INTERACTION OF SOIL ORDERS AND LEVELS OF APPLIED PHOSPHORUS ON P-STATUS OF SOIL CALTIVATED WITH WHEAT AT ELONGATION STAGE

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e-ISSN:2581-6063 (online), ISSN:0972-5210Plant Archives Volume 21, No 1, 2021 pp. 1270-1277
DOI Url: https://doi.org/10.51470/PLANTARCHIVES.2021.v21.no1.169
Plant Archives
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INTERACTION OF SOIL ORDERS AND LEVELS OF APPLIED PHOSPHORUS ON P-STATUS OF SOIL
CALTIVATED WITH WHEAT AT ELONGATION STAGE
Muslim R. Khoshnaw* and Akram O. Esmail
ABSTRACT
A pot experiment was carried out during autumn growing season of 2016-2017 at the Gerdarasha eld of College of
Agriculture Engineering Sciences, to study the eect of three dominant soil orders (Mollisols (M), Vertisols (V) and Aridisols
(A)), ve levelsof applied triple super phosphate (TSP) fertilizer (0, 80, 160, 240 and 320 kg TSP ha-1) and combination
between them on chemical availability of phosphorus (P) using solubility diagram at elongation stage and wheat yield. The
factorial experiment was depended using a completely randomized design (CRD) with three replicates. The results indicated
that the soil orders were aected on phosphorus status, it has appeared that the studied soil order was located between TCP
and HA for both Aridisols and Vertisols it means the solubility of phosphorus is low. but in Mollisols is slightly more than
Vertisols and Aridisols. It is the P-status and availability was very low since shifting towards TCP, it means precipitation of
P in a non-available form then decrease in its availability. The application of phosphorus fertilizers caused shifting the points
towards a more soluble form of phosphorus.
The results indicated that the application of TSP fertilizer increased the solubility of P in the studied dominate soil orders.
Then, the treatment combination (M, V, A) TSP0 were the nearest point to TCP falling between TCP and OCP which were
the lowest soluble of phosphorus there less available, phosphorus application of phosphorus caused to shifting towards DCP
In contrast, for treatment combination (M,V and A) TSP320 kg ha-1 were located between OCP and DCP the nearest point
treatment combination for DCP
Keywords: Solubility Diagram; Phosphate, Soil orders
(Date of Receiving-13-01-2021; Date of Acceptance-27-03-2021)
Department of Soil and Water, College of Agricultural Engineering Sciences, Salahaddin University-Erbil, Kurdistan Region, Iraq
*Email: muslim.khoshnaw@su.edu.krd
INTRODUCTION
Phosphorus is an essential macronutrient for plant growth,
and it is limiting crop production in many regions of the
world in many agricultural systems in which the application
of phosphorus to the soil is necessary to ensure plant
productivity, in calcareous soils the recovery of applied P
by crop plants in a growing season is very low, since more
than 80% of the P becomes immobile and unavailable for
plant uptake due to adsorption, or precipitation, (Partt,
1978, and Holford, 1997)
Iraqi soils are containing large amount of calcium
carbonate with slightly alkaline pH which causes chemical
and physical xation of 70-90% of applied phosphorus
fertilizers as reported by Esmail, (2012).
In a previous studies conducted by Roy et al., (2006)
and Shand, (2007.), phosphorus was absorbed as the
orthophosphate ion (either as H2PO4
- or HPO4
2-) depending
on soil pH. As the soil pH increased, the relative
proportion of H2PO4
- and HPO4
2- were increased. P is
essential for growth, cell division, root lengthening, seed
and fruit development, and early ripening. It is a part of
several compounds including oils and amino acids. The P
compounds adenosine di phosphate (ADP) and adenosine
triphosphate (ATP) act as energy carriers within the plants.
Phosphorus is one of the most important essential
macronutrients for plants, which contributes in numerous
vital functions in plants like photosynthesis, energy
transfer, respiration and cell division. The phosphorus
availability and status were studied by numerous of
investigators in Iraq like Hasan ; (1985), AlKhateeb et
al., (1986), Al- Sulaivani ;(1993), Saeed; (2008), Galaly;
(2010) and Rahman (2013) using solubility diagram.
Iraqi soils illustration dierent degrees of development
according to the dominant local conditions mainly climatic
and geological conditions. The results of the morphological,
physical and chemical soil properties indicated to presence
of ve soil orders included, Aridisols, Entisols, Inceptisols,
Mollisols and Vertisols (Ahmad, et al., (2014.).
For studying solubility equilibrium of phosphate the
double function parameters consisting of phosphate
potential logH2PO-
4-pH and lime potential (log Ca2+ +
2pH) were used to construct a solubility diagram for
calcium phosphate minerals. It was assumed that the free
ion activity of H2PO-
4 was controlled by lime potential and
pH based on published solubility product (KSP). It was
also assumed that the solubility of phosphate in calcareous
soils is controlled by a solid phase of calcium phosphate
minerals (Lindsay, 1979, Shang, Tiessen, 1998, Khoshnaw,
and Esmail, 2020)
Solubility equilibrium studies generally categorize soils
into those with low pH in which iron (Fe) or aluminium
(Al) phosphates control P solubility, or those with high
pH in which P solubility is controlled by calcium (Ca)
phosphates as reported by McDowell, et al., (2003).

1271
Muslim R. Khoshnaw and Akram O. Esmail
Table 1: Classication of the studied soils along with their geographic coordinates.
Sample No Location Governorate Order Elevation above mean sea level
(Altitude (m)) GPS Reading
N E
Hawler Vertisols Harrier Hawler Vertisols 619 36o32.793' 44o18.308'
Hawler Mollisols Hujran Hawler Mollisols 787 36 o 16.387' 44o17.796'
Hawler Aridisol Makhmur Hawler Aridisol 271 35.7773774 o 43.562006 o
Duhok Vertisols Semeel Duhok Vertisols 569 36.867697 o 42.969343 o
Duhok Mollisols Zawita Duhok Mollisols 967 36.900077 o 43.146660 o
Duhok Aridisol Fayda Duhok Aridisol 372 36.712639 o 42.971565 o
Sulaimani Vertisols Bakrajo Sulaimani Vertisols 731 35.529235 o 45.335274 o
Sulaimani Mollisols Halabja Sulaimani Mollisols 501 35.300880 o 45.954688o
Sulaimani Vertisols Kfry Sulaimani Aridisol 177 34.690550 o 44.864398 o
Phosphorus (P) retention and mobilization take place
due to precipitation and adsorption in calcareous soils;
however, it is not always easy to distinguish between the
two mechanisms. Water soluble P fertilizers applied to
soil react with the soil constituents to form less soluble
phosphates. When added to soil containing large amounts
of calcium, soluble P is usually precipitated as di calcium
phosphate or octa-calcium phosphate as mentioned by
Mam Rasul., (2016)., Muhawish,. and Al-Kafaje., (2017)
The high response for soil to orthophosphate O.P was
recorded with respect to dicalcium phosphate dihydrate
(DCPD) at high rate of application and within short and
long period of O.P supply within 15 and 60 days mentioned
by Rahman, (2013).
Rasheed, (2019) analyzed 120 soils from the wheat
grown elds the results indicated that soils that have more
available P, the P- compounds were in the form of DCP and
TCP but soils that have less available P the P compounds
were in the form of TCP and HA (un soluble form).
Since there are little or no studies about interaction of
soil orders and levels of phosphorus fertilizer for this
reason this studies was conducted to study the interaction
eect of soil orders and levels of applied phosphorus on
P-availability using solubility diagram
MATERIALS AND METHODS
The studied soils included three dominant soil orders
Mollisols (M), Vertisols (V) and Aridisols (A) according
to United State Department of Agriculture (USDA) soil
Taxonomy (soil survey sta, 1999), and Global Positioning
System (GPS) reading of the selected locations were
recorded from Table ( 1 )
Soils were included three dominant soil orders which were
collected from Hawler, Sulaimani and Duhok governorates
from the depth of 0-30 cm, then transported to Gerdarasha
eld then air dried and sieved by 4mm sieves for pot
experiment. On 24/11/2016 (18) seeds of wheat (Triticum
aestivum) directly planted in each pot, using factorial
(CRD) with three replicates. Each soil order was taken
from three locations and regarded as replications. The
weight of soil per pots was 10 kg air dried soil.
Five levels of phosphorus fertilizer (0, 80, 160, 240 and 320
kg TSP ha-1 ) which equivalent to (0, 0.2, 0.4, 0.6 and 0.8g
TSP for 10 kg -1 soil (pot) in three dominant soils orders
(M, V, and A), while xed amount of urea (0.6 g. urea 10
kg-1 soils) which equivalent to (240 kg urea ha1) was added
to all pots. After the seeds were planted the pots were
watered to eld capacity, while subsequently irrigation
depended on weighing method whenever needed. The
irrigation was done after depletion 75% of available water
depending on weighing method. The soil samples were
taken at elongation stage for preparing solubility diagram
Chemical and physical properties
The soils were air-dried, and sieved by 2 mm sieve and
stored for laboratory analysis, table (2) shows some
chemical and physical properties for the main soil order at
dierent locations.
The soil analysis included Electrical Conductivity, soil
calcium carbonate content (CaCO3) hygroscopic moisture
content (H M), moisture at eld capacity (FC) and wilting
point (W.P), Particle size distribution, Soil pH, and organic
matter content which were determined according to the
standard methods mentioned by (Bashour and Sayegh,
2007). Used the regression equations to estimate the
eld capacity and wilting point depending upon the clay
fraction % .( Karim, 1999).
Determination of soluble P for solubility diagram:
Phosphorus in soil has been extracted by using distilled
water with 0.01 M KCl and determined spectrometric ally
according to Murphy and Riley (1962) as described in
Black, (1980) using spectrophotometer model (Shimadzo
at wave length 880nm). The chemical analysis and
calculations for drawing solubility diagram were recorded
in table (3).
Phosphate solubility Diagram
Double function parameters consisting of phosphate
potential log H2PO-
4-pH and lime potential (log Ca2+ +
2pH) were used to construct a solubility diagram for
calcium phosphate minerals. It was assumed that the free
ion activity of H2PO-
4 was controlled by lime potential
and pH based constant of solubility product (Ksp). It was

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Interaction of soil orders and levels of applied phosphorus on p-status of soil caltivated with wheat at elongation stage
Table 2: The mean for some chemical and physical properties for dominant soil orders Mollisols, Vertisols, Aridisol in Hawler, Sulaimani and Duhok.
Treatment Particle Size Destitution H M FC WP SP CaCO3pH EC
% g kg-1 dS m-1
Mollisols Hawler
Sand 23.00
Silty loam 5.05 21.25 11.59 39.52 300 7.39 0.36Silt 56.93
Clay 20.06
Mollisols Sulaimani
Sand 11.41
Siltyloam 6.00 30.35 19.62 56.45 230 7.31 0.54Silt 45.59
Clay 43.00
Mollisols Duhok
Sand 17.62
Siltyclay 4.86 30.25 19.53 56.27 210 7.54 0.485Silt 39.63
Clay 42.75
Vertisols Hawler
Sand 45.24
Siltyclay 4.24 32.17 21.22 59.83 300 7.47 0.41Silt 7.19
Clay 47.57
Vertisols Sulaimani
Sand 4.32
Siltyclay 4.71 35.37 24.04 65.78 268 7.464 0.31Silt 40.05
Clay 55.63
Vertisols Duhok
Sand 3.50
Siltyclay 9.20 33.50 22.39 62.30 240 7.47 0.37Silt 45.58
Clay 50.92
Aridisol Hawler
Sand 22.02
Clay loam 2.34 24.01 14.03 44.65 488 7.78 0.51Silt 50.96
Clay 27.02
Aridisol Sulaimani
Sand 14.37 Siltyclay
loam 3.78 25.76 15.58 47.92 460 7.72 0.45Silt 54.18
Clay 31.45
Aridisol Duhok
Sand 22.11
Clay loam 2.89 27.78 17.35 51.67 590 7.92 0.46Silt 41.36
Clay 36.53

1273
Muslim R. Khoshnaw and Akram O. Esmail
Table 3: pH, (calcium and phosphorus activity), P-potential and lime potential for studied combination treatments.
Code pH Soluble P mgL-1 Ca mgL-1 P moleL-1 Ca moleL-1 Log H2PO-4 Log Ca+2 Log Ca+2+2pH Log H2PO-4 pH
Mollisols(H, S, D)TSP07.763 0.098 38 3.16E-06 0.00095 -5.49989 -3.02228 12.50372 -13.2629
Mollisols (H, S, D)TSP80 7.73 0.157 39 5.05E-06 0.000975 -5.29639 -3.011 12.449 -13.0264
Mollisols (H, S, D)TSP160 7.753 0.179 42 5.76E-06 0.00105 -5.23959 -2.97881 12.52719 -12.9926
Mollisols (H, S, D)TSP240 7.752 0.217 45 7.01E-06 0.001125 -5.15446 -2.94885 12.55515 -12.9065
Mollisols (H, S, D)TSP320 7.877 0.340 46 1.10E-05 0.00115 -4.96023 -2.9393 12.8147 -12.8372
Vertisols(H, S, D)TSP07.766 0.079 40 2.55E-06 0.001 -5.59317 -3 12.532 -13.3592
Vertisols(H, S, D)TSP80 7.9 0.147 44 4.74E-06 0.0011 -5.32404 -2.95861 12.84139 -13.224
Vertisols(H, S, D)TSP160 7.8 0.155 43 4.99E-06 0.001075 -5.30228 -2.96859 12.63141 -13.1023
Vertisols(H, S, D)TSP240 7.9 0.167 44 5.39E-06 0.0011 -5.26836 -2.95861 12.84139 -13.1684
Vertisols(H, S, D)TSP320 7.95 0.208 46 6.71E-06 0.00115 -5.17307 -2.9393 12.9607 -13.1231
Aridisols(H, S,D)TSP07.8572 0.076 43 2.45E-06 0.001075 -5.61163 -2.96859 12.74581 -13.4688
Aridisols(H, S,D)TSP80 7.81 0.120 48 3.88E-06 0.0012 -5.41138 -2.92082 12.69918 -13.2214
Aridisols(H, S,D)TSP160 7.87 0.130 49 4.20E-06 0.001225 -5.37631 -2.91186 12.82814 -13.2463
Aridisols(H, S,D)TSP240 7.94 0.142 48 4.58E-06 0.0012 -5.33907 -2.92082 12.95918 -13.2791
Aridisols(H, S,D)TSP320 7.98 0.165 55 5.32E-06 0.001375 -5.27388 -2.8617 13.0983 -13.2539
also assumed that the solubility of phosphate in
calcareous soils is controlled by a solid phase of
calcium phosphate minerals (Lindsay, 1979)
RESULTS AND DISCUSSION
The results in Figure (1) explains phosphorus
application on P status (solubility) at elongation
stage of wheat plant, for the studied soil orders.
Figure (1) shows that the application of phosphorus
fertilizers caused shifting the points towards more
soluble form of phosphorus minerals. The P status
in cause of (TSP0,TSP80, TSP160) kg ha-1 were
plotted or located between tri-calcium phosphate
TCP andoctacalcium phosphate OCP forms or the
availability of phosphorus is very low, while in case
of TSP 240 the point was located on OCP or the
phosphorus is in equilibrium with OCP which is
available form at rahizospher. On the other hand in
case of application 320 kg TSP ha-1 the point was
plotted between OCP and DCP line, it means the
application of 320 kg TSP ha-1 caused increase in
P-availability due to shifting the point towards the
more soluble form of phosphorus minerals.
The results of the current study indicated that OCP
and TCP minerals may be stable forms of P mineral
in all soil orders. This is in agreement with the
nding of Zhang et al., (2014) who found that the
solubility of phosphate in soil orders was controlled
by TCP while in unfarmed soil it was controlled by
HA. They also reported the increase in P-availability
in farmed calcareous soil after several years due
to P- fertilization. The increase in application of
P-fertilizers caused increased in availability of
phosphorus (Fig 1) which caused increase in wheat
yield from 2.27 to 3.44 Mg ha-1 for TSP0 and TSP320
respectively (table 4), supported by Saeed; (2008),
Galaly ;(2010) and Esmail,(2012).
The results in Fig (2) shows the eect of dominant
soil orders (Mollisols, Vertisols and Aridisols)
on phosphate solubility in Hawler, Sulaimani and
Duhuk soils of Kurdistan region at elongation stage
for wheat plant in the studied soils.
Figure (2) illustrated that the P status was located
between TCP and HA for Aridisols it means the
solubility of phosphorus is low due to low solubility
of phosphorus form (TCP and HA) for Aridisol
.It is the nearest point for TCP line it means low
phosphorus availability, but for Vertisols located
on the TCP line while for Mollisols was located
between TCP and OCP. Figure (2) explains the
solubility of P in Mollisols is slightly more than
Vertisols and Aridisols. It means the P-status and
availability was very low due to shifting towards
TCP, it means precipitation of P in non-available
form then decrease in its availability reported by
McDowell et al., (2003)and Rasheed, (2019).The

1274
Interaction of soil orders and levels of applied phosphorus on p-status of soil caltivated with wheat at elongation stage
Table 4. Eect of dierent levels of phosphorus on grain yield and total dry
Levels kg ha-1 Grain yield Mg ha-1
TSP0 2.27
TSP80 2.54
TSP160 2.85
TSP240 3.29
TSP320 3.44
Table 5. Eect of soil orders on grain yield and total dry matter
Orders Grain yield Mg ha-1
Mollisols 3.09
Vertisols 2.83
Aridisols 2.71
Figure 1 shows the eect of levels of applaied phosphorus on availability of phosphorus at elongation stage of wheat.
Figure 2 The eect of dominant soil orders (Mollisols, Vertisols and Aridisols) on the solubility equilibria of phosphorus at elon-
gation stage for wheat plant

1275
Muslim R. Khoshnaw and Akram O. Esmail
Figure 3 Combination eect soil orders and levels of applied phosphorus on the P- solubility equiliberiain Kurdistan region at
elongation stage of wheat plant
data analysis in the table (5) revealed the high mean yield
value were (3.09, 2.83, 2.712 ) recorded in soil orders
(Mollisols, Vertisols, Aridisols) respectively explains the
above results for P- availability depending on solubility
diagram
Figure (3) explains combination eect of soil orders
and levels of applied TSP fertilizers on P-availability at
elongation stage of wheat plant.
In general the combination between soil orders and levels
of applied phosphorus fertilizer aected on phosphorus
status.
The treatment combinations divided in to three groups.
First group included 9 treatment combinations (Mollisols-
TSP0), (Vertisols-TSP0), (Aridisols-TSP0), (Mollisols-
TSP80) , (Aridisols-TSP80), (Mollisols-TSP160), (Vertisols-
TSP160), (Aridisols-TSP160)and (Molisols-TSP240) which
were located between OCP and TCP. Second group,
included three treatment combinations (Vertisols-TSP80),

1276
Interaction of soil orders and levels of applied phosphorus on p-status of soil caltivated with wheat at elongation stage
Figure 4 Combination eect of levels applied phosphorus and soil orders on grain wheat
(Vertisols-TSP240) and (Aridisols-TSP240), the treatment
combinations were plotted on OCP line.Third group, three
of treatment combinations (Mollisols-TSP320), (Vertisols-
TSP320) and (Aridisols-TSP320) were located between OCP
and DCP. The phosphorus status in the last group was
better or more soluble than other groups due to solubility
of OCP and DCP in rhizospher.
As a result increase in the levels of TSP for soil orders
caused increase in availability of P, the best treatment
combination was (Mollisols- TSP320) because it is the
nearest point or treatment combination to DCP, it means
the increase in solubility of P caused increase in yield
(Fig 4). These results agree with Galaly, (2010), Rasheed,
(2019) and Khoshnaw, and Esmail, (2020) . While, the
results provide information about the relation between P
availability and the dominant soil orders. Organic matter
may also increase P solubility through calcium chelating
which caused either a permanent or a temporary delay in
the formation of basic calcium phosphate.
In general in calcareous soils phosphate solubility is
low due to rapid immobilization by calcium carbonate
and slow recrystallization as poorly soluble calcium
phosphate minerals. The initial formed phosphate mineral
is di-calcium phosphate, which is then converted into octa-
calcium phosphate and more basic hydroxyapatite.
As a result increase the of levels of TSP for soil orders
caused to increase solubility P, and increase availability
of phosphorus reported by Muhawish, and Al-Kafaje,
(2017), Rekani, et al., (2018),and Rasheed, (2019). While,
the results provide information about the relation between
P availability and the dominant soil orders. Organic matter
may also increase P solubility through calcium chelating
which causes either a permanent or a temporary delay in the
formation of basic calcium phosphate Organic matter plays
important roles in improving soil physical, chemical, and
biological properties. It is considered as a very important
parameter of soil fertility and productivity. It provides
nutrients to the soil, improves water holding capacity and
helps the soil to maintain better aeration and soil quality
for seed germination and plant root development (Ding, et
al., (2006), Oorts, et al., (2003) and Zia, (1993).
The studied soil orders, levels of applied phosphorus and
their combination had great eect on phosphorus status
and wheat yield, due to their eect on forming dierent
phosphorus compounds range between non soluble to
soluble form of phosphorus compound or from Hydroxy
apatite to Di- calcium phosphate di hydrate as explained
by solubility diagrams for phosphorus. Application of
dierent levels of phosphorus caused the shifting towards
di-calcium phosphate (DCP) and di-calcium phosphate
di-hydrate (DCPD). The treatment combination Mollisols
TSP320 was recorded the highest grain yield.
CONCLUSION
Phosphorus were less available in the treatment
combinations Mollisols-TSP0, Vertisols-TSP0 and
Aridisols-TSP0 refers to low soluble were falling between
TCP and OCP, then the lowest soluble phosphorus so as
less available, While application of dierent levels of
phosphorus caused the shifting of points towards dicalcium
phosphate (DCP) , then for treatment combination
Mollisols TSP320 kg ha-1 was the highest grain availability,
the best treatment combination was Mollisols TSP320 kg
ha-1. Application was shifted towards DCP, which are
more soluble phosphorus compounds, it is appear from
phosphorus solubility diagram.
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