Method of soil testing (IGKV RAIPUR C.G)

1. Presentation On
Soil Testing.

2. Introduction:
• Soil testing is an acceptably accurate and
rapid soil chemical analysis for assessing
available nutrient status for making
fertilizer recommendations.
• The result of a soil test is known as soil test
value.
• A soil test value measures a part of the
total nutrient supply in the soil and
represents only as an index of nutrient
ability.

3. Objectives:
• Soil test programmes have following
objectives:
To provide an index of nutrient ability.
To predict the probability of profitable
response to fertilizer.
To provide a basis for fertilizer
recommendation.
To evaluate the soil fertility status and a
county soil area or a statewide basis by
the use of the soil test summaries.

4. Phases:
• Phases of soil testing programme are as
follows:
Collecting the soil samples.
Extraction and determining the available
nutrients.
Calibrating and interpreting the analytical
results.
Making the fertilizer recommendation and
management.

5. 1. Soil Sampling
• Sampling is done to obtain a composed
soil sample representing a seemingly
uniform area or field with similar
cropping and management history.
A. SamplingTime
 Soil samples can be taken any time that
soil conditions permit, but sampling
directly after fertilization should be
avoided.
 It is important to sample at similar times
year after year for comparing analysis at
regular time intervals.

6. B. Samplingdepth
 For most purposes, soil sampling is done
to a depth of about 20cm.
 In some case , especially in irrigated
areas sampling to a depth of 60-100cm
is desirable, especially for monitoring
nitrate leaching.
 Depth wise soil samples should be taken
where there is a concern about Boron
toxicity.
C. SamplingTools
 Augers are generally used for soil
sampling.

7.  A uniform slice should be taken from the
surface to the depth of insertion of the
tool; the same volume of soil should be
obtained in each sub sample.
 Soil samples for micro nutrient analysis
should be taken using stainless steel
auger.
D. Drying ofSoilsamples
 The soil fresh samples received in the
laboratory should be dried in wooden or
enameled trays.
 During drying, the soils are allowed to dry
in the air. The trays may be placed in
racks in hot air cabinet with a

8. Only air drying is recommended for some
of the nutrients present in the sample.
E. Preparationofsoil samples
 After drying, the samples are ground
with a wooden pestle and mortar in
preparation and clods and large
aggregates are crushed and mixed.
 The purpose of grinding is to reduce
heterogeneity and to provide maximum
surface area for physical and chemical
reactions.
 After grinding, the soil is screened
through a 2mm sieve.
 To reduce the size of the large sample

9. Sample splitting can be performed with a
mechanical sample splitter, such as a
Riffle- type Sample Splitter.
Quartering can also be done by dividing
into four equal portions.
If the soil is to be analyzed for trace
elements, containers made of copper(Cu),
zinc(Zn) and brass must be avoided during
grinding and handling.

10. 2. Extraction
• Different extractants are used to extract
the specific nutrients from soil in the
laboratory.
• The ability of an extractant to extract a
plant nutrient in quantities related to plant
requirements depends on the reactions that
control nutrients supply and availability.
• The extractants commonly used in soil
testing programmes are given in the
following table:
S.No Plant Nutrient Common Extractant
1. Available Nitrogen Alkaline Permanganate
2. Available
Phosphorous
Sodium bicarbonate (for neutral or alkaline
soils), Bray and Kurtz extractant number 1
(for acid soils)

11. S.No Plant Nutrient Common Extractant
3. Available Potassium Ammonium Acetate
4. SO4
2- CaCl2
5. Micronutrient cations
(Zn, Cu, Mn, Fe)
Diethylene pentaacetic acid (DTPA)
6. Boron Hot water
7. Molybdenum Grigg’s Reagent (ammonium oxalate of
pH 3)
8. Organic Carbon Chromic acid

12. 3. Interpretation
• For macro nutrients, the result is generally
classified into categories of supply e.g: low,
medium and high.
• For these categories, the nutrient amounts
required for an optimal or state yield level
are estimated.
• For micronutrients, a critical level is
generally used to decide whether an
application of that nutrient is needed.
Available Nutrient Low Medium High
Nitrogen <280 280-560 >560
Phosphorous <10 10-24.6 >24.6
Potassium <108 108-280 >280

13. • For nutrients other than N,P,K, a single
critical level is usually designated.
S.No Nutrient Method/ Extractant Low Medium High
1. N(% organic C) Organic carbon <0.5 0.5-0.75 >0.75
2. N(kg/ha) Alkaline
permanganate
<280 280-560 >560
3. P2 O5 (kg/ha) Sodium Bicarbonate <23 23-56 >56
4. K2O (kg/ha) Ammonium acetate <130 130-335 >335
5. S (kg/ha) Heat soluble, CaCl2 <20 20-40 >40
6. Ca (%of CEC) Ammonium acetate <25
7. Mg (% of CEC) Ammonium acetate <4
8. Zn (µg/g) DTPA <0.6 0.6-1.2 >1.2
9. Mn (µg/g) DTPA <3.0
10. Cu (µg/g) DTPA/Ammonium
acetate
<0.2
11. Fe (µg/g) DTPA <2.5-
4.5

14. S.No Nutrient Method/ extractant Low Medium High
12. Fe (µg/g) Ammonium acetate <2.0
13. B (µg/g) Hot water <0.5
14. Mo (µg/g) Ammonium acetate <0.2

15. 4. FertilizerRecommendation
• Fertilizer recommendation refers to
the way conclusions are drawn based
on soil tests.
• In our country, following 3 methods
are generally used:
Fertility group approach
Critical level approach
Target yield approach
A. Fertilitygroup approach
 In this method, soil test results and
General Recommendation Dose (GRD)
are used.

16.  On the basis of soil test, soil is categorized into
low, medium and high fertility group and
fertilizer is recommended as per following table:
B. Critical level approach
 In this method, soils are divided into two
categories on the basis of soil fertility level.
This dividing level is known as critical level.
 This method is used for micronutrient
application as it doesn’t determine the quantity
of fertilizer to be used but only helps in
determining whether or not fertilizer should be
used.
Fertility level of soil Fertilizer recommendation
Low GRD + 50% of GRD
Medium GRD
High GRD - 50% of GRD

17. C. Target yield approach
 Fertilizer prescription for desired crop
yields based on available nutrient
status is the main concept of this
approach
 For obtaining a given yield, a definite
quantity of nutrient must be taken up
by plant.
 Once this is known, fertilizer to be
applied can be estimated by taking into
account the efficiency of contribution
from soil available nutrients and the
efficiency of uptake from applied
fertilizer nutrients towards total

18. Calculationof basic parameters.
1. Nutrient requirement
2. Percent nutrient contribution
from soil to total nutrient
uptake(Es)
3. Percent nutrient contribution
from fertilizer to total
uptake(Ef)
)
/
(
)
/
(
ha
q
yield
ha
kg
take
NutrientUp
NR 
100
)
/
(


ient
lueForNutr
SoilTestVa
ha
kg
il
takeFromSo
NutrientUp
s
E
100
)
/
(


plied
NutrientAp
Fertilizer
ha
kg
rtilizer
takeFromFe
NutrientUp
Ef

19. 4. Percent nutrient contribution from
FYM to total uptake(EFYM)
Considering the above basic parameters, fertilizer
recommendationequationsare derived as follows:
Where;
S=soil test value foravailable nutrient(kg/ha)
Y=Yield Target
FYM=Farmyard manure(t/ha)
100
)
/
(


ha
kg
FYMapplied
M
takeFromFY
NutrientUp
FYM
E
FYM
E
E
S
E
E
Y
EF
NR
F
f
FYM
f
s




20. THANK YOU!