Soil Degradation: Acidification

Soil degradation can happen in many ways. One of the ways that soils can be degraded is through soil acidification. Acidic soils can be found in a natural setting, such as; the soils in Australia were naturally acidic before agriculture took over [6]. What is soil acidification? Soil acidification is a process of making the soil acidic [7]. This means that the soil's pH level is lowered below 7.0. Although, the soil can naturally be slightly acidic, due to many human activities its pH level can be lowered even further thus causing soil acidification. Understanding what the human-causes have on the soil to make it acidic, the effects that acidic soil has, and the management of acidic soils are all important in the protection of the soil from becoming too acidic.

The burning of fossil fuels and vegetation are both causes of air pollution and then causing soil acidification. When fossil fuels and vegetation are being burned, they release carbon dioxide (CO₂), nitrates (NO₃^-), and sulfates (SO₄^2-) into the atmospheres. Although, the atmosphere already consists carbon dioxide humans have increased the amount that is in the air. When the carbon dioxide (CO₂) in the atmosphere mingles with the rainwater, (H₂O) then it will form into carbonic acid (H₂CO₃) [8]. However, when nitrates (NO₃^-) and sulfates (SO₄^2-) enter the atmosphere they become a huge problem because when either one combines with the rainwater (H₂O) they become either nitric acid (HNO₃) or sulfuric acid (H₂SO₄). These two acids are much stronger than the carbonic acid. Thus, when these acids meet the ground and they are percolated into the soil they cause the soil to lower its pH level, thus making the soil acidic. Another huge cause of soil acidification is the agriculture processes. Sometimes these processes of agriculture are to intentionally acidify the soil by using nitrogen in the form of "ammonium fertilizers or biological nitrogen fixation" [8]. For example, "in areas of Australia where clover has been grown continuously for more than 30 years, the soil pH has decreased about one unit" [3]. Also, "in New Zealand, intensive dairy pastures require applications of approximately 2.5 tones of lime per ha every 6 years to neutralize acidity mostly generated through N fixation and fertilizer use" [3]. In some cases, the input of nitrogen can take the soil to its limits. For instance, "In some areas of the southern and central Tablelands of New South Wales continuous legume cultivation has generated sufficient soil acidity that wheat cultivation has had to be abandoned" [3]. Some other cases of extreme acidity that are special include "mining and drainage of wetlands" [8]. Although, these few events are the human related activities that cause soils to be acidic, many damaging effects come with them.

Many damaging effects caused by humans come with acidic soils. The major effects felt in forests around the world. An example of this is the forests of North America. The "...acidic deposition in North America increasingly point towards base cation depletion from forest soils as one of the principal mechanisms by which air pollutants can affect forest sustainability and productivity, particularly in areas where soils are inherently low in base cations and where cation reserves have been further depleted by harvesting or other past land use activities" [4]. The depletion of the base cations is a huge issue because it is part of neutralizing acids [4]. With the depletion of nutrients such as, calcium, magnesium, and potassium can cause problems with the growth and health of trees [4]. These problems make it very difficult for forests to maintain their sustainability. Acidic soils also have a major effect on crops as well. Acidic soil makes it difficult to maintain a high yield and thus becoming very costly. Sometimes, there are fields abandoned due to such a high amount of acid just as it happened in southern and central Tablelands of New South Wales [3]. When a soils pH level is too low then heavy metals are released then it makes the soil very toxic [5]. Examples of heavy metals are aluminum (Al), manganese (Mg), and Iron (Fe) [8]. All of which when reached to its toxicity level become a huge problem for much of the species of crops [8]. Although, there are many damaging effects that acidic soils can have on vegetation, there are ways to counteract them.

There are several ways to counteracting the effects of acidic soils so that the soil can grow crops again. Flooding the soil is just one-way to do this [8]. This method normally is used for crops such as "rice and taro" [8]. Another way that is the most popular to use for crops is, "adding an amendment such as lime (liming) is the suitable correction" [8]. Liming "the addition of alkaline materials to soil" [8]. When the amendment is added to the soil, a lot happens. "The base-that is, hydroxide, carbonate, or silicate-reacts with H⁺..." [8]. Fertilizing is another way to help raise pH levels in soils. Although, there are ways to raise pH levels to a more desirable level for plants, they are merely Band-Aids covering up a problem. These treatments "cannot restore the soils buffering capacity, making soil acidification one of the most sever environmental threats in Europe, the full effects of which cannot be reversed" [5]. Unfortunately, Europe is not the only place that is having this kind of an environmental threat.

Soil acidification is like a wound. Understanding how this wound that is caused by human activities can have a huge impact on the Earth is very important. Also, understanding that there are ways to manage it and maybe even prevent it can be very important. After all once there is a deep enough of a wound, a scar tends to form. This concept is also the same for the Earth and its soil. Once it is damaged, it will take a lot of work to fix it and in some cases, it will never be able to be fixed.

Sources:

1. (1999, ). In Acidification - Definition & Cause. Retrieved Nov. 25, 2008, from http://web.ceu.hu/envsci/soe/problems/aciddef.htm

2. (2008). In Effects of Air Pollution on Soil Sustainability. Retrieved Nov. 23, 2008, from http://www.forestresearch.gov.uk/fr/infd-6269vz

3. Bolan, N.S., Hedley, M.J., & White, R.E. (1991). Processes of soil acidification during nitrogen cycling with emphasis on. Plants and Soil (134), 53-63. Retrieved Nov. 25, 2008, from http://www.springerlink.com/content/w21718758726v004/fulltext.pdf.

4. Fenn, M. E., Huntinton, T.G., McLaughlin, S.B, Eagar, C., Gomez, A., Cook, R.B. (2006,). Status of soil acidification in North America. Journal of Forest Science 3(52), 1-11. Retrieved Nov. 23, 2008, from http://www.fs.fed.us/ne/newtown_square/publications/other_publishers/OCR/ne_2006_fenn001.pdf.

5. In Soil Acidification. Retrieved Nov. 24. 2008, from http://greenpack.rec.org/soil/problems_and_threats_to_the_soil/03-03-02.shtml

6. Okazaki, M. In Soil Degradation Due to Acidification. Retrieved Nov. 23, 2008, from http://www-cger.nies.go.jp/lugec/Proceedings/28)Okazaki.pdf

7. Porter, W. M. In Soil Acidification - the Cause. Retrieved Nov. 24, 2008, from http://www.regional.org.au/au/roc/1981/roc198131.htm

8. Singer, M, &. Munns. (2005). Soils: An Introduction(6^th Edition). Prentice Hall.