Displays

Conservation or regenerative agriculture, i.e. reduction of mechanical soil disturbance, introduction of crop rotations, and especially cover crops as a form of natural soil amendment, has been shown to increase soil organic matter contents as well as soil health. One mechanism behind the increase in organic carbon under regenerative agriculture could be an increase in microbial biomass, as well as an enhanced carbon use efficiency (CUE) of the soil microorganisms in these systems. Such changes in microbial biomass and activity could also influence soil nitrogen (N) cycling. Here we show first results of on-farm research at four sites in Austria comparing crop fields under regenerative agriculture practices with conventional practices, and nearby perennial grasslands at each site. The four sites span different climate gradients, soil types and textures.

Soil organic carbon (SOC) content ranged from 1 to 2.3% in the agricultural soils and was significantly higher under regenerative management compared to conventional practices in two out of four sites. SOC contents in perennial grasslands were up to 5% and always higher than in agricultural fields. Extractable organic carbon was similar in the two agricultural fields of the respective site, while grasslands diverged. Microbial biomass carbon was highest in grasslands at all sites and significantly higher in fields under regenerative agriculture compared to conventional agriculture at three out of four sites.

Total nitrogen was highest in perennial grasslands at all sites, and similar in regenerative and conventional fields. The form of N however differed between soils under conventional and regenerative agriculture. Dissolved N, expressed per g total N was significantly higher or tended to be higher in conventional compared to regenerative agricultural fields. From this dissolved pool a higher proportion was in inorganic N forms that are more prone to leaching and gaseous loss compared to organic N forms. In soils from regenerative agricultural fields a higher proportion of the total N was found in the microbial biomass. This pool is considered to be highly dynamic, but also protected against losses. Less N in dissolved and inorganic form as well as a higher proportion of N in the microbial biomass indicates that the N cycle is more closed in soils managed regeneratively versus conventional.

A greater importance of the microbial biomass could also have effects on soil C cycling. Higher microbial biomass is often related to increased carbon use efficiency, which in turn could indicate increased soil carbon sequestration. The already mentioned results will thus be discussed with further measurements of microbial respiration, growth and CUE.

How to cite: Schnecker, J. and Bodner, G.: Impacts of conservation agriculture on soil nitrogen pools and microbial physiology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4706, https://doi.org/10.5194/egusphere-egu2020-4706, 2020.

 Cover crop cultivation is strongly recommended during fallow season to increase soil organic carbon (SOC) stock. However, since its biomass recycling as green manure can dramatically increase greenhouse gas (GHG) emission, in particular, methane (CH₄) during rice cropping season, smart cover crop management strategy should be developed. In our previous research, CH₄ emission during cropping season was dramatically reduced via short-term aerobic decomposition before irrigation (Lee et al.). However, due to a fast response rate of aerobic decomposition, the effect of mitigating CH₄ emission could be offset by SOC depletion which results in accelerating global warming. To evaluate the comprehensive impact of the short-term aerobic decomposition on global warming, net global warming potential (GWP), defined as the difference between GWP and SOC stock change was employed. SOC stock change was estimated using net ecosystem carbon budget (NECB), a balance between soil C input and output. The mixture of barley and hairy vetch cultivated during the dried fallow season, and then its whole biomass was incorporated 0-30 days before irrigation for rice transplanting. The aerobic decomposition of cover crop biomass significantly reduced CH₄ emission by 24-85% over control but negligibly influences N₂O emission. Total C input and output were unaffected by the aerobic digestion. Although carbon emission before flooding dramatically increased after biomass application in aerobic decomposition treatments, the mineralized C losses exhibited no differences among treatments. Based on these results, NECB values were similar in all treatments. This implies the aerobic decomposition did not stimulate SOC depletion, compared to the control. Finally, the net GWP highly decreased by 30-86% by the aerobic digestion due to the significant reduction of CH₄ emission. In conclusion, earlier application of cover crops before irrigation is a smart strategy to decrease methane emission, maintaining soil carbon sequestration effect of cover crop biomasses application.

How to cite: Song, H., Lee, J. H., Cho, S., Chae, H., and Kim, P. J.: Strong mitigation of net global warming potential (GWP) via short-term aerobic pre-digestion of green manured soil in rice paddy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3779, https://doi.org/10.5194/egusphere-egu2020-3779, 2020.

Biochar and nitrogen (N) fertilizers are frequently applied to improve soil properties and increase crop productivity. However, it remains unclear how root plasticity, soil enzyme activities, N and (phosphorus) P cycling in plant-soil system are changed after application of biochar, N or their combination. To address these questions, left and right parts of rhizoboxes were filled with silty-clay loam subsoil amended with biochar (15 g kg^-1 soil, wheat straw, 300 °C), N (0.05 g KNO₃-N kg^-1 soil) or a control (no amendments), resulting the following combinations (Cm): biochar/control (Cm1), N/control (Cm2) and biochar/N (Cm3). One seed of maize (Zea mays L.) was planted in the middle of each rhizobox, thus allowing roots to choose freely the growth direction. Root growth was quantified by a photographic approach constantly during the experiment (30 d), and soil enzyme activities, available N and P, root morphology and plant biomass were analyzed after plant harvest.

Maximum plant biomass was found for biochar/N application (0.91 g), whereas minimal values was for biochar/control (0.56 g). At the same time, decreased soil bulk density and increased availability of P in the biochar compartment (Cm1 and Cm3) stimulated root length by 1.4-1.8 times – an effect which was independent from the presence of N in the same rhizobox. Together with stimulated activities of ß-glucosidase and leucine aminopeptidase (by 33%-39%) in presence of biochar (Cm3) compared to N, this shows the coupling of C, N and P cycles in biochar/N treated soils. Application of N (Cm2) also increased ß-glucosidase activity compared to control soil, whereas root elongation stayed unaffected. Thus, combined application of biochar/N over-win benefits of biochar or N alone for plant growth, which is linked with i) the stimulation of microbial enzyme activity at the biochar locations to reduce C and N limitation for both plant and microorganisms, and ii) increasing of fine root proportion to improve N utilization efficiency in the N-treated compartment. Thus, strategy of combined biochar/N application can not only improve the above-ground biomass production, but also increase root-microorganism interactions to overcome nutrient limitation in low fertile agricultural soils.

How to cite: Song, X., Razavi, B., Ludwig, B., Zamanian, K., Zang, H., Kuzyakov, Y., Dippold, M., and Gunina, A.: Can combined application of biochar and nitrogen promote microbial functions and root plasticity for plant growth in low-fertile soils?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-672, https://doi.org/10.5194/egusphere-egu2020-672, 2020.

Due to the low consistency of the results obtained in field, the use of biochar as soil amendment is controversial. Thus, in general in acidic soils results are positive while in alkaline soils they are non-significant or even negative. The results regarding biochar action in acidic soils have been related to a lime-like effect due to its alkaline pH and the high doses normally used. However, the causes of biochar effects in alkaline soils remain unknown. We have used a well characterized biochar as a component of two complex N and PK granulated fertilizers at two different doses (1 and 5%). These fertilizers have been applied to wheat cultivated in pots containing an alkaline and calcareous soil and grown for 60 days. No effect was shown for the N-biochar fertilizer application. However, the PK-biochar fertilizer application caused a decrease in crop yield. Complementary, the absorption isotherms of Iron (Fe), Molybdenum (Mo), Manganese (Mn) and Phosphate (Pi) in biochar were also studied. The results showed that Fe was rapidly adsorbed in biochar, while Pi was only absorbed on the Fe-Biochar complex. Desorption experiments showed that P and Fe were no desorbed from the P-Fe-biochar complex by water or the Olsen reactant, while a partial desorption was observed when HCl 0.1 M was used. This blockage of Fe and P through Fe bridges in biochar could partially explain the negative effects in alkaline soils.

How to cite: Baigorri, R., Urrutia, Ó., San Francisco, S., and García-Mina, J. M.: The chemical interaction of biochar with iron and phosphate might explain the effects of biochar in alkaline and calcareous soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5384, https://doi.org/10.5194/egusphere-egu2020-5384, 2020.

The two primary problems currently facing agriculture are drought and the availability of mineable phosphorus minerals used for fertilization. More frequent and longer drought periods are predicted to threaten agricultural yields in future. The capacity of soils to hold water is a highly important factor controlling drought stress intensity for plants during the growing phase. High phosphorus availability in soils is necessary for high agricultural yield. For both drought and phosphorus availability in soils amorphous silica (ASi) has been suggested to be able to mitigate these problems. Amorphous silica pools in natural soils are in the range of 0-6%. However ASi pools have declined in agricultural soils since the development of high intensity agriculture to values of <1% due to yearly crop harvests, decreasing water the holding capacity of the soils. Here, we analyzed the effect of ASi on the water holding capacity (WHC) of soil and how the ASi effects the mobilization of phosphorus.  ASi was mixed at varying rates with different soils. Afterwards, the retention curve of the soils was determined. Here we show that ASi increases the soil water holding capacity substantially, by forming silica gels with a water content at soil saturation higher than 700%. An increase of ASi by 1% or 5% (weight) increased the water content at all studied water potentials and plant available water increased by >40% and >60%, respectively. Additionally, we fertilized soils with ASi and measured phosphorus mobilization from the solid phase into the soil pore waters. We found a strong mobilization of phosphorus by ASi. In a lysimeter experiment we found that ASi strongly increased the WHC of soils. Furthermore, as expected from the batch experiments the ASi is decreased phosphorus sorption to soil minerals and consequently increased its mobilization. Our results suggest that ASi addition to soils enhances the water availability, potentially decreases drought stress for plants as well as increasing phosphorus mobility in soil of terrestrial ecosystems.

How to cite: Schaller, J., Gilfedder, B., and Frei, S.: Amorphous silica increases the water holding capacity and the phosphorus mobility in soils - solving the two main problems of agriculture, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6926, https://doi.org/10.5194/egusphere-egu2020-6926, 2020.

Applying digestate to soil is of growing interest in agriculture. However, the impacts of digestate on soil biogeochemical cycles often remain unclear, especially after solid-liquid separation of whole digestate (WD). We used a 21 d incubation to examine the effects of WD and solid digestate (SD) on CO₂-C efflux, dissolved organic carbon (DOC), microbial biomass C (C_micro), phospholipid fatty acid (PLFA) and carbon use efficiency (CUE) within two grassland soils of contrasting nutrient status. Application rates for SD and WD were based on recommended N inputs to grassland soils for these organic materials. Compared to un-amended controls, cumulative CO₂-C efflux, C_micro and the fungal:bacterial in soils increased significantly following SD application, regardless of the soil nutrient content (+20% CO₂-C, +29% C_micro, +58% fungal:bacteria for high nutrient soil; +563% CO₂-C, +36% C_micro, +18% fungal:bacteria for low nutrient soil). In contrast, WD produced a significant effect on CO₂-C efflux and fungal:bacterial only in the low nutrient soil. Our results also indicated that both digestate fractions and the initial soil nutrient status affected CUE. Applying both SD and WD to a low nutrient soil potential leads to decreases in soil C stocks, whilst the application of SD to a high nutrient soil can potentially enhance soil C stocks. Digestate application must be carefully planned, accounting for both the nature of the digestate and of the soil, in order to avoid adverse impacts on soil C stocks.

How to cite: Cattin, M., Semple, K. T., Stutter, M., Romano, G., Lag-Brotons, A., Parry, C., and Surridge, B. W. J.: Application of Different Fractions of Anaerobic Digestate Significantly Influences the Carbon Cycle in Grassland Soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9510, https://doi.org/10.5194/egusphere-egu2020-9510, 2020.

Soil carbon (C), nitrogen (N), and phosphorus (P) contents and their stoichiometric ratios play modifying the microbial metabolism of C. Microbial populations vary in their strategies for C and nutrient acquisition to maintain the microbial biomass C:N:P balance. However, the regulation of soil C mineralization and microbial activities by stoichiometric ratios in input substrates becomes unpredictable in flooded soils because of the frequent redox fluctuations and general oxygen limitation. Stoichiometric control on input substrate (glucose) and soil organic carbon (SOC) mineralization were assessed by a manipulation experiment based on N or P fertilization in paddy soil. Glucose mineralization increased by nutrient addition up to 11.6% with combined N and P applications compared with addition without nutrients. During 100-days incubation, about 4.5% of SOC was mineralized in all five treatments, being increased by glucose and reduced by P fertilization. Glucose and SOC mineralization increased exponentially with the dissolved organic carbon (DOC):NH₄⁺-N, DOC:Olsen P, and microbial biomass (MB)C:MBN ratios. The glucose mineralization was negatively associated with the MBC:MBP ratio, suggesting that P addition relieved P limitation for microorganisms and increased microbial activities of labile C mineralization. The shift of bacterial community structure was significantly affected by the soil available and microbial biomass C:N:P stoichiometric ratios. The decrease of negative associations between bacterial taxa in the P-added soil indicated that microbial competition for nutrients was alleviated. 16S rRNA amplicon sequencing showed that combined C and nutrients application stimulated the Clostridia and β-Proteobacteria (r strategists) and increased the enzyme activities of β-glucosidase and β-acetyl-glucosaminidase. In contrast, after 100-day incubation, when the available substrate was exhausted, Syntrophus (K strategist) was found as the keystone species. Hence, soil microbial communities shifted their keystone species to acquire necessary elements to maintain the microbial biomass C:N:P stoichiometric balance in response to the change of resource C:N:P stoichiometry.

How to cite: Zhu, Z., Wei, X., Ge, T., wu, J., and Richter, A.: C:N:P stoichiometry regulates soil organic carbon mineralization and concomitant shift of microbial community in paddy soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8512, https://doi.org/10.5194/egusphere-egu2020-8512, 2020.

Taking into consideration economic viability, the doses of manure compost in Taiwan are recommended as 1% to 2%; however, some farmers apply more than 2% to 5% in intensive cultivation periods for short-term leafy crops, to add more N. Although many studies report positive effects of a biochar-compost mix on soil properties and plant growth, but there are no studies that have determined the changes in N availability over time after biochar (BC) application in compost over-applicated soil. In the present study, in vitro N mineralization kinetics were examined in further. We tested the hypothesis that BC addition may diminish mixed-soil N mineralization, enhance ammonium retention, reduce nitrate leaching, and decrease P and nutrients loss in compost over-applicated soils. The aim of our research was to evaluate the N and nutrient regulation or enhancement role of different BC addition rates in three compost over-applicated soils over time. The effect of four rates (0%, 0.5%, 1.0%, and 2.0% w/w) of BC co-applied with swine manure compost (5.0% w/w) on three Taiwan rural soils (topsoil, slightly acid Oxisols (SAO), mildly alkaline Inceptisols (MAI), and slightly acid Inceptisols (SAI)) was investigated during 371-d incubation study. BC was produced from lead tree (Leucaena leucocephala (Lam.) de. Wit) at 750 degree C. The incubation results indicated that soil, rate and interaction between soil and rate significantly influenced soil NO3-N and total inorganic N concentrations, but only soil significantly influenced soil NH4-N concentration. Soil NH4-Nand NO3-N concentrations on average during a 371-day incubation followed the order: SAO soil > SAI soil > MAI soil. In most cases the effect was insignificant and inconsistent in terms of time and rate of BC application, rendering it difficult to summarize the effects of BC on ammonium of our investigated soils. The negative effect of BC was prominent almost in all investigated soils during the incubation period and the amount of decline increased as the rate of BC application increased from 0.5% to 2%. In addition, only soil significantly influenced all Mehlich 3-extractable nutrient concentrations, and rate significantly influenced M3-K concentration. At the end of the incubation, adding 0.5% BC and 1.0% BC in SAI soil and 1.0% BC and 2.0% BC in MAI soil both had positive improvement on the nutrients (P, K, Mg, Fe and Mn), and application of BC in SAI soil led to improvement in Cu and Pb (2.0% BC), Zn and N mineralization (0.5% BC and 1.0% BC). In conclusion, the studied results confirmed the potential of biochar-compost blend is promising for preventing excess N and nutrients loss in compost over-applicated soil, as well as maintaining SOC. As adding a large amount of biochar in open fields would be unrealistic and not economically sustainable, we suggested that adding 0.5%~1.0% woody BC to three studied soils should be reasonable and appropriate.

How to cite: Tsai, C.-C. and Chang, Y.-F.: Nitrogen availability in biochar-amended soils with excessive compost application, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-51, https://doi.org/10.5194/egusphere-egu2020-51, 2020.

Due to the chemical composition and surface properties of biochar, a C-rich porous material produced by pyrolysis of biomass, it can act as an effective tool for the remediation of soils polluted with trace elements [1, 2]. However, its capacity to sorb these contaminants in a solution varies considerably depend on pyrolysis conditions, but also on the feedstock.  Thus, the major aim of this study is to evaluate the capacity of biochars from two crop residues to sorb Pb²⁺ and Cu²⁺.

For this purpose, rice husk and olive pit biochars (RHB and OPB, respectively) were produced in a continuously feed reactor (Pyreka reactor, max. temperature 500 ºC, residence time 12 min; N₂ atmosphere).

The efficiency of lead and copper ions (Pb²⁺, Cu²⁺) removal by the biochars was investigated through batch adsorption experiments. 20 mL of single-metal solutions with 0.05, 0.1, 0.5, 1, 2 and 5 mM of initial concentration of Pb²⁺ and Cu²⁺ were mixed with 20 mg of milled biochar during 48 h. After filtering at 0.45 µm, their concentrations were measured by ICP-OES (Varian ICP 720-ES, Varian Inc., CA, USA).

Removal efficiency of both heavy metals was over 80 % for RHB and OPB when the initial cation concentration was ≤ 0.5 mM. RHB removal capacity was 26 % for Cu²⁺ and 35 % for Pb²⁺ when the initial concentration of metal was 5 mM, whereas OPB removal capacity for both cations was lower than 20 %. The adsorption data fitted well to a Langmuir model for both cations for RHB as other authors found [3]. Although, the Langmuir maximum sorption capacity obtained in this work for Cu²⁺ was similar to that obtain by Samsuri et al. (2014) [3], it was lower for Pb²⁺. However, sorption data for OPB better fitted to a Temkin isotherm model for Cu²⁺ and Freundlich model for Pb²⁺.

The selection of the adequate biomass to produce biochars for the immobilization of trace elements, as Pb and Cu, in soils is very important, due to the huge differences in their adsorption efficiency. RHB showed a greater removal efficiency for Cu²⁺ and Pb² than OPB.

References:

[1] Uchimiya, M., Klasson, K.T., Wartelle, L.H., Lima, I.M., 2011. Chemosphere 82, 1438-1447.

[2] Zhao, J., Shen, X.-J., Domene, X., Alcañiz, J.-M., Liao, X., Palet, C., 2019. Sci. Rep. 9, 9869.

[3] Samsuri, A.W., Sadegh-Zadeh, F., She-Bardan, B.J., 2014. Int. J. Environ. Sci. Technol. 11, 967.

Acknowledgements:

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

How to cite: De la Rosa, J. M., Sánchez-Martín, Á., Sánchez-Martín, M. L., Hagemann, N., Knicker, H., and Campos, P.: Application of biochar from crop residues for the removal of lead and copper, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2662, https://doi.org/10.5194/egusphere-egu2020-2662, 2020.

Since peatlands are valuable habitats and provide important environmental services, the policy of several European countries is to decrease the use of peat in potting mixtures to preserve peat bogs as nature areas. As a consequence, alternative growing media are needed. Therefore, the impact of biochar addition to gardening soil on tomato plant growth has been investigated previously (García de Castro Barragán, 2018). Those studies revealed a positive effect on seed germination and plant development during the first growing stage. However after three months, leaf discoloration was observed and associated to the lack of macro or micronutrients. It was hypothized that adsorption of nutrients onto the biochar may have decreased their availability for plants. For a first evaluation of this hypothesis, we tested the adsorption of Cu²⁺ to three biochars derived from feedstocks with different chemical composition, aromaticity and content of polar groups.  We produced biochar from shrimp chitin which was highly aromatic and contained considerable amounts of N-heterocyclic aromatic structures. The biochar of shells of the oil seed of Acrocomia aculeata derived from a woody feedstock with high contribution of cellulose, but had a low charring degree. The peat biochar was prepared at a pyrolysis temperature of 500°C which resulted in a highly aromatic material.  The difference in the organic matter (OM) quality of the biochars went along with differences in their pH and electrical conductivity (EC); elemental composition and ash content. Concomitantly, different specific surface areas were measured using the BET method.

For the absorption test, copper nitrate solutions were used at increasing concentration, brought into contact with the biochar for 24 hours at 25 °C. In the equilibrium solution, the Cu²⁺ content was analyzed. The solid biochar was separated from the solution and dried. Due to the paramagnetic nature of Cu²⁺, solid-state NMR relaxometry was used to identify preferential adsorption sites within the organic network of the biochars.

Our results showed low Cu²⁺ adsorption for all three biochars. Neither biochar porosity, nor polarity could be identified as a responsible for Cu-adsorption. As revealed by NMR relaxation times (T_1H, T_1C, T_1rohH and T_1rohC), all organic C and H groups were affected by the interactions between OM and Cu²⁺, although no preferential adsorption site was revealed. We found indications that adsorbed Cu²⁺ act as bridging agent, lowering the mobility of aromatic domains. Based on our preliminary results, we suggest that in our biochars, metals are mainly adsorbed via bonding to π-orbitals of the aromatic rings. Based on the low adsorption potential of the studied cation, we conclude further that our biochars do not sequester Cu²⁺ (or other metals with comparable characteristics) sufficiently strong for preventing their uptake by growing plants. However, to which extend our findings may be generalized, has to be unveiled by ongoing studies.

How to cite: Knicker, H., Garcia Castro de Barragan, J. M., Elena Fernandez-Boy, E., Knicker, M., León-Ovelar, R., and Velasco-Molina, M.: Do chemical characteristics affect the potential of biochars to adsorb cations?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3075, https://doi.org/10.5194/egusphere-egu2020-3075, 2020.

Suitability of organic materials as growing media in plant production is dependent on physical properties of the media. Undecomposed Sphagnum moss growing media is an innovative and potentially more sustainable alternative to the commonly used peat-based media. However, the physical properties of the moss media are not comprehensively understood. Furthermore, amending the growing media with biochar has the potential to sequester carbon and enhance the properties of the receiving substance, but biochar impacts on organic growing media properties remain unknown.

This study aimed to (1) quantify differences in water retention, aeration and pore structure properties of three different low- or non-humified Sphagnum-based growing media with 3D X-ray imaging and conventional physical measurements, (2) determine impacts of intense drying-wetting cycles on their pore structure. Furthermore, we aimed to (3) quantify the 3D pore structure of three different plant-based biochars and (4) demonstrate their impact on moss growing media physical properties.

The drying of the media occurred in three distinct phases with (1) large changes in the air-filled porosity in the suction range 0.2-3.2 kPa, (2) clearly smaller changes in 3.2-312 kPa and (3) again large changes in 312-1585 kPa. In the phases 2 and 3, the aeration of the media was satisfactory for plant growth, but the amount of easily available water was low. This sets challenges for the suitability of the materials in conditions without regular irrigation. These properties of the moss media were comparable to the peat media. The pore structure of the media was not sensitive to drying-wetting cycles, but the pore size distributions was observed to shift slightly towards smaller pore size classes with increasing decomposition degree and stress impact of the drying-wetting cycles.

Regarding biochar physical properties, the 3D imaging results demonstrated that irrespective of the feedstock, the major share (0.80-0.94 m³ m^-3) of the biochar pore volume resided in pores with diameters 2-11 µm. Biochar pore properties reflected plant tissue structure of the raw materials. The application of biochar increased the water retention of the growing media in the pore diameter range 1-8 µm. The maximum increase was 0.06 m³ m^-3. This is relevant for plant-available water, which indicates the usability of the biochar amendments.

From methodological point of view, the value of combining 3D imaging with conventional measurements was shown. The approach revealed how water table continuum between biochar and surrounding growing media affect availability of water stored inside the biochar particles.  The results are based on a recently published article (Turunen et al. 2019) and an accepted manuscript (Turunen et al. 2020).

References:

Turunen, M., Hyväluoma, J., Heikkinen, J., Keskinen, R., Kaseva, J., Koestel, J. and Rasa, K., 2019. Quantifying Physical Properties of Three Sphagnum-Based Growing Media as Affected by Drying–Wetting Cycles. Vadose Zone Journal, 18:190033. doi:10.2136/vzj2019.04.0033

Turunen, M., Hyväluoma, J., Heikkinen, J., Keskinen, R., Kaseva, J., Hannula, M. and Rasa, K., 2020. Quantifying the pore structure of different biochars and their impacts on the water retention properties of Sphagnum moss growing media. Accepted for publication (Biosystems Engineering).

How to cite: Turunen, M.: Pore structure of different biochars and their impacts on physical properties of Sphagnum moss growing media, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8567, https://doi.org/10.5194/egusphere-egu2020-8567, 2020.

Biochar is a carbon-rich material obtained from the process of biomass pyrolysis. Due to its desirable properties, it is discussed as a soil amendment to improve soil quality; for example, adding biochar can change soil water retention by modifying soil textural and structural properties. However, the optimal fabrication conditions and proportions of biochar particles sizes, that would improve soil properties are still not precisely known. In our research, we investigated the influence of grain size and a dose of biochar on water retention of sandy soil. For this purpose, water retention curves (pF) were measured, as it indicates such important properties as plant available water, field water capacity, wilting point. The studies were carried out on podzol soil samples taken from meadow located in Sekow, Poland, mixed with different percentage mass content of sunflower husk biochar produced in 650-750°C (0.95, 2.36, 4.76 and 9.52% of sample weight). Samples contain one of biochar granulometric fraction: 250-100, 100-50 or less than 50 µm. The control included soil samples with the addition of mixed fractions of biochar and soil without biochar. The research method we used allows obtaining information about plant available water content by comparing differences in water content between 0.06 and 5 bar pressure points which corresponding to a 1.85-3.7 pF. In this range, most plants can use water for their growth and development. Our results revealed that, surprisingly, soil with all fractions of biochar reduces the amount of available water for plants compared to the control (soil without biochar), regardless of the biochar dose applied. However, fractionated biochar can both increase or decrease the soil water content, depending on the particle size and dose. Small doses of sunflower husk biochar (0.95 and 2.36%) and the finest fraction (<50μm) have the most beneficial effects for water retention of investigated soil. Our research may strongly suggest the biochar producers that the production of biochar with the right fraction may be more favourable for increasing soil water retention. 

Research was partially conducted under the project “Water in soil - satellite monitoring and improving the retention using biochar” no. BIOSTRATEG3/345940/7/NCBR/2017 which was financed by Polish National Centre for Research and Development in the framework of “Environment, agriculture and forestry” – BIOSTRATEG strategic R&D programme.

How to cite: Rafalska-Przysucha, A., Szlązak, R., Vitková, J., Gluba, Ł., Lukowski, M., Szewczak, K., and Usowicz, B.: How do grain size and dose of sunflower husk biochar influence the water retention of sandy soil?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4760, https://doi.org/10.5194/egusphere-egu2020-4760, 2020.

Every year agricultural soils lose significant amounts of nitrogen (N) over winter through N leaching and gas emissions as a result of freeze-thaw cycles. The incorporation of carbon amendments after harvest, such as crop residues or other carbon rich material, can help to promote soil microbial growth, and in doing so, immobilise N within the microbial biomass. It is still unclear which amendments are most effective at promoting microbial N immobilisation and at what time they should be incorporated into the soil to give best results.

In order to investigate this, we measured soil microbial biomass carbon (C_mic) and -nitrogen (N_mic) at 12 timepoints between harvest and spring in soils from an established agricultural field experiment in Kiel (Germany). We selected plots which had the same fertilisation regime and crop rotation (Faba bean-winter wheat-winter barley rotation) but differed in soil carbon amendment treatment; removal of residues (control), wheat straw, faba bean, and sawdust.  In addition to microbial biomass measurements, we measured microbial nutrient limitation at each timepoint via substrate induced respiration, in order to give a qualitative indication of microbial activity in respect to growth limiting nutrients.

Our data show that there was little effect of wheat straw in comparison to the control on the microbial biomass carbon or -nitrogen, but different patterns were observed for the latter amendments. C_mic generally decreased over time after harvest in all treatments, but again the decreases were less pronounced in the faba bean and sawdust treatments. N_mic decreased over time after harvest in control and wheat straw treatment but increased with time in the faba bean and sawdust treatments, suggesting improved N immobilisation by the microbial biomass for these treatments. We found that all soils were nearly always N limited throughout the winter and were never P limited. However, a shift to C limitation was observed after addition of fertiliser in spring, except for in the sawdust treatment, which remained N limited despite the addition of mineral N in the field. This result suggests that sawdust has a higher potential for N immobilisation compared to the other soil amendments.

In summary, there was little difference in the microbial post-harvest dynamics between the control and wheat straw treatments but stronger effects were observed in the faba bean and saw dust treatments, which suggested improved microbial N immobilisation. Interestingly, the sawdust amendment seemed to have the highest potential for microbial N immobilisation over winter and enduring into spring.

How to cite: Clayton, J., Rothardt, S., Reichel, R., and Bonkowski, M.: Effect of different soil carbon amendments on the post-harvest dynamics of soil microbial biomass carbon and -nitrogen in an agricultural field experiment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-867, https://doi.org/10.5194/egusphere-egu2020-867, 2020.

Plant survival and growth are greatly affected by moisture and nutrient loss around root zones. Water and nutrient retaining agents such as hydrogels have been gaining popularity to solve this problem, but most commercial hydrogels are composed of non-biodegradable and synthetic components.  In this study, we successfully prepared hydrogels made of biodegradable pectin and naturally-occurring calcium bentonite. The synthesized hydrogels contained varied loadings of fertilizer (equivalent to 0, 0.2, 0.6, and 0.85 g NPK L^-1 soil). We characterized the hydrogels in terms of morphology (scanning electron microscopy/SEM), nutrient P and K concentration (X-ray fluorescence/XRF analysis), and degree of swelling in water (gravimetric method). We also determined the nutrient retention capacity and release of the hydrogels using a soil column leaching setup coupled with periodic monitoring of conductivity and total dissolved solids of column leachate. 

SEM indicates the porous structure of the hydrogels, while XRF confirms the successful loading of fertilizer in the hydrogels. The hydrogel at 0.2 g NPK L^-1 soil has the highest degree of swelling in the water at 692.5%. The nutrient retentions of soil columns containing fertilizer-loaded hydrogels (0.2, 0.6, and 0.85 g NPK L^-1 soil) are greater by 35.5, 11.5, and 20.1%, respectively, compared to the control (soil column without hydrogel). Our measurements of fertilizer release rate also indicate that the presence of hydrogel in the soil column slows down the release of fertilizer as detected in the column leachates. We conclude that the pectin/calcium-bentonite hydrogels are effective in retaining water and reducing the release of fertilizer from the soil. With the biodegradability of pectin and natural occurrence of calcium bentonite, the hydrogel has the potential for sustainable management of slow-release fertilizer systems. 

How to cite: Pajarito, B., Kho, J. A., Mayo, R., Ong, J. S., and Jovellana, J. A. K.: Slow-release of fertilizer in soil using pectin/calcium-bentonite hydrogel, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2268, https://doi.org/10.5194/egusphere-egu2020-2268, 2020.

Abstract: Cr⁶⁺ adsorption by modified vermiculite

Valeria Medoro- University of Ferrara , Department of Physics and Earth Sciences, Italy

Celia Marcos Pascual-University of Oviedo, Department of Geology, Spain

Giacomo Ferretti- University of Ferrara , Department of Physics and Earth Sciences, Italy

Giulio Galamini- University of Ferrara , Department of Physics and Earth Sciences, Italy

Massimo Coltorti- University of Ferrara , Department of Physics and Earth Sciences, Italy

This work aimed at investigating the adsorption of Cr⁶⁺ in water by exfoliated vermiculite. The adsorbant tested in this experiment was a vermiculite (from China) which has been subjected to heating at 1000 °C for 1 minute, resulting in an exfoliated vermiculite.

Three effects were studied: 1) contact time; 2) initial concentracion of Cr⁶⁺; 3) adsorbent mass. Samples were analysed by X Ray Fluorescence (XRF), X Ray Diffraction (XRD) and the solutions with Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to quantify the adsorbed Cr⁶⁺ by the vermiculite.

Results from XRD diffraction showed a conversion of vermiculite into flogopite  after heating at 1000°C for 1 minute because of: 1) high content of potassium, 2) dehydration and 3) structural re-ordering; after the contact of vermiculite with Cr⁶⁺, the mineral structure did not change. The adsorption of Cr⁶⁺ was studied by Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich (DKR) isotherm models. DKR model, indicative of a cooperative process, described adsorption equilibrium better than the other two models and the maximum adsorption capacity obtained was of 2.81 mol/g. Kinetic was studied using pseudo-first and pseudo-second order kinetic models, with a better description of the process by pseudo-second order model with correlation coefficient almost unitary (R²=0.9984; other kinetic parameters were k₂=0.0015 and the absorption initial rate of 0.2x10^-8 mg g^-1 h^-1). 

The present study demonstrates the effectiveness of modified vermiculite adsorbents for the treatment of hexavalent chromium-contaminated waters and that its adsorption depends on the experimental conditions (such as contact time, initial concentracion of Cr⁶⁺ and adsorbent mass).

How to cite: Medoro, V., Marcos Pascual, C., Ferretti, G., Galamini, G., and Coltorti, M.: Cr6+ adsorption by modified vermiculite, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1394, https://doi.org/10.5194/egusphere-egu2020-1394, 2020.

Combined application of induced MAP (Magnesium Ammonium Phosphate) precipitation and adsorption through natural zeolites for reducing NH₄⁺ and PO₄^3- in swine wastewaters

Nicola Tescaro*1, Giulio Galamini1, Giacomo Ferretti1, Barbara Faccini, Negar Eftekhari, Massimo Coltorti

* Corresponding author

1) Department of Physics and Earth Science, University of Ferrara, Ferrara Via Saragat 1 44122, Italy.

Modern agriculture, in response to the constantly increasing need of high crop production, requires application of high levels of N and P fertilizers to soil. These substances are mainly composed by nutrients such as NH₄⁺ and PO₄^3- and are often applied in strong excess in order to assure high crop yield. The nutrients applied through fertilizers and not exploited by crops (estimated on average around 50%) can considerably impairs  environmental quality through nitrogen losses in atmosphere (N₂O, NO_x, NH₃) and eutrophication of water bodies.

In this work, a new method for reducing NH₄⁺ and PO₄^3- in swine wastewaters (commonly used as organic fertilizer) was studied. The aim is to reduce their environmental impact and concomitantly create a new slow-release fertilizer.

Two techniques have been combined: the induced MAP precipitation (magnesium ammonium phosphate) and natural zeolite ammonium adsorption for removing the NH₄⁺ excess that generally remains in solution after MAP precipitation. Given the complexity of working with real wastewaters, in this preliminary phase a synthetic analogue was used in order to better evaluate the efficiency of this method. Two synthetic wastewaters with different Mg²⁺ : NH₄⁺ : PO₄^3- molar ratio were tested:  MR1 (1:1,5:1) and MR2 (2:1:1), which according to the literature give the best reductions of NH₄⁺ and PO₄^3-.  Since swine wastewater are naturally rich of both NH₄⁺ and K⁺, isotherm studies were conducted on natural zeolites for evaluating their adsorption capacity of NH₄⁺ under different levels of K⁺ competition. Results showed that  the potential in NH₄⁺ adsorption decreased while competition with K⁺ increased.  The combination of MAP precipitation and NH₄⁺ adsorption by natural zeolite has been tested in 2 ways: 1) zeolite was added before inducing MAP precipitation 2) zeolite was added after inducing MAP precipitation.  These two treatments were compared to a blank in which only MAP precipitation technique was used.

The amount of NH₄⁺ and PO₄⁺ was monitored in various steps during the experiments as well as  SEM observations were conducted on precipitated obtained. Results showed that adding zeolites before MAP precipitation induce a variation in the  Mg²⁺ : NH₄⁺ : PO₄^3- ratio due to cation exchange processes before MAP precipitation which introduce interfering ions such as Ca²⁺ favoring calcium phosphates precipitation instead of MAP. The best test conditions, which produced the 75,1% of NH₄⁺ and 99,9% of PO₄^3- reductions, occurred when zeolites have been added after MAP precipitation using the MR2.  This new material obtained  combines good N and P concentration and have therefore potentialities to be a high-quality slow-release fertilizer.

How to cite: Tescaro, N., Galamini, G., Ferretti, G., Faccini, B., Eftekhari, N., and Coltorti, M.: Combined application of induced MAP (Magnesium Ammonium Phosphate) precipitation and adsorption through natural zeolites for reducing NH4+ and PO43- in swine wastewaters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3436, https://doi.org/10.5194/egusphere-egu2020-3436, 2020.

The use of natural sorbent geomaterials, like zeolitites (rocks containing > 50% of zeolites) is recognized as a valid method to recover N in the form of ammonium ions (NH₄⁺) from Zootechnical Wastewaters (ZoWs).

Using zeolite-rich tuff as N sorbent from ZoWs lead to varius advantages like the decrease in environmental impact of ZoWs (decreased N content) and the subsequent creation of a high-value soil amendment employable also in organic agriculture (NH₄-charged zeolite-tuff).

In order to understand the characteristics of NH₄-charged zeolites (CZ) as sorbent, it is mandatory a deep investigation on their sorption dynamics when they react with ZoWs. Scientific literature is rich of studies about sorption in sintetic solutions (especially NH₄CL) while it lacks studies about sorption in real ZoWs.

The aim of this work was therefore to characterize the NH₄ sorption dynamics of a chabazite zeolite tuff from swine manure. In particular, two grain sizes were selected, a micronized (< 125 µm, CHAµ) and a granular one (0.7-2.0 mm, CHAg). A series of batch experiments were performed to investigate the effects of temperature, contact time and grain size on sorption of NH₄. Equilibrium data were fitted with appropriate isothermal models; kinetic models were also investigated to characterize the kinetik sorption reactions and the thermodinamic parameters like change in free energy (ΔG), enthalpy (ΔH) and entropy (ΔS).

Results have shown a significant grain size effect with respect to the equilibrium loading (qe), with better performances for CHAµ in all the temperatures investigated; the isothermal data showed that the influence of temperature is less for CHAµ with respect to CHAg.

The kinetic data differs from the two grain size investigated, in particular CHAg showed an initial external surface adsorption and macropore diffusion during the first 60 minutes of contact, then the diffusion occurs also inside the micropores. The Intraparticle Diffusion model (ID) for CHAµ showed that the diffusion in the macropores are much more fast than CHAg and the intercept indicates the formation of a boundary layer thicker than CHAg. Pseudo-second-order kinetic model well explained CHAg behavior but not that of CHAµ. Both grain sizes were well explained by Elovich equation wich is a model used to explain the sorption kinetics for energetically heterogeneous solids surfaces (as likely the surface of the zeolite-tuff employed).

Thermodinamic data showed that the energy in the liquid-solid adsorption surfaces increased during adsorption (ΔH ˃ 0), thus the cation exchange reaction needs energy from the liquid phase.

The free standard entropy change (ΔS) is also positive, indicating that the NH₄ sorption is a directional process with no significant differences with respect to the tested temperatures and that the randomness at the solid-solution interface increased during adsorption.

The negative values of Gibbs free energy (ΔG) indicates that the NH₄ sorption is an exergonic process (spontaneous reaction).

How to cite: Galamini, G., Ferretti, G., Medoro, V., Tescaro, N., Faccini, B., and Coltorti, M.: Ammonium adsorption by chabazite zeolite-tuff from swine manure for soil amendment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17916, https://doi.org/10.5194/egusphere-egu2020-17916, 2020.

Abstract

Mining is an important industrial sector in Bangka Island (Indonesia) where about 70% of this area is tin mining. The separation of tin via flotation of tin-containing soils results in acidic nutrient-poor soils with very low organic matter contents. Hence, ex-tin mined areas are highly and unsuitable for plant growth due to their un-fertility. To improve soil fertility soil amendments are of vital importance. This research aims to evaluate the impact of different soil amendments on agricultural production and basic soil parameters on the ex-tin mined area.

The study was conducted on ex-tin mined area located in Bangka Regency, Indonesia (1^o47’22.9085 S and 106^o5’47.0461 E). Bangka Regency has a tropical climate with an average daily temperature of 27.2^oC, precipitation during the growing season is 191.5 mm per month. The field trial was set up in July 2018 by a randomized complete block design with five different soil amendments and control plots for comparison, with a size of 2 x 2 m in four replicates. The treatments consist of the: (1) Control, (2) Lime, (3) Compost; (4) Charcoal and combinations of (5) Charcoal and Compost, and (6) Charcoal and sawdust. The soil was amended with t.ha^-1 for the single amendments (treatments 2-4), and with rate 20 t.ha^-1 for combined amendments (treatments 5 and 6). The plots are used to grow cassava (Manihot esculenta) for 12 months as the main crop and Centrocema pubescens as used as a cover crop grown twice for 6 months to avoid soil erosion. Soil samples were taken before and after harvest to analyze soil properties. Soil samples were analyzed for the following parameters: pH, Dissolved Organic Carbon (DOC), and Electric Conductivity (EC). Crop yields were determined by weighing the total harvest of each crop per plot. The cover crop was harvested in December 2018, and replanted, until the main crop Cassava was harvested (30 July 2019), where the cover crop yield was also evaluated. Cassava yields were separated into belowground and aboveground yields.

Soil amendments showed positive effects on soil pH, DOC, and EC at harvest time. Lime treatment significantly improved soil pH and EC (7.40 and 72.30 µS.cm^-1 respectively), while DOC was significantly increased by compost treatment. Centrocema pubescens yields were significantly higher at the first harvest compared to the second one. The combined treatment with charcoal (10 t.ha^-1) + Compost (t.ha^-1) showed significantly the highest yield for both samplings. While another combined treatment, where, charcoal and sawdust was applied at 10 t.ha^-1 each, showed the highest total cassava belowground biomass (5.44 ton.ha^-1 ) as well as cassava aboveground biomass (3.06 ton.ha^-1).

Results of the present field experiment suggest that the application of soil amendments directly affected soil parameters. The effect on yields was positive but crop dependent, likely due to different nutrient requirements. Data on heavy metal uptake by plants regarding soil amendments will be presented. Soil amendments can provide the potential to improve food safety and security in the ex-tin mined area.

Keywords: ex-tin mined, soil fertility, soil amendments, soil parameters, crop yields

How to cite: Maftukhah, R., Ngadisih, N., Murtiningrum, M., Mentler, A., Keiblinger, K., Kral, R., and Gartner, M.: Soil Amendments to Re-establish Agricultural Production on Ex-tin Mined Area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21166, https://doi.org/10.5194/egusphere-egu2020-21166, 2020.

Among the essential plant nutrients, nitrogen (N) is the most needed. Farmer apply N fertilizer, predominantly urea to meet crop N demand. However, a greater proportion of the applied urea-N is not being used by plants and lost to the atmosphere as ammonia or greenhouse gases. Therefore, it is necessary to enhance N use efficiency (NUE) of applied urea by minimizing such losses, which has environmental and economic implications. Nitrification inhibitor, such as nitrapyrin (NP), has the most potential to minimise N losses and enhance crop yield. Similarly, plant hormones, such as GA3, has the potential to reduce abiotic stress and improve plant growth and yield.   
A field experiment was established on an arable site at University of Tehran, Karaj to determine the effect of urea applied with Nitrapyrin and GA3 on wheat yield in 2018-2019. Karaj has a Mediterranean climate with annual precipitation of 265 mm. A randomized complete block design in five replications was used in this study. Treatments were: T1 (control treatment - without urea), T2 (farmers practice - 138 kg N/ha), and T3 (best practice - 138 kg N/ha+NP+GA3). Urea was applied in three split applications (46 kg N/ha) at growth stage (GS 21) or tillering, (GS 32) or stem elongation, and (GS 40) or booting. GA3 in T3 treatment, was applied only at stem elongation stage. 
The crop yield data showed that, urea applied with NP and GA3 had a significant (p ≤ 0.01) effect on grain yield, biological yield, number of grains, 1000-grain weight and % Harvest Index (%HI) compared to other treatments. Urea applied with NP and GA3 increased grain yield (10.30 t ha-1) by 13.9% and 46.1% compared to farmer practices (9.04 t ha-1) and control treatment (7.05 t ha-1). These results suggest that co-application of urea with NP and GA3 has the potential to enhance wheat yield in semi-arid area of Iran.

How to cite: Mirkhani, R., Shorafa, M., and Zaman, M.: Wheat yield as influenced by urea applied with nitrification inhibitor and gibberellic acid , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4842, https://doi.org/10.5194/egusphere-egu2020-4842, 2020.

Land application of sewage sludge is an increasingly popular means of the reuse of sewage sludge as it allows for recycling of valuable components, such as organic matter, N, P and other nutrients. Indeed, sewage sludge amendment to the soil modifies the soil’s physico-chemical properties, such as plant-available macro/micro nutrient contents, organic matter content. Additionally, sewage sludge applications can significantly increase the amount of microbial biomass in the soil and can also increase the soil enzyme activities. The aim of the present study is to investigate the impact of low-dose municipal sewage sludge compost amendment on the nutrient status and the biological activity in Chernozem soils. 

The study area, located near Újkígyós (SE Hungary), is a 5.6 ha arable land, where 2.5 m³/ha/year municipal sewage compost has been regularly disposed since 2013. The pH (in H₂O) and humus content of soils were measured according to standard procedures. The macronutrients P₂O₅ and K₂O were extracted using ammonium-lactate, while the nitrogen forms (NO₂^- + NO₃^- -N) were extracted with KCl-solution. The nutrient content was then determined by a flow injection analysis photometer. In order to determine the bacterial composition and enzyme activity of the soil samples, the number of living cells (CFUs), the catalase enzyme activity (CAT) and the dehydrogenase activity (DHA) were determined. The CO₂ emission was measured by an EGM-5 Portable High Precision CO₂ Meter in the field.  

The sewage sludge compost applied to Chernozem soils improved soil properties by adding slowly decomposing organic matter, abundant in plant macronutrients (N, K, P). The anaerobic microorganisms and the DHA enzyme activity in the anaerobic soil layers did not increase in the compost-amended soils. The aerobic microorganisms (CFUs) and CAT activity tended to be higher in treated soils compared to the non-amended (control) site, however not significantly. These results suggest that the soil biological activity is only moderately affected by the low-dose municipal sewage sludge compost applications. According to our field CO₂ emission measurements, the yearly application of the sewage sludge compost in a low-dose seemingly did not affect the soil respiration rates, compared to a local control site.

The research was funded by the ‘Thematic Network for the Sustainable Use of Re-sources – RING2017’ project (program code: EFOP-3.6.2-16-201700010).

How to cite: Prof. Dr. Farsang, A., Dr. Perei, K., Bodor, A., Dr. Ladányi, Z., Csányi, K., Gombos, K., Dr. Babcsányi, I., and Dr. Barta, K.: Changes in soil nutrient content, biological activity and CO2 emission rate as a result of low-dose municipal sewage sludge compost application, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8959, https://doi.org/10.5194/egusphere-egu2020-8959, 2020.

The Twin Cities (Minneapolis and Saint Paul) of Minnesota (MN) in the United States incinerate sewage sludge for energy.  Every day at the Metropolitan Wastewater Treatment Plant, 650 million liters of wastewater are converted to an average of 5 MW of power and 32 MT of ash (SSA).  This ash is currently landfilled at a cost to taxpayers but contains 13% phosphorus (P), a limited natural resource required for all living things.  While some have reported that the P in this ash is unavailable for plant uptake, a previous greenhouse study of Twin Cities ash demonstrated that this SSA, as is, could be a safe and available source of P for corn and lettuce.  To follow up, we conducted three years of corn and soybean field studies from 2016-2019 in Rosemount, MN comparing various rates (0 to 180 kg P₂O₅/ha) of untreated SSA to equivalent rates (based on citrate soluble P) of triple superphosphate, a conventional P-only fertilizer, and two other residual products - Class A EQ (exceptional quality) biosolids and commercially available struvite.  Our objectives were to describe and compare responses from SSA and other P sources to assess the feasibility of SSA as an alternative agricultural fertilizer.  Response variables included harvest yield and plant and soil concentrations of P and other metals of concern.

Our results indicated that SSA as a soil amendment provided comparable amounts of P as the other P sources.  Final 2019 harvest yields in plots amended with SSA or any P source were significantly higher than control plots that had no P applied.  In 2017 and 2018, P uptake increased with increasing application rate, regardless of P source.  Similar trends were found within Bray-P and Olsen-P soil tests, which assess available soil P, and within buried ion exchange resin soil probes.  Except for copper (Cu) and zinc (Zn), no metal of concern was found to have increased significantly in either plant material or the soil.  Soil concentrations of Cu and Zn, but not plant concentrations, increased significantly with increasing rate in plots amended with biosolids and SSA but below levels dangerous to the environment or human health.  Taken together, we believe untreated SSA has the potential to be a safe and viable source of P and an additional option for returning a valuable natural resource to our food system.

How to cite: Ma, P. and Rosen, C.: How Available is Phosphorus from Sewage Sludge Incinerator Ash?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10042, https://doi.org/10.5194/egusphere-egu2020-10042, 2020.

Ceramsite is a typical substrate used in soilless culture systems. It is clean and durable but usually shows poor performance in water and nutrient retention capacity. In this study, we used reservoir sediment as the material to produce ceramsite to use as a growing medium. We sintered it under relatively low temperature (600°C, 800°C, and 1000°C) and anaerobic conditions with and without organic matter addition (5%, 10%, and 15%). We examined their water holding capacity, bulk density, mechanic strength, and pH, which were related to the essential characteristics using the growing media. The results showed that organic matter addition decreased bulk density and mechanic strength but increased water holding capacity and pH. The sintering temperature has less influence on bulk density and water holding capacity but increased mechanic strength and pH with the increasing sintering temperature. Compared with the commercial high-temperature ceramsite and lava rock, the water holding capacity in our ceramsite can be three times higher than those. The microstructure from scanning electronic microscopy indicated the rough surface in ceramsite at 600°C and 800°C but became glassy surface at 1000°C which was similar to the commercial ceramsite and lava rock that showed more glassy and non-porous surface. The addition of organic matter maintained rough surfaces at 1000°C, which can be the mechanism to have higher water and nutrient retention. Our results suggest that the ceramsite produced from reservoir sediment under lower temperature and anaerobic conditions with organic matter addition can be used as a growing medium to replace commercial ceramsite with its better water retention capability.

How to cite: Liu, Y.-H., Chu, Y.-H., and Cheng, C.-H.: Developing reservoir sediment ceramsite as a novel growing medium: I low temperature and anaerobic production, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22392, https://doi.org/10.5194/egusphere-egu2020-22392, 2020.

Over 36% of the arable area in England is at moderate to very high risk of surface sealing/crusting and erosion, including much of the better-drained and more easily worked land, especially sandy soils (Evans, 1990).

The intensive production of leafy greens consists of short growing cycles –between 21 and 28 days- and intensive seedbed preparation. From seeding to emergence, the bare soil is susceptible to rainfall and irrigation induced soil sealing. The direct consequence is an impeded seedling emergence, a delay in stand establishment and reduction in plant populations, with direct impacts on productivity. To avoid soil sealing, the grower is required to undertake additional field operations such as breaking the crust, applying supplementary low intensity irrigations or, in extreme cases, replanting crops, in a vicious cycle that spirals into soil structure degradation, loss of nutrients and further soil-sealing susceptibility.

Polyacrylamides (PAMs) are long-chained carbon polymers featuring an amide functional group that allows them to form bonds with an array of soil surfaces. The efficacy of PAMs to stabilise soil aggregates and prevent soil splash, capping and erosion has been documented for >25 yrs. Further, it has been demonstrated that PAMs consistently outperform bio-polymers and other synthetic alternatives. However, a technological innovation is required to effectively spray PAM on to the soil surface as typically PAM’s become extremely viscous when mixed with water making conventional spray application un-viable. This research investigates the efficacy of a dual-fluid nozzle to apply PAM to the soil surface. Conventional applications  to mitigate soil sealing are either in powder form or diluted within the sprinkle irrigation system and are effective at application rates ranging from between 10 and 20 kg ha^-1[SR1] (Levy et al. 1992). However, the powdered form is extremely susceptible to wind drift, and the sprinkle irrigation alternative is severely limited by the amount of water required to deliver the same amount of product.  Initial nozzle calibration results indicate that PAM can be applied at rates of 13-20 kg ha^-1 using 110-150 litres of water ha^-1 instead of 1000 m³ ha^-1(Levy et al. 1992). Subsequently, the effect of three PAM formulations with contrasting molecular weight and charge density were tested on a crust susceptible soil. Soil microcosms were subjected to two consecutive simulated rainfall events, representing pre-emergence conditions of field grown leafy salads. Treatment performance was assessed in terms of degree of crust formation. This was quantified by assessing pre and post rainfall changes in Soil Surface Roughness (SSR) using a Creaform HEXAScan laser scanner at 0.20 mm resolution, in infiltration rate using a Decagon Devices minidisk infiltrometer, and in crust penetrative resistance with a 3 mm diameter probe using an Instron 5542 tension and compression testing machine.

How to cite: Arpano, S., Simmons, R. W., and Deeks, L. K.: The efficacy of a novel polyacrylamide spray application method to mitigate soil crusting and enhance seedling emergence on crust susceptible soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22515, https://doi.org/10.5194/egusphere-egu2020-22515, 2020.

Reservoir sedimentation is an environmental issue that can be substantially detrimental to the lifetime of reservoirs. In this study, we tried to develop the ceramsite made from reservoir sediment and used it as a growing medium. Different from the traditional method, we sintered the material at a lower temperature (800^oC) under an anaerobic atmosphere. The low-temperature ceramsite might provide higher water and nutrient retention capacity compared to the high-temperature ceramsite. The anaerobic atmosphere could preserve organic matter as biochar, which may offer better water and nutrient retention capacity as well. Pot experiments using the low-temperature ceramsite along with commercial high-temperature ceramsite (1200^oC) and lava rock as the growing media were conducted. Two species Tagetes erecta and Melissa officinalis under the full water supply and limited water supply (100 ml per pot per week) conditions were planted. The results showed that the plants grown in low-temperature/anaerobic ceramsite had the best agronomic performance. Under the full water supply, the shoot height was higher in the low-temperature ceramsite than other treatments. The height was 45.8 - 48.2 vs. 16.28 - 18.73 cm in Tagetes erecta and 15.1 - 18 vs. 7.65 - 9.4 cm in Melissa officinalis. The dry weight in the low-temperature ceramsite was 5-10 times higher than those in other treatments after four months of growth. Under the water-limited condition, the plants are grown in the low-temperature ceramsite still performed better on shoot height (Tagetes erecta: 25.05 - 30.88 cm and Melissa officinalis: 14.08 – 14.75 cm) and dry weight (Tagetes erecta: 1.03 - 1.5 g and  Melissa officinalis: 0.67 – 0.89 g). The results suggest that the low-temperature/anaerobic ceramsite has the potential using as a novel growing medium and a new option for treating reservoir sediment.

How to cite: Chu, Y.-H., Liu, Y.-H., and Cheng, C.-H.: Developing reservoir sediment ceramsite as a novel growing medium: II pot experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22393, https://doi.org/10.5194/egusphere-egu2020-22393, 2020.

Industrial hemp as a renewable raw material for fiber extraction like for construction material or as biomass for energy generation is a potential agricultural product for low productive soils in temperate climates. Soil and climate conditions in Lower Lusatia, South Brandenburg, generally qualify this region suitable for growing industrial hemp. But due to the nutrient requirements of the plants, fertilization is necessary for optimal growth. Fertilization on sandy soils is, however, often problematic, since the groundwater risk is increased by the entry of nitrogen and phosphorus from the fertilizer supply. In addition, the costs of fertilizers make resource-efficient and sustainable use of the locations problematic. The liquid phase obtained in the course of municipal composting would be a suitable fertilizer in terms of nutrient concentrations, but due to the potential risk to groundwater, the use of the liquid phase from composting is currently not feasible. The aim of the project is the development of a closed cultivation system for industrial hemp using hydroponics, whereby sand and pelleted soil additives from composting are used as a supporting substrate. Nutrients from the liquid phase from the municipal composting will be used as fertilizer. The cultivation will take place under controlled conditions (light, temperature, watering water and leachate) in a glasshouse experiment. A mixture of sand and pelletized soil additives is to be tested as a plant substrate in various additional amounts. The sandy substrate is representative for the soils in Lower Lusatia. The use of pelletized soil additives in combination with the liquid phase from municipal composting is an innovative process and on the one hand contributes to the development of a new sales market and on the other hand promotes the local and resource-saving use of recyclables in the sense of the circular economy. The use of hydroponics is a promising process that can be used regardless of the climate and without endangering soil and groundwater.

How to cite: Hirsch, F., Matvejeva, A., Dietrich, N., and Raab, T.: Cultivation of industrial hemp using solid and liquid residues from municipal composting , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19138, https://doi.org/10.5194/egusphere-egu2020-19138, 2020.