Soil acidification and the importance of liming agricultural soils with particular reference to the United Kingdom

Soil acidification is caused by a number of factors including acidic precipitation and the deposition from the atmosphere of acidifying gases or particles, such as sulphur dioxide, ammonia and nitric acid. The most important causes of soil acidification on agricultural land, however, are the application of ammonium‐based fertilizers and urea, elemental S fertilizer and the growth of legumes. Acidification causes the loss of base cations, an increase in aluminium saturation and a decline in crop yields; severe acidification can cause nonreversible clay mineral dissolution and a reduction in cation exchange capacity, accompanied by structural deterioration. Soil acidity is ameliorated by applying lime or other acid‐neutralizing materials. ‘Liming’ also reduces N₂O emissions, but this is more than offset by CO₂ emissions from the lime as it neutralizes acidity. Because crop plants vary in their tolerance to acidity and plant nutrients have different optimal pH ranges, target soil pH values in the UK are set at 6.5 (5.8 in peaty soils) for cropped land and 6.0 (5.3 in peaty soils) for grassland. Agricultural lime products can be sold as ‘EC Fertiliser Liming Materials’ but, although vital for soil quality and agricultural production, liming tends to be strongly influenced by the economics of farming. Consequently, much less lime is being applied in the UK than required, and many arable and grassland soils are below optimum pH.     

土壤亚硝酸气体(HONO)排放过程及其驱动机制

气态亚硝酸(HONO)是大气中氢氧自由基(OH·)的重要来源,直接影响到大气氧化能力和空气质量。通过比较外场测定和模型计算的HONO浓度,发现白天时存在未知的大气HONO来源。研究表明,土壤可以向大气中排放HONO。其机理可能是土壤亚硝态氮和氢离子的化学平衡作用;或土壤夜间吸附和白天解吸附的动态物理化学过程;或氨氧化细菌等微生物的直接排放;也可能是硝化过程中产生的羟胺,在土壤颗粒物等表面的化学反应。因此,土壤HONO排放通量与土壤亚硝态氮浓度、pH、氨氧化细菌丰度、土壤矿物、土壤湿度及C/N值等相关。目前对于土壤HONO排放的研究尚在起步阶段,国内亦少见相关成果报道。本文综述了土壤HONO排放的研究背景、探讨了土壤HONO排放的机理及影响因素,以期为减少氮素损失、提高氮肥利用率、评估氮肥的环境效应及城市空气质量等提供理论依据和科学指导。     

Detectability of step trends in the rate of atmospheric sulphate deposition

Step trend analyses are performed on acid deposition rates using a combination of monitored sulphate deposition data and a long-range transport of acid precipitation (LRTAP) model. The step trend analyses consider Sudbury's emissions and eastern North America's emissions to explore strategies for reducing SO₂ emissions such that a decrease in sulphate deposition is detected in a specified time period. Results indicate Sudbury's emissions could be reduced with significant detectable reductions in sulphate deposition occurring at the Muskoka region. Significant detectable reductions do not occur elsewhere due to the variability of monitoring data ‘masking’ the small change in sulphate depositions associated with abatement. Reductions in eastern North America's emissions would result in widespread evidence of significant detectable reductions.     

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.     

Long-term trends in chemistry of precipitation after longscale transport-effects of atmospheric rehabilitation in East-Germany

Components in precipitation are dominantly dependent on structure and quantity of emissions on the course of the rainy air masses. It can be proved after meso-and long-range transport. Starting in 1982, precipitation is collected in 4-hour-periods at sites far from industry in East-Germany. For regions with specific geographical or uniform emission features arrival sectors are established, e. g. former GDR, Scandinavia, Poland, or Czech. The classification of the samples is done by back-trajectories. From the former GDR the anthropogenical components were most significantly raised before the political change, but acidity remained on an average level. After the change, the most emission products decline considerably —except NO_X. Consequently, those lead to essential changes of pollutants in precipitation. The reduction is not uniformly. The report represents long-term data and discusses clear differences between components in deposition from sectors of the former GDR and West-Germany. The effects of atmospheric rehabilitation are analysed. Specially starting in 1993 the acidity of rain from the former GDR increases very strikingly up to now threefold more than from West-Germany (average ≤pH 4 at some sites). An explanation in terms of emission components only is devious, a complex consideration of change of dust composition as neutralizing factors and of processes of cloud formation and dispersal is necessary. It must be mentioned, that the acidity of precipitation from West-Germany and Scandinavia declines slightly in recent period. Therefore only sector-classified data show the real range of acidity.     

Soil acidification during more than 100 years under permanent grassland and woodland at Rothamsted

Abstract Soil samples have been taken periodically from unlimed plots of the 130-year-old Park Grass Experiment and from the 100-year-old Geescroft Wilderness at Rothamsted. Changes in the pH of the samples show how acidification has progressed. The soils are now at, or are approaching, equilibrium pH values which depend on the acidifying inputs and on the buffering capacities of the soils. We have calculated the contributions to soil acidification of natural sources of acidity in the soil, atmospheric deposition, crop growth and nutrient removal, and, where applicable, additions of fertilizers. The relative importance of each source of acidification has changed as the soils have become more acid. Acid rain (wet deposited acidity) is a negligible source, but total atmospheric deposition may comprise up to 30% of acidifying inputs at near neutral soil pH values and more as soil pH decreases. Excepting fertilizers, the greatest causes of soil acidification at or near neutral pH values are the natural inputs of H⁺ from the dissolution of CO₂ and subsequent dissociation of carbonic acid, and the mineralization of organic matter. Under grassland, single superphosphate and small amounts of sodium and magnesium sulphates have had no effect on soil pH, whilst potassium sulphate increased soil acidity slightly. All of these effects are greatly outweighed under grassland, however, by those of nitrogen fertilizers. Against a background of acidification from atmospheric, crop and natural inputs, nitrogen applied as ammonium sulphate decreased soil pH up to a maximum of 1.2 units at a rate in direct proportion to the amount added, and nitrogen applied as sodium nitrate increased soil pH by between 0.5 and 1 unit.     

生物炭施用下中国农田土壤N2O排放的Meta分析

为明确施加生物炭对中国农田土壤N_2O排放的影响和主要控制因素,以公开发表的试验数据为研究对象,采用Meta-analysis法定量分析了施加生物炭条件下,气候、土壤性质、田间管理方式、生物炭性质与施加量对土壤N_2O排放的影响,并对各影响因素进行通径分析。结果表明,当年降雨量≥600 mm时,生物炭显著降低土壤N_2O排放量(P0.05),且随年降雨量的增加而增强;当年日照时数大于1 000 h时,生物炭对土壤N_2O的减排效果随年日照时数的增加而减弱。当土壤p H≥6.5时,生物炭对土壤N_2O的减排效果随土壤p H的增加呈先增后减趋势;在壤土中施加生物炭对N_2O的减排效果显著(P0.05),而砂土和黏土不显著(P0.05)。生物炭对覆膜土壤N_2O的减排效果优于不覆膜土壤;生物炭对土壤N_2O的减排效果随施氮肥量增加而减弱,而随生物炭比表面积的增加而增强。当生物炭C/N处于30~500时,生物炭施用下土壤N_2O排放量显著降低(P0.05);当生物炭施加量处于20~160 t×hm-2时,生物炭对土壤N_2O的减排效果随施加量增加而增强。生物炭对土壤N_2O减排的影响存在显著的区域性特征,对华南、华东、华中和东北地区影响显著(P0.05),而对西北地区不显著(P0.05);施氮肥量、生物炭施加量、年均温和年降雨量是影响生物炭减排效果的最主要因素,这些因素的相互作用共同影响生物炭对土壤N_2O的减排效果。该研究可为生物炭在我国农区的推广应用和农田N_2O减排提供参考。     

Biogenic hydrogen sulfide emissions from selected Florida wetlands

Biogenic H₂S emissions from Florida wetland surfaces enclosed by transparent polycarbonate cylinders were collected on silver nitrate impregnated filters and analyzed fluorometrically. The areal emission rates ranged from 0.024 to 0.272 g S M-2 yr^?1 for a mangrove and from 0.001 to 0.110 g S m^?2 yr^?1 for two freshwater wetlands (cypress swamp and riverine marsh) and a saltwater marsh. The total quantity of biogenic S emitted from these wetlands was estimated to range from 1.8 x 10⁹ to 3.0 × 10⁹ g yr^?1. While biogenic emissions from wetlands may be a factor in local patterns of acid deposition, they are probably insignificant contributors to Florida's atmospheric S burden and acidity of precipitation compared to anthropogenic S sources.     

Barium and manganese trends in tree-rings as monitors of sulfur deposition

Barium and manganese concentrations in radial growth increments of heartwood from Juniperus virginiana L. are used to examine changes in soil reaction and sulfur deposition. Barium and Mn trends from trees growing on 2 sites with acid, low-Ca soils, signaled sulfur-induced changes in soil acidity after 1870, while Ba and Mn trends before 1870 did not. Factors controlling Ba availability are hypothesized to have changed from soil acidity before 1870 to precipitation of BaSO₄ by increased soil sulfate after 1870.Research supported by USDA Grant 86-CRCR-1-2074 and McIntire-Stennis funds. This is Paper No. 11,757 in the University of Missouri's Agricultural Experiment Station Journal Series.     

Atmospheric monitoring network operations and results in Canada

Atmospheric monitoring activities in Canada relevant to the long-range transport of atmospheric pollutants and the ‘acid rain’ problem are reviewed. Particular aspects examined are network objectives, station density and location, sampling protocol, and quality assurance. Results from a number of these networks are presented for the purpose of outlining the nature and extent of air and precipitation contamination by pollution released in eastern North America. Examples discussed include: the spatial distribution of acidic wet deposition, the temporal variation of acid-related substances in both air and precipitation, an episode of long-range transport, and the impact of acidic emissions on the Arctic atmosphere. Acidic wet deposition is greatest in Canada east of the Manitoba-Ontario border. In 1978, it ranged from 18 to 46 mmol H⁺ m^?2 yr^?1 in the southern half of eastern Canada, with maxima in southern Ontario (44 mmol H⁺ m^?2 yr^?1) and southwestern Quebec (46 mmol H⁺ m^?2 yr^?1). Western Canada receives less acidity in precipitation, but areas of some concern are the Pacific Coast (10 mmol H⁺ m^?2 yr^?1) and to a lesser extent northern Alberta and Saskatchewan (3 to 5 mmol H⁺ m^?2 yr^?1). Acidic emissions from mid-latitude sources which reach the Arctic in winter cause an increase in the acidity of snow from a pH of approximately 5.6 in the summer to values of 4.9 to 5.1 in January through March.     

Temperature responses of NO and N2O emissions from boreal organic soil

Both NO and N₂O are produced in soil microbial processes and have importance in atmospheric physics and chemistry. In recent years several studies have shown that N₂O emissions from organic soils can be high at low temperatures. However, the effects of low temperature on NO emissions from soil are unknown. We studied in laboratory conditions, using undisturbed soil cores, the emissions of NO and N₂O from organic soils at various temperatures, with an emphasis on processes and emissions during soil freezing and thawing periods. We found no soil freezing- or thawing-related emission maxima for NO, while the N₂O emissions were higher both during soil freezing and thawing periods. The results suggest that different factors are involved in the regulation of NO and N₂O emissions at low temperatures.     

Impacts of acid precipitation on coniferous forest ecosystems

This paper summarizes the results from current studies in Norway. One main approach is the application of artificial acid ‘rain’ and of lime to field plots and lysimeters. Application during two growth seasons of 50 mm mo^?1 of ‘rain water’ of pH 3 to a podzol soil increased the acidity of the humus and decreased the base saturation. The reduction in base saturation was mainly due to leaching of Ca and Mg. Laboratory experiments revealed that decomposition of pine needles was not affected by any acid ‘rain’ treatment of the field plots. Liming slightly retarded the decomposition. No nitrification occurred in unlimed soils (pH 4.4-4.1). Liming increased nitrification. The soil enchytraeid (Ohgochaeta) fauna was not much affected by the acidification. Germination of spruce seeds in acidified mineral soil was negatively affected when soil pH was 4.0 or lower. Seedling establishment was even more sensitive to increasing soil acidity. Analysis of throughfall and stemflow water in southernmost Norway reveals that the total deposition of H₂SO₄ beneath spruce and pine is approximately two times the deposition in open terrain. A large part of this increase is probably due to dry deposition. Increased acidity of the rain seems to increase the leaching of cations from the tree crowns. Tree-ring analysis of spruce (Picea abies (L.) Karst.) and pine (Pinus sylvestris L.) has been based on comparisons between regions differently stressed by acid precipitation and also between sites presumed to differ in sensitivity to acidification. No effect that can be related to acid precipitation has yet been detected on diameter growth.     

Nutrient balance in Scots pine (Pinus sylvestris L.) forest 1. Design of experiments

The main objectives of the project described in the present and four following papers are:

1. To study tree growth and nutrient status of forest soil as influenced by atmospheric depositions of S and N.
2. To study the influence of plant growth, litter decomposition and atmospheric depositions on soil acidity.
3. To study the influence of atmospheric deposition on the release of N₂O from soil.

One field plot experiment in a Scots pine forest and one lysimeter experiment were established in 1990 on weakly podzolized soils (Cambic arenosol). The experiment was established in a young Scots pine forest. N, Mg and P were applied in a factorial design. The experiment includes 12 treatments and three blocks. Soil was collected in a long-term field experiment with acid rain and filled into lysimeters (bucket type) by horizon. Under each horizon tension lysimeters were installed. The lysimeters were under a roof to avoid input of natural precipitation. S was applied as sulphuric acid diluted to pH levels of 5.5, 4.0, 3.5 and 3.0 and applied in a quantity of 1000 mm ”rain” yr^?1. Nitrogen (NH₄NO₃) was applied in three quantities: 0, 30 and 90 kg N ha^?1 yr^?1. Seedlings of Scots pine were planted in the lysimeters. Lysimeters with no trees were also established. The experiment includes four replicates.     

Soil Respiration of Biologically-Crusted Soils in Response to Simulated Precipitation Pulses in the Tengger Desert, Northern China

Soil respiration (SR) is a major process of carbon loss from dryland soils, and it is closely linked to precipitation which often occurs as a discrete episodic event. However, knowledge on the dynamic patterns of SR of biologically-crusted soils in response to precipitation pulses remains limited. In this study, we investigated CO₂ emissions from a moss-crusted soil (MCS) and a cyanobacterialichen-crusted soil (CLCS) after 2, 4, 8, 16, and 32 mm precipitation during the dry season in the Tengger Desert, northern China. Results showed that 2 h after precipitation, the SR rates of both MCS and CLCS increased up to 18-fold compared with those before rewetting, and then gradually declined to background levels; the decrease was faster at lower precipitation amount and slower at higher precipitation amount. The peak and average SR rates over the first 2 h in MCS increased with increasing precipitation amount, but did not vary in CLCS. Total CO₂ emission during the experiment (72 h) ranged from 1.35 to 5.67 g C m-² in MCS, and from 1.11 to 3.19 g C m-² in CLCS. Peak and average SR rates, as well as total carbon loss, were greater in MCS than in CLCS. Soil respiration rates of both MCS and CLCS were logarithmically correlated with gravimetric soil water content. Comparisons of SR among different precipitation events, together with the analysis of long-term precipitation data, suggest that small-size precipitation events have the potential for large short-term carbon losses, and that biological soil crusts might significantly contribute to soil CO₂ emission in the water-limited desert ecosystem.     

The history and character of acid precipitation in eastern North America

The history and present distribution of precipitation acidity in eastern North America are reviewed. Precipitation chemistry from the 1920's indicates heavy ionic deposition, but low acidity (calculated) in Tennessee (pH 7.4) and New York (pH 6.15). However, high acidity was apparently widespread over northeast North America by 1955–56 and measured pH's below 4.5 were observed earlier. The geographic distribution of acid precipitation has spread through the present. Yearly average pH values for 1972–73 are not significantly different in New York and New Hampshire, indicating a regional consistency in acid (pH 4.10) deposition. Summer acidity is currently lower in Tennessee than in the Northeast. Precipitation chemistry of individual storms reveals some local variation even within a 3 km range, but a storm in central New York is generally homogenous over 70 km.     

华南红壤的交换性碱和交换性酸

本文提出了一个同时测定土壤的交换性酸和交换性碱的简易方法。将土壤的交换性酸和交换性碱区分为:Na-交换性酸、Ba-交换性酸和SO₄-交换性碱、F-交换性碱。用推荐的方法,在野外对华南地区由不同母质发育的砖红壤、赤红壤、红壤等10个剖面进行了测定。结果表明,红壤类土壤含有相当量的交换性碱,但其数量比交换性酸少。酸性母质发育的土壤的交换性酸和交换性碱量大于由基性岩发育的土壤者。红壤的交换性酸和碱的量随电性盐浓度的增高而增大,浓度大于0.1N后,数量基本不变。     

recent lake acidification and recovery trends in southern quebec,canada

A total of 51 lakes in southern Quebec, Canada, were sampled between 1985 and 1993 to study changes in water chemistry following reductions in SO₂ emissions (main precursor of acid precipitation). Time series analysis of precipitation chemistry revealed significant reductions in concentrations and deposition of SO₄ ^2- from 1981 to 1992 in southern Quebec as well as reductions in concentrations and deposition of base cations (Ca²⁺, Mg²⁺), NO₃ ^- and H⁺ in the western section of the study area. Reductions in atmospheric inputs of SO₄ ^2- have resulted in decreased lakewater SO₄ ^2- concentrations in the majority of the lakes in our study, although only a small fraction (9 of 37 lakes used in the temporal analysis) have improved significantly in terms of acidity status (pH, acid neutralizing capacity – ANC). The main response of the lakes to decreased SO₄ ^2- is a decrease in base cations (Ca²⁺+Mg²⁺), which was observed in 17 of 37 lakes. Seventeen lakes also showed significant increases in dissolved organic carbon (DOC) over the period of study. The resulting increases in organic acidity as well as the decrease in base cations could both play a role in delaying the recovery of our lakes.     

Buffer Capacity of Open Atmospheric Gas–Liquid Systems

Buffer capacity analysis of open atmospheric gas–liquid systems containing main acidic and basic atmospheric pollutants was carried out. Usually the buffer capacity is considered as a function of pH as an independent variable. In this work the buffer capacity is analysed including the dependence of pH on the composition of a system. Such an approach allows finding an important, from the viewpoint of atmospheric water acidification, relationship between the gas phase composition and the buffer capacity. It was found that buffer capacity of the open gas–liquid systems may be very high and it may cause the liquid phase pH to remain at low levels. The buffer capacity of the analysed systems is most strongly affected by the simultaneous presence of ammonia and strong acids in the gas phase. The higher concentrations of strong acid gases the lower NH₃ concentration is sufficient to achieve high buffer capacity. In the presence of strong acid gases, calcium ions affect both the buffer capacity and the liquid phase pH only at low NH₃ concentrations. High buffer capacity of open gas–liquid systems may be one of the reasons why the reduction in emissions of acidic gas pollutants has little effect on decrease in atmospheric water acidity.     

Influence of acid rain on CO2 consumption by rock weathering: Local and global scales

Sulphuric and nitric acids, which are supplied by acid precipitation, take over from carbonic acid in weathering reactions, which induced a decrease of the atmospheric/soil CO₂ consumption by weathering (WCO₂). In order to quantity this disturbance, one has compared the bicarbonate fluxes determined at the outlet of 2 small catchments (one is substantially disturbed and the other is is weakly disturbed by acid precipitation). Our study shows that, under the influence of acid precipitation, bicarbonate fluxes (i.e. WCO₂) are decreased by about 73%. It has also been attempted to simulate at the continental scale, the influence of acid precipitation on WCO₂, using a Global Erosion Model (GEM-CO₂) recently developed. Several simulations have been performed corresponding to different realistic scenarios of global acid precipitation. In the most pessimistic of these scenarios, the GEM-CO₂ simulation shows that the global WCO₂ would be decreased by no more than 10%.