There is an international commitment to monitor soil, as reflected in the new EU soil monitoring law on 5^th July 2023.  However, direct measurements of soil properties, such as water retention, cation exchange capacity, adsorption isotherms etc. are expensive and time-consuming. Pedotransfer functions (PTFs) utilize soil properties that are easy to measure and inexpensive as predictors of these critical soil parameters. Clay content plays a crucial role in the estimation of many PTFs.  However, it is often universally estimated by particle size, which fails to capture the diversity of clay mineral types which exhibit markedly different and diverse effects on the physico-chemical behaviors of soils^{1, 2}.  Non-clay minerals often constitute a significant portion of the clay size fractions. Furthermore, clay minerals may not disperse and instead remain in larger size fractions, further complicating the understanding of the effects of clay. The crucial question arising is: “How should we quantify clay content”? We have devised a predictive modelling framework that combines soil spectroscopy analysis, which is more widely available in soil databases worldwide, with X-ray Powder Diffraction (XRPD). This approach serves as a method for predicting the clay 'mineral' content, providing a  much more useful predictor of soil properties. The 703 soil samples from the National Soil Inventory of Scotland 2007-2009 (NSIS2)³ with both high-quality XRPD and IR spectral data are used to develop a predictive model for quantifying clay mineral content from MIR spectroscopy by correlating the spectral data to the quantitative assessment of clay minerals from XRPD (reduced using powdR package in R) using Machine Learning (ML) techniques (e.g., Cubist, Random Forest). Our current study attempts to answer two key scientific questions: 1. Can spectra data in the MIR region, combined with ML algorithms, accurately predict mineral clay concentrations generated from XRPD? 2. Which machine learning proves most effective in developing a national-scale calibration model for prediction?

References:

[1] Schmitz, R.M., Schroeder, C., Charlier, R., 2004. Chemo – mechanical interactions in clay : a correlation between clay mineralogy and Atterberg limits 26, 351–358. doi:10.1016/j.clay.2003.12.015

[2] Six, J., Conant, R.T., Paul, E.A., Paustian, K., 2002. Stabilization mechanisms of soil organic matter: Implications for C-saturation of soils. Plant Soil 241, 155–176. doi:10.1023/A:1016125726789

[3] Lilly A, Bell JS, Hudson G, Nolan AJ, Towers W. 2011. National Soil Inventory

of Scotland 2007-2009: Profile description and soil sampling protocols. (NSIS_2). Technical

Bulletin, James Hutton Institute. DOI: 10.5281/zenodo.7688040.

How to cite: Ghosh, U., Afriyie, E., Abd Elmola, A., Hillier, S., Robertson, J., and Baggaley, N.: How should we measure clay?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1058, https://doi.org/10.5194/egusphere-egu24-1058, 2024.

Potassium (K) is an essential macronutrient that takes part in a wide variety of processes in the plant,
from enzymatic activity to cell development and osmotic balance. Excess K has a minor effect on the plant,
mostly due to imbalanced nutrition. Accurately determining K requirements for optimal growth and high
fertilizer utilization efficiency is therefore challenging, and often results in excess fertilizer application. It
is customary to refer to four soil K reservoirs which vary greatly in their size and availability to the plant:
(1) soil solution is the smallest and the one from which plants uptake K, (2) exchangeable - K adsorbed
onto clay mineral surfaces, oxides and organic matter (1-2%), (3) interlayer - K fixed between clay mineral
sheets (up to 10%), and (4) structural K – most commonly found in K-feldspar and usually considered
unavailable to the plant (90-98%). The interlayered - K is a dynamic and important pool that may supply
K for the plant in case of K deficiency, or act as a sink by fixing excess K.
Fertilization recommendations often relay on soil tests that estimate the exchangeable-K pool. The
common paradigm is that exchangeable K represents the capacity of the soil to supply plant-available-K.
In alkaline soils, however, there is a growing number of studies from both short- and long-term experiments
(several growth seasons to a few decades), reporting little to no response to K fertilization, indicating that
the soils supply greater amounts of K than indicated the exchangeable K tests. These findings evoke
questions regarding the intrinsic soil K reservoirs and the extent to which the natural supply of K to the
soils from weathering or dust deposition, readily supply K to plants.
In this study, we examine the affect of different K-bearing mineral phases (soil K pools) on the soil K
cycle and K availability to the plant. Our study focusses on intensively used agricultural soils in Israel that
vary in their clay compositions- illite and illite-smectite and K-feldspar. We think that illite and illite-
smectite are instrumental in buffering the excess K fertilizer that we observe in short- and long-term
experimental plots. Over time, we suggest, that agriculturally driven enhanced weathering of the illite and
K-feldspar releases significant amounts of K, that had been previously considered unavailable. Taking into
consideration the abundance of these mineral phases in the regional dust, we further suggest that dust
deposition and location along the regional dust gradient play a significant role in replenishing and
maintaining soil K levels.

How to cite: Zaarur, S. and Erel, R.: The effect of soil mineral composition on K availability to plants, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21838, https://doi.org/10.5194/egusphere-egu24-21838, 2024.

Zinc (Zn) is an essential trace element for human nutrition as well as for plant growth and soil organisms. Cadmium has similar biogeochemical properties like Zn, but is non-essential for most biota and highly toxic. Due to the on the heterogeneous arrangement of soil mineral phases and organic compounds within a functional soil architecture, there is a lack of knowledge on how the microscale arrangement is interrelated with ecosystem-relevant soil functions such as the storage and cycling of nutrients and contaminants. Here, we present an analytical approach aiming to resolve the spatial distribution of Zn and Cd in a soil at the microscale. Zn and Cd were supplemented in three increasing concentrations to an arable soil from the Jura region, Switzerland. Our image-based investigation was obtained using a dual primary ion source workflow by Nanoscale secondary ion mass spectrometry (NanoSIMS) combining the Cs⁺ and the RF plasma O⁻ source. The dual workflow enabled correlating the distribution of Zn and Cd with Fe, Al, Si, P, Mg, Ca, S, C and N at a lateral resolution of 120nm. Our observations indicate a high co-localization of Zn and Cd hotspots, whereas these were not related with organic matter patches. Of the three mineral phases identified using a machine-learning image segmentation, most areas were occupied by Al-dominated regions followed by Si-dominated and Fe-dominated parts. Across the increasing supplementation, the Zn and Cd hotspots were preferably co-localized to mineral phases in the following order: Fe-dominated > Al-dominated > Si-dominated. With increasing Zn and Cd supplementation, the Cd/Zn ratio as well as the N/C ratio decreased indicating changes in the biochemical composition of . Our model soil approach illustrates how the spatial arrangement of essential and toxic trace elements at the microscale regulates their fate in the soil. The developed NanoSIMS-based dual primary ion source workflow enables emerging opportunities to characterize how environmental changes affect the spatial distribution of nutrients and contaminants in dynamic soil architectures.

How to cite: Schweizer, S. A., Bachelder, J., Hoeschen, C., Frossard, E., and Wiggenhauser, M.: The spatial distribution of Zn and Cd across the soil microscale architecture as mediated by different mineral phases in a supplemented arable soil, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20847, https://doi.org/10.5194/egusphere-egu24-20847, 2024.

Formation of ferromanganese nodules (FMNs) is an important pedogenic process which is commonly observed in the Ganga alluvium. We have studied geochemistry of the host alluvium and FMNs from the eastern Uttar Pradesh, India. The FMNs were categorized in three sizes (>5.6mm, 5.6 to 2mm, and 2 to 0.5mm). The major and trace elements present in the sediments and FMNs of three size ranges were analysed using XRF and ICP-OES. The geochemical composition of the sediments and FMNs were compared with the geochemical values of the Upper Continental Crust (UCC). The enrichment factor (EF) of the analysed elements were calculated for both the host sediments and the FMNs. Additionally, the Chemical index of weathering (CIA) was calculated to quantify the extent of chemical weathering of the sediments and FMNs in the alluvium. The sediments and FMNs both showed moderate chemical weathering. We propose that the weathering of aluminosilicate stages may have given Fe, Mn, and related trace elements for the nodule formation. Prolonged dry spells and monsoonal wet seasons in the Ganga plain region may be key contributors to the weathering, mobilization, precipitation, and redistribution of the Fe and Mn phases in nodules. Certain elements, such as Pb and Cr, which are considered to be harmful to the environment got sequestered in FMNs. This helped immobilization of these contaminants. Whereas, elements like P, Co, Zn, and Cu were also got sequestered during the formation of FMNs. Therefore, it has also impacted soil nutrient availability.

How to cite: Kumar, A., Sharma, D., and Tripathi, J. K.: Elemental mobilisation and redistribution during the ferromanganese nodule formation in the sediments of Ganga plain, India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2822, https://doi.org/10.5194/egusphere-egu24-2822, 2024.

The effect of a naturally occurring soil mineral, pyrite, on the degradation of 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) by Fenton process with micro scale zero-valent iron (ZVI) as the catalyst was studied in batch reactors. Our batch data show that while the CP degradation with ZVI/H₂O₂ system was adversely affected by the aggregation of ZVP particles, the use of pyrite in systems containing ZVI/H₂O₂ greatly improved the oxidative degradation of CPs. Surface measurements, including salt titration, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), revealed that the ZVI particles and surface oxidation precipitates dispersed on pyrite particles, thus preventing ZVI particle aggregation, and subsequently promoting iron redox cycling for enhanced ZVI corrosion and surface site regeneration. Following Fenton degradation, the oxidative degradation intermediate species of CPs became significantly more biodegradable relative to their mother compounds. Overall, combining ZVI and pyrite at the optimum dose might be a cost-effective technology for developing novel treatment methods for the treatment of groundwater and wastewater contaminated with chlorophenolic chemicals.

How to cite: Kantar, C., Oral, O., and Yildiz, I.: Role of pyrite on oxidative degradation of some chlorophenolic compounds with zero-valent iron/H2O2 system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-236, https://doi.org/10.5194/egusphere-egu24-236, 2024.

The abundance of short-range order (SRO) iron and aluminum minerals with high phosphorus (P) binding capacity makes this essential nutrient a major limiting factor for agriculture in tropical volcanic soils. These reactive minerals also possess a significant capacity to form organo-mineral associations, thereby contributing to stabilizing soil organic carbon. Adding organic amendments can enhance P use efficiency in volcanic soils due to the competitive effect of organic ligands with P for the adsorption on the surfaces of SRO minerals. Here, using two tropical volcanic soils from Costa Rica with low (LR) and high (HR) mineral reactivity, we assessed the effect of short-term incubations with compost at various rates (0%, 5%, and 20% m/m) on the solubility of different P fractions (measured as P-Olsen and P-CaCl₂). Additionally, we determined P adsorption isotherms to evaluate changes in the adsorption behavior of this nutrient. Furthermore, in a bioassay using Sorghum bicolor as a model plant, we investigated the potential influence of compost addition on the agronomic efficiency of P fertilizers in these volcanic soils.

The results of the incubation experiment showed that the addition of organic matter mostly affected the desorption of the P pool related to the capacity (Q) factor of soils (measured as P-Olsen), whereas the P intensity factor (I) (measured as P-CaCl₂) remained mostly unchanged. The I factor was significantly increased only at the highest rate of compost addition in the LR soil. Description of the adsorption isotherms using the Langmuir equation revealed changes in the adsorption behavior of P due to the addition of compost. The maximum P adsorption capacity (Q_max) of the soils decreased as the amount of added organic amendment increased, particularly in the HR soil. The binding affinity of P (K_L) to the mineral surfaces was also reduced due to the compost addition, and this effect was more pronounced in the HR soil. Lastly, higher agronomic efficiencies of P fertilizers were measured when compost was incubated in the HR soil, whereas in the LR soil the agronomic efficiencies of P fertilizers were unaffected by the compost addition. This study contributes to unraveling how the competitive interaction between organic ligands and P is modulated by the mineralogical properties of volcanic soils, particularly due to the reactivity of SRO minerals. Overall, our results indicate that the addition of organic amendments can be an effective alternative to improve P availability in soils with abundance of SRO minerals. From a broader perspective, adding organic amendments to soils with high P binding capacity would result in a “win-win” situation that contributes to improving the use efficiency of this limited resource while promoting the C storage in soils.

How to cite: Mendez, J. C. and Vargas, E.: Organic amendment addition distinctly influences phosphorus solubility in tropical volcanic soils with different mineralogical properties, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-183, https://doi.org/10.5194/egusphere-egu24-183, 2024.