Chemistry:Soil acidification

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Short description: Buildup of hydrogen cations, which reduces the soil pH

Soil acidification is the buildup of hydrogen cations, which reduces the soil pH. Chemically, this happens when a proton donor gets added to the soil. The donor can be an acid, such as nitric acid, sulfuric acid, or carbonic acid. It can also be a compound such as aluminium sulfate, which reacts in the soil to release protons. Acidification also occurs when base cations such as calcium, magnesium, potassium and sodium are leached from the soil.

Soil acidification naturally occurs as lichens and algae begin to break down rock surfaces. Acids continue with this dissolution as soil develops. With time and weathering, soils become more acidic in natural ecosystems. Soil acidification rates can vary, and increase with certain factors such as acid rain, agriculture, and pollution.[1]

Causes

Acid rain

Rainfall is naturally acidic due to carbonic acid forming from carbon dioxide in the atmosphere. This compound causes rainfall pH to be around 5.0-5.5. When rainfall has a lower pH than natural levels, it can cause rapid acidification of soil. Sulfur dioxide and nitrogen oxides are precursors of stronger acids that can lead to acid rain production when they react with water in the atmosphere. These gases may be present in the atmosphere due to natural sources such as lightning and volcanic eruptions, or from anthropogenic emissions.[2] Basic cations like calcium are leached from the soil as acidic rainfall flows, which allows aluminum and proton levels to increase.[3][4]

Nitric and sulfuric acids in acid rain and snow can have different effects on the acidification of forest soils, particularly seasonally in regions where a snow pack may accumulate during the winter.[5] Snow tends to contain more nitric acid than sulfuric acid, and as a result, a pulse of nitric acid-rich snow meltwater may leach through high elevation forest soils during a short time in the spring.[6] This volume of water may comprise as much as 50% of the annual precipitation. The nitric acid flush of meltwater may cause a sharp, short term, decrease in the drainage water pH entering groundwater and surface waters.[7] The decrease in pH can solubilize Al3+ that is toxic to fish,[8] especially newly-hatched fry with immature gill systems through which they pass large volumes of water to obtain O2 for respiration. As the snow meltwater flush passes, water temperatures rise, and lakes and streams produce more dissolved organic matter; the Al concentration in drainage water decreases and is bound to organic acids, making it less toxic to fish. In rain, the ratio of nitric-to-sulfuric acids decreases to approximately 1:2. The higher sulfuric acid content of rain also may not release as much Al3+ from soils as does nitric acid, in part due to the retention (adsorption) of SO42- by soils. This process releases OH− into soil solution and buffers the pH decrease caused by the added H+ from both acids. The forest floor organic soil horizons (layers) that are high in organic matter also buffer pH, and decrease the load of H+ that subsequently leaches through underlying mineral horizons.[9][10]

Biological weathering

Plant roots acidify soil by releasing protons and organic acids so as to chemically weather soil minerals.[11] Decaying remains of dead plants on soil may also form organic acids which contribute to soil acidification.[12] Acidification from leaf litter on the O-horizon is more pronounced under coniferous trees such as pine, spruce and fir, which return fewer base cations to the soil, rather than under deciduous trees; however, soil pH differences attributed to vegetation often preexisted that vegetation, and help select for species which tolerate them. Calcium accumulation in existing biomass also strongly affects soil pH - a factor which can vary from species to species.[13]

Parent materials

Certain parent materials also contribute to soil acidification. Granites and their allied igneous rocks are called "acidic" because they have a lot of free quartz, which produces silicic acid on weathering.[14] Also, they have relatively low amounts of calcium and magnesium. Some sedimentary rocks such as shale and coal are rich in sulfides, which, when hydrated and oxidized, produce sulfuric acid which is much stronger than silicic acid. Many coal soils are too acidic to support vigorous plant growth, and coal gives off strong precursors to acid rain when it is burned. Marine clays are also sulfide-rich in many cases, and such clays become very acidic if they are drained to an oxidizing state.

Soil amendments

Soil amendments such as fertilizers and manures can cause soil acidification. Sulfur based fertilizers can be highly acidifying, examples include elemental sulfur and iron sulfate while others like potassium sulfate have no significant effect on soil pH. While most nitrogen fertilizers have an acidifying effect, ammonium-based nitrogen fertilizers are more acidifying than other nitrogen sources.[15] Ammonia-based nitrogen fertilizers include ammonium sulfate, diammonium phosphate, monoammonium phosphate, and ammonium nitrate. Organic nitrogen sources, such as urea and compost, are less acidifying. Nitrate sources which have little or no ammonium, such as calcium nitrate, magnesium nitrate, potassium nitrate, and sodium nitrate, are not acidifying.[16][17][18]

Pollution

Acidification may also occur from nitrogen emissions into the air, as the nitrogen may end up deposited into the soil.[19] Animal livestock is responsible for nearly 65 percent of man-made ammonia emissions.[20]

Anthropogenic sources of sulfur dioxides and nitrogen oxides play a major role in increase of acid rain production.[clarification needed] The use of fossil fuels and motor exhaust are the largest anthropogenic contributors to sulfuric gases and nitrogen oxides, respectively.[21]

Aluminum is one of the few elements capable of making soil more acidic.[22] This is achieved by aluminum taking hydroxide ions out of water, leaving hydrogen ions behind.[23] As a result, the soil is more acidic, which makes it unlivable for many plants. Another consequence of aluminum in soils is aluminum toxicity, which inhibits root growth.[24]

Agriculture management practices

Agriculture managements approaches such as monoculture and chemical fertilization often leads to soil problems such as soil acidification, degradation, and soil-borne diseases, which ultimately have a negative impact on agricultural productivity and sustainability.[25][26]

Effects

Soil acidification can cause damage to plants and organisms in the soil. In plants, soil acidification results in smaller, less durable roots.[27] Acidic soils sometimes damage the root tips reducing further growth.[28] Plant height is impaired and seed germination also decreases. Soil acidification impacts plant health, resulting in reduced cover and lower plant density. Overall, stunted growth is seen in plants.[29] Soil acidification is directly linked to a decline in endangered species of plants.[30]

In the soil, acidification reduces microbial and macrofaunal diversity.[31] This can reduce soil structure decline which makes it more sensitive to erosion. There are less nutrients available in the soil, larger impact of toxic elements to plants, and consequences to soil biological functions (such as nitrogen fixation).[32] A recent study showed that sugarcane monoculture induces soil acidity, reduces soil fertility, shifts microbial structure, and reduces its activity. Furthermore, most beneficial bacterial genera decreased significantly due to sugarcane monoculture, while beneficial fungal genera showed a reverse trend.[33] Therefore, mitigating soil acidity, improving soil fertility, and soil enzymatic activities, including improved microbial structure with beneficial service to plants and soil, can be an effective measure to develop a sustainable sugarcane cropping system.[25]

At a larger scale, soil acidification is linked to losses in agricultural productivity due to these effects.[31]

Impacts of acidic water and Soil acidification on plants could be minor or in most cases major. In minor cases which do not result in fatality of plant life include; less-sensitive plants to acidic conditions and or less potent acid rain. Also in minor cases the plant will eventually die due to the acidic water lowering the plants natural pH. Acidic water enters the plant and causes important plant minerals to dissolve and get carried away; which ultimately causes the plant to die of lack of minerals for nutrition.[34] In major cases which are more extreme; the same process of damage occurs as in minor cases, which is removal of essential minerals, but at a much quicker rate. Likewise, acid rain that falls on soil and on plant leaves causes drying of the waxy leaf cuticle; which ultimately causes rapid water loss from the plant to the outside atmosphere and results in death of the plant. To see if a plant is being affected by soil acidification, one can closely observe the plant leaves. If the leaves are green and look healthy, the soil pH is normal and acceptable for plant life. But if the plant leaves have yellowing between the veins on their leaves, that means the plant is suffering from acidification and is unhealthy. Moreover, a plant suffering from soil acidification cannot photosynthesize.[35] Drying out of the plant due to acidic water destroy chloroplast organelles. Without being able to photosynthesize a plant cannot create nutrients for its own survival or oxygen for the survival of aerobic organisms; which affects most species of Earth and ultimately end the purpose of the plants existence.[36]

Prevention and management

Soil acidification is a common issue in long-term crop production which can be reduced by lime, organic amendments (e.g., straw and manure) and biochar application.[37][25][38][39][40] In sugarcane, soybean and corn crops grown in acidic soils, lime application resulted in nutrient restoration, increase in soil pH, increase in root biomass, and better plant health.[26][41]

Different management strategies may also be applied to prevent further acidification: using less acidifying fertilizers, considering fertilizer amount and application timing to reduce nitrate-nitrogen leaching, good irrigation management with acid-neutralizing water, and considering the ratio of basic nutrients to nitrogen in harvested crops. Sulfur fertilizers should only be used in responsive crops, with a high rate of crop recovery.[42]

Through reduction of anthropogenic sources of sulfur dioxides, nitrogen oxides, and with air-pollution control measures, let us[who?] try to reduce acid rain and soil acidification all over the world.[43]

This has been observed in Ontario, Canada over their several lakes and demonstrated improvements in water pH and alkalinity.[44]

See also

References

  1. ↑ Helyar, K. R.; Porter, W. M. (1989). "2 - Soil Acidification, its Measurement and the Processes Involved". in Robson, A. D.. Soil Acidity and Plant Growth. Academic Press. p. 61. doi:10.1016/b978-0-12-590655-5.50007-4. ISBN 9780125906555. https://books.google.com/books?id=KL8gWPuOET0C&pg=PA61. Retrieved 2020-03-25. 
  2. ↑ Blake, L. (2005), "ACID RAIN AND SOIL ACIDIFICATION", Encyclopedia of Soils in the Environment, Elsevier, pp. 1–11, doi:10.1016/b0-12-348530-4/00083-7, ISBN 9780123485304 
  3. ↑ Goulding, K. W. T. (September 2016). "Soil acidification and the importance of liming agricultural soils with particular reference to the United Kingdom". Soil Use and Management 32 (3): 390–399. doi:10.1111/sum.12270. ISSN 0266-0032. PMID 27708478. 
  4. ↑ "Acid Rain Effects on Forest Soils begin to Reverse". https://www.usgs.gov/news/acid-rain-effects-forest-soils-begin-reverse. 
  5. ↑ James, Bruce R.; Riha, Susan J. (1989). "Aluminum leaching by mineral acids in forest soils: I. Nitric-sulfuric acid differences". Soil Science Society of America Journal 53 (1): 259–264. doi:10.2136/sssaj1989.03615995005300010047x. Bibcode: 1989SSASJ..53..259J. 
  6. ↑ Likens, Gene E.; Bormann, F. Herbert; Pierce, Robert S.; Eaton, John S.; Johnson, Noye M. (1977). Biogeochemistry of a forested ecosystem. New York: Springer-Verlag. pp. 35–43. ISBN 0-387-90225-2. 
  7. ↑ Driscoll, C.T.; Schafran, G.C. (1984). "Short-term changes in the base neutralizing capacity of an acidic Adirondack, New York lake". Nature 310: 308–310. doi:10.1038/310308a0. 
  8. ↑ Cronan, C.S.; Schofield, C.L. (1979). "Aluminum leaching response to acid precipitation: Effects on high-elevation watersheds in the Northeast". Science 204 (4390): 304–306. doi:10.1126/science.204.4390.304. PMID 17800359. Bibcode: 1979Sci...204..304C. 
  9. ↑ Singh, Anita; Agrawal, Madhoolika (January 2008). "Acid rain and its ecological consequences". Journal of Environmental Biology 29 (1): 15–24. ISSN 0254-8704. PMID 18831326. https://pubmed.ncbi.nlm.nih.gov/18831326/. 
  10. ↑ James, Bruce R.; Riha, Susan J. (1989). "Aluminum leaching by mineral acids in forest soils: II. Role of the forest floor". Soil Science Society of America Journal 53 (1): 264–269. doi:10.2136/sssaj1989.03615995005300010048x. Bibcode: 1989SSASJ..53..264J. 
  11. ↑ Chigira, M.; Oyama, T. (2000), "Mechanism and effect of chemical weathering of sedimentary rocks", in Kanaori, Yuji; Tanaka, Kazuhiro; Chigira, Masahiro, Engineering Geological Advances in Japan for the New Millennium, Developments in Geotechnical Engineering, 84, Elsevier, pp. 267–278, doi:10.1016/S0165-1250(00)80022-X, ISBN 9780444505057 
  12. ↑ Tom, Nisbet (2014). Forestry and surface water acidification. Forestry Commission. ISBN 9780855389000. OCLC 879011334. 
  13. ↑ Alban, David H. (1982). "Effects of Nutrient Accumulation by Aspen, Spruce, and Pine on Soil Properties1". Soil Science Society of America Journal 46 (4): 853–861. doi:10.2136/sssaj1982.03615995004600040037x. ISSN 0361-5995. Bibcode: 1982SSASJ..46..853A. 
  14. ↑ Harker, Alfred (2011), "Mutual Relations of Associated Igneous Rocks", The Natural History of Igneous Rocks (Cambridge: Cambridge University Press): pp. 110–146, doi:10.1017/cbo9780511920424.006, ISBN 9780511920424, http://dx.doi.org/10.1017/cbo9780511920424.006, retrieved 2022-03-27 
  15. ↑ Wang, Jing; Tu, Xiaoshun; Zhang, Huimin; Cui, Jingya; Ni, Kang; Chen, Jinlin; Cheng, Yi; Zhang, Jinbo et al. (December 2020). "Effects of ammonium-based nitrogen addition on soil nitrification and nitrogen gas emissions depend on fertilizer-induced changes in pH in a tea plantation soil" (in en). Science of the Total Environment 747: 141340. doi:10.1016/j.scitotenv.2020.141340. PMID 32795801. Bibcode: 2020ScTEn.747n1340W. https://linkinghub.elsevier.com/retrieve/pii/S0048969720348695. 
  16. ↑ Schindler, D. W.; Hecky, R. E. (2009). "Eutrophication: More Nitrogen Data Needed". Science 324 (5928): 721–722. doi:10.1126/science.324_721b. PMID 19423798. Bibcode: 2009Sci...324..721S. 
  17. ↑ Penn, C. J.; Bryant, R. B. (2008). "Phosphorus Solubility in Response to Acidification of Dairy Manure Amended Soils". Soil Science Society of America Journal 72 (1): 238–243. doi:10.2136/sssaj2007.0071N. Bibcode: 2008SSASJ..72..238P. 
  18. ↑ "Don't let nitrogen acidify your soil". https://www.dpi.nsw.gov.au/agriculture/soils/improvement/n-acidify. 
  19. ↑ USGS. Acid Soils in Slovakia Tell Somber Tale.
  20. ↑ Henning Steinfeld; Pierre Gerber (2006). "Livestock's Long Shadow: Environmental issues and options". Food and Agriculture Organization of the United Nations. http://www.fao.org/docrep/010/a0701e/a0701e00.HTM. 
  21. ↑ Sparks, D. L. (2003). Environmental soil chemistry. Academic Press. ISBN 0126564469. OCLC 693474273. 
  22. ↑ Abrahamsen, G. (1987). "Air Pollution and Soil Acidification". in Hutchinson, T. C.; Meema, K. M. (in en). Effects of Atmospheric Pollutants on Forests, Wetlands and Agricultural Ecosystems. Berlin, Heidelberg: Springer. pp. 321–331. doi:10.1007/978-3-642-70874-9_23. ISBN 978-3-642-70874-9. https://link.springer.com/chapter/10.1007/978-3-642-70874-9_23. 
  23. ↑ Mossor-Pietraszewska, Teresa (2001). "Effect of aluminium on plant growth and metabolism". Acta Biochimica Polonica 48 (3): 673–686. doi:10.18388/abp.2001_3902. PMID 11833776. http://www.actabp.pl/pdf/3_2001/673-686s.pdf. 
  24. ↑ Delhaize, Emmanuel (1995). "Aluminum Toxicity and Tolerance in Plants". Plant Physiology 107 (2): 315–321. doi:10.1104/pp.107.2.315. PMID 12228360. 
  25. ↑ 25.0 25.1 25.2 Tayyab, Muhammad; Yang, Ziqi; Zhang, Caifang; Islam, Waqar; Lin, Wenxiong; Zhang, Hua (2021-04-26). "Sugarcane monoculture drives microbial community composition, activity and abundance of agricultural-related microorganisms" (in en). Environmental Science and Pollution Research 28 (35): 48080–48096. doi:10.1007/s11356-021-14033-y. ISSN 0944-1344. PMID 33904129. https://link.springer.com/10.1007/s11356-021-14033-y. 
  26. ↑ 26.0 26.1 Pang, Ziqin; Tayyab, Muhammad; Kong, Chuibao; Hu, Chaohua; Zhu, Zhisheng; Wei, Xin; Yuan, Zhaonian (December 2019). "Liming Positively Modulates Microbial Community Composition and Function of Sugarcane Fields" (in en). Agronomy 9 (12): 808. doi:10.3390/agronomy9120808. 
  27. ↑ Goulding, K. W. T. (2016-06-24). "Soil acidification and the importance of liming agricultural soils with particular reference to the United Kingdom". Soil Use and Management 32 (3): 390–399. doi:10.1111/sum.12270. ISSN 0266-0032. PMID 27708478. PMC 5032897. https://doi.org/10.1111/sum.12270. 
  28. ↑ Haling, R. E.; Simpson, R. J.; Culvenor, R. A.; Lambers, H.; Richardson, A. E. (2010-12-22). "Effect of soil acidity, soil strength and macropores on root growth and morphology of perennial grass species differing in acid-soil resistance". Plant, Cell & Environment 34 (3): 444–456. doi:10.1111/j.1365-3040.2010.02254.x. ISSN 0140-7791. PMID 21062319. 
  29. ↑ Horne, James E.; Kalevitch, Alexandre E.; Filimonova, Mariia V. (1996-05-03). "Soil Acidity Effect on Initial Wheat Growth and Development". Journal of Sustainable Agriculture 7 (2–3): 5–13. doi:10.1300/j064v07n02_03. ISSN 1044-0046. 
  30. ↑ Roem, W.J; Berendse, F (2000-02-01). "Soil acidity and nutrient supply ratio as possible factors determining changes in plant species diversity in grassland and heathland communities" (in en). Biological Conservation 92 (2): 151–161. doi:10.1016/S0006-3207(99)00049-X. 
  31. ↑ 31.0 31.1 B. Davis; N. Walker; D. Ball; A. Fitter (2002). Impacts of acid soils in Victoria : a report. Rutherglen, Vic.. ISBN 1741062462. OCLC 1034691965. 
  32. ↑ Hollier, Carole; Reid, Michael (April 2005). "Acid Soils". http://frds.dairyaustralia.com.au/wp-content/uploads/2012/01/DPI_Acid_Soils_Agnote_AG1182.pdf. 
  33. ↑ Zhang, Shuting; Liu, Xiaojiao; Zhou, Lihua; Deng, Liyuan; Zhao, Wenzhuo; Liu, Ying; Ding, Wei (2022-03-07). "Alleviating Soil Acidification Could Increase Disease Suppression of Bacterial Wilt by Recruiting Potentially Beneficial Rhizobacteria". Microbiology Spectrum 10 (2): e0233321. doi:10.1128/spectrum.02333-21. ISSN 2165-0497. PMID 35254141. 
  34. ↑ Nikbakht, Ali; Kafi, Mohsen; Babalar, Mesbah; Xia, Yi Ping; Luo, Ancheng; Etemadi, Nemat-allah (2008-11-14). "Effect of Humic Acid on Plant Growth, Nutrient Uptake, and Postharvest Life of Gerbera". Journal of Plant Nutrition 31 (12): 2155–2167. doi:10.1080/01904160802462819. ISSN 0190-4167. http://dx.doi.org/10.1080/01904160802462819. 
  35. ↑ Xiao, Hong; Wang, Bing; Lu, Shunbao; Chen, Dima; Wu, Ying; Zhu, Yuhe; Hu, Shuijin; Bai, Yongfei (August 2020). "Soil acidification reduces the effects of short-term nutrient enrichment on plant and soil biota and their interactions in grasslands". Global Change Biology 26 (8): 4626–4637. doi:10.1111/gcb.15167. ISSN 1365-2486. PMID 32438518. Bibcode: 2020GCBio..26.4626X. https://pubmed.ncbi.nlm.nih.gov/32438518/. 
  36. ↑ "What Is Acid Rain: Tips For Safeguarding Plants From Acid Rain Damage" (in en-US). https://www.gardeningknowhow.com/plant-problems/environmental/acid-rain-damage.htm. 
  37. ↑ Jiang, Yuhang; Arafat, Yasir; Letuma, Puleng; Ali, Liaqat; Tayyab, Muhammad; Waqas, Muhammad; Li, Yanchun; Lin, Weiwei et al. (2019-02-15). "Restoration of Long-Term Monoculture Degraded Tea Orchard by Green and Goat Manures Applications System" (in en). Sustainability 11 (4): 1011. doi:10.3390/su11041011. ISSN 2071-1050. 
  38. ↑ Tayyab, Muhammad; Islam, Waqar; Arafat, Yasir; Pang, Ziqin; Zhang, Caifang; Lin, Yu; Waqas, Muhammad; Lin, Sheng et al. (2018-07-06). "Effect of Sugarcane Straw and Goat Manure on Soil Nutrient Transformation and Bacterial Communities" (in en). Sustainability 10 (7): 2361. doi:10.3390/su10072361. ISSN 2071-1050. 
  39. ↑ Zhang, Caifang; Lin, Zhaoli; Que, Youxiong; Fallah, Nyumah; Tayyab, Muhammad; Li, Shiyan; Luo, Jun; Zhang, Zichu et al. (December 2021). "Straw retention efficiently improves fungal communities and functions in the fallow ecosystem" (in en). BMC Microbiology 21 (1): 52. doi:10.1186/s12866-021-02115-3. ISSN 1471-2180. PMID 33596827. 
  40. ↑ Tayyab, M (2018). "Biochar: An Efficient Way to Manage Low Water Availability in Plants". Applied Ecology and Environmental Research 16 (3): 2565–2583. doi:10.15666/aeer/1603_25652583. http://www.aloki.hu/pdf/1603_25652583.pdf. 
  41. ↑ Joris, Helio Antonio Wood; Caires, Eduardo Fávero; Bini, Angelo Rafael; Scharr, Danilo Augusto; Haliski, Adriano (2012-08-14). "Effects of soil acidity and water stress on corn and soybean performance under a no-till system". Plant and Soil 365 (1–2): 409–424. doi:10.1007/s11104-012-1413-2. ISSN 0032-079X. 
  42. ↑ Wortmann, Charles S. (2015-06-15). Management strategies to reduce the rate of soil acidification. Cooperative Extension, Institute of Agriculture and Natural Resources, University of Nebraska-Lincoln. OCLC 57216722. 
  43. ↑ "Acid Rain Effects on Forest Soils begin to Reverse". https://www.usgs.gov/news/acid-rain-effects-forest-soils-begin-reverse. 
  44. ↑ Keller, Wendel; Heneberry, Jocelyne H.; Dixit, Sushil S. (April 2003). "Decreased acid deposition and the chemical recovery of Killarney, Ontario, lakes". Ambio 32 (3): 183–189. doi:10.1579/0044-7447-32.3.183. ISSN 0044-7447. PMID 12839193. https://pubmed.ncbi.nlm.nih.gov/12839193/. 

Further reading



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