Prolonged simulated acid rain treatment in the subarctic: Effect on the soil respiration rate and microbial biomass

Humus chemistry and respiration rate, ATP, ergosterol, and muramic acid concentration as measures of chemical properties, microbial activity, biomass, and indicators of fungal and bacterial biomass were studied in a long-term acid rain experiment in the far north of Finnish Lapland. The treatments used in this study were dry control, irrigated control (spring water, pH 6), and two levels of simulated acid rain (pH 4 and pH 3). Originally (1985–1988), simulated acid rain was prepared by adding both H₂SO₄ and HNO₃ (1.9:1 by weight). In 1989 the treatments were modified as follows. In subarea 1 the treatments continued unchanged (H₂SO₄+HNO₃ in rain to pH 4 and pH 3), but in subarea 2 only H₂SO₄ was applied. The plots were sampled in 1992. The acid application affected humus chemistry by lowering the pH, cation exchange capacity, and base saturation (due to a decrease in Ca and Mg) in the treatment with H₂SO₄+HNO₃ to pH 4 (total proton load over 8 years 2.92 kmol ha^-1), whereas the microbial variables were not affected at this proton load, and only the respiration rate decreased by 20% in the strongest simulated acid rain treatment (total proton load 14.9 kmol ha^-1). The different ratios of H₂SO₄+HNO₃ in subareas 1 and 2 did not affect the results.     

湿地松林土壤生化特性和酶活性对模拟硫沉降的响应

以亚热带湿地松人工林为研究对象,通过3种水平(对照CK:pH 6.5;低硫LS:pH 4.5;高硫HS:pH 2.5)的模拟硫沉降控制试验,分析土壤生化特性及酶活性对硫添加的响应。结果表明:(1)硫输入促进了土壤酸化,0—5 cm土层土壤pH在HS处理下显著降低,5—10 cm土层土壤pH在LS和HS处理下显著降低(P0.05);(2)硫输入对土壤有机碳库存在一定影响,土壤总有机碳(TOC)对硫输入无显著响应,但土层间的差异性显著增加(P0.05),土壤可溶性有机碳(DOC)受影响有限,5—10 cm土层微生物量碳(MBC)LS显著降低(P0.05);(3)硫输入对土壤有效氮库影响存在差异,土壤可溶性有机氮(DON)、铵态氮(NH_4~+—N)尚未表现出显著变化,土壤硝态氮(NO_3~-—N)、土壤微生物量氮(MBN)均在HS处理下显著降低,且硫输入加剧土层间的差异性(P0.05);(4)硫输入抑制了酶活性,土壤脲酶活性在HS处理下显著降低(P0.05),土壤蔗糖酶活性无显著变化,但硫输入均弱化了土层间酶活性的差异性。综合分析所有处理下的土壤生化性质和酶活性等指标发现,对硫添加响应敏感的是土壤pH和酶,土层是另外一个主要影响因子,硫添加和土层的交互作用则影响有限。采用Pearson分析得出,硫输入改变了土壤生化特性、酶活性等指标间的相关性程度。可见,酸雨对土壤酸化的影响是一个逐渐累积的过程,外源性硫添加对土壤碳氮及酶活性的影响存在一定差异,这可为硫沉降环境胁迫下森林管理提供科学依据。     

Soil chemical and microbial effects of simulated acid rain on clover and soft chess

Effects of simulated acid rain, comprised of HNO₃ and H₂SO₄ in the mole ratio of 3:1, at pH 5.6, 4.5, 4.0 and 3.0, were tested on the grass, soft chess (Bromus mollis L.) and on clover (Trifolium subterraneum L. var. Woogenellup) in a sandy soil of granodiorite parent material. Soft chess was grown in unfertilized soil, whereas clover was grown in both unfertilized soil and soil fertilized with NH₄NO₃ and CaSO₄·2H₂O at the rates of 224 kg ha^?1 N and 78 kg ha^?1 S. Two acid-spray irrigation periods of 31 and 26 weeks duration, each delivering 400 mm and separated by a dry period of 23 weeks, simulated typical rainfall of northern California rangeland. Plants were harvested after each of the two spray periods. There were very few deleterious effects of acid rain on plant growth or soil and microbial processes. No significant (p<0.05) effects were shown by soil microbial biomass, CO₂ production, nodules per unit weight of clover root, acetylene reduction, denitrification and nitrification potentials, or for soft chess plant weights, and N and P uptake. Mineralizable-N was unaffected also, except in one case. However, pH of soil to 10 mm depths was significantly lower in the pH 3.0 treatment after the first spray period, with a corresponding decrease in exchangeable soil Ca; these effects became significant at greater soil depth only after the second spray period. There were significant effects of acid treatments shown by clover, some of which may be advantageous. Treatments of intermediate acidity generally provided added N and S, which acted as fertilizers, and compensated for possible decreases in plant productivity attributable to acidity per se. There was also evidence of decreased P uptake in unfertilized soil at pH 3. In conclusion, effects of simulated acid rain were minimal, and in some cases were advantageous because of the added N and S having a fertilizer effect on plant nutrition and growth.     

Adaptive responses of soil microbial communities under experimental acid stress in controlled laboratory studies

Soil samples from nine different beech forest sites (A_h horizon) with a mean initial soil pH close to neutral (6.4, SD 0.6) were treated with different amounts of H⁺-ions using acid water of pH 0.5 (H₂SO₄). The H⁺-input needed to lower the pH by one or more than three units was in the range between 0.006 and 0.6 mg H⁺ kg⁻¹, designated as mild, strong or extreme acid stress. The soil samples were incubated for a maximum of 200 days at 20°C and their microbial biomass-C (C_mic), qCO₂ and pH was measured at intervals. In addition, the ratio of fungal:bacterial contributions to total respiration was determined at the beginning and end of the experimental period. The extent of microbial biomass-C loss (32–87%) and the increase in the qCO₂ (1.8–>7 times) in comparison to acid-untreated samples followed the amount of initial H⁺-ion input. Differences between treatments based on one-way ANOVA were significant for C_mic depression at day 8 (p<0.01) and day 80 (p<0.05), and for qCO₂ at the beginning (p<0.001) and at day 80 only between mild and extreme acid stress (p<0.027). Over time some recovery of the microbial biomass was observed with a concomitant decrease in the qCO₂, an indication of adaptation to acidic conditions by the surviving and newly formed biomass. After 80 days of incubation microbial biomass values expressed as percent microbial-C in total soil carbon (C_mic:C_org) resembled those recorded for natural sites at comparable soil pH. There was a strong reduction in bacterial respiration following mild, strong or extreme acid treatment. A recovery here over time was only noted for mild or strong acid treatments. The results confirm that soil pH is a significant controlling parameter for microbial biomass build-up and the fungal:bacterial ratio as found previously with natural site studies.     

Chemical response of soil leachate to alternative approaches to experimental acidification

Abstract

One approach to evaluating computer models which predict terrestrial‐aquatic ecosystem response to acid deposition is the experimental acidification of soils with subsequent comparisons among predicted and measured soil solution response. Using a soil microcosm experimental approach, comparisions between simulated acid rain (i.e. dilute H₂SO₄), dry NH₄NO₃, and prilled reduced S were made for suitability for large‐scale field experiments. Soil microcosms consisting of reconstructed soil profiles received a background simulated throughfall dosing over the six month treatment period. Results indicated that simulated throughfall, applied at twice the ambient rate, acidified soil leachates approximately 0.5 pH units over the treatment period. Along with the decline in leachate pH was an apparent release of base cations as well as Fe and Al. Over the length of the treatment period, very little of the prilled S dissolved and the simulated acid rain treatment did not have significant effects on leachate chemistry.     

Rehabilitation of saline soil with biogas digestate,humic acid,calcium humate and their amalgamations

ABSTRACT

Amelioration of saline soil is a requisite in order to increase crop productivity. A soil incubation study was performed for 60 days using digestate, humic acid, calcium humate and their combinations to investigate the influence on physical, chemical, microbial and enzyme activities of saline soil. Overall, digestate combined with calcium humate followed by humic acid treatments have shown their potency in decreasing the soil pH, electrical conductivity (EC), and sodium ion (Na⁺) concentration, and increase in potassium ion (K ⁺), calcium ion (Ca ²⁺), magnesium ion (Mg ²⁺), mean weight diameter (MWD), soil enzyme activities, microbial biomass carbon (MBC), MBC: microbial biomass nitrogen (MBN) and soil respiration than control. The digestate, humic acid individually and their amalgamation evidenced greater MBN among all the treatments. The digestate alone efficiently improved the soil properties than humic acid and calcium humate individual groups except for the MWD where it is pronounced more in the latter groups. The greater metabolic quotient (qCO₂) was observed in control than organic matter amended treatments indicating the stress conditions. The increase in water-extractable organic matter (WEOM) with minimal aromaticity (specific ultraviolet absorbance at 254 nm-Suva ₂₅₄) in integrated amendments comprising groups, laid the ground reason to improve the properties of saline soil. Therefore, this study concludes that the fusion of fresh and humified substrates could facilitate reclamation.     

Changes in bulk precipitation reactivity throughout the vegetation/soil continuum in a Trachpogon savanna (Venezuela)

Abstract

The reactivity of bulk precipitation moving into the soil of a bush island Trachypogon savanna throughout a forest grove and the herbaceous layer was analyzed during four consecutive years. In the forest grove, there was a significant decrease of annual hydrogen (H⁺) content (meq/ha) of 44–75% as rainfall leached through the canopy, whereas the bulk throughfall pH in the grass layer was similar to the bulk precipitation pH. As throughfall passed throughout the soil profile of the grove, the H⁺ content decreased 87–70%. Results evidenced a buffering capacity of the system when bulk precipitation was acid during the last measured year. The savanna system retained 92–93% of H⁺ input from the bulk precipitation indicating that a redistribution of H⁺ ocurred instead of a net input or net loss. Canopy neutralization of bulk precipitation appears to take place in the grove canopy mainly by organic and bicarbonate salts.     

Chemical and biological relationships relevant to the effect of acid rainfall on the soil-plant system

This paper deals with problems concerning measurements of rainfall acidity and interpretation in terms of possible effects on the soil-plant system. The theory of acidity relationships of the carbon dioxide-bicarbonate equilibria and its effect on rainfall acidity measurements is given. The relationship of a cation-anion balance model of acidity in rainfall to plant nutrient uptake processes is discussed, along with the relationship of this model to a rainfall acidity model previously proposed in the literature. These considerations lead to the conclusion that average H+ concentration calculated from pH measurements is not a satisfactory method of determining H⁺ loading from rainfall if the rain is not consistently acid. Calculating loading from H⁺ minus HCO₃ ^? , strong acid anions minus basic cations, or net titratable acidity is suggested. The flux of H⁺ ions in soil systems due to plant uptake processes and sulfur and nitrogen cycling is considered. H⁺ is produced by oxidation of reduced sulfur and nitrogen compounds mineralized during decomposition of organic matter. Plant uptake processes may result in production of either H⁺ or OH^? ions. Fluxes of H⁺ from these processes are much greater than rainfall H⁺ inputs, complicating measurement and interpretation of rainfall effects. The soil acidifying potential due to the oxidation of the NH₄ ⁺ rainfall is examined, with the conclusion that acidity from this source is of a similar magnitude to direct H⁺ inputs common in rainfall.     

The impact of reduced atmospheric depositions on soil microbial parameters in a strongly acidified Norway spruce forest at Solling,Germany

To simulate a future ion input reduction scenario in forests, a large scale field experiment was set up in a (1999) 66‒year‒old Norway spruce plantation at Solling, central Germany. Throughfall input of H⁺, SO₄^2—, and N‒compounds is artificially reduced by means of a permanent roof construction below the canopy and a de‒ionizing equipment since 1991. Here we present long term soil solution records for SO₄^2—, NO₃^—, Al³⁺ and the pH of the 10 cm mineral soil sampling depth. A significant decrease in ion concentrations since the start of the treatment is observed, but no change of the soil solution pH. Even in the fourth year pH values remained well within the aluminium buffer range (pH < 4.2). Three years after the start of the experiment (July 1994) it was examined whether microbial biomass (C_mic), specific activity (heat production per unit biomass), and the percentage of C_mic in organic C material indicated any changes. Furthermore chemical standard parameters (CEC, base saturation, pH) were analyzed for all soil samples. Results indicate that despite of drastic decreases of soil solution ion concentrations in the upper soil horizons microbial parameters were not affected and that the soil solid phase is not deacidified by the treatment until now.     

Short‐term effects of pH and aluminium on mineral nutrition in maize varieties differing in proton and aluminium tolerance

In short‐term (24 h) nutrient solution experiments, the influence of different proton (pH 6.0 and pH 4.3) and aluminium (Al) (0, 20, and 50 μM) concentrations on root and coleoptile elongation, dry weight, and the uptake of selected mineral nutrients was studied in maize (Zea mays L.) varieties that differ in acid soil tolerance under field conditions. The acid‐soil‐tolerant maize varieties, Adour 250 and C525M, proved to be hydrogen (H⁺) ion sensitive, but Al tolerant, while the acid soil tolerant variety BR201F was H⁺ tolerant but Al sensitive. The acid soil sensitive variety HS 7777 was affected by both H⁺ and Al toxicity. The proton‐induced inhibition of root elongation was closely related to the proton‐induced decrease of the specific absorption rates (SAR) of boron (B), iron (Fe), magnesium (Mg), calcium (Ca), and phosphorus (P). In contrast, only the specific absorption rate of B (SARB) was significantly correlated to the Al‐induced inhibition of root elongation. It is concluded, that alterations of nutrient uptake may play an important role in H⁺ toxicity, while at least after short‐term exposure to Al, alterations of Ca, Fe, Mg, or P uptake do not seem to be responsible for Al‐induced inhibition of root elongation. Further attention deserves the Al‐B interaction, moreover taking into account that a highly significant correlation between Al‐induced increase of callose concentration in root tips and Al‐induced decrease of SAR_B could be established.     

电渗析与酸淋洗模拟紫色土酸化的效果比较

为了比较电渗析与酸淋洗试验模拟紫色土酸化的效果,在重庆地区采集了不同pH(5.00和7.06)的2个紫色土,分别进行不同天数(1,2,5,7,10天)的电渗析和酸淋洗试验处理,并分析了试验处理前后土壤的酸度特征和交换性盐基成分含量变化。结果表明,在整个10天的淋溶处理过程中,2种紫色土的pH均无显著变化,说明紫色土具有一定的酸缓冲能力,短期的酸雨淋溶不能实现紫色土的严重酸化。而采用电渗析处理10天后,中性紫色土和酸性紫色土的pH分别降低3.4和1.1个单位。在整个电渗析处理过程中,土壤的交换性酸含量显著升高,盐基离子大量淋失。电渗析可以实现对紫色土的快速酸化处理。2种紫色土中,电渗析处理后中性紫色土的酸化程度大于酸性紫色土。这是由于中性紫色土的表面负电荷量更高,导致更多致酸离子吸附在土壤胶体表面,最终造成中性紫色土的酸化程度更加严重。因此,电渗析处理比酸雨淋溶处理对紫色土酸化效果更好,且可用于紫色土的酸化机理研究。进一步结合2种方法的技术可操作性,认为电渗析法是研究紫色土酸化问题的一种有效技术手段。     

Lysimeter study with a cambic arenosol exposed to artificial acid rain: II. Input-output budgets and soil chemical properties

The effects of artificial precipitation with different pH levels on soil chemical properties and element flux were studied in a lysimeter experiment. Cambic Arenosol (Typic Udipsamment) in monolith lysimeters was treated for 6 1/2 yr with 125 mm yr^?1 artificial rain in addition to natural precipitation. Artificial acid rain was produced from groundwater with H₂SO₄ added. pH levels of 6.1, 4 and 3 were used. ‘Rain’ acidity was buffered, mainly due to cation exchange with Ca²⁺ and Mg²⁺, which were increasingly leached due to the acid input. The H⁺ retention was not accompanied by a similar increase in the output of Al ions, but a slight increase in the leaching of Al ions was observed in the most acidic treatment. The net flux of SO₄ ^2? from the lysimeters increased with increasing input of H₂SO₄, but in the most acidified lysimeters significant sorption of SO₄ ^2? was observed. The sorption was, however, most likely a concentration effect. The ‘long-term’ acidification effects on soil were mainly seen in the upper O and Ah-horizons, where an impoverishment of exchangeable Ca²⁺ and Mg²⁺ was observed. An increased proportion of Al ions on exchange sites in the organic layer was observed in the pH 3-treated soil. By means of budget calculations the annual release of base cations due to weathering was estimated to be between 33 and 77 mmol_c m^?2.     

Lysimeter Study on the Effects of Different Rain Qualities on Element Fluxes from Shallow Mountain Soils in Southern Norway

This study focuses on fluxes of elements from, and changes in the soil properties of shallow organic material rich soil as a result of changes in precipitation acidity. Intact soil columns including natural vegetation from two areas (one exposed to acidic precipitation and one unpolluted) were used in a lysimeter experiment. The lysimeters were watered with simulated normal rain (pH 5.3) or simulated acidic rain (pH 4.3) for four years. Sulphuric acid and ammonium nitrate were used to regulate the quality of the simulated rain. Significantly more SO₄ ^2? was leached from lysimeters receiving acid rain. Rain acidity had no significant effect on NO₃ ^? leaching. Significantly more Mg²⁺ was leached from lysimeters receiving acid rain, but this only applied for the soils from the unpolluted area. Four years of treatment did not cause any significant effect on the soil acidity and the amounts of base cations in the soil. The more acidic rain did, however, cause a significant lower cation exchange capacity. For the soils from the polluted area the acid precipitation did cause a lowering of the exchangeable K⁺ in the upper 5 cm of the soil. Different quality of the soil organic material indicated by different vegetation types appeared to cause significant differences in the amount of components leached from the soil, but did not cause any difference in response to the different rain qualities.     

Effect of simulated sulfuric acid rain on the chemistry of a sulfate-adsorbing forest soil

Simulated H₂SO₄ rain (pH 3.0, 3.5, 4.0) or control rain (pH 5.6) was applied for 3.5 yr to large lysimeter boxes containing a sulfate-adsorbing forest soil and either red alder (Alnus rubra Bong) or sugar maple (Acer saccharum Marsh.) seedlings. After removal of the plants and the litter layer, soil samples were obtained at 15-cm intervals to a total depth of 90 cm. Elevated SO₄ concentrations caused by the simulated H₂SO₄ rain were most pronounced for the top 15 cm, but extended down to 45 cm (maple) or 75 cm (alder). There were no effects on SO₄ concentrations at a depth of 75 to 90 em. This confirmed the existence of a sulfate front between 20 cm and 100 cm, as postulated earlier on the basis of extracted soil solutions. Decreases in Mg and Ca concentrations, base saturation, and soil pH were limited to the uppermost 15 cm and, in most cases, to the pH 3.0 treatment. Concentrations of Mg and Ca for the pH 3.0 treatments were greater than control at a depth of 15 to 30 cm, indicating transport of these cations from the soil surface. Concentrations of Na and K, and cation exchange capacity, were not affected by simulated H₂SO₄ rain. Elevated concentrations of NO₃ and extractable Zn throughout the alder systems indicated (1) either increased rates of symbiotic N-fixation or decreased rates of N immobilization; and (2) mobilization of Zn by all acid rain treatments.     

The role of neutral salts in the ion exchange between acid precipitation and soil

Theory and experimental results have shown that neutral salts in the precipitation or supplied to the ground by other means reduce the acidification of soils by acid precipitation. This salt effect is caused by the cation exchange occurring after the entry of the rain water into the soil.The acid components of precipitation consist of H₂SO₄, HNO₃ and HCl and of NH₄⁺ after nitrification in the soil. The magnitude of the salt effect depends on the relative bonding energy of H₃O⁺ and of Ca²⁺, Mg²⁺, Na⁺, K⁺, NH₄⁺ in the soil as well as on the concentrations of H₃O⁺ and the above cations in the precipitation. The salt effect may be considerable in very acid soils. It decreases with rising pH to become very small or negligible in neutral soils, chiefly due to the increasing bonding energy of H₃O⁺ in this direction.The adverse effect of acid precipitation, therefore, is likely to be less in very acid soils, such as podsols, than in slightly acid and neutral soils with low buffering capacity against pH change. Soil texture and calcite content are very important factors in this respect as fine material and calcite increase the buffering.     

Influence of Different Forms of Iron and Aluminum on the Nature of Soil Acidity of Some Inceptisols,Alfisols, and Ultisols

Abstract

Fifteen acid soils of Mizoram representing Ultisols and Inceptisols, and Madhya Pradesh, representing Alfisols, were studied to characterize the nature of acidity in relation to different forms of iron (Fe) and aluminum (Al). The mean contents of Fe and Al were extracted by various extracting reagents and were found to be in descending order as followed: dithionite>oxalate>pyrophosphate>ammonium acetate>KCl. The electrostatically bonded EB‐H⁺ and EB‐Al³⁺ acidity comprised 28.3 and 71.7% of exchangeable acidity whereas EB‐H⁺, EB‐Al³⁺, exchangeable, and pH‐dependent acidities comprised 9.8, 30.7, 40.5, and 59.5% of total potential acidity. All forms, of acidity showed significant correlation with pH_k and organic carbon. Among the different forms, Fe and Al caused most of the variations in different forms of soil acidity but the effect of different forms of Al are more active and directly participate in the formation of EB‐H⁺, EB‐Al³⁺, and exchangeable acidity.     

Effects of methyl bromide fumigation,chloropicrin fumigation and steam sterilization on soil nitrogen dynamics and microbial properties in a pot culture experiment

Abstract

The effects of steam sterilization (SS), methyl bromide (MeBr) fumigation and chloropicrin (CP) fumigation on soil N dynamics and microbial properties were evaluated in a pot experiment. All disinfection treatments increased the NH⁺ ₄-N level and inhibited nitrification. The additional NH⁺ ₄-N in the CP treatment probably originated from the decomposition of microbial debris by surviving microbes, while that in the SS treatment was attributable to deamination processes of soil organic N occurring in a less labile fraction in addition to the decomposition of microbial debris. The MeBr fumigation increased the level of NH⁺ ₄-N without changing the soil microbial biomass. Based on the determinations of soil microbial biomass, substrate utilization activity (Biolog method) and microbial community structure (phospholipid fatty acid method), the effects of the MeBr, CP and SS treatments on the microbial community were compared. The MeBr fumigation had relatively mild and short-term effects on microbial biomass and activity, but altered the community structure drastically by promoting the growth of gram-positive bacteria. The CP fumigation had large and long-term impacts on microbial biomass and activity; the community structure remained unaffected except for the gram-negative bacteria. Steam sterilization had severe and persistent effects on all parameters. The severity of the effects decreased in the order SS ≥ CP > MeBr.     

Using Organic Matter with Chemical Amendments to Improve Calcareous Sodic Soil

Abstract

Kangping soil in northeast China is a sodic soil characterized by a high pH and excessive sodium. The high pH and excessive sodium in sodic soils generally cause loss of soil structure, reduce hydraulic conductivity (HC), increase soil hardness, and make the soil unproductive land. After we mixed organic matter (rice straw) and chemical amendments (H₂SO₄, CaSO₄, and FeSO₄), a column experiment was conducted to evaluate the physical and chemical properties of the soil influenced by the changes in HC, penetrability of soil s`urface, pH, electrical conductivity, CO₃ ^2‐, HCO₃ ^?, Ca²⁺, Na⁺, sodium adsorption rate (SAR), available phosphorus (P) and iron (Fe), and leached P.

Organic matter decreased the concentrations of CO₃ ^2‐, HCO₃ ^?, and Na⁺ in soil solution and increased the total volume of the leachate. Organic matter also reduced the amount of available Fe and increased the available P. However, organic matter did not affect the penetrability of the soil surface as much as soil hardness, HC, and SAR within the short period of this experiment. Among the chemical amendments, H₂SO₄ and FeSO₄ were more effective than CaSO₄ to restore HC, electrical conductivity, Na⁺, and SAR. The chemical amendments, compared with organic matter, significantly leached P from the soil in this study, but the leaching was independent of the concentration of available P in the soil. The CaSO₄ had the strongest effect in increasing leached P from the soil without changing the concentration of available P in the soil. Organic matter with added CaSO₄ leached P from the soil more than all other treatments.     

Effects of acid deposition on acidity and exchangeable cations in podzols of the Kola Peninsula

Response of soil and soil water of podzols in the Kola Peninsula to acid deposition was estimated under both field and laboratory conditions. A significant increasing trend of exchangeable acidity in organic (O) horizons and exchangeable Al in podzolic (E) horizons of podzols with distance from the nickel smelter was observed. The simulated rain at pH 4.5 did not alter chemical properties of soils and soil solutions. As much as 95–99% of the applied H⁺ ions were retained by soils and appeared in the percolates after a treatment period that depended on acid load and soil thickness. Ca and Mg in soil solutions were highly sensitive to acid loading. Simulated acid rain enhanced the leaching of exchangeable base cations out of root zone. Acid inputs resulted in decreased pH, amount of exchangeable base cations and base saturation, in elevated exchangeable acidity and it's Al fraction in soil solid phase. The most significant changes occurred in O and E horizons. Substantial amounts of both Ca and Mg can be lost from the root zone of podzols in the north-western Kola, subjected to acid deposition, thus leading to forest productivity damage.     

Principles underlying the practice of determining lime requirements of acid soils by use of buffer methods

Abstract

A buffer is generally a mixture of a weak acid and a salt of the same weak acid. Hence it can neutralize both acids and bases, and thus resists marked changes in pH of a system. Yet systematic change in pH of a buffer caused by addition of an acidic substance can be used to indicate the total acidity represented by the change in buffer pH. Since acid soil is itself a buffer, when it is added to a buffer mixture for the purpose of measuring its acidity or lime requirement (LR), the resulting double‐buffer suspension (soil‐buffer) is a relatively complex system. Much of the complication in interpreting the changes in buffer pH brought about by mixing soil and buffer stems from the facts: i) that much of the acidity is pH‐dependent, and ii) that quick‐test methodology involves reaction of only a fraction of the total soil acidity with the buffer. Marked change in relative amounts of H ions dissociating from the soil‐SMP‐buffer system at soil‐buffer pH 6.9 and above accounts for relatively wide variations between buffer‐indicated and CaCO₃ incubation‐measured LR of low LR soils. Similarly, decreased reactivity of H⁺ in high organic matter soils and increased reactivity of H in acid‐leached soils cause errors in buffer‐indicated LR. Awareness of these principles helps avoid pitfalls of existing buffer methods, and has led to incorporation of the double‐buffer feature for improving the SMP method.