Effects of air-drying on the adsorption and desorption of phosphate and levels of extractable phosphate in a group of acid soils,New Zealand

The effects of air-drying field-moist soils on the adsorption and desorption of added phosphate and on the levels of extractable native soil phosphate were examined using the A and B horizons of a group of four acid soils.Air-drying increased the capacity of all the soil samples to adsorb phosphate. At an equilibrium solution concentration of 0.5 μg P ml^?1, the increase in the quantity of phosphate adsorbed following drying ranged from 23% to 70% of that adsorbed by the moist samples. Considerable hysteresis in phosphate adsorption—desorption isotherms was observed for both moist and dried soil samples indicating that the additional phosphate adsorbed by the dried samples was held with the same strength as that held by the moist samples.Air-drying the soil samples caused a small decrease in soil pH of approximately 0.1 pH unit and a general increase in levels of EDTA-extractable Fe, Al and organic matter. Quantities of native soil phosphate extractable with EDTA, resin and NaHCO₃ were also increased. Concentrations of oxalate- and pyrophosphate-extractable Fe and Al and exchangeable Al were, however, unaffected by drying.It was also shown that when the phosphate content of NaHCO₃ extracts is measured using the conventional molybdenum blue method, orthophosphate plus a differing amount of acid-hydrolysable organic P present in the extract is measured.     

Origin of the pH-dependent cation exchange capacities of Irish soil clays

Values of cation exchange capacity determined at pH 4.8 and at pH 8.2 are reported for peroxidized clay separates from a group of Irish soils derived from a variety of parent materials. The correlation between the two measurements was poor. The differences between the values (pH-dependent CEC's) ranged from 0.1 to 58.6 mequiv./100 g, with a mean of 12.9 mequiv./100 g. The highest values were associated with clays from spodic horizons and clays from basalt-derived soils. CEC at pH 8.2 and pH-dependent CEC were highly correlated with citrate-dithionite-bicarbonate (CDB) extractable Al. In contrast, CEC at pH 4.8 was negatively correlated with this parameter, suggesting that hydrous oxides reduced CEC at low pH values.Values of CEC of pH 4.8 and pH 8.2 are also reported for a selection of 16 clays subjected to sequential extraction with CDB and NaOH. CDB treatment reduced mean pH-dependent CEC from 20.4 to 9.0 mequiv./100 g, which was reduced to 3.9 mequiv./100 g by subsequent extraction with NaCH. The material removed by CDB was apparently positively charged at pH 4.8 and negatively charged at pH 8.2. Most of the pH-dependent CEC remaining after CDB treatment was associated with the clays from spodic horizons. The material extracted by NaOH was apparently negatively charged at both pH 4.8 and pH 8.2. No direct evidence of the physical nature of this material was obtained but it was present in sufficient amounts to suggest that it existed in particular forms in some of the clays from the spodic horizons. Following the dissolution treatments, the correlation between CEC values at pH 4.8 and pH 8.2 was very good (r = 0.99).     

Effects of drying on the ion exchange capacity and cation adsorption properties of some New Zealand soils

Abstract

The effect of drying on the cation (CEC) and anion (AEC) exchange capacity, and on potassium (K) and magnesium (Mg) adsorption by three New Zealand soils was investigated. Air‐drying resulted in no significant changes in these properties compared with the field‐moist samples. Oven‐drying at 105°C significantly decreased the CEC and increased the AEC of most soils compared with air‐dried samples. The decrease in CEC was related to increased solubility of organic matter and a decrease in surface area on which charge could be developed. The increase in AEC was attributed to a decrease in soil pH.

Potassium and Mg adsorption by two soils decreased following oven‐drying. This was consistent with the effect of drying on CEC. For the remaining soil, K adsorption increased following oven‐drying. This was attributed to K fixation.     

Microwave oven‐drying of soil samples for chemical testing in Brazil

Abstract

In this experiment, we investigated the effect of microwave oven‐drying on soil samples for chemical tests. Samples were irradiated until they achieved a constant weight and for one‐half the time required. Two other treatments were applied, air‐drying at room temperature and forced air oven‐drying at 60°C. Samples were analyzed for water pH, 0.01M CaCl2 pH, organic carbon (C), Mehlich 1 and resin available phosphorus (P), exchangeable potassium (K) and calcium (Ca) plus magnesium (Mg), and potential acidity [1N calcium acetate (pH 7.0) extractable hydrogen (H) plus aluminum (Al)]. The results showed that microwave‐drying can induce erroneous interpretations of the “fertility status”; of the soil, thereby affecting fertilizer recommendations and lime requirement determinations.     

Effects of Soil Drying on Soil pH and Nutrient Extractability

A sample set from a field experiment conducted at two sites, a commercial organic potato farm and a conventionally managed experiment station farm, was used to compare the extractability of nutrients in field-moist and air-dried soils. Standard soil characterization methods of the Maine Soil Testing Service were used to determine soil pH and extractable nutrient content. The data were analyzed with Systat using paired t-tests. Air drying decreased soil pH and increased extractability of calcium, micronutrients, and metals. Many of the observed changes were probably a result of increasing surface acidity with drying. Drying increased the extractability of inorganic phosphorus, probably because of disruption of aluminophosphate complexes, particularly in conventionally managed soils, which had received high amounts of inorganic phosphorus fertilizer. Drying also increased the extractability of complexed phosphorus, probably both organically and inorganically complexed phosphorus, and decreased the extractability of potassium, probably by enhancing potassium fixation in clay interlayers.     

An assessment of EDTA as an extractant of organic-complexed and amorphous forms of Fe and Al in soils

EDTA solutions proposed as selective extractants of amorphous and organic forms of Fe and Al in soils and synthetic materials were tested. Extraction of Fe and Al from some soil samples continued at a decreasing rate beyond 120 days. For some soil samples and synthetic materials the amounts of Fe and Al extractable by EDTA (90 days) were markedly lower than those extractable by acid ammonium oxalate (2 h). Extraction of samples for 1 h with EDTA was shown to release amounts of Fe and Al far below those considered to be complexed with organic matter. The EDTA extraction procedures tested should not replace either acid ammonium oxalate for estimating amorphous forms of Fe and Al or pyrophosphate for estimating organic forms of Fe and Al in soils.     

Release of Al by hydroxy-interlayered vermiculite and hydroxy-interlayered smectite during determination of cation exchange capacity in fine earth and rock fragments fractions

The fine earth (<2 mm) and rock fragments (>2 mm) fractions of two soils derived from Oligocene sandstone have been examined to assess the origin of the discrepancies between cation exchange capacity (CEC) and effective CEC (ECEC). The soils differ in terms of acidity: soil A is more acid than soil B. When the A samples are treated with BaCl₂, the solution became sufficiently acid (pH < 4·5) to dissolve and to maintain Al in solution. From these samples more Al is released than base cations. Aluminium was continuously replenished even after 192 h, so that the ECEC was always larger than the CEC. Samples from soil B contain less H and Al ions, and the BaCl₂ solution could not lower the pH below 5·0. In these samples little Al is released, and the base cations dominate the exchangeable pool of ions. This Al can be considered to be exchangeable, and a good agreement exists between the ECEC and the CEC. The source of non-exchangeable Al in the A samples is the OH-Al polymers of the hydroxy-interlayered vermiculite (HIV) and hydroxy-interlayered smectite (HIS) that tend to dissolve during the BaCl₂ treatments. In the less acid B samples the Al polymers are not affected by BaCl₂ treatment. Different results were obtained when the clays, extracted from an Na-dispersed suspension, were treated with BaCl₂ solution. Because the clays are no longer acid, no H⁺ is released, and the OH-Al polymers are not dissolved. Therefore, the saturating ions play an important role in the dissolution of the OH-Al polymers and cause differences between the CEC and ECEC. We discount organic matter and specifically Al-organo complexes as a source of non-exchangeable Al. Both A and B soils contain very similar pyrophosphate-extractable Al, but show substantial differences in the amount of exchangeable Al.     

Geochemistry of Aluminium and Iron in Mine Soils from As Pontes,Galicia (N.W. Spain)

The geochemical processes influencing iron and aluminium mobilization and immobilization processes in mine soils are discussed. The study was carried out on 11 soils from the As Pontes mine dump, in the process of reclamation. The soils differ in age, spoils nature, reclamation tasks and type of vegetation, covering a wide range of physico-chemical conditions. Oxalate and pyrophosphate extractable Al and Fe (Alo, Alp, Feo, Fep), and dithionite extractable Fe (Fed) were analysed. These fractions were related to the solution Al and Fe forms and contents and to other soil properties (Eh, pH, sulfides, organic matter, cation exchange capacity, and composition of the soil solution). Alo ranged between 2.2 and 111.2 cmolc kg-1; 5 to 80% of this Alo was organic aluminium (Alp). Fed ranged between 8.5 and 215.6 cmolc kg-1; 20 to 70% was poorly-criystalline iron (Feo). The solution concentrations of Al and Fe ranged between <0.1 and 319.2, and between <0.1 and 46.7 mg L-1, respectively. The results showed that the spoil nature (mostly carbonaceous clays and slates differing in sulfide content) and the reclamation tasks undertaken (topsoiling, liming with fly ash) determine the forms and contents of Al and Fe in the solid phase as well as in the soil solution and also its distribution between the solid and liquid phases.     

Influence of drying conditions on wettability and DRIFT spectroscopic C–H band of soil samples

This study assesses the effect of various drying procedures on water repellency measured by water drop penetration time ( WDPT ) and spectroscopic parameters gauged by Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFT) of two anthropogenically-influenced soils at sites in Berlin. Wettable and water-repellent samples were dried at various temperatures and at prescribed relative humidity. WDPT and DRIFT spectroscopic characteristics were obtained from both dried and field-moist subsamples. Normalization of DRIFT spectral C–H band intensity ('surface hydrophobicity') against the integral absorption intensity over the wave number range 4000–400 cm⁻¹ resulted in an apparent resolution between the effects of water content and changes in C-H absorption at the surface. To our current knowledge, the latter could be best explained with changes in the three-dimensional rearrangement of organic molecules or moieties on inner and outer soil organic matter (SOM) surfaces, whereas the former could be a direct consequence of the fraction of inner and outer soil surfaces covered with water and of the mean thickness of the respective water films. Further evidence for this model is required from other investigations focusing on the surfaces in soil, before drawing final conclusions. The results show that the method of drying affects WDPT to a greater extent than soil water content after drying. DRIFT spectra suggest that exposure to high temperature results in some reorganization of SOM in the outer layer. It is further suggested that short exposure may result in a heterogeneous distribution of water leading to localized variation and inconsistency in WDPTs. Drying for 4 weeks under controlled relative humidity at 20°C is suggested as a reference preparation method combining the benefits of an almost unchanged SOM surface compared with field-moist samples with homogeneous moisture distribution.     

Effect of sample pretreatment on aggregate stability measured by wet sieving or turbidimetry on soils of different cropping history

The effects of cropping history (pasture or arable) and sample pretreatment (field-moist, air-dried or air-dried and then tension or vacuum rewetted) on aggregate stability as measured by wet sieving or turbidimetry were compared. When field-moist samples were used there was a tendency for aggregate stability, as measured by wet sieving, to decline with increasing time under arable cropping (i.e. decreasing soil organic matter content). Air-drying samples caused a pronounced decline in stability of soils from under arable management and as a consequence there was a marked decline in stability with increasing time under arable. Use of tension or vacuum rewetted samples resulted in high values of stability which were unaffected by cropping history. For turbidimetry, there was a marked decline in measured stability with increasing time under arable cropping when field-moist samples were used. Air-drying caused an increase in measured stability that was relatively greater for the less stable samples. In comparison with air-dried samples, tension and vacuum rewetting caused a decrease in stability values for relatively unstable soils. It is suggested that, upon air-drying (and contraction of aggregates), additional intermolecular associations were formed between soil constituents thus conferring greater stability on aggregates. This resulted in reduced dispersion (and the release of particles <0.04 mm in diameter) from the surfaces of aggregates and slaked aggregate fragments following rapid rewetting. As a consequence stability as measured by turbidimetry was increased by drying. For aggregates from a predominantly arable history, this stabilization was not great enough to prevent slaking occurring following rapid rewetting, with the formation of a large proportion of stabilized fragments <0.5 mm in diameter. The stability of these aggregates as measured by wet sieving was therefore decreased by drying.     

Sesquioxidic components of selected Taiwan soils

Twenty two surface soils, representing six parent materials and four soil groups, were sampled in Taiwan for the present study.Except in the soil derived from volcanic ash, the sesquioxidic components and relatively easily extractable Si were present only in small amounts in the NaOAc and H₂O₂- NaOAc extractable fractions. In addition to Fe, both Si and Al were present in the dithionite-citrate-bicarbonate extracts in considerable amounts, indicating that Si and Al were either present separately or in association with Fe in the sesquioxidic fractions of the soils. The amounts of Si, Al and Fe extracted by the dithionite-citrate-bicarbonate and boiling KOH treatments differed from sample to sample, indicating that they are important variables in the nature of the soils studied.The amounts of the ammonium oxalate-extractable Al and Fe, representing the noncrystalline sesquioxidic products of relatively recent weathering, also differed with parent materials and pedogenic processes. The statistical data indicate that the ammonium oxalate-extractable Al and Fe are related to the contents of organic matter but not to acidity and the contents of clay. The percentage distribution of the extractable Al in the > 2 μm fractions of the selected soil samples ranged from 22.0 to 52.5% and that of the extractable Fe from 11.1 to 38.1%, indicating that the active non-crystalline Al and Fe components in the non-clay fractions deserve close attention in the study of pedogenesis and other soil physicochemical reactions in relation to soil fertility and environmental protection.     

Sources of soluble calcium and magnesium and their effects on sodium adsorption ratios of solutions in two soils of israel

Exchange reactions and dissolution of soil minerals in 0.01, 0.05 and 0.1 N NaCl solutions at three different times of contact between two soils and the solutions were studied. It was found that dissolution of soil minerals occurred continuously and the release of divalent cations from exchange sites did not stop the process. The amounts dissolved from both soils increased as the concentration of NaCl and time of contact increased. The minimum amounts of calcium and magnesium dissolved in 0.01 N NaCl during 10 min of contact between soil and solution were 0.7 and 0.9 mequiv./100 g from a noncalcareous terra rossa and a calcareous grumusol, and the maximum amounts of these cations dissolved in 0.1 N NaCl during two weeks of contact were 2.5 and 3.1 mequiv./100 g soil from the terra rossa and grumusol, respectively. The amounts released from exchange sites were proportional to the cation exchange capacities of the soils and the SAR of the soil solutions. The effects of calcium and magnesium released from dissolution of soil carbonates and aluminosilicate and from exchange sites on SAR of soil extracts were investigated.     

Interactions between soil organic matter status, cropping history, method of quantification and sample pretreatment and their effects on measured aggregate stability

 The effects of sample pretreatment (field-moist, air-dried or tension rewetted) on aggregate stability measured by wet sieving or turbidimetry were compared for a group of soil samples ranging in organic C content from 20 to 40 g C kg^–1. Concentrations of total N, total and hot-water-extractable carbohydrate and microbial biomass C were linearly related to those of organic C. Aggregate stability measured by wet sieving using air-dried or field-moist samples and that measured by turbidimetry, regardless of sample pretreatment, increased curvilinearly with increasing soil organic C content. However, when tension-rewetted samples were used for wet sieving, aggregate stability was essentially unaffected by soil organic C content. Measurements of aggregate stability (apart from wet sieving using rewetted soils) were closely correlated with one another and with organic C, total and extractable carbohydrate and microbial biomass C content of the soils. The short-term effects of aggregate stability were also studied. Soils from under long-term arable management and those under long-term arable followed by 1 or 3 years under pasture had similar organic C contents, but aggregate stability measured by turbidimetry and by wet sieving using air-dried or field-moist samples increased with increasing years under pasture. Light fraction C, microbial biomass and hot-water-extractable carbohydrate concentrations also increased. It was concluded that both total and labile soil organic C content are important in relation to water-stable aggregation and that the use of tension-rewetted samples to measure stability by wet sieving is unsatisfactory since little separation of values is achieved. Received: 6 January 1999     

Relationship between acidity and microbiological properties in some tea soils

The present study was conducted to investigate the effects of different forms of soil acidities on microbial biomass C, ergosterol content, microbial metabolic quotient, microbial respiration quotient, and fluorescein diacetate-hydrolyzing activity of some tea-growing soils of India. Total potential and exchangeable acidity and extractable and exchangeable aluminum were higher in Tripura followed by Jalpaiguri and Kharagpur soil. Different forms of acidity were significantly and positively correlated with each other. All the microbiological properties investigated were significantly and positively correlated with soil organic C content. The ratio of organic C with microbial parameters was significantly and negatively correlated with different forms of acidity. Principal component analysis indicated that the microbial activities were not directly affected by the extractable aluminum and total potential acidity. Although the tea soils had higher microbial biomass and activities because of higher organic matter content than other soils, the ratios of microbial parameters/organic carbon indicated that inhibition of microbial growth and activities had occurred because of acidity stress.     

Clay mineral distribution in two toposequences of tropical soils of India

The clay fractions of the soils of two toposequences derived from gneissic rocks (Peninsular gneiss) in southern India consist chiefly of kaolinite and amorphous ferrialuminosilicates (AFAS). The cation exchange capacity of the amorphous constituents, ranging between 21.4 and 107.6 mequiv./100 g, has been explained on the basis of a structural model. Considerable amounts of smectite were present in the clays of soils on the toeslopes. Two hypothetical pathways for the formation of the clay minerals are proposed.     

配位体交换在减慢由酸雨造成的可变电荷土壤酸化速度中的意义

For the purpose of evaluating the role of ligand exchange of sulfate ions in retarding the rate of acidification of variable charge soils,the changes in pH after the addition of different amounts of HNO3 or H2SO4 to representative soils of China were measured .A difference between pH changes caused by the two kinds of acids was observed only for variable charge soils and kaolinite,but not for constant charge soils and bentonite,The larger the proportion of H2SO4 in the HNO3-H2SO4 mixture,the lower the calculated H^ ion activities remained in the suspension.The difference in H^ ion activities between H2SO4 systems and HNO3 systems was larger for soils with a low base-saturation(BS) percentage than those with a high BS percentage.The removal of free iron oxides from the soil led to a decrease in the difference,while the coating of Fe2O3 on a bentonite resulted in a remarkable appearance of the difference.The effect of ligand exchange on the acidity status of the soil varied with the soil type.Surface soils with a high organic matter content showed a less pronounced effect of ligand exchange than subsoils did.It was estimated that when acid rain chiefly containing H2SO4 was deposited on variable charge soils the acidification rate might be slower by 20%-40% than that when the acid rain chiefly contained HNO3 for soils with a high organic matter content,and that the rate might be half of that caused by HNO3 for soils with a low organic matter content,especially for latosols.     

Air Drying Affects Extractable Sulfate in Soils of Variable Charge: Test of Two Extraction and Two Quantification Methods

Abstract

Fertilizer recommendations need to be based on reliable soil sulfate determinations. Airdrying samples changes irreversibly many properties of soils with variable charge and might affect the extractable sulfate. In this study, sulfate extracted from air‐dry and field‐moist samples was compared. Two extracting solutions [water and 00.1 M Ca(H₂PO₄) ₂] and two quantification methods (turbidimetry and ion chromatography) were assayed on A and B horizon samples of five Humic Acrisols from southeast Mexico. Air drying increased water‐extractable sulfate in Ah horizons, whereas in Bt horizons, it increased the 00.1 M Ca(H₂PO₄)₂‐extractable sulfate. Airdrying increased dissolved organic carbon contents in all samples and increased soil acidity and oxalate extractable iron in 70 and 60% of the samples, respectively. Results showed larger coefficients of variation in air‐dried samples. Turbidimetry resulted less sensible than ion chromatography. To enhance sensitivity and reproducibility, particularly organic soil samples should be analyzed field‐moist and by ion chromatography.     

Titratable Acidity and Alkalinity of Red Soil Surfaces

The surfaces of red soils have an apparent amphotenc character, carrying titratable acidity and titratable alkalinity simultaneously. The titratable acidity arises from deprotonation of hydroxyl groups of hydrous oxide-type surfaces and dissociation of weak-acid functional groups of soil organic matter, while the titratable alkalinity is derived from release of hydroxyl groups of hydrous oxide-type surfaces. The titratable acidity and titratable alkalinity mainly depended on the composition and content of iron and aluminum oxides in the soils. The results showed that the titratable acidity and titratable alkalinity were in significantly positive correlation not only with the content of amorphous aluminum oxide(Alo) and iron oxide(Feo) extracted with acid ammonium oxalate solution, free iron ox-ide(Fed) extracted with sodium dithionite-citrate-bicarbonate (DCB) and clays, but also with the zero point of charge (ZPC) of the samples. Organic matter made an important contribution to the titratable acidity.     

Particulate organic matter in water stable aggregates formed after the addition of C-labeled maize residues and wetting and drying cycles in vertisols

Development of soil structure and the dynamics of water stable aggregates (WSA) in many soils are known to be closely related to the cycling of soil organic matter. In some fine and medium textured soils particulate organic matter (POM) has been found to act as a nucleus for macroaggregate formation. However, this role of POM in aggregate formation has not been demonstrated in soils dominated by smectitic clay minerals. This study explored aggregation processes in a Vertisol from a semi-arid region in Northeastern Mexico in relation to the addition of ¹⁴C-labeled maize residues and application of wetting and drying cycles during 105 days of incubation. Fractionation of the WSA formed showed that labeled residues were preferentially accumulated in large macroaggregates (>2000 μm). Treatments with addition of organic residues had three to four times more intra-aggregate particulate organic matter (iPOM) in large macroaggregates than the control after 14 days of incubation. Residue-derived carbon accounted for 53% and 41% of the total carbon stored in the iPOM fraction in amended treatments with and without wetting and drying cycles, respectively. Conversely, residue-derived carbon represented <20% of the total carbon in the iPOM fraction from small macroaggregates (250-2000 μm) and microaggregates (53-250 μm). Results also showed that the amount and concentration of carbon per large macroaggregate did not differ between the large macroaggregates formed under wetting and drying and those formed in continuous moist conditions. However, due to formation of higher number of large macroaggregates per kg of soil, more carbon could be stored in amended soils under wetting and drying than in constantly wet soil: 1.4, 1.8 and 2.7 times more ¹⁴C kg⁻¹ soil after 14, 58 and 105 incubation days, respectively. The results in this study suggest that wetting and drying enhanced protection of the added maize residues inside large macroaggregates by forming more aggregates, rather than by increasing the amount of POM entrapped per aggregate. Therefore, after the addition of organic residues, this soil could accumulate more C than continuous moist soil through the influence that wetting and drying has on soil aggregation.     

有机肥替代化学氮肥提升红壤抗酸化能力

【目的】长期过量施用化学氮肥加剧了红壤区农田土壤酸化,严重制约着该区域农业的可持续发展。施用石灰和有机肥是防治红壤酸化的主要措施,我们研究了有机无机肥配合提高红壤抗酸化能力的作用与机理。【方法】本研究基于2009年在湖南祁阳中国农业科学院红壤站开展的有机肥替代化学氮肥长期定位试验,其中4个处理分别为单施化肥(由于酸化严重,于2018年底添加石灰改良)、有机肥替代化肥氮20%、40%和60%,供试有机肥为猪粪。采集2018和2020年的土壤样品,分析各施肥处理红壤pH、交换性酸铝、阳离子交换量、有机质、酸缓冲能力等指标的变化及相互关系。【结果】至2018年,单施化肥处理较试验之初土壤pH降低了0.48个单位,交换性酸、铝分别增加了2.74和1.06 cmol/kg;添加石灰改良后,土壤pH升高了0.58个单位,交换性酸、铝分别降低了2.62和1.45 cmol/kg。有机肥替代化肥氮40%和60%处理均可有效防治红壤酸化,其中以替代60%处理效果最佳;至2020年60%有机替代处理土壤pH较初始值提高了0.78个单位,交换性酸和交换性铝分别降低了1.10和1.25 cmol/kg。有机肥...