Sieved Soil Research Articles

Biochar from cashew residue enhances silicon adsorption and reduces cohesion and mechanical resistance at meso- and micro-structural scales of soil with cohesive character

Horizons with cohesive character impose physical restraints on plant development, particularly when it occurs near the soil surface. Howbeit, the genesis of cohesive character in soils is associated with temporary and reversible cementation by amorphous silica. Thus, we hypothesized that the biochar obtained from residues from cashew processing would improve soil porosity and promotes silicon adsorption, consequently reducing cohesion and mechanical resistance while improving the physical quality of soils with cohesive character. We collected soil samples with deformed structure from the Bt1 horizon of a Typic Haplustult with cohesive character in northeast Brazil. These samples were used to prepare test substrates by combining air-dried and sieved soil samples and biochar at application rates of 0, 5, 10, 20, and 40 Mg ha−1. All the samples in each treatment underwent ten cycles of wetting and drying (one cycle per week) to allow the manifestation of the cohesive character. Subsequently, we assessed silicon adsorption capacity, soil bulk density, porosity, soil penetration resistance, tensile strength, and rheometric properties. In the 5 and 10 Mg ha−1 doses, the physical quality remained like the control treatment (0 Mg ha−1). The 20 and 40 Mg ha−1 doses resulted in increased soil silicon adsorption capacity (+7.6 and +15.3%, respectively), total porosity (+2.0 and +1.9%, respectively), and macroporosity (+14.6 and +15.3%, respectively), compared to the treatment without biochar. Conversely, these doses led to a reduction in soil bulk density (-0.1 and −0.8%, respectively), penetration resistance (-16.2 and −16.1%, respectively), tensile strength (-24.2 and −36.5%, respectively), deformation at the end of the linear viscoelastic range (-6.3 and −10.5%, respectively), shear stress at the end of the linear viscoelastic range (-16.4 and −26.9%, respectively), and maximum shear stress (-13.7 and −22.3%, respectively). In conclusion, the application of biochar improved soil porosity and promoted silicon adsorption, thus reducing the bulk density, cohesion, and mechanical resistance, enhancing the physical quality of soils with cohesive character, especially for doses of 20 and 40 Mg ha−1.

Impacts of sample handling and storage conditions on archiving physiologically active soil microbial communities.

Soil microbial communities are fundamental to ecosystem processes and plant growth, yet community composition is seasonally and successionally dynamic, which interferes with long-term iterative experimentation of plant-microbe interactions. We explore how soil sample handling (e.g. filtering) and sample storage conditions impact the ability to revive the original, physiologically active, soil microbial community. We obtained soil from agricultural fields in Montana and Oklahoma, USA and samples were sieved to 2mm or filtered to 45µm. Sieved and filtered soil samples were archived at -20°C or -80°C for 50 days and revived for 2 or 7 days. We extracted DNA and the more transient RNA pools from control and treatment samples and characterized microbial communities using 16S amplicon sequencing. Filtration and storage treatments significantly altered soil microbial communities, impacting both species richness and community composition. Storing sieved soil at -20°C did not alter species richness and resulted in the least disruption to the microbial community composition in comparison to nonarchived controls as characterized by RNA pools from soils of both sites. Filtration significantly altered composition but not species richness. Archiving sieved soil at -20°C could allow for long-term and repeated experimentation on preserved physiologically active microbial communities.

Effects of subsurface rock fragment layers caused by simulated hoeing on near-surface rainfall-runoff processes

In hilly agricultural landscapes with shallow soil, cultivation activities can cause the fragmentation of bedrock and induce vertical spatial heterogeneity of rock fragments, modifying the hillslope architecture and flow paths. Previous research mainly focused on the impact of rock fragments in the topsoil on surface runoff, but the role of subsurface rock fragments in rainfall-runoff processes has received less attention. In order to investigate the role of the subsurface rock fragment layer in rainfall-runoff processes through artificial rainfall experiments, we used sieved soil to establish soil layers with thickness of 10 cm and subsurface rock fragment layers related to hoeing depths from 10 to 16 cm under the soil layer. Additionally, a rubber plate was employed to initiate subsurface flow and deep percolation during the rainfall experiments. Results show that the presence of subsurface rock fragment layers mainly influenced the runoff partitioning between subsurface flow and deep percolation, but had little effect on surface flow. When there was no subsurface rock fragment layer, the yields of subsurface flow and deep percolation were in the ranges of 2.78–5.32 mm and 6.35–25.52 mm, respectively, under 15° slope and 15–120 mm h−1 rainfall intensities. The presence of subsurface rock fragment layers resulted in a 30–110% increase of subsurface flow, compared with no subsurface rock fragment layer, and it resulted in deep percolation decreasing by 4–48%. Subsurface rock fragment layers with substantial thickness and content of coarse rock fragments facilitated runoff partitioning into subsurface flow, but reduced the fraction of deep percolation. Rainfall intensity and slope steepness both exerted positive effects on the magnitude of subsurface flow and deep percolation within the thresholds of 60 mm h−1 and 15°, respectively. With increasing rainfall intensity (or slope steepness), subsurface flow yield increased apparently for the thick subsurface layer with substantial coarse rock fragments. It indicates that the thick subsurface rock fragment layer with high content of large-sized particles together with the great rainfall intensity (or steep slope) can result in substantial lateral subsurface flow. This study has important implications for the management of water and environment in hilly agricultural landscapes.

Machine learning models for predicting soil particle size fractions from routine soil analyses in Quebec

AbstractSoil texture and particle size distribution are important soil properties for understanding and interpreting the multiple processes and interactions in soil agrosystems. However, soil particle size analysis is rarely included in routine soil laboratory analyses due to cost but can be derived from other soil physico‐chemical properties and from more powerful regressions using machine learning techniques. The performance of multiple linear regression and four machine learning algorithms (MLAs)—K‐nearest neighbor (KNN), Random Forest, extra‐gradient boosting (XGBoost), and multilayer neural network (NeuralNetwork)—was compared to predict particle size fractions of clay, sand, and silt using routine analyses of soil pH, cation exchange capacity, Mehlich‐3 extracted elements, and density of dried sieved soil from 8,364 soil samples distributed across Quebec. Particle size fractions were predicted as compositional data using isometric log ratio transformation. The XGBoost model performed best, with RMSE values of 7, 10, and 12% and R2 values of .77, .57, and .73 for the prediction of clay, silt, and sand fractions, respectively. Feature importance classification varied from one model to another, but the best predictors remained the same regardless of the model used. Sieved soil density measured in the laboratory and Mehlich‐3 Mg, K, Fe, and Zn ranked as better predictors of particle size fractions. Predicting soil particle sizes using routine soil physico‐chemical properties and MLAs appears an option for incomplete legacy datasets and a promising economic alternative to current methods carried out in commercial laboratories.

Utility of visible and near-infrared spectroscopy to predict base neutralizing capacity and lime requirement of quaternary soils

Detailed knowledge of a soil’s lime requirement (LR) is a prerequisite for a demand-based lime fertilization to achieve the optimum soil pH and thus sustainably increasing soil fertility and crop yields. LR can be directly determined by the base neutralizing capacity (BNC) obtained by soil-base titration. For a site-specific soil acidity management, detailed information on the within-field variation of BNC is required. However, soil-base titrations for BNC determination are too laborious to be extensively applied in routine soil testing. In contrast, visible and near-infrared spectroscopy (visNIRS) is a time and cost-effective alternative that can analyze several soil characteristics within a single spectrum. VisNIRS was tested in the laboratory on 170 air-dried and sieved soil samples of nine agricultural fields of a quaternary landscape in North-east Germany predicting the soil’s BNC and the corresponding lime requirement (LRBNC) at a target pH of 6.5. Seven spectral pre-processing methods were tested including a new technique based on normalized differences (ND). Furthermore, six multivariate regression methods were conducted including a new method combining a forward stagewise subset selection algorithm with PLSR (FS-PLSR). The models were validated using an independent sample set. The best regression model for most target variables was FS-PLSR combined with the second Savitzky-Golay derivation as pre-processing method achieving R2s from 0.68 to 0.82. Finally, the performance of the direct prediction of LRBNC (R2 = 0.68) was compared with an indirect prediction that was calculated by the predicted BNC parameters. This resulted in slightly higher correlation coefficients for the indirect method with R2 = 0.75.

Carbon Addition Modified the Response of Heterotrophic Respiration to Soil Sieving in Ectomycorrhizal-Dominated Forests

Soil heterotrophic respiration (Rh) is an important pathway of carbon (C) dioxide release from terrestrial soils to the atmosphere. It is often measured using sieved soil in a laboratory, but the uncertainty of how it is influenced by soil sieving persists, which limits the accuracy of predicting soil organic C dynamics in C models. To address how soil sieving during laboratory incubation affects Rh and its response to increased carbon availability, we investigated Rh in sieved and intact soil cores and its response to 13C-glucose addition. This was conducted through a 27-day laboratory incubation in four forests, including two ectomycorrhizal-dominated (ECM) forests and two arbuscular mycorrhizal-dominated forests. The significant influence of soil sieving on Rh in all forests was not observed during incubation when glucose was not added. After adding glucose, the Rh in the sieved soils on the 5th day of incubation was averaged 27.2% lower than that in intact soils in ECM forests. On the 27th day it was 22.1% lower in the Pinus massoniana forest, but 78.0% higher in the Castanea mollissima forest. Strong relationships were detected between Rh in sieved and intact soils (r2 = 0.888), and in soils both with and without the addition of glucose (r2 = 0.827). The measured soil variables explained 74.7% and 49.7% of the variation in Rh on the 5th and 27th day of incubation, and the role of soil nutrients and microbial PLFA groups in regulating Rh varied temporally. Our findings suggest that plant mycorrhizal types influenced the role of increased C availability to microbes in regulating the response of Rh to sieving in forest ecosystems.

Ex situ soil respiration assessment using minimally disturbed microcosms and dried–sieved soils; comparison of methods to assess soil health

Soil respiration measurements are commonly used as soil health indicators. Several ex situ soil respiration methods exist, but comparative performances between them have rarely been analyzed. Specifically, there is a lack of comparisons between intact microcosms and destructive methods. The objective of this study was to analyze and compare three different ex situ soil respiration methodologies: minimally disturbed microcosms using fresh soil, dried–sieved 24 h burst test, and dried–sieved 10-day incubation. We hypothesized that ( i) the respiration rates for the three methods are correlated to each other; ( ii) the respiration rates are strongly correlated with soil physico-chemical parameters; ( iii) disturbance caused by drying and sieving reduces regression coefficients compared with microcosms; and ( iv) drying and sieving soil produces larger respiration rates. Soil was collected in the Province of New Brunswick, Canada. Total carbon and nitrogen (C:N), pH, aggregate stability, total dissolved C and N, NO3 and NH4, texture, and labile C were determined prior to incubations. Our results showed that the three methods had CO2 efflux in similar ranges. However, all the methods had low to no significant correlations between soil physico-chemical parameters and respiration. Total dissolved N had the strongest correlation with CO2 efflux. The results of the microcosm method significantly correlated with the results for 24 h burst test but not with the 10-day incubation method. We conclude that drying and sieving soil prior to performing ex situ soil heterotrophic respiration measurements using the 24 h burst tests can produce cautiously reliable results. Despite the disturbance, results from the 24 h burst tests are comparable with the results of the microcosm method.

A comparative study of MIR and NIR spectral models using ball-milled and sieved soil for the prediction of a range soil physical and chemical parameters

This study evaluated the influence on predicted physical and chemical parameters of soil particle sizes commonly used in the infrared spectra acquisition, < 0.100 mm (ball-milled) and < 2 mm for MIR and NIR ranges, respectively. The influences were evaluated through the accuracy (RMSEP and RPIQ) results and the chemical information extracted by multivariate classification and regression models. For this a national population of soils containing 888 samples from 225 modal soil profiles, each with the reference values of sand, silt, clay, pH(CaCl2), pH(Water), total carbon, organic carbon (OC), cation exchange capacity, nitrogen, aluminium and bulk density, was used. Spectra were collected in MIR and NIR ranges using samples with both particle sizes. For each soil attribute, 29 random calibration and validation sets were generated and SVM, PLS and Cubist regression models were built. This same strategy was used to classify the soil samples according to their respective horizons (1 or 2-7) using SVM, PLS-DA and random forest algorithms. Results obtained by the randomised calibration and validation set did not present positive or negative bias on the RMSEP and RPIQ values based on soil particle sizes. In general, random variations of the RMSEP and RPIQ values were observed for all soil attributes. In addition, ball-milled and < 2 mm spectral models did not present large differences in both accuracy parameters simultaneously. The median Matthews correlation coefficient values calculated by the classification models showed minor variations of 2.61% and 0.65% for samples from both particle sizes in MIR and NIR ranges, respectively. The ‘Variable Importance in Projection’ or VIP scores, calculated by PLS and PLS-DA models, did not show any large variation in the chemical information extracted from MIR and NIR spectra for models built using samples from both particle sizes. The results from this study show that scanning ball-milled or < 2 mm sieved soil samples will result in spectra models in MIR and NIR ranges with the same accuracy and same chemical information. This suggests there is a big potential to eliminate the ball-milling sample step in soil laboratories that use MIR and NIR vibrational spectroscopy techniques to predict soil attributes, thereby reducing the time and costs associated with soil analysis.

Wind Tunnel Studies on the Prevention of Particle Accumulation Onto the Bogie of High-Speed Train

When high-speed train runs in the environment with a large number of airborne particles, these particles may accumulate on the bogie of the train, which will further challenge the normal operation of the bogie and reduce the riding comfort and train safety. In order to prevent particles entering into the bogie area, different protective devices around the bogie are used. However, up to present, the systematical analysis on the protective effects of diverse protective measures against different types of particles are still very limited. In this study, with the widely-used shirt boards and spoilers as protective devices, the airborne particle transport processes around the bogie were simulated in the wind tunnel Lab. Three kinds of typical particles, including artificial snow particle, wheat bran (substitute of snowflake) and sieved soil, were chosen to represent different airborne particles under real conditions. Three evolution indexes, including the relative reduction ratio of artificial snow particles, the relative particle flux reduction ratio of fine wheat bran, and the relative concentration reduction ratio of fine sieve soil particles, were used to assess their protective effects. Results showed that the combination of short-skirt board and straight triangular spoiler (i.e., in A5 case, the straight triangle spoilers installed at the front and rear ends of the train bogie, and the short-skirt boards installed on both sides of the train bogie) was the best protection with the studied three particles. The relative reduction ratio of the average snow mass in this case was 75.59%, the relative reduction ratio of the flux in the level of fine wheat bran exceeded 78%, and the relative reduction ratio of the fine soil particle concentration was more than 96%.

The dominant microbial metabolic pathway of the petroleum hydrocarbons in the soil of shale gas field: Carbon fixation instead of CO2 emissions

In shale gas mining areas, indigenous microorganisms degrade organic pollutants such as petroleum hydrocarbons into carbon dioxide (CO2) and water (H2O) through aerobic metabolism. A large quantity of CO2 emissions will exacerbate the “Greenhouse effect”. Based on the clean sieved soil and oil-based drilling fluid in the shale gas mining area, this experiment set three concentration gradients (3523 ± 159 mg/kg, 8715 ± 820 mg/kg and 22,031 ± 1533 mg/kg) to treat the soil, and each group was disposed for the same amount of time (63 days). By analyzing the dynamic changes of microbial diversity and the abundance of key functional genes for carbon fixation, the impact of petroleum hydrocarbons on carbon fixation potential was discovered, and the natural attenuation law of petroleum hydrocarbons in contaminated soil was explored. It provided the scientific research basis of ecology for the carbon cycle, carbon allocation, and carbon fixation in microbial remediation of petroleum hydrocarbon contaminated soil. The results obtained indicated the following: i) The removal rate of petroleum hydrocarbons under high-concentration pollution (45.33 ± 3.90%) was significantly lower than low and medium-concentration pollution. The TPH concentration removal rate of each group was the largest in the early stage of culture (1-5d), and there was no significant correlation between the TPH content and the community composition (R2 = 0.0736, P > 0.05). ii) Composition and function of Carbon Fixation associated microbiota were assessed by 16S rRNA sequencing and PICRUSt (phylogenetic investigation of communities by reconstruction of unobserved states) analysis. The main carbon fixation pathway in this study is the reductive citric acid cycle, because there was no shortage of enzymes that can affect subsequent reactions.

Sieving soil before incubation experiments overestimates carbon mineralization but underestimates temperature sensitivity

The sensitivity of soil organic carbon (SOC) mineralization to temperature could affect the future atmospheric CO2 levels under global warming. Sieved soils are widely used to assess SOC mineralization and its temperature sensitivity (Q10) via laboratory incubation. However, sieved soils cause a temporary increase in mineralization due to the destruction of soil structure, which can affect estimates of SOC mineralization, especially in soils managed with no-till (NT). To identify the effects of soil sieving on SOC mineralization and Q10, soil was collected from an 11-year field experiment under a wheat-maize cropping system managed with a combination of tillage [NT and plow tillage (PT)] and residue [residue returning (RR) and residue removal (R0)]. Soil was either sieved or left in an undisturbed state and incubated at 15 °C and 25 °C. SOC mineralization in sieved soils at 25 °C was 47.28 g C kg−1 SOC, 160.1% higher than SOC mineralization in undisturbed soils (P < 0.05). Interestingly, Q10 values in sieved soils were 1.29, 77.6% lower than Q10 in undisturbed soils (P < 0.05). Highly significant correlations (P < 0.01) were observed between sieved and undisturbed soils for SOC mineralization (r = 0.85–0.98) and Q10 (r = 0.78–0.87). Soil macro-aggregates had lower SOC mineralization by 6.1–21.9%, but higher Q10 values by 4.7–6.5% compared with micro-aggregates, contributing to lower mineralization and higher Q10 under NT and RR. Furthermore, structure equation and random forest modelling showed that increased SOC contents in NT and RR could not only reduce SOC mineralization, but also constrained the improvement of Q10 in NT and RR. Overall, these results indicated that although sieved soils overestimated SOC mineralization and underestimated Q10 due to the destruction of macro-aggregates, the patterns between treatments were similar and sieving soil for incubation is considered as a suitable approach to evaluate the relative impacts of NT and RR on SOC mineralization and Q10.

Soil water repellency in sandy soil depends on the soil drying method, incubation temperature and specific surface area

Soil water repellency (SWR) is problematic in rainfed cropping soils as it decreases plant water use efficiency. The occurrence of SWR is often dependent on the prevailing soil water content, but the response of SWR to soil water content varies among studies. We undertook three experiments to investigate how the (i) drying method prior to experimentation (oven-dried at 105 °C or vacuum-dried at 20 °C), (ii) incubation temperature (4 °C, 20 °C and 40 °C), and (iii) specific surface area (SSA) of four sieved soil fractions (0.49 m2 g−1, 0.59 m2 g−1, 0.65 m2 g−1 and 1.61 m2 g−1) influenced the response of SWR to soil water content. In all experiments, SWR (measured by molarity of ethanol droplet) remained constant up to a ‘threshold soil water content’, and then responded linearly with increasing soil water content. However, oven-dried soil at 105 °C had lower SWR than soil dried anoxically at 20 °C, which remained constant up to a threshold soil water content. The SWR response rate to soil water content above the threshold was also lower in the 105 °C oven-dried soil than the 20 °C anoxically vacuum-dried soil. Whereas, increasing the incubation temperature increased the SWR response rate to soil water content above the threshold. The four sieved soil fractions had increasing threshold soil water contents with increasing SSA, which could be related to the total carbon content of the soil. In conclusion, the same drying method and incubation temperature should be used throughout an experiment and between studies when investigating the response of SWR to soil water content to avoid methodological errors.

Influence of continuous application of feedlot manure and legacy treatments on soil organic carbon, soil hydrophobicity, and soil water repellency

Continuous or discontinued manure applications to agricultural soils may impact soil organic carbon (SOC) and water balances because of manure carbon inputs and the potential for manure-induced soil hydrophobicity (SH) and soil water repellency (SWR). A laboratory study was conducted using a long-term (44 yr) field experiment on a clay loam soil to determine the effect of application rate of feedlot manure under dryland (0, 30, 60, and 120 Mg·ha−1 wet weight) and irrigation (0, 60, 120, and 180 Mg·ha−1) on SOC, SH, and SWR. In addition, we compared the effect of 44 yr of continuous annual manure applications (C44) to legacy treatments which had discontinued applications for 14 (D14) or 30 yr (D30). Laboratory measurements were conducted on air-dried and sieved (&lt;2 mm) soil to determine SOC, SH using Fourier transform infrared spectroscopy, and SWR using the repellency index (RI) method. Mean RI values for all treatments ranged from 2.20 to 13.0, indicating subcritical (RI &gt; 1.95) SWR. Manure application rate had a significant (P ≤ 0.05) and positive effect on SOC and SH, and both followed an exponential model. In contrast, RI had a negative response to the application rate under dryland and had no response under irrigation. Overall, positive responses of SOC and SH to application rate supported our hypothesis, but it was not supported for RI. The hypothesis of greater SOC, SH, and RI for continuous versus discontinued treatments was also supported for SOC and SH but not for RI.

Effect of Effluent from Biodigestion of Pre-Treated Rice Bran and Animal Manure on the Dry Matter Yield and Nutrient Uptake of &amp;lt;i&amp;gt;Amaranthus viridis&amp;lt;/i&amp;gt;

The effect of effluents from biodigestion of pre-treated rice bran in combination with two types of animal manure on dry matter yield of Amarathus viridis was investigated using two pre-treatment methods: Soaking in ordinary distilled water and boiled in distilled water at 100&degC. The pre-treated rice bran and animal manure were mixed (w/w basis) to give carbon to nitrogen ratio of 35:1 and 37:1 prior to loading into the digester to make eight different treatment combinations as follow: 1) Cow dung with no rice bran (NRB + CD); 2) Raw rice bran + cow dung (RRB + CD); 3) Soaked rice bran in ordinary distilled water + cow dung (SRB + CD); 4) Boiled rice bran + cow dung (BRB + CD); 5) Poultry manure with no rice bran (NRB + PM); 6) Raw rice bran + poultry manure (RRB + PM); 7) Soaked rice bran + poultry manure (SRB + PM); 8) Boiled rice bran + poultry manure (BRB + PM). Samples of different treatment combinations were collected before digestion, both the samples and resultant effluents were subjected to elemental analysis using AAS. The effluents from the biodigestion of these combinations were applied at two rates (80 and 150 kg N ha-1) to 3 kg air-dried and sieved soil samples (0 - 20) cm in the greenhouse, control (0 kg N ha-1) and reference pot with NPK fertilizer at the 80 kg N ha-1 were arranged in a completely randomized design replicated three times. Amaranthus plants were introduced into each treated pot, left for four weeks before harvest, dry matter yields were recorded. Results of chemical analysis of raw materials and effluents obtained after biodigestion revealed the presence of all plant nutrients in both the raw materials and resultant effluents though the former had higher values in some nutrients than the effluent, for examples treatment combination of CD, the values for organic carbon (42.85%), Ca (3.41%) and Mg (0.61%) were higher than in the resultant effluent for CD, a similar trend was observed with other treatment combinations. Drastic reduction in heavy metal concentration was observed after digestion, Pb content in the raw materials for poultry manure reduced by 94.7% in the resultant effluent from BRB: PM thus making the effluent a better soil amendment. Raw chicken manure was richer in the nutrients needed for optimal crop growth however, raw cow dung had the highest. The amendment of effluent from boiled rice bran with poultry manure at 150 kg N ha-1 significantly increased the dry matter yield of Amaranthus viridis over control pots, NPK pots and all other amendments thus making it a good alternative to NPK fertilizer.

New method for quantifying water stability of soil aggregates from air bubbling after immersion

Existing methods for estimation of water stability of aggregates suffer from intrinsic uncertainties and are not more than semi-quantitative. New method for quantitative measurement of aggregate destruction rate in water was developed basing on monitoring of air bubbling after aggregate immersion by recording a decrease in buoyancy of the aggregate during air evolution. The method allows to estimate destruction mechanism and to calculate kinetic parameters of the destruction process. The rate of the destruction of spherical aggregates made from 2-mm sieved soil material was successfully fitted to a shrinking sphere model. The time of the complete destruction divided by the initial surface of the aggregate was constant for a given soil regardless the aggregate size and it was used as a parameter distinguishing different soils. The proposed method allows for studying rapidly destroyed aggregates for which all available methods generally fail.

Influence of crop residues and nitrogen fertilizer on soil water repellency and soil hydrophobicity under long-term no-till

Crop residues and N fertilizer under no-till may increase soil water repellency (SWR) and soil hydrophobicity, but few studies have examined these two treatment factors and their interaction. A laboratory study was conducted using a long-term (since 1999) field experiment on a clay loam soil to determine the effect of three crop residues and two N fertilizer levels on SWR and soil hydrophobicity under no-till within the Dark Brown soil zone of the semi-arid Canadian prairies. The three residue treatments were residues removed from soil (Rx0), residues returned to soil (Rx1), and residues supplemented to soil (Rx2). The two fertilizer N treatments were 0 (N0) and 45 kg N ha−1 (N1). Surface (0–10 cm) soil samples were taken in the spring of 2017 after 17 yr. Laboratory measurements were conducted on air-dried and sieved (&lt;2 mm) soil to determine SWR using the repellency index method (RI), soil organic C, hydrophobic CH and hydrophilic CO functional groups, and soil hydrophobicity (CH/CO ratio). Mean RI values ranged from 2.19 to 2.75, indicating subcritical (RI &gt; 1.95) SWR. Similar (P &gt; 0.05) RI values were found for the three residue and two N fertilizer treatments, but the trend was for greater RI with increased residue addition (by 12%–26%) and N fertilizer (by 8%). Soil hydrophobicity was significantly greater by 47%–82% for straw returned or supplemented than straw removed treatments, and by 33% for fertilized than unfertilized treatments. Overall, greater residues and N fertilizer had no effect on SWR, but significantly increased soil hydrophobicity.

Zinc Accumulation in Amaranthus caudatus and Corchorus olitorius: Relevance for Phytoextraction

Aim: In a pot experiment the accumulation of zinc in Amaranthus caudatus and Corchorus olitorius from contaminated soil and its relevance for phytoextraction were studied.&#x0D; Study Design: Plants were exposed to three levels of zinc concentration as zinc sulphate heptahydrate (0,150, 300, 450 ppm), laid in completely randomized design.&#x0D; Place and Duration of Study: The study lasted for a total of 37 days in a housing facility used for phytoplankton culture at National Institute for Freshwater Fisheries Technology New-Bussa Nigeria.&#x0D; Materials and Methods: Seeds were raised in a nursery for 16 days, and transplanted to pots containing each 2 kg of air-dried and sieved soil. Zinc was artificially applied to soil for each vegetable. They were watered at 60-70 % field capacity and growth parameters measured every 7 days. Plants were carefully uprooted after 3 weeks of transplanting, washed, and weighed before and after oven drying. They were analyzed for zinc concentration.&#x0D; Results: Results of this study showed decreases in growth and yield at 300 and 450 ppm zinc concentrations. Plant height for both vegetables increased at 150 ppm however these increases were significantly different (P≤0.05) with control for Corchorus only. There were also significant differences (P≤0.05) between treatments in zinc accumulation. Results further showed that zinc was accumulated in the leaves more than the roots. Concentrations of zinc in plant tissues of both vegetables followed a similar order of leaves &gt; roots &gt; stem indicating their efficiency in zinc translocation from roots to leaves. Translocation factors were generally greater than unity.&#x0D; Conclusion: Despite their lack of hyperaccumulation properties, both vegetables exhibited good potential for phytoextraction. The higher translocation factor of C. olitorius indicated better phytoextraction potential.

Elemental analysis of Cerrado agricultural soils via portable X-ray fluorescence spectrometry: Inferences for soil fertility assessment

Conventional soil chemical analyses are time-consuming and laboratory-based. Spectroscopic techniques have been introduced to make soil measurements more rapid and cost-effective. While portable X-ray fluorescence spectrometry (pXRF) has been increasingly adopted for advanced soil analysis in temperate regions, comparatively few applications have been developed for tropical soils. Using PXRF, soil total elemental composition can be obtained in seconds, with properties inferred from the collected data. In the present study, pXRF was used to screen samples (n = 252) from tropical Cerrado agricultural areas under different land uses in Brazil. The objective was to determine the total elemental composition of soil samples and predict soil fertility properties using simple or multiple linear regression with pXRF data as a proxy. Air-dried and sieved soil samples (<2 mm) under laboratory conditions were screened using a pXRF, then compared to soil chemical characterization by conventional methods. pXRF data properly corroborated the known soil mineralogy and geochemical background of Cerrado soils. Based exclusively on pXRF data, clay content was successfully predicted. Also, soil organic matter and plant-available forms of Ca, Mn and Cu were reasonably predicted from pXRF results.

Growth and colonization of organic matter in soil by Fusarium proliferatum

Fusarium proliferatum is a broad host range, mycotoxin-producing, seed-borne pathogen of maize. A green fluorescent, hygromycin-resistant F. proliferatum transformant (Fp-70–2-5-G2) was developed to provide markers to track movement and colonization of bait organic matter in non-sterile soil microcosms. Maize seeds that were heat-killed and re-colonized with Fp-70–2-5-G2 served as sources of inoculum. They were added to non-sterile soil together with heat-killed, non-colonized maize seeds (baits), at several temperatures, soil matric potentials, and source-to-bait distance combinations. Baits were retrieved from soil and plated onto Nash-Snyder medium amended with 1 µg mL−1 hygromycin. Fp-70–2-5-G2 grew through non-sterile sieved soil and colonized maize seed; distance, temperature and soil matric potential had significant effects (P < 0.0001, P = 0.0365 and P < 0.0001, respectively) on growth and colonization. The maximum distance that Fp-70–2-5-G2 grew and colonized maize seed was 1.5 cm at 25°C and −0.005 MPa matric potential. The maximum colonization of baits by Fp-70–2-5-G2 occurred at 0 cm (80%) and 0.5 cm (50%) source-to-bait distance at 25°C and −0.005 MPa matric potential. Growth through soil and colonization of bait organic matter was significantly less in soil with an intact field structure. In addition to plant and seed colonization, F. proliferatum may have an active soil inhabitant phase in its life cycle.

Relative soil water content as a factor for wind erodibility in soils with different texture and aggregation

Abstract The soil water content is one of the main factors influencing the beginning of soil particle movement by the wind. Although, some authors studied the effect of soil water content on threshold wind velocity and have defined a value to prevent wind erosion, the critical relative soil water content (HRc), most of them used disturbed and/or sieved soil samples. Under these conditions, the effect of aggregation, i.e. the natural state of the soil, cannot be evaluated. So, our objective was to determine HRc in soils with different textures in Semiarid Argentinian Pampas Region (SAPR) using uncrushed soil samples under variable wind velocities. Wind tunnel simulations were performed at three wind speeds (2.1, 8.0 and 10.5 m s−1) during 3 min in each case. Results indicated that the quantity of collected soil (Q) decreased with increasing relative soil water contents (HR) up to a HRc value at which it became negligible. HRc values were lower in fine textured soils than in coarse soils. All soils showed increasing HRc values as wind velocity increased from 2.1 to 10.5 m s−1, while the wind velocity effect is more important in coarse textured soils. HRc was negatively related to micro-aggregation in a linear way. For that reason, soils with high fine silt and clay content need lower HRc values to inhibit wind erosion. In conclusion, not only texture is important factor in defining the HRc value at a specific wind velocity but also the micro and macro-aggregation of the soils.