The document discusses the use and efficiency of rock phosphate (RP) in agriculture, highlighting its origins, reactivity, and application methods. It outlines the benefits of RP, including cost-effectiveness and gradual phosphorus release, while also identifying factors affecting its effectiveness, such as soil properties and management practices. Additionally, it presents various strategies to improve RP efficiency, including biological, chemical, and physical methods.

1. INCREASING EFFICIENCY OF ROCK
PHOSPHATE IN PROBLEMATIC
SOILS
PRESENTED BY:
Samanyita Mohanty

2. INTRODUCTION
PHOSPHATE ROCK-
• Phosphate rock denotes the product obtained from
the mining and subsequent metallurgical processing
of P-bearing ores.
• PRs can be used-
1. as raw materials in the industrial manufacture of
WSP fertilizers,or
2. as P sources for direct application in agriculture.

3. Phosphate rocks as raw materials for P-fertilizer
manufacturing
• Sulphuric acid and PR are the raw materials used in the
production of single superphosphate (SSP) and phosphoric
acid.
• Phosphoric acid is an important intermediate by-product that
is used to make triple superphosphate (TSP) and ammonium
phosphate.
• It is used for industrial purposes and for the production of
animal feed supplements and food products.
• used in the manufacture of elemental P and its derivatives, in
particular sodium tri-polyphosphate(a major component of
heavy-duty laundry detergents).

4. Rock phosphate for direct application
• As mentioned above, PRs mainly of sedimentary origin
are suitable for direct application because they consist of
fairly open, loosely consolidated aggregates of micro
crystals with a relatively large specific surface area.
• They show a considerable proportion of isomorphic
substitution in the crystal lattice and contain a variable
proportion and amounts of accessory minerals and
impurities.
• Advantages – less expensive
slow and steady supply of P
More P restoration capacity

5. Major producer and consumer of rock phosphate

7. Phosphate concentrates
• Of the total rock phosphate deposits,
1. 80% sedimentary rock origin.
2. 17% igneous rock origin.
3. 3% residual sedimentary and guano deposits.
SEDIMENTARY ORIGIN:
 These are deposits of biological origin (particularly marine
fauna) which is formed after the chemical breakdown of bones,
animal manure and beneficiated rocks.
 This apatite (sometimes called phosphorite) is less
crystalline and practically amorphous and therefore more
soluble than beneficiated rocks – it dissolves partially in diluted
weak acids such as citric acid, and in beneficiated and finely
milled form it can be used as a phosphate fertilizer, especially
in acid soils.

8. • IGNEOUS ORIGIN:
 These are solidified magma occurring as intrusions in
other rock formations or as vertical pipes.
 They contain a strong crystalline apatite mineral that is
hard and practically insoluble in water and weak
acids. As such, it is unsuitable as a fertilizer and must
first be treated with strong acids.

9. Factors affecting the effectiveness of rock phosphate
A. Reactivity of RP: Reactivity is a measure of its rate of dissolution.
Particle size:
• Finer the particle size, more is the dissolution.
• Usually less than 0.15mm.
Soil properties:
• Low pH (less than 5.5 )
• high organic-matter content.
• low solution concentration of Ca ions.
Soil acidity:
Cation exchange capacity, and exchangeable calcium and magnesium:
• Low calcium in soil solution will help to adsorb calcium from
dissolution of RP.
• Mg2+ helps in further dissolution.
• High CEC results in more dissolution.

10. Soil organic matter:
• the high cation exchange capacity of organic matter(increased Ca
retention capacity)
• Humic and fulvic fractions( Calcium OM complex)
• production of numerous organic acids, such as oxalic, citric and
tartaric acids.
Crop species
• Plantation crops, perennial pastures, tree crops steady supply of P.
• Legumes (1) because of its high affinity for calcium and (2) N
fixation.
Soil solution ‘P’ concentration and retension capacity
B. Management practices:
• PR placement
• Rate of PR application
• Timing of PR application
• Lime application

11. ways for improving efficiency of rock phosphates
Depends on various factors:-
• the physical and chemical properties of PRs;
• soil and climate factors;
• plant species and the cropping system; and
• farming management practices.
BIOLOGICAL MEANS:
• Phosphocompost:
• RP is added to organic materials in the composting technique.
• Various organic acids are produced by micro organisms(bacteria and fungi)
• Main reasons for the enhancement of P release is:
i. acidification of PR by organic acids.
ii. chelating ability on Ca,Mg,Fe and Al
Effectiveness:
• Increase in water soluble and citrate soluble P contents.
• When applied to alkaline soil, it dissolves easily compared to RP and is
available.

12. • Innoculation of seedlings with endomycorrhiza:
VAM : Glomus fasiculatum, G. margarita, G. mosseae
• Fungal hyphae explore greater volume of soil for P.
• It dissolves the sparingly soluble portion of RP.
• Increasing the rate of P uptake by increasing diffusion gradient.
• Use of phosphate solubilising micro organisms:
• Group of heterotrophic MO solubilise P to inorganic form and make it
available to plants.( B. circulans, B. subtilis, P. digitatum etc)
• This is mainly achieved by excreting organic acids and its chelating
properties.
CHEMICAL MEANS:
• Partial acidulation of RP (PAPR):
• This is prepared by reacting RP with either sulphuric or phosphoric acid in
amounts less than that needed to make SSP or TSP.
• As phoshoric acid contains water soluble P, partial acidulation of RP with it
results in PAPR’s containing more total and water soluble P.
• Total P decreases when treated with sulphuric acid as formation of CaSO4
takes place but water soluble P increases with increasing acidulation.

13. • Major components of PAPR products are water soluble monocalcium
phosphate and sparingly soluble acid unreacted RP.
• PAPR are traded in the name of ‘longlife super ‘ and are mainly
manufactured in New Zealand.
PHYSICAL MEANS:
• Compacted RP with water soluble phosphate products.
Fertilizers similar to PAPR can be prepared indirectly by compacting dry PR
with soluble phosphatic fertilizers such as SSP and TSP under pressure.
• Dry mixtures of with RP with water soluble phosphate fertiliser.
• Phosphate rock elemental sulphur assemblages
Efficiency can be increased when RP are applied after admixing or
cogranulating with sulphur ( sometimes are innoculated with S oxidising
bacteria Thiobacillus spp. ) and the product is referred to as ‘biosuper’.

15. References:
• Anderson, D.L., Kussow, W.R. & Corey, R.B. 1985. Phosphate rock
dissolution in soil: indications from plant growth studies. Soil Sci. Soc. Am.
J., 49: 918–925
• Attoe, O.J. & Olson, R.A. 1966. Factors affecting rate of oxidation in soils
of elemental sulphur and that added in rock phosphate-sulphur fusions.
Soil Sci., 101: 317–324.
• Bolland, M.D.A. & Gilkes, R.J. 1997. The agronomic effectiveness of
reactive phosphate rocks, 2. Effect of phosphate rock reactivity. Aus. J. Exp.
Agric., 37: 937–946.
• British Sulphur Corporation Limited. 1987. World survey of phosphate
deposits. London. 247 pp
• Chien, S.H. & Menon, R.G. 1995a. Agronomic evaluation of modified
phosphate rock products: IFDC’s experience. Fert. Res., 41: 197–209.

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