Optimum conditions for extraction of Al,Fe, and Si from soils with acid oxalate

Abstract

Acid oxalate reagent was used at various concentrations, pH values, shaking times, and soil to solution ratios to find the optimum conditions for the extraction of Al, Fe, and Si from short‐range‐order materials in soils and stream‐bed deposits. The optimum conditions vary with the nature of the soil sample and its components. For most soils maximum amounts of Al, Fe, and Si were extracted with 0.15M acid oxalate reagent at pH 3.0 with a soil to solution ratio of 1:100 and shaking for 4 h in the dark at 20°C. Soils with more than 5% oxalate‐extractable Al or Fe require a 0.20M oxalate solution at pH 3.0 with a soil to solution ratio of 1:200.

Allophane is extracted by acid oxalate reagent after shaking for 2 h and it may be estimated from the 4 h oxalate‐extractable Si values. Ferrihydrite is extracted after shaking for 4 h, and it may be estimated from the oxalate‐extractable Fe values. Either sodium oxalate or ammonium oxalate may be used     

Special features of humus acids extraction from soils by sodium pyrophosphate solutions of different alkalinity

The regularities of extracting humus acids from soils of different types with solutions of sodium pyrophosphate at the equilibrium pH values of 5–13 were studied. The increase in the humus acids yield from the soils with the increasing alkalinity of the solution applied is directly related to the capability of acid functional groups (carboxyl and phenol hydroxyl) for dissociation at definite pH values. The regularities of the changes in the chemical nature and degree of humification of humus acids extracted from the soils related to the pH of the solution were revealed. A sodium pyrophosphate solution (pH 10) was suggested for extracting the humus acids most active in the given soil.     

Effect of liming on organically complexed aluminum of nonallophanic Andosols from northeastern Japan

Aluminum–humus complexes are believed to be highly stable under natural conditions in nonallophanic Andosols. However, it has been shown that the aluminum complexed with humus is easily released by acidic buffer solutions and possibly controls the aluminum solubility of these soils. Thus, it is highly probable that Al–humus complexes are easily influenced by rather simple chemical treatments. We examined the effects of liming (CaCO₃ treatment) on Al–humus complexes of A and B horizons from Andosols. It was observed that liming reduced the Al release rates from soil samples with pH 3.5 acetate buffer solution and the amounts of the KCl-extractable Al, suggesting the formation of precipitation from easily exchangeable Al. A much larger decrease with liming was also obtained for 0.1 M sodium pyrophosphate-extractable Al (decrease rates of 7–52%) and 0.5 M CuCl₂-extractable Al (decrease rates of 9–43%). These results strongly indicate that liming reduces significant amounts of organically complexed Al as well as the exchangeable Al. The increase in the cation exchange capacity of soils at pH 7 after liming further suggested that the carboxyl group of humus complexed with Al was partly liberated from the Al complexation and became to develop negative charges.     

石灰性土壤有效硒浸提剂和浸提条件研究

采用外源硒加入土壤中得到硒污染土壤,6种有效硒的浸提剂NaHCO3、KH2PO4、K2SO4、EDTA、AB-DTPA和DTPA＋TEA＋CaCl2的最佳浸提时间和土液比进行了筛选,并通过盆栽试验对所选择的土壤有效硒浸提剂进行生物学校验,以找出石灰性土壤有效硒提取适宜的浸提剂及其浸提条件。结果表明,NaHCO3、KH2PO4、K2SO4、EDTA、AB-DTPA和DTPA＋TEA＋CaCl26种浸提剂有效硒浸提量都随着浸提土液比的减小而增大,且随浸提时间的增长而增大。其中NaHCO3和KH2PO4最佳土液比为1/15,振荡时间90min;K2SO4和AB-DTPA的最佳土液比为1/15,振荡时间60min;EDTA和DTPA＋TEA＋CaCl2的最佳土液比则为1/20,振荡时间30min。6种浸提剂在各自最佳的提取条件下提取的土壤有效硒量与白菜地上部分硒含量达极显著正相关,但土壤有效硒的提取量以DTPA＋TEA＋CaCl2及K2SO4最少,只占KH2PO4、AB-DTPA及EDTA提取量的14%～48%,故不适用于作为石灰性土壤有效硒的提取剂。NaHCO3适用于土壤硒含量高于5mg·kg^-1的石灰性土壤有效硒提取。KH2PO4、AB-DTPA及EDTA3种浸提剂既可提取土壤中水溶态硒,亦可提取部分的吸附态硒,提取硒数量较多,过程简单,重复性好,都可作为石灰性土壤有效硒提取的浸提剂。     

EFFECTS OF solUTION: SOIL RATIO AND VIGOUR OF SHAKING ON THE RATE OF PHOSPHATE ADSORPTION BY SOIL

The effects were measured of varying the solution: soil ratio, and the vigour of shaking on the rate of adsorption of phosphate. One soil appeared to break down with vigorous shaking, prior to adding phosphate, especially at low solution: soil ratio. As a result, subsequent phosphate adsorption was faster. With gentle shaking, there was no effect of solution: soil ratio with the soil. Another soil was more stable and there were only small differences due to vigour of shaking and no effect of solution: soil ratio with any method of shaking. The change in phosphate concentration was not proportional to the reciprocal of time as reported by Ryden and Syers (1975) and Hope and Syers (1976). Hence the validity of extrapolating from short sections of reciprocal-time graphs in order to estimate equilibrium is questioned.     

SELECTIVE EXTRACTION OF AMORPHOUS IRON OXIDES BY EDTA FROM A DANISH SANDY LOAM

EDTA extracts (pH 7.5–10.5) from a Danish sandy loam showed no significant (95% level) increase in amounts of aluminium, calcium, iron, and magnesium between three and nine months' shaking. The amounts were independent of the soil: solution ratio (1:10–1:50), the EDTA concentration (0.01 M–0.2 M), and crushing the soil (< 0.25 mm or < 2 mm). IR spectroscopy and X-ray diffraction showed no change in the mineral composition of the soil during the extraction. The extracted iron was equal to that extracted after 2 h by ammonium oxalate at pH 3.0. EDTA extraction at pH > 7.5 seems to extract selectively iron oxides with solubility products > ～ 10^?41.     

Sodium bicarbonate as an extractant for soil phosphate,II. Effect of varying the conditions of extraction on the amount of phosphate initially displaced and on the secondary adsorption

The effects of varying the period of shaking, the concentration of bicarbonate, the pH, and the dryness of the soil on the phosphate extracted by sodium bicarbonate were investigated. A regression procedure in which the soil: solution ratio was the independent variable was used to separate the effects on the amount of phosphate initially displaced from those on the secondary adsorption.Both the amount initially displaced and the amount of secondary adsorption increased with period of extraction. At small soil:solution ratios the effect on displacement was dominant and the net effect was a continuing increase in the amount of phosphate in the extract. At large soil:solution ratios, secondary adsorption eventually predominated and caused a decrease in the amount of phosphate in the extract.Increasing the bicarbonate concentration from 0.01 M to 1.0 M decreased secondary adsorption but had no significant effect on the initial displacement. The effects of changing the concentration were most marked at low concentrations.Increasing the pH of 0.5 M bicarbonate solutions increased the amount of phosphate initially displaced but had no significant effect on secondary adsorption. In the absence of bicarbonate, the effects of pH differed: increasing the pH decreased secondary adsorption. Secondary adsorption was important when the ratio of soil to solution was large and in these cases the net effect of pH on bicarbonate - as measured by difference - was greatest near the pK₂ of carbonic acid.Drying the soil increased the amount of phosphate displaced from the soil after 30 min extraction but the effect was eliminated by extending the period of extraction to 16 h.     

酸性土壤水溶性氟浸提方法的研究

本文比较研究了振荡、超声、沸水浴和烘箱4种浸提酸性土壤水溶性氟的方法,然后采用离子色谱法对浸提液进行测定,并通过对测定数据进行统计与方差分析来确定最佳浸提方式。结果显示,水土比5:1,浸提时间20 min、温度60℃是振荡法与超声法浸提酸性土壤水溶性氟含量的最佳条件。在此条件下,振荡法与超声法浸提的土壤水溶性氟含量无显著差异,标准偏差均小于0.3%。超声法浸提的酸性土壤水溶性氟含量显著高于各自最佳处理条件下的沸水浴法与烘箱法浸提的水溶性氟含量。在离子色谱测定水溶性氟过程中,质量控制样品均在1倍标准偏差范围内。因此,采用离子色谱法测定超声法或振荡法浸提的酸性土壤水溶性氟是一种可行的、准确的试验方法,特别对于批量土壤样品的测定具有重要意义。     

Composition and Characteristics of Organo—Mineral Complexes of Red Soils in South China

The objective of the present study is to reveal the composition and characteristics of organo-mineral complexes in red soils (red soil,lateritic red soil and latosol) of south China in terms of chemical dissolution and fractional peptization methos.In the combined humus,most of the extractable humus could dissolve in 0.1 M NaOH extractant and belonged to active humus (H1),and there was only a small amount of humus which could be further dissolved in 0.1 M Na4P2O7 extractant at pH 13 and was stably combined humus (H2).The H1/H2 ratio ranged from 3.3 to 33.8 in red soils,and the proportions of both H1 and total extractable organic carbon (H1 H2) in total soil organic carbon and the ratios of H1 to H2 and H1 to (H1 H2) were all higher in lateritic red soil and latosol than in red soil.The differences of combined humus composition in various red soils were directly related to the content of Fe and Al oxides.In organo-mineral complexes,the ratio of Na-dispersed fraction (G1) to Na-ground-dispersed fraction (G2) was generally smaller than 1 for red soils,but there was a higher G1/G2 ratio in red soil than in lateritic red soil and latosol.G1 fraction had a higher content of fulvic acid (FA),but G2 fraction had a higher content of humic acid (HA).The ratios of H1 to H2 and HA to FA were higher in G2 than in G1.The differences in the composition and activity of humus between G1 and G2 fractions were related to the content of free Fe and Al oxides.The quantities of complex Fe and Al,the Fe/C and Al/C atomic ratios were higher in G2 than in G1,and the ratio of Al/C was much higher than that of Fe/C.It may be deduced that aluminum plays a more important role than iron in the formation process of organo-mineral complexes in red soils.     

Assessment of phosphate solubility in forest and highly fertilized Andisols and Andic soils

Abstract

Phosphate solubility in Andisols and Andic soils (forest and fertilized) has been studied in soil solutions at two soil:solution ratios (1:2.5 and 1:25). Forest soils approached the variscite solubility (pIAP=30.4±0.3) while fertilized soils were closer to the amosphous analog of variscite (pIAP= 29.8±0.2). In some samples, phosphorus (P) activities were consistent with simultaneous equilibrium between aluminum (Al) and iron (Fe) phosphates. The dilution ratio, DR=10(P)_1:25/(P)_l:25, was 10.0±0.4 for all samples. This suggests a dissolution of phosphate minerals attaining apparent saturation in 24 h. However, the high content of dissolved organic carbon and Al in aqueous extracts also pointed to the existence of soluble ternary complexes of P with Al(Fe)‐humus complexes. These results could be consistent with simultaneous control between the dissolution of variscite‐like minerals and humus‐Al(Fe)‐P associations. Nevertheless, DR seems a valuable criterion to assess soil P status, especially in fertilized soils with high active Al and Fe contents.     

施肥结构对冷浸田土壤肥力及水稻生长的影响

冷浸田因长期受冷泉水浸渍,土体封闭,难以通气与氧化,土壤溶液Eh下降,有效养分低,水稻产量低。本研究通过田间小区试验和动态取样与室内测定,探求了单质化肥、稳定性肥、复合肥配施生鸡粪和熟鸡粪等施肥方式对冷浸田土壤肥力及水稻生长的影响。结果表明:与单质化肥处理比较,复合肥与熟鸡粪配施处理土壤松结态腐殖质占重组腐殖质的比例提高10.8%,紧结态腐殖质占重组腐殖质的比例降低15.5%,土壤有机质和活性有机质含量分别提高8.9%和4.0%,土壤阳离子交换量提高10.2%,早稻土壤细菌数和微生物活性分别提高390.0%和13.0%;同时土壤磷酸铝盐和磷酸钙盐含量分别提高40.0%和28.0%,且磷酸铝盐和磷酸钙盐占无机磷总量的比例提高,闭蓄态磷占无机磷总量的比例降低,促使土壤中难溶性磷向易溶性磷转化,提高土壤有效磷含量;最终早稻磷、钾吸收量分别提高14.0%和127.0%,早、晚稻产量分别增加11.0%和8.0%。由此得出,有机无机平衡施肥是适合于冷浸田土壤培肥、水稻增产的施肥方式。     

Liquid extraction of low molecular mass organic acids and hydroxamate siderophores from boreal forest soil

Low molecular mass organic acids (LMMOAs) and hydroxamate siderophores (HS) are molecules secreted by microbes and have previously been found in soil solution and in cultures. Mycorrhizal fungi are suggested to be involved in the nutrient uptake processes of trees and weathering of minerals. In this study soil samples taken from the O and E horizons of a podzol were extracted with 10 mM potassium phosphate buffer at pH 7.2. Variable parameters included addition of methanol to the extraction buffer and the use of ultrasonication or rotary shaking during extraction. LMMOAs and HS content of the soil extracts were determined. Analysis of soil extracts were carried out by liquid chromatography mass spectrometry (LC–MS) and the extraction results compared to results for soil solution samples obtained by centrifugation of the soils sampled. The extraction yields were significantly increased by addition of methanol to the extraction buffer, especially for the O horizon samples. Rotary shaking of the samples for 90 min gave slightly higher yields than ultrasonication for 15 min but the reduction in extraction time makes ultrasonication an attractive option. Of the HSs determined, ferricrocin was found in all samples. Optimal extraction conditions showed citric acid and isocitric acid to be the most abundant organic acids in the O and E horizons, respectively.     

单宁酸对不同pH茶园土壤中活性铝形态分布的影响

采集云南省普洱市和江西省南昌县两地典型的茶园土壤,通过添加HCl和Ca(OH)2调节土壤pH,研究不同pH(3.0、3.5、4.0、4.5)茶园土壤添加0.4 mmol·kg 1、2.0 mmol·kg 1、4.0 mmol·kg 1、8.0 mmol·kg 1、12.0 mmol·kg 1单宁酸后,活性铝形态交换态铝(Al3+)、单聚体羟基铝[Al(OH)2+、Al(OH)+2]、酸溶无机铝[Al(OH)03]和腐殖酸铝[Al-HA]的分布特征。结果表明:单宁酸添加量为0~0.4 mmol·kg 1和0~2.0 mmol·kg 1时,江西南昌和云南普洱茶园土壤中交换态铝随土壤pH的增加呈明显下降趋势,而羟基态铝、酸溶无机铝和腐殖酸铝呈逐渐上升趋势;当单宁酸浓度增至2.0 mmol·kg 1以上时,随土壤pH的增加,单宁酸对活性铝释放的抑制作用增强,各形态活性铝含量都较低,且不同pH处理土壤间的差异不显著。0~20 cm土层土壤与20~40 cm土层土壤变化规律大致相似,总体上看,下层土壤活性铝总量高于上层。云南普洱茶园土壤活性铝总量明显高于江西南昌的茶园土壤。相关分析表明,0~20 cm土层土壤中,pH与羟基态铝、腐殖酸铝、土壤酸碱缓冲容量(pHBC)呈正相关(r=0.796,P0.01;r=0.960,P0.01;r=0.852,P0.01);pHBC与交换态铝、羟基态铝呈负相关(r=0.904,P0.01;r=0.645,P0.05),而与腐殖酸铝呈正相关(r=0.795,P0.01)。同时,单宁酸加入浓度为0~0.4 mmol·kg 1时,土壤pH明显上升,之后随着单宁酸加入浓度的增加土壤pH持续下降,土壤pH(YpH)与单宁浓度(CDN)在此阶段基本符合方程:YpH=0.04CDN+3.82(R2=0.95,P0.01)的线性变化趋势,在单宁酸浓度达到8.0~12.0 mmol·kg 1时,土壤pH基本不再变化。     

Liquid extraction of low molecular mass organic acids and hydroxamate siderophores from boreal forest soil

Low molecular mass organic acids (LMMOAs) and hydroxamate siderophores (HS) are molecules secreted by microbes and have previously been found in soil solution and in cultures. Mycorrhizal fungi are suggested to be involved in the nutrient uptake processes of trees and weathering of minerals. In this study soil samples taken from the O and E horizons of a podzol were extracted with 10 mM potassium phosphate buffer at pH 7.2. Variable parameters included addition of methanol to the extraction buffer and the use of ultrasonication or rotary shaking during extraction. LMMOAs and HS content of the soil extracts were determined. Analysis of soil extracts were carried out by liquid chromatography mass spectrometry (LC–MS) and the extraction results compared to results for soil solution samples obtained by centrifugation of the soils sampled. The extraction yields were significantly increased by addition of methanol to the extraction buffer, especially for the O horizon samples. Rotary shaking of the samples for 90 min gave slightly higher yields than ultrasonication for 15 min but the reduction in extraction time makes ultrasonication an attractive option. Of the HSs determined, ferricrocin was found in all samples. Optimal extraction conditions showed citric acid and isocitric acid to be the most abundant organic acids in the O and E horizons, respectively.     

Phosphate fixation by ando soils different in their clay mineral composition

The phosphate fixation capacity at pH 4.5 and an equilibrium concentration of 250 mM phosphate was measured. The soil samples were divided into five groups according to their clay mineralogical composition. The first group soils contain opaline silica and allophanelike constituents, and some unidentified minerals, the second opaline silica and crystalline layer .i1icates, the third opaline silica and crystalline layer silicates with additional allophanelike constituents or aluminarich gel-like materials, the fourth allophanelike constituents, allophane and imogolite and the fifth crystalline layer silicates, allophanelike constituents and alumina-rich gel-like materials, plus some halloysite-like minerals, respectively. The first group soils had phosphate fixation capacities of 3,000 to 8,000, the second group soils 1,000 to 3,000, the third group loib 2,000 to 13,000, the fourth group soils 8,000 to 15,000 and the fifth group soil. 5,000 to 12,000 mg P₂O₅/100 g oven-dry soil, respectively. The fourth group soils in which allophane and imogolite predominated showed the highest phosphate fixation capacity.

The fractions which dissolved from almost all soil samples by treatments with 6% H₂O₂ Na₂S₂O₄-NaHCO₂-Na citrate and 2% Na₂CO₃ were estimated to have very high phosphate fixation capacities (8,000 to 19,000 mg P₂O₅/100 g dry-matter), and there was not much difference among the soil samples examined. Iron and aluminum combined with humus, allophanelike constituents, alumina-rich gel-like materials and halloysite-like minerals in addition to allophane and imogolite contribute to the phosphate fixation of Ando soils.     

Extractability of manganese and iron oxides in typical Japanese soils by 0.5 mol L−1 hydroxylamine hydrochloride (pH 1.5)

We investigated the extractability of manganese (Mn) and iron (Fe) oxides from typical Japanese soils (Entisols, Inceptisols, and Andisols) by 0.5?mol?L^?1 hydroxylamine hydrochloride (NH₂OH-HCl) extraction (pH 1.5; 16?h shaking at 25°C; soil:solution ratio 1:40), referred as to HH_mBCR, which is Step 2 (used for the reducible fraction) of the modified BCR (Community Bureau of Reference) sequential extraction procedure. The HH_mBCR procedure extracted almost all Mn oxides from the non-Andisol samples, but failed to extract a part of the Mn oxides from some Andisol samples. The procedure extracted most short-range ordered Fe oxides from non-Andisol samples, but it extracted only 7.5% and 13% of the short-range ordered Fe oxides from allophanic and non-allophanic Andisol samples, respectively. This remarkably low extractability of Fe oxides suggests that the HH_mBCR method is not suitable for extracting oxide-occluded heavy metals from Andisols. Since the extraction rate of short-range ordered Fe oxides from various soils with the extractant was negatively correlated with the amounts of oxalate- and pyrophosphate-extractable Al even when the variability of the extraction pH was reduced by increasing the soil:solution ratio from 1:40 to 1:500, the extractability of Fe oxides would be negatively affected by the presence of active Al, including allophane/imogolite, amorphous Al, and Al-humus complexes. Because these Al constituents are abundant in Andisols, they would be at least partially responsible for the lower extractability of Fe oxides by HH_mBCR from Andisols.     

The reduction mechanism of manganese in paddy soils

Hydroquinone method manganese (soluble in pH 7.0, 1 N-ammonium acetate solution containing 0.2 percent hydroquinone) and microbially active manganese (soluble in pH 7.0, 1 M-magnesium sulfate solution after flooding soils with or without Chinese milk vetch for 12 or 20 days respectively at 30°C) of 22 paddy soils were determined. The amounts of manganese reduced with sodium oxalate under acid conditions (oxalate method manganese (a) and (b), the former was determined under more rigorous conditions than the latter) were also determined and compared with hydroquinone method manganese and microbially active manganese.

Their levels of many soil samples representing soil groups were also determined to examine the dlfferences In amounts of active manganese among soil groups. The results obtained are as follows.

The relationship between microbially and chemically active manganese. 1) The amounts of microbially active manganese in soils were 48 to 68 mg Mn per 100 g oven-dried soil and these were increased by the addition of Chinese milk vetch. 2) The amounts of hydroquinone method manganese were less than microbially active manganese, and the amounts of oxalate method manganese (b) were larger than microbially active manganese. The amounts of oxalate method manganese (a) were the largest of all the types of manganese. 3) There were high correlations between the amounts of various types of active manganese described in 2). The levels of microbially and chemically active manganese. 1) The amounts of microbially active manganese lay between the amounts of chemically active manganese determined by the hydroqulnone method and by the oxalate method (b) In all soil samples representing soil groups. High correlations were found between these types of active manganese. 2) The hydroquinone method was considered to be unsuitable for quantitatively determining the amounts of chemicallY active manganese in soils of high organic matter content. 3) In both cases of microbially active manganese and chemically active manganese, tha widest range and the largest amount determined were both observed in strongly gley soila. The averages of theae types of active manganese were high in strongly gley soils, pea, and muck soils, and black soils. The differences among soil groups were smalle1 than the differences among soil samples, and little tendency was observed in the differences among soil groups.

From these findings described above it is suggested that the oxalate methoo (b) is more appropriate than the hydroqulnone method for determining chemically active manganese as an index of microbially active manganese.     

Organo-metallic complexes in an Andosol: a comparative study with a Cambisol and Podzol

Current soil-forming processes were studied in a nonallophanic Andosol from the Vosges mountains (north-eastern France). For this purpose, we conducted comparative studies on the organo-metallic fraction dynamics of selected profiles of an Andosol and other typical soils from this region, Cambisol and Podzol. These soils are derived from old volcanic rocks under mesic soil temperature and udic soil moisture regimes. The Andosol profile displayed the characteristics of nonallophanic Andosols: large accumulation of humus, active Al mostly complexed with humus, and low pH. Special attention was given to physical and microbial stability of these organo-metallic associations, respectively by disaggregation tests and incubation experiments. The results indicated that these associations showed a strong resistance against disaggregation by water and against biodegradation. Moreover, the very low concentration of DOC, Al and Fe in soil solutions collected by zero-tension lysimeters, coupled with very low amounts of water-dispersed clays obtained after dispersion tests, suggested that no significant translocations of these components occurred in this Andosol profile. Low mobility together with a strong resistance against mineralization may account for the large accumulation of carbon in this Andosol.     

Die Bedeutung von hohen Aluminiumgehalten für die Humusanreicherung in sauren Waldböden

The role of aluminium on humus accumulation in acid forest soils The impact of soil-borne aluminum on humus accumulation was investigated in a forest soil of the chestnut zone (Castanea sativa) in southern Switzerland (Ticino). Soil samples of two soils formed on bedrocks which differ mainly in their aluminum content were extracted with HNO₃, NH₄Ac.-EDTA, NH₄Cl, KCl, and NH₄F-HCl and analyzed for the most abundant elements. On gneiss which contains up to about 10% of total aluminum the common soil type in this area is a Cryptopodzol. This soil is similar to the nonallophanic Udands. It is rich in wellhumified organic matter and shows dark-colored A_h-, A(E)- and B_h-horizons. The soil samples of these horizons are extremely rich in nonexchangeable aluminum which is, however, extractable with NH₄Ac.-EDTA. It is assumed that this Al is intimately bound to the organic matter. The soil samples of these horizons contain large amounts of HNO₃-extractable phosphorus. Up to 90% of this P appears in the organic fraction. The content of NH₄F-HCl-extractable P is only 0.7 to 3.4 mg/kg. It is concluded that due to excessive Al in the organic matter the humus mineralization is inhibited compared to the Haplumbrepts of the region.     

Difference in the pH values of hydromorphic soils in field and laboratory analyses

There are marked differences in the pH values determined in water suspension under laboratory conditions and in soil solution under field conditions in hydromorphic soils (gleysols and stagnosols). The value δpH = pH_susp–pH_sol can be either positive or negative. Among the main factors that affect the value of δpH are the laboratory preparation of soil samples and the suspension effect. The sign of the pH effect (value of δpH) depends on the participation of humus, carbonate, and exchange bases in the formation of aggregates destructed in the laboratory. The value of δpH is negative in noncalcareous soils with low content of exchangeable bases and fulvate composition of humus and positive in calcareous soils or soils enriched with exchangeable bases and humate composition of humus. In cases of a significant δpH effect, the value of pH_susp cannot be regarded as an adequate measure of soil acidity.