Soil Systems

The adoption of technologies for N fertilization has become essential for increasing the N use efficiency in no-till (NT) systems in Brazil. Thus, this study aimed to quantify ammonia losses, N removal in grains, and second crop season yield in no-till and conventional (T) areas that received the application of different N fertilizers and their technologies. Ammonia volatilization, N extraction in grains, and corn yield in response to the application of conventional fertilizers were compared to urea treated with urease inhibitors in NT and conventional systems. The treatments were: no-N (Control); Prilled urea (PU); urea + N-(n-Butyl) thiophosphoric triamide (U_NBPT); urea + Cu + B (U_CuB); ammonium nitrate (AN), and ammonium sulfate (AS). In the NT system, the N-NH₃ losses were 49% higher than in the conventional; without differences in corn yield. The fertilizers AN and AS had the lowest N-NH₃ losses, regardless of the tillage system. U_NBPT reduced the mean N-NH₃ loss by 33% compared to PU. U_NBPT (1200 mg kg⁻¹) and U_NBPT (180 mg kg⁻¹) reduced the N-NH₃ losses by 72% and 22%, respectively, compared to PU in the NT system. We noticed that the NBPT concentration to be used in soils under NT should be adjusted, and a reduction of N-NH₃ losses does not directly reflect an increase in yield and N extraction by corn. Full article

Per- and polyfluorinated alkyl substances (PFAS) are an environmentally persistent group of chemicals that can pose an imminent threat to human health through groundwater and surface water contamination. In this review, we evaluate the subsurface behavior of a variety of PFAS chemicals with a focus on aqueous film forming foam (AFFF) discharge sites. AFFF is the primary PFAS contamination risk at sites such as airports and military bases due to use as a fire extinguisher. Understanding the fate and transport of PFAS in the subsurface environment is a multifaceted issue. This review focuses on the role of adsorbent, adsorbate, and aqueous solution in the fate and transport of PFAS chemicals. Additionally, other hydrogeological, geochemical, ecological factors such as accumulation at air–water interfaces, subsurface heterogeneity, polyfluorinated PFAS degradation pathways, and plant interactions are discussed. This review also examines several case studies at AFFF discharge sites in order to examine if the findings are consistent with the broader PFAS literature. We present the most crucial future research directions and trends regarding PFAS and provide valuable insights into understanding PFAS fate and transport at AFFF discharge sites. We suggest a more comprehensive approach to PFAS research endeavors that accounts for the wide variety of environmental variables that have been shown to impact PFAS fate and transport. Full article

Soils and agriculture are inextricably linked, in the past as well as today. The Pacific islands, which often represent organized gradients of the essential soil-forming factors of substrate age and rainfall, represent excellent study systems to understand interactions between people and soils. The relationship between soil characteristics and indigenous agricultural practices are well documented for some locations, but there is a paucity of data for much of the region. Given the extent of ecological adaptation that has been documented, specifically for Hawai‘i, new Pacific datasets are expected to provide important insights into indigenous agricultural practices. To contribute to this discussion, we analyzed patterns in soil chemistry and vegetation in the Manu‘a islands of American Samoa. Soils were sampled along transects that crossed through precontact settlement zones in the upland of Fiti‘uta on Ta‘ū island, a location characterized by young (<100 ky) volcanic substrates and very high (>3800 mm y⁻¹) annual rainfall. Soils were analyzed for several soil fertility properties that have been proposed as predictors of intensive rainfed tuber production in Hawai‘i and Rapa Nui. Surveys of remnant economic plants were conducted to assess patterns of past land use. Soils demonstrated moderate values of soil fertility as measured by pH, base saturation, exchangeable calcium, and total and exchangeable phosphorus, despite the high rainfall. Previously identified soil fertility indicators had some application to the distribution of traditional agriculture, but they also differed in important ways. In particular, low exchangeable calcium in the soils may have limited the agricultural form, especially the cultivation of tubers. Significant shifts in both soil parameters and remnant economic crops were documented, and alignment suggests cropping system adaptation to soil biochemistry. Archaeological samples combined with surveys of relict vegetation suggest that agroforestry and arboriculture were key components of past agricultural practices. Full article

Wetting and drying (W-D) cycles are responsible for significant changes in soil structure. Soil often undergoes irreversible changes affecting infiltration and solute retention through W-D cycles. Thus, it becomes essential to evaluate how soils under natural conditions are altered by W-D cycles. This study analyzed two non-cultivated (from grassland and secondary forest) Oxisols (Typic Hapludox and Rhodic Hapludox) of different textures under 0 and 6 W-D cycles. The main results obtained showed that soil water retention was mainly affected in the driest regions (smaller pore sizes). The contribution of residual pores to total porosity increased with 6 W-D and transmission pores decreased in both soils. The Rhodic Hapludox presented differences in water content at field capacity (increase), while the Typic Hapludox showed alterations at the permanent wilting point (increase), affecting the amount of free water (Rhodic Hapludox) and water available to plants (Typic Hapludox). Both soils showed increases in imaged porosity with 6 W-D. Variations in the contribution of small and medium rounded pores, mainly large and irregular (with an increase in both soils not significant in the Rhodic Hapludox), could explain the results observed. The micromorphological properties were mainly influenced by changes in the number of pores, in which smaller pores joined, forming larger ones, increasing the areas occupied by larger pores. Overall, this study showed that the investigated soils presented pore systems with adequate water infiltration and retention capacities before and after continuous W-D cycles. Full article

Gully erosion is a worldwide threat with numerous environmental, social, and economic impacts. The purpose of this research is to evaluate the performance and robustness of six machine learning ensemble models based on the decision tree principle: Random Forest (RF), C5.0, XGBoost, treebag, Gradient Boosting Machines (GBMs) and Adaboost, in order to map and predict gully erosion-prone areas in a semi-arid mountain context. The first step was to prepare the inventory data, which consisted of 217 gully points. This database was then randomly subdivided into five percentages of Train/Test (50/50, 60/40, 70/30, 80/20, and 90/10) to assess the stability and robustness of the models. Furthermore, 17 geo-environmental variables were used as potential controlling factors, and several metrics were examined to evaluate the performance of the six models. The results revealed that all of the models used performed well in terms of predicting vulnerability to gully erosion. The C5.0 and RF models had the best prediction performance (AUC = 90.8 and AUC = 90.1, respectively). However, according to the random subdivisions of the database, these models exhibit small but noticeable instability, with high performance for the 80/20% and 70/30% subdivisions. This demonstrates the significance of database refining and the need to test various splitting data in order to ensure efficient and reliable output results. Full article

Grape pomace (GP) has an added value because of its contribution to carbon (C) and nitrogen (N) in soils when applied as an organic fertilizer. Macronutrients from GP are translocated into the soil after amendment, but little is known about the factors that may influence the mobility of C, N and bioactive molecules, i.e., polyphenols, in the soil column. We investigated the mobility of the macronutrient content of GP, derived from two red (Dornfelder and Pinot noir) and two white grape varieties (Riesling and Pinot blanc). For that, three different soils (loamy sand RefeSol01A, silt loam RefeSol02A and a vineyard soil) were evaluated in a column model using a GP application rate of 30 t ha⁻¹. The three-step lab-scale approach included the analysis of total C, N and polyphenols expressed as total polyphenolic content (TPC) in: (a) the fresh GP, representing the total amount of C, N and TPC; (b) the mobility with rainwater, representing the aqueous extractable fraction and (c) the mobility in the soil column and leaching potential. Our results showed that total C/N ratios were wider in the white GP varieties compared with the red ones. Higher TPC values were measured in Dornfelder and Pinot noir compared with white varieties. Analysis of the water-extractable fraction showed that the C recovery may reach up to 48% in Pinot blanc, which also corresponds to the highest N contribution. Extractable polyphenols were higher in the red compared with the white varieties by a factor of 2.4. C and N were mobilized with rainwater from the GP through the soil column. However, the application rate used in the experiment was not indicative of an accumulation in the soil. Compared with the control (no GP application), C values were significantly higher in the leachates from GP-treated soils, in contrast to N values. Up to 10% of the TPC of the pomace was leached into the soil. The TPC recovery in the soils strongly depended on the combination of soil type and GP variety. Generally, the sandy and more acidic soil showed an even distribution of phenolics with a high recovery rate (up to 92%) compared with more neutral and silty soil. Most of the polyphenol content could accumulate in the upper soil layer (0–10 cm). These results provide the first insights on the mobility of macronutrients in the soil using a column model and point out the need to relate those experiments to soil and GP properties in order to avoid the accumulation of nutrients in soil or mobility to adjacent ecosystems. Full article

Agriculture faces a significant challenge in maintaining crop production to meet the calorie demand of the ever-growing population because of limited arable land and climate change. This enforces a search for alternative multifarious agricultural-based solutions to meet the calorie demand. In search of alternatives, agricultural soil management has been highlighted and is expected to contribute to climate change mitigation through soil carbon sequestration and reduce greenhouse gas emissions through effective agricultural management practices. The addition of biochar to the soil significantly improves the soil nitrogen status, soil organic carbon, and phosphorus, with greater effects under the different tillage systems. This symbiosis association could further change the bacterial structure in the deeper soil layer which thus would be important to enhancing productivity, particularly in vertisols. Biochar also has an environmental risk and negative consequences. Heavy metals could be present in the final food products if we use contaminated raw materials to prepare biochar. However, there is a need to investigate biochar application under different climatic conditions, seasons, soil tillage systems, and crop types. These indicate that the positive effect of proper biochar fertilization on the physiology, yield formation, nutrient uptake, and soil health indicators substantiate the need to include biochar in the form of nutrients in the crop production sector, especially in light of the changing climate and soil tillage systems. Full article

Salt-affected soils are related to salinity (high content of soluble salts) and/or sodicity (excess of sodium), which are major leading causes of agricultural land degradation. This study aimed to evaluate the performances of three machine learning (ML) algorithms in predicting the soil exchangeable sodium percentage (ESP), electrical conductivity (EC_e), and salt-affected soil classes, from soluble salt ions. The assessed ML models were Partial Least-Squares (PLS), Support Vector Machines (SVM), and Random Forests (RF). Soil samples were collected from the High Valley of Cochabamba (Bolivia). The explanatory variables were the major soluble ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, HCO₃⁻, Cl⁻, CO₃²⁻, SO₄²⁻). The variables to be explained comprised soil EC_e and ESP, and a categorical variable classified through the US Salinity Lab criteria. According to the model validation, the SVM and RF regressions performed the best for estimating the soil EC_e, as well as the RF model for the soil ESP. The RF algorithm was superior for predicting the salt-affected soil categories. Soluble Na⁺ was the most relevant variable for all the predictions, followed by Ca²⁺, Mg²⁺, Cl⁻, and HCO₃⁻. The RF and SVM models can be used to predict soil EC_e and ESP, as well as the salt-affected soil classes, from soluble ions. Additional explanatory features and soil samples might improve the ML models’ performance. The obtained models may contribute to the monitoring and management of salt-affected soils in the study area. Full article

Soils contaminated with potentially toxic elements (PTEs) and salt manifest a large number of physical, chemical, and structural problems by various processes such as reduced water availability, water and air movement in soil space, water holding capacity of soil, as well as perilous effects on plant growth and physiology. Halophytes have the ability to grow in saline environments and are better adapted to accommodate environmental constraints including PTE ions. An experiment was designed to study the response of the halophyte Atriplex halimus to a range of salinities and different concentrations of Cd and Ni. Tolerance and soil remedial potential of the plant were quantified in terms of PTE uptake and portioning, plant biomass, root/shoot ratio, chlorophyll and anti-oxidative enzyme production, along with stress markers such as lipid peroxidation, proline, and glycine betaine. The plant was also evaluated for its potential to phytoremediate PTE contaminated soil. The results suggest that A. halimus can tolerate moderate concentrations of both the PTEs and salt. The species holds promise for bio-reclamation of saline and PTE-contaminated soil. Full article

Soil contains an enormous diversity of microorganisms and can act as a reservoir of antibiotic resistance determinants. This study identified and compared the bacterial diversity and the antimicrobial resistance profile of clinically-relevant isolates around a newly developed hospital and university precinct. Eight soil samples were collected, genomic DNA was extracted and 16S rRNA gene sequencing was performed. Bacterial isolates cultured from the soil were identified using MALDI-TOF. Antibiotic sensitivity testing (AST) was performed on a subset of isolates. The soil from both precincts were similarly diverse. Phylum Proteobacteria was prevalent in all samples and was the most abundant in one of the hospital sites. Cyanobacteria was abundant in two hospital sites closer to a sewage treatment plant. Bacterial diversity was only significantly different between two of the hospital sites. A total of 22 Gram-negative organisms were isolated by culture. AST revealed that the soil isolates from both precincts exhibited low resistance. The unidentified bacteria closer to the hospital precinct with human interactions possibly hints at the role of anthropogenic activities on the soil microbial diversity. The abundance of Proteobacteria (causing majority of human infections) and Cyanobacteria nearer to the hospital premises, comprising more immunocompromised and immunocompetent individuals, is concerning. Full article

Black rice (Oryza sativa L.) contains high concentrations of bioactive compounds that are associated with human-health benefits. Arbuscular mycorrhizal fungi (AMF) can increase plant performance and concentrations of these bioactive compounds. In a pot experiment, the effects of four different species of AMF (Claroideoglomus etunicatum; Rhizophagus variabilis; Rhizophagus nov. spec.; Acaulospora longula) were assessed on growth performance, grain yield, concentrations of phenolic compounds and anthocyanin, and antioxidant activity of two black-rice cultivars. The experiment was a completely randomized factorial design with two factors, viz. cultivar (Niew Dam Hmong and Maled Phai) and treatment (four different species of AMF and two non-inoculated treatments, without and with mineral fertilizer). Results showed that cultivar, treatment, and their interaction were almost always significant sources of variation for both plant performance parameters and concentrations of bioactive compounds. Maled Phai showed higher performance and higher concentrations of phenolics and anthocyanins but lower antioxidant activity than Niew Dam Hmong. The non-inoculated treatment without mineral fertilizer showed the lowest performance. The non-inoculated treatment with mineral fertilizer resulted in larger root and shoot biomass than the mycorrhizal treatments, but grain yield was higher in the mycorrhizal treatments. Inoculation with R. variabilis resulted in the highest concentration of phenolics and anthocyanins. We conclude that R. variabilis was the best inoculum for increasing grain yield and bioactive compounds, especially in Maled Phai. Full article

Different types of soil data are used in process-based crop models as input data. Crop models have a diverse range of applications, and soil research is one of them. This bibliographic analysis was conducted to assess the current literature on soil-related applications of crop models using two widely used crop models: Agricultural Production Systems Simulator (APSIM) and Decision Support System for Agrotechnology Transfer (DSSAT). The publications available in the Scopus database during the 2000–2021 period were assessed. Using 523 publications, a database on the application of process-based crop models in soil research was developed and published in an online repository, which is helpful in determining the specific application in different geographic locations. Soil-related applications on APSIM and DSSAT models were found in 41 and 43 countries, respectively. It was reported that selected crop models were used in soil water, physical properties, greenhouse gas emissions, N leaching, nutrient dynamics, and other physical and chemical properties related to applications. It can be concluded that a crop model is a promising tool for assessing a diverse range of soil-related processes in different geographic regions. Full article

This study relates the spatial heterogeneity (or patterning) of geochemical elements in the topsoil of a semi-arid floodplain/hillslope system in north-eastern Australia to vegetation distribution and rates of flood inundation. A total of 540 topsoil samples were collected from six flood frequency zones, ranging from a frequently flooded area (RI = 1:1–2 yrs) to two zones that have not flooded in living memory (RI > 50 yrs). Within each zone, topsoil samples were collected from both vegetated and non-vegetated surfaces, and each sample was analysed for 26 parameters. A combination of multi- and univariate analyses reveals that vegetation is an important contributor to topsoil heterogeneity. In zones subject to relatively frequent flooding, the spatial distribution of parameters in the topsoil is greatly influenced by the movement of water, with vegetation acting as a sink rather than a source. However, as floods become increasingly rare, distinct resource-rich units become evident in the topsoil beneath the vegetation. These findings indicate that topsoils in semi-arid floodplains are altered when their natural flooding regimes are reduced, beginning to approximate hillslopes when flood frequencies exceed 1-in-7 to 10 years. This points to the need for frequent flood (overbank) releases that are able to cover the 1-in-20-year floodplain to maintain the character of the soils and support vegetation growth in these environments. Full article

Adoption of the right rice variety and water-saving irrigation method could reduce greenhouse gas (GHG) emissions in lowland rice cultivation. A study was conducted at the research farm of Bangladesh Agricultural University, Mymensingh, Bangladesh, in 2019 during the Boro (dry) season to determine the impacts of different rice varieties (BRRI dhan29, BRRI dhan47, BRRI dhan69, Binadhan-8, Binadhan-10, and Binadhan-17) on methane (CH₄) emissions under two irrigation methods, i.e., alternate wetting and drying (AWD) and continuous flooding (CF). The treatments were laid out in a split-plot design, considering water regime as the main plots and rice variety as the sub-plots. The emission rates of CH₄ were determined by collecting air samples using the closed chamber technique and measuring the concentrations using a gas chromatograph. CH₄ emission rates varied with the growth and development of the rice varieties. The lowest cumulative CH₄ emission rate was observed in Binadhan-17, particularly under AWD irrigation. Across the rice varieties, AWD irrigation significantly reduced the cumulative CH₄ emissions by about 35% compared with CF. No significant variation in rice yield was observed between AWD (5.38 t ha⁻¹) and CF (5.16 t ha⁻¹). This study suggests that the cultivation of Binadhan-17 under AWD irrigation could be effective at reducing the carbon footprint of lowland rice fields. Full article

Combined paper mill biosolids (PB) and forest-derived liming by-products improve soil properties, but their residual effects following several years of application have hardly been investigated. A 13-year (2009–2021) field study was initiated at Yamachiche, QC, Canada, to assess the residual effects of PB and liming materials on the properties of a loamy soil. The PB was applied during nine consecutive years (2000–2008) at 0, 30, 60, and 90 Mg wet·ha⁻¹, whereas the 30 Mg PB·ha⁻¹ rate also received one of three liming materials (calcitic lime, lime mud, wood ash) at 3 Mg wet·ha⁻¹. No amendment was applied during residual years. Past liming materials continued to increase soil pH but their effect decreased over time; meanwhile, past PB applications caused a low increase in residual soil NO₃-N. Soil total C, which represented 40% of added organic C when PB applications ceased, stabilized to 15% after six years. Soil Mehlich-3-extractable contents declined over the thirteen residual years to be not significant for P, K, and Cu, while they reached half the values of the application years for Zn and Cd. Conversely, Mehlich-3 Ca was little affected by time. Therefore, land PB and liming material applications benefited soil properties several years after their cessation. Full article

The use of forest biomass to produce energy is increasingly viewed as a means to reduce fossil fuel consumption and mitigate global warming. However, the impact of such practices on soils in the long term is not well known. We revisited forest plots that were subjected to either whole-tree (WTH, n = 86) or stem-only (SOH, n = 110) harvesting 30 years ago in the boreal forest in Quebec, Canada. The objective of the present study was to find soil properties that could explain the lower soil C and N stocks at the sites subjected to WTH compared to SOH after 30 years. Compared to SOH, lower soil C and N stocks attributable to WTH occurred when soil particle content <20 µm was below 30%. The theoretical separation of soil organic matter into two fractions according to soil particle content <20 µm—a recalcitrant and a labile fraction—could explain the observed pattern of soil C and N differences between WTH and SOH. Imperfect or poor soil drainage conditions were also associated with lower soil C and N in WTH compared to SOH. Limiting additional biomass harvesting from these sites would help to preserve soil C and N from potential losses. Full article

The goals of the current research were to assess the immediate impact of invasive wild boar (Sus scrofa L.) in olive orchards of southern Italy. Over a one-year study, in grubbed and ungrubbed areas, we measured the seasonal changes on the fast soil biological and chemical responses at depths of 0–15 cm and 15–40 cm, and several leaf and fruit characteristics. The impact factor, IF_G, was used to quantify the effects of wild boar on individual soil parameters. Grubbing induced an increase in the soil moisture at both depths. Soil pH, organic matter, and C/N ratio were higher in grubbed soils at 0–15 cm and lower at 15–40 cm compared to ungrubbed soils. These trends were reflected in the higher microbial community biomass and the inhibition of fungal fraction in grubbed topsoil, while an opposite tendency at 15–40 cm was found. Microbial biomass had the highest IF_G in topsoil (94%) and metabolic quotient (85%) at a 15–40 cm depth. Microbial stress condition and C loss were found in grubbed soil at both depths. Furthermore, these soils were also shown to be of lower quality than ungrubbed soils, especially at 0–15 cm (SQI = 0.40 vs. 0.50, respectively). A stronger negative impact of wild boar grubbing was observed in the Autumn/Winter and for fruit polyphenol content. Full article

The phospholipid fatty acid method was used to determine the shifts in microbial biomass due to irrigation with reverse-osmosis (RO) concentrate (or highly saline reject water) and brackish groundwater (BGW). In this greenhouse study, RO concentrate and BGW were applied to irrigate pecan trees for 8 months for two consecutive seasons. The objectives of the study were to (i) evaluate how irrigation with RO concentrate and BGW impacts soil microbial composition in pecan rhizospheres using microbial phospholipid fatty acid (PLFA) biomarkers as indicators, and (ii) evaluate its implications on soil health. Three treatments of RO concentrate (EC = 8.0 dS/m), BGW (EC = 4.0 dS/m), and the city of Las Cruces’s water (EC = 0.8 dS/m) as a control were used to irrigate pecan trees. EC, pH, and organic matter (OM%) content of the soil samples were measured, and PLFA biomarkers for the microbial community were determined. Na-, Cl-, and K-ion concentrations were 26.16, 32.54, and 5.93 meq/L in 2017 and 25.44, 24.26, and 5.49 meq/L in 2018, respectively, in RO irrigation pots. For two seasons, gram-positive bacteria were dominant, while gram-negative bacteria were not detected in the second season. PLFA biomarkers of fungi were found among all three treatments in the first season; however, they appeared only with BGW in the second season. Actinomycetes were recorded in the first season while they were not seen in the second season. Increases in soil salinity and microbial shifts could have important implications for soil health. Irrigating with RO and BGW shifted the soil microbial composition; therefore, long-term irrigation with BGW and RO concentrate would be deleterious for pecan production and soil health. Full article

Soil health is not explicitly included in current stream and floodplain restorations. This may be one of the many reasons that stream restorations are not achieving their full restoration and ecological benefits. The lack of design and implementation procedures for providing healthy soils and the absence of specific soil metrics for evaluation are some of the reasons for the non-inclusion of soil health in floodplain restorations. Here, we have brought together a team of researchers and practitioners to provide a blueprint for the inclusion of soil health in floodplain restorations, with a specific emphasis on approaches that may be easily accessible for practitioners. We describe the challenges posed by current restoration procedures for physical, chemical, and biological soil conditions. The top ten soil metrics that could be easily measured and could be leveraged by practitioners to assess floodplain soil conditions before and after restorations were identified and selected. The best design and construction practices for improving soil health on floodplains are presented. We also recommend that the current crediting approaches and regulatory mechanisms for stream restorations be updated to incentivize soil health. The inclusion of soil health will help us attain the ecological services and functional uplift goals that are being targeted by environmental agencies and the restoration community. Full article