Evaluation of Soil Fertility PDF

SOIL FERTILITY
EVALUATION
SOIL FERTILITY EVALUATION
1.Quantitative methods
a)Soil analysis
b)Plant tissue analysis
c)Field fertilizer tests
d)Pot experiments
2.Qualitative methods
a)Nutrient deficiency symptoms
3.Why soil fertility declines
Quantitative Diagnostic Techniques
Laboratory Soil Test
• Soil test provide a scientific basis for
formulating a sound fertility management
practice.
– it consists of actual chemical analyses of
soil samples to determine the amounts of
available soil nutrients.
– from the results gathered, which are
compared with the economic optimum
amounts, the soil must contain the amount
of nutrients needed in a testing laboratory.
– Soil testing has to be done according to a
standard procedure so as to avoid
erroneous interpretation of the test results.
Four phases of a soil testing program:
1. Collecting the soil samples
2. Extracting and determining the available
nutrients
3. Interpreting the analytical results
4. Making the fertilizer recommendation.
FIELD SAMPLING
• Samples should accurately reflect the field’s
true nutrient status.
• Except for pH values, soil properties like
nutrients vary greatly.
• The required number of subsamples (to make
a composite sample) is 15-40 equally
distributed in the field.
• This corresponds to 15.8 to 25% error
variance.
• For soil test-yield correlations, take 40
subsamples per replicate (block) before
application of fertilizer experiments
• For most crops (annual) sampling depth is 15-
25 cm.
• For grasslands, 5-7 cm.
General guidelines for fertility rating of soils.a
Soil Fertility Adequate Marginal Deficient
Factor (favorable)a (Moderately (Unfavorable)b
Unfavorable)
pH H2O 1:1 5.5-8.5 5.0 – 5.5 < 5.0
Base Saturation > 35 20 – 35 < 20

Percentage
Cation Exchange > 20 10 – 20 < 10
Capacity (meg/100 g soil)
Organic matter (%) > 4.5 2.1 – 4.5 < 2.0
Available P (ppm) > 30 11.5 – 30 < 11
Exchangeable K (ppm) > 250 100 - 250 < 100
a Data refer to weighted averages in the top 30 cm

b < = less than
> = greater than

Plant Tissue Analysis
• The nutrient content in the plant tissue is
related to the available nutrient supply of the
soil
• thus, a chemical laboratory analysis of the
plant tissue would reveal the available nutrient
status of the soil on which the plant is grown
• this is the principle behind plant tissue
analysis
• when correlated with the results of fertilizer
field trials, fertilizer recommendations using this
method become more reliable.
– sampling of plant parts to be analyzed,
however, must be given due attention
– plant parts to be sampled for different
crops vary
– this depends on the type and age of the
crop tissue
– like visual diagnostic symptoms, the effect
of abnormal amounts of soil nutrients may
already have its effect on yield before
detection and correction can be made
Optimum Levels of Nutrients in 3rd leaf of Banana
Nutrients Optimum
Concentration
N (%) 2.7 – 3.6
P (%) 0.18 – 0.27
K (%) 3.5 – 5.4
Ca (%) 0.25 – 1.2
Mg (%) 0.27 – 0.60
Cl (%) 0.70 – 0.84
Mn (ppm) 200 – 2000
Zn (ppm) 20 – 50
Fe (ppm) 80 – 360
Cu (ppm) 6 - 30
Fertilizer Field Trials
• Fertilizer field trials in the farmer’s field are
employed to assess the effect of fertilizers and
their interactions with all existing factors of
crop growth and development in any given
location.
– these methods are done with appropriate:
1. experimental design
2. efficient cultural methods or techniques
3. proper field layout
4. accurate collection of harvest data
5. observation and proper interpretation of
results
– the actual use of plants in field
fertilizer trials is unquestionably the
most reliable of the best know biological
test.
– fertilizer recommendations formulated
through these methods are generally
more realistic and dependable than the
previous methods mentioned when
employed singly.
 For a farmer’s own purpose:
 he/she may want to conduct his own
fertilizer field trial
 he/she may have three plots for testing
and apply varying amounts of fertilizers
 based on the yield and growth
characteristics of the crop, he/she can
determine the right amount of fertilizers to
apply.
 Fertilizer field trials are often used
to simulate actual field conditions such
that these may serve as field
demonstrations at the same time.
Advantages of field trials:
1. They are the best way to determine the
nutrient needs of crops and soils and for
advising farmers on their fertilizer needs.
2. They will show you how accurate
recommendations based on soil and plant
testing are in relation to the yield obtained.
3. They permit an economic evaluation, i.e., the
calculation of the return can be used as the
most motivating argument to a farmer to use
fertilizers.
4. Demonstrations or simple trials show the
benefits of fertilizers to farmers and
agricultural workers.
5. The growing crops can be photographed
and the pictures can be used in publicity
and demonstrations for many years.
POT EXPERIMENT
• comparison of several fertilizer treatments
including a control using small amount of soil
in pots to have a better control of
environmental factors.
• this is under artificial condition.
• soil is in pot
• short duration
• preliminary in nature
Qualitative Diagnostic Techniques
Visual Symptoms of Nutrient Deficiency in

Plants
• deficiency of a certain nutrient element
results in poor growth and, hence, low yield.
• in extreme cases, this may lead to death of
the crops.
The occurrence of nutrient deficiencies
may be due to the following:
a) insufficient amount and supply of soil
nutrients.
b) unavailability of forms of the nutrients
present.
c) no proper balance among different
nutrient levels.
Crop removal – absorption of nutrients by
plants.
Erosion – process whereby surface soil is
carried away by wind or water.
Leaching – downward movement of
nutrient with water.
Denitrification – conversion of nitrate to
nitrogen gas.
Ammonia volatilization – escape of nitrogen
from the soil as gas.
Fixation – nutrients are temporarily converted
to unavailable forms (e.g., clay
minerals)
Immobilization – conversion of an element
from inorganic to organic form
THE END

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SOIL FERTILITY

Base Saturation > 35 20 – 35 < 20

Available P (ppm) > 30 11.5 – 30 < 11

Exchangeable K (ppm) > 250 100 - 250 < 100

a Data refer to weighted averages in the top 30 cm

> = greater than

Visual Symptoms of Nutrient Deficiency in

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