Soil Testing

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Introduction:

We all know that health of soil is equally important as health of any person. It is more applicable when it comes to ‘farming’. But, it is observed that now a day, ‘health of soil’ doesn’t get enough attention. People care more about only ‘cash crops and increasing quantity of the crop’. As a result of this, soil becomes unproductive. Awareness about ‘soil health’ should be increased to avoid this.

Why do we need ‘Soil Testing’?

Soil is an important matter for cultivation of any type of crop. Soil supplies many necessary nutrients required for healthy growth of a crop. The yield is largely dependent on the soil in which the crop grows. So, before cultivation, it is very important to check the soil for its nutrients. By checking the soil you will know whether the soil is having enough amount of nutrients or not. If any nutrient is less or more than the required amount, necessary measures can be taken.

In short following are the benefits of ‘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. 

When and How 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.

Do not take soil samples from the following areas:

Where cattle grazeUnder a treeGarbage area

Only 0.5 kg soil is required for soil testing.

Following is the correct procedure to collect soil for ‘soil sample’.

Procedure1. 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.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’.

Dig the pits as per the following figure. Yellow circles show location for the pit.

Dig each pit as shown in the figure. Take soil from the area shown in ‘brown’.

Floor surface

Plants need 16 essential nutrients for healthy growth and development.

Necessary nutrients for crop growth:Main nutrients:

Nitrogen (N), Phosphorus (P), Potassium(K)Secondary nutrients:

Calcium (Ca), Magnesium (Mg), Sulphur (S)Micro nutrients:

Iron (I), boron (B), zinc (Zn), copper (Cu), molybdenum (Mo), chlorine (Cl),

maganese(Mn)Nutrients from air:

Carbon (C), hydrogen (H)Nutrients from water:

Oxygen (O)Apart from above nutrients, there are some other parameters which also affect plant growth. These parameters are: Soil pH, Soil EC (Electrical Conductivity) and Soil OC (Organic Carbon). To judge the health of soil, these parameters should be checked.

Signs shown on plants because of nutritional deficiency

Nitrogen – Tree doesn’t get averageheight. 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.

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.

Boron – Young leaves become light in colour from petiole and start folding.

Molybdenum – Yellow/orange spots all over on matured leaves.

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.

pH testing is important because nutrient mobility ( transfer of nutrients ) from soil to plant through roots depends on pH of the soil.

Diagrams shows availability of nutrients according to its pH -

**We are using a readymade kit from ‘Prerana Lab’ for all the tests. So, the procedures are given assuming that you have ‘Prerana Lab kit’ with you to carry out the tests. Contact Details of Prerana Lab are given on the last slide.**

Checking pH of soil

1. Take 5 ml of pH-1 solution in the test bottle no. 1.2. By using a funnel, add two teaspoon (approx. 2 gm)

soil sample in the test bottle no. 13. Put the cap on the bottle and gently shake it for a

minute.4. Then keep the bottle still for 10 minutes. Now the soil

will settle down and there will be a layer of clear liquid on the top of it.

5. Place the test bottle in the pH colour comparator and compare the colour of the liquid in the test bottle with the colour on the comparator.

6. Note down the pH accordingly.

Soil type according to its pH value:

pH value Soil type

Below 4.5 Extremely acidic4.5-5.0 Highly acidic5.0-6.0 Medium acidic6.0-6.5 Slightly acidic7.0 Neutral7.0-7.5 Slightly alkaline7.5-8.0 Medium alkaline8.5-9.0 Highly alkalineAbove 9.0 Extremely alkaline

How to increase pH of the soil?

According to the existing pH of the soil, use Lime powder (Calcium carbonate or dolomite limestone) to increase the pH. 0.5-2.50 tons of Lime powder per hector of farm.

Use organic and grass fertilizers.

How to reduce pH of the soil?

If pH of soil is more, that means –ve ion deposited, soil becomes salty (alkaline). For small correction (if pH is slightly high @ 8 to 8.5) leaching of these ions will be useful. For leaching these deposited ions preparing trenches toward slop of land / fixing purported pipes (earthen / PVC) below 3 ft in soil can be done. Similarly, green manuring with crops like sunhemp (dencha) , Jute (Tag) etc are also helpful.For highly alkaline soils ( pH more than 8.5), gypsum (Sulphar) can be used. (Quantity of Sulphar is decided on the basic of soil type and pH of soil).

How to reduce the salts in the soil?

Scratch out all the salts which are there on the surface of the soil.

Make small compartments (of a height of 1 feet) of the field and fill it with water. Keep the water there for some time and let it go at once through an outlet. This way all salts will be washed off.Make sure that water is draining out properly.Use plenty of organic fertilizers.

Checking Nitrogen content in the soil

We are using a readymade kit from ‘Prerana Lab’ for this test.

1. Take 6 ml AN-1 solution in the test bottle no. 1.2. By using a funnel, add one teaspoon (approx. 1 gm) soil

sample in the test bottle no. 13. Put the cap on the bottle and gently shake it for a minute.4. Then keep the bottle still for 5 minutes. Now the soil will settle

down and there will be a layer of clear liquid on the top of it.5. Now, in an another test bottle (test bottle no. 2), take 2 ml

clear liquid from test bottle no. 1 with the help of a dropper. Make sure that there won’t be any traces of soil from test bottle no. 1 in the dropper.

6. Add 4 drops of AN-2 solution in test bottle no. 2.7. Put the cap on the bottle and shake it gently.8. Keep the bottle still for 5 minutes.9. Now shake the bottle and compare the colour of the solution in

the bottle (test bottle no. 2) with the colour screen given in the kit.

10.Note down the Nitrogen content in the soil accordingly.

Checking Phosphorus content in the soil

We are using a readymade kit from ‘Prerana Lab’ for this test.

1. Take 6 ml of EP-1 solution in the test bottle no. 1.2. By using a funnel, add one teaspoon (approx. 1 gm) soil sample in

the test bottle no. 1.3. Put the cap on the bottle and gently shake it for a minute.4. Then keep the bottle still for 5 minutes. Now the soil will settle down

and there will be a layer of clear liquid on the top of it.5. Now, in an another test bottle (test bottle no. 2), take 3 ml clear

liquid from test bottle no. 1 with the help of a dropper. Make sure that there won’t be any traces of soil from test bottle no. 1 in the dropper.

6. Add 6 drops of AP-2 solution in test bottle no. 2.7. Put the cap on the bottle and shake it gently.8. Now add 2 drops of AP-3 solution in test bottle no. 2.9. Put the cap on the bottle and shake it well.10.Now, the solution in test bottle no. 2 will look blue in colour.11.Compare this colour with the colour on ‘Phosphorus colour chart’

and accordingly note down the available phosphorus content in the soil.

Checking Potassium content in the soil:

We are using a readymade kit from ‘Prerana Lab’ for this test.1. Take 6 ml of AK-1 solution in test bottle no. 1.2. By using a funnel, add two teaspoon (approx. 2 gm) soil sample in

the test bottle no. 1.3. Put the cap on the bottle and gently shake it for a minute.4. Then keep the bottle still for 5 minutes. Now the soil will settle

down and there will be a layer of clear liquid on the top of it.5. Now, in an another test bottle (test bottle no. 2), take 2 ml clear

liquid from test bottle no. 1 with the help of a dropper. Make sure that there won’t be any traces of soil from test bottle no. 1 in the dropper.

6. Add one tablet of AK-2 in the test bottle no. 2. 7. Let the tablet dissolve in the solution. (Do not put the cap on the

bottle. It will take 5 to 6 minutes for the tablet to dissolve completely)

8. By now, colour of the solution in the test bottle no. 2 will change to light purple.

9. Now, take 1 ml of AK-4 solution in the red coloured syringes (available in the kit).

10.Add this solution (AK-4) in the test bottle no. 2 drop by drop till the colour of the solution in the bottle becomes blue.

Continued…

Colourchange

Drop count of AK-4

Available Potassium (kg/hector)

Potassium content in the soil

More than 22 drops Less than 100 Very less

21 to 22 drops 100-150 Less

19 to 20 drops 150-200 Medium

17 to 18 drops 200-250 Average

15 to 16 drops 250-300 High

Less than 15 drops More than 300 Very high

Continued from last slide…11.Keep a count of no. of drops of AK-4 solution added in the test

bottle no. 2 to change the colour of the solution.12.Refer the following chart to know the potassium content in the

soil.

Organic Carbohydrates (OC)

OC is a measure of organic matter available in the soil. It shouldn’t be less than 2% and shouldn’t be more than 30%. Bacteria grow properly if OC is in a proper limit. Carbon-Nitrogen (C:N) ratio also remains good in proper OC limit.

*C:N ratio - C:N ratio means ratio between Carbon present in the soil to the ration of nitrogen present in the soil. Say for example if C:N ration of soil is 10:1 that means there is 10 part of carbon to each part of nitrogen in the soil. All living organisms require to produce energy for their survival and for that they need carbon as their main source of energy. But if carbon (OC) contain in soil is very less then micro-organisms will try to use nitrogen for their energy needs. This will lead to reduction in nitrogen content of soil, which is very important for plant growth.

Checking OC content available in the soil

We are using a readymade kit from ‘Prerana Lab’ for this test.

1. Take 100 mg sample soil in test bottle no. 1. 2. Take 0.5 ml of OC-1 solution with the help of Green syringes

and add that to test bottle no. 1.3. Then add 80 drops of OC-2 solution in the same test bottle.

(Do this very carefully as this contain concentrated acid).4. Put the cap on the bottle and shake the bottle gently.5. Take 5 ml of OC-3 solution and add it in the test bottle no. 1.

Now keep the bottle still for 5 min. so that soil will set down and you will get a clear layer of liquid on the top. This liquid will have a colour.

6. Place this bottle in ‘organic carbon colour comparator’ to compare the colour of the liquid in the bottle with matching colour on the comparator.

7. Note down the percentage of organic carbon available in the soil accordingly.

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%.

Contact Details of Prerana Lab:

Prerna Laboratory, Prerna house, Plot No- 8, Near Chatrapati Bank, Vishal Nager (Jagtap dairy), Aundh-Wakad road, Pune -411028.Phone – 27274958 / 9371015199.

References:

www.vasat.icrisat.orgwww.faculty.rpcs.orghttp://www.terragis.bees.unsw.edu.au/terraGIS_soil/sp_soil_reaction_ph.html