Bulk Soil Samples Research Articles

Evaluating the diversity and composition of bacterial communities associated with Vachellia pachyceras - the only existing native tree species in the Kuwait desert.

We investigated the diversity and composition of bacterial communities in rhizospheric and non-rhizospheric bulk soils as well as root nodule bacterial communities of Vachellia pachyceras - the only native tree species existing in the Kuwait desert. Community fingerprinting comparisons and 16S rDNA sequence identifications were used for characterization of the bacterial population using specific primers. The bacterial characterization of soil samples revealed four major phyla: Acidobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. In situ (desert) samples of both rhizospheric and non-rhizospheric bulk soil were dominated by the bacterial phyla Firmicutes and Bacteroidetes, whereas the phylum Betaproteobacteria was present only in non-rhizospheric bulk soil. Ex situ (nursery growing condition) V. pachyceras resulted in restricted bacterial communities dominated by members of a single phylum, Bacteroidetes. Results indicated that the soil organic matter and rhizospheric environments might drive the bacterial community. Despite harsh climatic conditions, data demonstrated that V. pachyceras roots harbor endophytic bacterial populations. Our findings on bacterial community composition and structure have major significance for evaluating how Kuwait's extreme climatic conditions affect bacterial communities. The baseline data obtained in this study will be useful and assist in formulating strategies in ecological restoration programs, including the application of inoculation technologies.

The structure and function of the global citrus rhizosphere microbiome

Citrus is a globally important, perennial fruit crop whose rhizosphere microbiome is thought to play an important role in promoting citrus growth and health. Here, we report a comprehensive analysis of the structural and functional composition of the citrus rhizosphere microbiome. We use both amplicon and deep shotgun metagenomic sequencing of bulk soil and rhizosphere samples collected across distinct biogeographical regions from six continents. Predominant taxa include Proteobacteria, Actinobacteria, Acidobacteria and Bacteroidetes. The core citrus rhizosphere microbiome comprises Pseudomonas, Agrobacterium, Cupriavidus, Bradyrhizobium, Rhizobium, Mesorhizobium, Burkholderia, Cellvibrio, Sphingomonas, Variovorax and Paraburkholderia, some of which are potential plant beneficial microbes. We also identify over-represented microbial functional traits mediating plant-microbe and microbe-microbe interactions, nutrition acquisition and plant growth promotion in citrus rhizosphere. The results provide valuable information to guide microbial isolation and culturing and, potentially, to harness the power of the microbiome to improve plant production and health.

Mulching-induced preservation of soil organic matter quality in a burnt eucalypt plantation in central Portugal

Mulching has amply proven its effectiveness to mitigate post-fire soil erosion but its impacts on soil organic matter (SOM) quality and quantity continue poorly studied. The present study addressed this knowledge gap for a eucalypt plantation in central Portugal that had been burnt and, immediately after the wildfire, mulched with 13.6 Mg ha−1 of eucalypt logging residues some five years before. This was done by performing a range of analytical techniques (elemental and isotope analyses, analytical pyrolysis and 13C NMR spectroscopy) not only on the bulk soil samples but also on their humic acids (HAs) and free organic matter (FOM) fractions. While mulching reduced soil and SOM losses with 91 and 93%, respectively, it also improved SOM quality of the topsoil, in particular in terms of HAs and FOM. At 0–4 cm depth, both HAs and FOM contents were roughly twice as high in the mulched plots as in the control plots. The effects of mulching on the molecular composition of HAs and FOM fractions, however, varied markedly. Analytical pyrolysis (Py-GC/MS) revealed that mulching had led to a noticeable accumulation of labile, aliphatic SOM constituents such as carbohydrate-derived and alkyl compounds (fatty acids and n-alkanes) but that it hardly affected the composition of HAs. Even so, solid-state 13C NMR spectroscopy showed that mulching had resulted in a relative increase in aryl C in the FOM fraction, suggesting an enhanced preservation of the pyrogenic OM. Overall, the combined use of a range of analytical techniques allowed to conclude that, five years after their application, the forest logging residues had led to a greater preservation of the fire-derived pyrogenic OM (mainly aromatic compounds) in the topsoil as well as to higher contents of SOM's most labile molecular constituents (mainly carbohydrates and n-alkyl compounds). The former reflected the reduced erosion rates, while the latter was probably due to a combination of reduced erosion rates with the additional input of fresh organic matter.

Assessment of soil texture from spectral reflectance data of bulk soil samples and their dry-sieved aggregate size fractions

Diffuse reflectance spectroscopy (DRS) continues to emerge as a rapid approach for estimating several soil properties including soil texture. To improve the accuracy of DRS approach for soil texture assessment, a data fusion approach was tested in which the reflectance spectra of bulk soil and its aggregate size fractions obtained by dry sieving approach were combined with three chemometric models such as partial-least-squares regression (PLSR), a locally-weighted PLSR (PLSRLW) and PLSR with feature selection (PLSRFS). This newly developed approach was tested using three different soil (Vertisols, Alfisols and Mixed) spectral libraries containing a total of 1013 soil samples each with 9 different aggregate size fractions. Because soil aggregation is influenced by the nature of clay minerals in addition to organic carbon, iron and aluminum oxides, XRD analyses were carried out in selected aggregate fractions. Results showed that there was reasonable improvement in the estimation accuracy of sand, silt and clay contents in KVS and KAS when an aggregate size fraction spectrum was added to bulk soil spectrum. For example, consideration of PLSRFS or PLSRLW models along with best-performing aggregate spectra could reduce RMSE values in the validation datasets in the order of 18% for clay to 31% for silt in KVS samples, 32% for silt to 49% for clay in KAS samples, and 6% for sand to 15% for silt in WBODS samples compared to when PLSR model was used alone in the F0 spectra. Correlation analysis showed that textural fractions were more strongly correlated to spectra of macroaggregates (aggregate size >0.20 mm) than those of microaggregates (aggregate size <0.13 mm). Correlation analysis between soil separates and the amount of soil mass within each aggregate size fraction showed that the microaggregates contained more information for soil textural components than macroaggregates. The proposed approach of using bulk soil spectra and aggregate fraction spectra may be a step forward in texture analysis through DRS approach. Although extra time is required for collecting soil aggregate fraction spectra, the method has advantage of allowing the measurement of geometric mean diameter using traditional methods.

Deciphering the bacterial composition in the rhizosphere of Baphicacanthus cusia (NeeS) Bremek

Rhizobacteria is an important ingredient for growth and health of medicinal herbs, and synthesis of pharmacological effective substances from it. In this study, we investigated the community structure and composition of rhizobacteria in Baphicacanthus cusia (NeeS) Bremek via 16S rRNA amplicon sequencing. We obtained an average of 3,371 and 3,730 OTUs for bulk soil and rhizosphere soil samples respectively. Beta diversity analysis suggested that the bacterial community in the rhizosphere was distinctive from that in the bulk soil, which indicates that B.cusia can specifically recruit microbes from bulk soil and host in the rhizosphere. Burkholderia was significantly enriched in the rhizosphere. Burkholderia is a potentially beneficial bacteria that has been reported to play a major role in the synthesis of indigo, which was a major effective substances in B. cusia. In addition, we found that Bacilli were depleted in the rhizosphere, which are useful for biocontrol of soil-borne diseases, and this may explain the continuous cropping obstacles in B. cusia. Our results revealed the structure and composition of bacterial diversity in B. cusia rhizosphere, and provided clues for improving the medicinal value of B. cusia in the future.

Response of the Bacterial Communities Associated With Maize Rhizosphere to Poultry Litter as an Organomineral Fertilizer

Maize is an important food source worldwide and is of considerable industrial importance. Low maize yields are mostly due to low soil fertility, so expensive mineral fertilizers are often used to offset the lack of nutrients. Poultry litter (PL) is one of the most valuable and phosphorous-rich animal wastes. However, PL usually contains veterinary antibiotic residues, particularly fluoroquinolones (FQs), which may alter soil microorganism diversity and resistance patterns. In this study, we aimed to understand the impact of applying mineral (triple superphosphate - STP) or organomineral (STP with PL and reactive Bayovar phosphate with PL) fertilizers (130 or 260 kg/ha of total P2O5) on the structure and composition of the soil bacteriome and on phosphate-mineralizing bacteria associated with the maize rhizosphere. Maize plants were sampled at 60 and 90 days after sowing and a clear rhizosphere effect was observed in all samples. No specific groups of bacterial genera predominated (>3% relative abundance) according to the different fertilizer treatments and most of the genera were shared among samples. Multivariate analyses of 16S rRNA sequences revealed clear clustering based on sampling time and distinct separation from bulk soil samples. Abundances of phosphate-mineralizing bacteria varied depending on the sampling time. We observed a positive effect on phytase activity under the 260 kg STP with PL treatment. Although the FQ enrofloxacin and its main metabolite ciprofloxacin were detected in PL, their concentrations in fertilized soils were below quantification thresholds. Quinolone resistance genes were not detected in the maize rhizosphere or bulk soil. Together, these results suggest that the rhizosphere effect, plant age and applied amounts of fertilizer are more influential on bacterial communities than the type of fertilizer used. Thus, application of PL as an organomineral fertilizer does not appear to have extensive impacts on the bacterial diversity of maize rhizosphere, so it could be an excellent option for enhancing maize production.

Preferential flow pathways in paddy rice soils as hot spots for nutrient cycling

Crop rotations with maize and flooded rice lead to temporally aerobic soil conditions. This promotes the development of desiccation cracks in the soil, which can act as preferential flow pathways for water and solutes. We hypothesized that these cracks are enriched with organic carbon (C), plant nutrients and microbial residues (amino sugars) and that they can thus also serve as hot spots of fertilizer and C cycling. To test this hypothesis, we applied 13C-labelled rice straw and 15N-labelled urea to rice fields of the International Rice Research Institute (Los Baños, Philippines). We then traced the fate of the 13C-labelled rice straw and the 15N-labelled urea in crack and bulk soil and in microbial residues in two approaches, i) in the short term, i.e., 24 h after application of straw and fertilizer jointly with a dye tracer (Brilliant Blue) prior to maize seeding in the paddy - maize cropping system, as well as ii) in the long-term, i.e., during one year and for three different crop rotations (continuous paddy rice, paddy rice – maize, and paddy rice – maize with straw mulching and cover cropping). The short-term analyses of the dye tracer depth profiles showed that flow path areas decreased with increasing depth. A typical impermeable plough pan was not identified. Instead, we observed rapid infiltration of irrigation water down to 60 cm soil depth. The dyed flow paths were enriched in organic C (+12%) and plant nutrients (N: +21%, Ca2+: +59%, K+: +39%, Mg2+: +39%) relative to the bulk soil. The labelled straw and fertilizer quickly reached 60 cm depth with the dye tracer. We could not identify elevated microbial biomass along the flow paths, however, we did find larger microbial activities along the cracks in the long-term experiment than in the surrounding bulk soil. The increased activity fostered microbial uptake of fertilizer 15N along the cracks, which was detected mainly for fungal residues and only in the trials receiving straw (crack soil: 0.6 ± 0.1 mg glucosamine-15N kg soil−1, bulk soil: 0.2 ± 0.1 mg glucosamine-15N kg soil−1). We conclude that analysis of homogenized bulk soil samples can underestimate C and nutrient availability, as well as their microbial processing in paddy rice soils, when crack systems are not considered.

VegeSafe: a community science program generating a national residential garden soil metal(loid) database.

VegeSafe is a national community science initiative aimed at characterising soils in Australian residential gardens and community gardens. The program has been operating for over 5years and has generated soil metal(loid) data from over 8600 residential garden and community garden soil samples, submitted by almost 2000 community scientists. The VegeSafe program represents the largest archive of soil metal(loid) data and associated metadata for residential garden soils in Australia. Samples were collected across Australia, with 61% of samples collected from NSW (n = 5284), Victoria (VIC) 20% (n = 1688) of samples and Queensland (QLD) 7% (n = 592) of samples. Soil metal(loid) data obtained by analysis of bulk soil samples by portable X-ray florescence spectrometry (pXRF) for As, Cu, Cr Mn, Pb and Zn showed spatial patterns of greater soil metal(loid) concentrations around city areas, particularly in NSW and VIC. The Australian Health Investigation Levels for low-density residential land uses (HIL-A) were used in this study as guideline values for soil metal(loid) concentrations. Overall, there was a relatively small number of HIL-A exceedances in the dataset, with most metal(loid)s exceeding their HIL-A concentration in < 5% of incidences. The notable exception to this was for Pb, which had HIL-A (300mg/kg) exceeded in 27% (n = 1427) of samples in NSW, 17% (n = 280) in VIC and 10% (n = 61) in QLD. Through the power of community engagement and community science, the VegeSafe program presents an unprecedented insight into soil metal(loid) concentrations in Australian residential gardens.

GEOTECHNICAL INFLUENCE OF UNDERLYING SOILS TO PAVEMENT FAILURE IN SOUTHWESTERN PART OF NIGERIA

Roads in Nigeria are usually constructed without in-depth knowledge of the subsoil that serves as the foundation for the road elements. Road failures are often associated to poor construction materials or inadequate design without cognisance of the underlying soils. Engineering properties of ten bulk soil samples collected from the subgrade of Arigidi/Oke-Agbe highway were investigated to determine their suitability for highway pavement. Results show that all the subgrade soils below the failed locations have higher plasticity indices, which is an indication of their high swelling potential, and they are classified as A-7-6 clayey soils with high-water adsorption capability (16.1 – 22.4%) compared to subgrade soils from the stable locations. Low compacted density (1325 – 1928 Kg/m3), extremely poor CBR values; 8 – 31% (unsoaked) and 3 – 8% (soaked) which indicate percentage reduction in strength of the soils up to 77% on exposure to excessive moisture and the predominance of fines (&gt; 59%) in the soils are responsible for the degree of instability. Furthermore, soft to low stiffness (49 – 131 kN/m2) and poor permeability of the subgrade materials underlying the pavement result to the failure characteristics witnessed. This study shows that the suitability and behaviour of subgrade soil is dependent on its engineering properties.

Linking land use changes to variation in soil properties in a Mediterranean mountain agroecosystem

Several decades of intensive rainfed farming in Mediterranean mountains and later land abandonment has led to rapid land use and land cover changes. During recent centuries, the conversion of rangelands into croplands has increased the surfaces prone to erosion. In the southern Pre-Pyrenees, the process was reversed during the middle of the twentieth century, allowing the recovery of vegetation and subsequent variation in land cover. This work aims to assess how land use changes after generalised land abandonment affect some major soil properties related to soil quality. For this purpose, 98 replicate bulk soil samples were collected in a 23 km2 catchment that was mostly cultivated at the beginning of the last century. Soil samples were distributed over areas representing the main land uses (agricultural land, natural forest, pine afforestation and scrubland). Bulk density, stoniness, grain size, pH, carbonates, electrical conductivity, soil organic carbon (SOC), total nitrogen (TN), water retention capacity and magnetic properties (low frequency magnetic susceptibility (LF) and frequency dependence (FD)) were analysed in the samples from different land use areas. A past scenario was recreated using estimated data from the SPEROS-C model in order to evaluate changes in SOC over time. Furthermore, a multitemporal analysis of the Normalised Difference Vegetation Index of Landsat images was performed between 1972 and the present in order to assess the dynamics of revegetation. After land abandonment, 16.5% of the area remained as croplands, but afforestation and natural revegetation occupied 83.5% of the catchment. The highest mean value for SOC was found in the pine afforested area and the highest TN mean value was found in the natural forest. The lowest mean values for SOC and TN were recorded on the agricultural land. These results show the impact of soil changes produced by land use changes in fragile Mediterranean mountain agroecosystems.

Investigation of fissile materials collected from a non-critical nuclear explosion site using non-destructive analytical techniques

In this work, we identify, isolate, and characterize hot particles from bulk soil samples collected from a non-critical nuclear detonation site. Several non-destructive techniques were used to identify and isolate the nuclear fuel particles from soil samples. Digital autoradiography was used to indicate and localize individual “hot particles”, while γ-spectroscopy was employed to confirm plutonium presence. In addition, scanning electron microscopy and energy dispersive spectroscopy were used to study the surface morphology and elemental composition of the hot particles. Initial sample analyses indicate that explosively dispersed non-critical fuel morphology may be markedly different from other non-critical accidents.

Effect of different biochars on phosphorus (P) dynamics in the rhizosphere of Zea mays L. (maize)

To investigate the effects of biochar on biological and chemical phosphorus (P) processes and identify potential interactive effects between P fertilizer and biochar on P bioavailability in the rhizosphere of maize. We conducted a pot-experiment with maize in a sandy loam soil with two fertilizer levels (0 and 100 mg P kg −1) and three biochars produced from soft wood (SW), rice husk (RH) and oil seed rape (OSR). Sequential P fractionation was performed on biochar, bulk soil, and rhizosphere soil samples. Acid and alkaline phosphatase activity and root exudates of citrate, glucose, fructose, and sucrose in the rhizosphere were determined. RH and OSR increased readily available soil P, whereas SW had no effect. However, over time available P from the biochars moved to less available P pools (Al-P and Fe-P). There were no interactive effects between P fertilizer and biochar on P bioavailability. Exudates of glucose and fructose were strongly affected by especially RH, whereas sucrose was mostly affected by P fertilizer. Alkaline phosphatase activity was positively correlated with pH, and citrate was positively correlated with readily available P. Biochar effects on biological and chemical P processes in the rhizosphere are driven by biochar properties.

Order from disorder: do soil organic matter composition and turnover co-vary with iron phase crystallinity?

Soil organic matter (SOM) often increases with the abundance of short-range-ordered iron (SRO Fe) mineral phases at local to global scales, implying a protective role for SRO Fe. However, less is known about how Fe phase composition and crystal order relate to SOM composition and turnover, which could be linked to redox alteration of Fe phases. We tested the hypothesis that the composition and turnover of mineral-associated SOM co-varied with Fe phase crystallinity and abundance across a well-characterized catena in the Luquillo Experimental Forest, Puerto Rico, using dense fractions from 30 A and B horizon soil samples. The δ13C and δ15N values of dense fractions were strongly and positively correlated (R2 = 0.75), indicating microbial transformation of plant residues with lower δ13C and δ15N values. However, comparisons of dense fraction isotope ratios with roots and particulate matter suggested a greater contribution of plant versus microbial biomass to dense fraction SOM in valleys than ridges. Similarly, diffuse reflectance infrared Fourier transform spectroscopy indicated that SOM functional groups varied significantly along the catena. These trends in dense fraction SOM composition, as well as ∆14C values indicative of turnover rates, were significantly related to Fe phase crystallinity and abundance quantified with selective extractions. Mossbauer spectroscopy conducted on independent bulk soil samples indicated that nanoscale ordered Fe oxyhydroxide phases (nano-goethite, ferrihydrite, and/or very-SRO Fe with high substitutions) dominated (66–94%) total Fe at all positions and depths, with minor additional contributions from hematite, silicate and adsorbed FeII, and ilmenite. An additional phase that could represent organic-FeIII complexes or aluminosilicate-bearing FeIII was most abundant in valley soils (17–26% of total Fe). Overall, dense fraction samples with increasingly disordered Fe phases were significantly associated with increasingly plant-derived and faster-cycling SOM, while samples with relatively more-crystalline Fe phases tended towards slower-cycling SOM with a greater microbial component. Our data suggest that counter to prevailing thought, increased SRO Fe phase abundance in dynamic redox environments could facilitate transient accumulation of litter derivatives while not necessarily promoting long-term C stabilization.

Seasonal variation in winter wheat field soil arbuscular mycorrhizal fungus communities after non-mycorrhizal crop cultivation

Intensive farming practices that implement deep and frequent tillage, high input inorganic fertilization, cultivation with non-host species, and pesticide use are widely reported to be detrimental for arbuscular mycorrhizal fungi (AMF), which are one of the most important plant biofertilizers. The effect of the reduction of agricultural input on AMF community dynamics following conversion from conventional non-mycorrhizal to lower input mycorrhizal crop cultivation has not yet been fully elucidated. We investigated the effect of the reduction of agricultural input, rotation, and season on AMF communities in winter wheat field soil after conversion from long-term (more than 20years) non-mycorrhizal (sugar beet) crop cultivation. We described AMF communities from bulk soil samples by specifically targeting the 18S ribosomal gene using a combination of AMF specific primers and 454 pyrosequencing. No effect was found after 3years' reduction of agricultural input, and only marginal effects were due to rotation with specific crops preceding winter wheat. Instead, season and year of sampling had the most appreciable influence on the AMF community. We suggest that, after conversion from long-term non-mycorrhizal to mycorrhizal crop cultivation, AMF diversity is low if compared to similar agroecosystems. Seasonal and successional dynamics play an important role as determinants of community structure.

Inorganic Nitrogen Application Affects Both Taxonomical and Predicted Functional Structure of Wheat Rhizosphere Bacterial Communities.

The effects of fertilizer regime on bulk soil microbial communities have been well studied, but this is not the case for the rhizosphere microbiome. The aim of this work was to assess the impact of fertilization regime on wheat rhizosphere microbiome assembly and 16S rRNA gene-predicted functions with soil from the long term Broadbalk experiment at Rothamsted Research. Soil from four N fertilization regimes (organic N, zero N, medium inorganic N and high inorganic N) was sown with seeds of Triticum aestivum cv. Cadenza. 16S rRNA gene amplicon sequencing was performed with the Illumina platform on bulk soil and rhizosphere samples of 4-week-old and flowering plants (10 weeks). Phylogenetic and 16S rRNA gene-predicted functional analyses were performed. Fertilization regime affected the structure and composition of wheat rhizosphere bacterial communities. Acidobacteria and Planctomycetes were significantly depleted in treatments receiving inorganic N, whereas the addition of high levels of inorganic N enriched members of the phylum Bacteroidetes, especially after 10 weeks. Bacterial richness and diversity decreased with inorganic nitrogen inputs and was highest after organic treatment (FYM). In general, high levels of inorganic nitrogen fertilizers negatively affect bacterial richness and diversity, leading to a less stable bacterial community structure over time, whereas, more stable bacterial communities are provided by organic amendments. 16S rRNA gene-predicted functional structure was more affected by growth stage than by fertilizer treatment, although, some functions related to energy metabolism and metabolism of terpenoids and polyketides were enriched in samples not receiving any inorganic N, whereas inorganic N addition enriched predicted functions related to metabolism of other amino acids and carbohydrates. Understanding the impact of different fertilizers on the structure and dynamics of the rhizosphere microbiome is an important step toward developing strategies for production of crops in a sustainable way.

Lead Speciation and Association with Organic Matter in Various Particle-Size Fractions of Contaminated Soils.

Lead (Pb) stabilization in polluted soils treated by a Pb immobilization technique may be dependent on the speciation of Pb present in specific particle-size fractions of the soil. However, the scale-dependency of Pb speciation in contaminated soils is still not clearly understood. In this study, the natures and amounts of Pb chemical forms were determined in five Pb-polluted soil samples from Klity Village, Thailand, and their particle-size fractions. This was achieved using multiple analytical tools, including bulk extended X-ray absorption fine structure (EXAFS) spectroscopy at the Pb LIII edge. Results suggested that cerussite, Pb sorbed to goethite, and Pb-humate were present in specific amounts in all bulk samples and their particle-size fractions. The highest amounts of Pb-humate were found in the smallest particles of the soil samples. This Pb form was present in the fine particles of a soil sample, but remained undetected when analyzing the bulk sample. Since Pb-SOM association may impede the formation of pyromorphite in soils, the results implied that the extent of Pb immobilization in a polluted soil treated by P may be less than predicted if Pb speciation is only characterized at the macroscopic scale from the bulk soil sample prior remediation.

Assessing the relationship between soil quality parameters of Nigerian alfisols and cocoa yield

Soil quality is widely regarded as an important factor in sustainable agriculture and is often assessed by evaluating the pertinent physical, chemical and biological properties of soils. The aims of this study were to (i) establish a minimum data set (MDS) of soil quality parameters capable of monitoring changes in soil condition and ecosystem functioning in smallholder cocoa production systems on tropical alfisols in southwest Nigeria; and (ii) examine the relationship between selected MDS of soil quality parameters and cocoa yield along a chronosequence of 3-, 7-, 15-, 22-, 30-, 40-, 60- and 80-year-old farm plots. To achieve these aims, five plots were identified for each plantation age group and bulk soil samples were collected at a depth of 0–20 cm. The samples were analysed for a total data set (TDS) of twenty-three separate soil quality parameters. Principal component analysis (PCA) was employed to reduce the dimensionality of the TDS to five principal components. The PCA results showed that five principal components with eigenvalues > 1 explained more than 78% of the variability in the soil properties. Within PC1–PC5, eleven (11) soil quality parameters with high loadings were identified and selected as the MDS. A stepwise multiple regression analysis of cocoa yield and MDS revealed that soil organic matter and cation exchange capacity are the key parameters influencing cocoa yield. To maintain the yield as well as long-term sustainability of smallholder cocoa farming systems, inorganic fertilizer application is needed. Considering the poor transportation system in rural areas and prohibitive costs associated with inorganic fertilizer application in cocoa plantations, it is suggested that organic materials such as cocoa pod husk should be used to improve soil health. Another proposed approach for improving the N content of cocoa soils is to inter-crop nitrogen-fixing legumes.

Pollution characteristics and health risk assessment of potentially toxic elements in school playground soils: A case study of Lagos, Nigeria

Soil samples were collected in February 2014 from 25 school playgrounds in Lagos, Nigeria to assess the potential adverse effects of the exposure of children to potentially toxic element (PTE). In each of the playgrounds, about 500 g of bulked soil samples were collected, dried, sieved, acid digested, and analyzed by inductively coupled plasma mass spectrometry (ICP‐MS). Results showed that soils studied were characteristically unpolluted as the average PTE concentration at each site did not exceed the soil guideline values. Considering the pollution assessment tools employed, some soil samples showed some form of anthropogenic input from PTE. Health risk assessment was employed to assess PTE exposure from ingestion, inhalation, and dermal contact. Result indicated that the highest risk is associated with ingestion followed by dermal contact and inhalation. For non‐carcinogenic effects, exposure to school playground soils poses no threat to children as the overall value of hazard index is less than the safe level of 1. For carcinogenic effects, only Cr and Ni were considered and were below the threshold of 1 × 10–6. This study has demonstrated that minimal risk arises from the investigated playgrounds and that regular monitoring is required to keep the PTE contents low in soils to avoid risk to human health. Abbreviations: SH, school playground; PTE, potentially toxic elements

Soil changes associated with land use in volcanic soils of Patagonia developed on dynamic landscapes

This paper aimed to identify indicators of soil degradation in volcanic soils developed in the ecotone between the Andean Forests and the Patagonian steppe. The study area is located in the Percy River Basin, Argentine, on alluvial fans with volcanic soils. Sampling was conducted in two adjacent hillslopes where native forest was replaced by a rangeland with grass-shrub vegetation and a 32-years old Pinus radiata plantation. Sectioned and bulk soil samples were collected along three transects in each land cover up to 40 cm depth. Two forest patches of Maytenus boaria were selected as controls. Physical, chemical and magnetic properties were analyzed. Native forest soils were rich in silt fraction, organic matter and non-crystalline minerals, and presented the lowest values of magnetic susceptibility. Rangeland and plantation soils differed from forest soils in these properties. Soil changes were mainly associated to changes in mineralogy resulting from soil desiccation and to the selective removal of fine particles by erosion, together with differences in the effects of recent volcanic events on the soils. Changes in soils associated with land use affected key properties related to pedogenetic processes. Magnetic susceptibility, organic matter content, texture, and pH NaF were key for understanding soil degradation processes in this dynamic environment.

Particle Size Distribution of Heavy Metals and Magnetic Susceptibility in an Industrial Site.

This study was conducted to explore the relationships between magnetic susceptibility and some soil heavy metals concentrations in various particle sizes in an industrial site, central Iran. Soils were partitioned into five fractions (< 28, 28-75, 75-150, 150-300, and 300-2000µm). Heavy metals concentrations including Zn, Pb, Fe, Cu, Ni and Mn and magnetic susceptibility were determined in bulk soil samples and all fractions in 60 soil samples collected from the depth of 0-5cm. The studied heavy metals except for Pb and Fe displayed a substantial enrichment in the < 28µm. These two elements seemed to be independent of the selected size fractions. Magnetic minerals are specially linked with medium size fractions including 28-75, 75-150 and 150-300µm. The highest correlations were found for < 28µm and heavy metals followed by 150-300µm fraction which are susceptible to wind erosion risk in an arid environment.