UNDERSTANDING THE DILEMMA OF UNDERSTANDING THE DILEMMA OF PHOSPHORUS IN AGRICULTUREPHOSPHORUS IN AGRICULTURE

BYBY

DR. MIDRAR UL HAQDR. MIDRAR UL HAQ

1. History1. History

Hinning BrandHinning Brand

Hinning Brand is boiling Urine

Krafft German Chemist

Robert Boyle

Phosphorus extraction from Phosphorus extraction from Phosphate RockPhosphate Rock

John Bennett LawesRothemsted Experimental Station

Phosphorus necessity for seed formationPhosphorus necessity for seed formation

Justus Von Liebig (1803-Justus Von Liebig (1803-1873) was the first one, 1873) was the first one, who developed the who developed the concept of fertilizer concept of fertilizer recommendations based recommendations based on the chemical analysis on the chemical analysis of the plants and of the plants and interpretation of the interpretation of the analysis.analysis.

Also highlighted the Also highlighted the necessity of phosphorus necessity of phosphorus for seed formation.for seed formation. German Chemist Justus Von Liebig

waxy white (yellow cut), red (granules center left, chunk center right), and violet phosphorus

2. World Phosphate Reserves2. World Phosphate Reserves

CountryCountry Reserves (*000 Metric tons)Reserves (*000 Metric tons)

United States United States

AustraliaAustralia

BrazilBrazil

CanadaCanada

ChinaChina

EgyptEgypt

IndiaIndia

IsraelIsrael

JordanJordan

MoroccoMorocco

RussiaRussia

SenegalSenegal

South AfricaSouth Africa

SyriaSyria

TogoTogo

TunisiaTunisia

Other Countries (including Pakistan 7.45 million metric tons)Other Countries (including Pakistan 7.45 million metric tons)

1,200,0001,200,000

77,00077,000

260,000260,000

25,00025,000

6,600,0006,600,000

100,000100,000

90,00090,000

180,000180,000

900,000900,000

5,700,0005,700,000

200,000200,000

50,00050,000

1,500,0001,500,000

100,000100,000

30,00030,000

100,000100,000

800,000800,000

World total (rounded)World total (rounded) 18,000,00018,000,000

aa

3. Why phosphorus is shown P2O5 3. Why phosphorus is shown P2O5 on the fertilizer bag?on the fertilizer bag?

Before the invention of modern sophisticated Before the invention of modern sophisticated instruments, chemists used to analyze P and K instruments, chemists used to analyze P and K through gravimetric (weighing) ignition method. through gravimetric (weighing) ignition method. In that method, it was difficult to isolate P from In that method, it was difficult to isolate P from fertilizer, so they used the method of expressing fertilizer, so they used the method of expressing P and K as P2O5 and K2O.P and K as P2O5 and K2O.

Fertilizer companies prefer to use these Fertilizer companies prefer to use these notations because these show more notations because these show more concentration than that in the elemental form concentration than that in the elemental form and hence attract customers.and hence attract customers.

4. 4. When fertilizer is applied to soil, it When fertilizer is applied to soil, it dissolves in water and gives dissolves in water and gives phosphorus ions, which have phosphorus ions, which have negative charges while the clay negative charges while the clay mineral in soil have also negative mineral in soil have also negative charges then how it is adsorbed charges then how it is adsorbed and retained in soil?and retained in soil?

Schematic diagram of the phosphate cycleSchematic diagram of the phosphate cycle

How Can organically complexed metals affect P adsorption?

P is complexed with OM through metal bridges?

OM interferes with Ca-P and metal oxide precipitation by coating the calcite surfaces?

Phosphorus in soilPhosphorus in soil

P adsorption & P adsorption & precipitation in precipitation in calcareous soils.calcareous soils.

Traditional Concepts Adding P Fertilizer to High pH/ High Calcium Soils

First few weeks, P initially precipitates as First few weeks, P initially precipitates as MCP…. Then DCPDMCP…. Then DCPDAfter 3 to 5 months, octacalcium phosphate After 3 to 5 months, octacalcium phosphate precipitatesprecipitatesAfter 8 to 10 months, tricalcium phosphate formsAfter 8 to 10 months, tricalcium phosphate formsLong periods (years) hydroxyapatite minerals Long periods (years) hydroxyapatite minerals form…form…(mineral with lowest solubility controls P (mineral with lowest solubility controls P concentration- while intermediates are unlikely concentration- while intermediates are unlikely to persist)to persist)

5. How fertilizer P becomes unavailable?5. How fertilizer P becomes unavailable?

When phosphatic fertilizer is applied to the When phosphatic fertilizer is applied to the alkaline soils of Pakistan, due to high alkaline soils of Pakistan, due to high calcium carbonates in the parent material calcium carbonates in the parent material of these soils, calcium activity is high, of these soils, calcium activity is high, which makes the phosphorus in the which makes the phosphorus in the fertilizer unavailable due to the formation of fertilizer unavailable due to the formation of calcium phosphate compounds, some of calcium phosphate compounds, some of which have low availability and some have which have low availability and some have very low availability.very low availability.

6.6. How phosphorus moves How phosphorus moves to the plant roots?to the plant roots?

Plant Availability of Soil and Plant Availability of Soil and Fertilizer PhosphorusFertilizer Phosphorus

Plant roots take up phosphorus from soil Plant roots take up phosphorus from soil solution as orthophosphate:solution as orthophosphate:

1.1. H2PO4-H2PO4- (acidic soil)(acidic soil)

2.2. HPO4--HPO4-- (alkaline soil)(alkaline soil)

Movement of Phosphorus to RootsMovement of Phosphorus to Roots

1.1. Mass Flow Mass Flow (2% of available P )(2% of available P )

2.2. Diffusion Diffusion (97 % of available P) (97 % of available P)

3.3. Root Interception (1% of available P)Root Interception (1% of available P)

1. Mass Flow1. Mass Flow

Assume P in soil Assume P in soil solution=10-5M=0.31mg solution=10-5M=0.31mg P/lit=0.2kg P/ha.P/lit=0.2kg P/ha.

If a crop uses 37cm of If a crop uses 37cm of water during its growth, water during its growth, there will only be about there will only be about 1kg P/ha dissolved in the 1kg P/ha dissolved in the soil solution, yet it may soil solution, yet it may take up 20-40 kg P/ha take up 20-40 kg P/ha during its growth season.during its growth season.

Very highVery high

(10-4M=3.1mg P/ha)(10-4M=3.1mg P/ha)

DeficientDeficient

(10-6 M=0.031 mg P/ha)(10-6 M=0.031 mg P/ha)

Very low fertility levelVery low fertility level

(10-8M=0.00031mg P/ha)(10-8M=0.00031mg P/ha)

Roots InterceptionRoots Interception

7. Measuring soil and fertilizer phosphorus recovery 7. Measuring soil and fertilizer phosphorus recovery and defining phosphorus –use efficiencyand defining phosphorus –use efficiency

There are several methods for determining the There are several methods for determining the efficiency of phosphorus but the most important efficiency of phosphorus but the most important are:are:

1.1. Direct MethodDirect Method

i. Agronomic efficiency (YN-YO)/FN*100i. Agronomic efficiency (YN-YO)/FN*100

ii. Apparent efficiency (UN-UO)FN*100ii. Apparent efficiency (UN-UO)FN*100

2.2. Balance Method (UP/FP)*100Balance Method (UP/FP)*100

3.3. Difference Method (UN-UC)/FP*100Difference Method (UN-UC)/FP*100

Measuring soil and fertilizer phosphorus recovery Measuring soil and fertilizer phosphorus recovery and defining phosphorus –use efficiencyand defining phosphorus –use efficiency

Balance methodBalance method has been used has been used occasionally and is an appropriate method occasionally and is an appropriate method for calculating P recovery and efficiency.for calculating P recovery and efficiency.

Difference methodDifference method is an appropriate is an appropriate method for calculating N efficiency method for calculating N efficiency because very little of an N application because very little of an N application remains in the soil as mineral N to benefit remains in the soil as mineral N to benefit a subsequent crop.a subsequent crop.

Percentage recovery of three amounts of applied P at two Percentage recovery of three amounts of applied P at two levels of Olsen P, sandy clay loam soil, saxmundhamlevels of Olsen P, sandy clay loam soil, saxmundham

Olsen P (mg/kg)Olsen P (mg/kg)

P appliedP applied

(kg/ha)(kg/ha)

4 33 4 33 4 33

P uptake in 4 years (kg p/ha)

% recovery by the difference method

Formula usedFormula used % recovery by the balance method

Formula Formula usedused

00 23.3 75.2

5555 46.9 77.0 43 3 (46.9-23.3)/55(46.9-23.3)/55

*100*100

85 140 46.9/5546.9/55

*100*100

110110 57.2 79.4 31 4 Ditto FormulaDitto Formula 52 72 Ditto Ditto FormulaFormula

165165 63.8 82.2 24 4 Ditto FromulaDitto Fromula 39 50 Ditto Ditto FormulaFormula

Data are the mean of two 4-year rotations, 1969-1972 and 1970-73.Rotation: sugar beet, barley, potatoes, barleyTotal P applied in 4 years was 55, 110 and 165 kg P/ha.

P offtake 1856-2001 by arable crops growing on plots that had P offtake 1856-2001 by arable crops growing on plots that had received no P or a total of 1410 kg/ha from 1865-1901 and none since, received no P or a total of 1410 kg/ha from 1865-1901 and none since,

Exhaustion Land, RothamstedExhaustion Land, Rothamsted

PeriodPeriod No of No of YearsYears

CroppingCropping Plot 7 (NPK)2

p offtake

Total of Total of the the variable variable periodperiod

Plot 7 (N)2

p offtake

Total of Total of the the variable variable periodperiod

DifferenDifference in ce in annual P annual P offtakeofftakeTotal Per

yearTotal Per

year

1856-751856-75 2020 wheatwheat 160 8 93 4.65 3.353.35

76-190176-1901 2626 PotatoesPotatoes 169 6.5 329329 (56- (56-01)01)

45 1.73 138 138 (56-(56-01)01)

4.774.77

1902-401902-40 3939 BarleyBarley 235 6.02 636636 (56- (56-1948)1948)

131 3.36 308308(56-(56-1948)1948)

2.662.66

1941-481941-48 99 BarleyBarley 72 9 307307 (02- (02-48)48)

39 4.9 170170 (02- (02-48)48)

4.14.1

1949-741949-74 2626 BarleyBarley 248 9.54 116 4.46 5.085.08

1976-911976-91 1616 BarleyBarley 135 8.44 65 4.06 4.384.38

92-200192-2001 1010 WheatWheat 96 9.63 1115 1115 (56-(56-2001)2001)

42 4.18 531531 (56- (56-2001)2001)

5.455.45

1 P in winter wheat and spring barley grain plus straw and in potato tubers.2 Except 1902-1940 when no N was applied.

Cumulative recovery by arable crops of P applied between Cumulative recovery by arable crops of P applied between 1856 and 1901, Exhaustion Land, Rothamsted.1856 and 1901, Exhaustion Land, Rothamsted.

PeriodPeriod CropsCrops IndividualIndividual

offtake by offtake by cropcrop

Total P offtake

Recovery (%)Recovery (%)

Kg/haKg/ha Kg/ha Balance Balance MethodMethod

FormulaFormula Difference Difference MethodMethod

FormulaFormula

1856-1856-19011901

Wheat (W)+Wheat (W)+

Potato (P)Potato (P)

160+169160+169 329 2323 329/1410329/1410

*100*100

1414 (329-138)/(329-138)/14101410

*100*100

1856-1856-19481948

W+P+BarleyW+P+Barley+Barley (B)+Barley (B)

160+169+235160+169+235+72+72

636 4545 636/1410636/1410

*100*100

2323 (636-308)/(636-308)/14101410

*100*100

1856-1856-20012001

W+P+B+B+BW+P+B+B+B+B+W+B+W

160+169+235160+169+235+72+248+135+72+248+135+96+96

1115 7979 1115/14101115/1410

*100*100

4141 (1115-531)/(1115-531)/14101410

*100*100

Percentage recovery by the balance method of the residue Percentage recovery by the balance method of the residue of P applied between 1856 and 1901that remained in the of P applied between 1856 and 1901that remained in the

soil in 1901 and 1948, Exhaustion Land, Rothamsted.soil in 1901 and 1948, Exhaustion Land, Rothamsted.

PeriodPeriod P residue (kg/ha)

Formula Formula UsedUsed

P offtake

(kg/ha)

Formula & Recovery %Formula & Recovery %

FormulaFormula Recovery (%)Recovery (%)

1902-1902-19481948

1081 1410-3071410-307 235+72= 307

307*100/1081307*100/1081 2828

1949-1949-20012001

774 1410-4791410-479 248+35+96= 479

479*100/774479*100/774 6262

Immediately High Low Very lowAccessible Accessibility Accessibility Accessibility

In Solution Readily extractable Low extractability Very low extractability

Immediately Readily low Very lowAvailable available availability availability

Soil SolutionSurface-

adsorbed P

Strongly-bondedOr

Absorbed P

Very strongly-bondedOr inaccessible or mineral

Or precipitated P

8. Conceptual diagram for the forms of inorganic P in soils categorized in terms of accessibility, extractability and plant availability.

9. Strategies for improving P use efficiency9. Strategies for improving P use efficiency

Modifying surface soil properties.Modifying surface soil properties.

Managing surface soil and its P contentManaging surface soil and its P content

Managing P sourcesManaging P sources

Optimizing P use through the use of Optimizing P use through the use of economically appropriate rates and timing.economically appropriate rates and timing.

10. Conclusions

1. Most of the inorganic P added to soils in fertilizers and manures is usually adsorbedinitially, which is held with a continuum of bonding energies on the surfaces of, or within, soil components, and that this gives rise to the differing extractability of soil P and its differing availability to plants.

2. The P use efficiency must be measured over an adequate period i.e. at least a decadeand must be estimated by using balance method. However, the difference method is

10. Conclusions

2. Inappropriate because it does not consider the residual effect of added P.3. Residual P contributes to the readily plant available pool, but the rate of release may not be sufficient to maintain the critical value required to meet the P requirement of high yielding cultivars. In such situations, P must be added to maintain critical value for optimal crop yields.5. Phosphorus must be applied to plants through the most appropriate method to

minimize phosphorus conversion in soil to the least available forms.6. On many soils, the added P is not irreversibly fixed in forms that are unavailable to plants.

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