Soil Syst., Volume 8, Issue 2 (June 2024) – 15 articles

The Somma–Vesuvius volcanic complex emitted huge quantities of volcanic materials over a period from before 18,300 years BP to 1944. The activity during the last period, from post-AD 1631 to 1944, primarily produced lava and pyroclastics via effusive and strombolian eruptions. We investigated the pedogenesis on rocks formed from post-AD 1631 to 1944, occurring on the slopes of Mt. Vesuvius up to Gran Cono Vesuviano and in the northern valley separating Vesuvius from the older Mt. Somma edifice. Pertinent morphological, physical, chemical, and mineralogical (XRD and FT-IR) soil properties were studied. The results indicated the existence of thin and deep stratified soils on lava, as well as the presence of loose detritic covers formed via pyroclastic emplacement and redistribution. The soils showed minimal profile differentiation, frequently with layering recording the episodic addition of sediments. We found that the dominant coarse size of primary mineral particles was preserved, and there was a low level of clay production. The main mineralogical assemblage present in sands also persisted in clays, indicating the physical breaking of the parent material. Chemical weathering produced mineral modifications towards the active forms of Al and Fe and was also attested in selected soils by glass alteration, allophane production, and the presence of analcime in clay as a secondary product from leucite. The differences in glass alteration and analcime production found in the selected soils on lava were related to soil particle size and soil thickness. Concerning the youngest soil present on Gran Cono Vesuviano, other factors, such as the substratum’s age and site elevation, appeared to be implicated. Full article

More exact information on soil nutrient management is crucial due to environmental protection, nature conservation, decreasing sources for mining, general precaution, etc. Soil magnesium (Mg) analytical methods of potassium chloride (KCl), Mehlich 3 (M3), water (WA) and cobalt hexamine (CoHex) extractions are compared with an elemental analysis and X-ray fluorescence (XRF) analysis. The ratio of the available to the total Mg content was calculated and compared on the whole dataset. The results showed that the linear regressions between all the pairs of Mg content measurement methods were significant. The linear relationship between the KCl and CoHex methods has the highest determination coefficient (R² = 0.96), followed by WA–M3 (R² = 0.68), M3–CoHex (R² = 0.66) and M3–KCl (R² = 0.60). The M3 solution demonstrated a greater capacity for extracting Mg from the soil. The second part is the analysis of the influence of CaCO₃, pH, soil texture and clay content on the measurable magnesium content of soils. It was established that the extraction methods, the soil and the classification method of the soil properties affect the evaluation. These results may help through the nutrient replenishment and the melioration of soils. These results can help the examination of mineral nutrients, especially the Mg uptake. Full article

Estimating soil erodible fraction based on basic soil properties in arid lands is a valuable research topic in the field of soil science and land management. The Proximal Sensing (PS) technique offers a non-destructive and efficient method to assess wind erosion potential in arid regions. By using Partial Least Squares Regression (PLSR) and Support Vector Machine (SVM) models and combining soil texture and chemical properties, determined through Visible-Near Infrared (vis-NIR) spectroscopy in 96 soil samples, this study aims to predict soil erodibility, soil organic matter (SOM), and calcium carbonate equivalent (CaCO₃) in arid lands located in Elkobaneyya Valley, Aswan Governorate, Egypt. Results showed that the soil erodibility fraction (EF-Factor) had the highest values and possessed a strong relationship between slope and SOM of 0.01% in determining soil erodibility. The PLSR model performed better than SVM for estimating SOM, CaCO₃, and EF-Factor. Furthermore, the results showed that the spectral responses of CaCO₃ were observed in separate places in the wavelengths of 570, 649, 802, 1161, 1421, 1854, and 2362 nm, and the wavelengths with SOM parameter were 496, 658, 779, 1089, 1417, 1871, and 2423 nm. The EF-factor shows the highest significant correlation with spectral reflectance values at 526, 688, 744, 1418, 1442, 2292, and 2374 nm. The accuracy and performance of the PLSR model in estimating the EF-Factor using spectral reflectance data and the distribution of data points for both the calibration and validation data-sets indicate a good accuracy of the PLSR model, with RMSE values of 0.0921 and 0.0836 Mg h MJ⁻¹ mm⁻¹, coefficient of determination (R²) values of 0.931 and 0.76, and RPD values of 2.168 and 2.147, respectively. Full article

For large infrastructure projects, such as high-voltage underground cables or for evaluating the very shallow geothermal potential (vSGP) of small-scale horizontal geothermal systems, large-scale geothermal collector systems (LSCs), and fifth generation low temperature district heating and cooling networks (5GDHC), the thermal conductivity (λ) of the subsurface is a decisive soil parameter in terms of dimensioning and design. In the planning phase, when direct measurements of the thermal conductivity are not yet available or possible, λ must therefore often be estimated. Various empirical literature models can be used for this purpose, based on the knowledge of bulk density, moisture content, and grain size distribution. In this study, selected models were validated using 59 series of thermal conductivity measurements performed on soil samples taken from different sites in Germany. By considering different soil texture and moisture categories, a practicable guideline in the form of a decision tree, employed by empirical models to calculate the thermal conductivity of unconsolidated soils, was developed. The Hu et al. (2001) model showed the smallest deviations from the measured values for clayey and silty soils, with an RMSE value of 0.20 W/(m∙K). The Markert et al. (2017) model was determined to be the best-fitting model for sandy soils, with an RMSE value of 0.29 W/(m∙K). Full article

Unique worldwide, nitrate/iodine deposits (NIDs) are located along a 700 km geological belt in the Atacama Desert, Chile. They serve as the primary source of mineral ores for the extraction of iodine, sodium, and potassium nitrates. NIDs have been relatively underexplored from a biological perspective. To address this, we collected sixteen soil samples from abandoned mines in Oficinas Pissis and Savona for chemical, mineralogical, and metagenomic analyses. The soils primarily consisted of halite and darapskite, with only one sample being predominantly composed of thenardite. Deliquescence and water activity measurements yielded values ranging from 0.02% to 0.40% and 0.47 to 0.62, respectively. To investigate the presence, identification, relative abundance, and diversity of microbial life in NID soils, we employed MiSeq high-throughput sequencing and bioinformatic tools. The dominant phyla observed were Firmicutes and Proteobacteria, with Actinobacteria and Cyanobacteria being predominant in two soil samples. Furthermore, we detected nitrate/perchlorate-reducing bacterial activity in enriched cultures from the soil samples. This study sheds light on the resilience of microbial life in the Atacama Desert NIDs, providing compelling evidence for its existence and offering insight into factors that could facilitate it within this unique environment. Full article

There is an urgent demand to change our intensive crop production systems, replacing them with soil use and management systems that recover, preserve, or improve soil health and are environmentally sustainable, producing healthy and good-quality food. In this work, we compile and present strategies and public policies aimed toward soil and water conservation and food production in Brazil. The results presented may help Brazilian farmers adopt practices to recover, maintain, or improve soil health and politicians to create or modify public policies for healthy soil and food, without the necessity of increasing agricultural areas. Food insecurity was also addressed, with family farming playing an important role in food production and decreasing food insecurity. But these challenges need the combined efforts and engagement of the whole society. Full article

Integrated production systems composed of trees, crops and pastures have shown good results in improving soil quality and the capacity to store carbon in the soil, being efficient in mitigating greenhouse gas emissions. Despite this, changes in carbon stocks and soil organic matter fractions in the initial stages of implementing an agroforestry system remain unclear. This study evaluated the carbon balance and the dynamics of soil organic matter fractions in an agroforestry system conducted over a decade. Total carbon, labile carbon, carbon from particulate organic matter, organic carbon associated with minerals and inert carbon were determined at depths 0–10 cm, 10–20 cm and 20–40 cm. Soil carbon stocks were also estimated for the 0–40 cm depth. Total carbon increased in the agroforestry system compared with a low-productivity pasture. The total carbon stock in the last growing season (68.57 Mg ha⁻¹) was close to the original soil stocks under native Cerrado vegetation (76.5 Mg ha⁻¹). After 10 years, there was a positive balance in the soil carbon stock of both the total carbon and the soil organic matter fractions. The successional agroforestry system is a good alternative to increasing soil total carbon stocks and labile and non-labile fractions of soil organic matter. Full article

Soil parent material is a fundamental natural resource for the generation of new soils. Through weathering processes, soil parent materials provide many of the basic building blocks for soils and have a significant bearing on the physico-chemical makeup of the soil profile. Parent materials are critical for governing the stock, quality, and functionality of the soil they form. Most research on soil parent materials to date has aimed to establish and measure the processes by which soil is generated from them. Comparatively little work has been performed to assess the rates at which soil parent materials erode if they are exposed at the land surface. This is despite the threat that the erosion of soil parent materials poses to the process of soil formation and the loss of the essential ecosystem services those soils would have provided. A salient but unanswered question is whether the erosion of soil parent materials, when exposed at the land surface, outpaces the rates at which soils form from them. This study represents one of the first to detect and measure the loss of soil parent material. We applied Uncrewed Aerial Vehicle Structure-From-Motion (UAV-SfM) photogrammetry to detect, map, and quantify the erosion rates of an exposed saprolitic (i.e., weathered bedrock) surface on an agricultural hillslope in Brazil. We then utilized a global inventory of soil formation to compare these erosion rates with the rates at which soils form in equivalent lithologies and climatic contexts. We found that the measured saprolite erosion rates were between 14 and 3766 times faster than those of soil formation in similar climatic and lithological conditions. While these findings demonstrate that saprolite erosion can inhibit soil formation, our observations of above-ground vegetation on the exposed saprolitic surface suggests that weathered bedrock has the potential to sustain some biomass production even in the absence of traditional soils. This opens up a new avenue of enquiry within soil science: to what extent can saprolite and, by extension, soil parent materials deliver soil ecosystem services? Full article

Interest in improving the long-term sustainability of agricultural production systems has focused on identifying management practices that promote soil health. No tillage, cover cropping, and amending soils with broiler (Gallus gallus domesticus L.) litter are commonly adopted conservation practices that have been shown to improve soil fertility and crop yield. However, the overall influence of these conservation practices on soil health in the southeastern US are not well understood. Thus, a study was conducted to evaluate the influence of tillage, broiler litter (BL) applications, and cropping systems on soil biochemical properties. Soils were collected from field research plots under long-term management (>than 25 years of tillage, 15 years of broiler litter application, and 15 years of cropping system). Soil microbial biomass, C, N, and P, amidohydrolases, and dissolved organic matter (DOM) were evaluated as indicators of soil health. Adopting tillage and BL into the agricultural management system modified the biochemical parameters of the soils evaluated. Most of these modifications occurred in the 0–5 cm depth. Higher microbial biomass carbon (MBC; 85%) and nitrogen (MBN; 10%) and enzyme activities of asparaginase (65%) and glutaminase (70%) were observed in the 0–5 cm depth under no tillage (NT) compared to conventional tillage (CT), indicating greater biological activities were established in these soil ecosystems. Broiler litter applications increased microbial biomass N and activities of asparaginase and glutaminase in both soil depths. In addition, microbial biomass phosphorus (MBP) was increased following BL application in the 0–5 cm depth. The results suggest that long-term management of NT and BL additions can improve the health of eroded southeastern US soils by altering the soil biochemical parameters. Full article

This study aimed to investigate the impact of biosolids-derived biochar on the remediation of Australian soil contaminated with diesel while investigating the role of biochar in the remediation. To achieve the latter aim, sodium azide (NaN₃) was added to a separate biochar treatment (BN) to alter the bacterial community structure. Biochar (B) reduced detectable hydrocarbons by 2353 mg/kg compared to the control (C) treatment at week 24. However, the BN treatment reduced the hydrocarbon concentration by 3827 and 6180 mg/kg, relative to B and C, respectively. Soil toxicity significantly decreased at week 24 compared to the start of the remediation in B, but not in the control. Biochar and control treatments generally showed a similar bacterial community structure throughout the incubation, while the bacterial community structure in BN differed significantly. Biodegradation was found to play a significant role in hydrocarbon removal, as the variation in the bacteria community coincided with differences in hydrocarbon removal between B and BN. The increased removal of hydrocarbons in the BN treatment relative to B coincided with increased and reduced relative abundances of Gordonia and JG30-KF-CM45 genera, respectively. This study showed that NaN₃ led to a transient and selective inhibition of bacteria. This study makes an important contribution towards understanding the use of NaN₃ in examining the role of biochar in the remediation of diesel-contaminated soil. Overall, we conclude that biochar has the potential to enhance the remediation of diesel-contaminated soil and that biodegradation is the dominant mechanism. Full article

The use of plant growth-promoting rhizobacteria (PGPR) inoculated on plants has shown that it can increase the success of reforestation and accelerate soil recovery by improving soil microbial diversity. Three PGPR isolated from natural pine populations were selected for their metabolic capabilities and taxonomic affiliation (Z4.3; Bacillus sp., Z5.4; Arthobacter sp., and Z7.15; and Pseudomonas sp.) when inoculated alone or in combination (consortium) on stone pine seedlings before transplanting to the field. Before transplanting and after nine months, rhizospheric soil samples were collected for structural and functional metagenomic studies. First, the data were analyzed using EasyMAP. Neither alpha nor beta diversity showed significant differences between the samples, although unique taxa representative of each sample were detected. The predominant phylum in all cases was Proteobacteria, followed by Bacteroidetes and Acidobacteria. The linear discriminant analysis (LDA) effect size (LEfSe) found significantly over-represented taxa in some samples, highlighting different representatives of the order Sphingomonadales in several of them. Functional inference performed with PICRUSt also showed significantly over-represented functions in some samples. The study demonstrates that PGPR have a positive effect on plants and cause detectable changes in microbial communities in terms of both structure and function. Full article

The soils of the high-elevation mountains along the East African Rift Valley are poorly understood. Assessing the potential of soils for agriculture, climate change mitigation, and environmental functioning requires insight into how they relate to the factors influencing soil formation. Between 3000 and 4120 m a.s.l., 85 soil profiles of Mount Guna were described and sampled. Standard physicochemical analyses were done on all pedons. Additionally, X-ray diffraction, Al_ox and Fe_ox content, and P fixation were performed on six selected profiles. Soils on Mount Guna included Andosols, Phaeozems, Leptosols, Regosols, Cambisols, Luvisols, and Vertisols. With increasing elevation, clay content, bulk density, and pH decreased while the C:N ratio remained constant. In contrast, sand, silt, silt-to-clay ratio, SOC, Ntotal, and SOCS increased. With a factor analysis, the soil-forming factors’ elevation/climate could be disentangled from the factor’s parent material as these affect topsoil and subsoil differently. In the ordination based on climate/elevation and parent material, Andosols and Vertisols stood out while other Reference Soil Groups (RSG) showed indistinct patterns. Soil erosion appeared as an additional soil-forming factor not accounted for by the factor analysis. The distribution of the RSG was significantly associated with elevation belts (p < 0.001), lithology (p < 0.001), and landcover (p < 0.003). On the summital ridge, the Andosols were crucial for groundwater storage due to high precipitation. Shallow and stony soils in the mid-elevation belt contributed to runoff generation. Average soil carbon stock ranged from 8.1 to 11 kg C m⁻² in the topsoil and from 29.2 to 31.9 kg C m⁻² in the upper meter, emphasizing the global importance of high-elevation areas for carbon sequestration. Full article

During the last decades, forest soils in Central Europe recovered from former sulfur and acid deposition. As external S input into forests has strongly decreased and legacy S pools in the soils are diminishing, internal S cycling through mineralization will increasingly become important for ecosystem nutrition. However, it is not known how microbial biomass is affected by the S pool change in the formerly S surplus soils. Here, we present data on the status quo of C, N, and S in microbial biomass in relation to contents in mineral soil and organic layer. The results of forest soil in Eastern Germany (low and high liming), which is slowly recovering from former pollution, are compared to those of a site remote from air pollution in the Swiss Alps. The contents of C, N, and S in soil as well as in microbial biomass were clearly higher in the organic layer than in mineral topsoil at all sites. Despite the generally low content in the mineral A-horizon, the clean-air site showed indications of a more active S-turnover as compared to the high-pollution site. Liming at the high-pollution site improved the conditions for microbial growth (pH increase) in the organic layer resulting in more mobile S. Full article

The migration of heavy metals and radionuclides is interrelated, and this study focusses on the interaction and complex influence of various toxicants. The rehabilitation of radioactively contaminated territories has a complex character and is based on scientifically supported measures to restore industrial, economic, and sociopsychological relations. We aim for the achievement of pre-emergency levels of hygienic norms of radioactive contamination of output products. This, in its sum, allows for further economic activity in these territories without restrictions on the basis of natural actions of autoremediation. Biosorption technologies based on bacterial biomass remain a promising direction for the remediation of soils contaminated with radionuclides and heavy metals that help immobilise and consolidate contaminants. A comprehensive understanding of the biosorption capacity of various preparations allows for the selection of more effective techniques for the elimination of contaminants, as well as the overcoming of differences between laboratory results and industrial use. Observation and monitoring make it possible to evaluate the migration process of heavy metals and radionuclides and identify regions with a disturbed balance of harmful substances. The promising direction of the soil application of phosphogypsum, a by-product of the chemical industry, in bioremediation processes is considered. Full article