This document discusses phosphorus availability in calcareous soils. It covers several factors that affect phosphorus availability, including time, phosphorus fertilizer source, organic matter content, temperature, and inherent soil properties. Case studies and literature reviews are presented that show how the addition of organic and inorganic phosphorus fertilizers can increase phosphorus availability over time in calcareous soils, with organic sources providing more long-term availability. Proper phosphorus management strategies for calcareous soils include maintaining optimal soil pH, applying phosphorus frequently in small amounts, banding or injecting fertilizers, and placing fertilizers near plant roots.

1. An Assignment
On
“Phosphorus Availability In Calcareous Soil”
Submitted To:
Dr. A.V. Rajani
Assistant professor
Dept. Of Agril. Chemistry and Soil Science
College Of Agriculture,
Junagadh Agricultural University
Junagadh
Submitted By:
Vikram Singh
Reg. No.: 2010115095
M.Sc. (Agri.) Student

2. Contents:
1. Introduction
2. Phosphorus nutrition
3. Factors affecting phosphorus availability in calcareous soil
4. Inherent Factors Affecting Soil Phosphorus
5. Phosphorus Management
6. Case studies
7. Reviews of literature
8. Summary
9. References

3. 1. Introduction:
Phosphorus (P) availability in calcareous soils is almost always limited. After P
fertilizer is added to a calcareous soil, P undergoes a series of chemical reactions with
Calcium that decrease its solubility with time (a process referred to as P fixation). Addition of
organic manure not only provides additional sources of nutrients, but improves the soil
physical and chemical conditions and may increase the efficiency of added P fertilizers.
Information on the availability of P following chemical fertilizer and compost application to
soil may improve the management of P fertilization. Studies on P reactions over time and the
role of organic matter in calcareous soils are important for developing P fertilizers and
manure management practices.
2.Phosphorus nutrition:
Phosphorus (P) is an essential macronutrient, being required by plants in relatively
large quantities (~0.2 to 0.8%) .Potassium and nitrogen are the only mineral nutrients
required in larger quantities than P. Providing adequate P to plants can be difficult, especially
in alkaline and calcareous soil.
Alkaline soil is defined as soil with pH greater than neutral, typically 7.5 to 8.5.
Calcareoussoil is defined as having the presence of significant quantities of free excess lime
(calcium or magnesium carbonate). Lime dissolves in neutral to acid pH soil, but does not
readily dissolve in alkaline soil and, instead, serves as a sink for surface adsorbed calcium
phosphate precipitation. The bioavailability of P is strongly tied to soil pH. The formation of
iron and aluminium phosphate minerals results in the reduced solubility of P in strongly
acidic soil, improving as pH approaches nearly neutral. This maximum solubility and plant
availability of P at pH 6.5 declines again as the pH increases into the alkaline range. This
effect of reduced P availability in alkaline soil is driven by the reaction of P with calcium,
with the lowest solubility of these calcium phosphate minerals at about pH 8. The presence of
lime in alkaline soil further exacerbates the P availability problem. The lime in calcareous
soil reacts with soil solution P to form a strong calcium phosphate bond at the surface of the
lime. These alkaline and calcareous soils are common in arid and semi-arid regions with little
rainfall. Soil in regions with a long history of excess rainfall tends to have a low pH due to
calcium and other bases being leached from the soil, being replaced by the hydrogen ion
found in water.
The resulting effect of low P solubility in alkaline and calcareous soil is relatively
poor fertilizer P efficiency. Plants grown in these conditions can be stunted with shortened

4. internodes and poor root systems due to P deficiency. Deficiency symptoms are sometimes
observed as a darkening of the leaf tissue, although it is more common to observe yield loss
with no readily seen symptom. Simply adding fertilizer P at “normal” rates and with
conventional methods may not result in optimal yield and crop quality. Several fertilizer P
management strategies have been found to improve P nutrition for plants grown in alkaline
and calcareous soil, namely:
1) relatively high P fertilizer rates,
2) concentrated P fertilizer bands,
3) complexed P fertilizer,
4) slow release fertilizer P,
5) cation complexing P fertilizer,
6) in-season P fertilizer application, and
7) balancing P with other nutrients.
3.Factors affecting phosphorus availability in calcareous soil:
1.) Time: Insoluble rock P is treated after mining from geologic deposits to enhance
its solubility and usefulness for plants. Fertilizer P is most soluble immediately after addition
to soil, then it undergoes many chemical reactions that result in gradually diminished
solubility (Figure 1). Residual fertilizer P continues to be available for plant uptake for
many years, but freshly applied P is generally most soluble and available for plant uptake.
The common practice of building soil P concentrations to appropriate agronomic ranges
provides a long term source of this nutrient to crops.

5. 2.) Phosphorus Fertilizer Source: Many studies have demonstrated that there are
no consistent agronomic differences in most commercially available P fertilizers added to
calcareous soils. The selection of a specific P source should be based on other factors such as
application equipment, suitability of fluids or granules, and price. However, considerable
work is currently underway to improve P availability with new P products and fertilizer
additives. This topic will be explored in greater detail in future articles. For example, recent
work from Australia in extremely calcareous soils has suggested that fluid P sources may
have somewhat greater solubility and enhanced plant availability than granular fertilizers. It
has been hypothesized that granule dissolution may be suppressed in these soil conditions.
Additional work is underway in the U.S. to see if these results hold for soil conditions more
typical of North America.
There is large variability in the solubility and availability of P from various materials
added to calcareous soil (Figure 2). These large differences are largely due to the unique
properties of the materials, rather than any unique character associated with a specific soil.
For example, the polymer-coated, slow release P source has very low apparent solubility, but
is able to support high levels of plant P accumulation. The soluble P sources and liquid
manures have very high solubility and also are able to maintain high P recovery by barley.

6. 3.) Organic Matter: In the soil solution, there are several chemical components that
will delay or prevent the reaction of P with lime. Organic matter has been found to interfere
in the fixation reactions of P with lime. This inhibition of Pfixation may account for the
observation that P availability is frequently greater in manured soils and with the addition of
humic substances in lime-rich soil. Higher levels of soluble Fe, Al, and Mn are also related to
increased P fixation in calcareous soils,
4.) Temperature: Soil temperature has two opposing effects on soil P availability.
When fertilizer P is added to soil, it continually reacts and forms increasingly stable
compounds for many months after application. The kinetics of the conversion of P to less
soluble forms is more rapid under warmer conditions than in cooler soil(Figure 3). An
opposite effect occurs as increased soil temperature raises the solubility of soil P forms (both
adsorbed or precipitated P). This well-known phenomenon accounts for frequent crop
responses from added P in cool soils in the spring. In addition to improved solubility, higher
soil temperature increases P diffusion to plant roots and enhances overall root activity and
proliferation.
When planting early in the season, or in high-residue conditions, cold soil temperatures can
induce an early-stage P deficiency in many types of soil. A starter P fertilizer application may
help overcome these limitations.
Adjusting for Calcareous Soils: Since the presence of lime in soils can reduce P availability
to crops, fertilizer recommendations are frequently adjusted to account for this condition. For

7. example, the University of Idaho recommendations for potato fertilization statethat an
additional 10 lb P2O5/A needs to be applied for every 1% increase in soil lime (Figure 4).
Calcareous soils can be extremely productive when managed properly.Maintaining an
adequate supply of plantavailable P is essential to profitable and sustainable crop production.
Since a variety of soil reactions tend to decrease the plant availability of added fertilizer P in
calcareous soil, regular soil testing should be conducted to avoid crop loss due to plant
nutrient deficiency.
4. Inherent Factors Affecting Soil Phosphorus:
Inherent soil properties and climate affect crop growth and how crops respond to
applied P fertilizer, and regulate processes that limit P availability. Climatic and site
conditions, such as rainfall and temperature, and moisture and soil aeration (oxygen levels),
and salinity (salt content/electrical conductivity) affect the rate of P mineralization from
organic matter decomposition. Organic matter decomposes releasing P more quickly in warm
humid climates and slower in cool dry climates. Phosphorus is released faster when soil is
well aerated (higher oxygen levels) and much slower on saturated wet soils.

8. Soils with inherent pH values between 6 and 7.5 are ideal for P-availability, while pH
values below 5.5 and between 7.5 and 8.5 limits P-availability to plants due to fixation by
aluminum, iron, or calcium (Figure 2), often associated with soil parent materials. Soil P
cycles in many different forms some that are readily available and some that are not (Figure
1).
Soil Phosphorus – Soil Quality Kit:
Phosphorus does not readily leach out of the root zone; potential for P-loss is mainly
associated with erosion and runoff. Soils and sites that are most prone to erosion and runoff,
or are in close proximity to streams, lakes and other water bodies need to be closely managed
to avoid P loss.

9. 5.Phosphorus Management:
Adequate P levels encourage vigorous root and shoot growth, promote early maturity,
increase water use efficiency and grain yield. Thus, P-deficiency stunts vegetative growth and
grain yield. Soil phosphorus is relatively stable in soil, and moves very little compared to
nitrogen. This lack of mobility and low solubility reduces availability of P-fertilizer as it is
fixed by soil P-compounds. Fixed P is not lost, it becomes slowly available to crops over
several years depending on soil and P-compound type.
Four major P-management strategies are:
1) Lime acid soils to increase soil pH to between 6.5 and 7.0 (Figure 2.);
2) Apply small amounts of P fertilizer frequently rather than large amounts at one time;
3) Reduce P tie-up by banding/injecting P fertilizer or liquid manure; and
4) Place P fertilizers near crop row or in furrow where roots are most active.

10. 6.Case study:
Objective:
To study the combined effect of various levels and types of organic and inorganic P
fertilizers on P availability in a calcareous soil through an incubation experiment.
Experimental Design:
Treatments included four rates of P (20, 40, 80 and 160 mg P2O5 kg-1
soil) and
control. Phosphorus was from one inorganic source (KH2PO4) and from two organic
sources(cattle manure and sludge compost). The soil was incubated at 25o
C and was
maintained at 80% water holding capacity. Change in the amount of available P was
measured during 16 weeks. Analysis of variance (F-test) was used to determine significant
differences among treatments and the least significant difference (LSD 0.05) was employed
for mean separation.
Results are expressed in below figures:

13. Conclusion of case study:
By increasing the time of incubation, P availability in soil significantly decreased
forboth organic and inorganic fertilizers. It was concluded that the most critical time for
incubation was the first week. During this period, the soil lost about 50% of the added P.
During the first week, inorganic P fertilizer yielded more extractable P compared with the
two organic sources. During the rest of incubation period, the amount of P available from the
cattle manure compost was the highest.
7.Reviews of literature:
Westermann (1992) concluded that Phosphorus applications increased solution P and
resin extractable P and decreased equilibrium buffer capacity (EBC) within a given lime
concentration. These data indicate that the soil-test P concentration or P fertilizationrate
should increase as the lime concentration increases to provide the same degree of P
availability and plant P uptake in this calcareous soil.
Frischke et al. (2004) reported that more than 1 million hectares of South Australia’s
cereal production area consists of highly calcareous alkaline soils. Despite decades of applied
fertiliser phosphorus (P), productivity in some of these areas has not increased. Six years of
trial work on Eyre Peninsula using fluid fertilisers as an alternative to high analysis granular
fertilisers such as MAP and DAP, have shown wheat yields can be increased through
improved P availability by 15%23% over a range of seasons.
Wandruszka (2006) observed that both surface reactions and precipitation take place,
especially in the presence of calcite and limestone. The principal products of these reactions
are dicalcium phosphate and octacalcium phosphate, which may interconvert after formation.
The role of calcium carbonate in P retention by calcareous soils is, however, significant only
at relatively high P concentrations – noncarbonated clays play a more important part at lower
concentrations. In the presence of iron oxide particles, occlusion of P frequently occurs in
these bodies, especially with forms of the element that are pedogenic in origin. Progressive
mineralization and immobilization, often biological in nature, are generally observed when P
is added as a fertilizer, manures serves both as a source of subsurface P and an effective
mobilizing agent. Blockage of P sorption sites by organic acids, as well as complexation of
exchangeable Al and Fe in the soil, are potential causes of this mobilization. Swine and
chicken manure are especially rich P sources, largely due the practice of adding the element
to the feed of non ruminants.

14. Al-oud (2011) concluded that the availability of P from rock phosphate was increased
by increasing incubation period up to 90 days. For example, the percentage of P-availability
reached 243.4, 420.4, 481.5, 554.6, 542.0, 487.2% as a result of incubating calcareous soil for
a period of 15, 30, 45, 60.75, and 90 day, respectively, regardless of the rate of applied rock
phosphate (RP). On the other hand the solubility and /or availability of RP were increased by
increasing the rate of applied elemental sulphur and /or organic manure. The maximum P
releasing capacity for the soil treated with RP was attained by treating calcareous soil with
combined treatment (6% O.M + 1% S).
Xiaoqiang et al. (2015) obseved that soil residual-P supply intensity regulatedbiomass
production, growth rate, P uptake rate and the time of attaining maximum average daily
biomassproduction rate, depending on growth stages. it is suggested that exploration of soil
residual P by plant is closely associated with growth stages and the soil residual P supply
intensity.
Antoniadis et al. (2016) concluded that oxides are the key soil property influencing P
sorption among soils of different weathering (even if these soils also differ in pH and
CaCO3), while within the same taxonomic order, CaCO3 and pH becomes the important
factor.
Spohn, et al. (2016) observed increases in TOC concentrations and TOC/TN ratios
during the secondary succession of both south- and southwest-exposed sites, indicating that
the post-agricultural soils turned into C sinks. We found that labile P concentrations
decreased during the first 50 years after land use abandonment most probably due to sorption
and plant uptake, while TOP concentrations initially increased as expected. The TOP
concentrations decreased again 50 years after cessation of viniculture. Together with the
increasing TOC/ TOP concentrations this indicates high organic P mineralization rates at the
later stages of the succession and presumably litter inputs with lower C/P ratio. Taken
together, our results indicate that P dynamics during long-term secondary succession are
similar to the dynamics during primary succession, but occur over a shorter period of time.
Hopkins,B. and Ellsworth, J. (2016 ) reported that relatively high P fertilizer rates are
required for crops grown in alkaline soil, with increasing rates needed as lime content in these
soils increases. Concentrated P fertilizer bands improve P solubility with resulting yield
increases, even when applied to crops grown in soil with relatively high soil test P
concentrations. Applying organically complexed P in the form of bio solids or as a mixture
of liquid P and humic substances can also enhance P nutrition and result in yield increases.

15. Application of slow release and cation complexing specialty fertilizer P materials has also
been shown to effectively increase yields in calcareous soil. In-season applied P through the
irrigation water can deliver P to plant roots when deficiencies are observed, but the
effectiveness and results are less than with P incorporated into the soil. Finally, it is important
to maintain a proper balance of P with other nutrients for general plant health and to avoid
excess nutrient induced deficiencies of other nutrients. In some cases, these methods are
relatively new and need further refinement with regard to rates, timing, and technique; but all
are potential methods for improving P supply to plants grown in alkaline and calcareous soil.
8.Summary:
Phosphorus (P) is an essential nutrient required by plants for normal growth and
development. The availability of P to plants for uptake and utilization is impaired in alkaline
and calcareous soil due to the formation of poorly soluble calcium phosphate minerals.
Adding fertilizer P at “normal” rates and with conventional methods may not result in
optimal yield and crop quality in these soils common in arid and semi-arid regions. Several
fertilizer P management strategies have been found to improve P nutrition for plants grown in
alkaline and calcareous soil. Research results show that relatively high P fertilizer rates are
required for crops grown in alkaline soil, with increasing rates needed as lime content in these
soils increases. Concentrated P fertilizer bands improve P solubility with resulting yield
increases, even when applied to crops grown in soil with relatively high soil test P
concentrations. Applying organically complexed P in the form of biosolids or as a mixture of
liquid P and humic substances can also enhance P nutrition and result in yield increases.
Phosphorus is an important and essential nutrient for all plants. Availability of P in
high Ph soils, especially those with excess lime, is relatively poor. Lowering pH is not an
economical option for most crops and, as such, other strategies must be employed to enhance
P uptake byroots, including: 1) relatively high P fertilizer rates, 2) concentrated P fertilizer
bands, 3) complexed P fertilizer, 4) slow release fertilizer P, 5) cation complexing P fertilizer,
6) in-season P fertilizer application, and 7) balancing P with other nutrients.

16. 9. References:
Al-oud S. S. (2011). Improving phosphorus availability from phosphate rock in calcareous soils by
amending with: organic acid, sulfur, and/ or organic manure. Ozean journal of applied
sciences, 4(3).
Antoniadis,V.; Koliniati, R.; Efstratiou, E. and Golia, E.(2016). Effect of soils with varying
degree of weathering and pH values on phosphorus sorption. S. Petropoulos catena.
139,: 214–219.
Frischke,B.M.; Holloway,R.E.; McLaughlin,M.J. and Lombi,E.(2004).Phosphorus
Management and Availability in Highly Calcareous Soil. Journal of Agricultural
Physics. 9,:1-8.
Hopkins,B. and Ellsworth,J.2016 phosphorus availability with alkaline/calcareous soil. Better
Crops.9 (No. 2.).
Khalid A.R.; Ghoneim A. M.;Modaihsh,A. S.;Mahjoub, M. O. and Zekri M.(2016).
Phosphorus availability in calcareous soils amended with organic and inorganic
phosphorus sources. University of Florida, Hendry County Extension Office, P.O. Box
68, La Belle, FL 33975, USA.
Leytem A.B. and. Mikkelsen. R.L.(2005). The Nature of Phosphorus in calcareus soil. better
crops.89 (no. 2.).
Spohn, M,; Novák, T.J.; Incze ,J. and Giani ,L. 2016.Dynamics of soil carbon, nitrogen, and
phosphorus in calcareous soils after land-use abandonment. A chronosequence study
.Plant Soil; 401:185–196.
Wandruszka, R.V.(2006). Phosphorus retention in calcareous soils and the effect of organic
matter on its mobility. Science Society of America Journal,18: 11–17.
Westermann, D. T.(1992.) Lime Effects on Phosphorus Availability in a Calcareous Soil. Soil
Science Society of America Journal.56:2
Xiaoqiang J, Rengel,.; Fusuo Z, and Shen,Z(2015).Dynamic growth pattern and exploitation
of soil residual p by brassica campestris throughout growth cycle on a calcareous soil.
Field crops research .180: 110–117.