1. Soil fertility can be evaluated through various qualitative and quantitative techniques including soil testing, plant tissue analysis, and the use of indicator plants and microorganisms. 2. Key evaluation methods discussed are soil testing to determine available macronutrients; plant tissue analysis to identify nutrient deficiencies; and the use of diagnostic ratios and indicators like the chlorophyll meter that can reveal nitrogen status. 3. Proper soil testing calibration using techniques like target yield approach and isotopic dilution are needed to effectively translate soil test results into optimized fertilizer prescriptions for crops.

1. SOIL FERTILITY EVALUATION
Approaches / Concepts / Applications

2. Concepts of Soil fertility evaluation
•Several techniques are commonly
employed to assess the fertility
status of a soil.
•Any evaluation procedure would
give an idea about the nutrient
supplying power of soil
•There are various diagnostic
techniques employed to evaluate
the soil fertility

3. (i) Qualitative Diagnosis of deficiencies
(ii) Plant Analysis:
Tissue analysis; whole plant analysis
(iii) Soil Testing:
Chemical indices of nutrients available
(iv)Biological indices of nutrient
availability:
•Growth of either higher plants;
•Certain MOs is used as a measure of soil
fertility

4. 1.Qualitative diagnosis of deficiencies
Symptoms
•Careful inspection of the growing plant can
help to identify a specific nutrient stress.
• If a plant is lacking in a particular nutrient,
characteristic symptoms may appear.
•In most cases considerable experience is
necessary for their recognition.
•Visual evaluation of nutrient stress should
be used only as a supplement to other
diagnostic techniques (i.e. soil and plant
analysis)

5. 2. Plant Analysis
Tissue testing & whole plant analysis
Tissue testing:
Determination of the amount of a plant
nutrient in the sap of the plant, a semi-
quantitative measurement of the unassimilate
soluble content.
Green plant tissue can be tested for several
nutrients, NO3-N, P, K and sometimes Mg, Mn
and Fe.
However, it takes a lot of practice and
experience to interpret the results, especially
those for the micronutrients.

6. •In India tissue testing is used in a limited
way for giving fertilizer recommendations
for plantation crops in the southern states.
•However in the western countries, tissue
test kits are available.
• When properly used, tissue tests work
well with soil tests and plant analyses as
another good diagnostic tool (Dev, 1997).
• Time of testing, plant parts to be
tested and interpretation are very
important

7. Total plant analysis
•Plant parts may be chopped up and
extracted with reagents.
•The intensity of the color developed is
compared with standards and used as a
measure of supply of the nutrient.
• Rapid test plant tissue is squeezed with
pliers to transfer plant sap to filter paper;
•Color developing reagents are added and
the resulting color is compared to a plant
analysis

8. Methods employed based on tissue
testing/plant analysis
Critical nutrient concentration (CNC)
•The CNC is used in interpreting plant
analysis results and diagnosing nutritional
problems.
•The CNC is located in that portion of the
curve where the plant nutrition conc.
changes from deficient to adequate;
•Therefore CNC is the level of a nutrient
below which crop yield or quality is
unsatisfactory.

9. Chlorophyll meter
•Also called as SPAD (Soil and Plant
Analysis Division, Japan) is a simple
diagnostic tool to measure the chlorophyll
content of leaves.
•Meter readings are given in Minolta
company defined SPAD values which
indicate the relative amount of chlorophyll
present in plant leaves
•This is a new technique under the
concept of using tissue testing to provide
an assessment of crop N status.

10. Nutrient Ratios
•Ratio of nutrients in plant tissue is
frequently used to study nutrient balance in
crops.
•For example, N/S, K/Mg, K/Ca, Ca+Mg/K,
N/P and other ratios are commonly used.
•When the ratio is optimum – optimum yield
occurs unless some other limiting factor
decreases the yield.

11. •When N/S ratio is in this optimum range or
balanced, it will be identified by a horizontal
arrow (→).
• Ratios above the optimum will be
recognized by an upward vertical arrow (↑),
and those below it will be assigned a
downward vertical arrow (↓)
•In situations with N/S = → or in its optimal
range, 3 possibilities exist
N → N↑ N↓
------- or -------- or -------
S → S↑ S↓

12. N N→ N↓
------- = ↑ --------- or -----------
S S↑ S →
S insufficiency N excess
N N→ N↓
------- = ↓ --------- or -----------
S S↑ S →
S excess N insufficiency

13. Diagnosis and Recommendation Integrated
System (DRIS):
• DRIS is a system that identifies all the
nutritional factors limiting crop production
and, thus, increases the chance of
obtaining high crop yields by improving
fertilizer recommendations.
• To develop a DRIS for a given crop, the
following requirements must be met
whenever possible.

14. Establishment of DRIS Norms:
•A survey is first employed in
obtaining the data required to
establish DRIS norms.
•A large number of sites where a
crop is growing are selected at
random in order to represent the
whole production area of a country,
state, or district.
•At each site, plant and soil
analyses for all essential nutrients
are conducted.

15. •Secondly, the entire population of
observations is divided into two
populations (high and low yielders)
based on vigor, quality and yield.
•Using N-P-K, in corn leaves as an
example, the significant ratios have
been found to be N/P, N/K, and K/P.
•Determination of Relative N-P-K
Requirements.

16. Crop logging
•Carried out for sugarcane in Hawaii
•The crop log, which is a graphic record of
the progress of the crop, contains a series
of chemical and physical measurements
indicate the general condition of the plants
and suggest changes in management that
are necessary to produce maximum yields.
•A critical nutrient concentration approach
is used in the crop log system
•Nutrient concentrations in leaf sheaths are
utilized for diagnosis of macro and
micronutrient deficiencies.

17. Biological Test:
i) Use of higher plants as extractants
a) Field Trials
Simple Fertilizer trials (SFT)
•gives an idea about the hidden hunger
•effect of macronutrients are tested
mainly.
• Control, N alone, P alone, K alone, NP,
PK, NK and NPK.

18. Complex field trials (CFT)
•Hidden Hunger can easily be detected
•Many interaction studies are possible
•Many combinations of nutrients are
included
N0P0K0, N1P1K1, N0P0K1 , N2P2K2 etc.

19. Pot culture/ greenhouse
When large numbers of seedlings
are grown in a minimum quantity of soil,
it is expected that the seedlings would
completely exhaust the soil nutrients
i) Mitscherlich technique
ii) Neubauer test

20. Use of indicator plants
•Plants that are used to show the
deficiency of certain nutrients.
•If they are grown on sand culture, very
characteristic symptoms occur.
N - Cauliflower, cabbage
P - Rape; K- Potato
Ca - Cauliflower, cabbage
Fe - Cauliflower, cabbage, potato
Mg - Potato; Na - sugar beet
Mn - Sugar beet, oats; B-sunflower

21. Microbiological methods
•In the absence of nutrients certain
Microorganisms exhibit behavior similar
to that of higher plants.
Ex: growth of Aspergillus niger
Azotobacter plaque test for P:
•Azotobacter is very sensitive to P
deficiency.
•The abundance of the colony is the
effective measure of P.
• This method is also an effective tool in
detecting deficiencies of lime and K.

22. Aspergillus niger test:
•The weight of mycelial pad is taken into
account.
•The lesser the weight, less of nutrient
content for K and also for Cu, Mg, Mo, Mn.
Cunninghamella plaque test:
Diameter of the particular cunninghamella
mycelia is used as criteria for the amount of
P present.

23. CO2 evolution method:
•CO2 evolved is a measure of microbial
activity which in turn is a measure of
soil fertility.
•Addition of deficient nutrient increases
the CO2 quantity.

24. A.Soil Testing
•A measurement qualifies to be termed a
soil test for a particular nutrient if it provides
information on the fertilizer requirement of a
crop for that nutrient
-Colwell

25. Soil Testing…
•Soil Testing is to the Art of Crop Production what
the Blood Testing is to the Medical Profession.
•A tool for rapid chemical analysis to assess the
available nutrient status of a soil, interpretation of
the results and making fertilizer recommendations
based on crop responses and economic consideration
through soil test calibrations.

26. Fertilizer Prescriptions
Soil testing is a phase where the basic research
in soil chemistry culminates and applied
research on soil fertility begins. The combined
research efforts of soil chemist and soil fertility
expert, are reflected in and translated to farmers
as fertilizer recommendations"
(Goswami, 1982)

27. Soil Test Methods
pH, EC, CEC, OC
Macronutrients
Micronutrients
Lime requirement / Gypsum requirement

28. Soil test calibration and Fertiliser prescription
Inductive cum Targeted yield approach
Ramamoorthy et al. (1967)
 Law of minimum
 Inductive methodology
 Gradient & Test crop experiments
 Generation of basic data
- NR, Cs, Cf and Co

29. Calculation of nutrients from soil, fertiliser and organics
Cs= (Total Up Nutri./ STV )x 100
Cf=[Total Up Nutri-(STV x Cs)]/ Fertiliser Nutri(kg/ha)x 100
Co=[Total Up Nutr-(STV x Cs)]/Organic nutri. (kg/ha) x 100

30. NR (Cs x S) (Co x O)
FD = ------- T - ------------- - ----------
Cf Cf Cf
General equation for optimising nutrient doses

31. Fertiliser Prescription Equations
FN = 4.39 T – 0.52 SN – 0.80 ON
FP2O5 = 2.22 T – 3.63 SP – 0.98 OP
FK2O = 2.44 T – 0.39 SK – 0.72 OK

32. Maize Season: Kharif Soil: Inceptisol (P.N. palayam series)
Initial Soil Test (kg ha-1) Nutrients required (kg ha-1)
Yd. target-50 q ha-1
N P K N P2O5 K2O
180 8 300 131 98 111
200 12 340 120 91 91
220 16 380 109 84 72
240 20 420 98 77 52
260 24 460 87 70 33
STCR based fertiliser recommendation

33. Soil Testing
Isotopic techniques
1) Mitscherlich 'b' value:
An index of nutrient availability in soils.
Log (A-Y) = Log A-C (x+b)
b - availability of the nutrient in the soil and
seed when none is added as fertilizer (Soil
test value); Y - is the yield with the quantity
X of the nutrient in the fertilizer.
A–maximum yield obtainable with increasing X; C–
efficiency factor that denotes the rate at which the
yield approaches the maximum value with addition
of X(Fertilizer efficiency)

34. 2. Isotopic Dilution method
(Fried&Dean, 1954)
(i) Dean 'A' value Technique: Radioactive
elements are used. For assessing the availability
of 'P' in soils it is followed. 'A' – values are the
amount of the nutrients in soil which behaves in
a similar way as that of the nutrients added thro'
fertilizer. This can be calculated by adopting the
formula, (1-y)
A = B ---------
y
A - soil available nutrient; B - amount of nutrient
(P) added through fertilizer ; y - fraction of the
fertilizer nutrient extracted or taken up by the
crop.

35. Eg. 32p- it will differentiate the amount of added
fertilizer taken up by the plant from the soil.
One of the best reliable methods of evaluating soil
fertility.
In practical terms for P
sp. activity of P in fert.
i)A value : mg P added as test x --------------------------------- mg P/100g soil
PO4
3- / 100g soil sp. activity of P in plant

36. ii) The ( Larsen, 1950) 'L' value:
It is a measure of isotopically
exchangeable fraction of PO4
3- in soil and
has been used to determine the quantity of
soil PO4
3- in labile form. It differs from A-
value in concept and basic experimental
requirements S*1
α = W* ----------- - (1)
S*2
where,S*1 and S*2 are the specific
activities of the applied P and the plant P,W*
- amount of 32P - labelled P applied
α -amount of isotopically exchangeable soil

37. iii) The 'E' - value
It is a measure of the amount of
isotopically exchangeable phosphate of that
soil. S* S
Et = W ---------
S* F
where, Et – ε value at a given temp
S*
s – specific activity of the added PO4
3-
solution; S*
F – specific activity of the filtrate
W – amount of PO4
3- added per unit of
soil