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Ultra-acidic soils (pH < 3.5) and very strongly alkaline soils (pH > 9) are rare. [2] [3] Soil pH is considered a master variable in soils as it affects many chemical processes. It specifically affects plant nutrient availability by controlling the chemical forms of the different nutrients and influencing the chemical reactions they undergo.
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 .
The AASHTO Soil Classification System was developed by the American Association of State Highway and Transportation Officials, and is used as a guide for the classification of soils and soil-aggregate mixtures for highway construction purposes.
Limits between classes are arbitrary as there are few sharp divisions of the soil continuum in nature. Differences in soils are the result of the interaction of many factors: climate, organisms, parent material, relief and time. The soil classification system changes as knowledge grows through soil mapping and research in Canada and elsewhere.
A pH of 9.5 has 10 −9.5 moles hydronium ions per litre of solution (and also 10 −2.5 moles per litre OH −). A pH of 3.5 has one million times more hydronium ions per litre than a solution with pH of 9.5 (9.5 − 3.5 = 6 or 10 6) and is more acidic. [115] The effect of pH on a soil is to remove from the soil or to make available certain ions.
Nutrients in the soil are taken up by the plant through its roots, and in particular its root hairs.To be taken up by a plant, a nutrient element must be located near the root surface; however, the supply of nutrients in contact with the root is rapidly depleted within a distance of ca. 2 mm. [14] There are three basic mechanisms whereby nutrient ions dissolved in the soil solution are brought ...
Sulfuric material refers to soil material that has a pH of less than 4 owing to the oxidation of sulfidic material. [ 27 ] Sulfidic material refers to “soil materials containing detectable inorganic sulfides (≥0.01% sulfidic sulfur) that can exist as horizons or layers at least 30 mm thick or as surficial features”, [ 27 ] and is further ...
The original Proctor test, ASTM D698 / AASHTO T99, uses a 4-inch-diameter (100 mm) by 4.584-inch-high (116.4 mm) mold which holds 1/30 cubic feet of soil, and calls for compaction of three separate lifts of soil using 25 blows by a 5.5 lb hammer falling 12 inches, for a compactive effort of 12,375 ft-lbf/ft 3.