phosphorus in agriculture
Post on 27-Nov-2014
748 Views
Preview:
DESCRIPTION
TRANSCRIPT
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.
ThanksThanks
top related