GB2297547A

GB2297547A - A plant growth support medium

Info

Publication number: GB2297547A
Application number: GB9502024A
Authority: GB
Inventors: Robert Irvine
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-02-02
Filing date: 1995-02-02
Publication date: 1996-08-07
Anticipated expiration: 2015-02-02
Also published as: GB2297547B; GB9502024D0

Abstract

A plant growth support medium comprises a matrix of porous granular material at least some of the granules of which have plant nutrients adsorbed to their surfaces in a substantially dry state. The granular material is preferably a mineral material such as perlite and vermiculite and the nutrient-enrichment step may be performed by spraying a concentrated aqueous solution of the plant nutrients directly on to hot granules of the material substantially immediately after a heat treatment process which creates a humidity vacancy such that the nutrients are adsorbed to the surface of the granules in a substantially dry state.

Description

A PLANT GROWTH SUPPORT MEDIUM The present invention relates to a plant growth support medium, which may be used for hydroponic plant culture, or as a soil supplement or a peat substitute in conventional horticulture.

Hydroponics is the science of growing plants without the use of soil. Perlite has been used as a growth medium for hydroponic culture; it is an expanded volcanic mineral the use of which in horticulture is well established. As produced commercially, perlite is present in a wide range of particle sizes from dust up to granules of one to four millimetres in diameter. The plants are nourished by means of a nutrient solution containing all the necessary minerals, such as calcium, potassium, ammonium, phosphate, nitrate and trace elements, to ensure healthy vigorous growth. In one conventional hydroponic system, plants are supported above a trough through which is passed a film of nutrient solution. The plant roots grow in a film of solution.

The use of vermiculite and perlite to facilitate seed germination and seedling growth is well known. Favourable growth media have been obtained, but these prior art materials are essentially wet mixes (which may be dried subsequently). To obtain these wet mixes, the constituents, perlite and vermiculite, undergo rigorous mixing which destroys the structure oftheir newly expanded grains. A further disadvantage of prior art wet mixes is that they are susceptible to contamination from bacteria, thus shortening the functional life-span of the mixture. Should the wet mix be dried to overcome the problem of contamination, significant energy input is required. The present invention seeks to provide a plant growth support medium which is at all times during production substantially dry and which may remain dry until deliberately wetted for use.

According to the present invention there is provided a plant growth support medium comprising a matrix of porous granular material at least some of the granules of which have plant nutrients adsorbed to their surfaces in a substantially dry state.

The present invention avoids damage to the granules which occurs in the wet blending stage, helping to maintain the structure of the vermiculite grains. Using a dry mix has the added advantage that it allows controlled release nutrient granules to be added into the medium for long term storage, thereby giving the mixture a much longer active life than previous growth media.

The plant growth support medium of the invention may be a matrix of porous granular material which comprises a mixture of perlite and vermiculite with the plant nutrients adsorbed to vermiculite granules.

Carolina vermiculite, as opposed to say, South African vermiculite, is preferred as it has the lowest pH of all vermiculite with the advantage of acting as a pH buffer, and therefore as a safety valve for excessive nutrients. The dust component of perlite can vary. Granule sizes may range from lmm to 4mm. Fine vermiculite granules may replace those of perlite thus providing an increase in all the advantages of vermiculite due to the increase in surface area. In a further embodiment of the present invention, the granule size of the perlite may be varied in accordance to the needs of a plant, because the finer the granules the more water can be absorbed, and the coarser the granules, the less water can be absorbed - coarse granules would suit say, the growth of orchids which require relatively little water.

The porous granular material may include a component of magnesium lime stone and may further include a component of vermiculite filter dust.

The nutrients may be preliminarily dissolved in water. The precise composition of the nutrients may be varied in order to complement and/or comply with a particular environment, for example, calcium may be added in soft water areas. Typically the plant nutrients may comprise or include calcium nitrate and/or ammonium nitrate and/or phosphoric acid and/or a composition containing nitrogen, phosphorous and potassium in predetermined ratios. There may be two different compositions containing nitrogen, phosphorous and potassium in two different ratios. These ratios may be 5-11-26 and 10-52-10 respectively. The said two compositions may be present in a ratio order of 3:1.Preferably, the pH ofthe plant growth support medium is under pH6 but may vary between pH5.5 - 6.5 without substantially affecting the performance of the medium.

Soilless media generally have low fertility reserves and as nutrient levels are increased, salinity pH and toxicity troubles appear because of insufficient buffering capacity.

Trace element imbalances are frequent problems as well. Peat-like mixes are also difficult to wet and they posses low reserves of moisture available to the plant. The improved plant growth medium of the invention may have slow release nutrients added in the preparation ofthe medium so as to make feasible the complete containergrowing of horticultural plants without additional fertilisation. For this purpose the plant growth support medium of the invention may further include a component of enriching nutrients in pellet form having a coating of material which breaks down gradually in the presence of moisture to release the nutrients slowly over a period of time. Consequently, such a medium may require less attention and skill in management of the plant growth.

Both vermiculite and perlite are characterised by low density and high porosity, which are desirable properties, but these materials provide only minimal nutrients to support plant growth. The present invention provides an improved plant growth medium containing vermiculite and perlite by incorporating nutrients into a dry state mixture thereby forming a matrix having increased capillarity and available moisture retention and fertility reserves than conventional mixes. The improved growth media are also characterised by greater buffering capacity so as to resist pH changes and the salinity and toxicity effects that follow from the addition of increased levels of nutrients.

Another aspect of the invention comprises a method of producing a plant growth medium in the form of a substantially dry mixture of expanded porous granular mineral material enriched with plant nutrients, including the step of spraying a concentrated aqueous solution of the nutrient directly on to hot granules of the mineral material substantially immediately after a heat treatment process which creates a so-called humidity vacancy such that the nutrients are adsorbed to the surfaces of the granules in a substantially dry state.

A physical property of vermiculite when exfoliated under heat is a humidity vacancy of 5% (approximately), which in the period after the heat treatment is taken up with atmospheric moisture leaving the vermiculite totally dry in appearance. The humidity vacancy of exfoliated vermiculite is exploited in performing the method of the invention in that it is taken up with the nutrients (due to the cation exchange facility of vermiculite). These nutrient molecules are locked in the vermiculite and given off in the presence of water, thereby providing means for the delayed release of nutrients.

After wetting the dry composition of the present invention nutrients are released individually, such that nitrogen is the last to be released. A germinating seed does not require nitrogen until a later stage; the late release ofthis nutrient component therefore serves to aid and enhance plant growth and continuous nutrient supply. Nutrients are sprayed on to vermiculite immediately after its expansion so that its capacity to adsorb dry materials and hold them in place by an exchange process is utilised: the addition of water for bonding is not required. The enriched dry porous granular material may be subsequently admixed with a further granular material in a predetermined or preselected ratio to determine the nutrient concentration in the final mixture of granular material and nutrient enriched granular material.

Further nutrients in the form of pellets having a coating allowing controlled release of the said further nutrients may be admixed to the said mixture of granular material and nutrient enriched granular material.

The conductivity ofthe plant nutrients in the growing medium will typically be around 1000 microsiemens/cm. This may depend on the growth requirements of the plant.

The slow release fertilizer granules (such as Osmocote) may take approximately 2 weeks to become active. The conductivity (for primary charge) can therefore be lowered.

Embodiments of the invention will now be described by way of example only.

Example 1 A general purpose mixture for sowing and cuttings was made up from the following ingredients: 1000 litres expanded perlite, fines reduced 100 litres C4 carolina vermiculite 5 litres carolina filter dust 1 kilogram ground magnesium lime stone Nutrient enrichment for the above quantities comprises 175 grammes calcium nitrate 335 grammes peters 5/11/26 hydrosol 120 grammes peters 10/52/10 plant starter 15 grammes ammonium nitrate phosphoric acid (optional) 1-2 killogrammes of controlled release Osmocote The method of producing a plant growth medium according to this invention is performed by dissolving the nutrients above with the exception of the Osmocote in 5 litres of water. The nutrients are then sprayed on to the carolina vermiculite just after the latter has been exfoliated in great heat. The solution is taken up by the humidity vacancy in the 100 litres of newly exfoliated material and produces a dry result.

The remainder of the components of the growing medium are then added in a very gentle blending process which does not require great energy because all the components are substantially dry. The Osmocote is added at the last moment to individual bags and containers in due measure and with regard for purpose.

Claims

1. A plant growth support medium comprising a matrix of porous granular material at least some of the granules of which have plant nutrients adsorbed to their surfaces in a substantially dry state.

2. A plant growth support medium as claimed in Claim 1 in which the matrix of porous granular material comprises a mixture of perlite and vermiculite and the plant nutrients are adsorbed to vermiculite granules.

3. A plant growth support medium as claimed in Claim 1 or Claim 2, in which the porous granular material includes a component of magnesium limestone.

4. A plant growth support medium as claimed in any of Claims 1 to 3 in which the porous granular material includes a component of vermiculite filter dust.

5. A plant growth support medium as claimed in any preceding claim in which the plant nutrients comprise or include calcium nitrate and/or ammonium nitrate and/or phosphoric acid and/or a composition containing nitrogen, phosphorus and potassium in predetermined ratios.

6. A plant growth support medium as claimed in Claim 5 in which there are two different compositions containing nitrogen, phosphorus and potassium in two different ratios.

7. A plant growth support medium as claimed in Claim 6, in which the said two ratios of nitrogen, phosphorus and potassium are in the region of 5:11:26 and 10:52:10.

8. A plant growth support medium as claimed in claim 6 or Claim 7, in which the two said compositions are present in a ratio of about 3:1.

9. A plant growth support medium as claimed in any preceding claim, further including a component of enriching nutrients in pellet form having a coating of water soluble material which allows a release the nutrients slowly over a period of time in the presence of water.

10. A plant growth support medium substantially as hereinbefore described with reference to the examples.

11. A method of producing a plant growth support medium comprising a substantially dry mixture of expanded porous granular material enriched with plant nutrients, including the step of spraying a concentrated aqueous solution of the nutrients directly onto hot granules of the material substantially immediately after a heat treatment process which creates a so-called humidity vacancy such that the nutrients are adsorbed to the surfaces of the granules in a substantially dry state.

12. A method as claimed in Claim 11, in which the enriched dry porous granular material is a mineral material and subsequently admixed with a further granular mineral material in a predetermined or preselected ratio to determine the nutrient concentration in the mixture of further granular mineral material and nutrient-enriched granular mineral material.

13. A method as claimed in Claim 12, in which further nutrients in the form of pellets having a coating allowing gradual release of the said further nutrients are added to the said mixture of further granular mineral material and nutrient enriched granular mineral material.

14. A method of producing a plant growth medium substantially as hereinbefore described with reference to the examples.