phosphorus in agriculture

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Dr. Midrar Ul Haq

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  • 1. UNDERSTANDING THE DILEMMA OF PHOSPHORUS IN AGRICULTURE
    • BY
    • DR. MIDRAR UL HAQ
  • 2. 1. History
    • Hinning Brand
  • 3. Hinning Brand is boiling Urine Krafft German Chemist
  • 4. Robert Boyle
  • 5. Phosphorus extraction from Phosphate Rock John Bennett Lawes Rothemsted Experimental Station
  • 6. Phosphorus necessity for seed formation
    • Justus Von Liebig (1803-1873) was the first one, who developed the concept of fertilizer recommendations based on the chemical analysis of the plants and interpretation of the analysis.
    • Also highlighted the necessity of phosphorus for seed formation.
    German Chemist Justus Von Liebig
  • 7. waxy white (yellow cut), red (granules center left, chunk center right), and violet phosphorus
  • 8. 2. World Phosphate Reserves 18,000,000 World total (rounded) 1,200,000 77,000 260,000 25,000 6,600,000 100,000 90,000 180,000 900,000 5,700,000 200,000 50,000 1,500,000 100,000 30,000 100,000 800,000 United States Australia Brazil Canada China Egypt India Israel Jordan Morocco Russia Senegal South Africa Syria Togo Tunisia Other Countries (including Pakistan 7.45 million metric tons) Reserves (*000 Metric tons) Country
  • 9.
    • a
  • 10. 3. Why phosphorus is shown P2O5 on the fertilizer bag?
    • Before the invention of modern sophisticated instruments, chemists used to analyze P and K through gravimetric (weighing) ignition method. In that method, it was difficult to isolate P from fertilizer, so they used the method of expressing P and K as P2O5 and K2O.
    • Fertilizer companies prefer to use these notations because these show more concentration than that in the elemental form and hence attract customers.
  • 11. 4. When fertilizer is applied to soil, it dissolves in water and gives phosphorus ions, which have negative charges while the clay mineral in soil have also negative charges then how it is adsorbed and retained in soil?
  • 12. Schematic diagram of the phosphate cycle
  • 13.
  • 14. 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?
  • 15. Phosphorus in soil
    • P adsorption & precipitation in calcareous soils.
  • 16. Traditional Concepts Adding P Fertilizer to High pH/ High Calcium Soils
    • First few weeks, P initially precipitates as MCP. Then DCPD
    • After 3 to 5 months, octacalcium phosphate precipitates
    • After 8 to 10 months, tricalcium phosphate forms
    • Long periods (years) hydroxyapatite minerals form
    • (mineral with lowest solubility controls P concentration- while intermediates are unlikely to persist)
  • 17. 5. How fertilizer P becomes unavailable?
    • When phosphatic fertilizer is applied to the alkaline soils of Pakistan, due to high calcium carbonates in the parent material of these soils, calcium activity is high, which makes the phosphorus in the fertilizer unavailable due to the formation of calcium phosphate compounds, some of which have low availability and some have very low availability.
  • 18.
    • 6. How phosphorus moves to the plant roots?
  • 19. Plant Availability of Soil and Fertilizer Phosphorus
    • Plant roots take up phosphorus from soil solution as orthophosphate:
    • H2PO4- (acidic soil)
    • 2. HPO4-- (alkaline soil)
  • 20. Movement of Phosphorus to Roots
    • Mass Flow (2% of available P )
    • 2. Diffusion (97 % of available P)
    • 3. Root Interception (1% of available P)
  • 21. 1. Mass Flow
    • Assume P in soil solution=10-5M=0.31mg P/lit=0.2kg P/ha.
    • If a crop uses 37cm of water during its growth, there will only be about 1kg P/ha dissolved in the soil solution, yet it may take up 20-40 kg P/ha during its growth season.
    • Very high
    • (10-4M=3.1mg P/ha)
    • Deficient
    • (10-6 M=0.031 mg P/ha)
    • Very low fertility level
    • (10-8M=0.00031mg P/ha)
  • 22.
  • 23. Roots Interception
  • 24. 7. Measuring soil and fertilizer phosphorus recovery and defining phosphorus use efficiency
    • There are several methods for determining the efficiency of phosphorus but the most important are:
    • Direct Method
    • i. Agronomic efficiency (YN-YO)/FN*100
    • ii. Apparent efficiency (UN-UO)FN*100
    • Balance Method (UP/FP)*100
    • Difference Method (UN-UC)/FP*100
  • 25. Measuring soil and fertilizer phosphorus recovery and defining phosphorus use efficiency
    • Balance method has been used occasionally and is an appropriate method for calculating P recovery and efficiency.
    • Difference method is an appropriate method for calculating N efficiency because very little of an N application remains in the soil as mineral N to benefit a subsequent crop.
  • 26. Percentage recovery of three amounts of applied P at two levels of Olsen P, sandy clay loam soil, saxmundham Data are the mean of two 4-year rotations, 1969-1972 and 1970-73. Rotation: sugar beet, barley, potatoes, barley Total P applied in 4 years was 55, 110 and 165 kg P/ha. Ditto Formula 50 39 Ditto Fromula 4 24 82.2 63.8 165 Ditto Formula 72 52 Ditto Formula 4 31 79.4 57.2 110 46.9/55 *100 140 85 (46.9-23.3)/55 *100 3 43 77.0 46.9 55 75.2 23.3 0 Formula used % recovery by the balance method Formula used % recovery by the difference method P uptake in 4 years (kg p/ha) 33 4 33 4 33 4 P applied (kg/ha) Olsen P (mg/kg)
  • 27. 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, Exhaustion Land, Rothamsted 1 P in winter wheat and spring barley grain plus straw and in potato tubers. 2 Except 1902-1940 when no N was applied. 531 (56-2001) 170 (02-48) 308 (56-1948) 138 (56-01) Total of the variable period 5.45 4.18 42 1115 (56-2001) 9.63 96 Wheat 10 92-2001 4.38 4.06 65 8.44 135 Barley 16 1976-91 5.08 4.46 116 9.54 248 Barley 26 1949-74 4.1 4.9 39 307 (02-48) 9 72 Barley 9 1941-48 2.66 3.36 131 636 (56-1948) 6.02 235 Barle

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