Phosphorus fractions - Keys to soil based P management - TRƯỜNG CÁN BỘ QUẢN LÝ GIÁO DỤC THÀNH PHỐ HỒ CHÍ MINH

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Int.J.Curr.Microbiol.App.Sci (2017) 6(11): 281-294

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Original Research Article

Phosphorus Fractions- Keys to Soil based P Management

M. Chandrakala1*, C.A. Srinivasamurthy2, V.R.R. Parama3,

S. Bhaskar4, Sanjeev Kumar5 and D.V. Naveen6

National Bureau of Soil Survey and Land Use Planning, Regional Centre, Hebbal,
Bangalore-560 024, Karnataka, India

Director of Research, Central Agricultural University, Imphal, Manipur, India
3

Department Soil Science and Agricultural Chemistry, UAS, Bangalore-560 065,
Karnataka, India

Department of Agronomy, UAS, Bangalore-560 065, Karnataka, India
5

NDRI, Karnal, India
6

Deptartment of Soil Science and Agricultural Chemistry, Sericulture College,
Chintamani, Karnataka, India

*Corresponding author

A B S T R A C T

Introduction

The total phosphorus level of soil is not only
low but also P compounds are mostly
unavailable for plant uptake. The
concentrations of phosphorus in the soil
solution (intensity) and capacity of the soil to

supply phosphorus to the soil solution are
important factors affecting P availability. As
the basic raw material rock phosphate
available in the country is only 10 per cent of
the total requirement hence, fertilizer industry

International Journal of Current Microbiology and Applied Sciences

ISSN: 2319-7706 Volume 6 Number 11 (2017) pp. 281-294

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Red soils (Alfisols) of Karnataka are low in total and available phosphorus (P). When

soluble P sources are added, undergo transformation into unavailable forms with time.
Native P compounds, some being highly insoluble are unavailable for plant uptake. Thus,
knowing the changes in P fractions in different soils is much important for P
recommendation. The objective of the study was to find out the fate of the applied
phosphorus in soils of different P fertility in a finger millet-maize cropping system. An
experiment with creation of five P fertility gradient strips (Very low, Low, Medium, High
and Very high) in one and the same field followed by response of finger millet and maize
crops to graded levels of P was undertaken at UAS, Bangalore. Soil P fractions were
determined in a soil after the harvest of maize in a finger millet- maize cropping system.
There was an increase in total-P, organic-P, reductant soluble-P, occluded-P and calcium-P
fractions with the increased gradient strips from very low to very high applied with levels
of P. Whereas, saloid-P, aluminium-P and iron-P are the slowly and plant available
labile-P forms which were decreased as the labile-P fertility gradients and dose of labile-P addition increased.
There was a direct relationship with addition, fixation and distribution of P fractions.
Hence, continuous P fertilization can be restricted in soils of high and very high initial P
status as the PUE was 20-40 per cent only in general leads to build-up and transformation
in to non-labile P forms.

K e y w o r d s

Fertility gradients,
Finger millet – maize
cropping system,
Graded levels of P,
Soil phosphorus
fractions.

Accepted: 
04 September 2017
Available Online:

10 November 2017

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in India is not self sufficient in meeting the
requirement of P therefore, depends on
imports for the balance of 90 per cent
(Chandrakala, 2014).

Phosphorus (P) dynamics in soil and
maintenance of its adequate supply are
important for sustainability (Song et al.,

2007). The application of P to each crop in a
rotation and low recovery of added P has been
found to result in its significant build up in
soils (Brar et al., 2004). Application of
fertilizer phosphorus is essential for raising
the available P content in soils in order to
meet the crop requirements at different stages
of growth. The availability of soil P to plants
depends on the replenishment of labile P from
other P fractions. Nwoke et al., (2004)
observed that the changes in different
inorganic-P fractions in soils under a wide
range of management conditions. The extent
of P depletion ranged from 33 to 129 per cent
over a period of 11 years (Nambiar and
Ghosh, 1984; Tandon, 1987).

Knowing the initial soil test value and
recovery of added phosphates, it will be
possible to work out the amount of fertilizer
phosphorus needed to build-up the soil
phosphate to a given critical limit. Soil based
P management relies on maintenance of
adequate soil P fertility and replenishment of
P nutrient removed by harvested grain.
However, there is a need to know the effect of
P addition and distribution in soils of different
P status for sustained P management and
improved PUE in the region. In the light of
the above facts, a field experiment was
undertaken involving gradient creation
followed by response of finger millet
(Eleusine coracana L.) - maize (Zea mays L.),
are the major crops cultivated in Karnataka
among millets and cereals, respectively.
The objective of the investigation is to assess
the availability of phosphorus and their
different fractions in soils of different

phosphorus fertility gradients applied with
graded levels of P to finger millet- maize
cropping system.

Materials and Methods

The field experiment comprised of two stages.

Fertility gradient creation was the preparatory
step as per the procedure of Ramamoorthy et 
al., (1967) followed by finger millet-maize
cropping system in the subsequent seasons.
Experimental site

The experiment was conducted during
2009-2010 at D-16 Block, Zonal Agricultural
Research Station (ZARS), GKVK, UAS,
Bengaluru which is located in Eastern Dry
Zone of Karnataka at latitude of 12058' N and
longitude of 75035' E with an altitude of 930
m above mean sea level.

Soil characteristics of experiment site 
Surface soil (0-15 cm) was analyzed for
physical and chemical properties and also
determined phosphorus fractions by adopting
standard procedures. Soils are reddish brown
laterite derived from gneiss under subtropical
semiarid climate. The soil of experimental site
was red sandy clay loam in texture, acidic in
reaction, low in available nitrogen (203.84 kg
ha-1) and phosphorus (18.42 kg ha-1) and
medium in available potassium (147.12 kg
ha-1) content (Table 1).

Experimental details

Creation of fertility gradient strips

Five equal strips (45 × 8.2 m2) were created in
one and the same field and named very low
(VL), low (L), medium (M), high (H) and
very high (VH) gradient strips as P0, P1, P2, P3

and P4, respectively. Graded doses of

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per cent each so as to achieve Very low (<15
kg P2O5 ha-1), Low (16-30 kg P2O5 ha-1),

Medium (31- 45 kg P2O5 ha-1), High (46 - 60

kg P2O5 ha-1) and Very high (> 60 kg P2O5

ha-1) P levels in the respective strips.
Exhaustive crop fodder maize (South African
tall) was grown provided with recommended
doses of nitrogen (100 kg ha-1), phosphorus
(50 kg P2O5 ha-1) and potassium (25 kg K2O

ha-1) and green fodder was harvested at 60
days after sowing. Soils in each strip analyzed
for available nutrients status. Available P2O5

content obtained in P0, P1, P2, P3 and P4,was

14.82, 27.37, 38.76, 52.25, 80.72 kg ha-1,
respectively.

Studies on the changes in soil P and 
different P fractions

After harvest of exhaustive crop, each strip
was divided in to three replications and
further each replication was sub divided in to
seven treatment plots of equal size. Finger
millet (GPU-28) was grown (spacing: 20 x 10
cm) during summer followed by maize
(Nithyashree Hybrid) was grown (spacing: 60
x 30 cm) during kharif 2011 by imposing
treatments in a factorial RCBD design.
Treatment details as follows; T1: Absolute

control; T2: Package of Practice

(NPK+FYM); T3: 100 % Rec. N, P &K only

(no FYM); T4: 75 % Rec. P + rec. dose of

N&K (no FYM); T5: 75 % Rec. P + Rec. dose

of N&K only+ Rec. FYM; T6: 125 % Rec. P

+ Rec. dose of N&K (no FYM); T7: 125 %

Rec. P + Rec. dose of N&K + Rec. FYM.

Recommended dose of fertilizer for finger
millet was 50- 40- 25 kg N- P2O5- K2O ha-1

whereas for maize 100-50-25 kg N-P2O5-K2O

ha-1 was given. Recommended dose of FYM
given was 7.5 t ha-1.

Soil sampling and analysis

After the harvest of maize in a finger
millet-maize cropping system, The representative

soil samples were collected at 0-15 cm depth
from all the plots separately, which were
analyzed for available P and their fractions as
per the standard procedures as follows.
Total phosphorus was estimated by
vanado-molybdo phosphoric yellow colour method
(Hesse, 1971). Organic phosphorus was
determined by deducting the sum of total
inorganic phosphorus from total phosphorus
as suggested by Mehta et al., (1954). The
available phosphorus was extracted using
Bray’s No.1 extractant for the soils having pH
less than 6.5 and Olsen’s extractant for the
soils having pH 6.5 and above. The extracted
phosphorus was estimated by chloro-stannous
reduced molybdo-phosphoric blue colour
method (Jackson, 1973).

The method outlined by Peterson and Corey
(1966) was followed to fractionate soil
inorganic phosphorus. Saloid-P was estimated
by molybdo-sulphuric acid reagent, using
stannous chloride as reductant. Aluminium
phosphorus (Al-P) determined by
molybdic-boric acid reagent and
chloro-stannous reductant using the soil residue left
after saloid-P estimation. The soil sediment
from Al-P estimation, was then used to
determine iron phosphorus (Fe-P) by
molybdic-boric acid reagent and
chloro-stannous reductant.

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Data computation

The experimental data were analyzed using
ANOVA (One-Way). Critical differences
among treatments were estimated at 5 %
probability level of significance. Correlation
studies were made and the values of
correlation coefficient (r) were calculated and
tested for their significance (Panse and
Sukhatme, 1967).

Results and Discussion

Data presented in Table 2 to 6 depicted
changes in phosphorus fractions after harvest
of maize in a finger millet-maize cropping
system which showed significant differences
among mean values of P gradients, treatments
and their interaction.

Fertility gradients effect

There was an increase in, total-P (Table 2),
organic-P (Table 3), RS-P (Table 5),
occluded-P (Table 6) and Ca-P (Table 6)
fractions with the increased fertility gradient
strips from very low to very high strip. This
might be due to application of P in the
increasing dose in order to create fertility
gradients. Enrichment of the total and
available P (Fig. 1) status as the PUE (Table
8) by the crops was 20-40 per cent only in
general. There was a positive correlation
exists (Table 7a) between T-P and Org-P,
RS-P, Occl-P and Ca-P fractions (0.997*, 0.999*,
0.974* and 0.992*, respectively). There were
also recorded increased Org-P, RS-P, Occl-P
and Ca-P fractions with the increased T-P
content of soil.

Unlike T-P, org-P, RS-P, occl-P and Ca-P
fractions, S-P (Table 3), Al-P (Table 4) and

Fe-P (Table 4) fractions were decreased as the
P fertility gradients increased. This may be
due to transformation of these fractions in to
non-labile forms of P. The Al-P and Fe-P

fractions were higher in very low and low
gradient strips, might be due to acidic soil pH
resulting in transformation of added P in to
Al-P and Fe-P fractions. Majumdhar et al.,

(2007) observed that the contribution of
Org-P to T-Org-P was 48.90 to 53.70 per cent. They
also noticed significant increase in S-P, Al-P,
Fe-P and Ca-P but decrease in
reductant-soluble and occluded-P fractions. Setia and
Sharma (2007) observed that application of P
@ 17.50 or 35 kg P ha-1 increased all the
forms of P in 22 years of maize-wheat cycles.
The relative abundance of P fractions was in
the order of saloid-P < Fe-P < Al-P < Ca-P.
Jakasaniya and Trivedi (2004) also noticed
that the increase in S-P, Al-P, Fe-P and Ca-P
fractions with increase in rate of P addition in
different soils. Org-P showed a buildup due to
sorghum cropping in all soils.

Treatments effect

Application of graded levels of P with
gradient strips had direct relationship with

quantity and distribution of P fractions. The
quantity of P fractions was higher as the rate
of P application was higher. Application of
125 % rec. P + rec. N&K + rec. FYM to very
high gradient strip recorded higher T-P and
Org-P followed by nutrients application as per
package of practice and 125 % rec. P + rec.
N&K. Labile-P forms (S-P, Al-P and Fe-P)
were higher when P was added along with
manure may be due to lesser fixation of P and
chelating action of manures which keeps the P
in solution there by reducing the
transformation of labile P in to non-labile P
forms. Non labile pool was enriched when P
was added at higher rate without manure
application. Anil kumar (2013) reported that
application of manures recorded significantly
higher available P over control.

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comparison to their initial concentration.
Sukhvir Kaur (2015) reported that the
application of integrated fertilizers recorded

significantly higher Sa-P concentration
compared to inorganic only.

Fig.1 AvP2O5 in soils of different P fertility strips as influenced by graded levels of applied P

Table.1 Initial soil properties of experimental site

Parameters Values

Coarse sand (%) 33.2

Fine sand (%) 36.3

Silt (%) 7.5

Clay (%) 23.0

Textural Class Sandy Clay loam

CEC [c mol (p+) kg-1] 11.10

pH (1:2.5) 5.55

EC (dS m-1) 0.26

Organic Carbon (%) 0.45

Available N (kg ha-1) 203.84

Available P2O5 (kg ha
-1

) 18.4

Available K2O (kg ha
-1

) 147.1

Exchangeable Ca [c mol (p+) kg-1] 6.75
Exchangeable Mg [c mol (p+) kg-1] 3.60

Avail. S (mg kg-1) 10.82

DTPA-Fe (mg kg-1) 55.8

DTPA-Mn (mg kg-1) 59.5

DTPA-Cu (mg kg-1) 2.21

DTPA-Zn (mg kg-1) 2.35

B (mg kg-1) 0.54

Phosphorus fractions

Total P (mg kg-1) 1115.0

Saloid–P(mg kg-1) 48.70

Al-P (mg kg-1) 70.52

Fe-P (mg kg-1) 135.66

Reductant soluble-P (mg kg-1) 146.85

Occluded-P (mg kg-1) 11.07

Calcium-P (mg kg-1) 10.53

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Table.2 Changes in total soil phosphorus fraction (Total P) after harvest of maize

P levels/Treatments

Total- P(mg kg-1)

P0 P1 P2 P3 P4 Mean

T1 726.33 1086.50 1113.33 1331.67 1517.92 1155.15

T2 1288.67 1543.67 1676.67 1724.67 1810.83 1608.90

T3 1033.33 1220.83 1337.67 1430.42 1563.08 1317.07

T4 959.00 1198.17 1247.75 1436.25 1501.58 1268.55

T5 1121.33 1308.75 1403.75 1538.00 1757.58 1425.88

T6 1075.33 1431.00 1533.67 1694.17 1797.07 1506.25

T7 1381.00 1619.00 1701.33 1890.33 1989.75 1716.28

Mean 1083.57 1343.99 1430.60 1577.93 1705.40 1428.30

F S.Em± CD (p=0.05) CV

P S 37.06 104.58

11.89

T S 43.85 123.74

P x T NS - -

T1: Absolute control P0: Very low Phosphorus fertility strip

T2: Package of Practice (rec. NPK+FYM) P1: Low Phosphorus fertility strip

T3: 100 per cent rec. N, P & K (no FYM) P2: Medium Phosphorus fertility strip

T4: 75 per cent rec. P + rec. N&K (no FYM) P3: High Phosphorus fertility strip

T5: 75 per cent rec. P + rec. N&K+ rec. FYM P4: Very high Phosphorus fertility strip

T6: 125 per cent rec. P + rec. N&K (no FYM)

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Table.3 Changes in organic and saloid soil phosphorus fractions (mg kg-1) after harvest of maize

P levels/ 
Treatments

Org-P S- P

P0 P1 P2 P3 P4 Mean P0 P1 P2 P3 P4 Mean

T1 425.91 646.00 674.71 889.70 1066.52 740.57 47.98 53.81 50.73 39.27 36.07 45.57 
T2 691.64 924.07 1105.90 1132.47 1197.97 1010.41 84.07 89.25 54.03 44.60 43.67 63.12 
T3 418.03 614.30 758.43 864.18 971.38 725.26 64.82 72.49 49.73 40.23 34.00 52.25 
T4 415.16 614.73 725.73 921.25 1065.17 748.41 64.14 77.59 48.43 41.09 36.28 53.51 
T5 593.89 722.71 879.12 1020.05 1230.28 889.21 70.73 81.77 55.61 52.89 47.96 61.79 
T6 466.37 792.52 933.56 1089.97 1160.29 888.54 50.20 66.47 38.95 39.55 37.93 46.62 
T7 706.63 969.11 1141.60 1318.74 1417.07 1110.63 85.84 90.52 45.74 42.21 35.73 60.01 
Mean 531.09 754.78 888.43 1033.77 1158.38 873.29 66.83 75.99 49.03 42.83 38.81 54.70

F S.Em± CD (p=0.05) CV F S.Em± CD (p=0.05) CV

P S 12.74 35.96

6.68

S 1.92 5.42

16.11

T S 15.08 42.55 S 2.27 6.42

P x T S 33.72 95.15 S 5.08 14.35

T1: Absolute control P0: Very low Phosphorus fertility strip

T2: Package of Practice (rec. NPK+FYM) P1: Low Phosphorus fertility strip

T3: 100 per cent rec. N, P & K (no FYM) P2: Medium Phosphorus fertility strip

T4: 75 per cent rec. P + rec. N&K (no FYM) P3: High Phosphorus fertility strip

T5: 75 per cent rec. P + rec. N&K+ rec. FYM P4: Very high Phosphorus fertility strip