Soil Acidity

Soil reaction (pH) The relationship between the environment and development of acid or alkaline conditions in soil has been discussed with respect to formation of soils from the parent rock materials. Soil acidity comes in part by the formation of carbonic acid from carbon dioxide of biological origin and water. Other acidic development may come from acid residues of weathering, shifts in mineral types, loss of alkaline or basic earth elements by leaching, formation of organic or inorganic acids by microbial activity, plant root secretions, and man-made pollution of the soil, especially by industrial wastes. 

Soil Acidity. Ulrich, B. Sumner, M.E. Eds. Springer-Verlag Berlin. 1991. 

Plants are highly sensitive to soil acidity because many equilibria involving plant nutrients are affected by pH. Phosphorus is a primary example. This essential element for plant growth occurs in soils mainly as phosphates, which are subject to phosphate-hydrogen phosphate equilibria. Consequently, phosphorus is... 

The colors of flowering plants such as hydrangeas are highly sensitive to soil acidity. At pH > 6.5, these showy flowers are deep pink, but at pH < 5, the blossoms are vivid blue. The chemistry of these changes involves complexation of aluminum by pigments that have acidic groups, as the structures show. 

Several processes act to increase soil acidity. As organic matter decays, it forms many organic carboxylic acids. Peat moss, for example, is entirely organic and has quite low pH, around 4. Acid rain, the result of... 

To reduce soil acidity and keep cropland productive, farmers amend the soil by liming, which is the application of limestone. Limestone is calcium carbonate, and the carbonate anion is the conjugate base of hydrogen carbonate. Liming therefore increases the concentration of hydroxide in the soil, thereby increasing the pH C03 ((3 q) + H2 0(/) HC03 (<3 g) + OH (<3 q)... 

Tolley MD, DeLaune RD, Patrick WH. The effect of sediment redox potential and soil acidity on nitrogen uptake, anaerobic root respiration, and growth of rice (Oryza saliva). Plant Soil. 1986 93 323-331. 

Thomas GW. Soil pH and soil acidity. In Bartels JM (ed.), Methods of Soil Analysis Part 3 Chemical Methods. Madison, WI Soil Science Society of America and American Society of Agronomy 1996, pp. 475 490. 

Titration is a general word used in many different disciplines. Any time a solution of known concentration is used to find the amount of an unknown component in another solution, it can be called a titration. Although this type of analysis is very old, it still finds widespread used in chemical analysis. Titrations are used in soil analysis to measure soil acidity, soil organic matter content, and various constituents isolated from soil, particularly ammonia. 

The relative contribution of the pairs H3O+-H2O and H2CO3-HCO3 to the overall soil acidity diffusion coefficient is given by the term in parentheses in Eqnation (2.33) and is plotted at different pHs in Figure 2.9(a). The figures shows... 

Nye PH, Ameloko AY. 1986. A comparison of measured and theoretical soil acidity diffusion coefficients over a wide range of pH. Journal of Soil Science 37 191-196. 

The hydrolysis half-lives at pH 7.4 and 20 and 37.5 °C were 130 and 27 d, respectively. At pH 6.1 and 20 °C, the hydrolysis half-life was 170 d (Freed et al, 1979). When equilibrated with a prereduced pokkali soil (acid sulfate), parathion instantaneously degraded to aminoparathion. The quick rate of reaction was reportedly due to soil enzymes and/or other heat labile substances. Desethyl aminoparathion was also identified as a metabolite in two separate studies (Wahid and Sethunathan, 1979 Wahid et al., 1980). The half-lives for the degradation of parathion in a silty clay (pH 5.5) and sandy clay (pH 6.9) were 23 and 22 d, respectively (Sattar, 1990). 

Aluminum reacts with acids and strong alkali solutions. Once aluminum is cut, the fresh surface begins to oxidize and form a thin outer coating of aluminum oxide that protects the metal from further corrosion. This is one reason aluminum cans should not be discarded in the environment. Aluminum cans last for many centuries (though not forever) because atmospheric gases and soil acids and alkalis react slowly with it. This is also the reason aluminum is not found as a metal in its natural state. 

Jansen S, Malaty AM, Nabara S, Johnson E, Ghabbour E, Davies G, Vamum JM (1996) Structural modeling in humic acids. Mater Sci Eng C4 175-179 Kerr HW (1928) The identification and comparison of soil aluminosilicate active base exchange and soil acidity. Soil Sci 26 385-398... 

Sometimes it may be desirable to add nutrients in a form more quickly available or more concentrated than those derived from the above soil-building techniques. It may also be desirable to adjust the soil acidity so the nutrients present are more available to vegetable plants. There are a number of ways to add nutrients and adjust soil pH that are acceptable to organic gardeners. 

Approximately 40 to 50% of the total amount of phenolics sorbed was retained by the organic matter fraction (27). In surface soil layers, organic matter is frequently intimately associated with the mineral components present, providing a large surface area and reactive sites for surface interaction. Soil acidity has a major influence on phenolic adsorption by the organic carbon fraction, since the degree of dissociation of the phenolic acids is pH-dependent. Whitehead and coworkers (28) observed that the extractability of several phenolic acids was highly dependent upon the extractant pH between pH 6 and 14. The amount extractable continually increased with extractant pH thus the extracted acids could not be readily classified into distinct fractions. 

Soil (acid extractable) Shake soil with 0.1 A hydrochloric acid for 5 minutes complete 3 times AAS No data No data Baker and Amacher 1982... 

Neutral and alkaline soils Acidic soils Chronic use Short-term use Canada... 

Agriculture therefore depends on there being a sufficient supply of inorganic nutrients to plants. Cereals, vegetables, fruit-bearing trees or plants, and animal fodder require bioavailable nutrients, that is, nutrients in forms that they can use. Since intensive agriculture depletes many natural nutrients, synthetic nutrients (fertilizers) must be supplied.1-7 In particular, we need to fix the inert N2 of the atmosphere as soluble, reactive compounds such as nitrates, ammonia, and ammonium salts. Other major fertilizer components are sulfate, potassium, and phosphate ions. It may also be necessary to provide trace nutrients, such as cobalt compounds, or to remove excess soil acidity by treatment with lime (CaO). World fertilizer demand in the year 2001 is expected to be about 1.5 x 10s metric tons N, 7.6 x 107 metric tons P2O5, and 6.7 x 107 metric tons K2O these projections represent an... 

The most important industrial alkalis are the weak alkali ammonia (Section 9.3), caustic soda (sodium hydroxide), and lime (calcium oxide).1-6 For many industrial and agricultural purposes, the most economical source of alkali is lime, which is used in steelmaking and other metallurgical operations ( 45% of U.S. production of lime), in control of air pollution from smokestack gases (Chapter 8), in water and sewage treatment (Sections 9.6 and 14.5), in pulp and paper production (Section 10.4), in reduction of soil acidity, in cement and concrete manufacture (indirectly, as discussed later), and in many chemical processes such as paper making (Section 10.4). In short, lime is one of the most important of all chemical commodities. 

Soil - Acidic food fat, oil and grease Surface - Cotton, cotton/polyester, polyester Application Method - Industrial washing machine Manufacture - Mix tank with propeller stirrer... 

Soil - Acidic food fat, oil and grease blood, sebum and body waste... 

The soils of humid regions are commonly low in calcium thus, ground limestone usually is applied tu add the clement, reduce the toxicity uf aluminum and manganese, and correct soil acidity. The soils of dry areas are frequently rich in calcium. There is little evidence to indicate a strung relationship between human nutrition and calcium excesses or deficiencies in the soil. Even wiih farm livestock, most calcium deficiencies are not related to levels of av ailable calcium in the sail. The reason for this anomaly is evident when one examines some of the controls over the movement of calcium in Ihe food chain. 

Adding limestone to soils to correct soil acidity and to supplement available calcium will, of course, indirectly affect human and calcium nutrition, but this is a difficult quantity in measure. 

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