira, M.F., Merino, A., De la Rosa, J.M., 2020. Waste Manag. 105, 256-267.

[5] De la Rosa, J.M.; Rosado, M.; Paneque, M.; Miller, A.Z.; Knicker, H.; 2018. Sci. Tot Environ. 613-614, 969-976.

Acknowledgements: The Spanish Ministry of Economy, Industry and Competitiveness (MINEICO), CSIC and AEI/FEDER are thanked for funding the project CGL2016-76498-R. P. Campos thanks the “Fundación Tatiana Pérez de Guzmán el Bueno” for funding her PhD.

How to cite: Santa-Olalla, A., Fernandez-Boy, E., Campos, P., Knicker, H., Lopez, R., Gonzalez-Pérez, J. A., and De la Rosa, J. M.: Impact of biochar amendment on soil organic matter composition in a heavy-metals polluted soil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-865, https://doi.org/10.5194/egusphere-egu21-865, 2021.

Tree species capable of forming symbiosis with N-fixing bacteria planted on reclaimed wastelands may increase not only their N content but also increase availability of P. The aim of our study was to compare the effect of rhizobial and actinorhizal N-fixing tree species and non-N-fixing species on the activity of phosphatases in various technosols. Soil samples were taken under black locust (Robinia pseudoaccaccia), black alder (Alnus glutinosa), silver birch (Betula pendula) and Scots pine (Pinus sylvestris) from two depths (0-5 cm and 5 – 20 cm) of technosols developing from different parent materials (Quaternary sands, fly ashes after lignite combustion,  acid and alkaline Tertiary clays). The samples were measured for the activities of acid and alkaline phosphatase, inorganic pyrophosphatase, microbial biomass (C_mic), texture, as well as contents of organic C (C_org), total N (N_t) and total P (P_t). Activities of acid (Pho_Aci), alkaline (Pho_Alk), total phosphatase (Pho_Sum) and inorganic pyrophosphatase (Pyro_Pho) were expressed per soil dry mass and per unit of C_mic (specific enzyme activities - Pho_Aci_SP, Pho_Alk_SP and Pho_Sum_SP for acid, alkaline and total phosphatase, respectively, Pyro_Pho_SP for pyrophosphatase). The soils under black locust exhibited higher Pho_Aci activity and higher specific activities of all enzymes (Pho_Aci_SP, Pho_Alk_SP,, Pho_Sum_SP and Pyro_Pho_SP) than the soils under both non-N-fixing trees. For alder  Pho_Aci activity was significantly higher only when compared to pine. However, the values of Pho_Aci_SP and Pho_Sum_SP were higher under alder than under both non-N-fixing trees. There were no differences in the activities or specific activities of measured enzymes between the soils under pine and birch. Our results indicated that rhizobial black locust stimulated activity of soil enzymes involved in P cycling much stronger than non-N-fixing tree species. This effect of black locust was consistent in technosols developing from various parent materials. The effect of actinorhizal black alder was less pronounced, but also evident.  The results of our study indicated that both N-fixing trees stimulated activity of enzymes involved in P cycling stronger than the non-fixing trees. Thus, the N-fixing trees may alleviate P deficiency in technosols as they stimulate development of phosphatase releasing microorganisms and increase P availability.

The study was financed by The National Science Centre, Poland, grant No. 2018/31/B/ST10/01626.

How to cite: Chodak, M., Sroka, K., and Pietrzykowski, M.: Activity of phosphatases in technosols afforested with N-fixing and non-N-fixing tree species, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4005, https://doi.org/10.5194/egusphere-egu21-4005, 2021.

Land cover, productivity and carbon stocks are among the widely acknowledged indicators of the land’s degradation and development status. The indicators’ assess-ability, however, differs across global ecosystems and location. Despite the complexity of carbon stocks, soil carbon in particular is receiving increasing attention for its potential in both climate change mitigation and economic growth in developing carbon markets. 
The degraded drylands of Jordan have been targeted by multiple investment programs to rehabilitate their arid agro-pastures, including through the application of mechanized micro-water harvesting structures combined with the plantation of native shrub seedlings. Whilst both local and remote land cover and biomass change monitoring indicate variable rehabilitation success, the related carbon stock changes remain largely under-investigated and unclear.
An international research consortium designed and implemented a study to investigate the actual and potential future carbon stocks per ecosystem status at an agro-pastoral research site located in central Jordan’s ‘Badia’, considering both conventionally managed (degraded) and rehabilitated lands. Field experiments conducted by scientists and  local and former tribal community collaborators were combined with carbon modeling using RothC. This enabled the development of multiple scenarios considering both natural and enhanced, or human induced, processes; for example, through landscape modification (mechanized micro-water harvesting), vegetation plantation as well as optional soil amendment through biosolids. Preliminary results suggest that the implementation of water harvesting structures leads to a pronounced increase in soil carbon sequestration when compared to baseline conditions of between 15% and 45% over a 5 year period , with work ongoing to quantify the uncertainties around these results. The selected rehabilitation scenarios match the criteria for vast potential upscaling across global drylands. The study outcomes will eventually support a comprehensive ecosystem services valuation approach with (soil) carbon as an integral factor and moving towards reversing degradation and crediting the dry ecosystem’s values beyond their marginal agricultural services.

How to cite: Hall, L., Haddad, M., Strohmeier, S., Rawashdeh, H., Bani-Hani, N., Al-Widyan, J., Hasan, H., and Sterk, G.: Carbon stock changes through dryland rehabilitation: a case study from central Jordan’s agro-pastures, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15998, https://doi.org/10.5194/egusphere-egu21-15998, 2021.

Sand transport is the main manifestation of sand damage in the arid and semiarid desert regions globally. It is still a challenge for ecologists to stabilize mobile sandy and to change them into stable productive ecosystems. The establishment of stimulated shrubs is one of the most effective measures as a novel sand-barrier. Meanwhile, it has a beautiful visual effect in deserts. To better understand its role in the process of ecological restoration, we conducted a wind tunnel experiment to analyze the overall characteristics of soil grain-size variation of different spatial configurations with simulated shrubs in row spaces under different net wind speeds. The results present that the average grain-size content was dominated by medium sand and fine sand, and the total percentage was more than 90%. The average grain-size content for other soil grain-size was almost the same and the proportion was less than 10%. Moreover, the sand deposition of simulated shrubs with different spatial configurations increased with the improvement of wind speed. And the average sand deposition of spindle-shaped simulated shrubs in 17.5×17.5cm and broom-shaped simulated shrubs in 17.5×26.25cm under different wind speeds was the least. There was less variation of the soil grain-size parameters among different spatial configurations of stimulated shrubs, row spaces, and net wind speeds. The effects of row spaces on average grain-size parameters would be improved with the increase of wind speed. By calculating the “correct” characteristics of any specific shelter device, all of these findings suggest that the application of the simulated shrubs will be an important component to further extend ecological engineering projects in arid and semiarid desert regions.

How to cite: Pan, X., Wang, Z., Gao, Y., Meng, Z., Dang, X., and Han, Y.: Variation in Grain-size Characteristics of Stimulated Shrubs As a Novel Sand-barrier in a Wind Tunnel Experiment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1560, https://doi.org/10.5194/egusphere-egu21-1560, 2021.

The South-American palm Acrocomia aculeata has great potential as a sustainable source for vegetable oils, but its industrialization implies the production of huge amounts of organic waste. Currently, this material and in particular the endocarp is mostly used for energy generation, but this traditional method is very inefficient because a considerable part of the energy is lost.  An environmentally more sustainable use may be its conversion into biochar, via pyrolysis. This material has recently gained considerable interest as a strategy to recycle agro-industrial waste by its conversion into a soil amendment with a high carbon sequestration potential. In addition, biochars derived from woody feedstocks show  high porosity and low biochemical degradability which may turn them into suitable alternative to peat as planting substrate in horticulture. Although the woody nature of the shells (endocarp) of Acrocomia represent a promising candidate for such porous biochars, this alternative has been widely neglected up to now. Therefore, in a first attempt a physical and chemical characterization of these residues and their biochars was performed and its suitability as growing substrate for tomato cultivation was evaluated. By analyzing biochars derived from feedstock with different particle size, we tested if aside from the pyrolysis conditions and the nature of the feedstock, the size of the latter may affect the nature of the pyrolyzed product.

Our results confirmed the increase of aromaticity with increasing pyrolysis temperature which has already been described for other organic feedstocks. The heat increase the pH only moderately (pH= 8.4 at 450°C). NMR spectroscopic analysis confirmed that this was caused mainly by the the selective enrichment of cations rather than by the loss of acid C groups. However, tomato plants prefer a soil pH around 6 to 6.8 which turns the biochar produced a 325°C with a pH = 7.2 into a more suitable growing substrate. Statistical analysis did not reveal a significant impact of particle size of the feedstock on chemical composition or pH of the resulting biochar. Comparably,  greater feedstock particle size did not affect the specific surface area of the biochars but considerably decreased the water holding capapcity. 

The Olsen-P increased from 39 mg kg^-1 for the natural sample to 81 mg P kg^-1 for the biochar produced at 450°C. K and Mg concentration were 2.6 g kg^-1 and 279 mg kg^-1 for the biochar yielded at 450°C.  For tomato plant cultivation, Sainju et al., (2003) recommended for P, K and Mg, 60 to 70 mg  kg^-1, 0.6 -0.7 g kg^-1. 0.4-0.7 g kg^-1.  Thus, with respect to those nutrients, the obtained biochar can provide sufficient macronutrients if used as a growing substrate for tomatos. However, due to the low N contents of the biochars, sufficient N fertilization – either by addition of mineral or organic fertilizers - is still required if such materials are intended to be used as growing substrate in tomato cultivation.

Acknowledgement: Financial support was provided by MINECO/FEDER (CGL2015-64811-P)

Sainju, U.M., Dris, R., Singh, B., 2003. Mineral nutrition of tomato. Food, Agric. Environ. 1, 176–184.

How to cite: León Ovelar, R., Fernández-Boy, M. E., and Knicker, H.: Characterization of the residue (endocarp) of Acrocomia aculeate and its biochars as potential peat substitute in tomato cultivation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3224, https://doi.org/10.5194/egusphere-egu21-3224, 2021.

Anaerobic digestion (AD) of organic wastes is a promising alternative to landfilling for reducing greenhouse gas emission and it is encouraged by current regulation in Europe. AD represents a source of green energy, while the by-product digestate still generates concerns for a safely disposal. The sustainability of AD plants partly depends on the management of digestion residues. Digestate could be used in organic amendment straightaway or after composting to limit possible phytotoxicity effects on crops. This study has been focused on the environmental benefits of digested olive mill wastewater (OMW), recalcitrant agricultural waste. OMW require a complex management due to high production volume in a limited time, fermentative processes occurring during the storage, and toxicity due to phenol compounds. These latter might compromise the AD process affecting microbial metabolism. As biochar is able to adsorb and retain organic and inorganic pollutants, we used biochar as additives during AD to remove phenols, stimulate microbial activity and therefore hydrogen and methane production. The resulted digestates including biochar could be used in order to increase the carbon stock in soil as a valid alternative to other organic amendments.

The aim of this work was to evaluate the effect of solid and liquid digestates, obtained from the AD process of OMW with biochar (30 and 45%), as additive, on soil chemical and biochemical properties in order to validate its use in organic amendment in lab-scale experiment. The liquid and solid digestates were added to soil according to the maximum dose allowed by the Italian nitrates directive concerning non-vulnerable areas (91/676/EEC, DGR 209/2007). Pots containing soil differently amended with liquid and solid digestates were prepared also for the growth of Lactuca sativa L. seedlings.

Thirty days after treatments, positive changes in chemical and biochemical properties in soil pots with biochar-treated digestates, in particular with liquid ones, occurred. Soil organic carbon, microbial biomass carbon and some soil enzymatic activities such as dehydrogenase, phosphomonoesterase, β-glucosidase and fluorescein diacetate hydrolysis significantly improved. Besides an enhancement of lettuce biomass, a significant decrease of nitrate content in plant tissue was registered when pots were amended with biochar-treated digestates.

The assessment of the agronomic quality of liquid and solid digestates, obtained by biochar assisted AD of OMW, as organic soil amendment, demonstrated that also critical biomass such as OMW, if opportunely treated, can entry in a re-use process where biogas and by-products can be part of virtuous circular economy.

This work was part of the project “Mitigation of the environmental impact of olive mill waste water through sustainable bioprocess with energy recovery” funded by the Università degli Studi di Napoli Federico II.

How to cite: Di Rauso Simeone, G., Cesarano, G., Micoli, L., Toscano, G., Turco, M., and Rao, M. A.: Chemical and biochemical changes in soil after biochar-treated OMW digestate amendment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10407, https://doi.org/10.5194/egusphere-egu21-10407, 2021.

In the context of global soil degradation, biochar is being promoted as a potential solution to improve soil quality, besides its carbon sequestration potential. Burying biochar in soils is known to effect soil physical quality in the short-term (<5 years), and the intensity of these effects depends on soil texture. However, the long-term effects of biochar remain largely unknown yet and are important to quantify given biochar’s persistency in soils. The objective of this study was therefore to assess the long-term effect of biochar on soil physical properties as a function of soil texture and biochar concentration.  For this purpose, soil physical properties (particle density, bulk density, porosity, water retention and hydraulic conductivity curves) were measured in the topsoil of three fields with former kiln sites containing charcoal more than 150 years old in Wallonia (southern Belgium).  The fields had a silt loam, loam and sandy loam texture.  Samples were collected along 3 transects in each field, from the center of the kiln sites outwards. 

Particle density and bulk density slightly decreased as a function of charcoal content. Because particle density and bulk density were affected to a similar extent by charcoal content, total porosity was not affected by the presence of century-old charcoal. Regarding the soil water retention curve, charcoal affected mostly water content in the mesopore range. This effect was strongest for the sandy loam. On the other hand, the presence of century-old charcoal increased significantly the hydraulic conductivity at pF between 1.5 and 2 for the silt loam, while no effect of charcoal was observed for the loamy soil.  The study highlights a limited effect of century-old charcoal on the pore size distribution (at constant porosity) and on the resulting soil physical properties for the range of soils and charcoal concentrations investigated here.  Further research may be needed to confirm the observed trends over a wider range of soil types. 

How to cite: Zanutel, M., Garré, S., and Bielders, C.: Long-term effect of biochar on soil physical properties of agricultural soils with different textures, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8588, https://doi.org/10.5194/egusphere-egu21-8588, 2021.

Soil surveys are critical for maintaining sustainable use of natural resources while minimizing harmful impacts to the ecosystem. A key soil attribute for many environmental parameters, such as CO2 budget, soil fertility and sustainability, is soil organic matter (SOM), and its sequestration. Soil spectroscopy is a popular method to assess SOM content rapidly in both field and laboratory domains. However, the SOM source composition differs from soil to soil and the use of spectral-based models for quantifying SOM may present limited accuracy when applying a generic approach for SOM assessment. We therefore examined the extent to which the generic approach can assess SOM contents of different origin using spectral-based models. We created an artificial big dataset composed of pure dune sand as a SOM-free background which was artificially mixed with increasing amounts of different organic matter (OM) sources obtained from commercial compost of different origins. Dune sand has high albedo and yields optimal conditions for SOM detection. This study combined two methods: partial least squares regression for the prediction of SOM content from reflectance values across the 400–2500 nm region, and soil spectral detection limit (SSDL) to judge the prediction accuracy. Spectral-based models to assess SOM content were evaluated with each OM source as well as with a merged dataset that contained all of the generated samples (generic approach). The latter was concluded to have limitations for assessing low amounts of SOM (<0.6%), even under controlled conditions. Moreover, some of the OM sources were more difficult to monitor than others; accordingly, caution is advised when different SOM sources are present in the examined population.

How to cite: Francos, N., Ogen, Y., and Ben-Dor, E.: Spectral assessment of organic matter with different composition using reflectance spectroscopy , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-190, https://doi.org/10.5194/egusphere-egu21-190, 2020.

The conversion of tropical forest for cassava cultivation is widely known to decrease the soil organic matter (OM) and nutrient contents of highly weathered soils in the tropics. Amazonian Dark Earth (ADE) might be more resistant to this process due to their historical anthropogenic amelioration with e.g. charcoal, ceramics and bones, leading to higher soil OM and nutrient concentrations. In this study, we analyzed the effect of land use change on the OM dynamics under tropical conditions and how this is related with P distribution at the microscale, using ADE and an adjacent Acrisol (ACR) as model systems. Soil samples were obtained south of Manaus (Brazil), from a secondary forest and an adjacently located 40-year-old cassava plantation. The land use change induced a severe decrease of organic carbon (OC) concentrations in ADE (from 35 to 15 g OC kg^‑1) while OC in the adjacent ACR was less affected (18 to 16 g OC kg^‑1). The analysis by ¹³C NMR spectroscopy showed that the conversion of secondary forest to cassava changed the chemical composition of OM to a more decomposed state (increase of alkyl:O/N-alkyl ratio) in the ADE whereas the OM in ACR changed to a less decomposed state (decrease of alkyl:O/N-alkyl ratio). According to neutral sugar and lipid extraction analyses, land use change led to a larger impact on the microbial-derived and plant-derived compounds in the ADE compared to the ACR. In order to analyze the interactions of OC and P at the microscale, we conducted an incubation experiment with ¹³C glucose for the analysis with Scanning X-ray Microscopy (SXM) and Nano scale Secondary Ion Mass Spectrometry (NanoSIMS). In both soil types ADE and ACR, land use change caused a reduction of the total ¹³C glucose respiration by approximately one third in a 7-days incubation, implying lower microbial activity. Microorganisms in both soil types appear to be more readily active in soils under forest, since we observed a distinct lag time between ¹³C glucose addition and respiration under cassava planation. This indicated differences in microbial community structure, which we will be assessed further by determining the ¹³C label uptake by the microbial biomass and the microbial community structure using ¹³C PLFA analysis. Preliminary results from synchrotron-based STXM demonstrate a distinct arrangement of OM at fine-sized charcoal-particle interfaces. From ongoing NanoSIMS analyses, we expect further insights on the co-localization of P and ¹³C-labelled spots at the microscale. Despite the high loss of OC in the ameliorated ADE through land use change, the remaining OM might foster nutrient dynamics at the microscale thanks to charcoal interactions compared to the ACR. Our results contribute to a better understanding of the C and P interactions and how these respond to land use change in highly weathered tropical soils.

How to cite: Jarosch, K. A., Colocho Hurtarte, L. C., Gavazov, K., Westphal Muniz, A., Müller, C., Angst, G., and Schweizer, S.: Consequences of land use change on soil organic matter composition and C-P relationships in Amazonian Dark Earth and Acrisol, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15580, https://doi.org/10.5194/egusphere-egu21-15580, 2021.