Radio Tracer Techniques Uses Brief Description What Is Tracer? Radioactivity in soil fertility evaluation. Beta Counting.

1. Use Of Radio-Tracer Technique In Soil Fertility
Evaluation
Aditya Parashar

2. A radioactive tracer, radiotracer, or radioactive label, is a chemical compound in which
one or more atoms have been replaced by a radionuclide [radioisotopes] so by virtue of
its radioactive decay it can be used to explore the mechanism of chemical reactions by
tracing the path that the radioisotope follows from reactants to products .
It works on Dilution Principle..
What Is Tracer Technique ?

3. Properties of a Tracer :
• Used to follow particular element through various pathways and quantitative
measurements can be made
• They behave same as there stable counterparts but can be easily traced
• May be linked with colored dye
• The major physical properties determining the usefulness of a tracer are -
 Half life
 Mode of Decay
 Decay Energy

4. Important Radio Tracers
Elements (Radioisotope) Uses
32P Soil fertility & root distribution
14C Photosynthesis
40K Soil Fertility & K balance
22Na Soil Tolerance & Cell premiability

5. Use of Tracer Tech. to determine fertility of soil :
1. Rate of nutrient release of any particular fertilizer or manure
2. Contribution of other non conventional fertilizers or manure in the soil fertility
3. Uptake and Translocation of nutrients
4. Measurement of labile Phosphorous content of soil
5. Root distribution of plant inside soil
6. Screening and selection of better genotype of plant
7. Determining water transport and storage in unsaturated area

6. Rate of nutrient release of particular fertilizer or manure
• Radio labelled fertilizer (eg., Radiolabelled phosphate 32P) is applied to the sample soil then
slowly it starts releasing the element.
• Then the plant uptake of (P) can be easily traced and its movement in the plant can also be
easily monitored.
• The total activity of the plant after a predetermined time shows the efficacy and usefulness of
that fertilizer or manure.
Example Image :-
Imaging of radio-cesium uptake
dynamics in a plant body by using a
newly developed high-resolution gamma
camera

7. Contribution of non conventional nutrient source in soil fertility
• The contribution of non conventional sources {such as Guano, Sludge, Phosphate rocks } of
nutrient supply in soil nutrient pool can't be easily traced.
• In that case the radioisotopes are added into the sample soil ,the dilution of them determines
the nutrient release by these sources.
• This helps in proper incorporation of fertilizer doses.

8. Uptake and translocation of nutrients
• Some experiments using Micro-autoradiography some experiments were conducted using P,
Ca, S radioisotopes enlightened the movement of nutrient some herbaceous plants.
Fertilizer
applied through
Leaf/Root of
plant 1
A part of it is
released into
Soil, sand,
Water medium
A part of it is
again
reabsorbed by
the same plant
1
Some part of the
fertilizer is
absorbed by the
just immediate
adjacent plant 2
Same process
repeats in
plant 2
Nutrient
reaches to
plant 3
Process
repeats in
plant 3
Nutrient
reaches to the
farther points
from the site of
application
In this way the nutrient translocation and
spread can be traced

9. Measurement of labile Phosphorus content in soil
• The known amount of radioactive 32P is added to sample soil .
• The measurement of amount of radiophosphorus and stable phosphorus taken up by plant
will show that how much of phosphorus has come from fertilizer and how much from already
present P in soil.
• Equation to know the already available P in soil : 𝑸 𝟐 = 𝑸 𝟏(
𝑺𝑨 𝟏
𝑺𝑨 𝟐
− 𝟏)
Where Q1= Exchangeable P in soil
Q2= Exchangeable P in labelled fertilizer
SA1= Specific activity of labelled P added to soil
SA2= Specific activity of plant after uptake of P(stable & radioactive)

10. Determining water transport and storage in unsaturated areas
• Tritium the radioactive heavier isotope of Hydrogen is found very useful in tracking water
movement in unsaturated areas.
• Velocity of infiltration and evaporation flux
• Soil Moisture And Neutron Probe [SMNP] is ideal for measurement of soil water in the
immediate vicinity of the crop root.

11. Root distribution in soil matrix
• It can be determined by using radioisotopes using methods like Soil Injection.
• This tech provide qualitative information about the presence of function , dormant roots upto
farthest lateral spread and maximum death.

12. Screening and selection of better genotype of plants
• Use of radioisotopes such as 15 𝑁 & 13 𝐶 allowed us to quantify the contribution of N2 fixing
plant and plant litter for soil N pool.
• Also used to identify Al toxicity and P deficiency in acid soil.

13. All these techniques are used to replace the time consuming and hectic
laboratory methods for soil fertility analysis and screening plants….they
focus on more precise data and time saving.
Tracing is done by measuring the activity per unit mass of the sample
conclusion

14. Miscellaneous
Beta Counting
• Liquid Scintillation Counting
 Energy of the released beta particles is only upto 1/3rd of the Emax
 A window can be set to detect particles with a specific energy renge
• Cerencov Counter
 Beta particle when emitted, travels with the speed approaching to speed of light in vac. but the
speed of light in medium is lower, this produces shock waves.
 These shock waves are counted