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

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

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

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.

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.

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

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.

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.

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.

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 25oC 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:

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.

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.

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.

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.