1. PRESENTATION
SOIL SAMPLING
H. E. J. Research Institute of Chemistry, International Center for
Chemical & Biological Sciences, University of Karachi-75270,
Pakistan.
3. Why do we need Soil Testing ??
•Soil testing encourages plant growth by providing
the best fertilizer recommendations.
•It diagnoses whether there is too little or too much of
a nutrient.
•‘Soil testing’ promotes environmental quality.
•It also saves money that might otherwise be spent
on unneeded fertilizer.
4. Soil sampling
When to take a sample of a soil?
Soil sample must be taken at the right time and in the right way as
described here:
• Before planting anything in the field and after you take out the crop
• Before application of any organic or chemical fertilizers
• Three months after application of any organic or chemical
fertilizers.
5. Do not take soil samples from the
following areas:
Where cattle graze
Under a tree
Garbage area
6. How to take a sample of a soil?
Only 0.5 kg soil is required for soil testing.
Following is the correct procedure to collect soilfor‘soil
sample’.
Procedure
1. For ‘soil testing 'soil is taken from 15 different places.
2. Dig a‘V’shape pit in the ground which is 15 cm deep.
Take soil sample (2 to 3 cm thick) from one side of it.
7. 3. Follow the same procedure to take samples from 15 different places.
4. Clean the samples by removing any garbage if present in the soil.
5. Mix all the samples very well (Make 4 equal parts of the mixed
sample. Then mix two diagonally opposite parts with each other. Repeat
the procedure for 4/5 times)
6. Take 0.5 kg of the sample for ‘soil testing’.
8. Dig the pits as per the following figure. Yellow circles
show location for the pit.
9. Dig each pit as shown in the figure. Take
soil from the area shown in ‘brown’.
11. Signs shown on plants because of nutritional
deficiency
Nitrogen – Tree doesn’t get average height.
Leaves become yellow.
Phosphorus – Growth of a plant stops
Potassium – Leaves become reddish yellow on
the edges while inner part of the leaves remain
green.
12. Calcium –Tender leaves dry and plant dies
Magnesium – Leaves start drying from the tip.
Sulphur –Brownish spots on leaves.
Iron – Main veins of a leaf become green.
Manganese –Younger leaves show chlorotic
spots between the veins.
Copper – leaves become yellow and stop growing
and then fall off.
13. pH of soil
• Apart from soil nutrients one more factor affect the yield. That
factor is ‘pH’.
• The soil pH is a measure of the acidity or basicity in soils. It is
measured in pH units. The pH scale goes from 0 to 14 with pH 7 as the
neutral point.
• Hydrogen ions present in the soil decide pH value of the soil. When
+ve ions get washed off through water, soil becomes acidic.
Similarly, when amount of Calcium, Sodium in soil increases, soils
become alkaline. Simply we can say that low pH means sour and high
pH means salty soil.
14. Soil type according to its pH value:
pH value
• Below 4.5
• 4.5-5.0
• 5.0-6.0
• 6.0-6.5
• 7.0
• 7.0-7.5
• 7.5-8.0
• 8.5-9.0
• Above 9.0
Soil type
• Extremely acidic
• Highly acidic
• Medium acidic
• Slightly acidic
• Neutral
• Slightly alkaline
• Medium alkaline
• Highly alkaline
• Extremely alkaline
15. Suggesting fertilizers according to the ‘soil testing’ results
• Main objective of soil testing is to know the content or amount of nutrients (for eg.
Nitrogen, Phosphorus, Potassium, pH, Organic carbon etc.) available in the soil. Balanced
amount of all these nutrients are very important for healthy growth of any crop.
• Fertilizers are suggested depending upon the amount of nutrients available in the soil as
well as requirement of the same for the crop. Soil nutrients are generally measured as ‘low,
medium and high’.
•If available soil nutrients are very low, increase the dose of fertilizer by
50%.
•If available soil nutrients are low, increase the dose of fertilizer by 25%.
•If available soil nutrients are medium or slightly more than medium, no need to change the
fertilizer dose.
•If available soil nutrients are very high, reduce the dose of fertilizer by 50%.
•If available soil nutrients are high, reduce the dose of fertilizer by 25%.
