土壤pH值

土壤pH值是衡量土壤中酸度或鹼度所代表的意義。是溶液离子活度的一种标度,也就是通常意义上溶液程度的衡量标准。土壤pH被認為是土壤中的主要變量,因為它控制發生的許多化學過程。

土壤pH的全球變化,=酸性土、黃色=中性土、藍色=鹼性土、黑色=無數據

它通過控制營養物的化學形式特異性地影響植物營養物的可用性。

大多數植物的最佳pH範圍在5.5和7.0之間,然而許多植物已經適應在該範圍之外的pH值下生長。

土壤pH值範圍分類

美國農業部,將土壤pH範圍分類如下: [1]

名稱 pH範圍
超酸性< 3.5
極酸性3.5–4.4
極強酸性4.5–5.0
強酸性5.1–5.5
中等酸性5.6–6.0
微酸性6.1–6.5
中性6.6–7.3
微鹼性7.4–7.8
中等鹼性7.9–8.4
強鹼性8.5–9.0
非常強鹼性> 9.0

土壤pH值的來源

酸度的來源

土壤中的酸性來自土壤溶液中的氫離子和鋁離子並且吸附到土壤表面。While pH is the measure of H+ in solution, Al3+ is important in acid soils because between pH 4 and 6, Al3+ reacts with water (H2O) forming AlOH2+, and Al(OH)2+, releasing extra H+ ions。 Every Al3+ ion can createdo authors know something about chemical equilibrium? 3 H+ ions.許多其他過程有助於形成酸性土壤,包括降雨量,肥料使用,植物根系活動和初級和次級土壤礦物的風化。酸性土壤也可能由污染物引起,例如酸雨和礦渣。

  • :酸性土壤最常見於降雨量大的地區。 過量的降雨量從土壤中浸出鹼性陽離子。另外,由於雨水中的碳酸與 CO 2的反應,所以雨水俱有5.7的微酸性pH值。
  • 肥料使用: (NH4+)肥料在稱為硝化的過程中在土壤中反應形成硝酸鹽(NO3),並在過程釋放氫離子。
  • 植物根系活力:植物吸收離子形式的營養物質(NO3, NH4+, Ca2+, H2PO4, etc.),吸收比例來說陽離子比陰離子吸收還多。然而植物必須在其根部保持中性電荷。為了補償額外的正電荷,它們將從根部釋放氫離子。 一些植物還將有機酸滲出到土壤中以酸化其根周圍的區域,以幫助溶解在中性pH下不溶的金屬營養物質,例如鐵 (Fe)。
  • 風化作用:Both primary and secondary minerals that compose soil contain Al. As these minerals weather, some components such as Mg, Ca, and K, are taken up by plants, others such as Si are leached from the soil, but due to chemical properties, Fe and Al remain in the soil profile. Highly weathered soils are often characterized by having high concentrations of Fe and Al oxides.
  • 酸雨:當大氣中的水與工業過程產生的硫和氮化合物反應時,結果可能是雨水中形成硫酸和硝酸。
  • 酸性礦井水:由於黃鐵礦的氧化,在礦井附近可能形成嚴重的酸性土壤。
  • Potential acid sulfate soils naturally formed in waterlogged coastal and estuarine environments can become highly acidic when drained or excavated.
  • 通過微生物分解有機物質釋放 CO2 當其與土壤水混合時可形成碳酸 (H2CO3)。[2]

鹼度來源

鹼性土壤具有高的鹼性陽離子飽和度 (K+, Ca2+, Mg2+ 和 Na+)。This is due to an accumulation of soluble salts which are classified as either 土壤鹽化, sodic soil, saline-sodic soil or alkaline soil。所有鹽水和鈉鹼土壤具有高鹽濃度,鹽鹼土以鈣和鎂鹽為主,鈉鹼土以鈉為主。鹼性土壤的特徵在於存在碳酸鹽。在靠近表面的石灰石區域中的土壤是來自石灰石中的碳酸鈣的鹼性土壤,與土壤不斷混合。[3]這些地區的地下水源含有溶解的石灰石。

土壤pH值對植物生長的影響

與土壤pH相關的營養物利用度[4]

酸性土壤的影響

[5] 在酸性土壤中生長的植物可能會有各種各樣的症狀出現,包括 (Al)、 (H)、和/或 (Mn)的毒性, 以及 (Ca) 和 (Mg)的營養缺乏。

的毒性是酸性土壤中最普遍的問題。鋁存在於所有土壤中,但溶解的 Al3+ 對植物有毒;Al3+ is most soluble at low pH, above pH 5.2 little Al is in soluble form in most soils.[6]

鋁不是植物養分,並且因此不被植物主動吸收,而是通過滲透被動地進入植物根。鋁抑制根生長;側根和根尖變粗、根缺乏精細分枝;根尖可變成棕色。在根中,已經顯示鋁干擾許多生理過程,包括鈣和其他必需營養物的攝取和轉運,細胞分裂,細胞壁形成和酶活性[7]

在含有含量高的礦物的土壤中,錳的毒性在pH5.6以下會成為問題。錳如鋁,隨著pH下降變得越來越可溶解,並且在pH水平低於5.6時可以看到錳的毒性症狀出現。錳是葉綠素的組成物之一,因此植物將錳轉運到葉中。錳毒性的經典症狀是葉子皺縮呈現托起狀態。

關於土壤pH養分有效性

[8] 由植物大量需要的營養物被稱為大量營養素,包括 (N)、 (P)、 (K)、 (Ca)、 (Mg) 和 (S)。植物需要微量的元素被稱為微量營養素或是微量營養素物。微量營養物不是植物組織的主要成分,但是對於生長是必需的。它們包括 (Fe)、 (Mn)、 (Zn)、 (Cu)、 (Co)、 (Mo)、和 (B)。

大量營養素和微量營養素的可用性受土壤pH的影響。在輕度到中度鹼性的土壤中,鉬和大量營養素(除了磷外)的可用性增加,但是 P、Fe、Mn、Zn Cu、和 Co水平降低並且可能不利地影響植物生長。

In acidic soils, micronutrient availability (except for Mo and Bo) is increased。氮通過固氮或肥料調節作為銨 (NH
4
) 或硝酸鹽 (NO
3
) 供應,溶解的氮在土壤pH為6.0至8.0時將具有最高濃度。

Concentrations of available N are less sensitive to pH than concentration of available P.為了使磷可用於植物,土壤pH需要在6.0至7.5的範圍內。

如果pH低於6.0,磷開始與 (Fe) 和 (Al) 形成不溶性化合物,如果pH高於7.5,則開始與 (Ca)形成不溶性化合物。 在5.5至6.5的pH範圍內可以避免大多數養分缺乏,條件是土壤礦物質和有機物質含有開始的必需營養素。

水資源的可利用有關土壤pH

確定pH值

測定pH的方法包括:

  • Observation of soil profile: Certain profile characteristics can be indicators of either acid, saline, or sodic conditions. Strongly acidic soils often have poor incorporation of the organic surface layer with the underlying mineral layer. The mineral horizons are distinctively layered in many cases, with a pale eluvial (E) horizon beneath the organic surface; this E is underlain by a darker B horizon in a classic podzol horizon sequence. This is a very rough gauge of acidity as there is no correlation between thickness of the E and soil pH. E horizons a few feet thick in Florida usually have pH just above 5 (merely "strongly acid") while E horizons a few inches thick in New England are "extremely acid" with pH readings of 4.5 or below.[9][10][11] In the southern Blue Ridge Mountains there are "ultra acid" soils, pH below 3.5, which have no E horizon.[12] Presence of a caliche layer indicates the presence of calcium carbonates, which are present in alkaline conditions. Also, columnar structure can be an indicator of sodic condition.[13]
  • Observation of predominant flora. Calcifuge plants (those that prefer an acidic soil) include Erica, Rhododendron and nearly all other Ericaceae species, many birch (Betula), foxglove (Digitalis), gorse (Ulex spp.), and Scots Pine (Pinus sylvestris). Calcicole (lime loving) plants include ash trees (Fraxinus spp.), honeysuckle (Lonicera), Buddleja, dogwoods (Cornus spp.), lilac (Syringa) and Clematis species.
  • 使用便宜的pH測試試劑盒,其中在小樣本的土壤中與根據酸度/鹼度改變顏色的指示劑溶液混合。
  • 使用石蕊試紙,小的土壤樣品與蒸餾水混合,其中插入石蕊試紙條。如果土壤是酸性的,紙張變紅,如果鹼性,藍色。
  • 使用市售的電子pH計,插入潮濕的土壤中測量氫離子的濃度。

改變土壤酸鹼度

增加酸性土壤pH值

The most common amendment to increase soil pH is lime (CaCO3 or MgCO3), usually in the form of finely ground agricultural lime. The amount of lime needed to change pH is determined by the mesh size of the lime (how finely it is ground)and the buffering capacity of the soil. A high mesh size (60–100) indicates a finely ground lime, that will react quickly with soil acidity. Buffering capacity of soils is a function of a soils cation exchange capacity, which is in turn determined by the clay content of the soil, the type of clay and the amount of organic matter present. Soils with high clay content, particularly shrink–swell clay, will have a higher buffering capacity than soils with little clay. Soils with high organic matter will also have a higher buffering capacity than those with low organic matter. Soils with high buffering capacity require a greater amount of lime to be added than a soil with a lower buffering capacity for the same incremental change in pH.

可用於增加土壤pH的其它修正包括木灰,工業 CaO (生石灰)和牡蠣殼。白木柴灰包括對於需要離子如 Na+ (鈉), K+ (鉀), Ca2+ (鈣),的過程重要的金屬鹽,其對於選擇的菌群可能是或可能不是好的,但降低土壤的酸性質量。

這些產品通過 CO32− 與 H+ 反應產生 CO2 和 H2O,從而提高土壤的pH值。矽酸鈣通過除去游離氫離子來中和土壤中的活性酸度,從而增加pH。由於其矽酸鹽陰離子捕獲 H+離子(提高pH), 它形成單矽酸 (H4SiO4),中性溶質。

降低鹼性土壤pH值

參見

參考資料

  1. Soil Survey Division Staff. . Soil Conservation Service. U.S. Department of Agriculture Handbook 18. [2011-03-12]. (原始内容存档于2011-05-14).
  2. Sparks, Donald; Environmental Soil Chemistry. 2003, Academic Press, London, UK
  3. . [2016-12-22]. (原始内容存档于2020-09-28).
  4. Finck, Arnold. . Kiel: Hirt. 1976: 80. ISBN 3-554-80197-6.
  5. Brady, N. and Weil, R. The Nature and Properties of Soils. 13th ed. 2002
  6. Hansson et al (2011) Differences in soil properties in adjacent stands of Scots pine, Norway spruce and silver birch in SW Sweden. Forest Ecology and Management 262 522–530
  7. Rout, GR; Samantaray, S; Das, P. (PDF). Agronomie. 2001, 21 (1): 4–5 [11 June 2014]. doi:10.1051/agro:2001105. (原始内容存档 (PDF)于2014-08-19).
  8. . [2011-07-20]. (原始内容存档于2012-04-01).
  9. 页面存档备份,存于 Soilinfo PSU
  10. . [2009-01-28]. (原始内容存档于2009-02-07). USDA Myakka data
  11. . [2009-01-28]. (原始内容存档于2009-03-20). USDA Berkshire data
  12. 页面存档备份,存于 USDA Cataloochee data
  13. Buol, S. W., R. J. Southard, R.C. Graham and P.A. McDaniel. Soil Genesis and Classification. (5th) Edition, Ia. State Press p. 494. 2002
  14. Brady, N. and Weil, R. The Nature and Properites of Soils. 13th ed. 2002

外部連結

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