Plant husbandry – Water culture – apparatus or method
Patent
1986-11-04
1988-12-27
Hafer, Robert A.
Plant husbandry
Water culture, apparatus or method
47DIG10, 47DIG3, 71 77, A01G 910, C05G 300
Patent
active
047930950
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an aqueous rooting gel, which is preferably translucent.
Plants are frequently propagated by taking cuttings and placing them in a growth medium such as soil or a peat based compost. These conventional growth media suffer from the disadvantage that the growth medium has to be kept moist. Furthermore, the composition of naturally occurring materials such as peat or soil varies and consistently reproducible agronomic results from a number of samples are difficult to obtain.
Thixotropic gels, of various types including gels prepared from silica, clays and organic materials have been proposed in European patent application No. 0 006 299 as propagating media for cuttings. However, we have found that gels prepared in accordance with European patent application No. 0006299 are unsatisfactory in a number of respects and in particular do not comprise a reliable medium for the rooting of cuttings.
We have found that two essential elements are required for a satisfactory cutting medium; firstly the gel has to be a hectorite gel; secondly the gel has to contain at least 60 pm calcium ions.
According to the invention there is provided an aqueous rooting gel which comprises a thixotropic gel of hectorite in water containing at least 60 ppm calcium ions.
The gel preferably contains at least 75, more preferably at least 90 ppm calcium ions.
The gel suitably contains not more than 200 ppm calcium ions, preferably not more than 150 ppm calcium ions and especially not more than 130 ppm. The gel most suitably contains between 60 and 130 ppm calcium ions, e.g. 100.+-.10 ppm calcium ions.
The gels in accordance with the invention are generally clear, and to ensure such clarity it is desirable that the calcium ion concentration is less than 130 ppm.
Gels with a calcium ion concentration of greater than 130 ppm which are sufficiently clear to enable visualisation of roots less than 0.2 cm in length on cuttings placed in the centre of a 7 cm diameter transparent pot may be prepared by adding a calcium ion complexing agent, e.g. sodium hexametaphosphate, to the gel. The quantity of complexing agent to be added to obtain a sufficiently clear gel will depend on the nature of the complexing agent and on the quantity of calcium ions to be complexed. However we have found that it is possible to prepare clear gels with a total calcium ion concentration of 150 ppm by adding 315 mg/litre of sodium hexametaphosphate. A clear gel having a calcium ion concentration of 200 ppm may be prepared by adding 840 mg/litre sodium hexametaphosphate to the gel.
By the term hectorite is meant a trioctahedral clay which is a member of the saponite sub-group of smectites. The term hectorite has been ascribed to the natural trioctahedral smectites found at Hector, California, USA. Hectorites can be represented by the general or idealised formula: (OH).sub.2 number which is generally less than 1.0.
The hectorite may be of natural origin, but more usually is synthetic.
The hectorite preferably comprises from 58 to 63 parts by weight SiO.sub.2, 25 to 30 parts by weight MgO, 2.2 to 2.8 parts by weight Na.sub.2 O, 0.65 to 0.90 parts by weight Li.sub.2 O and from 0.15 to 0.40 parts by weight sulphate. It is preferably fluoride free.
The particle size of the hectorite used in the preparation of the gel is preferably such that at least 98% passes through a 0.25 mm sieve.
The calcium ion concentration is preferably obtained by the addition of a calcium salt to the water used to prepare the gel, but other methods of incorporation may also be used, such as addition during formation of the gel. The calcium salt should be of sufficient solubility to dissolve in the aqueous medium, and may be calcium sulphate, calcium chloride, calcium nitrate or monocalcium phosphate. It is preferred to use calcium sulphate dihydrate.
The concentration of hectorite in the aqueous phase should be sufficient to yield a thixotropic gel which comprises the rooting gel of the invention. It is preferred that the concentration of hectorite is in the range 1 to 10%, pr
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DeMille Danton D.
Fisons plc
Hafer Robert A.
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