Technical Field

The invention refers to a process for the direct infusion of nutrients of organic and/or synthetic origin into prepared bark pieces of any desired size such that the nutrients are released in a balanced manner. The integrity of the bark pieces may be retained for any desired situation in which aesthetic appeal is a consideration.

The invention also relates to a fertilizer or growth medium made from such nutrient infused bark.

Background of Invention

Processes are known for the production of bark based fertilizers.

One process involves the production of potting media using softwood tree bark - either aged or pH adjusted Pinus radiata bark, Pinus contorta , Pinus nigra or Pinus Corsica . This process involves the preferably controlled decomposition of bark in an aerobic situation in which there exists for thermophyllic activity, sufficient moisture, available nitrogen and a satisfactory method of supplying oxygen/ controlling the heat generated by bioactivity to within acceptable parameters.

This process may utilise animal, fish and/or other organic waste where bark is the "bulking" agent to facilitate air flow through the mass. The bark pieces are reduced to particulate matter through the decomposition process. This is the desired result.

Evidence suggests that competition from micro-organisms for available nitrogen can reduce the post process net available nitrogen to zero. This is particularly the case where optimum conditions facilitate the rapid incubation of therophylls with a corresponding demand for available nitrogen. This situation is generally referred to as "Nitrogen Draw Down" or "NDD".

Media produced by this method tends to be batch variable. In addition, nitrogen consumption may continue after the product is deemed to be "finished".

Another process involves the addition of nutrient element salts encapsulated in a slow release agent, usually polymer or co-polymer matter which, when added to bark pieces or other base media, reacts with water to release salts in a restricted manner. The product is applied as a surface coating.

Another process is known where nutrient element salts in powdered form are blended with moist bark pieces. Some of the powder may adhere to the bark chips and may be absorbed into the surface area. The amount of salts absorbed is totally arbitrary and incidental to the main objective of solubilising sufficient nutrient salts. The relative volume of applied water is critical and generally extremely difficult to accomplish satisfactorily.

Disclosure of the Invention

It is an object of the present invention to provide an encapsulated fertilizer which overcomes some of the problems associated with prior art processes or which provides a practical alternative.

It is known that leachate from fresh softwood bark is both acidic and toxic. Applications of unmodified fresh bark can cause die back in young plants shrubs and trees. It is further known that aged and therefore at least partially neutralised bark applied directly to the soil can have a significantly adverse affect on the soil quality due to nitrogen draw off by bacteria in the decomposition cycle. Essentially, to be of any benefit to plant life, some modification to the bark is necessary.

The cell structure of dead Pinus radiata bark may be important to the invention. Dead Pinus radiata bark is generally known as rhytidome. It comprises irregular strata of phloem and more or less complete strata of periderm (of which pelloderm and phellum are the major constituents).

The cell structure of each group differs considerably and their abilities to absorb and release nutrients and fluids varies accordingly. These sorbency variations between the cell types are important in the invention. Pressure levels under which the nutrient liquid is infused provide an optimum loading of nutrient elements in the particular cell types, whilst minimising cell wall damage by pressure rupture.

Further, certain pressure levels associated to dwell periods may have a beneficial effect on periderm cells which are coated with a film of material identified as suberin. Suberin is resistant to water, making periderm cells difficult to access for nutrient storage. It appears probable that some nutrient salts will, under certain conditions, at least partially denature the suberin film, facilitating access to periderm cells. Therefore within determinable parameters, the rate of nutrient release may be determined by the combined structures of all cell types within the rhytidome. The sieve cells or phloem will be relatively more functional in transferring liquids. This is the means by

which the nutrient release may be calculated. Under normal conditions, progressive denaturation will occur through microbial activity. This is accepted as a normal function of this product.

The invention provides a method of producing fertilizer or a growth medium comprising direct infusion of nutrients under pressure into bark pieces.

The invention also provides a method of producing infused bark comprising: a) dehydrating bark pieces to be infused; b) determining the required concentration of nutrients to be infused; c) blending the desired concentration of nutrients with water; d) removing free air from the bark via a vacuum; e) flooding the bark with the desired concentration of nutrients in water; f) applying pressure to bring about infusion of the nutrients into the bark; and g) removing the pressure.

Further, the invention provides infused bark pieces suitable as a fertilizer or as a growth medium comprising nutrients infused into dried and dehydrated bark pieces under pressure.

Preferably, the concentration and type of nutrients to be infused is pre-determined.

The process method preferably involves the specific preparation of screened bark which can be of any average size, into which is infused, nutrients in precise and pre-determined ratios. The application of water to the product will progressively solubilise the nutrients which are released into

the soil. There is a direct correlation between the "flushing" factor and subsequent nutrient movement by osmosis and the progressive cell wall denaturation from chemical action and microbial activity.

As part of the process, the surface area of the bark pieces is coated with nutrients. When in contact with water, these nutrients which are readily accessible are flushed from the surface to yield a "charge" solution. This is considered important as the required nutrients are made immediately available in a volume sufficient to satisfy plant requirements, also allowing a nominal surplus of nitrogen to cover the probability that micro activity will cause some draw down of nitrogen when conditions are suitable.

The diminishing availability of nutrients from the initial "charge" is progressively stabilized by the dissemination of infused nutrients solubilised in contact with water.

Throughout this specification , the term "nutrients" takes a broad meaning and includes those chemicals of organic and synthetic origin. Both macro and micro chemicals are included.

In addition, elements and chemical salts are included.

Embodiments of the invention are described by way of example only below.

Best Mode of Carrying out the Invention

Any softwood tree bark can be utilised but for the purpose of this application bark from Pinus radiata has been selected. Bark which has been sourced from well grown mature trees is mechanically crushed into chunks of varying sizes, the placed in a trommel or rotary screens to recover volumes of bark in various grades.

The graded bark is placed in drying zones that facilitates preferably complete dehydration but not less than 95% of free moisture.

Dehydration can be effected by natural or forced air flow the latter of which can be heated. Air flow must be of sufficient volume to ensure that the bark pile does not enter a denaturation or composition cycle. Further, handling should be avoided to minimise damage to the drying mass.

At the conclusion of the drying cycle, random samples of bark from each batch to be infused are removed and analysed to determine the status of macro and micro elements.

Bark has generally very low levels of both macro and micro elements however, the exact value can only be quantified by analysis. Once confirmed, values will require differential calculations to establish the exact additional volume of each element that is required to achieve the required pre-infusion status.

Similarly, the bark samples are tested to determine the pH factor. This is important to the invention. It is known that negative or positive pH can have direct affect on the ability of some elements to be released.

By way of example, a pH factor of 5 or less is likely to cause progressive manganese, copper and zinc toxicity and decreased calcium availability. Conversely, a pH factor of 7 or greater can progressively affect the release of iron. Other elements are similarly affected to varying degrees.

Generally, unmodified bark is acidic and pH readings of 4.5 have been noted.

The invention asserts that a pH factor of approximately 6.2 is necessary to ensure that macro and micro nutrients are released in the pre-determined rations.

Adjustment of pH from negative to positive is effected bj the addition of a pre-determined quantity of MgCO- _j .CaCO.-. or CaCO to the infusion liquid.

Stage I

The required volumes of nutrients elements for infusion are prepared by gentle blending to form an homogenous dry matrix.

It is important to the accuracy of infusion rations that the declared purity of commercial or technical grade element salts be confirmed by independent analysis. This is of particular importance where very low levels of macro and micro elements are required.

Stage II

The blended nutrient elements are then gradually added to a pre-determined volume of preferably de-ionised water. (The infusion volume will relate directly to the size of the infusion chamber and the supply lines) . This is ideally achieved in a stainless steel or high density plastic vat with a conical base connected to a low pressure and volume centrifugal pump of stainless steel or high density plastic construction. The conical base will ensure that nutrient, granules and powders will continuously be fed into the pump inlet. The nutrient element salt hydration period will vary according to the type of raw material chosen however it is important that all the solids are fully liquified. Preferably the infusion liquid is prepared as required and is kept in circulation until infusion commences.

Stage III

Once hydration has been completed, the infusion liquid is tested to determine the pH factor. This figure is then correlated with the averaged pH status of the bark assessed from previous random samples. Correction of pH can then be achieved by the addition of CaCO-. or MgC0-,.CaC0 ₃ to the circulating infusion liquid. Prior to infusion, the liquid should again be tested to confirm the pH factor is within the required parameters.

Stage IV

All free air is removed from the prepared bark using a pressure chamber to which a vacuum is applied. The chamber must be capable of both negative and positive pressure, the latter to withstand 1880 kpa. A cylinder is for example an appropriate apparatus.

Control of negative and positive pressures is critical to the invention. It is important that air is removed from the bark cells incrementally to facilitate the gradual collapse of cell walls, without causing inverse rupture. This is particularly important in respect of phloem cells which are required to perform a crucial function in the subsequent release of nutrients.

In the completed trials, the vacuum level was set at 5"Hg and when reached, the vacuum pump was switched off allowing partial equalisation (2"Hg). These cycles were repeated increasing the vacuum by 5"Hg per cycle and allowing partial equalisation. On the final cycle at 28"Hg, there was no longer equalisation as all free air had been progressively evacuated.

Stage V

The chamber is then flooded with the infusion liquid. It is important to maintain a full vacuum during this phase to ensure that any air in the transfer system is removed. The vacuum has sufficient negative pressure to pull the infusion liquid into the chamber. Once flooded, the chamber is sealed by closing the vacuum valve. Infusion begins immediately as the liquid permeates the bark cells. It is recommended that (depending on the capacity of the chamber), 15 minutes be allowed of limit equalisation.

Following the initial dwell period, the nutrient solution is pumped into the chamber at specific pressure levels and for specific dwell periods.

This is important. The sieve cells are now in reversal phase, that is, moving from a generally inverse cell wall state (under vacuum), to a converse cell wall state (under pressure) . Within the bounds of practicality, the nutrient solution should be forced into the sieve cells areas in a manner that utilises the existing phloem and xylem interconnecting cell access. The capacious ability of those cells should be utilised whilst avoiding cell wall damage from pressure rupture. This can be achieved by applying pressure at increments of 100 kpa. Closing the inlet valve allows assimilation of the infusion liquid. The indicated pressure falls as the liquid is forced into the bark cells. At the conclusion of the infusion cycle, the pressure drop is zero, indicating complete infusion.

The pressure is gradually eased, allowing surplus liquid to return to the storage tank.

The infused bark is removed from the infusion chamber and placed in a drying zone dry state. Without moisture, there is no biological activity and the finished product can be held in this manner indefinitely.

Samples of finished product are taken and analysed to confirm that the macro/micro status of the finished product is within the tolerance parameters.

Nutrient Elements

The following technical grade nutrient elements may be used in varying ratios by weight or percent according to the final infusion requirement. However, other nutrients may be used instead of, or in addition to those given below.

ammonium molybdate, ammonium nitrate, ammonium sulphate, borax pentahydrate, calcium chloride, calcium nitrate, cobalt sulphate, copper chelate, copper sulphate, di-ammonium phosphate, di-potassium phosphate, ferrous sulphate, iron chelate, manganese sulphate, magnesium sulphate, monoammonium phosphate, monopotassium phosphate, nitric acid, phosphoric acid, potassium chloride, potassium hydroxide, potassium iodate, potassium nitrate, potassium sulphate, sodium molybdate, sodium nitrate, sulphate of potash, sulphur powder, urea, ulexite, zinc chelate and zinc sulphate hepta and mono) .

The following, non-limiting examples illustrate specific uses of the invention.

Example 1

A sample was analysed, the sample being a random representation of 1 litre from an infused mass of 38 litres. The batch comprised bark pieces ranging from 5mm to 35mm average diameter. This was done to confirm that the infusion conditions would be adequate for all grades of bark.

Nitrogen (ammonium) and phosphorus were infused at extreme levels, potassium was infused at standard. The value of other elements has been recorded, but are incidental. Values are expressed in milligrams per litre.

ANALYSIS LEVEL LEVEL NORMAL

INFUSED FOUND RANGE

pH 0 7.0 5.2 - 6.5

Nitrate-N 0 8 40 - 80

Ammonium-N 209 215 03 - 20

Phosphorus 107 103 10 - 20

Calcium 0 4 30 - 70

Magnesium 0 2 12 - 25

Sodium 0 7 10 - 40

The pH was neutral although no correction was intended. It is possible that because commercial grade elements were used rather than technical grade, bulking agents of a carbonate nature are likely to be responsible for neutralising pH in this sample.

Example 2

Polyanthus seedlings were transplanted into a base of unmodified top soil ( - 70% by volume) to which 30% infused bark (5mm to 10mm grade as per the sample sent for independent analysis) was placed on top. Seedlings were planted into a core of unmodified top soil.

The control seedlings were transplanted into 100% unmodified top soil.

Both samples were potted into polythene B8 pouches and were watered as necessary being given identical volumes of de- ionised water at each watering (1 litre). Both trial and control samples were placed in a sheltered situation.

From day 5, the difference in plant stature was being visually evident. The high level of ammonium nitrate infused into the bark sample predictably, culminated in continuously rapid leaf growth at the expense of balanced flower development in the trial lots.

By contrast, the control samples had a comparatively diminutive status, however they also had acceptable general conformation and reasonable balance of leaf to flower mass though by comparison they lacked vigour.

The trial was established to confirm that under prescribed conditions, infused nutrients would be made available to the plants in ratios originally infused.

It is to be understood that the scope of the invention is not limited to the described embodiments and therefore that numerous variations and modifications may be made to the embodiments without departing from the scope of the invention as set out in the claims.

Industrial Applicability

The invention provides a process of infusion of nutrient elements of organic and/or synthetic origin into prepared ioark pieces such that the nutrients are released in a balanced manner whilst the integrity of the bark pieces is maintained. The type and amount of nutrient elements can be pre-deter Λned according to the use to which the infused bark pieces are to be put.

A possible use would be to place direct nutrient infused bark of a desired grade and nutrient content around trees, shrubs, bushes and other plants to depths extending to the "drip line" or any circumference from the plant which would make the nutrients available to the plant. Areas which were not required for planting can be covered with standard, unmodified bark of identical grade. This would ensure minimal visual variation between the infused and unmodified bark and thus be more aesthetically pleasing.

Another use would be to add direct nutrient infused bark of particular size and chemical or nutrient content to soil around forest tree seedlings. The slow release of nutrients and gradual decomposition of the infused bark would be extremely beneficial to root development and growth rate of the seedlings.

Of course, the infused bark fertilizer may be used in potted plant pots. The size of the bark pieces used would depend on the size of the plant pot.

The direct nutrient infused bark may provide a complete growing medium.

The ability of the infused bark to hold water and release nutrients has significant production benefits. Rice production is a possibility, for example.

It is therefore apparent that the invention provides an advantageous growth medium/fertilizer for the growth of plants.