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The soil pH usually increases when the total alkalinity increases, but the balance of the added cations also has a marked effect on the soil pH. For example, increasing the amount of sodium in an alkaline soil tends to induce dissolution of calcium carbonate , which increases the pH.
Original file (1,650 × 1,275 pixels, file size: 78 KB, MIME type: application/pdf, 2 pages) This is a file from the Wikimedia Commons . Information from its description page there is shown below.
English: I retrieved the soil pH maps from . In GIMP 2.4.3 I used the "Select by Color Tool" (threshold 15.0) to create pH-specific maps. Note that the original maps do not indicate actual pH values in the pH scale. For soils with acidic pH, I included the colors indicated by the leftmost 14 bars in the pH scale, ranging from red to pink.
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.
Effect of soil pH on cation-exchange capacity. The amount of negative charge from deprotonation of clay hydroxy groups or organic matter depends on the pH of the surrounding solution. Increasing the pH (i.e. decreasing the concentration of H + cations) increases this variable charge, and therefore also increases the cation-exchange capacity.
The Unified Soil Classification System (USCS) is a soil classification system used in engineering and geology to describe the texture and grain size of a soil. The classification system can be applied to most unconsolidated materials, and is represented by a two-letter symbol. Each letter is described below (with the exception of Pt):
Water with excess H 3 O + ions is called acid (pH < 7), and water with excess OH – ions is called alkaline or rather basic (pH > 7). Soil moisture with pH < 4 is called very acid and with pH > 10 very alkaline (basic). H 2 CO 3 (carbonic acid) is unstable and produces H 2 O (water) and CO 2 (carbon dioxide gas, escaping into the atmosphere).
English: Effect of pH on the root availability of the essential elements in soil. Blue denotes the ideal soil pH for the majority of plants (slightly acidic). Inspired by an illustration from the North Carolina Extension Gardener Handbook