🧫 FERTILITY EVALUATION

This lesson explains key concepts in a structured way and connects them to practical agricultural applications and exam-oriented understanding.

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FERTILITY EVALUATION

LECTURE 15

FERTILITY EVALUATION BY PLANT ANALYSIS

Plant analysis is a useful diagnostic tool to ascertain if a nutrient has

been or is being assimilated. Plant analysis is also important in ascertaining

the nutrient requirements and nutrient status of plants during various stages

of growth.

A reasonably simple laboratory test of plant sample provides a

measure of nutrient availability in soil or nutrient status of plant at the time

the sample was collected. If these tests are to be useful in making fertilizer

recommendations, a coordinated laboratory-field research program must be

conducted in order to obtain the desired information.

Deficiency symptoms

Careful inspection of growing seedling or plants can help identify specific

nutrient stress. If a plant is lacking in a particular nutrient, characteristic

symptoms may appear. Nutrient deficiency symptoms must be related to

some function of the nutrient in the plant. Visual symptoms may be

caused by more than one nutrient. In a set of nutrient omission and

addition pot experiments, exact limiting nutrients can be identified.

Tissue tests

The concentration of the nutrients in the cell sap is usually a good

indication of how well the plant is supplied at the time of testing. These

semi-quantitative tests are intended mainly for verifying or predicting

deficiencies of N, P, K, S and several micronutrients.

Method: the plant parts may be chopped up and extracted with reagents.

The intensity of color developed is compared with standards and used as

a measure of nutrient concentration. Tissue tests are quick, easy to

conduct and interpret.

For tissue tests, the time of sampling and plant part to be sampled have

already been standardized for many crops. Tissue test can be done 5-6

times in a season and concentration can be monitored in the farm

premises .

There can be two peak periods of nutrient demand, one during maximum

vegetative growth and second during reproductive stage. Fertilization

can be done to maintain the peak concentration at critical stages.

Total plant analysis

As in tissue tests, a standardized method for time and method of

sampling of plant part are available for total analysis, which is done at

laboratory . The critical nutrient concentration is commonly used in

interpreting plant analysis results and diagnosing nutritional problems.

Diagnosis and Recommendation Integrated System (DRIS) 23 (12/16)

DRIS is a system that identifies all the nutritional factors limiting crop

production. Index values measure how far particular nutrients in the leaf

or plant are from optimum levels. Index values are used in the calibration

to classify yield factors in the order of limiting importance. To develop a

DRIS for a given crop, the following criteria are to be well considered.

- All factors having effect on yield

• Relationship among factors

• Calibration norms

• Continually refined recommendations

DRIS was developed based on nutrient ratios . When compared to

concentration that normally varies with season, nutrient ratio does not vary

much. When a nutrient ratio has an optimal value, optimum yield occurs

unless some other limiting factor reduces the yield.

N → N ↑ N ↓

P → P ↑ P ↓

Both numerator

and denominator

optimal

Both numerator

and denominator

excessive

Both numerator and

denominator

insufficient

When the ratio is too low a response in the numerator will be obtained

if it is limiting. If the nutrient in the denominator is excessive, a yield

response may or may not occur depending on the level of other yield factors.

23 (13/16)

N/P

K ↑

Optimum nutrient balance

Satisfactory nutrient balance

General diagram for a DRIS; constructed on

nutrient ratios for N-P-K

When the ratio is too high the reverse it true. Usually N/S, K/Mg,

K/Ca, Ca + Mg /K, N/P ratios are commonly used. Initially relationship

among N-P-K is calibrated.

Thus, DRIS has several advantages to integrate much nutrient

concentration at various stages, in different seasons suitable for many

cultivars of a crop.

DRIS has been found suitable for several grain crops and perennial

fruit trees.

CROP LOGGING

23 (14/16)

An excellent example of the use of plant analysis in crop production is

the 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. Critical nutrient concentration approach is

used in the crop log system.

In sugarcane, plant is sampled at 35 days and analyzed for N, sugar,

moisture and weight of young sheath tissue. Nutrients like P and K are

monitored at critical stages. Based on moisture, irrigation is scheduled.

Based on nutrient content, fertilizer application is done. By this record

keeping, the productivity of crop is increased.

BIOLOGICAL TESTS

Simpler and rapid laboratory/ green house techniques utilize small

quantity of soil to quantify nutrient supplying power of a soil.

Tests using higher plants:

Neubauer seedling method: The neubauer technique is based on the uptake

of nutrients by a large number of plants grown on a small amount soil. The

roots thoroughly penetrate the soil, exhausting available nutrient supply

within a short time. Usually 100 seedlings of rye or oats made to feed 100 g

soil mixed with 50 g sand. Blank without soil is also run. Total P 23 (15/16) 2O5 and

K2O uptake is calculated and blank value is detected to get root soluble

P2O5 and K2O. Values designated as Neubauer Nos. (mg/ 100 g soil) are

used to determine the deficiency. These tables give the maximum values

of available macro and micronutrients for satisfactory yields of various

crops.

Standard and Demont technique: It is a modified neubauer technique. Round

cardboard cartons with bottom removed are nested in a container and filled

with sand. Seeds are sown. After 2-3 weeks of growth, a carton containing

the plants is nested in a second carton holding 200 g soil or soil + fertilizer.

When the mat of roots meets soil, it is allowed to feed for 3-4 days. Then

nutrient uptake is estimated.

Deficiency test of sunflower for Boron

Sunflower is grown in the test soil supplied with nutrient solution with

all essential nutrients excepting boron. From the day of appearance of B

deficiency symptoms of leaves, the soil is identified as deficient (<28 days),

moderately deficient (28-36 days), and not deficient (>36 days).

Microbiological methods:

In the absence of nutrients, certain microorganisms exhibit behavior

similar to that of higher plants. For example, growth of Azotobacter or

Aspergillus niger reflects nutrient deficiency in the soil. The soil is grouped

from very deficient to not deficient in the respective elements, depending on

the amount of colony growth. In comparison with methods that utilize

growing of higher plants, microbiological methods are rapid, simple and

require little space.

Sacket and Stewart technique

23 (16/16)

For identifying P and K deficiency test soil is divided in to 4 portions.

Solution containing soluble P, K, and P+K are added in 3 portions and one

portion was allowed as check. They are inoculated with Azotobacter and

incubated for 72 hrs. Based on colony growth deficiency is identified.

Melich Cunninghamella – plaque test :

Cunninghamella is sensitive for P. Test soil is mixed with nutrient

solution and a paste is prepared. The paste is spread on a clay dish.

Cunninghamella is inoculated at the centre and incubated for 5-6 days.

Based on the diameter of mycelial growth, the soil is diagnosed as deficient

(<10 cm), moderately deficient (11-21 cm), or not deficient (>22 cm).

Mulder _ Aspergillus niger _ test for Cu and Mg

Colours of mycelial and spores are used to delineate the deficiency of

Cu and Mg. This method is used for Mo, Co, Mn, S, Zn also.

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Summary Cheat Sheet

Key Recall Points

• FERTILITY EVALUATION is exam-relevant for SSAC122 and objective questions in soil science.
• Use soil-test based interpretation with focus on pH, CEC, and nutrient availability.
• Apply the 4R principle: right source, right rate, right time, and right method.

Exam Traps

• Do not mix up soil fertility concepts with fertilizer quantity alone.
• Numerical and term-based questions often test definitions, units, and threshold values.
• In problem-solving, interpretation must follow soil reaction, crop stage, and management context.

References

3 sources • [1] [2] [3]

[1]

ICAR e-Course: Soil Chemistry, Soil Fertility and Nutrient Management

Official

[2]

Brady and Weil, The Nature and Properties of Soils

Book

[3]

Indian Council of Agricultural Research

Official