低分子量有机酸对可变电荷土壤铝活化动力学的影响

从动力学角度研究了几种低分子量有机酸对2种酸性土壤中铝的活化和活化铝在土壤固/液相之间分配的影响。结果表明:对于络合能力弱的醋酸和乳酸,主要通过质子作用活化铝,且活化作用明显小于盐酸。而络合能力较强的苹果酸、草酸和柠檬酸,主要通过络合作用促进铝的释放,且这种作用随有机酸根阴离子络合能力的增强而增加。在氧化铁含量较高的砖红壤中,苹果酸、草酸和柠檬酸通过专性吸附增加土壤表面负电荷,从而增加土壤交换态铝;但在氧化铁含量较低的红壤中,草酸和柠檬酸主要通过形成可溶性铝络合物降低交换态铝。活化铝在土壤固/液相间的分配主要决定于溶液中有机阴离子与土壤固相表面对铝离子的竞争。醋酸和乳酸活化的铝主要以交换态铝存在;而草酸和柠檬酸活化的铝主要以有机酸-铝络合物存在于溶液中,特别是在氧化铁低的红壤中,这将促进铝在土壤-水体中的迁移。     

低分子量有机酸对石灰性土壤有机磷组成及有效性的影响

为探索提高土壤磷素有效性的途径,采用室内培养的方法,研究不同有机酸对土壤速效磷含量及有机磷组分的影响。结果表明,添加有机酸后土壤速效磷含量发生显著变化,其中草酸处理下土壤速效磷含量显著高于其他处理,而柠檬酸和苹果酸对土壤速效磷含量具有抑制作用,其活化量为负值;随着培养时间的延长,速效磷含量缓慢降低。速效磷含量随着草酸浓度的升高而升高,随着苹果酸、柠檬酸浓度的升高而降低;有机酸处理后,土壤活性、中活性、中稳性有机磷升高,高稳性有机磷降低,这说明有机酸能促进土壤有机磷由有效性低的形态逐步向有效性高的形态转化,其中草酸的作用效果总体上较柠檬酸和苹果酸强。     

磷的吸附和表面电荷特征及其与华南地区某些土壤矿物的关系

The phosphate adsorption and surface charge characteristics of the tropical and subtropical soils derived from different parent materials in China were determined, and their relations to soil mineralogy were analysed. The results showed that all soil phosphate adsorption curves were well fitted by Freundlich equation and Langmuir equation. The maximum buffering capacity of P ranged from 66 to 9 880 mg kg^-1, with an increasing order of purple soil, skeletal soil, red soil, lateritic red soil, yellow soil and latosol; and the highest value was 149 times the lowest value, which indicated great differences among these soils in phosphate adsorption and supplying characteristics. The pH₀ (zero point of charge) values obtained by salt titration-potential titration varied from 3.03 to 5.49, and the highest value was found in the latosol derived from basalt whereas the lowest value was found in the purple soil. The correlation analysis indicated that the main minerals responsible for phosphate adsorption in the soils were gibbsite, amorphous iron oxide and kaolinite; and the pH₀ was mainly controlled by kaolinite, gibbsite and oxides.     

有机酸和磷对两种污染土壤铅的释放作用研究

用土壤培养和化学浸提法研究了不同低分子量有机酸和磷对污染土壤中铅释放的影响。结果表明,随有机酸浓度增加,铅污染红壤、棕壤中可溶出铅量均增加。当供试有机酸浓度≥1mmol·L-1时,相同浓度有机酸溶出铅量为柠檬酸〉乙酸〉草酸;当有机酸浓度≤0.5mmol·L-1时,溶出铅量为草酸〉柠檬酸〉乙酸。将2g·kg-1磷及50mmol·kg-1有机酸与铅污染红壤以不同方式混合后,柠檬酸处理的溶出铅比率（在污染土壤中加入P、有机酸后溶出铅含量与单加有机酸溶出铅含量之比）为66%（先加有机酸再加磷）、58%（有机酸与磷同时加入）、70%（先加磷再加有机酸）,草酸处理（方式同上）的溶出铅比率为90%、89%、94%,乙酸处理（方式同上）的为10%、8%、10%。铅污染棕壤上,以上处理的溶出铅比率分别为106.46%、104.43%、105.19%（柠檬酸）;43%、48%、58%（草酸）;38%、42%、55%（乙酸）。供试条件下,红壤最低溶出铅比率低于棕壤。     

低分子量有机酸对促进可变电荷土壤中铝溶解的影响

Low-molecular-weight （LMW） organic acids exist widely in soils and play an important role in soil processes such as mineral weathering, nutrient mobilization and A1 detoxification. In this research, a batch experiment was conducted to examine the effects of LMW organic acids on dissolution of aluminum in two variably charged soils, an Ultisol and an Oxisol. The results showed that the LMW organic acids enhanced the dissolution of A1 in the two investigated soils in the following order： citric 〉 oxalic 〉 malonic 〉 malic 〉 tartaric 〉 salicylic 〉 lactic 〉 maleic. This was generally in agreement with the magnitude of the stability constants for the Al-organic complexes. The effects of LMW organic acids on Al dissolution were greater in the Ultisol than in the Oxisol as compared to their controls. Also, the accelerating effects of citric and oxalic acids on dissolution of A1 increased with an increase in pH, while the effects of lactic and salicylic acids decreased. Additionally, when the organic acid concentration was less than 0.2 mmol L-I, the dissolution of A1 changed Iittle with increase in acid concentration. However, when the organic acid concentration was greater than 0.2 mmol L^-1,the dissolution of A1 increased with increase in acid concentration. In addition to the acid first dissociation constant and stability constant of Al-organic complexes, the promoting effects of LMW organic acids on dissolution of A1 were also related to their sorption-desorption equilibrium in the soils.     

几种有机酸对可变电荷和恒电荷土壤吸附镉的影响

The objectives of this study were to illustrate the reaction processes, to identify and quantify the precipitates formed, and to estimate the porosity losses in order to eliminate drawbacks during remediating monochlorobenzene （MCB） and trichloroethylene （TCE）-contaminated aquifers using the ORC-GAC-Fe^0-CaCO3 system. The system consisted of four columns （112 cm long and 10 cm in diameter） with oxygen-releasing compound （ORC）, granular activated carbon （GAC）, zero-valent iron （Fe^0）, and calcite used sequentially as the reactive media. The concentrations of MCB in the GAC column effluent and TCE in the Fe^0 column effluent were below the detection limit. However, the concentrations of MCB and TCE in the final calcite column exceeded the maximum contaminant level （MCL） under the Safe Drinking Water Act of the US Environmental Protection Agency （US EPA） that protects human health and environment. These results suggested that partitioning of MCB and TCE into the gas phase could occur, and also that transportation of volatile organic pollutants in the gas phase was important. Three main precipitates formed in the ORC-GAC-Fe^0-CaCO3 system： CaCO3 in the ORC column along with Fe（OH）2 and FeCO3 in the Fe^0 column. The total porosity losses caused by mineral precipitation corresponded to about 0.24% porosity in the ORC column, and 1% in the Fe^0 column. The most important cause of porosity losses was anaerobic corrosion of iron. The porosity losses caused by gas because of the production and entrapment of oxygen in the ORC column and hydrogen in the Fe^0 column should not be ignored. Volatilization, precipitation and porosity losses were considered to be the main drawbacks of the ORC-GAC-Fe^0-CaCO3 system in remediating the MCB and TCE-contaminated aquifers. Thus, measurements such as using a suitable oxygen-releasing compound, weakening the increase in pH using a buffer material such as soil, stimulating biodegradation rates and minimizing the plugging caused by the relatively high dissolved oxygen levels should be taken to eliminate the drawbacks and to improve the efficiency of the ORC-GAC-Fe^0-CaCO3 system.     

七种钾释放动力学方程的比较和动力学参数的应用

Batch equilibrium experiments were conducted to investigate cadmium （Cd） sorption by two permanent-charge soils, a yellow-cinnamon soil and a yellow-brown soil, and two variable-charge soils, a red soil and a latosol, with addition of selected organic acids （acetate, tartrate, and citrate）. Results showed that with an increase in acetate concentrations from 0 to 3.0 mmol L^-1, Cd sorption percentage by the yellow-cinnamon soil, the yellow-brown soil, and the latosol decreased. The sorption percentage of Cd by the yellow-clnnamon soil and generally the yellow-brown soil （permanent-charge soils） decreased with an increase in tartrate concentration, but increased at low tartrate concentrations for the red soil and the latosol. Curves of percentage of Cd sorption for citrate were similar to those for tartrate. For the variable-charge soils with tartrate and citrate, there were obvious peaks in Cd sorption percentage. These peaks, where organic acids had maximum influence, changed with soil type, and were at a higher organic acid concentration for the variable-charge soils than for the permanent charge soils. Addition of cadmium after tartrate adsorption resulted in higher sorption increase for the varlable-charge soils than permanent-charge soils. When tartrate and Cd solution were added together, sorption of Cd decreased with tartrate concentration for the yellow-brown soil, but increased at low tartrate concentrations and then decreased with tartrate concentration for the red soil and the latosol.     

低分子有机酸去除土壤中重金属条件的研究

采用化学萃取实验,以湖南郴州柿竹园和湖南衡阳水口山矿区的重金属污染农田土壤为研究对象,采用柠檬酸、草酸、酒石酸作为低分子有机酸萃取剂,在一定的条件下对污染土壤中重金属进行萃取实验,确定各个单因素的适宜条件。结果表明,对于湖南郴州和衡阳两个污染地区土壤运用化学萃取技术萃取重金属来进行土壤修复是实际可行的;柠檬酸、酒石酸、草酸对各种土壤中的重金属都表现出了良好的萃取能力,是高效的土壤重金属萃取剂;单因素的适宜萃取条件为100mmol·L^-1有机酸溶液,固液比1∶5,恒定温度35℃,pH为3,反应时间24h,且萃取率随着电解质浓度的增大而提高;土壤中重金属存在形态与萃取效果有一定的相关性,稳定态（残渣态、硫化物和有机结合态、铁-锰氧化物结合态）金属含量高,表现为较低的萃取率;反之,萃取率高;柠檬酸、草酸、酒石酸3种萃取剂均能有效地降低衡阳污染土壤中的重金属浓度,3种萃取剂的萃取效率依次为酒石酸〉草酸〉柠檬酸。     

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.     

低分子量有机酸对砖红壤动电性质的影响

研究了 5种低分子量有机酸 ,即醋酸、柠檬酸、马来酸、苹果酸和草酸 ,对昆明和徐闻两种砖红壤动电性质的影响。结果表明 ,在试验条件下 ,两种砖红壤的 ζ电位随醋酸浓度的递增逐渐正移 ,而后 ζ电位正移速率显著增大 ,再后 ζ电位渐趋稳定 ;两者的 ζ电位随柠檬酸浓度的增加向更负的方向移动 ,在试验浓度范围 (0～ 0 .1 5mmolL-1 )内 ,负移的速率没有明显差别。在pH 3.2至 6 .0之间 ,含有不同有机酸的两种砖红壤悬液的ζ电位均具有如下顺序 :醋酸 >马来酸 >苹果酸 >柠檬酸 >草酸 ;含同一有机酸的悬液在相同pH下的 ζ电位 ,昆明砖红壤总是高于徐闻砖红壤。在不同有机酸存在下 ,两种砖红壤悬液等电点的顺序与上述的 ζ电位顺序相同 ;对于相同处理来说 ,昆明砖红壤的等电点高于徐闻砖红壤者 0 .5～ 1 .0pH单位。     

红壤中低分子量有机酸的吸附动力学

低分子量有机酸在土壤中广泛存在尤其是在根际土壤中,其主要来源于动植物残体的分解、微生物的代谢、植物根系的分泌和土壤中有机物的转化等。由于羧基的强络合作用,低分子量有机酸一旦进入土壤将很快被土壤吸附,影响土壤的表面电荷性质和动电性质,进而影响其在土壤中的作用。关于低     

红壤中低分子量有机酸的吸附特征

应用平衡法研究了红壤对草酸、柠檬酸、酒石酸和苹果酸的吸附行为。结果表明:红壤对有机酸的吸附量随着有机酸平衡溶液浓度的增加而增加,有机酸种类不同,吸附量也不同。有机酸在红壤中的吸附行为均可以很好地用Langmuir、Freundlich和Temkim方程描述,其中以Langmuir方程的拟合效果最好。红壤对有机酸均具有较高的吸附率,在0.5～20mmolL-1初始浓度范围内,草酸、柠檬酸、酒石酸和苹果酸的吸附率最大分别可达89.2%、77.5%、67.4%和47.1%。红壤对柠檬酸、酒石酸和苹果酸的吸附率均随着有机酸初始浓度的增加先急剧下降(<5mmolL-1),之后缓慢下降至趋于平稳;草酸的吸附率则随着初始浓度的增加而增加,在3mmolL-1左右时达到最大,随后降低至趋于平稳。     

Desferrioxamine-B promoted dissolution of an Oxisol and the effect of low-molecular-weight organic acids

This study was conducted to quantify the adsorption of desferrioxamine-B (DFO-B), a commercial trihydroxamate siderophore, onto an Oxisol and particularly examine the DFO-B-promoted soil dissolution in the presence of two small organic acids (citric and oxalic acids). Adsorption of DFO-B to Oxisol was rapid, and the adsorption isotherms yielded maximum surface concentrations of 9.59 μmol g^?1 at pH 5.0, much lower than the soil cation exchange capacity. After reaching the maximum concentration within several minutes, the DFO-B adsorption to the soil subsequently decreased and attained a steady state, followed by a slight increase at the end of the reaction. Release of Fe, Mn, and Al from the soil was greatly enhanced in the presence of DFO-B. No competitive or synergic effect between the DFO-B and citric or oxalic acids was found on dissolution of Al- or Fe-containing minerals. However, a synergic effect between DFO-B and citric acid on dissolution of Mn-containing minerals was found, and a slight competitive effect of oxalic acid on release of Mn promoted by DFO-B was observed. These results can enhance our understanding on the role of siderophores in soils dissolution and weathering as well as the release of nutrient elements in the presence of low-molecular-weight organic acids.     

Influence of low-molecular-weight organic acids on the solubilization of phosphates

A range of low-molecular-weight organic acids were identified in rhizosphere soil, leaf litter, and poultry manure compost. Laboratory and greenhouse experiments were carried out to examine the effects of seven low-molecular-weight organic acids on phosphate adsorption by soils, and the solubilization and plant uptake of P from soil pre-incubated with monocalcium phosphate and North Carolina phosphate rock. Acetic, formic, lactic (monocarboxylic), malic, tartaric, oxalic (dicarboxylic), and citric (tricarboxylic) acids were used in the study. The addition of organic acids decreased the adsorption of P by soils in the order tricarboxylic acid>dicarboxylic acid>monocarboxylic acid. The decreases in P adsorption with organic acid addition increased with an increase in the stability constant of the organic acid for Al (logK _Al). Organic acids extracted greater amounts of P from soils meubated with both monocalcium phosphate and phosphate rock than water did. Although more phosphate was extracted by the organic acids from monocalcium phosphate — than from phosphate rock — treated soils in absolute terms, when the results were expressed as a percentage of dissolved phosphate there was little difference between the two fertilizers. The amount of P extracted by the organic acids from both fertilizers increased with an increase in logK _Al values. The addition of oxalic and citric acids increased the dry matter yield of ryegrass and the uptake of P in soils treated with both fertilizers. The agronomic effectiveness of both fertilizers increased in the presence of organic acids and the increase was greater with the phosphate rock than with the monocalcium phosphate. The results indicated that organic acids increase the availability of P in soils mainly through both decreased adsorption of P and increased solubilization of P compounds.     

几种有机酸对恒电荷和可变电荷土壤吸附Cu2+的影响

以恒电荷土壤(黄褐土和黄棕壤)和可变电荷土壤(红壤和砖红壤)为供试材料,研究了乙酸、草酸、酒石酸和柠檬酸对土壤吸附重金属铜离子(Cu2 )的影响。结果表明,在相同酒石酸浓度下,土壤对酒石酸的吸附量依次为黄棕壤(2 1 8mmolkg-1) >红壤(15 4mmolkg-1) >砖红壤(9 5mmolkg-1) ,土壤吸附有机酸后负电荷量增加,相同条件下增幅为砖红壤>红壤>黄棕壤;无有机酸配体时,供试土壤对Cu2 的吸附量为黄褐土>黄棕壤>砖红壤>红壤;加入有机酸时,随有机酸浓度增高,土壤对Cu2 的吸附一般表现为“峰”形曲线,峰所对应的有机酸浓度因有机酸类型而异,且随土壤可变电荷性质增强而增高;土壤吸附有机酸后对Cu2 的次级吸附不同于有机酸与铜共存时的竞争吸附,且因土壤性质表现迥异。这些结果意味着在存在有机酸配体的根际环境中,恒电荷土壤与可变电荷土壤对Cu2 的吸附明显不同,并将影响重金属离子在根际的转化与有效性     

红壤主要土壤组分对低分子量有机酸吸附的研究

通过一次平衡法研究了双氧水去除有机质、添加1%腐殖酸和DCB法(连二亚硫酸钠-柠檬酸钠-碳酸氢钠)去除游离氧化铁、铝对红黏土发育的红壤吸附草酸、柠檬酸、酒石酸和苹果酸的影响。结果表明,去除有机质后,由于受溶液pH、表面吸附点位变化、土壤结构变化、表面基团活性变化、草酸根生成等多种因素的影响,红壤对低分子量有机酸的吸附量虽略有增加,但增加并不明显。添加腐殖酸培养一个月后,由于受土壤表面电荷变化、吸附点位覆盖、氧化铁活性改变、基团质子化等因素的影响,红壤对低分子量有机酸的吸附量虽有轻微的减少,但减少也不明显。去除占土壤总量3.79%的游离氧化铁、铝后,土壤表面正电荷将会显著减少,而导致红壤对低分子量有机酸的吸附量显著减少,其减少程度因有机酸种类而异,与原土对有机酸的最大吸附量(Sm)大小顺序相反。     

温度和水土比对红壤吸附低分子量有机酸的影响

通过一次平衡法考察了温度和水土比对红壤吸附草酸、柠檬酸、酒石酸和苹果酸的影响。结果表明,有机酸的吸附量、最大吸附量（Sm）及吸附亲和力常数（K）均随温度的升高而增加,随着水土比的增加而降低。温度和水土比变化对有机酸吸附的影响程度因有机酸种类而异,影响程度大小与土壤对有机酸的吸附亲和力（K）大小顺序相反。45℃ 时,土壤对草酸、柠檬酸、酒石酸和苹果酸的吸附量分别是 25℃ 时的 1.19、1.22、1.24 和 1.28 倍;100:1 水土比条件下,草酸、柠檬酸、酒石酸和苹果酸的吸附量分别较 10:1 水土比条件下减少了 48.3%、54.9%、63.5% 和 76.1%。     

Effect of Oxalic and Citric Acids on Zinc Release Kinetic in Two Calcareous Soils

Rate of zinc (Zn) release from solid to solution phase by organic acids can influence Zn availability in calcareous soils. The objective of the present study was to investigate the effect of different concentrations (1.1, 2.2, and 3.3 mM) of oxalic acid and citric acid on the kinetic release of Zn from two calcareous soils from Eastern Iran. The two organic acids showed significant difference in Zn release from studied soils. Cumulative Zn release during 72 h ranged from 5.85 to 10.4 mg kg^?1 in soil 1 and ranged from 8.7 to 16.9 mg kg^?1 in soil 2 using different concentrations of oxalic acid. The amount of cumulative Zn release after 72 h in soil 1 ranged from 13.65 to 28.77 mg kg^?1 and from 17.63 to 23.13 mg kg^?1 when different concentrations of citric acid was used. In general, Citric acid released 38% more Zn from soils than oxalic acid. The release of Zn from soils increased with citric acid concentration but decreased with increasing of oxalic acid concentrations in the solution. The simplified Elovich equation best described Zn release as a function of time (r² = 0.93 and SE = 0.78). From the present study, Zn release from soils can be limited by the higher concentration of oxalic acid, while citric acid is suitable for enhancing soil lability of Zn.     

Influence of vegetation on low-molecular-weight carboxylic acids in soil solution—a review

Low-molecular-weight (LMW) carboxylic acids found in soils and soil solutions comprise mainly aliphatic mono-, di- and tricarboxylic acids and substituted benzoic and cinnamic acids. This review compiles current information on the content of LMW carboxylic acids in soil solutions collected by centrifugation and in lysimeters, and soil extracts in relation to type of vegetation, soil type and soil depth. Contents of LMW carboxylic acids are highest in soil solution from the upper soil layers where carbon in LMW carboxylic acids constitutes up to 10% of DOC. The concentrations of aliphatic LMW di-/tricarboxylic acids (oxalic, malonic, malic, succinic, tartaric and citric acid) are usually in the range 0–50 μM with the higher concentrations in soil solutions from meadow, permanent pasture and forest soils as compared to ley and cultivated soils. In contrast, the concentrations of aliphatic LMW monocarboxylic acids (formic, acetic, propionic, butyric, valeric and lactic acid) are commonly in the range 0–1 mM with high concentrations found in soil solutions from both cultivated and forested soils. Especially insence cedar (Calocedrus decurrens (Torr.) Florin), ponderosa pine (Pinus ponderosa Dougl.), Douglas fir (Pseudotsuga menziesii Franco) and Norway spruce (Picea abies (L.) Karst.) seem to cause higher contents of LMW carboxylic acids in soils and soil solutions as compared to other tree species. Soil solution concentrations of substituted benzoic and cinnamic acids are submicromolar for all vegetations, whereas similar amounts in the range 0–800 μmol kg⁻¹ of aliphatic LMW carboxylic acids and substituted benzoic and cinnamic acids are extractable from mineral soils with alkaline and dilute acid extractants. Seasonal variations are observed in soil solutions isolated by centrifugation and soil extracts with highest concentrations in 2–4 months in a period from mid spring to early summer, minimum concentrations around early autumn, and increasing concentrations during autumn.     

低分子有机酸/盐对森林暗棕壤铁的释放效应

模拟森林凋落物淋洗液中草酸/草酸盐和柠檬酸/柠檬酸盐的浓度范围,设计了不同浓度草酸/草酸盐和柠檬酸/柠檬酸盐溶液一次性浸提和多次连续浸提等系列实验,结果表明,草酸/草酸盐和柠檬酸/柠檬酸盐对暗棕壤铁具有活化作用,活化作用大小因有机酸/盐种类、浓度和土壤性质而异。随着低分子有机酸/盐浓度的增加,A1层和B层暗棕壤活化释放的铁也逐渐增多。pH 5.16的低分子有机盐溶液对A1层和B层暗棕壤铁的活化作用强于同浓度的相应低分子有机酸,即柠檬酸盐>柠檬酸,草酸盐>草酸,因此推断草酸盐和柠檬酸盐溶液促进暗棕壤铁活化释放的机理主要在于低分子有机酸阴离子的配位反应。柠檬酸/柠檬酸盐对A1层和B层暗棕壤铁的活化作用强于同浓度的草酸/草酸盐,即柠檬酸>草酸,柠檬酸盐>草酸盐,这主要与柠檬酸对铁较强的络合能力及较大的离解常数有关。A1层与B层相比,草酸/草酸盐和柠檬酸/柠檬酸盐均对B层暗棕壤释放的铁量较高。另外,低分子有机酸对暗棕壤铁的释放并不是一次就能完成的,第一次以后的连续4次浸提仍源源不断释放出数量可观的铁。