Water Dispersible Clay Research Articles

Characteristics of clay dispersion and its influencing factors in saline-sodic soils of Songnen Plain, China

Under the influence of salinity-sodicity stress, soil salinization and sodification tend to be severe and the dispersion of clay particles increases, which threatens agricultural production and food security. To explore the characteristics of clay dispersion in saline-sodic soils and their influencing factors, the quantitative relationship between clay dispersion indices and soil physicochemical parameters in saline-sodic soils of the Songnen Plain in China was investigated, to provide theoretical and data support for clay dispersion control in saline-sodic soils. Forty-two natural soil samples (0–0.2 m) were collected from saline-sodic soils in Songnen Plain, northeast China, and their physicochemical parameters and clay dispersion indices were determined. Correlation analysis, random forest analysis, and multivariate linear regression analysis were used in this study. The results showed that water-dispersible clay (WDC) ranged from 0.60 % to 18.38 % and total clay (TC) ranged from 4.70 % to 20.68 %. The maximum value of the clay dispersion ratio (CDR) is nine times the minimum value. In terms of turbidity, mechanical dispersion turbidity (MDT) ranged from 39.60 to 59,433 NTU, while spontaneous dispersion turbidity (SDT) ranged from 1.11 to 154.67 NTU. In terms of zeta potential, the minimum value of mechanical dispersion ZETA potential (MDZP) was −46.42 mV, and the maximum value was close to 0 mV. There was a significant correlation between soil physicochemical parameters and clay dispersion indices. Exchangeable sodium percentage (ESP) was the most important explanatory variable for CDR, followed by pH, Na+ex, HCO3-, Na+, CEC, CO32-, SAR, CROSS, and SOC, which could help construct the following multiple linear regression model: CDR=0.143+0.015*ESP −0.036*CO32- −0.006*Na+. Exchangeable sodium percentage has the strongest effects on clay dispersion among the soil parameters. Clay dispersion indices vary with soil physicochemical parameters. Compared to MDT, SDT, MDZP, and SDZP, CDR is more suitable for evaluating and predicting the clay dispersion condition in saline-sodic soils.

Root Influences Rhizosphere Hydraulic Properties through Soil Organic Carbon and Microbial Activity.

Processes of water retention and movement and the hydraulic conductivity are altered in the rhizosphere. The aim of this study was to investigate the physical-hydric properties of soil aggregates in the rhizosphere of annual ryegrass (Lolium multiflorum) cropped in a Kandiudalfic Eutrudox, taking into account aspects related to soil aggregate stability. Soil aggregates from rhizosphere soil (RZS) and soil between plant rows (SBP) were used to determine soil water retention curves (SWRCs) and saturated hydraulic conductivity (Ksat). In addition, properties related to soil aggregate stability, such as water-dispersible clay, soil organic carbon (SOC), and microbial activity, were also assessed. The higher microbial activity observed in the RZS was facilitated by increased SOC and microbial activity, resulting in improved soil aggregation (less water-dispersible clay). For nearly all measured matric potentials, RZS had a higher water content than SBP. This was attributed to the stability of aggregates, increase in SOC content, and the root exudates, which improved soil water retention. The increase in total porosity in RZS was associated with improved soil aggregation, which prevents deterioration of the soil pore space and results in higher Ksat and hydraulic conductivity as a function of the effective relative saturation in RZS compared to SBP.

Water dispersible clay and micro-structure of soils from coastal plain sands, shale and false-bedded sandstones

Information regarding water-dispersible clays in soils of contrasting textures is needed to evaluate soil qualities that influence susceptibility of soils to slaking in water. Water-dispersible clays (WDCs), plastic limits, and basic properties of soils on Coastal Plain Sands (CPS), Shale (Shale), and False-Bedded Sandstones in southern Nigeria were quantified for use in evaluating management options of some tropical soils. Results revealed that WDCs, micro-aggregate indices, and plastic limits differed significantly amongst the parent materials. At 0–15 cm depth, clay content was 29.7%, 11.2 and 3.8%, for Shale, CPS and False-Bedded sandstones, respectively, indicating significant high clay content in Shale. The highest SOC of 29.8 g kg−1., and very slow saturated hydraulic conductivity (Ksat) of 6.33 cm h−1 were found in Shale. False-Bedded Sandstone had the lowest SOC content of 7.7 g kg−1 and highest Ksat value of 31.10 cm h−1 at 0–15 cm topsoil. Micro-aggregate stability indices measured by aggregated silt+clay (ASC) and clay flocculating index (CFI) were significant in CPS at 0–15 cm, whereas water-dispersible clay (WDC) was significantly higher (p < 0.05) in Shale at 8.32%, compared to very low value of 0.76% in False-Bedded Sandstone. Plastic limit (PL) of 16.5%, was significantly higher (p < 0.05) in Shale, indicating its high sensitivity to mechanical deformation when wet. There was a significant positive correlation between clay content and WDC (r = 0.815, p < 0.01), indicating the positive influence of clay content on WDCs and micro-structural indices, and the tendencies for quick degeneration of the soils.

Exploring soil-root interactions: A comparative study of wheat species and soil types

Soil-plant interactions of different wheat species (e.g., common, synthetic, durum and wild emmer ancestor) have not been studied yet. Therefore, our study was conducted to examine the interactive effect of 39 treatments including four wheat species (twelve varieties) and three soil types (loamy sand, sandy loam and sandy clay loam) on soil physical and biophysical quality indicators in a greenhouse pot experiment. The rhizosphere data were compared with the no plant (control) soil as well. The results revealed that the rhizosphere soils had a greater soil organic carbon (SOC) storage compared to the no plant soil, with the synthetic wheat species possessing the highest SOC content (order of SOC: synthetic > durum > emmer > common > control). The highest and the lowest SOC values (0.79 and 0.69 kg 100 kg−1) were observed in the rhizosphere of synthetic wheat S88 and common wheat CK varieties, respectively. The SOC showed a positive correlation with root morphological traits such as root volume and root dry weight. Basal soil respiration (BSR) showed significant variation among the four wheat species, and common and emmer ones had the highest BSR values. The maximum and minimum values of BSR (21.9 and 10.9 mg CO2 kg−1 soil day−1) were observed in the rhizosphere of the common species planted in sandy loam soil and in the loamy sand bulk soil (control), respectively. The presence of plant roots significantly increased BSR compared to the control (bulk soil); on average, the BSR in the rhizosphere was 21% greater than the control. Both the wheat species and soil type significantly affected the soil water repellency index (RI) and wettability parameters, but the interactive effects of treatments (i.e., wheat species and soil type) were not significant. The soils in all of the studied treatments were sub-critically or slightly water repellent (i.e., contact angle lower than 90°). The RI values were measured in the order emmer > durum > common > control ≥ synthetic; however, the difference between the synthetic species and bulk soil was not significant. Plant roots increased the soil hydrophobicity by increasing the SOC storage and significant variations in RI among the wheat species indicated that the emmer, durum and common species with greater RI might have better soil physical quality in the rhizosphere. The wheat plants substantially increased water-stable aggregates and decreased water-dispersible clay in the rhizosphere compared to the bulk soil. These findings showed that wheat roots were able to alter the structural stability of the rhizosphere soil. Correlation analysis indicated that soil structural stability was closely related to the SOC, microbial activity, water repellency and root morphological traits. Principal component analysis was used to enhance visualization, identify interrelationships between soil quality indicators and categorize wheat varieties.

Gliricidia intercropping supports soil organic matter stabilization at Makoka Research Station, Malawi

Intercropping agriculture with legume trees is a promising strategy to improve soils with low soil organic matter (SOM) and nitrogen (N) contents, which is a common problem in many Southern African regions. Objective of this research was to explore long-term effects of legume-intercropping on SOM pools and soil fertility. We examined a maize-based cropping system with gliricidia (Gliricidia sepium) as intercropping legume tree on a Ferric Lixisol in Southern Malawi. The experimental trial at Makoka Research Station was in its 29th year of management with leaf biomass incorporated into the soil regularly. We determined concentrations of organic carbon (C) and N, exchangeable cations, and available phosphorus (P) of topsoil samples (0–20 cm). We used density fractionation of SOM to gain fractions that roughly approximate SOM pools with fast turnover (not associated to soil minerals), intermediate turnover (occluded within soil aggregates) and slow turnover (mineral associated SOM). We further determined water dispersible clay (WDC) and pedogenic oxides, as these are often involved in the C-stabilization process in tropical soils. Maize-gliricidia intercropping plots showed higher soil pH-values, and higher concentrations of exchangeable Mg and Ca than plots with maize monoculture. In addition, significantly higher contents of C (17.3 vs. 7.03 g kg−1) and N (1.51 vs. 0.7 g kg−1) were found at intercropping plots indicating a C-sequestration rate of 0.3 g C kg−1 a−1, while monoculture induced the loss of SOM with a rate of −0.1 g C kg−1 a−1. C and N contents doubled in pools with fast and with slow turnover and increased by >300% in SOM pool where C and N is bound in soil aggregates. Concomitantly, WDC was significantly lower in intercropping plots than in monoculture plots. Our data emphasize the fast turnover of SOM in subtropical soils and indicate that SOM in arable soils decreases continuously without suitable C-input strategy. Maize-gliricidia intercropping had positive effects on biomass production and C-input at Makoka Research Station and improved soil fertility. In addition, aggregate formation was enhanced and storage of SOM within aggregates and at mineral surfaces increased. Our results indicate a great potential of maize-gliricidia intercropping for improved C management in subtropical Lixisols. Intensive monitoring seems to be promising to validate and quantify the impacts of this measure.

Compactabilidade de solos coesos dos tabuleiros costeiros do nordeste sob influência de água residuária de mandioca

ABSTRACT Consolidation tests give important insights into soil compactibility. However, it requires equipment that is not always available. The costal tablelands in Northeastern Brazil have extensive areas of cohesive soils where compaction is an expressive problem. This region is a prominent producer of food and fibers with cassava as one of the leading products. Part of the cassava is used for flour production, generating wastewater, which is often applied as organic fertilizer to the soil. This can affect the compaction properties of soil due to its dispersing-flocculating characteristics. Uniaxial-compression tests and mathematical models are the primary methods to measure or estimate soil compaction. This study measured soil compression with a centrifuge, seeking a simple-quick method. We used specific loads (stainless-steel cylinders: mass) and increasing G-force (weight) to simulate the pressure on the samples used in most consolidation apparatus. Soils, sampling layers, and the presence of cassava wastewater (manipueira) were also compared since they may affect compactibility-related attributes. Samples of a Gray Cohesive Argisol and Dystrocohesive Yellow Latosol (depths of 0-0.20 m and 0.20-0.40 m) from the Tablelands of the state of Bahia, Brazil, were used. Wastewater affected water-dispersible clay, aggregate stability, pH, ∆pH, flocculation, and organic carbon, thus influencing compactibility but not the moisture and maximum density measured by the Proctor test. Centrifugation caused lower density than the Proctor test. The results were close to those estimated by the mathematical models, thus considered a promising alternative to estimating consolidation. This method also provides insight into the root growth-limiting density and the moisture content that leads to it.

Clay stabilization and recovery of soil functions of a degraded solodic planosol through incorporation of agrominerals: A case study in southern Brazil

This paper describes the performance of addition rates of basaltic breccia and agricultural gypsum on clay stabilization and nutrients release of a solodic Planosol from a degraded borrow area located in Southern Brazil. A leaching experiment was carried out in PVC cylinders filled with 1.5 kg of soil (C horizon), in which two chemical amendments were added in three different proportions: a) basaltic breccia in 7, 14 and 21 Mg ha−1 doses; b) agricultural gypsum in 7, 14 and 21 Mg ha−1 doses; and c) a standard soil, without chemical correction. Distilled water (300 mL) were added every 7 days for 20 weeks and the pH, electrical conductivity, calcium, magnesium, sodium and potassium contents and the water-dispersible clay were analyzed in the collected leachates. Gypsum was more efficient than basaltic breccia to promote clay flocculation, even at the lower rate (7 Mg ha−1). The application of basaltic breccia up to 21 Mg ha−1 reduced the amount of nutrients released directly to the soil solution, reducing soil leaching. The application of basaltic breccia at the dosage of 7 Mg ha−1 was able to reduce more than 65% of the water-dispersive clay from the degraded solodic Planosol.

Effect of slope curvature and gradient on soil properties affecting erodibility of coastal plain sands in Akwa Ibom State, Nigeria

A study was conducted to assess the effect of slope curvature and gradient on soil properties affecting erodibility of coastal plain sands in Akwa Ibom State. Twelve locations comprising six each of concave (CC) and convex (CV) slopes, and three slope gradients, namely, gentle (GS), moderate (MS) and steep slopes (SS) in CC and CV were identified for the study. Bulk and core soil samples were collected from the top 30 cm soil depth at three slope positions of slope curvature and gradient categories for physical and chemical characterization, and derivation of microaggregate stability indices and erodibility factor, K. Results showed that coarse sand (CS), fine sand (FS), bulk density (Bd), total porosity (TP) and saturated hydraulic conductivity (Ksat) were significantly (p ≤ 0.05) higher on CC than CV, and among the slope gradients, GS &gt; MS &gt; SS. The interaction of slope curvature and gradients was significantly higher on CC than CV. A similar pattern of differences was also observed inorganic matter (SOM), calcium (Ca), magnesium (Mg), and other exchangeable cations, but the effect of slope curvature and gradients interaction was not significant. The microaggregate stability indices, water dispersible clay (WDC), water dispersible silt (WDS), dispersion ratio (DR), clay dispersion ratio (CDR), modified clay ratio (MCR), clay flocculation index (CFI), aggregated silt + clay (ASC) and aggregated clay (AC) were significantly higher on CV than CC, and differences among slope gradients and interaction of slope curvature and gradients were not significant. The erodibility factor, K, was significantly higher on CV than CC, while the slope gradients were similar in their effects on K. Linear regression analysis showed that K-factor was highly significantly related to CS, FS, Si, Cl, Bd, TP and Ksat, as well as WDC, WDS, CDR, DR, CR, MCR, CFI, ASC and AC. However, CS, Si, Ksat, Cl, ASC and WDS which explained &gt; 40% of the variability in Kfactor could be relied upon as indices of soil erodibility in the coastal plain sands in Akwa Ibom State.

Evaluation of Sheep Trampling at Different Grazing Periods on Soil Attributes

With the objective of evaluating the possible deterioration in some physical and chemical soil attributes, caused by sheep trampling in pasture areas compared to preserved areas. The study was conducted at the Instituto Federal de Educação, Ciência e Tecnologia da Paraíba - Campus Sousa, located in the Irrigated Perimeter of São Gonçalo, between the geographic coordinates 06o 50` 22 "S; 38o 17 ` 42" W; at 220 meters of altitude. The statistical design was in Randomized Blocks (DBC), with 3 treatments composed of: T1= no animals (preserved); T2= rainy period sheep grazing; T3= dry period sheep grazing, with six repetitions each. To determine the chemical attributes, soil samples were collected at a depth of 0 - 20 cm to determine (pH, phosphorus, potassium, sodium, calcium, magnesium, aluminum and organic matter) and physical attributes (sand, silt clay, soil density, total porosity, water dispersed clay) except for bulk density was taken from unformed samples at a depth of 0 - 10 cm from the soil. The sheep grazing in the different periods promoted soil compaction expressed by increased soil density, reduced total porosity and lower clay aggregate content. The permanence of grazing animals promoted a reduction in soil chemical quality, notably for phosphorus, calcium, magnesium and SOM contents in grazed sheep during the dry season and an increase in sodium and PST, compared to the area without grazing (preserved).

Residual effects of phosphogypsum rates and machinery traffic on soil attributes and common-bean (Phaseolus vulgaris) yield in a no-tillage system

Phosphogypsum (PG) affects many soil attributes, but its long-term effects on soil structure and physical properties remain unclear. We evaluated the residual effects of PG and induced soil compaction on selected soil chemical and physical attributes, and on common bean (Phaseolus vulgaris) yield. The experiment was initiated on a Typic Hapludox soil using a split-plot design with four replicates. In November (2009), PG at rates of 3, 6, 9, 12 Mg ha−1 was broadcast on the soil surface. In November (2012), traffic compaction was applied to the soil and the treatments were wheel-track (WTR), between wheel tracks (BWT) and no traffic/reference (REF) zones. Compaction was applied with a four-wheel-drive tractor with 2.4 and 3.6 Mg on the front and rear axles, respectively, at field water capacity (FC). Common bean was sown in February (2013) and its yield was assessed at physiological maturity. Forty-two months after application of traffic treatments, the 0.0−0.1 and 0.1−0.2 m soil layers were sampled. Phosphogypsum decreased exchangeable acidity and Al3+ concentrations, and increased pH and Ca2+ in both soil layers, as well as SO42- in the 0.1−0.2 m layer. Despite increasing water-dispersible clay (WDC), PG decreased aggregate tensile strength (TS) at the WTR and BWT zones. Phosphogypsum rates increased organic carbon concentrations in soil aggregates. Machinery traffic increased the values of WDC and TS, but also decreased common bean yield. PG application alleviated the negative impacts of wheel traffic on TS. We conclude that the residual effect of PG can positively affect soil chemical and physical attributes and contribute to alleviate the impacts of machinery traffic.

Impact of Iron and Aluminum on the Aggregate Stability of Some Latosols in Central and Southern Liberia (West Africa)

Problem: Latosols of Liberia are marked by intense surface leaching, strong acidity, low soil organic matter (SOM) content, and low nutrients status, caused by low aggregate stability, which are limiting factors to crop production.&#x0D; Aim: to evaluate the effect of soil organic carbon (SOC) different forms of Fe and Al on the aggregate stability of latosols.&#x0D; Methodology: Composite surface (0-20 cm depth) samples of four latosols at different localities in Liberia (Lat1, Phebe; Lat2, Felela; Lat3, Salala; Lat4, Todee) were collected and analyzed for aggregate stability parameters and factors by standard laboratory methods.&#x0D; Results: the studied soils are sandy clayey, very acidic and poor in SOC. The cation exchange capacity (CEC) ranges from 10.28 to 14.80 mmol.kg−1. Dominant forms of Al and Fe are free Fe (Fed) and Al [1], followed by amorphous Fe (Feo) and Al (Alo) and chelated Fe (Fep) and Al (Alp). The highest levels of water dispersible clay (WDC) and clay dispersible index (CDI) in Lat1 and Lat2 implied that these two soils are less stable compared to Lat3 and Lat4. The Fe and Al in all forms seem to contribute to soil aggregate stability. The SOC, although very low, also contributes to soil aggregate stability. SOC correlated positively with WDC, CDI and ASC, indicating the impact of SOC both as an aggregating agent and as a dispersing agent, in contrast to previous studies.&#x0D; Conclusion: The study reveals that Fe, Al and SOC are cementing materials which impact the aggregate stability in Latosols.

Characterization and identification of contemporary diagnostic (B) horizons of some soils in Ideato North local government area of Imo state Southeastern Nigeria

Most soils in Nigeria have not been characterized and classified based on diagnostic B horizon and identification of diagnostic B horizon is essential in the study of soils. As a result, this study was carried out to characterize and classify these soils with special emphasis on the identification of diagnostic B- horizons. A free survey method was employed to locate the representative profiles. Ten profile pits were dug, studied macromorphologically, georeferenced and sampled based on identified horizons. Results were presented using descriptive statistics. Soil textural classes consisted of sand, loamy sand, sandy loam and sandy clay loam. Soil bulk density was low to high ranging from 1.23g/cm3 to 1.94g/cm3. Soil pH values were extremely acidic (pH 4.4) to slightly acidic (pH 6.1). Exchangeable calcium and magnesium were low to high, ranging from 0.20cmol/kg to 6.20cmol/kg for calcium and from trace to 30.20cmol/kg for magnesium while that of sodium and potassium were very low ranging from 0.005 to 0.052cmol/kg for sodium and from 0.003cmol/kg to 0.016cmol kg-1 for potassium. Cation exchange capacity was low to high ranging from 5.20cmol kg-1 to 51.20cmol kg-1. Exchangeable acidity was trace to low; soil organic matter was low to high ranging from 0.07 g/kg to 5.00 g/kg. Percentage base saturation was low to very high ranging from 2.32% to 82.20%. Effective cation exchange capacity were low (1.457cmol kg-1) to high (35.56cmol kg-1). The available phosphorus is low ranging from 0.004cmol/kg to 0.013cmol/kg. Water dispersible clay values range d from 4.32% - 20.32%. The diagnostic criteria such as clay coatings/cutans, subsurface to surface clay ratio of 1.2, lithologic discontinuity, abrupt textural changes, artefacts, CEC. ECEC, etc. were identified. The two diagnostic B- horizons identified in the study areas were Kandic horizon and Argillic horizon (USDA) which correlate with Argic horizon (FAO/UNESCO (WRB).

Land-use change and its impact on physical and mechanical properties of Archaeological Black Earth in the Amazon rainforest

The intense pressure of anthropic actions to change the use and management can promote the degradation of anthropogenic soils with high natural fertility and high content of organic matter such as the Archaeological Black Earths of the Brazilian Amazon. Therefore, this study aimed to quantify the impact of land use and occupation in the Amazon biome on the physical and mechanical properties of Archaeological Black Earth. The research was carried out in the municipality of Novo Aripuanã, in the south of Amazonas State (Brazil), in a Chromic, Pretic, Acrisol with native forest, pasture, and pigeon pea. The soil properties of bulk density, mean weighted diameter, soil resistance to penetration, macroporosity, microporosity, particle size distribution (sand, silt, and clay), water-dispersible clay, flocculation index, total organic carbon, and preconsolidation pressure were assessed in the 0.0–0.1 and 0.1–0.2 m soil layers. Archaeological black earth under native forest showed better soil structural properties such as greater macroporosity and lower bulk density and resistance to penetration. The conversion to other uses promotes soil compaction and increases the resistance to compression. However, the greatest negative impacts on soil properties occurred when the land-use change was for pasture than for pigeon pea. The pigeon pea crop promoted the increase of soil total organic carbon in the 0.0–0.1 m layer. The soil mechanical behavior showed a greater load-bearing capacity in the native forest area for the surface layer than the subsurface layer. The preconsolidation pressure allowed to determine that the pasture land-use has a greater occurrence of compaction and might suffer additional compaction if the applied pressures on the soil during grazing are larger than the higher limit of the confidence interval of load-bearing capacity models when compared to the pigeon pea land-use.

The influence of pistachio shell biochar and barley residues on soil properties

&lt;p&gt;This research was conducted to evaluate the effects of biochar and barley residues on some physicochemical properties of silty loam soil and water erosion using water erosion simulator. Biochar was produced from pistachio shells under slow pyrolysis at 500°C under anaerobic condition. Biochar and barley residues were mixed to soils at three rates of 0, 0.5 and 1% (by weight), and 6.5 kg of soil was filled in trays with length, wide and height of 35 × 20 × 10 cm, respectively. The experiments were performed in 3 repetitions for 4 months as a completely randomized design. The results showed that application of 1% of biochar significantly increased P (phosphorus), K (potassium) and OC (organic carbon) of the soil in comparison with control. Also, application at both levels (0.5 and 1%) of barley residues significantly increased P, K, TN (total nitrogen), and OC. Application of biochar and barley residues significantly increased the mean weight diameter of aggregates, plant available water content, and saturated moisture content and significantly decreased water dispersible clay (p &amp;lt; 0.05). Consequently, the amount of water erosion decreased at the rainfall intensity of 60 mm·h-1 during 20 minutes. Generally, the effect of barley residues to improve soil properties was higher than the biochar.&lt;/p&gt;

Pedogenesis of bleached topsoils occurring on weakly structured, high chroma subsoils in South Africa

Topsoil bleaching is a common occurrence in South African soils. Bleaching is usually associated with the removal of soil pigmenting agents through redox stripping, clay eluviation and/or podzolisation. Thus topsoil bleaching above non-podzolic, high chroma red and yellow, supposedly well-drained subsoils is difficult to explain. These deep, weakly structured, red and yellow subsoils are some of the best agricultural soils in the country, and when climate allows, are farmed intensively. Bleached topsoils are known for their unfavourable physical characteristics, therefore understanding how these soils form is important to guide their taxonomic discrimination so that they can be managed sustainably.Profiles showing bleached and non-bleached (high chroma) topsoils were sampled from two different geographical regions; the summer rainfall eastern Highveld region and the winter rainfall, Western Cape Boland region. These samples were statistically compared to identify differences between bleached and non-bleached variants. Topsoil bleaching was shown to be hydrologically driven in catenal sequences in the summer rainfall region. In the red – yellow – grey topographic sequence, subsoil colour changes lag behind topsoil colour changes resulting in a zone where bleached topsoils overly high chroma yellow subsoils. The significantly higher (p = 0.05) acid oxalate/citrate dithionite bicarbonate Fe ratio (Far) in bleached topsoils adds further evidence to a redox driven system. Bleached profiles from the Highveld show indicators of increased subsoil clay accumulation, but it is proposed this is not a dominant process and is likely to be a result rather than the cause of bleaching.Bleaching mechanisms in the Western Cape are harder to establish. Only water dispersible clay differs significantly (p = 0.01) between bleached and non-bleached variants. Extractable Fe fractions do not provide significant evidence of redox pathways, although Far is slightly higher in bleached topsoils, despite a lower absolute oxalate extractable Fe concentration. Although not significant (p = 0.11), exchangeable Na, is higher in the bleached profiles and this may account for the more dispersible nature of the bleached profiles. These results suggest that topsoil bleaching in the Western Cape red apedal soils should be used as an indicator for poor structural stability and that these soils require more stringent management to prevent degradation.

Rice straw biochar effects on Atterberg limits and aggregate characteristics of an Acrisol in Ghana

ABSTRACT The stability and strength of soil aggregates to external forces such as raindrop impact and tillage may be affected by biochar application. In line with this, a three-year field experiment was conducted to investigate the effect of rice straw biochar (0, 15, and 30 t ha−1) on the Atterberg limits (plastic limit, PL and liquid limit, LL), water-dispersible clay content (WDC), and the aggregate characteristics of an Acrisol. Aggregate characteristics were measured on four size classes (1–2, 2–4, 4–8, and 8–16 mm). The 30 t ha−1 treatment significantly (p < 0.05) increased PL and LL by 27% and 20%, respectively, compared to the control. The plasticity index, WDC and tensile strength were unaffected by biochar addition. For all treatments, there was a decreasing trend in tensile strength with increasing aggregate size. The 15 and 30 t ha−1 treatments increased friability by 21% and 38%, respectively, relative to the control. The 30 t ha−1 treatment significantly increased workability of the smaller aggregates but marginally increased the workability of the larger aggregates. Thus, there is potential for increased optimum water content at tillage (inferred from the PL) and increased workability after biochar application at 30 t ha−1.

A new approach on the structural stability of soils: Method proposal

Water-dispersible clay analysis is used to evaluate soil structural stability, and two clay classes are quantified from it: the water-dispersible clay and the aggregated clay. We suggest here that three clay classes exist in soils with respect to structural behavior, and we propose a method for their quantification. Here, the aggregated clay is divided in two new classes, non-dispersible clay and water-re-flocculable clay. The method is based on a ten-fold dilution of the suspension obtained from water-dispersible clay analysis and successfully allowed the quantification of the proposed clay classes. The proposed method is inexpensive and does not require extra soil or chemical dispersants. Based on the distribution of these classes in different soils, seven groups of clay structural stability were defined. The method provides insights regarding soil structure-related processes, such as soil surface crusting, soil pore clogging, water erosion, and particles transport.

Variability of physical attributes in tropical weathered soil cultivated with irrigated beans (Phaseolus vulgaris L.)

Soil physical attributes are affected by several events. The ability to identify the variation of those attributes can be used to decide the best crop management. Although it is known that smaller grids are more representative, predicting the least number of points while maintaining accuracy is a tool that might reflect a gain in yield and time. The aims of this study were to evaluate the spatial physical variability and to define the minimum sampling density in a tropical Typic Haplustults soil using a scaled semivariogram in a central pivot area with pinto bean (Phaseolus vulgaris L.) after the eighth bean harvest in Cristalina, Goias State. Soil samples were collected at a regular grid of 10-m intervals, totaling 180 points, and at depths of 0.00–0.10 m, 0.10–0.20 m, and 0.20–0.30 m to determine total sand content (TS), silt (SIL), clay (CL), water-dispersed clay (WDC), mean weight diameter of soil aggregates (MWD), soil penetration resistance (PR), soil macroporosity (Ma), soil microporosity (Mi), and soil bulk density (BD). The results demonstrated that management promoted superficial soil compaction with increasing BD and Mi and decreasing Ma and TP. The scaled semivariogram demonstrated similarity between attributes in the three studied soil layers, evidencing strong spatial dependency. The sample density showed a strong influence of WDC in the irrigated soil properties. Adoption of a scaled semivariogram is a strategy that can be used to determine a minimum number of points that represents the spatial variability of soil physical attributes and to assist the best management in irrigated soils.

Assessing the impacts of land use and land cover changes on soil functions using landscape function analysis and soil quality indicators in semi-arid natural ecosystems

Assessing soil quality indicators is essential for ecosystem function evaluation. This study aimed to compare soil quality indicators of semi-arid forests and rangelands with different condition classes using direct soil quality indicators and landscape function analysis (LFA). Vegetation and soil properties were studied in three forest sites with different densities and 16 rangeland sites. A total of 72 soil samples were collected from various land use/cover types and their physical and chemical properties were measured. Eleven soil quality indicators were assessed from each patch and inter-patch zone along the established transects in each land use/cover type to obtain three functional indices including soil stability, infiltration, and nutrient cycling. The accuracy of the stability and infiltration indices of the LFA was verified by their correlations with some soil quality indicators. The results revealed a similar trend in soil quality indicators among the land use/cover types indicating that soil organic carbon (SOC), particulate soil organic matters (POM), mean weight diameter (MWD), soil stability index (SSI), and macronutrients had more appropriate conditions in rangelands with good conditions and dense forest sites compared to other land uses/covers. The soils in rangelands with poor conditions and sparse forests required substantial input of organic carbon to achieve an appropriate level of soil quality. The results highlighted the importance of SOC, POM, and soil texture for the prediction of aggregate stability in the region. The regression model showed a significant relationship between MWD and SSI. Moreover, nitrogen and SOC had significant relations with nutrient cycling and the relation between water dispersible clay and infiltration index was also significant (p < 0.01). The methods used in this study underscored the importance of conserving natural ecosystems. These methods can be implemented for assessing other semi-arid ecosystems. Holistic land management is required to conserve natural and productive ecosystems and to prevent soil degradation.

Changes on soil structural stability after in natura and composted chicken manure application

PurposeMany studies evaluate the effect of successive applications of chicken manure on soil attributes. In Brazil, the commercialization of this waste is common, implying on its sporadic use instead of many applications at the same area. The short-term effects of a single application of chicken manure and the role of its composting on soil structural stability are not fully understood. This study investigated application of in natura (uncomposted) and composted chicken manure on the structural stability of a Rhodic Ferralsol after a short period following single application.MethodsThe experiment was performed in a Rhodic Ferralsol in Londrina, Paraná. Brazil. We applied in natura and composted chicken manure at doses of 4.5, 9.0, 13.5, and 18.0 Mg ha−1 plus a control without application. Soil samples were collected after 185 days at the 0.0–20.0 cm layer for laboratorial analysis.ResultsThe composting of chicken manure did not affect soil structural stability. Chicken manure did not alter water-dispersible clay (bar{x}=21.7%), but increased the mean weight diameter of water-stable aggregates (MWD = 5.43 + 0.068 × dose) through the agglomeration of aggregates with 0.5–4 mm into 8–19 mm.ConclusionEven after a short period of 185 days, the application of chicken manure increases the structural stability of Rhodic Ferralsols and its composting, in the way performed by many farmers, is not associated with the improvement of soil structural stability in short-term. However, other advantages arise from the composting of the manure and need to be considered prior its use.