Soil Syst., Volume 8, Issue 1 (March 2024) – 35 articles

The increase in soil salinity has a negative effect on the growth and yield of plants. Mitigating the negative effects of soil salinity is therefore a difficult task and different methods are being used to overcome the negative effects of salt stress on crop plants. One of the often-used approaches is seed priming that can increase plants’ vigor and resilience. In this paper, we tested the effects of hydropriming, proline priming, and salicylic acid priming on the mitigation of the negative effects of salt stress on two bell pepper varieties (Capsicum annuum L.): Herkules and Kurtovska kapija. Sweet bell pepper seeds were primed following desiccation to achieve the original water content, and subsequently cultivated in salt-supplemented medium. The positive effects on vigor (in the form of increased germination and seedling establishment) as well as on level of tolerance for salt stress were recorded for both cultivars. The positive effects varied between the priming treatments and pepper cultivar used. The results of germination, seedling performance, photosynthetic pigments, and osmolytes were measured for seedlings grown from unprimed and primed seeds with under 0, 25, and 50 mM of NaCl. Both cultivars demonstrated greater germination when primed with proline and salicylic acid, while the Herkules cultivar demonstrated a higher tolerance to salt when proline was used as the priming agent. Priming with salicylic acid and proline in the seed improved germination and seedling performance, which could be related to the increase in proline content in the seedlings. Full article

The input of fresh organic carbon into soils can stimulate organic carbon mineralization via priming effects (PEs). However, little is known about the characterization of PEs in coastal wetlands. We investigated the PEs of two salt marshes (Suaeda salsa and Phragmites australis) in the Yellow River Delta by adding ¹³C-labeled glucose to soils collected from the 0–10 cm and 20–30 cm layers of both salt marshes. The addition of glucose produced a significant positive PE in both soil layers for both vegetation types. There were no differences in the PE of the topsoil layer between the two vegetation types (p > 0.05), whereas the PE of S. salsa was 19.5% higher than that of P. australis in the subsoil layer (p < 0.05). In addition, the topsoil layer showed a higher average PE of 29.1% compared to that of the subsoil layer for both vegetation types (p < 0.05). The differences in the PEs between the two vegetation types and the two layers could be associated with a differential soil salinity, substrate availability, and microbial community structure. Our findings highlight the important role of PEs in regulating the soil carbon storage of coastal salt marshes, which should be considered when assessing and modeling the soil carbon cycling of coastal wetlands. Full article

Approximately 95% of urban solid waste worldwide is disposed of in landfills. About 14 million metric tonnes of this municipal solid waste are disposed of in landfills every year in Malaysia, illustrating the importance of landfills. Landfill leachate is a liquid that is generated when precipitation percolates through waste disposed of in a landfill. High concentrations of heavy metal(loid)s, organic matter that has been dissolved and/or suspended, and inorganic substances, including phosphorus, ammonium, and sulphate, are present in landfill leachate. Globally, there is an urgent need for efficient remediation strategies for leachate-metal-contaminated soils. The present study expatiates on the physicochemical conditions and heavy metal(loid)s’ concentrations present in leachate samples obtained from four landfills in Malaysia, namely, Air Hitam Sanitary Landfill, Jeram Sanitary landfill, Bukit Beruntung landfill, and Taman Beringin Landfill, and explores bioaugmentation for the remediation of leachate-metal-contaminated soil. Leachate samples (replicates) were taken from all four landfills. Heavy metal(loids) in the collected leachate samples were quantified using inductively coupled plasma mass spectrometry. The microbial strains used for bioaugmentation were isolated from the soil sample collected from Taman Beringin Landfill. X-ray fluorescence spectrometry was used to analyze heavy metal(loid)s in the soil, prior to the isolation of microbes. The results of the present study show that the treatments inoculated with the isolated bacteria had greater potential for bioremediation than the control experiment. Of the nine isolated microbial strains, the treatment regimen involving only three strains (all Gram-positive bacteria) exhibited the highest removal efficiency for heavy metal(loid)s, as observed from most of the results. With regard to new findings, a significant outcome from the present study is that selectively blended microbial species are more effective in the remediation of leachate-metal-contaminated soil, in comparison to a treatment containing a higher number of microbial species and therefore increased diversity. Although the leachate and soil samples were collected from Malaysia, there is a global appeal for the bioremediation strategy applied in this study. Full article

The application of biochar is considered an alternative amendment strategy for improving soil fertility. In this study, we performed pot experiments using soils of low and medium fertility to assess the effects of different combinations of biochar and organic manure on the chemical properties of paddy rice soils and determined the best combination to improve the grain yield without increasing N₂O and CH₄ emissions. The applied treatments were without biochar (control), the application of rice husk biochar alone (5 and 10 t ha⁻¹), and biochar combined with chicken or cow manure. The results indicated that for both soils, the application of 5 t ha⁻¹ biochar combined with 5 t ha⁻¹ chicken manure increased grain yield by improving soil total nitrogen and soil NH₄⁺-N without increasing cumulative N₂O and CH₄ emissions. Multiple regression analysis showed that when combined with biochar, chicken manure significantly contributed to a higher grain yield and was negatively associated with cumulative CH₄, N₂O emissions, and total GWP. Furthermore, regardless of soil type, combined applications of biochar and cow manure promoted significant increases in soil available P. Our findings indicate that the C/N ratio of organic manure influences CH₄ fluxes, and soil type was identified as a factor driving greenhouse gas emissions. Full article

Soil water infiltration is an important component of the hydrological cycle, and it is best evaluated when the raindrop impacts the ground surface. For this reason, it is affected by changes in land use and land cover and by the characteristics and physical–hydric properties of the soil. This study aimed to evaluate soil water infiltration in areas occupied by annual crops (soybean and corn) and pastures in two watersheds of the Teles Pires River-MT, using simulated rainfall, physical models, and principal component analysis. Infiltration rates were evaluated based on simulated rainfall with an average intensity of 75 mm h⁻¹, with four repetitions per region (upper, middle, and lower) of the hydrographic sub-basins of the Caiabi and Renato rivers, and soil use with cover, without cover, and disturbed. Soil tillage provided higher water infiltration rates into the soil, especially in pasture areas in the two hydrographic sub-basins. There were significant adjustments to the mathematical models based on the infiltration rate data for all land use and land cover conditions. The soil attributes that most interfered with the infiltration rate were microporosity, bulk density, and total porosity in the crop areas of the middle Caiabi and microporosity, clay content, total porosity, and silt content in the areas farming at the source of the Renato River. The Horton and Philip models presented the best adjustments in the hydrographic sub-basins of the Caiabi and Renato Rivers, which are recommended for estimating the water infiltration rate into the soil in different uses, coverages, and regions. Full article

Landfills have the potential to contribute to mercury (Hg) pollution, due to the burial of waste containing mercury. Mercury from domestic waste can enter the soil surrounding landfills through surface runoff and leachate. In this study, we assessed the levels of Hg in the paddy soil around the Nam Son landfill, the largest landfill in the North of Vietnam, during both rainy (September 2021) and dry (January 2022) seasons. The concentration of Hg was in the range of 20.5 to 79.7 μg/kg dry w.t. in Bac Son and Nam Son, and 16.6 μg/kg dry w.t. at a higher reference site. In most of the samples, the rainy season showed higher Hg concentrations than the dry season. Soil samples taken closer to the landfill exhibited higher levels of Hg contamination compared to those in more distant paddy areas, suggesting a decreasing trend of Hg concentration as one moves away from the pollution source. Additionally, Hg concentration was found to decrease vertically from the surface, with the higher value observed in the surface layer (0–5 cm), and the lower in the bottom layer (20–25 cm). The geo-accumulation index showed that all the sampling points were moderately to heavily polluted, indicating that Hg was lost from the waste source in the landfill. This study provides valuable insights into the spatial and vertical distribution of Hg pollution in the topsoil and highlights the importance of managing and assessing the risks of Hg-containing waste. Full article

The United Nations (UN) Sustainable Development Goals (SDGs) offer an opportunity to improve soil science education on sustainability because they provide specific context to educate faculty and students from various disciplines, including Science, Technology, Engineering, and Mathematics (STEM) about SDGs. Soil science is a STEM discipline with a wide range of applications in the SDGs. The objectives of this study were to use a matrix approach (framework for presenting options for discussion and implementation) to integrate SDGs into an existing introductory soil science course taught to undergraduate students from different STEM fields (environmental and natural resources; wildlife biology; and forestry). The course was enriched with a lecture on SDGs and students were asked to link soil properties and class activities to specific SDGs. A post-assessment survey revealed an increase in students’ familiarity with SDGs, and their relevance to soil properties and course activities. Students acknowledged the importance of soils and individual actions for achieving the SDGs. There was an overall increase in student familiarity (+59.4%) with SDGs. Most students agreed (46.7%) and strongly agreed (23.3%) that the course activities were an effective way to learn about SDGs with examples from soil science. Identified learning gaps in subject matter found through the surveys on SDGs were clarified during later classroom discussions. The advantage of this teaching approach is that it seamlessly integrates SDGs with existing course materials while relying on students’ critical thinking skills to effectively analyze soil science information and form a judgement on how it relates to SDGs. Full article

The influence of the quantities and ratios of dissolved organic carbon (DOC) and dissolved nitrogen (DN) generated by different chemical quality classes of organic residues on soil microbial processes in the decomposition process is not well understood. If the DOC-to-DN ratio (hereafter, ratio) of the substrate is close to that of the microbial C-to-N ratio, then the DOC-and-DN stoichiometry of the substrate is balanced, resulting in enhanced microbial processing, i.e., carbon use efficiency (CUE). Uncertainty exists about the influence of DN and the DOC-to-DN ratio on CUE, particularly in high-quality class (high nitrogen) residue-treated soils. A long-term field experiment was used to explore the effect of the annual application of residues of different quality classes on decomposition processes, focusing on the effects of DOC, DN, and the ratio on the microbial metabolic quotient (qCO₂), which is the inverse of CUE. DOC and DN were extracted from soils during the 13th year of the experiment. Soils treated with high-quality class groundnut residue (high-nitrogen) had higher DN (5.4 ± 2.6 mg N kg⁻¹) and a lower ratio (6.8 ± 2.6) than those treated with medium-quality (medium-nitrogen) tamarind (3.0 ± 0.6 and 10.7 ± 2.2, respectively). The positive influence of DN on qCO₂ (R² = 0.49 *) in groundnut-treated soil suggested that the high bioavailability of DN reduced CUE due to imbalanced DOC-and-DN stoichiometry. This contradicted earlier published findings on high-nitrogen residues which had balanced DOC-and-DN stoichiometry. The positive influence of the ratio on qCO₂ under the tamarind-treated soil (R² = 0.60 *) indicated that its balanced DOC-and-DN stoichiometry enhanced CUE. High-quality class organic residues can result in either higher or lower CUE than their lower-quality class counterparts depending on whether the resulting DOC-and-DN stoichiometry is balanced or imbalanced. Full article

Soil makes important contributions to the United Nations (UN) Land Degradation Neutrality (LDN) concept and targets; however, currently, soil is not integrated into measurable information (e.g., indicators, metrics) to monitor land degradation (LD) patterns and trends. This study examines the role of soil in LDN in the UN Convention to Combat Desertification (UNCCD), and UN Sustainable Development Goal (SDG 15: Life on Land). This study is specifically focused on the LDN and biodiversity loss as they relate to an indicator 15.3.1 Proportion of land that is degraded over total land area. Tracking of LD status can be improved by using detailed soils databases combined with satellite-derived land cover maps. This study has applied these newly improved methods to quantify and map the anthropogenic LD status and trends in the contiguous United States of America (USA), as well as to identify potential land areas for nature-based solutions (NBS) to compensate for LD. Anthropogenic LD in 2016 in the contiguous USA affected over two million square kilometers, about one-third of the country’s total area, with high variability by state. Between 2001 and 2016, LD in the USA showed an overall increase of 1.5%, with some states exhibiting increases in degraded land while other states had overall improvements to their land. All ten soil orders present in the contiguous USA have been anthropogenically degraded, with Mollisols, Alfisols, and Vertisols having the highest LD levels. Compensating for LD requires a variety of strategies and measures (e.g., NBS), which often require additional land. In 2016, the potential land area for NBS was over two million square kilometers, an area approximately equal to that of degraded land. Some of the states that have high proportions of land available for potential NBS are dominated by soils (Aridisols) typical of deserts and therefore may have less promise for NBS. The variability of LD needs to be evaluated at finer spatial scales for realistic LDN analysis. Full article

Agroecological practices can be used to optimise ecological functions and improve the health of agroecosystems. The present study aimed to determine the effects of two agroecological systems (AG and AGSPP) on soil biodiversity and ecosystem services in tropical market gardens. The AG (agroecological) cropping system allows the use of organic phytosanitary products, unlike the second one (AGSPP, agroecological without phytosanitary products). The cropping systems were established in the open field and compared in terms of (i) soil fauna, (ii) soil fertility, (iii) soil aggregation, (iv) pest regulation, and (v) crop production. A total of eighteen months after the establishment of the experiment, the macrofaunal communities of the two cropping systems were significantly different. The AGSPP cropping system was characterised by a higher abundance of predators, a better soil structure, a higher tomato fruit set rate, and a lower pest proliferation. The increase in plant diversity and the non-use of phytosanitary products could modify the macrofaunal communities and, consequently, the provision of some ecosystem services. We also observed an effect of repellent and host plants on pest control in both systems, promoting high crop production. Overall, we showed that small changes in agroecological practices can have positive effects on soil biodiversity, pest regulation, and crop production. Full article

Typical successions in land use affect the dynamics of carbon (C) and nitrogen (N) in the soil. This study aimed to determine the effects of land use change on soil organic carbon and N content and stocks in pastures, crops, and forests in the Amazon. Soil C and N stocks were assessed at depths of 30 and 100 cm to determine ¹³C isotopic abundance. The concentrations of C and N in crops were lower (p < 0.05) than those in other land use types. Soil organic C and soil N stocks for pasture (67.6, 144.8, 5.7, and 13.3) and forest (77.1, 137.5, 6.3, and 13.8) systems were similar, but greater than those of the crop area (36.4, 63.9, 3.0, and 6.0), regardless of depth (30 and 100 cm for C and N). Land use change for pastures in the Arc of Deforestation region of the Amazon maintains SOC and N stocks in the soil and is more sustainable than the agricultural system with black pepper, as long as the conditions of soil, climate, and cultivation are similar. Part of the C3-derived carbon from the forest was replaced by C4-derived C from grasses at soil depths up to 100 cm. Full article

Conservation units are strategic territories that have a high demand for public use, as they protect attractions of great scenic beauty, geodiversity sites, and numerous leisure areas. However, when carried out in an intensive and disorderly manner, tourist activity in these areas tends to catalyze environmental degradation, triggering, for example, water erosion processes caused by intensive soil trampling on the trails. In this sense, the aim of this study was to determine the soil’s physicochemical characteristics, and to spatiotemporally monitor the microtopography of those areas degraded by erosion along two trails on Serra da Bocaina National Park coast of the Paraty Municipality. The findings verified that intensive trampling, the values of some soil physicochemical characteristics, and the specific meteorological conditions of the coastal region of this protected area were factors that contributed significantly to the evolution of erosion features monitored on these trails. Finally, strategies for appropriate management and recovery actions for these degraded areas are proposed in order to not only stop the erosive processes and re-establish the local ecosystem balance, but also avoid accidents involving the numerous tourists who visit the coastal region. Full article

Over the last few decades, different types of plastics have been found in different soil types with documented or potential negative effects on the environment, the flora and fauna inhabiting the soils, and subsequently human health. This article is a global review of the consequences of the interactions of plastics with soil, plants, soil microbes, and organic or inorganic pollutants depending on land use. It focuses on the various types of polyethylene, a widely used material with a strong presence in both agricultural and urban soils. Although the chemical formula (C₂H₄)_n remains the same in its various classifications, the chemical behavior of polyethylene in soil varies and directly depends on its density, branching, crystallinity, and relative molecular mass, resulting in many and various differences in the properties but also in the behavior of the two main forms of polyethylene, low and high density. However, beyond the chemical composition of plastics, the climatic conditions that apply in both urban and rural areas determine the degree of corrosion as well as their shape and size, also affecting the chemical reactions that directly or indirectly affect them. In agricultural soils, plants and the microbiome present mainly in the rhizosphere seem to dramatically influence the behavior of plastics, where the interaction of all these parameters leads to changes in the availability of nutrients (phosphorus and potassium), the percentage of organic matter and the nitrogen cycle. In urban soils, the increase in temperature and decrease in humidity are the main parameters that determine the adsorption of heavy metals and organic pollutants on the surface of plastics. Although the presence of plastics is considered inevitable, perhaps a more thorough study of them will lead to a reduction in the risks of pollution in urban and rural environments. This research provides a promising perspective on the potential contribution of MP PEs to the sustainable management of soil systems. Full article

Soil organic carbon (SOC) is a crucial factor influencing soil quality and fertility. In this particular investigation, we aimed to explore the possibility of using diffuse reflectance infrared fourier transform spectroscopy (DRIFT-FTIR) in conjunction with machine-learning models, such as partial least squares regression (PLSR), artificial neural networks (ANN), support vector regression (SVR) and random forest (RF), to estimate SOC in Sohag, Egypt. To achieve this, we collected a total of ninety surface soil samples from various locations in Sohag and estimated the total organic carbon content using both the Walkley-Black method and DRIFT-FTIR spectroscopy. Subsequently, we used the spectral data to develop regression models using PLSR, ANN, SVR, and RF. To evaluate the performance of these models, we used several evaluation parameters, including root mean square error (RMSE), coefficient of determination (R²), and ratio of performance deviation (RPD). Our survey results revealed that the PLSR model had the most favorable performance, yielding an R² value of 0.82 and an RMSE of 0.006%. In contrast, the ANN, SVR, and RF models demonstrated moderate to poor performance, with R² values of 0.53, 0.27, and 0.18, respectively. Overall, our study highlights the potential of combining DRIFT-FTIR spectroscopy with multivariate analysis techniques to predict SOC in Sohag, Egypt. However, additional studies and research are needed to improve the accuracy or predictability of machine-learning models incorporated into DRIFT-FTIR analysis and to compare DRIFT-FTIR analysis techniques with conventional soil chemical measurements. Full article

Information on how bacteria in plants and soil, along with extracellular enzymes, affect nutrient cycling in Encephalartos villosus growing in phosphorus deficient and acidic scarp forests is lacking. Bacteria in coralloid roots, rhizosphere, and non-rhizosphere soils were isolated to determine the potential role of soil bacterial communities and their associated enzyme activities in nutrient contributions in rhizosphere and non-rhizosphere soils. The role of soil characteristics and associated bacteria on E. villosus nutrition and nitrogen source reliance was investigated. Encephalartos villosus leaves, coralloid roots, rhizosphere, and non-rhizosphere soils were collected at two scarp forests. Leaf nutrition, nitrogen source reliance, soil nutrition, and extracellular enzyme activities were assayed. A phylogenetic approach was used to determine the evolutionary relationship between identified bacterial nucleotide sequences. The clustering pattern of isolated bacterial strains was primarily dictated by the ecological niches from which they originated (rhizosphere soil, non-rhizosphere soil, and coralloid roots), thus indicating that host-microbe interactions may be a key driver of this pattern, in line with the hologenome theory. There were insignificant differences in the phosphorus and nitrogen cycling enzyme activities in E. villosus rhizosphere and non-rhizosphere soils in both localities. Significantly positive correlations were recorded between nitrogen and phosphorus cycling enzymes and phosphorus and nitrogen concentrations in rhizosphere and non-rhizosphere soils. Additionally, more than 70% of the leaf nitrogen was derived from the atmosphere. This study challenged the conventional expectation that environmental filters alone dictate microbial community composition in similar habitats and revealed that host-microbe interactions, as proposed by the hologenome theory, are significant drivers of microbial community structuring. The isolated bacteria and their plant growth promoting traits play a role in E. villosus nutrition and nitrogen source reliance and secrete nutrient cycling enzymes that promote nutrient availability in rhizosphere and non-rhizosphere soils. Full article

The intensification of cropping systems in the salt-affected coastal zones of the Ganges Delta can boost food security in the region. The scarcity of fresh water, coupled with varying degrees of soil and water salinity are however limiting factors for the expansion of irrigated cropping in that area. In this study, we assessed the potential of growing sunflowers using combinations of low and medium saline water for irrigation. The experiments were conducted at two locations with six irrigation treatments in 2016–2017 and 2017–2018. The treatments were: T1—two irrigations at early vegetative (25–30 days after sowing; DAS) and flowering stages (60–65 DAS) with low salinity water (LSW, electric conductivity, EC_w < 2 dS m⁻¹); T2—two irrigations, one at the vegetative stage with LSW and one at the flowering stage with medium salinity water (MSW, 2 < EC_w < 5dS m⁻¹); T3—two irrigations, one at the vegetative stage with LSW and one at seed development stage (75–80 DAS) with MSW; T4—three irrigations at the vegetative, flowering and seed development stages with LSW; T5—three irrigations, at vegetative stage with LSW, and flowering and seed development stages with MSW; and T6—three irrigations, two at the vegetative and flowering stages with LSW and one at the seed development stage with MSW. Irrigation with LSW at early growth stages and MSW at later growth stages did not significantly (p < 0.05) affect the yield compared to the LSW irrigation at early and later growth stages. Crop water productivity and irrigation water productivity of sunflowers (p < 0.001) increased substantially with the decreasing amount of irrigation water with an average of 1.18 kg m⁻³ and 2.22 kg m⁻³ in 2017 and 0.92 kg m⁻³ and 1.29 kg m⁻³ in 2018, respectively. Grain yield was significantly correlated with root zone solute potential. The flowering and seed development stages of sunflowers in February–March were sensitive to both low and medium saline water irrigation for seed yield. Overall, the results show that irrigation with LSW (EC_w < 2dS m⁻¹) at early growth stages and MSW (2 < EC_w < 5dS m⁻¹) at later growth stages could be an option for dry-season sunflowers in the coastal zones of the Ganges Delta which would allow double cropping in this area. Full article

This study aimed to simulate dynamic irrigation management zones (MZs) in two maize fields for a variable rate hose reel fertigation machine (VRFM) with a four-section boom control. Soil moisture content was measured from nine and four soil moisture sensors in Field 1 (8.2 ha) and Field 2 (2.5 ha), respectively, on different dates during the 2022 crop season. Three and five MZs scenarios were simulated per irrigation and the theoretical maps were processed for implementation. The application maps fitted to the VRFM showed significant spatiotemporal variations in irrigation requirements. For instance, in Field 1, 3-MZ modelling showed that the areas requiring high (H), medium (M), and low (L)-level irrigation on 21 July were 1.60, 4.84, and 1.85 ha, respectively, even though the farmer applied uniform rate over the whole field. H-level sub-areas ranged between 1.22 ha (25 July) and 3.25 ha (7 July), showing a coefficient of variation (CV) of 43.32% for the three MZs, whereas H-level sub-areas for the five MZs varied from 0.41 ha (2 July) to 1.49 ha (7 July) with a CV value of 48.84%. High levels of within-field variability can be addressed using precise and dynamic irrigation MZs fitted to the irrigation technology used. Full article

The agricultural sector faces the dual challenge of enhancing crop productivity and mitigating environmental impacts. Optimizing nutrient management is vital for sustainable agriculture, particularly in sloping terrains like the Himalayan region, where damaged soils require restoration. This study explores the synergistic effects of urea, poultry manure, and zeolite on wheat growth and yield in degraded mountainous soils. A total of twelve treatments were implemented in a randomized complete block design, replicated three times. The treatments included a control (T1); urea nitrogen at 120 kg N ha⁻¹ (UN₁₂₀) (T2); poultry manure (PM) at 120 kg N ha⁻¹ (T3); zeolite-1 (Z1) at 5 t ha⁻¹ (T4); zeolite-2 (Z2) at 5 t ha⁻¹ (T5); UN₁₂₀ + Z1 (T6); PM + Z1 (T7); UN₁₂₀ + Z2 (T8); PM + Z2 (T9); ½ UN + ½ PM + Z1 (T10); ½ UN + ½ PM + Z2 (T11); and ½ UN + ½ PM + ½ Z1 + ½ Z2 (T12). The UN₁₂₀ treatment demonstrated significant improvements in wheat growth, with notable increases in shoot length (79.7%), shoot fresh weight (50.8%), root length (50.6%), chlorophyll content (53.6%), and leaf area (72.5%) compared to the control. Wheat yield and its components experienced significant improvements when treated with urea nitrogen (UN) and zeolites. Among these treatments, UN₁₂₀ exhibited the highest efficacy. Nutrient content analysis revealed substantial increases in shoot nitrogen (70.6%), phosphorus (33.3%), and potassium (15.6%) with UN₁₂₀ treatment compared to the control. The concoction of UN and PM with zeolites further enhanced nutrient levels. Integrating mineral nitrogen sources with organic amendments and zeolites proved effective in enhancing wheat productivity in degraded mountainous soils. Despite positive results, further research is essential for widespread recommendations. Full article

Nickel (Ni) is extremely toxic to plants at high concentrations. Phytoliths have the potential to sequester the heavy metals absorbed by plants and act as a detoxification mechanism for the plant. The authors of the present study aimed to evaluate the effects of Ni on the growth and phytolith yield of grasses in two artificially contaminated soils. Two experiments separated by soil types (Typic Quartzipsamment and Rhodic Hapludox) were conducted in a completely randomized design in a 2 × 4 factorial scheme with three replications. The factors were two species of grass (Urochloa decumbens and Megathyrsus maximus) and three concentrations of Ni (20, 40, and 120 mg kg⁻¹) and control treatment. The grasses were influenced by the increase in Ni rates in the soils. Ni exerted a micronutrient function with the addition of 30 mg kg⁻¹ of Ni in soils, but this concentration caused toxicity in grasses. Such a level is lower than the limits imposed by the Brazilian environmental legislation. Higher Ni availability in Typic Quartzipsamment promoted Ni toxicity, with reduced growth and increased phytolith yield in the shoot, increased Ni in the shoot, and Ni occlusion in phytoliths by grasses, in comparison with Rhodic Hapludox. The yield and Ni capture in phytoliths by grasses in Ni-contaminated soils are related to the genetic and physiological differences between grasses and Ni availability in soils. Ni capture by phytoliths indicates that it may be one of the detoxification mechanisms of Urochloa decumbens to Ni contamination, providing additional tolerance. Megathyrsus maximus may be a future grass for the phytoremediation technique in Ni-contaminated soils. Full article

Volcanic tuffs rich in chabazite zeolites have been extensively examined for their potential to enhance soil properties and increase fertilizer efficiency, both in their natural state and when enriched with nitrogen (N). However, there is a scarcity of data regarding their utilization in acidic sandy soil, particularly when used alongside organic fertilizers. This paper presents the findings of a 50-day laboratory incubation study that investigated the dynamics of N pools in an acidic sandy-loam agricultural soil treated with various N sources. These sources included urea, N-enriched chabazite zeolite tuff, and pelleted composted manure applied at a rate of 170 kg N/ha. Additionally, the N sources were tested in combination with chabazite zeolite tuff mixed into the soil to assess its role as a soil conditioner. The results revealed distinct behaviours among the tested N sources, primarily impacting soil pH and N dynamics. Soil fertilized with manure exhibited slow N mineralization, whereas N-enriched zeolite displayed a more balanced behaviour concerning net NO₃⁻-N production and NH₄⁺-N consumption. Both N-enriched zeolite and urea temporarily altered the soil pH, resembling a “liming” effect, while pelleted manure facilitated a prolonged shift towards neutral pH values. Considering the water adsorption capacity of zeolite minerals, caution is advised when adjusting water content and employing combustion methods to measure soil organic matter in zeolite-treated soil to avoid potential inaccuracies. In summary, N-enriched chabazite zeolite tuff emerged as a valuable N source in acidic sandy-loam soil, offering a promising alternative to synthetic fertilizers and showcasing a sustainable means of N recycling. Full article

Soil inorganic carbon (SIC), a potential carbon sink especially in arid and semi-arid environments, contributes to soil development, landscape stability, carbon (C) sequestration, and global C dynamics but due to the lack of SIC scientific reporting in most C sequestration research, its importance is unclear. A detailed overview of primary and secondary carbonate occurrence, formation, and importance is much needed to understand the role of pedogenic (PC)/secondary carbonate (a common biogeochemically derived soil mineral over time) in the SIC. The mechanisms involved in the formation of PC including carbon dioxide (CO₂) from microbial respiration and precipitation, silicate mineral weathering, dissolution, and reprecipitation are highlighted. The isotopic composition of carbonates related to biological C₃ or C₄ carbon fixation pathways and other paleoecologic and/or climactic factors responsible for new soil carbonate formation are discussed in detail. To address the lack of knowledge associated with SIC, this review attempts to highlight the currently known aspects of the literature, and briefly describe the formation and methodologies that can aid in addressing the research gaps surrounding SIC sequestration. The authors also suggest that greater focus needs to be provided on the actual measurement of SIC to develop a more comprehensive SIC inventory to provide sound data for future research direction, and modeling efforts and to predict C terrestrial storage and change efficiently. Full article

The use of organic fertilizers to replace chemically synthesized fertilizers has assumed an important role in managing plant nutrition and soil fertility. The various organic matrices currently available as organic byproducts and digestates are relatively abundant and have shown promising effects in terms of plant-available nutrients. However, like mineral fertilizers, organic fertilizers must be carefully managed to avoid negative effects on the environment, especially when they are repeatedly applied over time. The aim of the present study was to assess the effect of the single (DIG) and repeated application (DIGP) of solid anaerobic digestates compared to an unamended control (CTR) on the denitrifying enzymatic activity (DEA), which is responsible for nitrous oxide emissions into the atmosphere, and some related soil properties, such as total soluble nitrogen (TSN), nitrate (NO₃⁻-N), extractable carbon (C_extr), microbial biomass carbon (MBC), and basal respiration (R_bas), for a period of ~3 months after application. The application of solid anaerobic digestates progressively boosts N and C concentrations in the soil, with the degree of enhancement directly correlated with the frequency of application over the sampling period. Depending on the textural properties of soils, there was a notable rise in denitrification enzyme activity (DEA), particularly during the DIGP treatment, suggesting that clay soils are highly susceptible to denitrification under suitable conditions. The results of this study recommend the careful management of soils subjected to repeated digestate amendment to prevent the occurrence of conditions conducive to denitrification and the promotion of N₂O emissions. Full article

In Mediterranean countries characterized by increasingly extended hot and dry periods, olive trees are often conventionally practiced in low fertility and rainfed soils. This study investigated over a 15-month period how conventional tillage, combined with or without incorporated solid digestate, and no tillage affected selected soil properties, photosynthetic activity and productivity of mature olive trees growing in highly clayey acid soil with an unbalanced nutrient content and Mn excess. Neither in soil nor in drupes were Mn, Fe, Cu and Al contents affected by the managements. However, in soil, exchangeable Mn that was always larger than 200 mg kg⁻¹ threshold and unbalanced Ca, Mg, and K contents were evidenced in all treatments. Non-tilled soil showed the highest (p < 0.05) stomatal conductance and photosynthetic rate, and the highest (p < 0.05) fruits and oil yields. Instead, conventional tillage negatively (p < 0.05) affected plant physiology and productivity, likely due to the tilled increase in aeration, enhancing soil water loss and organic C mineralization. Conversely, digestate addition increased TOC, TN and EC. Stomatal conductance, the photosynthetic rate and plant yield significantly recovered (albeit not to no-tillage values) in tillage combined with incorporated digestate, suggesting that digestate-derived organic matter created soil conditions less constraining to plant growth and productivity than the conventional tillage did. Dealing with soil properties and climatic conditions is the key for adopting the best management practice for preserving plant productivity and soil fertility. Full article

The mulching of agricultural soils has been identified as a viable solution to sequester carbon into the soil, increase soil health, and fight desertification. This is why it is a promising solution for carbon farming in Mediterranean areas. Models are used to project the effects of agricultural practices on soil organic carbon in the future for various soil and climatic conditions, and to help policy makers and farmers assess the best way to implement carbon farming strategies. Here, we modified the widely used RothC model to include mulching practices and their direct and indirect effects on soil organic matter input, soil temperature changes, and soil hydraulic balance. We then calibrated and tested our modified RothC (RothC_MM) using the dataset collected in two field mulching experiments, and we used the tested RothC_MM to estimate the expected soil carbon sequestration due to mulching by the year 2050 for the Valencian Community (Spain). Our results show that RothC_MM improved the fit with the experimental data with respect to basic RothC; RothC_MM was able to model the effects of mulch on soil temperature and soil water content and to predict soil organic carbon (SOC) and CO₂ observations taken in the field. Full article

Soil salinity is a serious problem facing many countries globally, especially those with semi-arid and arid climates. Soil salinity can have negative influences on soil microbial activity as well as many chemical and physical soil processes, all of which are crucial for soil health, fertility, and productivity. Soil salinity can negatively affect physiological, biochemical, and genetic attributes of cultivated plants as well. Plants have a wide variety of responses to salinity stress and are classified as sensitive (e.g., carrot and strawberry), moderately sensitive (grapevine), moderately tolerant (wheat) and tolerant (barley and date palm) to soil salinity depending on the salt content required to cause crop production problems. Salinity mitigation represents a critical global agricultural issue. This review highlights the properties and classification of salt-affected soils, plant damage from osmotic stress due to soil salinity, possible approaches for soil salinity mitigation (i.e., applied nutrients, microbial inoculations, organic amendments, physio-chemical approaches, biological approaches, and nano-management), and research gaps that are important for the future of food security. The strong relationship between soil salinity and different soil subdisciplines (mainly, soil biogeochemistry, soil microbiology, soil fertility and plant nutrition) are also discussed. Full article

Irrigation of calcareous soil with saline–sodic water can modify the composition of the soil solution and exchange complexes in agricultural land of arid and semi-arid regions with low water resources. The objective of this study was to monitor (medium-term) potential changes in a calcareous clay soil irrigated with two types of sodic waters without cropping. Irrigation water with two high sodium adsorption ratios (SAR = 20 and 40) and electrical conductivity (EC < 3 dS m⁻¹) was prepared using NaCl and NaHCO₃ salts. The sodic irrigation waters were applied (June–October) in three periods (1, 2, and 4; one period = five irrigations) to bare non-saline soil with drip irrigation during two growing seasons; no irrigation action was taken in the winter–spring rainy season (period 3). Sampling (0–30 cm) was made after each period to determine the changes in soil pH, EC, water-soluble Na⁺, Ca²⁺, Mg²⁺, K⁺, Cl⁻, and HCO₃⁻. Relative to the control, irrigation with both sodic waters increased soil pH, EC, and water-soluble Na⁺ and decreased or did not change water-soluble cations (Ca²⁺, Mg²⁺). The Cl⁻ concentration increased rapidly with NaCl-type water application, but it was leached away quickly by winter–spring rains. The HCO₃⁻ concentration increased with NaHCO₃-type water application, yet it leached out slowly in the rainy period. The movement of HCO₃⁻ ions in the upper soil profile (0–30 cm) was significantly slower compared to Cl⁻ ions. Dissolution of slightly soluble soil CaCO₃ by irrigation increased the solution concentration of Ca²⁺ and its mobility, yet the kinetics of processes depended on water type and irrigation period. The released Ca²⁺ interacted with other cations in the soil, causing further significant positive physicochemical changes in the soil solution and exchange capacity (comparable with control soil) at the end of the irrigation period. The CaCO₃ content in the soil would be a long-term guarantee of the Ca²⁺ resource in soils, even if the amount of water-soluble Ca²⁺ may decrease for the short-term period during irrigation. The results should be considered for rational irrigation management (with various water qualities) in semi-arid and arid regions. Full article

This work describes the microbial community structure of the continuously revegetated chronosequence of a former sand quarry, which demonstrates a unique example of nearly complete soil restoration in less than 100 years. Samples were collected at five time points (0, 3, 30, 70 years and mature soil) from the entire set of soil horizons, revealing the history of pedogenesis. Real-time PCR was applied to quantitatively describe the bacterial and archaeal communities. High-throughput sequencing of the bacterial and archaeal V4 variable region of the 16S rRNA gene was used to identify abundant microbial taxa. A beta-diversity analysis revealed that the prokaryotic community structure responded strongly to the processes of organic matter accumulation and the corresponding evolution of the soil into discrete horizons. Changes in soil microbiota in the course of soil profile evolution revealed three groups of prokaryotes, which tended to accumulate in the specific soil horizons and might be associated with the certain soil-forming processes, including plant roots growth. This research showed the heuristic potential of soil horizon profiling in microbiological studies as opposed to the formal depth-dependent separation of the soil layers. The results allowed us to trace the relationship between the structure of the soil prokaryotic community and the peculiarities of the evolution of the podzolic soil profile as well as to identify the microbial indicators and drivers of primary pedogenesis. Full article

Phytomining (PM) is defined as the process of using plants capable of bio-extracting metals from soil in order to explore them economically. This relatively new, innovative method has been gathering significant attention in both the academic and commercial domains. Conventional mining methods are often economically unviable when applied to lean ores, and they can lead to secondary pollution in soil—a situation that applies to all excavated metals. On the other hand, PM is an environmentally friendly and economically viable solution that addresses the growing demands for metal resources, while simultaneously contributing to energy production by harnessing biomass energy. This comprehensive review presents the current PM techniques, challenges, and the hyperaccumulator plant species that may be used for the extraction of the main targeted elements in the process. Typically, the targeted metals are those of economic value, which can later be deposited or sold to various industries. This review also analyzes the factors influencing the economic viability of PM and proposes potential enhancements. Undeniably, PM offers the opportunity for economically sustainable exploration of metal-rich soils, but its full commercial viability remains constrained under current conditions as scientists are actively searching for the identification and utilization of new hyperaccumulator plant species in different locations worldwide, while creating new relationships and business avenues within the mining industry. Overall, this review highlights the current status of PM technology and the plants used, emphasizing the need for further research to enhance its commercial implementation and its potential to assist the mining industry. We conclude that PM, although a relatively new and unexplored concept, may provide economic and environmental benefits to soil end-users and managers who must cultivate on metal-contaminated soils as PM may turn yield shortages (of specific commercial crops) to benefits if high-yield hyperaccumulators are cultivated for industrial valorization of their high metal-content biomass. Full article

The bioaccumulation of selenium (Se) and heavy metals (HMs) in plants is important because it can affect plant health and human nutrition. Recognizing the factors affecting Se accumulation in plants may have important implications for agricultural practices and human health in selenium-rich regions. The study primarily focused on the interactions between Se and HMs in the soil–plant system of the Lower Dniester Valley. Total concentrations of HMs (Cu, Mn, Zn) were determined by atomic absorption spectrometry, while Se concentrations were determined by a sensitive single-test-tube fluorometric method in solutions and extracts. Water-soluble Se (0.09 ± 0.03 mg·kg⁻¹) in soils was 32.1% of the total Se (0.33 ± 0.13 mg·kg⁻¹) and increased with the total rising Se content (r = 0.845). The results indicated that plants had a greater Zn accumulation capacity than that of the other HMs, suggesting its importance as a trace element for plant requirements. Se also had a high bioaccumulation rate. Se and Zn accumulation varied in different soil types, reflecting differences in bioavailability. In contrast, Mn and Cu showed low bioaccumulation, which varied with soil conditions and anthropogenic Cu pollution. Despite the Cu contamination of the soils in the investigated region, it can be inferred that the hydrogeochemical province with high Se content in groundwater has favorable conditions for Se mobilization in soils. The absence of antagonistic interactions with HMs in the soil–plant system contributes to the enhanced Se accumulation in plants in the Lower Dniester Valley. These results emphasize the complexity of the interactions between Se and HMs in the soil–plant system and their potential impact on agricultural practices. Full article

Conservation alternatives that include no-tillage (NT) and cover crops (CCs) reduce soil erosion in row-crop agroecosystems. However, little information is available about how these alternatives affect soil textural properties responsible for soil fertility. This study evaluated the soil particle size distribution and volumetric water content after three years of consistent management in a raised bed system. There were four treatment systems in a dryland maize/soybean rotation on a silt loam soil (Oxyaquic Fraglossudalfs) that included: NT + CCs, conventional tillage (CT) + CCs, CT + winter weeds, and CT + bare soil in winter in northwest Mississippi. The NT + CC system retained 62% more coarse sand in the furrow than the other systems (2.1% compared to 1.3%; p = 0.02). Regardless of the location, the NT + CC system (2.5%) retained 39% more fine sand than the CT + CC system (1.8%; p = 0.01), suggesting that coarse and fine sands were being trapped in furrows combining NT + CC systems, minimizing their off-site transport. In furrows, CCs increased soil volumetric water content by 47% compared to other winter covers. In beds, NT + CCs increased bed water contents by 20% compared to CT + CCs (17.1 to 14.3%; p < 0.01). Implementing conservation alternatives may promote the retention of sand fractions in silty loam soils that are important in supporting soil fertility and crop sustainability. Full article