GB1570199A - Controlled release fertiliser - Google Patents

Description

(54) CONTROLLED RELEASE rF ERTILIS'ER (71) We, STANDARD TELEPHONES AND CABLES LIMITED a British Company of 190 Strand, London W.C.2. England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be porticularly described in and by the following statement: This invention relates to controlled release fertiliser and in particular to a nitrogen containing fertiliser of the slow release glass type.

Our co-pending application No. 33573/74 1,512,637 (C.F. Drake 49) described a biologically active slow release medium consisting of vitreous matrix incluaXing one or more water soluble biologically active constituents together with phosphorus pentoxide which vitreous matrix may include one or more dispersed phases the vitreous matrix having a slow rate of solution in water such that when the medium is lim- mersed in water biologically active constituents are slowly released into solution.

According to the present invention there is provided a controlled release fertiliser composition, including a water soluble glass containing phosphorus oxynitride ((POIN)n) together with potassium oxide, phosphorus pentoxide and an oxide of one or more metals of group II or III of the periodic table.

The fertiliser material is of the phosphate glass type which, when applied to damp soil, slowly dissolves to release its reactive constituents. Conveniently the rate of solution of such a glass can be adjusted to a suitable value for a slow release fertiliser by the incorporation of calcium oxide into the glass. It is to be understood however that alternative oxides such aR silica, alumina or iron oxide can also be employed to lower the rate of solution.

The glass compositions are based on phos- phorus pentoxide which constitutes the glass forming oxide. The composition also contains modifying oxides, in particular an alkali metal oxide, and a potassium oxide, together with an oxide of one or more metals of Group II or III of the peroidic table. Alkali metal oxides have the effect of increasing the water solubility of the glass whilst the Group II or III oxides reduce the solubility. Thus by varying the composition ratio of metal oxide in the glass the solubility rate may be adjusted to a desired value.

The nitrogen content of the fertiliser is provided by co-melting phosphorus oxy nitride - (PON)n - together with the other constituents. In this way inorganic nitrogen in a plant available form is dispersed into the glass matrix. The glass is allowed to cool allo solidify and is then ground into a powder.

The vitreous phase may contain, in add tion to nitrogen and phosphorus, and the major elements of mixed fertilisers, such as potassium, magnesium and calcium, small quantities of trace elements such as iron, boron, manganese, sulphur, vanadium, copper, zinc and molybdenum. Normally the trace elements are incorporated at a total of not more than 1 wt % in aggregate Normally the chemical composition of a slow release fertiliser will be determined by relative quantities of the constituents that are required to be released for the specific purpose of the fertiliser.This will give a rate of release which can then be altered by changing the composition with biologically neutral constituents such as alumina and silica for slowing down the release rate, and soda for increasing it. In this context it will be appreciated that for certain crops, such as sugar-beet, the demand for soda is so great that a fertiliser is required to release soda, and, under these particular circumstances, soda can not properly be considered as a biologically neutral ingredient of the fertiliser.

In order to match the specific require- ments of a particular crop it may be desirable to mix slow release fertiliser powders of different chemical compositions and particle size idistributions so that the pattern of release changes with time. Thus the nitrogen containing material may be mixed with a general fertiliser such as that described in our Specification No. 1,512,637.

WHAT WE CLAIM IS: - 1. A controlled release fertilizer composition, including a water soluble glass containing phosphorus oxynitride ((PON)n) together with a potassium oxide, phosphorus pentoxide and an oxide of one or more metals of Group II or III of the periodic table.

2. A fertiliser composition as claimed in claim 1 and which includes a total of not more than 1 wt % of trace elements.

3. A fertiliser composition as claimed in claim 1 or 2, and which includes silica.

4. A fertiliser composition as claimed in claim 1 substantially as described here in.

5. A fertiliser comprising two or more fertiliser compositions as claimed in any one of claims 1 to 4.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. with a general fertiliser such as that described in our Specification No. 1,512,637. WHAT WE CLAIM IS: -

1. A controlled release fertilizer composition, including a water soluble glass containing phosphorus oxynitride ((PON)n) together with a potassium oxide, phosphorus pentoxide and an oxide of one or more metals of Group II or III of the periodic table.

2. A fertiliser composition as claimed in claim 1 and which includes a total of not more than 1 wt % of trace elements.

3. A fertiliser composition as claimed in claim 1 or 2, and which includes silica.

4. A fertiliser composition as claimed in claim 1 substantially as described here in.

5. A fertiliser comprising two or more fertiliser compositions as claimed in any one of claims 1 to 4.