Disintegration of the clay fraction in the eluvial horizons of some Danish podzolized soils

Abstract

Using sequential extractions, total elemental analysis, and X‐ray diffraction, we have investigated the impact of the podzolization process on component composition of the clay fraction in the eluvial horizons of eight more or less podzolized Danish soils. The results indicate that podzolization is highly aggressive towards all clay components in the eluvial horizons eventually leading to their disintegration. The 2:1 layer silicate clay minerals, illite and chlorite, are first transformed into other 2:1 layer silicate clay minerals. After passing through a microcrystalline phase high in Si but low in Al, Fe, Mg, and K, they finally disintegrate completely. Even gibbsite and kaolinite disintegrate under the aggressive conditions, caused among other things by the presence of dissolved complex forming organic molecules in these horizons. Application of lime and fertilizers seems to be able to reverse the process in case of the 2:1 layer silicate clay minerals.     

Cation exchange capacity and base saturation of imperfectly drained surface coastal plain soils

Abstract

Testing three imperfectly drained forest soils (Alfisols and Ultisol) by nine methods showed that cation exchange capacities were highly pH dependent. Adding lime increased CEC values obtained by buffered and unbuffered methods but decreased CEC values when total bases were added to total acidity or salt replaceable acidity. No method tested completely explained the change in CEC caused by liming. Fractionation of the whole soil CEC Indicated an appreciable masked charge caused by an apparent complexing of amorphous metal oxides with clay or organic matter. In both buffered and unbuffered solutions, calcium saturation usually gave higher CEC values than monovalent ion saturation.     

Phosphorus fractions in argentine soils of different pedogenesis

Abstract

The distribution of phosphorus (P) in different organic and inorganic fractions was examined in five Argentinean soils of different pedogenesis. Soils were sequentially extracted to determine resin‐P, bicarbonate‐P, and hydroxide‐P fractions. Inorganic P (IP) predominated in all soils, specially moderately resistant IP (MRIP) in Entisol, Vertisol, and Ultisol. Both MRIP and labile IP (LIP) were important in Mollisol. Organic P (OP) was at a lower concentration in all soils and moderately resistant OP (MROP) was highest in all soils, except for the Mollisol. In intermediate evolution soils, labile P (LP) was very important, Mollisol had the highest value of LP%, and the lowest was for the Ultisol, demonstrating greater dynamics of P fractions in the Mollisol, soils of high productivity in the Pampean Prairie.     

Importance of the textural fraction and its mineralogic characteristics in the potassium contents of different argentine soils

Abstract

Our purpose was to determine the influence of the textural fraction and its mineralogical characteristics on the contents of the exchangeable (Ki) and nonexchangeable (Knoi) forms of soil potassium (K). Contributions of each textural fraction on Ki were as follows: 73–80% for clay, 8–18% for silt, and 2–10% for sand. The clay fraction relative to the contribution to Ki was not the same for all the soils studied. Thus, not only the quantity of clay must be taken into account, but also the cation exchange capacity (CEC) of the involved minerals. For Knoi, the total contribution showed a greater dispersion, the corresponding figures being as follows: clay 35–68%, silt 25–52%, and sand, 4–25%. Therefore, clay was not always the main contributor. In some soils, silt was the most important fraction due to the presence of muscovite.     

Soil type-dependent effects of drying-wetting sequences on aggregates and their associated OC and N

Evaluating the impacts of drying-wetting (DW) cycles on soil aggregates and their associated organic carbon (OC) and nitrogen (N) is crucial to understand the OC and N cycles. Soils are likely subjected to DW cycles with different sequences depending on seasons or in agroecosystems. However, studies on how DW sequences influence OC and N dynamics within aggregates, and whether this effect is dependent on soil type, are relatively limited. Herein, two DW sequences, i.e., drying-wetting-drying-wetting (2DW) and wetting-drying-wetting-drying (2WD) treatments were designed, and a consistent wetting (CW) was set as a control to assess the effects of DW sequences. Four soils (Entisol, Ultisol, Anthrosol and Mollisol) varying in texture and OC content were used. The aggregate size distribution, the OC, total N (TN), readily oxidizable OC (ROOC) and mineral N (Min-N) content in aggregates were determined. Results showed that 2DW treatment increased but 2WD treatment decreased the large aggregates of Entisol and Ultisol, while 2DW and 2WD treatments synchronously increased the large aggregates of Anthrosol but decreased them of Mollisol. Two DW treatments increased the OC in each aggregate of Entisol, Anthrosol and Mollisol but decreased them of Ultisol. The 2DW didn't affect but 2WD treatment decreased ROOC in 1–2 mm aggregates of Entisol and <0.25 mm aggregates of Ultisol and Mollisol. The 2DW and 2WD treatments minimally affected TN but potentially influenced Min-N in aggregates. The 2DW and 2WD treatments both decreased the Min-N in each aggregate size class of Entisol and Mollisol, while 2DW increased but 2WD treatment decreased Min-N in each aggregate of Ultisol and Anthrosol. These results indicated that the varied effects of DW sequences and the interactive effects of soil type with DW sequences on aggregate turnover and OC and N cycling should be reconsidered to provide more precisive evidences for global C and N cycles under the scenario of future climate changes.     

Effect of soil acidification on the growth and nitrogen use efficiency of maize in Ultisols

Purpose

To examine the effect of soil acidification on growth and nitrogen (N) uptake by maize in Ultisols.

Materials and methods

A clay Ultisol derived from Quaternary red earth and a sandy Ultisol derived from tertiary red sandstone were used in this study. A pot experiment was conducted with maize growing in the two Ultisols acidified to different pH values. Urea with ¹⁵N abundance of 10.11% was used to investigate the distribution of N fertilizer between soil and plant. Total N content and ¹⁵N abundance in plant and soil samples were determined by elemental analysis-isotope mass spectrometry.

Results and discussion

Critical soil pHs of 4.8 and 5.0 were observed for maize growing in the clay and sandy Ultisols, respectively. Below the critical soil pH, increasing soil pH significantly increased maize height and the yield of maize shoots and roots (both P < 0.05), but changes in soil pH showed no significant effect on maize growth above the critical soil pH in both Ultisols. Maize growing in the sandy Ultisol was more sensitive to changes in soil pH than in the clay Ultisol. Increase in the pH in both Ultisols also increased N accumulation in maize, the N derived from fertilizer in maize, physiological N use efficiency, and N use efficiency (NUE) by maize. Changes in soil pH had a greater effect on these parameters below the critical soil pH, compared to above. The change in soil pH had a greater effect on N accumulation in maize, the N derived from fertilizer in maize, and NUE in the sandy Ultisol than in the clay Ultisol. The NUE increased by 24.4% at pH 6.0, compared with pH 4.0 in the clay Ultisol, while the NUE at pH 5.0 was 4.8 times that at pH 4.0 in the sandy Ultisol. The increase in soil pH increased the ratio of N accumulation in maize/soil residue N and decreased the potential loss of fertilizer N from both Ultisols.

Conclusions

Soil acidification inhibited maize growth, reduced N uptake by maize, and thus, decreased NUE. To maintain soil pH of acidic soils above the critical values for crops is of practical importance for sustainable food production in acidic soils.

     

Indian land use in the Raposa–Serra do Sol Reserve,Roraima, Amazonia,Brazil: Physical and chemical attributes of a soil catena developed from mafic rocks under shifting cultivation

Native Indians (Macuxi, Ingarikó and Uapishana) in the Raposa–Serra do Sol Indian Reserve have been cultivating forest soils since the early XIX century, especially those derived from dolerite sills, scattered within the quartzitic dominated landscape. Representative soils developed from mafic rocks under Indian shifting cultivation in northeastern Roraima, were submitted to physical, chemical and mineralogical analyses to characterize their pedogenetic characteristics and infer on their status under native Indian shifting cultivation. The soil profiles were classified as: Orthic Ebanic Chernosol (USDA Mollisol), vertic Orthic Ebanic Chernosol (USDA Mollisol), Eutrophic Haplic Cambisol (USDA mollic Inceptisol) and Eutrophic Red Nitosol (USDA Red Alfisol), which occupy, respectively, lower slopes and less dissected terrains (Mollisols) and steeper slopes (Alfisols). The first two are eutrophic, and not typical of the Amazon region. Their mineralogies range from kaolinite/goethite rich upland, deeply weathered Nitosol, to 2:1 clay rich downslope Chernosols. The latter has primary minerals in the silt fraction and high CEC resulting in high fertility. The Nitosols reveal a process of severe topsoil loss, due to widespread sheet erosion from deforestation and shifting cultivation. Chemical analyses showed varied soil fertility, ranging from high levels in the Chernosols to a low level in the non-cultivated Nitosol. Phosphorus levels are limited in all soils, despite the high fertility. The Chernosols located in lowland, flat areas close to the valley floor are more suitable environments for the slash-and-burn native farming system. In the Chernosols and Cambisols, the clay activity below the value limit for this class indicates a current natural process of increasing leaching. The more weathered and eroded Nitosol showed low Fe-oxalate and Si-oxalate levels. Micronutrients such as total zinc and copper, decreased with depth and weathering. The Nitosols showed the highest phosphate adsorption levels (1.574 mg g^− 1 of soil) which can be attributed to its clayey texture. Chernosols showed overall lower P adsorption values, increasing with depth. All soils under native Indian cultivation display signs of physical and chemical degradation due to shortened fallow under intense land use pressure in the Raposa–Serra do Sol Reserve.     

The nature and composition of amorphous material and free oxides in some temperate region and tropical soils

Abstract

Amorphous clay separated from pedons of a highly weathered soil previously classified as Oxisol and an Ultisol of the Southern States and, from the surface horizons of an Oxisol and two Andepts of the tropics were studied by chemical, DTA, infrared and X‐ray analysis.

Considerable amounts of amorphous material, 20–37% in temperate region and 29–40% in tropical soils, were extracted by differential dissolution using 0.5 N NaOH. The molar SiO₂/Al₂O₃ ratios of the dissolved material varied from sesquioxidic to siliceous (0.36–9.1) in temperate region soils, whereas those of the Andepts were allophonic (1.5–1.7). DTA and infrared analysis confirmed these results, however the strong gibbsite peaks in the X‐ray analysis of temperate region soils suggested that the aluminum fraction dissolved was in part, if not all, crystalline in nature. Indications were obtained with DTA and infrared that Na‐dithionite treatment might have altered the nature of the clay.     

中南地区淋溶土的层间羟基物矿物

将北纬 3 0°～ 3 2°亚热带花岗岩发育的两个淋溶土B层黏粒样分别用连二亚硫酸钠—柠檬酸钠—重碳酸钠 (DCB)溶液溶提处理和经DCB溶液处理后再用柠檬酸钠溶液溶提处理。从上述处理后样品的X射线衍射图谱中可看出 :供试土壤的膨胀性矿物层间有羟基物质 ,它们能被DCB溶液—柠檬酸钠溶液所溶解提取 ,含羟基物质的黏土矿物主要来源于蛭石 ,少量来自蒙皂石。DCB溶液—柠檬酸钠溶液处理前后黏粒红外差分光谱上显示的 980～ 970cm- 1 ,91 0～940cm- 1 吸收带 ,标志着供试土壤膨胀性矿物层间含有羟基铝硅酸和羟基铝离子。从而首次揭示了中国中南地区淋溶土的膨胀性矿物层间有羟基铝硅酸。     

Characterization of organic and inorganic phosphorus in the highland plateau soils of Ethiopia

Abstract

Surface horizon samples from two Vertisols, an Andisol, and an Alfisol were collected from farmers’ fields, research station farms, and from uncultivated/ nonfertilized areas to characterize the organic and inorganic forms of phosphorus (P) in the highland plateau soils of Ethiopia using the Hedley soil P fractionation scheme. The total P values ranged from 226 mg‐kg^‐1 in the Akaki Vertisol samples developed on alluvial deposits to 1570 mgkg^‐1 in the Andisol samples, where the HCl fraction dominates the inorganic soil P pool. The Alfisol samples contained 400 mg‐kg^‐1 of total P, with the NaOHand residual P being the dominant P fractions. The resin inorganic phosphorus (Pi) and bicarbonate Pi fractions generally accounted for less than 15% of the total P in all soils, and were positively correlated with organic C. The NaOH P fraction, which was most prominent in the surface horizon samples of the Alfisols, accounted for 4–15% of total P. The HCl P fraction, ranged from 1% in the Alfisols to 46% in the Andisols, and positively correlated with pH. All of the P fractions were negatively correlated with clay and extractable Al contents. The organic P (Po) fractions were positively related to organic carbon (C) and dithionate extractable iron (Fe). All samples collected from farmers’ fields showed a loss of P from the residual, and HCl fractions as compared to the uncultivated/nonfertilized samples. There is also a decrease in the labile P (resin Pi, bicarbonate Pi, and Po) fractions, except for the Akaki Vertisol samples. However, under research station management, the amount of labile P fractions either increased or remained at the same level as the uncultivated/nonfertilized samples, except for the Andisol. Addition of P fertilizer at the recommended rates to the Debre Zeit research station Vertisol appears to have resulted in a slight increase in the labile P and prevented loss of P from the HClP and residual P fractions.     

Retention of dissolved organic matter by illitic soils and clay fractions: Influence of mineral phase properties

The dependency of the retention of dissolved organic carbon (DOC) on mineral phase properties in soils remains uncertain especially at neutral pH. To specifically elucidate the role of mineral surfaces and pedogenic oxides for DOC retention at pH 7, we sorbed DOC to bulk soil (illitic surface soils of a toposequence) and corresponding clay fraction (< 2 μm) samples after the removal of organic matter and after removal of organic matter and pedogenic oxides. The DOC retention was related to the content of dithionite‐extractable iron, specific surface area (SSA, BET‐N₂ method) and cation exchange capacity (pH 7). The reversibility of DOC sorption was determined by a desorption experiment. All samples sorbed 20–40 % of the DOC added. The DOC sorption of the clay fractions explained the total sorption of the bulk soils. None of the mineral phase properties investigated was able to solely explain the DOC retention. A sorption of 9 to 24 μg DOC m^–2 indicated that DOC interacted only with a fraction of the mineral surface, since loadings above 500 μg m^–2 would be expected for a carbon monolayer. Under the experimental conditions used, the surface of the silicate clay minerals seemed to be more important for the DOC sorption than the surface of the iron oxides. The desorption experiment removed 11 to 31 % of the DOC sorbed. Most of the DOC was strongly sorbed.     

Nonexchangeable potassium extraction and associated structural changes of mica dominant clay minerals

Abstract

Six mica dominant soils representing a landform sequence were used for the present investigation. The effect of extraction of nonexchangeable potassium (K) by boiling 1 M HNO₃ treatment and its associated structural changes of micaceous clay minerals was studied by employing x‐ray diffraction technique. Potassium release was rapid in the first three extractions and slowed down to a constant rate thereafter in all the clay samples. The first extraction contributed about 45.57–62.69% towards the total K release. The calculated values of rate constant (first order) decreased sharply from 0.065–0.025 min^‐1 after third extraction and reached a constant value thereafter. The calculated integral width of first order reflection of mica peak (10Å) decreased considerably with nitric acid treatment, but no such effect was observed in 5Å peak. The differential x‐ray diffraction (DXRD) traces showed that the HNO₃ treatment dissolved finer particles of mica particularly trioctahedral component and mixed layer minerals, smectite, chlorite and vermiculite.     

Characterization of maghemite in B horizons of three soils from Southern Portugal

Maghemite with an unusual habit was identified in the sandy fraction of two Alfisols and one Ultisol by X-ray and electron diffraction. Hematite was also present. Morphological analyses by scanning and transmission electron microscopy showed needle-like particles of maghemite with average lengths of 200–500 nm depending on the degree of the crystallinity. Those particles are arranged in star-like patterns as shown by ultrathin sections. Experimental synthesis of maghemite was successfully attempted in the presence of quartz sand with the freshly-formed crystals displaying the same particular morphology. Formation of acicular maghemite catalysed by quartz surfaces is, therefore, postulated.     

Predicting carbon content in illitic clay fractions from surface area, cation exchange capacity and dithionite-extractable iron

We used the specific surface area (SSA), the cation exchange capacity (CEC) and the content of dithionite‐extractable iron (Fe_d) to predict the content of organic carbon in illitic clay fractions of topsoils from loess. We determined SSA (BET‐N₂ method) and CEC of clay fractions after removing organic C or reducing oxides or both. The CEC and the SSA of the carbon‐ and oxide‐free clay fraction explained 56% and 54% of the variation in C content, respectively. The Fe_d content of the clay fractions was strongly and negatively related to the C content, and with the SSA of the carbon‐free clay fraction it predicted C content almost completely (R² = 0.96). The results indicate that the amount of cations adhering to the silicate clay minerals and the size of the silicate mineral surface area are important properties of the mineral phase for the storage potential of C. The reason for the negative relation between iron oxides and C content remains unclear.     

Soil phosphorus mobilization in different taxonomic orders

Changes in P fractions using Hedley's sequential fractionation of organic and inorganic soil P, were studied in soils covering a wide range of developmental stages and original materials. A greenhouse experiment was performed in order to make an exhaustive P uptake by Lolium perenne and to study soil phosphorus mobilization from different fractions. Samples were obtained at 30, 60 and 90 days from sowing, with two fertilization rates added as KH₂PO₄. The exhaustion produced by plants resulted in different patterns of mobilization according to soil characteristics. For control soils the contents of inorganic labile fraction (LIP) decreased at the end of the experience in Mollisol (31%), Vertisol (24%) and Andisol (17%). The mobilization of organic P was greater for Ultisol and Andisol (77 and 75% respectively) than for the other soils. Fertilization affected mainly inorganic P, with a significant increase in contents of LIP in Entisol (46%) and moderately resistant inorganic P (MRIP) in Andisol (15%). Inorganic P/organic P relationship tended to increase during the experiment, while labile P/moderately resistant P increased in Entisol and Mollisol.     

Short-term effects of tillage practices on soil aggregate fractions in a Chinese Mollisol

Abstract

Soil aggregate-size distribution and soil aggregate stability are used to characterize soil structure. Quantifying the changes of structural stability of soil is an important element in assessing soil and crop management practices. A 5-year tillage experiment consisting of no till (NT), moldboard plow (MP) and ridge tillage (RT), was used to study soil water-stable aggregate size distribution, aggregate stability and aggregate-associated soil organic carbon (SOC) at four soil depths (0–5, 5–10, 10–20 and 20–30 cm) of a clay loam soil in northeast China. Nonlinear fractal dimension (D_m) was used to characterize soil aggregate stability. No tillage led to a significantly greater aggregation for >1 mm aggregate and significant SOC changes in this fraction at 0–5 cm depth. There were significant positive relationships between SOC and >1 mm aggregate, SOC in each aggregate fraction, but there was no relationship between soil aggregate parameters (the proportion of soil aggregates, aggregate-associated SOC and soil stability) and soil bulk density. After 5 years, there was no difference in D_m of soil aggregate size distribution among tillage treatments, which suggested that D_m could not be used as an indicator to assess short-term effects of tillage practices on soil aggregation. In the short term, > 1 mm soil aggregate was a better indicator to characterize the impacts of tillage practices on quality of a Chinese Mollisol, particularly in the near-surface layer of the soil.     

Comparison of the surface chemical properties of four soils derived from Quaternary red earth as related to soil evolution

The surface chemical properties of soil samples i.e., surface charge and zeta potential, and the mineralogy of soil clay fraction were investigated with reference to soil weathering extent for four different soils derived from Quaternary red earth using the ion adsorption method, a micro-electrophoresis method and the X-ray diffraction analysis. Results indicated that all these soil samples contained kaolinite and gibbsite. The Ultisols from Guizhou, Hunan and Jiangxi possessed the 2:1 type clay minerals of mica and vermiculite. Hematite and magnetite were found in the Ultisols from Guangxi, Hunan and Jiangxi. Goethite was found in the Ultisols from Jiangxi, Hunan and Guizhou. The positive surface charge for these soils decreased with the order: the Ultisol from Guangxi ≅ the Ultisol from Guizhou > the Ultisols from Hunan and Jiangxi from south to north when pH < 5.0. This is consistent with the content of free Fe/Al oxides present in these soils. On the other hand, the value of negative surface charge on the Ultisol from Guangxi was found much lower than the other soils perhaps because of the intensive weathering of the soil. Both permanent and variable negative charges for the former were also lower than the latter, whereas the point of zero salt effect (PZSE) for the former was greater than that of the latter. The variability of soil negative surface charge followed the order: the Ultisol from Guangxi > the Ultisol from Guizhou > the Ultisol from Jiangxi ≅ the Ultisol from Hunan. The zeta potential and isoelectric point (IEP) of soil colloids and soil net surface charge followed the same order: the Ultisol from Guangxi > the Ultisol from Guizhou > the Ultisols from Hunan and Jiangxi. A good correlation between zeta potential and net surface charge of these soils was observed. Therefore, the magnitudes of the PZSE, IEP and zeta potential of these soils were in agreement with the weathering extent of the soils and can be employed as reference criteria for classification and evolution of soils.     

Clay materials in the soils of the Baraba Steppe and the Priobskoe Plateau

The composition and the regularities of the profile distribution of the clay minerals in the solods of the Baraba Steppe (ground moistening) and the Priobskoe Plateau (atmospheric moistening) were studied. The two profiles have the distinct eluvial-illuvial distribution of the clay fraction. The composition of the clay fraction in the eluvial layer is dominated by illite. The content of chlorite and labile minerals of the montmorillonite group increases downwards in the profile. The revealed regularities in the profile distribution of the clay fraction and some groups of clay minerals are explained by the joint influence of the mineral dissolution under the influence of the gleying and alkaline hydrolysis, as well as the processes of illitization and lessivage. The major differences in the content and distribution of the clay minerals between the solods and the podzolic soils are the following. The solods have a clear illuvial layer in the clay, while the majority of podzolic soil profiles have the eluvial distribution of the silty fraction. The solods in the eluvial part of the profile and sometimes in even the bottom layers have an unusually high content of the illite minerals in the clay fraction due to illitization. The podzolic layers of the solods do not contain soil chlorites common for the eluvial layers of the podzolic soils, which is due here to a less acidic medium that can not provide the proper conditions of aluminum mobilization and migration needed for the development of chloritization.     

Organoclays reduce arsenic bioavailability and bioaccessibility in contaminated soils

Purpose  

Naturally occurring layer silicate clay minerals can be value added by modifying their surface properties to enhance their efficacy in the remediation of environmental contaminants. Silicate clay minerals modified by the introduction of organic molecules into the mineral structure are known as organoclays and show much promise for environmental remediation applications. The present study assesses the extent of decrease in bioavailable and bioaccessible arsenic (As) via enhanced adsorption by soil treated with organoclays.     

The Role of Soil Mineralogical Characteristics in Sustainable Soil Fertility Management: A Case Study of Some Tropical Alfisols in Nigeria

The pedogenic horizons of nine profile pits dug across three toposequences were studied to determine the soil mineralogical characteristics and its implications on sustainable management of the fertility of some tropical Alfisols in Nigeria. Results showed that the epipedon which were predominantly ochric had textures that ranged from sand to sandy loam, while the subsurface (B/Bt) horizons had sandy clay loam to sandy clay texture and were gravelly (31.79–83.04%). The soil reaction ranged from strongly acid to neutral (pH 5.10 to 7.05). Calcium and magnesium dominated the exchange sites and accounted for about 75% of the exchangeable bases. Illite/mica and kaolinite were the dominant minerals in the clay fractions, while quartz, mica, and feldspars dominated the fine sand and silt fractions of the soils. While the presence of illite and mica could be important for potassium nutrition in these soils, kaolinite and oxides of iron could also cause phosphorus fixation.