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This study presents the effects of moisture variation and the influence of matric suction on the permanent deformation (PD) of three tropical soils with different geological-geotechnical characteristics used in road subgrades in southern Brazil. The experimental programme consisted in determining the soil-water characteristic curves and in dynamic triaxial tests to obtain the PD in different compaction and post-compaction moisture contents. The variation of compaction moisture content caused microstructural changes, influencing the plastic behaviour of soils: the higher the initial moisture content, the greater their accumulated permanent deformations. As expected, the post-compaction moisture variation (wetting process) tended to increase the plastic deformation of materials, evidencing the influence of the suction variation on the performance of the soils studied. In addition, matric suction proved to be the best variable to represent the effects of moisture variation on the plastic behaviour of soils subjected to cyclic loading. Thus, a PD prediction model for tropical soils with the inclusion of this parameter was proposed. The model proved to be highly predictive and may become an important tool to be incorporated into current mechanistic-empirical design methods. [ABSTRACT FROM AUTHOR]

Ground source heat pump (GSHP) systems have been widely used to harvest shallow geothermal energy from the ground, providing renewable and low carbon energy sources. A comprehensive investigation of ground thermal properties is critical for effective design of GSHP systems in building heating and cooling applications. This study assesses the effectiveness of Thermal Cone Penetration Test (T-CPT) as a method for determining ground thermal conductivity of unsaturated tropical soils, in which saturation degree can vary seasonally, altering soil thermal properties. This work conducted laboratory model T-CPT tests on sand and clay soils with varying saturation degrees. For field measurements, T-CPT tests were carried out at three different sites of unsaturated tropical soils in South and Southeast regions of Brazil. As a result, measured thermal conductivity values were consistent with data available in literature. Furthermore, laboratory measurements demonstrate that soil thermal conductivity increases with saturation degree and soil density. Results indicate that T-CPT test is an efficient and practical method to capture the impact of saturation degree on thermal conductivity of unsaturated soils. The ease of test performing is a great advantage, because the field test used for this purpose is Thermal Response Test (TRT), which is a much longer test that requires prior installation of heat exchanger tubes in the soil, needs specific equipment for its execution and has a complex interpretation of results. [ABSTRACT FROM AUTHOR]

Anthropogenic land cover change is directly responsible for the deforestation and degradation of tropical forests. In this context, assessing soil organic carbon (SOC) stocks is key to understanding the impact of anthropogenic activities on SOC so that we can implement management practices that effectively reduce emissions or promote carbon sequestration. Our objective was to assess the effect of land-use change on the dynamics and distribution of SOC in three systems (agriculture, pasture and agroforestry) after 40 years of deforestation in a tropical dry forest in the central–eastern region of Honduras. For this purpose, the bulk density, percentage of coarse fragments (>2 mm) and soil organic carbon content were determined at three depths (0.00–0.10 m, 0.10–0.20 m and 0.20–0.30 m). The results showed an increase in bulk density for all new uses, although soil compaction had not yet occurred. In terms of total soil organic carbon (TOC) stocks, deforestation caused a decrease from 17% to 48% in agricultural and agroforestry soils, respectively; on the other hand, grasslands did not show significant differences compared to tropical dry forest, suggesting that they have a high potential as carbon sinks in deforested tropical areas. However, this did not imply a better state of the system, as the greatest increases in bulk density were found in pastures. [ABSTRACT FROM AUTHOR]

Climate change poses an immediate threat to tropical soils with changes in rainfall patterns resulting in accelerated land degradation processes. To ensure the future sustainability of arable land, it is essential to improve our understanding of the factors that influence soil erosion processes. This work aimed to evaluate patterns of soil erosion using the activity of plutonium isotopes (Pu) at sites with different land use and clearance scale in the Winam Gulf catchment of Lake Victoria in Kenya. Erosion rates were modelled at potential erosive sites using the MODERN model to understand small-scale erosion processes and the effect of different management practices. The lowest soil redistribution rates for arable land were 0.10 Mg ha−1 yr−1 showing overall deposition, resulting from community-led bottom-up mitigation practices. In contrast erosion rates of 8.93 Mg ha−1 yr−1 were found in areas where steep terraces have been formed. This demonstrates the significance of community-led participation in effectively managing land degradation processes. Another key factor identified in the acceleration of soil erosion rates was the clearance of land with an increased rate of erosion over three years reported (0.45 to 0.82 Mg ha−1 yr−1) underlining the importance vegetation cover plays in limiting soil erosion processes. This novel application of fallout plutonium as a tracer, highlights its potential to inform the understanding of how soil erosion processes respond to land management, which will better support implementation of effective mitigation strategies. Modelling of soil erosion and deposition patterns using the MODERN model to calculate the depth of soil loss/gain. [ABSTRACT FROM AUTHOR]

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Alien flora in urban ecosystems may have differing impacts on plant diversity and soil. In this study, vegetation and soil characteristics were investigated under the two contrasting herb layer conditions influenced by exotic invasive herb Ageratum conyzoides and introduced alien tree Eucalyptus globulus in an Indian dry tropical urban ecosystem. Phytosociological analysis of 120 randomly sampled quadrats (each of size 1m × 1m, n=60 at each site) was carried out. Nine random seasonal soil samples (0-10 cm) from both study sites were analyzed for soil pH, moisture content, organic carbon, total nitrogen, exchangeable Na, K and Calcium. A total of 82 species were recorded, representing 32 families. Poaceae and Fabaceae constituted dominant families. Cynodon dactylon dominated all sites and seasons. Number of rainy flora was comparable but varied distinctly in drier months. Alpha diversity, estimated higher at EG site in rainy season, ranked sites differently in drier months. Beta diversity, indicative of heterogeneity, was higher at AC sites in drier months in summer. Soil moisture content varied significantly with site and season. EG site recoded higher organic carbon and total nitrogen compared to AC site. In conclusion, the observed variations highlight the complex interplay of environmental factors, seasonal dynamics, and species interactions shaping plant community structure and composition and emphasize the need for further research to elucidate underlying mechanisms driving observed patterns. [ABSTRACT FROM AUTHOR]

Laborious and time-consuming tests are required for the determination of the soil–water characteristic curve (SWCC), often leading to the adoption of estimation methods. To answer the challenge of SWCC prediction, numerous pedotransfer functions (PTF) have been developed. Yet, previous studies have not considered the special behavior of bimodal tropical soils. These materials present dual porosity that is generally attributed to particle aggregation. This paper presents a novel PTF, specifically designed for bimodal tropical soils and based on artificial neural networks (ANNs). The model was trained and tested utilizing a database that was assembled containing soils from tropical regions of Brazil and featuring data for the grain-size distribution (GSD), consistency limits, and SWCC. Natural and remolded soils were included in the training database, but no distinction between soil conditions was made in the ANN. GSDs in the aggregated and disaggregated states were used to offer information to the ANN regarding the effect of particle aggregation on the water retention. The developed model was able to reproduce the typical SWCC shape of bimodal soils. Predictions for the degree of saturation were moderately correlated with directly measured data, with a coefficient of determination of 0.69. The air-entry value and residual suction of the macropores proved to be the most difficult SWCC attributes to be estimated. The ANN presented superior performance when compared to other PTFs not designed specifically for bimodal tropical soils, such as the Arya-Paris and ROSETTA models. It can be concluded from the obtained results that the developed ANN architecture and general approach showed a high capability to capture the main features of the SWCC. [ABSTRACT FROM AUTHOR]

The combined use of electric arc furnace slag fines (EAFSF) and ladle furnace slag fines (LFSF) for soil stabilisation was not evaluated in previous works. Previous studies reported limited information on the microscale behaviour of steel slag materials used in soil stabilisation. This work evaluated synergistic effects provided by the combination of EAFSF and LFSF on the stabilisation of clayey and sandy soils. It provided a detailed microscale analysis of raw materials and slag-soil mixes with scanning electron microscopy, X-ray diffraction, X-ray fluorescence, Raman spectroscopy, thermogravimetric analysis, and derivative thermogravimetry. Their compaction behaviour, unconfined compressive strength (UCS), CBR index, swelling, and resilient modulus were also determined. Filler effects, cementitious, pozzolanic, and ion-exchange reactions were discussed. A positive synergistic behaviour was observed when combining 10% LFSF and 5% EAFSF (by soil weight), which provided a structural arrangement that provided increases in UCS and CBR up to 651% and 1500%, respectively [ABSTRACT FROM AUTHOR]

We present an analytical method to detect and quantify residues of currently used pesticides (CUPs), which include 31 active ingredients (ai) and seven transformation products (TPs) in tropical and agricultural soils of Cuba. Ten isotopically labeled analogous compounds served as internal standards (IL-IS). The novelty of this research is the inclusion of different tropical soils type scarcely studied for CUPs and TPs, based on the QuEChERS (quick, easy, cheap, effective, rugged and safe) method, followed by chromatography tandem mass spectrometry. All figures of merit proved to be satisfactory according to SANTE guidelines 2020 and 2021. Matrix effects (ME) calculated by the external standard method were significant (|ME| > 20% for almost all compounds; grand mean ± standard deviation (STD) 104 ± 108%) in all soils. The internal standard method compensated ME to non-significant levels (8 ± 50%), even for analytes with a non-structure identical IL-IS (STD, 13 ± 57%). Repeatability (relative standard deviation, RSDr) and reproducibility (RSDR) for skeletic regosol (SR) were 7.5 ± 2.8% and 11.7 ± 4.7%, respectively. Absolute (quantified for 11 analytes with structure identical IL-IS) and relative recovery from SR was 92 ± 13% (mean ± STD) and 90 ± 12%, respectively. Limits of quantification for SR ranged from 0.1 to 10 ng/g, except metalaxyl and oxyfluorfen (25 ng/g each). Linearity of matrix-matched (MM) calibration curves (5 to 100 ng/g) had an R2 of ≥ 0.99 for all soils and almost all analytes. The method was successfully applied to 30 real soil samples. [ABSTRACT FROM AUTHOR]

One of the largest uncertainties in the terrestrial carbon cycle is the timing and magnitude of soil organic carbon (SOC) response to climate and vegetation change. This uncertainty prevents models from adequately capturing SOC dynamics and challenges the assessment of management and climate change effects on soils. Reducing these uncertainties requires simultaneous investigation of factors controlling the amount (SOC abundance) and duration (SOC persistence) of stored C. We present a global synthesis of SOC and radiocarbon profiles (nProfile = 597) to assess the timescales of SOC storage. We use a combination of statistical and depth‐resolved compartment models to explore key factors controlling the relationships between SOC abundance and persistence across pedo‐climatic regions and with soil depth. This allows us to better understand (i) how SOC abundance and persistence covary across pedo‐climatic regions and (ii) how the depth dependence of SOC dynamics relates to climatic and mineralogical controls on SOC abundance and persistence. We show that SOC abundance and persistence are differently related; the controls on these relationships differ substantially between major pedo‐climatic regions and soil depth. For example, large amounts of persistent SOC can reflect climatic constraints on soils (e.g., in tundra/polar regions) or mineral absorption, reflected in slower decomposition and vertical transport rates. In contrast, lower SOC abundance can be found with lower SOC persistence (e.g., in highly weathered tropical soils) or higher SOC persistence (e.g., in drier and less productive regions). We relate variable patterns of SOC abundance and persistence to differences in the processes constraining plant C input, microbial decomposition, vertical C transport and mineral SOC stabilization potential. This process‐oriented grouping of SOC abundance and persistence provides a valuable benchmark for global C models, highlighting that pedo‐climatic boundary conditions are crucial for predicting the effects of climate change and soil management on future C abundance and persistence. [ABSTRACT FROM AUTHOR]

Urea is widely used as nitrogen (N) source for rice fertilization in Costa Rica, despite its low efficiency linked to ammonia losses. To assess urea management alternatives, two field experiments were conducted in the Central Pacific region of Costa Rica to study the effect of N-(n-butyl) thiophosphoric triamide (NBPT) on rice yield and N use efficiency (NUE). In Experiment 1 (Exp1) three tillage treatments (commercial-CT-, reduced-RT-, and reduced tillage with previous subsoiler-RTS-) were evaluated with three N managements: control (without N), urea at 124 kg N ha-1 with and without NBPT. In Experiment 2 (Exp2), a 100 kg N ha-1 rate (with and without NPBT) was evaluated along with a control (without N). NUE was estimated using 15N urea isotopic labeling technique for both trials. In Exp1, a significant difference of 4.8% in NUE for grain was observed among urea with and without NBPT, but no tillage effect was observed. No statistically significant differences were observed in yield among the fertilization treatments (Exp1: 3.56 ± 0.98 t ha-1 for urea and 3.85 ± 0.85 t ha-1 for urea with NBPT; Exp2: 3.38 ± 0.39 t ha-1 for urea and 3.40 ± 0.58 t ha-1 for urea with NBPT) or due to different tillage practices (CT: 3.33 ± 0.79 t ha-1, RT: 3.56 ± 0.74 t ha-1, and RTS: 4.23 ± 0.98 t ha-1). Although the NBPT is a viable option to reduce ammonia losses, its adoption in tropical conditions might be restricted by the small impact on yield. [ABSTRACT FROM AUTHOR]

Despite knowing better, water‐stable aggregates like pseudosands are still disintegrated into their clay‐ and silt‐sized bits and pieces to serve standardization in texture determination. Lacking yet a viable alternative, this deliberately committed mistake seems the contemporary best practice for modeling purposes, which is far from being ideal. Here, we propose this misconception to be a major cause for flawed process understanding of tropical soils, leading to substantial uncertainties in model development. There is enough evidence as to why pseudosands are neither sand nor the plain sum of their clay‐ and silt‐sized units and should therefore better be defined as an additional soil texture class for which properties have yet to be examined across the tropics. [ABSTRACT FROM AUTHOR]

The adsorption to container walls, syringes, injectors and analytical columns by strongly hydrophobic organics in aqueous media presents challenges in accurate estimation of sorption parameters of chemicals such as chlorpyrifos (CPF). To minimize this phenomenon, mixed solvents and Teflon-lined centrifuge tubes were used. The study aimed at investigating the sorption kinetics and equilibrium parameters in tropical soils. In addition, the persistence and leaching potential of CPF under submerged and field capacity moisture conditions were studied. Batch sorption studies utilizing the Solvophobic theory revealed time-dependent kinetics on Teflon container walls, where CPF sorption diminished exponentially with increasing methanol fraction. Sorption parameters for soils showed diverse kinetics and equilibrium times across soils and methanol fractions. The Solvophobic theory was used to predict the soil-sorption coefficients KW and KOC. Chlorpyrifos sorption exponentially decreased with increasing methanol fraction, reaching equilibrium in 4–8 h. Container wall KW measured was 0.19 mL/g, while soil KW values ranged from 46.53 to 56.71 mL/g. Chlorpyrifos KOC values varied from 1551 to 1890. The degradation studies under submerged and field capacity conditions indicated microbial and abiotic influences on chlorpyrifos persistence, resulting in half-lives ranging from 18 to 52 days in submerged conditions and 18 to 33 days at field capacity. The Groundwater Ubiquity Index suggested no leaching potential in the examined soils. This study represents the first investigation of chlorpyrifos sorption kinetics only Teflon-lined centrifuge tube container walls, revealing that chlorpyrifos sorption is not instantaneous but rather time-dependent. Future analyses should explore CPF's environmental fate, considering microbial interactions and organic matter content, to contribute to a comprehensive understanding and develop sustainable pest management strategies in tropical regions.Highlights: The study examines Chlorpyrifos's aqueous sorption kinetics and equilibria parameters in Teflon Lined Centrifuge Container walls and tropical soils and its persistence in these soils. Varying methanol fractions were used in batch sorption kinetics experiments, and the Solvophobic theory was employed to predict sorption coefficients KW and KOC indirectly. Degradation experiments on ten soils under flooded and field capacity moisture conditions shed light on the influence of biotic and abiotic processes. KW value for container walls is 0.19 mL/g, while soil KW values range from 46.53 to 56.71 mL/g. KOC values range from 1551 to 1890. Degradation half-lives range from 18 to 52 days for sterilized flooded soils, 30–132 days for unsterilized flooded soils, 18–21 days for sterilized field capacity soils, and 32–33 days for unsterilized field capacity soils. The Groundwater ubiquity index demonstrates that Chlorpyrifos does not leach in the selected soils, ranging from 1.013 to 1.536. [ABSTRACT FROM AUTHOR]

Heavy metals can play an important biological role as micronutrients but also as potentially toxic elements (PTEs). Understanding the natural concentrations of PTEs-Pb and Zn included-in soils allows for the identification and monitoring of contaminated areas and their role in environmental risk assessment. In this study, we aim to determine semi-total or natural and available concentrations of Pb and Zn in topsoils (0–20 cm depth) from 337 samples under native vegetation in the State of Minas Gerais, Brazil. Additionally, we sought to interpret the spatial geochemical variability using geostatistical techniques and quality reference values for these elements in soils were established. The semi-total concentrations were determined by flame and graphite furnace atomic absorption after microwave-assisted nitric acid digestion method. The available concentrations were extracted using the Mehlich-I extractor and determined by atomic absorption spectrometer. Spatial variability was modeled using semivariance estimators: Matheron's classic, Cressie and Hawkins' robust, and Cressie median estimators, the last two being less sensitive to extreme values. This allowed the construction of digital maps through kriging of semi-total Pb and Zn contents using the median estimator, as well as other soil properties by the robust estimator. The dominance of acidic pH and low CEC values reflects highly weathered low-fertility soils. Semi-total Pb contents ranged from 2.1 to 278 mg kg−1 (median: 9.35 mg kg−1) whereas semi-total Zn contents ranged from 2.7 to 495 mg kg−1 (median: 7.7 mg kg−1). The available Pb contents ranged from 0.1 to 6.92 mg kg−1 (median: 0.54 mg kg−1) whereas available Zn contents ranged from 0.1 to 78.2 mg kg−1 (median: 0.32 mg kg−1). The highest Pb and Zn concentrations were observed near Januária, in the northern part of the territory, probably on limestone rocks from the Bambuí group. Finally, the QRVs for Pb and Zn in natural soils were lower than their background values from other Brazilian region and below the prevention values suggested by Brazilian environmental regulations. [ABSTRACT FROM AUTHOR]

Many biogeochemical processes are modulated by dissolved organic matter (DOM), but the drivers influencing the chemodiversity of DOM compounds in Amazonian soils are poorly understood. It has also been theorized whether deforestation controls the decline of DOM. In this study, we collected soil samples from thirty sites across different regions of Brazil's Legal Amazon, and we investigated the trade-offs among soil physical–chemical properties and DOM chemodiversity. We employed optical spectroscopy, Fourier transform ion cyclotron resonance, and multivariate analysis. Our results indicated that, despite variations in land use and soil physical–chemical properties, factors such as the deforested site, geometric mean diameter, weighted average diameter, and soil organic carbon were the main influencers of DOM chemodiversity variation. These findings highlight the importance of considering DOM chemodiversity as closely related to land use and its potential use in developing deforestation models for predicting soil quality decline in Brazil's Legal Amazon. [ABSTRACT FROM AUTHOR]

ABSTRACT Plantation forests can be efficient C sinks in biomass and soil organic carbon (SOC), but the latter depends on many factors, including climate. Tropical humid, mountain areas have cooler temperatures, slowing microbial decomposition, and thus can store considerable SOC. However, the effects of forest plantations on SOC of these montane areas are still poorly studied. Here, we aimed to assess changes in SOC, and related soil properties, after conversion of native rainforest to plantations of five tree species, with rotation cycles varying from 7 to 30 years, on the Mantiqueira Range, Minas Gerais, Brazil. We measured SOC contents and stocks (0.00-0.40 m layer) under a native montane rainforest (control) and plantations of Eucalyptus, Pinus, Cunninghamia, Cupressus and Araucaria, all planted in 3 × 3 m spacing, at an altitude of ca. 1,300 m, marked by humid and cool climate, where SOC contents are naturally high. Soil organic carbon varied from 55 g kg-1 under Eucalyptus to 105 g kg-1 under Araucaria (0.00-0.05 m layer), decreasing in depth (0.20-0.40 m) to the still high values of 20-40 g kg-1. Soil organic carbon stocks for the top 0.20 m were also high, reaching ca. 140 Mg ha-1 under Araucaria, significantly higher value than the native forest (ca. 90 Mg ha-1, p

Sustainable construction materials and local solutions are crucial for meeting urbanisation demands in tropical regions like French Guiana. Poured earthen construction, primarily composed of local soil, offers a cost-effective and environmentally friendly alternative. To ensure good consistency for pouring, the use of dispersants to deflocculate clay particles is an effective strategy that reduces water demand while enhancing the material's physical and mechanical properties. However, the variability of soil impacts the effectiveness of dispersants and the earth's material properties. It is currently unknown how the specific properties of tropical soils can influence the mix design of poured earth and how it impacts their resulting physical and mechanical characteristics. This work examines the soil properties that could help select suitable soil for poured earth construction. Four tropical soils of French Guiana were characterised in detail and used to prepare mortars with varying amounts of water and dispersant (sodium hexametaphosphate). The consistency and compressive strength of the mortars correlated with the mineralogical and geotechnical characteristics of the soils. In particular, soils with high levels of metal oxides produced mortars with the highest compressive strength. Using a dispersant consistently increased the compressive strength and dry density of the mortars and enabled a reduction in water content. Importantly, the analysis revealed that two easily measurable soil properties, the passing at 63 µm and the pH measured in potassium chloride (pH KCl), could predict the mechanical properties of the mortars and the amount of dispersant needed. Specifically, the pH KCl correlated with the proportion of iron and aluminium oxide and showed a positive linear correlation with the compressive strength. Overall, this study identifies easily measurable soil properties, in particular the pH KCl, for selecting and designing high-performance earth materials with tropical soils. It offers promising prospects for industrialising poured earth construction.

Topography significantly influences soil development and characteristics within an uneven agricultural field. Therefore, a comprehensive understanding of soil attributes and processes through detailed pedological knowledge is crucial for effective soil management. This research was carried out in Wasinmi, southwestern Nigeria, to delineate and categorise the soils across different slopes for agricultural insights. Three soil profiles were excavated across the topographical sequence, specifically designated as upper, middle, and lower slope positions. The prevailing soil texture was sandy loam with a discernible trend of lighter soil colour as the slope descended and soil depth increased. The pH of the soil ranged from moderately acidic to slightly acidic. The saturated hydraulic conductivity and soil organic matter content were lowest on the lower slope. Available phosphorus distribution varied inconsistently with higher concentrations of heavy minerals observed at the upper slope. The study underscored the influential role of topography in soil property variations and the need for tailored management practices. The classification of the soils revealed Typic Plintustults in the upper and middle slope positions, while the soils in the lower slope were identified as Typic Kandiaquults. This study demonstrated that topography significantly influenced soil properties, thereby emphasising the need for informed practices to better support the long-term sustainability of land use and agricultural outputs in topographically diverse landscapes.

Anthropogenic land cover change is directly responsible for the deforestation and degradation of tropical forests. In this context, assessing soil organic carbon (SOC) stocks is key to understanding the impact of anthropogenic activities on SOC so that we can implement management practices that effectively reduce emissions or promote carbon sequestration. Our objective was to assess the effect of land-use change on the dynamics and distribution of SOC in three systems (agriculture, pasture and agroforestry) after 40 years of deforestation in a tropical dry forest in the central–eastern region of Honduras. For this purpose, the bulk density, percentage of coarse fragments (>2 mm) and soil organic carbon content were determined at three depths (0.00–0.10 m, 0.10–0.20 m and 0.20–0.30 m). The results showed an increase in bulk density for all new uses, although soil compaction had not yet occurred. In terms of total soil organic carbon (TOC) stocks, deforestation caused a decrease from 17% to 48% in agricultural and agroforestry soils, respectively; on the other hand, grasslands did not show significant differences compared to tropical dry forest, suggesting that they have a high potential as carbon sinks in deforested tropical areas. However, this did not imply a better state of the system, as the greatest increases in bulk density were found in pastures.

The study examined the composition and forms of iron and aluminium oxides in benchmark soils of central southwestern Nigeria. Soils developed from distinct parent rock types, including coarse-grained granite and gneiss, fine grained biotite gneiss and schist, and the amphibolite complex which correspond to the parent rocks of the soils of Iwo (Typic Paleustults), Egbeda (Rhodic Kandiustults) and Itagunmodi (Typic Haplustults) Associations, respectively, were selected for the study. Notably, these soils collectively encompass approximately 60% of the total land area in central southwestern Nigeria. The less than 2 mm soil fractions were pre-treated with hydrogen peroxide to remove soil organic matter. Thereafter, oxides of Fe and Al were extracted using three different extractants: dithionite-citrate-bicarbonate (DCB) mixtures, acidified ammonium oxalate and sodium pyrophosphate solution. The quantification of Fe and Al oxides contents in the respective extracts were carried out using Inductively Coupled Plasma—Atomic Emission Spectrometry. The research findings indicated that the DCB extractable forms of Fe and Al oxides were more abundant compared to other forms of these oxides, and a substantial portion of these oxides within the soils existed in crystalline form. Among the soil series studied, Itagunmodi series exhibited the highest amount of DCB- and oxalate extractable Fe oxides, while Iwo series had the highest content of Fe and Al oxides extracted by sodium pyrophosphate solution. Importantly, the presence of Fe oxides were found to negatively impact the reactivity of SOM in the soils. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is a key limiting nutrient in tropical and subtropical soils but with unknown responses to climate change. We hypothesized that storage and distribution of P pools differ between reference soil groups, but P availability increases with an increase in precipitation in native sub‐Saharan Africa, an underrepresented region in the global P database. To test these hypotheses, we sampled topsoils (0–10 cm; Arenosols, Lixisols, Acrisols) of uncultivated Savannah woodlands along climate gradients stretching from Mozambique to Zambia. Mean annual precipitation (MAP) ranged from 365 to 1227 mm. We extracted P fractions using Hedley's sequential fractionation, yielding resin‐exchangeable P, P in 0.5 M NaHCO3, 0.1 M NaOH, 1 M HCl and aqua regia. Extracts were analysed for total P using inductively coupled plasma–optical emission spectroscopy and inorganic P using the colorimetric molybdenum blue method. We found that total P contents were highest in Acrisols (235 ± 76 mg kg−1), followed by Lixisols (214 ± 45 mg kg−1) and Arenosols (133 ± 74 mg kg−1). Beside P storage, also P distribution differed between soils. Mean annual temperature (MAT) did not reveal significant correlations with P fractions. However, with increasing MAP, concentrations of almost all P pools increased; available Pi (Resin‐P) increased significantly in Arenosols while potentially bioavailable P (NaHCO3‐Po) increased in all soils, with MAP explaining 43% of data variability in Arenosols, 74% in Lixisols and 85% in Acrisols. Hence, P availability increased with an increase in MAP to different degrees, that is, climatic effects on P dynamics were soil‐group‐specific. Therefore, different regions in the native sub‐Saharan woodlands are likely prone to different soil fertility responses when climate changes. [ABSTRACT FROM AUTHOR]

Soils on many smallholder farms in Southern Africa are severely depleted in plant nutrients, in particular phosphorus (P), following years of maize monocropping with little or no fertilizer input. Past studies suggest that pigeon pea (Cajanus cajan (L.) Millsp.) may increase plant-available P. Pigeon pea is not a common crop in much of Southern Africa, and the effect of locally grown pigeon pea varieties on plant-available P is unknown. We assessed the changes in plant-available P after growing pigeon pea varieties MPPV-2, MPPV-3, and Babati White in Zambia, viz. Lixisols of Choma and Mkushi, Acrisols of Chipata and Kasama, and Arenosols of Kaoma. The selected soils were not fertilized. Baseline soils (0–20 cm), sampled after long-term maize monocropping and soils from the same fields after growing pigeon pea were collected from field trials in Kaoma, Chipata, Choma, and Mkushi and analyzed for plant-available P. Further, a greenhouse study was conducted with soils from Kasama, Choma, Kaoma, and Chipata, under which soil P was determined before and after growing pigeon pea, soybean (Dina), and maize (SC 419) without fertilizer addition. Pigeon pea under field studies had no significant (p > 0.05) effect on plant-available P in Choma, Kaoma, and Chipata. In Mkushi, pigeon pea cropping resulted in a 47.5% significant decline (p ≤ 0.05) in plant-available P, amounting to a loss of 11.2 kg ha−1. The greenhouse study showed a significant decline (p ≤ 0.001) in plant-available P after seven weeks of maize growth, while there was no significant (p > 0.05) effect on plant-available P after soybean and pigeon pea cropping. The latter was primarily due to the significantly higher P uptake associated with larger biomass production of maize after seven weeks in the greenhouse. During the initial seven weeks, pigeon pea biomass had significantly higher P concentrations than maize. Thus, P deficiency symptoms were exhibited in maize, while pigeon pea appeared healthy. However, mobilized P, calculated as the sum of plant P and soil P after cropping minus soil P before planting, was significantly lower (p ≤ 0.01) in pigeon pea compared to soybean and maize. Synthesizing field and greenhouse experiments suggests that there is a low net decline of plant-available P from soils after pigeon pea cropping. Therefore, rotation with these pigeon pea varieties could be beneficial to resource-poor farmers due to low P removal and its ability to grow in P-deficient soil. [ABSTRACT FROM AUTHOR]

The banana sector contributes to 3% of the Colombia total exports, becoming the most important crop in the north of the country, benefiting more than 2.5 million families. Banana production is concentrated on the Colombian Caribbean coast where most of 90% of the soils are affected to some degree of salt affection in soils. This study was carried out in the municipality of Zona Bananera, Department of Magdalena (Colombia) elsewhere eleven geomorphological units were delimited through geomorphological surveying with geopedological methods. Given the high costs of implementing salt monitoring and management programs in the field, the implementation of Near Infrared spectroscopy (NIR) and image analysis are proposed as an alternative for mapping soils salt affectation. Geostatistical methods, traditional soil laboratory methods and multispectral analysis of 697 soil samples were analyzing using machine learning and spectral models. The Orthogonal Partial Linear Square- Discriminant Analyses (OPLS-DA), Principal Component Regression (PCR), Partial Linear Square (PLS–PLSR), Least Absolute Shrinkage and Selection Operator (LASSO) were implemented. Soil cartographies for SAS were designed in areas under banana cultivation, determining the affectation degree. The results obtained showed that 45.1% of the soils are affected by salts, with R2 0.76 and RMS 0.15 for the applied of supervised models. OPLS-DA had a better performance being the high above sea level was the principal covariable to improve the model accuracy. LASSO and PLS were useful to Mg+2 and K+ with RMSE 0.92 and 0.34 and R2 of 0.37 and 0.44, while Saitsky&Golay filter improved the predictions model for pH and Ca+2. The use of combined techniques of geopedology, geostatistics and spectroscopy were efficient, practical and cheap methodologies for evaluate soil properties associate to SAS in the stablished banana crops. [ABSTRACT FROM AUTHOR]

In the tropics, anthropogenic activities can lead to water and wind erosion, a loss of biodiversity, and a reduction in sequestered carbon, fertility, and organic matter content in the soils concerned, potentially resulting in their degradation. This study therefore aims to identify the mechanisms used by plant species to restore degraded tropical soils and plant species characteristics that are best suited to achieve this through a critical scoping review of the peer-reviewed literature. Soil restoration leads to the re-establishment of ecosystem services and an increase in soil production potential, the regeneration of biodiversity, the stopping of organic matter losses, and the creation of favorable conditions for carbon sequestration and nitrogen fixation. The choice of appropriate plant species depends on the restoration objectives to be achieved. Five key mechanisms by which plant species contribute to restore degraded tropical soils include: (1) nitrogen fixation, (2) carbon sequestration, (3) organic matter addition, (4) structure stabilization, and (5) erosion control. The main characteristics of plant species and vegetation involved in these mechanisms are (a) the capacity to form symbiotic associations with N-fixing bacteria and mycorrhizae, (b) the production of abundant root biomass releasing litter and exudates, (c) roots having a high length density, branching intensity, and depth distribution, (d) the production of an abundant and easily decomposed above ground litter, (e) the production of a vast canopy, and (f) the presence of different vegetation strata. Targeting these characteristics will contribute to acting on several mechanisms simultaneously, which will increase the chance of success in tropical soil restoration. [ABSTRACT FROM AUTHOR]

Urea is widely used as nitrogen (N) source for rice fertilization in Costa Rica, despite its low efficiency linked to ammonia losses. To assess urea management alternatives, two field experiments were conducted in the Central Pacific region of Costa Rica to study the effect of N-(n-butyl) thiophosphoric triamide (NBPT) on rice yield and N use efficiency (NUE). In Experiment 1 (Exp1) three tillage treatments (commercial-CT-, reduced-RT-, and reduced tillage with previous subsoiler-RTS-) were evaluated with three N managements: control (without N), urea at 124 kg N ha-1 with and without NBPT. In Experiment 2 (Exp2), a 100 kg N ha-1 rate (with and without NPBT) was evaluated along with a control (without N). NUE was estimated using 15N urea isotopic labeling technique for both trials. In Exp1, a significant difference of 4.8% in NUE for grain was observed among urea with and without NBPT, but no tillage effect was observed. No statistically significant differences were observed in yield among the fertilization treatments (Exp1: 3.56 ± 0.98 t ha-1 for urea and 3.85 ± 0.85 t ha-1 for urea with NBPT; Exp2: 3.38 ± 0.39 t ha-1 for urea and 3.40 ± 0.58 t ha-1 for urea with NBPT) or due to different tillage practices (CT: 3.33 ± 0.79 t ha-1, RT: 3.56 ± 0.74 t ha-1, and RTS: 4.23 ± 0.98 t ha-1). Although the NBPT is a viable option to reduce ammonia losses, its adoption in tropical conditions might be restricted by the small impact on yield.

Net rhizodeposition corresponds to the portion of living root carbon (C) that remains in the soil after microbial processing and partial decomposition. Although it is assumed that this C input exerts an important role in the formation of soil organic matter (SOM), its contribution to distinct SOM pools is still not fully understood. In this study, we aimed to (i) quantify the retention of net rhizodeposition C in the different SOM fractions and in reactive Al and Fe mineral phases and (ii) investigate how rhizodeposition drives the spatial distribution of microbial communities in the rhizosphere. To track the transfer of net rhizodeposition into the soil, we used artificially labeled eucalypt (Eucalyptus spp.) seedlings under a 13C-CO2 atmosphere (multiple-pulse labeling). Combining physical SOM fractionation and the chemical extraction of aluminum (Al) and iron (Fe) reactive phases, we studied the distribution of net rhizodeposition into different soil fractions. We also assessed the 13C incorporation into microbial phospholipid fatty acids (PLFAs) at different distances from the roots. Our results show that 76 % of the net rhizodeposition 13C was retained within the mineral-associated organic matter (MAOM) fraction. About 28 % of net rhizodeposition 13C within the MAOM fraction was retained within the Al and Fe reactive phases, indicating that this is a sizeable mechanism for the retention of net rhizodeposition in soil. Rhizodeposition increased the abundance of microbial PLFAs exclusively in the soil close to the roots (0–4 mm), with prominent incorporation of net rhizodeposition 13C into fungal biomarkers. Overall, our findings underscore the importance of mineral associations for the retention of net rhizodeposition in the soil. We also highlight the role of fungi in transferring the root-derived C beyond the root vicinity and promoting the formation of occluded SOM.

Soil erosion is one of the main causes of soil degradation and an important environmental problem, often accelerated by human activities. Different types of soil and water conservation measures (SWCM) have been implemented in worldwide to control soil loss, such as Staggered Contour Trenches (SCT) and Hillside ditches (HD) which are recommended in topographies up to 40 % slope. This study measured the effects of STC and HD, on surface runoff, soil loss, exposed of organic matter and soil moisture content, in a shaded coffee crop with steep slopes in an Entisol soil. Nine runoff plots were installed in Llano Brenes, Costa Rica, in the upper basin of the Jesús María River in a study area with slopes between 50 and 71 ± 7.92 %. We conclude that this study could make an important contribution to research on the use of SWCM on tropical soils with slopes greater than 50 %. Due to the non-compliance of assumptions, a logarithmic transformation of the data was used, and they were evaluated using the Kruskal-Wallis one-way nonparametric test. Spearman correlation and linear regressions were used to assess the effect of the precipitation and intensity in the soil loss and runoff in each treatment. The amount of organic matter exposed by soil removal was not statistically different between HD and SCT, but both were different to the control (R2 = 0.81, P < 0.05). Spearman correlation analysis showed the rainfall depth contributed more to runoff depth (HD R = 0.62; SCT R = 0.62; Control R = 0.60; P < 0.001) and soil loss (HD R = 0.50; STC R = 0.53; Control R = 0.50; P < 0.001) than other variables. Regression analysis showed that runoff and soil loss were significant (P < 0.05) and positively correlated with rainfall depth for each treatment. In this study, HD was shown to be efficient in erosion control on steeper slopes. HD helped reduce soil loss compared to the control, by 88 % in 2018 and 83 % in 2019. HD also reduced runoff generation by 55 % in 2018 and 60 % in 2019 compared to the control. While SCT was not statistically different in the generation of surface runoff and soil loss compared to the control.

This paper presents an experimental and analytical investigation of the influence of variables related to soil weathering on the geomechanical performance of sand-silt mixtures containing lateritic soils, i.e. intensely weathered tropical soils with the influence of interparticle bonding. The sand-silt mixtures containing different relative proportions between uniform sand and lateritic soil were produced, and geomechanical soil characterization tests were performed. Based on the results, a transition from a primarily coarse-to a fine-grained prevailing soil structure was found to cause considerable impact on the geomechanical performance of these soils, as evidenced by design variables related to soil mineralogy and size distribution characteristics. Specifically, fines contents of both individual soil particles and soil aggregations were found to correlate with experimental results, while the relative proportion between sesquioxides (aluminum, and iron oxides), and silica, i.e. sesquioxide-silica ratios (SSR−1), facilitated estimates concerning changes in geomechanical performance. Finally, the application of the sand-silt mixtures containing lateritic soil on soil walls reinforced with polymeric strips was also evaluated, further emphasizing the potential advantages of adopting variables related to soil weathering on design guidelines concerning tropical soils.

The Atlantic Forest exhibits remarkable floristic diversity over short distances, and when combined with altitude, it results in variations in soil biological properties and hydrological dynamics. This study aimed to quantify the distribution pattern of soil biological properties along a small topographic gradient and identify how these properties are related to soil chemical, physical, and topographical attributes in an Atlantic Forest fragment in Brazil. Plots were established along hillslope positions varying from 100 to 180 m of altitude. Soil biological characterization was performed at a depth of 0.0–0.10 m in both summer and winter seasons. The lowland showed higher microbial biomass nitrogen in summer (57.28 ± 5.57 μg g−1 soil) and higher anaerobically mineralizable nitrogen in summer and winter (42.70 ± 2.14 mg kg−1 and 41.06 ± 3.37 mg kg−1, respectively). The midland showed lower microbial biomass carbon, enzymatic activity, and soil moisture in both seasons, and higher metabolic coefficients in summer. Soil chemical properties exerted a greater influence on the variability of biological properties in both seasons. The land slope conditioned lower microbial activity and organic cycling in the midland. Soil biological properties were affected by seasonality. Even a small altitudinal gradient (up to 100 m) in the Sea of Hills regions of the Atlantic Forest can lead to significant changes in soil biological and chemical attributes. [ABSTRACT FROM AUTHOR]

Background: Particle size distribution (PSD) is a fundamental soil measurement that is crucial for agriculture, engineering, hydrological, and environmental applications as well as in basic research such as in developing water release curves in flow and transport modeling. The accurate determination of PSD, particularly clay content, is especially critical in ascertaining the magnitude and rates of many physical, chemical, and hydrological processes in soils. The accuracy of the hydrometer method for PSD, which relies on the settling velocity of soil particles in a soil suspension, could be affected by the density of the suspension, which in turn, depends on the initial sample mass, texture, and mineralogy of the soil. Aims: We hypothesized that (1) initial mass determines the concentration and the physical interaction of particles in a soil suspension and affects particle settlement, recovery, and the accuracy of the hydrometer method, and (2) the widely used initial air‐dry mass of 50 g underestimates the clay percentage of medium to heavy textured tropical soils. The objective of this study was to investigate the effect of mass and KCl on clay recovery in tropical soils with varying texture and mineralogy using the hydrometer method. Methods: The experiment comprised seven soils, four soil masses (10, 20, 30, 50 g), and two KCl treatments in a 7 × 4 × 2 factorial design replicated three times. Results: Results showed a general trend of increasing estimates of clay % as the soil mass decreased from 50 to 10 g and the KCl concentration increased from 0 to 0.0025 M. This implies that using an initial sample mass of 50 g in sedimentation methods, underestimates, and 10 g overestimates the clay % in predominantly medium to heavy textured tropical soils. Interestingly, there was a drastic change in texture for most of the soils as the sample mass decreased to 10 g. Conclusions: We conclude that the initial air‐dry mass affects the clay recovery of medium to heavy textured humid tropical soils. Results suggest that the ideal initial mass for these soils lies between 20 and 30 g. Furthermore, the mechanistic pathway that drives the observed decrease in clay recovery as soil sample mass increase could be due to the flocculating tendency of KCl. [ABSTRACT FROM AUTHOR]

Food production in sandy soils has evolved significantly, most notably through the advent of integrated crop–livestock systems (ICLSs). ICLSs increase soil cover, which maintains soil moisture and sequesters carbon (C). Here we investigate the influence of ICLSs on soil physical, chemical, and biochemical properties, and grain yield (GY) in tropical sandy soils in short-time. We compared seven ICLSs in two consecutive crops seasons (with soybean or maize as cash crops) in southeastern Brazil. These were (1) corn + Urochloa brizantha cv. BRS Paiaguás—soybean (ICL-Paiaguás); (2) corn + U. brizantha cv. BRS Piatã—soybean; (3) corn + U. ruziziensis—soybean; (4) corn–soybean under conventional tillage (CT) as a negative control; (5) corn–soybean under no-tillage (NT) as a positive control; (6) Paiaguás grass—continuous grazing (Perennial Paiaguás); (7) and Piatã grass—continuous grazing (Perennial Piatã). Soybean and corn GY data, soil physical and chemical attributes, and soil enzymatic activity were subjected to descriptive statistics and multivariate analysis. CT and NT shared high loadings of H + Al, Al, and soil temperature and low loadings of soil pH, SOM physical and chemical fractions, cationic exchange capacity, and arylsulfatase activity. ICL-Paiaguás and Perennial Piatã had a similarly high loading of total N, humin, total organic carbon, and mineral-associated carbon stocks. The fulvic acid fraction was the most sensitive to C accumulation in the sandy soil under ICLSs. Soil water and thermal regimes were limiting in both CT and NT. The study not only confirms the capacity of conservation mechanisms to enhance soil-based ecosystem functions, but it also highlights the potential of ICLSs to aid sustainable food production even in the context of tropical sandy soils, which frequently receive limited attention in intensive agricultural practices. [ABSTRACT FROM AUTHOR]

Mammal diversity affects carbon concentration in Amazonian soils. It is known that some species traits determine carbon accumulation in organisms (e.g., size and longevity), and are also related to feeding strategies, thus linking species traits to the type of organic remains that are incorporated into the soil. Trait diversity in mammal assemblages – that is, its functional diversity – may therefore constitute another mechanism linking biodiversity to soil organic matter (SOM) accumulation. To address this hypothesis, we analyzed across 83 mammal assemblages in the Amazon biome (Guyana), the elemental (by ED‐XRF and CNH analysis) and molecular (FTIR‐ATR) composition of SOM of topsoils (401 samples) and trait diversity (functional richness, evenness, and divergence) for each mammal assemblage. Lower mammal functional richness but higher functional divergence were related to higher content of carbonyl and aliphatic SOM, potentially affecting SOM recalcitrance. Our results might allow the design of biodiversity management plans that consider the effect of mammal traits on carbon sequestration and accumulation in soils. [ABSTRACT FROM AUTHOR]

Bioturbation by termites is considered a key process in the regulation of soil properties in tropical soils. The concentration of clay and the presence of 2:1 clay minerals in termite soil are usually explained by the need for termites to build stable biogenic structures and/or to have access to water only available in the lower soil layers. However, while these hypotheses are attractive, they do not always offer a sufficient explanation for understanding termite bioturbation behavior. Here, we used ecological stoichiometry theory to propose a third hypothesis that bioturbation can also be explained by the limitation of termites for Na+. This chemical element is missing from the vegetation consumed by termites, while it plays an important role in the regulation of termites' physiological processes. In old and highly weathered soils, such as those found in the tropics, a significant source of Na+ for termites likely comes from 2:1 minerals, which are only available in the deeper soil layers. Therefore, this article aims to propose the hypothesis of the use of bioturbation by termites as a means to fulfill their need for Na+. The impacts of this ecological process on ecosystem functioning and soil fertility are discussed. [ABSTRACT FROM AUTHOR]

Understanding the factors controlling soil total N (TN) is helpful in simulating N cycling at local and regional scales. This study was conducted with the aim to; (i) understand the distribution of TN in specific soil horizons (A and B horizons) of three reference soil groups: Acrisols, Cambisols and Ferralsols, common in humid tropical environments, and (ii) to identify factors controlling TN variations among the various soil groups. Twenty-eight Acrisols, 21 Cambisols and 8 Ferralsols profiles spanning a wide range of precipitation gradients, vegetation type/land use and parent materials, from the Northwestern Highlands (NWH) of Cameroon were considered. Soil properties were analyzed following standard procedures. TN had very high coefficients of variation (>35%) in all the reference soil groups (RSGs), with highest mean TN (0.31 ± 0.03%) observed in the A horizons of Acrisols and the lowest (0.05 ± 0.01%) in B horizons of Ferralsols. Variations in TN content were significantly (p < 0.05) influenced by parent material, land use type, precipitation and slope gradient. In surface (A) horizons of all the RSGs, TN correlated positively and significantly with clay (p < 0.05), silt (p < 0.01) and soil organic carbon (SOC) (p < 0.01), and negatively with sand (p < 0.01). This observation was slightly different in subsurface (B) horizons. This study provides data which contributes to a better understanding of soil fertility in tropical highlands. [ABSTRACT FROM AUTHOR]

One-fourth of Brazilian Amazonia is managed for timber production, but only a small portion of active logging sites follow sustainable forest management plans (SFMPs). Amazon forests without SFMPs are susceptible to deforestation because such plans integrate the use of forest products and conservation goals by allowing selective wood extraction following regulations aimed at reducing the long-term impact of logging. However, it remains uncertain whether reduced-impact selective logging typical of SFMPs (17-20 m3 ha-1 yr-1 of 38-70 species) changes forest regeneration, carbon (C) stocks, and nutrient cycling. Here, we tested the hypothesis that litter and soil biogeochemical parameters serve as indicators of sustainable logging as forest regeneration, C stocks, and C-to-nutrient ratios in soil and litter become progressively similar to those of primary forests as time elapses after logging. We used a chronosequence spanning nine years since logging to relate litter and soil (at 0-10, 10-30, 30-50 cm depth) C stocks and 12 and 15 biogeochemical parameters, respectively, as well as canopy cover and tree seedling density (10-150 cm tall) in upland evergreen Amazon forests. In one unlogged and four logged stands sampled three, five, seven, and nine years after logging, we compared 15 permanent plots (three replicated 0.5 ha plots per time-since-logging category). We found that five parameters explained >80% of the variation in soil and litter properties among logged and unlogged stands. Litter parameters were more sensitive to logging than soil parameters, as litter C stocks and C-to-nutrient ratios increased systematically after logging. Canopy cover decreased over time and was ~14% lower nine years after logging. Total seedling density did not change consistently over time but was ~54% higher seven years after logging. Our data suggest that the SFMP guidelines have served the purpose of maintaining soil quality and forest regeneration. Litter and soil parameters can be useful indicators of sustainable forest management in upland evergreen forests in Central Amazonia.

In this study, we investigate the biogeochemical consequences of fire in seasonally flooded Amazon forests, where recent declines in forest cover have been linked to increases in fire frequency and severity. Previous studies have hypothesized that a quasi-permanent state-shift transition from typical Amazon forests to open savannas can occur when fire results in further depletion of already impoverished soil nutrient pools. Asymbiotic N2 fixation (ANF) is an essential pathway for fire-affected forests to acquire nitrogen (N) after disturbance, but ANF response to fire has yet to be quantified in Amazonia. Here, we quantify ANF through field sampling and laboratory incubations using 15N-labeled dinitrogen (15N2) and measurement of 14 biogeochemical parameters in surface (0–10 cm) and subsurface (10–30 cm) soils. Our data represent burned and unburned replicated sampling sites, across five stands, spanning a gradient from infrequent (once in 13 years) to frequent (five times in 13 years) fire occurrences. ANF did not vary with fire frequency but was, on average, 24% lower in burned than in unburned surface soils across all stands. Burned and unburned subsurface soils had similar ANF rates. About 58% of ANF variance was explained by the joint effect of carbon (C):N ratio and available phosphorus (P) in burned and unburned soils. ANF increased linearly with C:N and P availability in unburned soils, but a highly non-linear relationship was observed in burned soils. Our findings show that fire alters soil C-to-nutrient stoichiometry, which resulted in lower N inputs via ANF into burned relative to unburned tropical forest soils.

Abstract Background C:N:P homeostasis in plants guarantees optimal levels of these nutrients in plant metabolism. H However, one of the causes to the effects of deficit irrigation is the loss of C:N:P homeostasis in leaves and stems that causes reduction in the growth of sugarcane. Being able to measure the impact of water deficit on C:N:P homeostasis in plants from the stoichiometric ratios of the concentrations of these nutrients in leaves and stems. This loss causes a decrease in nutritional efficiency, but can be mitigated with the use of silicon. Silicon favors the homeostasis of these nutrients and crop productivity. The magnitude of this benefit depends on the absorption of Si by the plant and Si availability in the soil, which varies with the type of soil used. Thus, this study aims to evaluate whether the application of Si via fertigation is efficient in increasing the absorption of Si and whether it is capable of modifying the homeostatic balance of C:N:P of the plant, causing an increase in nutritional efficiency and consequently in the production of biomass in leaves and stems of sugarcane ratoon cultivated with deficient and adequate irrigations in different tropical soils. Results Water deficit caused biological losses in concentrations and accumulation of C, N, and P, and reduced the nutrient use efficiency and biomass production of sugarcane plants cultivated in three tropical soils due to disturbances in the stoichiometric homeostasis of C:N:P. The application of Si increased the concentration and accumulation of Si, C, N, and P and their use efficiency and reduced the biological damage caused by water deficit due to the modification of homeostatic balance of C:N:P by ensuring sustainability of the production of sugarcane biomass in tropical soils. However, the intensity of attenuation of such deleterious effects stood out in plants cultivated in Eutrophic Red Oxisols. Si contributed biologically by improving the performance of sugarcane ratoon with an adequate irrigation due to the optimization of stoichiometric ratios of C:N:P; increased the accumulation and the use efficiency of C, N, and P, and promoted production gains in biomass of sugarcane in three tropical soils. Conclusion Our study shows that fertigation with Si can mitigate the deleterious effects of deficient irrigation or potentiate the beneficial effects using an adequate irrigation system due to the induction of a new stoichiometric homeostasis of C:N:P, which in turn improves the nutritional efficiency of sugarcane cultivated in tropical soils.

The different forms of heavy metals may be significantly extracted from soils by plant roots. In a glasshouse experiment, the shifting of soil heavy metal forms under thorny amaranth was examined. To accomplish the research goal, thorny amaranth was planted for four weeks at field water content in soils with varying Cu and Zn contents. Copper and Zn levels in the soil were measured both before and after planting. High soil Cu and Zn levels reduced this plant's height and dry biomasses. Thorny amaranth considerably reduced the exchangeable and available Cu and Zn in the soil. The soil exchangeable and available Cu and Zn had a good correlation with the plant uptakes of these elements. Copper and Zn reductions by planting significantly lower than the available Cu and Zn. A significant portion of the soil exchangeable Cu and Zn shifted to stronger bonding during the incubation time. It was demonstrated that plants absorbed more Cu and Zn from forms different than the soil-exchangeable forms.

It is no more news that the deterioration of our mother Earth has resulted in many hardships faced in many lands of the world. Research statistics has shown that about 80% of the environmental problems faced in Asia, especially the loss of soil biodiversity results from deforestation. Africa has been intensely affected by the hazards of climate change at a rate of more than 50%, also Near East and North Africa has recorded more than 48% loss of her biodiversity in soils due to habitat alteration and loss. This list is inexhaustive and heart-broken, presenting a view that if sustainable remediation is not taken then we will have more malnourished and sick people in years to come, our environment will be more polluted and toxic, our water system will become more and more difficult to remediate, there could be increase in local, national and international conflict among other unforeseen unpleasant happenings. To contribute as a modality towards solving this problem this study investigated the current soil organic carbon-soil biodiversity variability in the ecosystem-nexus of soils. The study took place within the University of Abuja landmass. Spatial and temporal data were collected on earth-system properties, were analysis and simulations were done. The Area was model and interpolated to find hot spots with grave threat. Explorative and descriptive statistics was applied in the study. Results indicated that the soils of the study area are compacted and hence unfit to support sustainable survival of the living entities within the soil system, with soil Bulk density value range at 2.1g cm-3–2.71g cm-3. Organic carbon of the area was low. Geotechnical and geomorphological evaluation and interactions revealed only two (2) points having earthworm length of 1 cm which presented a view that the soils spore is too tight to enable sustainable flourishing of below and above ground biodiversity in the sites investigated. Hence ecological tool like the use of Vetiver Grass Technology was recommended for the study area environmental regeneration and for healing the soils impediment.

Calcium (Ca) and potassium (K) are essential nutrients for plant growth but the antagonistic effect between these nutrients may reduce crop yield. A two–year field trial was carried out in a loamy sand soil to evaluate cassava response to Ca (0, 50, 100, and 200 kg ha−1, as ground limestone, GL) and K (0, 50, 100, and 200 kg K2O ha−1, as potassium chloride, KCl). Calcium addition, especially 200 kg Ca ha−1, adversely affected soil K availability with more pronounced on water–soluble K than on exchangeable and non–exchangeable K from day–7 onwards. Both Ca and K had no antagonistic impact on cassava. However, growth and yield responded positively to K more promptly than to Ca. Combined rates, except 100 kg Ca ha−1 with no K fertilizer, significantly increased fresh tuber yield by 7.6–41.1 % over the control. To gain the highest fresh tuber yield by adding 200 kg Ca ha−1, 200 kg K2O ha−1 must be implemented. This light–textured soil was physically preferable for cassava tuberization, and the optimum yield can be achieved by proper Ca and K fertilization.