isotopes of phosphorous and its application in agriculture

8/13/2019 Isotopes of Phosphorous and its application in agriculture

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Use of 32P in Agriculture

Chairman Presented by

DR. R. SANKARS. DHARUMARAJAN

04-617-013



Isotopes

Isotopes are different forms of an atom of the same

chemical element. They have identical chemical

properties but a different relative atomic mass.

While the number of protons is the same, the number

of neutrons in the nucleus differs

Radioactive nature of unstable isotopes, usually

referred to as 'radioisotopes„



Radioisotopes in agriculture

With the help of radioisotopes, we can easily locate the presence of a

single atom and molecule and their movement. Hence, they give researchworkers the opportunity to follow up step by step all kinds of processes thatare related to the nutrition of plant from germination to maturity.

Very small quantities of labelled nutrients can be accurately measuredin presence of large quantities of other nutrients.

The location of materials can be identified by radio- autography.

( method of determine the distribution of radioactive material )

Tracer technique enables one in tracing those elements taken by the plants

accurately and precisely.

Interaction among the mineral nutrients.



Phosphorus isotopes The chemical element phosphorus has one stable isotope (31P) and

several radioisotopes (from 26P to 30P and from 32P to 38P).

but only two of them (32

P and33

P) are suitable for agronomic studies.

Beta energy emitted by 32P is high compared to 33P

The lower energy emitted by 33P presents less radiation hazard, and its

longer half-life (24.4 days) allows studies to be conducted forrelatively longer time periods.



Contd.,

The 32P can be easily monitored because of its high beta energy andits use is limited to P uptake studies with duration of 60 upto 90 daysdue to its short half-life (14.3 days).

The availability of these two isotopes also makes it possible to usedouble labeling techniques in root activity studies and P placementexperiments

The 32P being far cheaper than 33P and also easier and faster toobtain.



Main Characteristics of P isotopes used in plant nutrition studies

Isotopes Half-life

Radiation

characteristics Typical applications

Type Energy

32P14.3

days -

1.71

MeV(Emax)

Exchangeable P in soils

P availability from P fertilizers

Plant root distribution / activity

Residual P fertilizer availability

33P24.4

days -

0.248

MeV(Emax)

Auto-radiography

Diffusion in soils

Double labeling with 32P



Disintegration of

32

P radioisotopes The unstable nucleus of a radioactive isotope has an excess energy

To achieve stability, it undergoes random rearrangement during whichenergy is released in the form of particles or radiations

The radioactive nuclide has excess neutrons, which is usually the casewith higher elements such as 32P

The stability is achieved by the conversion of neutron into proton with

in the nucleus and beta particle is emitted.

n -----------------------------------------------> p+ + -

32P15--------------------------------------------->32S16 +

- + Energy



Basic concepts in using isotope as tracers

The first extensive use of isotopes as tracers in plant nutrition was made in the1940s.

The radioactive isotope of P (32P) was used to study the utilization of P fertilizers by various crops in a series of greenhouse experiments and field trials (Fried andDean, 1952)

A tracer was incorporated into a fertilizer material or the nutrient source of interest,and the amount of tracer taken up by the plant was measured directly.

In phosphate studies, 32P carrier-free materials, i.e. contain only 32P atoms, are

normally utilized as tracers.

They can be also used for labeling commercial P fertilizers such as superphosphatesduring manufacturing or for preparing 32P labelled solutions of known

concentration



contd..,

• In case of natural fertilizer sources, like phosphate rocks (PR) it is

not possible to directly label these materials with P isotopes,

because of the changes induced in their physical and chemical

characteristics during labeling.

• Therefore, techniques based on reverse isotopic dilution have been

widely used to investigate P availability from Phosphate rock

sources to plants



Basic terminologies and definition

Radioactive tracer

A small quantity of radioisotope is used to follow a biological or chemical process.

Carrier

A quantity of stable isotopes of the element, which may be added toa radioactive isotope of that element to give a ponderable quantity to facilitatechemical operation.

Carrier free

A carrier free isotopes of an element are one in which all the atoms of theelement present are radioactive.



Contd.,

Specific activity

Pertaining to a radioactively sample, the amount of tracer activity(disintegrations per second) per unit amount of trace (mole)

Units of specific activity- Curie = 3.7×1010 disintegrating atoms per secondSI unit: Becquerel

1 milli curie =37 MBq

Phosphorus in the plant derived from fertilizer (Pdff)=Specific activity of the P in the plant

Specific activity of P in the fertilizer

Total P in the plant derived from the fertilizer (K)

Pdff × total P in the plant

Percentage utilization of fertilizer of the applied fertilizer

K×100

Amount of applied fertilizer P



32P isotopic techniques

Direct neutron irradiation of Phosphate rock

materials

Direct labeling of P fertilizer

Methods based on Isotope dilution



Direct neutron irradiation of Phosphate Rock materials

It involved the incorporation of 32P by direct activation of phosphate

compounds in the Phosphate rock through thermal neutron irradiation in a

nuclear reactor and the use of this irradiated material as a labelled source in

the evaluation of P uptake from Phosphate rock.

This method has serious drawbacks such as the changes in the Phosphate

rock structure, formation of non-orthophosphate 32P component and of a

number of radioisotopes in the Phosphate rock matrix complicating the

determinations.

This method is not adequate for evaluating Phosphate rock sources and it

is not used anymore.



Direct labeling of P fertilizer

P from the fertilizer is labelled with an isotope of P (32P or 33P), it is possible to differentiate between soil- and fertilizer derived P in the plant.

Thus, the amount of P taken up from the labelled P fertilizer can bemeasured directly.

This direct method can be used to compare several P fertilizers that can belabelled during their manufacture. This includes superphosphate,ammonium phosphates and nitro phosphates (Fried, 1954).

The efficiency of P fertilizer management practices such as timing, placement, mixing of P sources, etc; can be also measured



A-value technique The "A" value represents a quantitative measure of the availability of a soil nutrient in terms

of a standard fertilizer.

The basic assumption is that when two sources of a nutrient are present in the soil, the plantwill absorb from each of these sources in proportion to the respective quantities “available” tothe plant.

The amount of available (A-value) nutrient in the soil can be determined in terms of astandard, provided that the proportion of the nutrient in the plants derived from this standard isdetermined.

This is done by using an isotopically labelled fertilizer (standard), which will give a directmeasurement of the proportion of the nutrient that was derived, from the standard fertilizer

Fried and Dean (1952)

A= B (1-y)/y

Where,

A is the amount of available nutrient in the soil,

B is the amount of fertilizer nutrient (standard) applied,

y is the proportion of nutrient in the plant derived from fertilizer nutrient(standard).



E Value

• This method is a direct application of the isotopic dilution principle and isan attempt to measure the amount of nutrient in the soil that is inequilibrium with the same nutrient in the soil solution

• when 32P added to a system containing 31P, the 32P will distribute itself suchthat equilibrium ratio of 32P to 31P (specific activity) will be constant for all

the phosphate participating in the equilibrium • Reaction

Surface 31P + solution 32P =========> surface 32P= solution 31P

At equilibrium,

Surface 31P Solution 31P

Surface 32 P = Solution 32P

(Russell et al ., 1954).



L- value technique

It was first suggested by Larsen (1952).

The L-value is defined as the amount of labile P (in the soil and the soilsolution) that is exchangeable with 32P labelled orthophosphate ions added

to the soil, as measured by a plant growing in the equilibrated soil.

• The index of relative fertilizer efficiency

= (LF - LO) / P application rateWhere,

LF is the L value of the fertilized treatment.

LO is the L value of the treatment without Paddition.



Evaluation phosphorus use efficiency



Evaluation phosphorus use efficiency

To clearly define the optimum conditions for placement of phosphorusfertilizers

To define the relative efficiency of major sources of different nutrients

To achieve better understanding of the effect of time of application onthe efficiencies of fertilizer.

To obtain, by direct measurements, precise information on the proportion of applied fertilizer actually taken up by crops.

To asses the extent of wastage that takes places if improper placement orincorrect source of fertilizer is used



P- sources

Dry matter

yield

( g/pot)

Total P uptake

(mg/Pot)

Pdff

(%)

P utilization

(%)

Control 7.2 7.5 - -

DAP 23.3 23.4 24.9 11.8

SSP 22.4 22.9 22.5 10.4

ANP 21.0 17.5 26.8 9.4

P sources on drymatter production and utilization of P by rice

(Dravid, 1989)



Parameters P sources

P2O5 level

0 30 60 90 mean

Dry matter uptake(g/ Pot)

SSP

DAP

DAP+Gypsum

Mean

2.9

-

-

4.8

4.4

4.7

4.6

5.5

4.9

5.5

5.3

6.3

5.6

6.4

6.1

5.5

5.0

5.5

P contents

(%)

SSP

DAP

DAP+Gypsum

Mean

0.18

-

-

-

0.26

0.24

0.29

0.28

0.29

0.26

0.29

0.28

0.32

0.30

0.32

0.31

0.29

0.26

0.29

Total P uptake

(mg/Pot)

SSP DAP

DAP+ Gypsum

Mean

5.3-

-

-

12.310.4

12.2

11.6

15.713.0

16.0

14.9

20.216.5

20.7

19.1

16.113.3

16.3

Pdff (%)SSP

DAP

DAP+ Gypsum

Mean

35.8

33.6

36.3

35.3

38.6

35.9

38.2

37.6

41.6

39.0

41.4

40.7

38.7

36.2

38.6

Fertilizer P uptake

(mg/pot)

SSPDAP

DAP+ Gypsum

Mean

4.43.5

4.4

4.1

6.14.7

6.1

5.6

8.46.4

8.6

7.8

6.34.9

6.3

P utilization (%)SSP

DAP

DAP+ Gypsum

Mean

37.5

30.0

37.7

35.0

26.0

19.9

26.1

24.0

23.9

18.4

24.5

22.3

29.1

22.7

29.4

Effect of levels and sources of phosphorus on P uptake parameters in mustard

(Sharma and Kamath, 1990)



S.NoP level

(kg P2O5 ha-1)

Pdff (%) P utilization (%)Dry matter yield

(g/ Pot)

GG BG GG GG BG C GG BG C

1 0 - - - - - - 3.76 3.38 7.15

2 30 14.6 11.2 16.9 7.4 5.0 22.2 4.40 3.84 8.72

3 60 25.2 17.6 24.6 8.0 4.9 20.5 5.07 4.22 9.43

4 90 32.4 24.1 26.9 7.4 5.1 16.7 5.03 4.42 9.81

5 Mean 24.1 17.6 22.8 7.6 5.0 19.8 4.56 3.97 8.78

Effect of applied P On % Pdff and % P utilization by green

gram, Bengal gram, and cowpea

(Thind et al ., 1990)



S.No Treatments Mustard linseed

Dry matteryield

(g/pot)

Total Puptake

(mg/pot)

Pdff(%)

Putiliza

tion

(%)

Drymatter

yield

(g/pot)

Total Puptake

(mg/pot)

Pdff(%)

Putiliz

ation

(%)

1 DAP 4.50 12.2 36.5 10.1 9.45 11.1 37.1 8.0

2 DAP+ potassium

silicate

(100 kg/ ha)

5.80 15.9 38.4 13.7 9.22 11.0 38.2 8.1

3 DAP+ calcium

silicate

(100 kg/ ha)

4.55 12.5 36.7 10.3 9.20 11.3 35.4 7.8

4 DAP+ compost

(15 tons/ha)

5.73 16.1 40.7 14.6 10.50 13.9 38.3 10.4

5 DAP+ pressmud

(15 tons/ha)

6.24 17.5 42.2 16.2 13.46 18.1 37.6 13.3

SEm

CD (5%)

0.19

1.48

0.50

1.48

0.72

0.12

0.33

0.97

0.35

1.03

0.41

1.20

0.21

2.11

0.18

0.53

Influence of silicates and organic amendments on dry matter yield

and P uptake parameters

(Singh and Sharma, 1999)



Method and time of application of P use

efficiency



S.No treatments Pdff

(%)

P utilization

(%)

1982-83 1983-84 1982-83 1283-1984

1 SSP broadcast 18.3 17.9 17.9 18.5

2 SSP placement 26.5 24.6 25.2 26.0

3 Blended SSP broadcast22.4 22.3 21.4

4 Blended SSP placement26.0 24.1 25.9 24.6

5 SSP split application 29.5 27.8 31.7 29.9

CD (at 5% level)3.6 4.0 3.1 2.7

Effect of methods of placements on Pdff and P utilization by mustard

Singh and kamath., (1990)



S.No Treatment Fertilizer p uptake

(mg/pot)

A values

(kg P2O5/ ha)

Utilization of fertilizer

P (%)

yield of

fruits(Kg/pot)

Flowering Harvest Flowering Harvest Flowering Harvest

1 Placement at 5

cm depth

688 763 89.8 158 11.5 12.7 3.99

2 Placement at

10 cm depth

763 1045 84.4 99.7 12.6 17.0 4.33

3 Placement at

15 cm depth

674 931 94.3 105 11.2 17.1 4.69

4 Band

placement on

one side offurrow

457 908 99.4 119 7.6 15.3 4.51

5 Placements in

two bands of

seed furrow

688 708 85.7 174 11.5 11.8 4.68

Effect of methods of placement on fertilizer uptake, A values and

utilization by okra

(Shivananda and Iyengar., 1990)



Treatment CROP 1 CROP 2

%Pdfssp %Pdfpr %Pdfsoil %Pdfssp %Pdfpr %Pdfsoil

SOIL 1

Control- - 100 - - 100

PR uniform placement - - 100 - - 100

SSP uniform placement 87.7 - 12.3 81.4 - 18.6

SSP fraction placement 91.7 - 8.3 85.5 - 14.5

SSP-PR uniform placement 90.1 2.8 9.9 81.7 - 18.3

SSP-PR fraction

placement90.4 - 6.8 80.9 5.4 13.7

SOIL 2

Control - 5.0 - - 100

PR uniform placement - - 95.0 - 1.1 98.9

SSP uniform placement 86.0 - 14.0 81.9 - 18.1

SSP fraction placement 90.2 - 9.8 84.0 - 16.0

SSP-PR uniform

placement

85.4 0.77 13.9 81.7 0.20 18.1

SSP-PR fraction

placement

89.0 1.33 9.67 81.1 3.5 15.4

Table 2: Utilization of P from different sources by crop 1 and 2 of rye grass as affected by

method of application (Xiong et al ., 1996)

(Xiong et al., 1996)



Nutrient interaction



S.No N ( Kg ha-1) Flowering stage At harvest

Dry matter

(q ha-1)

Pdff (%) P utilization

(%)

Seed yield

(q ha-1)

1 0 5.41 32.6 4.5 1.54

2 30 9.33 57.1 11.7 3.12

3 60 14.19 58.3 18.5 4.24

4 90 17.80 48.3 18.3 5.64

CD at 5% level 0.74 17.2 4.9 0.10

Effect of Nitrogen on dry matter, Pdff, and P utilization at

flowering and seed yield at harvest.

Venkata Reddyet al

., 1997



P levels

P uptake (mg/pot) Pdff (%) P utilization (%)

S levels

0 25 50 mean 0 25 50 mean 0 25 50 mean

0 7.3 7.8 8.3 7.8 - - - - - - - -

17.5 9.1 9.0 8.8 9.0 20.6 23.7 23.1 22.5 10.7 12.1 11.6 11.5

35 10.0 10.9 11.1 10.7 26.6 31.6 35.0 31.1 76 9.9 11.1 9.5

mean 8.8 9.2 9.4 - 23.6 27.7 29 9.2 9.2 11.0 11.4 -

Effect of P and S levels on total P uptake, percent Pdff and fertilizer P

utilization by soybean seeds.

(Khajanchi Lalet al

., 1997)



Treatments

Dry matter (g/ pot) Total P uptake Pdff (%)P utilization

(%)

Normal Saline Normal Saline Normal Saline Normal Saline

control 4.4 3.7 5.1 4.4 - - - -

P 11.4 9.4 19.2 14.4 22.0 22.1 10.7 8.2

P + Zn 15.0 13.4 23 16.1 24.9 26.4 14.8 10.9

Zn 9.8 10.9 12.8 14.6 - - - -

CD at 5% 0.84 1.54 1.62 1.43

P-Zn interaction on the utilization of P by wheat under varying

levels of salinity.

(Dravid , 1996)



Residual effect of phosphorus

• The rapid reversion of Added soluble phosphatic fertilizers is a common phenomenon in almost all soils, resulting in very low recovery, about 15- 20 percent.

• Rest of the added P remains in the soil in the form of compounds which widedegree of variation in the composition, mobility and availability to the plants.

• Consequently large variation in the persistence of fertilizer residue and recoveryranging from 40 to 124 per cent, depending upon the number and type ofsubsequent crops grown.

• This indicates that a large portion of P remaining after the first crop is not fixed, butis indeed available to the subsequent crops.

• However, direct quantification of residual effect in terms of percent recovery of phosphorus is tedious and often less precise.



S.No P levels

( kg P ha-1)Green gram Rice

Pdff

(%)

Fertilizer p

uptake (mg

P / pot)

A value (mg

P / pot)

Pdff

(%)

Fertilizer P

uptake

(mg P / pot)

A value

(mg P /

pot)

1 0 43.23 1.89 22.91 36.23 2.49 30.71

2 30 38.93 3.85 27.37 28.13 2.56 44.58

3 60 29.23 3.78 42.24 27.30 3.49 46.47

4 90 28.46 3.16 43.86 17.53 3.40 82.09

5 mean 34.96 3.17 34.09 27.29 2.98 50.96

Samaresh kundu et al., 1986

Effect of different levels of initially applied P on percent Pdff and

fertilizer P uptake from the directly applied basal applied doses by

the succeeding crops



utilization of initially applied P by the component of the

cropping system

P levels

(kg P/ha)

Wheat Green gram Rice Total P

utilizati

on (%)Fertilizer P

uptake

(mg P/ pot)

Utilization

P

(%)

Fertilizer

P uptake

(mg P/

pot)

Utiliza

tion P

(%)

Fertilizer P

uptake (mg

P/ pot)

Utilization

P

(%)

30 9.18 15.30 3.55 5.91 2.19 3.65 24.86

60 12.40 10.33 6.69 5.57 4.93 4.10 20.00

90 17.90 9.44 5.49 3.03 11.63 6.45 19.42

Mean 13.16 11.85 5.24 4.83 6.25 4.73 21.42

Samaresh kundu et al., 1986



Efficiency of micro organism on P utilization

• Mycorrhizal symbiosis is the most common existing symbiotic relationshipin the plant kingdom.

• Nuclear techniques have improved the way of more precise measurementsof nutritional elements absorbed by plant and where about they are

transferred in the plant and soil system.

• 32P was used to determine the relatively more precision effect ofmicroorganism in nutrient absorption by plant root system

Eff f P l l d li i Pdff Pdf d h h



Effect of P levels and vam application on Pdff, Pdfs, and phosphorus use

efficiency in tomato plant

S.No treatments P uptake

(mg/pot)

Pdff

(%)

Pdfs

(%)

PUE

(%)

1 VAM control+100kg P205 SSP 147 27.3 72.7 18.12

2 VAM control+ 75 kg P205 SSP 120 26.4 73.6 19.8

3 VAM inoculated +100 kg P205

SSP

189 33.1 66.9 28.5

4 VAM inoculated + 75 kg P205

SSP

140 23.1 76.9 20.2

(Dhinakaran and Savithri, 1997)



S.No Biofertilizers root

colonization

Root dry weight

(g plant-1)

Pdff

(%)

P

utilization

(%)P0 P60 P0 P60

1 No inoculation 2.8 1.5 0.089 0.230 32.5 13.1

2 Glomus faciculatum 90.7 74.8 0.214 0.385 34.1 18.3

3 Pseudomonas striata - - 0.149 0.312 35 16.6

4 Glomus macrcarpum 77.8 60.8 0.179 0.348 35.8 17.7

mean 57.1 45.7 0.157 0.318 34.3 16.4

Effect of different biofertilizers on root dry weight (g plant-1), Pdff and P

utilization of chickpea

Mukherjee et al , (1999)



32P in soil root environment studies

• The root studies are extremely important in given soil and to device

adequate cultural practices for maximizing the yield.

• The growth of the plants depends not only on the total quantity of nutrients

present in the soil but also on the capacity of the root system to extractwater and nutrients.

Tracer techniques for root studies

Placement or injection of career free or labelled compounds in the soil

Plant injection technique



Placement or injection of career free or labelled compounds

in the soil

• 32P was introduced into the soil in angular pattern of spots at differentdepths from the plants.

• Once the radioisotope is traced in the plant above ground, it was calculatedthat roots have extended to, or beyond this spot.

• This method is especially suited for field crops and disturbs soil minimum.

• In principle any radioisotope, not liable to much dispersion from the zoneof placement and having nuclear characteristics of easy detection issuitable.



Plant injection technique

• The amount of radioactivity proportional to the amount live roots in acertain spot.

• At any given stage of growth of healthy plant under a given soil,environmental conditions the ratio between root weight and shoot weight is

more or less constant.

• If the root weight/shoot weight is proportional to specific activity of root/specific activity of shoot, then it is possible to estimate root weight byknowing the shoot weight and the ratio of the specific activities of root and

shoot.



32P uptake is an indicator of drought tolerance

Radioisotope technique is the easiest, précised technique to evaluate orscreening the drought tolerance varieties.

The aim was to relate the P uptake under moisture stress to droughttolerance.

Drought tolerant cultivars had low P uptake under controlled (non stress)condition.

Under moisture stress, the absorption and translocation of 32P wasinhibited and the effect was more pronounced on translocation.

The severity of 32P uptake was related to moisture stress tolerance of thecultivar, “lesser the inhibition more was the tolerance”.

Hence, 32P uptake could be employed as an indictor of drought tolerance indeveloping a screening test based on radiotracer technique.



Conclusion

32P isotopic techniques to get a better understanding of the dynamics of soil P

and evaluating the agronomic effectiveness of local rock phosphate sources in

cropping systems of well-defined agro-ecological zones.

32P techniques are useful in the identification genotypes which are P deficient

and Al tolerant

32P helps to study the environmental pollution caused by phosphatic fertilizers

32P helps to study the mechanism of mobility of P ions, i.e. rate and extent of

soil-solution transfer of orthophosphate ions, in P- deficient and heavily Pfertilized soils

isotopes of phosphorous and its application in agriculture

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