Testing Soil pHSoil usually has pH between 4.5 and 8.5. Soils at pH 4 to 5 are very acid.Soils over 7.8 are too alkaline for most plants. Most vegetables, field crops, fruits and flowers do best in soils that have pH 6.5 to 7 (slightly acid to neutral). Other pH Paper pH Books Test Water |
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All
Range pH Paper- 0 to 14 $19.00 a kit. Covers the entire pH range with 2 rolls of pH paper: 0-11 pH and 12-14 pH. Each roll is15 feet. Includes dispenser for each roll and color charts. The roll of 0-11 pH paper is graduated in steps of 1.0 pH unit. The roll of 12-14 pH paper is graduated in steps of 0.5 pH unit. All purpose pH paper. Tests all ranges of soil pH. |
We ship to USA only. See larger pH Paper photo 4.5 to 7.5 pH |
pH
Paper 4.5 - 7.5 $19.90 for a package of 75 feet. 1 Package=5 Rolls of 15 feet each. A total of 75 feet of litmus paper. The pH paper is graduated in steps of 0.5 pH units. Two small color charts furnished within each refill. Includes free large pH color chart. This will test soil pH in ranges that are not too acidic or alkaline. |
Testing Soil pH
Soil pH is important for growing plants. Soils usually have pHs between 4.5 and 8.5. Soils at pH 4 to 5 are very acid or sour and only a few plants will grow in them. Likewise, soils over 7.8 are too alkaline or sweet for most plants to thrive. Most vegetables, field crops, fruits and flowers do best in soils that have a pH of 6.5 to 7 (very slightly acid to neutral).
The procedure below works with commercial pH indicator paper as well as with litmus paper. The commercial pH paper, which has a different color for each pH, will be more informative. Carbon dioxide must be removed from the water used in this activity, as it will lower the pH. CO2(aq) + H2O <-> H2CO3(aq) <-> H+(aq)+ HCO3-(aq). The hydrogen ion (H+) released by this equilibrium increases the acidity and decreases the pH of the solution.
Distilled water needs to be boiled to remove the CO2(aq) [carbon dioxide gas which is in solution]. Store in a sealed container after boiling to keep out CO2.
Material Needed
Soil. There may be considerable variation in the soil pH from one spot in a field or lawn to another. To determine the average soil pH of a field or lawn, collect soil from several locations and combine into one sample.
Acid-base or pH indicator paper
Filter paper or coffee filter
Plastic cup
Boiled and cooled distilled water
How to Test Soil
1. Lay a strip of acid-base or pH indicator paper in the bottom of a plastic cup.
2. Place a piece of filter paper or a coffee filter over the indicator paper. The edges of the filter should form a cup shape within the plastic cup.
3. Put the soil sample into the cup formed by the filter.
4. Add enough of the boiled, cooled water to moisten the soil without soaking it.
5. Let sit for 5 minutes. During this time, the water should move through the soil and filter and reach the indicator paper. The acid- base or pH character of the soil will be transferred to the water.
6. Invert the cup over a container to catch the soil.
7. Check the indicator paper to determine the acid-base character or pH of the soil.
pH Affects Nutrients, Minerals and Growth
Soil pH greatly effects the solubility of minerals or nutrients. Fourteen of the seventeen essential plant nutrients are obtained from the soil. Before a nutrient can be used by plants, it must be dissolved in the soil solution. Most minerals and nutrients are more soluble or available in acid soils than in neutral or slightly alkaline soils.
Phosphorus is never readily soluble in the soil but is most available in soil with a pH range centered around 6.5. Extremely and strongly acid soils (pH 4.0-5.0) can have high concentrations of soluble aluminum, iron and manganese which may be toxic to the growth of some plants. A pH range of approximately 6 to 7 promotes the most ready availability of plant nutrients.
But some plants, such as azaleas, rhododendrons, blueberries, white potatoes and conifer trees, tolerate strong acid soils and grow well. Also, some plants do well only in slightly acid to moderately alkaline soils. However, a slightly alkaline (pH 7.4-7.8) or higher pH soil can cause a problem with the availability of iron to pin oak and a few other trees causing chlorosis of the leaves which will put the tree under stress leading to tree decline and eventual mortality.
The soil pH can also influence plant growth by its effect on activity of beneficial microorganisms. Bacteria that decompose soil organic matter are hindered in strong acid soils. This prevents organic matter from breaking down, resulting in an accumulation of organic matter and the tie up of nutrients, particularly nitrogen, that are held in the organic matter.
Changes in Soil pH
Soils tend to become acidic as a result of: (1) rainwater leaching away basic ions (calcium, magnesium, potassium and sodium); (2) carbon dioxide from decomposing organic matter and root respiration dissolving in soil water to form a weak organic acid; (3) formation of strong organic and inorganic acids, such as nitric and sulfuric acid, from decaying organic matter and oxidation of ammonium and sulfur fertilizers. Strongly acid soils are usually the result of the action of these strong organic and inorganic acids.
Lime is usually added to acid soils to increase soil pH. The addition of lime not only replaces hydrogen ions and raises soil pH, thereby eliminating most major problems associated with acid soils but it also provides two nutrients, calcium and magnesium to the soil. Lime also makes phosphorus that is added to the soil more available for plant growth and increases the availability of nitrogen by hastening the decomposition of organic matter. Liming materials are relatively inexpensive, comparatively mild to handle and leave no objectionable residues in the soil.
Some common liming materials are: (1) Calcic limestone which is ground limestone; (2) Dolomitic limestone from ground limestone high in magnesium; and (3) Miscellaneous sources such as wood ashes. The amount of lime to apply to correct a soil acidity problem is affected by a number of factors, including soil pH, texture (amount of sand, silt and clay), structure, and amount of organic matter. In addition to soil variables the crops or plants to be grown influence the amount of lime needed. In addition to monitoring soil pH, the nutrient status of the soil should be examined.
Nutrient availability and microbial activity as affected by soil pH.
The wider the band, the greater the availability or activity.
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