Editing Soil pH (section)

==Determining pH==
Methods of determining pH include:
*Observation of soil profile: certain profile characteristics can be indicators of either acid, saline, or sodic conditions.  Examples are:<ref>{{cite book |isbn=978-0813828732 |title=Soil genesis and classification |edition=Fifth |year=2003 |access-date=12 February 2023 |url=https://archive.org/details/soilgenesisclass0000unse_h4i0 |editor-last1=Buol |editor-first1=Stanley W. |editor-last2=Southard |editor-first2=Randal J. |editor-last3=Graham |editor-first3=Robert C. |editor-last4=McDaniel |editor-first4=Paul A. |publisher=[[Wiley-Blackwell|Wiley–Blackwell]] |location=Hoboken, New Jersey }}</ref>
**Poor incorporation of the organic surface layer with the underlying mineral layer – this can indicate strongly acidic soils;
**The classic [[podzol]] [[Soil horizon|horizon]] sequence, since podzols are strongly acidic: in these soils, a pale eluvial (E) horizon lies under the organic surface layer and overlies a dark B horizon;
**Presence of a [[caliche]] layer indicates the presence of calcium carbonates, which are present in alkaline conditions;
**Columnar [[Soil structure|structure]] can be an indicator of [[Soil salinity|sodic]] condition.
*Observation of predominant flora. [[Calcifuge]] plants (those that prefer an acidic soil) include ''[[Erica (plant)|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 (plant)|Cornus]]'' spp.), lilac (''[[Syringa]]'') and ''[[Clematis]]'' species.
*Use of an inexpensive pH testing kit, where in a small sample of soil is mixed with [[pH indicator|indicator]] solution which changes colour according to the acidity.
*Use of [[litmus paper]]. A small sample of soil is mixed with distilled water, into which a strip of litmus paper is inserted. If the soil is acidic the paper turns red, if basic, blue.
*Certain other fruit and vegetable pigments also change color in response to changing pH. [[Blueberry]] juice turns more reddish if acid is added, and becomes indigo if titrated with sufficient base to yield a high pH. Red [[cabbage]] is similarly affected.
*Use of a commercially available electronic [[pH meter]], in which a glass or solid-state [[electrode]] is inserted into moistened soil or a mixture (suspension) of soil and water; the pH is usually read on a digital display screen.<ref>{{Cite web |title=Evolution of the pH Meter |url=https://www.labmanager.com/evolution-of-the-ph-meter-19282 |access-date=2023-09-22 |website=Lab Manager |language=en}}</ref>
* In the 2010s, [[Spectrophotometry|spectrophotometric]] methods were developed to measure soil pH involving addition of an indicator dye to the soil extract.<ref>{{cite journal |last1=Bargrizan |first1=Sima |last2=Smernik |first2=Ronald J. |last3=Mosley |first3=Luke M. |title=Development of a spectrophotometric method for determining pH of soil extracts and comparison with glass electrode measurements |journal=[[Soil Science Society of America Journal]] |date=November 2017 |volume=81 |issue=6 |pages=1350–58 |doi=10.2136/sssaj2017.04.0119 |bibcode=2017SSASJ..81.1350B |url=https://www.researchgate.net/publication/318960029 |access-date=12 February 2023}}</ref> These compare well to [[glass electrode]] measurements but offer substantial advantages such as lack of drift, liquid junction and suspension effects.

Precise, repeatable measures of soil pH are required for scientific research and monitoring. This generally entails laboratory analysis using a standard protocol; an example of such a protocol is that in the [[United States Department of Agriculture|USDA]] Soil Survey Field and Laboratory Methods Manual.<ref name="USDA2014">{{cite book |last1=Soil Survey Staff |editor1-last=Rebecca Burt and Soil Survey Staff |title=Kellogg Soil Survey Laboratory Methods Manual. Soil Survey Investigations Report No. 42, Version 5.0 |date=2014 |publisher=United States Department of Agriculture, Natural Resources Conservation Service |pages=276–279 |url=https://data.neonscience.org/documents/10179/2357445/KelloggSSL_MethodsManual_Report42Version5_2014/da9589dd-3278-402b-a5d4-02dc0c9c762c |access-date=19 February 2023}}</ref> In this document the three-page protocol for soil pH measurement includes the following sections: Application; Summary of Method; Interferences; Safety; Equipment; Reagents; and Procedure.{{Quote frame |quote=
Summary of Method
<poem>
The pH is measured in soil-water (1:1) and soil-salt (1:2 <chem>CaCl2</chem>) solutions. For convenience, the pH is initially measured in water and then measured in <chem>CaCl2</chem>. With the addition of an equal volume of 0.02 M <chem>CaCl2</chem> to the soil suspension that was prepared for the water pH, the final soil-solution ratio is 1:2 0.01 M <chem>CaCl2</chem>.
A 20-g soil sample is mixed with 20 mL of reverse osmosis (RO) water (1:1 w:v) with occasional stirring. The sample is allowed to stand 1 h with occasional stirring. The sample is stirred for 30 s, and the 1:1 water pH is measured. The 0.02 M <chem>CaCl2</chem> (20 mL) is added to soil suspension, the sample is stirred, and the 1:2 0.01 M <chem>CaCl2</chem> pH is measured (4C1a2a2).
</poem>
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|source=Summary of the USDA NRCS method for soil pH determination<ref name="USDA2014"/>}}