Soil Fertility Evaluation
Soil fertility is the inherent
capacity of the soil to supply plant nutrients in available amount, usable form
and required proportion while soil productivity is its capacity to produce crop
and is expressed in terms of yield/ha. Soil productivity is the broader term
and fertility is only one out of number of factors that determine the magnitude
of crop yields i.e. productivity.
Fertility evaluation methods
Knowledge on soil fertility is very
important to improve the crop yield and save the crops from nutrient deficiency
1.
Field
Experiments
Fertilizers of different types are
applied in different quantities in replicated trials to a particular crop to
find out the right amount and right type of fertilizer for various soil types
and crops. The treatments are assigned to the plots at random. This is the
oldest technique and reliable one but it is labourious, time consuming and
expensive.
2.
Pot
culture experiments
Representative soil samples are
collected and measured quantity of composite sample is drawn. They are filled
in pots and fertilizers of different quantities are applied. 2-3 seeds are sown
in each pot and observed for growth and development. Though the method is
simple, needs lot of standardization to stimulate the field conditions.
3.
Visual
method or hunger signs
This method is based on the deficiency
symptoms or toxicity symptoms noticed in crop plants. Depending upon the
mobility of nutrients, the symptoms are first developed on lower or upper plant
parts.
- Symptoms
on lower/old leaves in case of mobile nutrients like N, P, K and Mg
- Symptoms
on younger leaves in case of immobile nutrients like Ca, Zn, Cu, Mn, Fe
and B.
This method is very simple, but
symptoms may also result due to some other factors like, weather conditions, soil
conditions, insect pests and diseases etc.
4. Use of indicator plants
Indicator plants are specifically
susceptible to small change in the nutrient status and their deficiency can be
easily detectable.
- Cabbage
and cauliflower indicate the deficiency of N, Ca and Fe
- Potato
indicates deficiency of K and Mg
- Sugarbeet
indicates deficiency of Na, Mn and B
There are no indicator plants for many
of the nutrients.
5. Rapid plant test
Plants accumulate NO3, P and K in
inorganic form as ions and they can be estimated b chemical test. The
percentage content of a nutrient in plant varies according to the supply of
nutrients available to the plant. On the basis of plant tests, the nutrient
status in soil can be predicted and fertilizer schedules can be worked out as
per the results.
6. Soil analysis method
This method is rapid, scientific and
accurate. Representative samples are collected from soil and are subjected to
chemical analysis. As per the results, the amount of P, N, K etc. can be
estimated and accordingly fertilizers can be applied. This method is not very
effective, because by the tie it may be too late to correct any nutritional
deficiencies that may be indicated.
7. Microbiological Methods
Microbiological tests are based on the
principle that the general requirement of mneral nutrients for microorganisms
is similar to those of crop plants, although the absolute amounts differ.
- Azotobacter
plaque test: Azotobacter
is particularly sensitive to soil acidity and low level of
phosphorous. Deficiency of lime, P and K in the soil on the basis of
number of Azotobacter colonies can be determined.
- Aspergillus
niger test: It
is used to determine the Cu, Mg, Mo, Co and Mn status of soil
No comments:
Post a Comment