The present industrial invention pertains to a water-soluble powder fertilizer whose formulation contains Phosphorous (P₂O₅) and Calcium (CaO) in the presence of a specific co-formulant.

With regard to chemical fertilizers in general, it may be affirmed that the fertilizers today available on the market use Urea Phosphate as a raw material for supplying Phosphorous to be mixed with other elements, including Calcium. This is due to the fact that dry mixtures of phosphate sources other Urea Phosphate with Calcium nitrate or other Calcium salts and microelements that are not chelated, result in turbid aqueous solutions and hence the formation of precipitates.

The aim of the present invention is primarily to eliminate this drawback by introducing into the production formula a "co-formulant" which prevents Calcium and other elements from precipitating in the presence of Phosphates.

The co-formulant to which this invention pertains allows the dry mixture of:

• Monoammonium phosphate 12/61
• Diammonium phosphate 21/53
• Monopotassium phosphate 52/34
• Sodium Phosphate or other phosphates
  
     With:
  • Calcium nitrate or other Calcium salts
  • Magnesium nitrate or other Magnesium salts
  • Iron sulphate or nitrate or chloride
  • Copper sulphate or nitrate or chloride
  • Manganese sulphate or nitrate or chloride
  • Zinc sulphate or nitrate or chloride
  • Sodium or ammonium molybdate
  • Boric acid or Sodium borate
  • Potassium nitrate or chloride
  • Ammonium nitrate
  • Urea
  • Each of these ingredients, depending on titre one wishes to obtain, may be used in percentages ranging from a minimum of 1% to a maximum of 99%, insofar as regards:
    • Monoammonium phosphate
    • Diammonium phosphate
    • Monopotassium phosphate
    • Sodium Phosphate or other phosphates
    • Calcium nitrate or other Calcium salts
    • Magnesium nitrate or other Magnesium salts
    • Potassium nitrate or chloride
    • Ammonium nitrate
    • Urea
    • Whereas as regards:
      • Iron sulphate or nitrate or chloride
      • Copper sulphate or nitrate or chloride
      • Manganese sulphate or nitrate or chloride
      • Zinc sulphate or nitrate or chloride
      • Sodium or ammonium molybdate
      • Boric acid or Sodium borate

The co-formulant is added in a percentage that will vary according to the quantity of CaO provided by Calcium Nitrate or other Calcium Salts and of Phosphorous (P₂O₅) provided by the above-specified phosphates.

These and other aims are accomplished by the co-formulant of the present invention, which basically consists in a dry mixture of the following ingredients:

• Phosphorous acid (H₃PO₃)
• EDTA acid (EDTA-H₄)
• Citric acid (C₆H₈O₇)

The percentages of each in the mixture may range from 0.5 to 99.5%.

is the base of this co-formulant, but it is obviously also possible to use its derivates, i.e. hypophosphorous acid, polyphosphorous acid and poly-hypophosphorous acid.

Phosphorous acid is already known both as source of phosphorous and for its characteristic of facilitating the solubility of different elements in aqueous solutions.

Furthermore, it prevents the formation of precipitates in solutions containing Ammonium, Sodium or Potassium phosphates together with Calcium salts.

This characteristic is enhanced by the presence of citric acid or any other organic acid.

despite being known for its low solubility, it plays a role in the preparation of the co-formulant by improving the latter's activity. The solubility of EDTA increases when it meets complexable cations in the aqueous solution.

it plays a role together with phosphorous acid in enhancing the solubility of saline solutions. It also performs a complexing action on meso-elements and microelements.

In the preparation of the co-formulant, it may be replaced with any other organic acid.

These and other characteristics will be clarified in relation to a simple application of the invention, whose illustration does not restrict the scope of this patent.

Regardless of the other macro- and meso-elements which may be present in the formulation (K₂O, MgO), the co-formulant is used on the basis of the following calculation:

For every percentage point of P₂O₅ provided by the above-specified phosphates, 0.4% of the co-formulant must be added.

For every percentage point of CaO provided by the above-specified Salts, 0.1% of the co-formulant must be added.

In this case, 4.8% of co-formulant will have to be added in the production formula.

In this case, 3% of co-formulant will have to be added in the production formula.

In this case, 8.8% of co-formulant will have to be added in the production formula.

It is preferable to use phosphates other than urea phosphate to obtain Calcium-containing mixtures in order to avoid the presence of ureic Nitrogen, not welcomed by farmers.

In fact, all the different formulations will result in only nitric and ammoniacal Nitrogen. However, this does not preclude the possible presence of ureic Nitrogen as well, as it may be added simply by including urea in the formula.

Compared to other phosphates, urea phosphate has the drawback of being more hygroscopic; hence it may more easily cause hardening of the fertilizer when present in formulations with a high P₂O₅ content.

Urea phosphate contains 44% P₂O₅ whereas other phosphates contain 52%, 53% and 61%; therefore, using other phosphates it is possible to obtain in NPK or NP or NK or PK with a higher content of macroeelements.

In practice the formulation details, ingredients and other aspects of the invention may vary without departing from the scope of the present industrial patent; in fact, the invention thus conceived lends itself to numerous adaptations and variants, all falling within the realm of the inventive concept. In addition, all the elements may be replaced by other chemically equivalent ones.