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1.
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Phosphorous (P) is an important plant nutrient element. P content is conventionally expressed as percent P2O5. |
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2.
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• Plants take up P in water soluble form, e.g. PO4-3, HPO4-2, H2PO4-1.
• P present in the soil (naturally present or added) may be in a form insoluble in water or soluble in 2% citric acid or soluble in water. The latter two forms are known as available forms.
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3.
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The following factors effect the uptake of P by plants:
• Soil pH between 5.5 to 7 is most favorable for P uptake by plants. Soils fix P below 5.5 pH due to the presence of Al, Fe and Mn ions. Above 7pH Mg and Ca ions in the soil fix P.
• The presence of organic matter enhances P availability to the plants.
• Plants exude organic acids ( e.g . citric and malic acids) through their roots that dissolve soil phosphorous which in turn are taken up by plants through the roots.
• Organic acids (citric acid for example) released by several microorganism present in the soil also dissolve P present in the soil very effectively. |
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| 4. |
Most of the chemical phosphatic fertilizers ( e.g. di ammonium phosphate or single super phosphate) contain P2O5 in water soluble form. However after few days of application water soluble P2O5 turns to unavailable forms due to soil fixation. Only 30% to 40% of P2O5 of the chemical fertilizers are effectively used. Further excessive use of chemical fertilizers destroy soil flora and fauna, thereby disturbs natural fertility of soils. |
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| 5. |
Phosphate Rich Organic Manure (PROM) is produced by composting organic matter with high grade (+32% P2O5 ) rock phosphate in very fine (+95% passing through 74 micron) size. 3 to 4 metric tonnes of FYM alongwith 200 kg of rock phosphate (or more depending on soil requirement) is recommended per hectare.
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| 6. |
PROM works more efficiently than DAP as may be seen from the following Table I.
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Table I Effect of different treatments and residual effect on the seed output of Cyamopsis tetragonoloba (Linn.)Taub.(Gauvar Phali) {Percentage increase/decrease is given in parenthesis}, field trials soil pH = 7.6
Seed Output per Plant(g)
(residual effect ) |
Treatment No., Treatment
Seed Output per Plant (g)
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PR(34/74) @40 kg P2O5ha-1
6.69(+31.26)
8.63 (+25.43) |
0 |
Control (Soil)
4.62
6.88 |
1 |
PR(34/74) @40 kg P2O5ha-1 + Urea@18 kg N2ha-1
7.76(+67.96)
7.69 (+11.77) |
2 |
| DAP @ 40 Kg P2O5ha-1 |
3 |
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| 7. |
The dissolution of rock phosphate mineral in PROM is mainly due to biotic activity. FYM naturally contains a variety of micro organism that dissolve rock phosphate mineral. Advertant addition of phosphate solubilising micro organism further enhances the efficiency of PROM. |
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| 8. |
Fine grinding results into mechano chemical activation of rock phosphate minerals
(See Table II). |
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Table II
Mechano-Chemical Activation of Rock Phosphate Mineral
S.No. |
Source of rock
phosphate |
Size expressed as d 80, in microns |
Total P2O5 % |
% P2O5 soluble in 2% citric acid |
1. |
Jhamarkotra, RSMML |
23.14 |
34 |
3.5 |
2. |
- do - |
7.55 |
34 |
3.9 |
3. |
El Nasar, Egypt |
29.43 |
31.3 |
13.0 |
4. |
Phalaborwa, Foskor, South Africa
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178.07 (as received)
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36.8 |
1.6 |
5. |
- do - |
31.84 |
36.8 |
5.8 |
Note: d 80 = size in microns, where 80% particles are finer than. |
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