How cab ph of soil be determined
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Methods of pH Measurement
There are many different ways of measuring the pH of soil. Some use a saturated paste extract, others use a 1:5 dilution of soil: water, and then take a pH measurement on the resulting solution with a laboratory meter. Others use the 1:5 dilution, but instead of water they use a dilute Calcium Chloride (CaCl²) solution. As a rough guide, the pH in CaCl² is usually 0.8 pH lower than in water, but can be as much as 2.0 pH units lower on grey sands. Ensure that you check the method used to measure you soil pH so that you are comparing similar methods.
USING A CALCIUM CHLORIDE SOLUTION FOR SOIL TEST
Using a dilute CaCl² solution will probably give more consistent results than using rainwater or diluted water. When the soil is diluted with water , most of the H+ ions tend to remain attracted to the soil particles and are not released into the soil solution. The addition of small amounts of calcium chloride provides Ca2+ ions to replace some of the H+ ions on the soil particles, forcing the hydrogen ions into the solution and making their concentration in the bulk solution closer to that found in the field. The pH measured in CaCl² is almost always lower than pH of the same soil measured in water due to the higher concentration of H+. The procedure gives a value similar to that for natural soil solution because the soil solution also contains dissolved Ca2+ and other ions
Make up a dilute CaCl² solution with distilled/deionised water to use as you need it. Ready made calcium chloride solutions often do not keep for very long, so buy CaCl² and make the solution yourself. The calcium chloride is usually the dehydrate form (water is attached to the crystals - it will have this written on the label of the container - CaCl².2H²O). Dissolve approximately 7.5g of the salt in 5 litres of distilled/deionised water. If you are using a form of calcium chloride crystals without any water attached (CaCl²), dissolve about 5.5g of the salt in 5 litres. There is no need to be very accurate in your weighing as small errors will not effect the results.
Methods for Soil pH
Use the spoon to weigh out about 10g (to the nearest half gram), of your soil into the container. Add 50ml of distilled water to the soil. Any rough measurement ensuring a 1:5 diluted will suffice. Shake the container for about 2-3 minutes then allow the soil to settle for 2 minutes. If your soil has a high clay content and you require a very accurate result, it may not be necessary to filter the suspension. If filtering is note required, measure the pH value on the water above the soil in the container. Ensure you get a steady reading on the digital readout. Always wash your containers out before testing your next sample.
Testing Soil pH Using pH Tester
Measurement of pH in soil is very common as it affects the relative availability of soil nutrients. If the pH is not within an acceptable range, growth will be curtailed and erosion potential is increased. The ability of the soil to provide adequate nutrition to the plant depends on four factors:
- the amount of various essential elements present in the soil
- their forms of combination
- the processes by which these elements become available to plants
- the soil solution and its pH
The amount of various elements present in the soil depends on the nature of the soil and on its organic matter content since it is a source of several nutrient elements. Soil nutrients exist both as complex, insoluble compounds and as simple forms usually soluble in soil water and readily available to plants. The complex forms must be broken down through decomposition to the simpler and more available forms in order to benefit the plant. These available forms are summarized in Table A. The pH value is a measure of acidity or alkalinity. The effect of pH on availability of essential elements is shown below.
Table A The effect of soil pH on availability of plant nutrients (From Hunger Signs in Crops, edited by H.B. Sprague, 1964, pg. 18)
Iron, manganese and zinc become less available as the pH is raised from 6.5 to 7.5 or 8.0. Molybdenum and phosphorus availability, on the other hand is affected in the opposite way, being greater at the higher pH levels. At very high pH values the bicarbonate ion (HCO3) may be present in sufficient quantities to interfere with the normal uptake of other ions and thus detrimental to optimum growth. When inorganic salts are placed in a dilute solution they dissociate into electrically charged units called ions. These ions are available to the plant from the surface of the soil colloids and from salts in the soil solution. The positively charged ions (cations) such as potassium (K+) and calcium (Ca2+) are mostly absorbed by the soil colloids, whereas the negatively charged ions (anions), such as chloride (Cl-) and sulphate (SO4-) are found in the soil solution
There are many different ways of measuring the pH of soil. Some use a saturated paste extract, others use a 1:5 dilution of soil: water, and then take a pH measurement on the resulting solution with a laboratory meter. Others use the 1:5 dilution, but instead of water they use a dilute Calcium Chloride (CaCl²) solution. As a rough guide, the pH in CaCl² is usually 0.8 pH lower than in water, but can be as much as 2.0 pH units lower on grey sands. Ensure that you check the method used to measure you soil pH so that you are comparing similar methods.
USING A CALCIUM CHLORIDE SOLUTION FOR SOIL TEST
Using a dilute CaCl² solution will probably give more consistent results than using rainwater or diluted water. When the soil is diluted with water , most of the H+ ions tend to remain attracted to the soil particles and are not released into the soil solution. The addition of small amounts of calcium chloride provides Ca2+ ions to replace some of the H+ ions on the soil particles, forcing the hydrogen ions into the solution and making their concentration in the bulk solution closer to that found in the field. The pH measured in CaCl² is almost always lower than pH of the same soil measured in water due to the higher concentration of H+. The procedure gives a value similar to that for natural soil solution because the soil solution also contains dissolved Ca2+ and other ions
Make up a dilute CaCl² solution with distilled/deionised water to use as you need it. Ready made calcium chloride solutions often do not keep for very long, so buy CaCl² and make the solution yourself. The calcium chloride is usually the dehydrate form (water is attached to the crystals - it will have this written on the label of the container - CaCl².2H²O). Dissolve approximately 7.5g of the salt in 5 litres of distilled/deionised water. If you are using a form of calcium chloride crystals without any water attached (CaCl²), dissolve about 5.5g of the salt in 5 litres. There is no need to be very accurate in your weighing as small errors will not effect the results.
Methods for Soil pH
Use the spoon to weigh out about 10g (to the nearest half gram), of your soil into the container. Add 50ml of distilled water to the soil. Any rough measurement ensuring a 1:5 diluted will suffice. Shake the container for about 2-3 minutes then allow the soil to settle for 2 minutes. If your soil has a high clay content and you require a very accurate result, it may not be necessary to filter the suspension. If filtering is note required, measure the pH value on the water above the soil in the container. Ensure you get a steady reading on the digital readout. Always wash your containers out before testing your next sample.
Testing Soil pH Using pH Tester
Measurement of pH in soil is very common as it affects the relative availability of soil nutrients. If the pH is not within an acceptable range, growth will be curtailed and erosion potential is increased. The ability of the soil to provide adequate nutrition to the plant depends on four factors:
- the amount of various essential elements present in the soil
- their forms of combination
- the processes by which these elements become available to plants
- the soil solution and its pH
The amount of various elements present in the soil depends on the nature of the soil and on its organic matter content since it is a source of several nutrient elements. Soil nutrients exist both as complex, insoluble compounds and as simple forms usually soluble in soil water and readily available to plants. The complex forms must be broken down through decomposition to the simpler and more available forms in order to benefit the plant. These available forms are summarized in Table A. The pH value is a measure of acidity or alkalinity. The effect of pH on availability of essential elements is shown below.
Table A The effect of soil pH on availability of plant nutrients (From Hunger Signs in Crops, edited by H.B. Sprague, 1964, pg. 18)
Iron, manganese and zinc become less available as the pH is raised from 6.5 to 7.5 or 8.0. Molybdenum and phosphorus availability, on the other hand is affected in the opposite way, being greater at the higher pH levels. At very high pH values the bicarbonate ion (HCO3) may be present in sufficient quantities to interfere with the normal uptake of other ions and thus detrimental to optimum growth. When inorganic salts are placed in a dilute solution they dissociate into electrically charged units called ions. These ions are available to the plant from the surface of the soil colloids and from salts in the soil solution. The positively charged ions (cations) such as potassium (K+) and calcium (Ca2+) are mostly absorbed by the soil colloids, whereas the negatively charged ions (anions), such as chloride (Cl-) and sulphate (SO4-) are found in the soil solution
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For checking the pH of the soil, the steps are given underneath:
Take about 2 gram of soil in a test tube and add 5 ml of water to it. Shake the test tube well. Filter the contents of the test tube through a filter paper and colours the filtrate. Find the pH of this filtered by using the universal indicator paper. This will give us the pH of the given sample of soil.
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To maintain the pH of a soil-Chemicals are added to soil to adjust its PH and make it suitable for growing plants such as crops.
Most often the soil in the fields is too acidic. If the soil is too acidic (having low pH) then it is treated with materials like quicklime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate). .
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I HOPE THIS'LL HELP YOU
Take about 2 gram of soil in a test tube and add 5 ml of water to it. Shake the test tube well. Filter the contents of the test tube through a filter paper and colours the filtrate. Find the pH of this filtered by using the universal indicator paper. This will give us the pH of the given sample of soil.
.
.
To maintain the pH of a soil-Chemicals are added to soil to adjust its PH and make it suitable for growing plants such as crops.
Most often the soil in the fields is too acidic. If the soil is too acidic (having low pH) then it is treated with materials like quicklime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate). .
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.
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I HOPE THIS'LL HELP YOU
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