WO2004035508A1

WO2004035508A1 - Compost based on mineral fertiliser

Info

Publication number: WO2004035508A1
Application number: PCT/NZ2003/000238
Authority: WO
Inventors: Clive Prebble Sinclair; William Arthur Sinclair; Angus Peter Robson
Original assignee: Kagree Holdings
Priority date: 2002-10-21
Filing date: 2003-10-21
Publication date: 2004-04-29
Also published as: AU2003278641A1; AU2008203399B2; AU2008203399A1

Abstract

The compost includes living and dead microorganisms together with a mineral substrate (such as rock phosphate) partly digested during a relatively dry, self-heated composting process. A fish hydrolysate nutrient and first inoculum including thermophiles is mixed with ground rock, which has been made lighter and more porous by addition of sawdust. The composting process is aerobic as a result of air blown through the composting mass. A second inoculum is mesophilic and persists until application. The dry product has a neutral pH.

Description

TITLE COMPOST BASED ON MINERAL FERTILISER

FIELD

This invention relates to a fertiliser; to a fertiliser based on a phosphate rock, and to improved methods for manufacturing fertilisers providing available phosphate and other nutrients. BACKGROUND

Fertilising the soil is a way of increasing the ability of arable land to support the growth of farmed plants by overcoming shortages in one or more nutrients and/or trace elements; sometimes also modifying the soil pH or its physical properties. Historically, a wide range of inorganic fertilisers have been applied. They comprise a small range of major elements required for plant growth. In addition a range of minor elements, as well as a range of trace elements may be mixed with those fertilisers and a customised selection from those ranges for use in any given fertiliser application may be made on the basis of experience, prior soil tests, plant mineral analysis, or animal pathology reports from the land to be treated. An ideal fertiliser would be cost-effective, release specifically those nutrients that are required, and release the nutrients at a controlled rate so that for example they are not leached out of the application site and washed away, such as into a lake.

"Organic fertilisers" has at least two meanings; one is fertilisers including carbon-based materials such as manure, dung, litter, compost, or peat and another meaning is fertilisers free of harmful chemical or other contamination (such as free of artificially modified life forms) in accordance with the agreed definitions of "organic farming". There have been a number of problems with efficiently producing such fertilisers. These include production problems resulting from the bacterial contamination that is often carried into the plant with the raw materials used.

Phosphorus availability is a limiting factor, at least under New Zealand conditions. Rock phosphate is a mined material available in considerable quantities in deposits in some parts of the world, such as Egypt, Morocco, and the United States of America. The active composition is calcium phosphate (apatite) although a varying amount of fluoride and carbonate exists in practice.. Because it is well-known that even finely ground phosphate rock is of little practical use due to the low solubility of the phosphate within, one commercial product is made by grinding the rock to perhaps 200-mesh size, then treating the rock with concentrated sulphuric acid (optionally also phosphoric acid) to make "superphosphate". Although much of the phosphate is made available to plants in that way, and aerial topdressing with superphosphate has been an important aspect of New Zealand agriculture for many years, the phosphate is released too easily from this product. A significant proportion is leached out and enters waterways and lakes with consequent eutrophication. Much of the rest becomes locked into the soil. The very low pH of that fertiliser often damages foliage and reduces the population of beneficial soil micro-organisms.

Chitralekha R et al showed recently that on an allophanic New Zealand soil, superphosphate treatment gave a peak P solution concentration (availability) of 0.2 micrograms/ml by 15 days but which dropped back to less than 0.12 thereafter. A biologically reacted phosphate fertiliser gave P levels which rose gradually to 0.2 micrograms/ml by about 70 days, and which continued to rise up to 120 days when tests stopped.

Naturally occurring soil micro-organisms (of which there is an almost infinite variety) are capable of extracting the phosphorus from soil or minerals including phosphate rock, and making it available to plants. For example see Rose (1957) N Z J Sci Tech (B) (38) 773- who refers to earlier work on such micro-organisms back to the beginning of the 20th century. 12 of 25 soil isolates by Rose had a solvent action on rock phosphate. Thien & Myers, Soil Sci Soc. Am J 56 814-818 (1992) showed that more active soil microbial activity resulted in heightened release of phosphate, possibly owing to the release of organic acids (reviewed eg in Goenadi et al Soil Sci Soc. Am J 64 927-932 (2002)). The latter paper describes use of a strain of phosphate solubilising fungus, Aspergillus niger BCC F.194 for solubilising Moroccan phosphate rock under laboratory conditions. Interestingly, citric-acid soluble phosphate rather than water- soluble phosphate was produced by the fungus. The paper concluded that a process could treat ground phosphate rock with liquid culture supernatant as an alternative to sulphuric acid; a process that could be called "bioactivation".

Fertilisers have previously been developed by the inventors' group in which non-thermophilic micro-organisms together with a nutrient source are mixed together with a mineral substrate (phosphate rock) with the primary intention of increasing the bioavailability of phosphate through the action of the added phosphate solubilising fungi on the rock after application. The mixing action takes place shortly before application. These methods have been the focus of earlier international applications PCT/NZ93/ 00076 WO9506623 and PCT NZ94/00099. WO9508521, the contents of which are incorporated herein by way of reference. These specifications, like others which provide a "package" of phosphate rock with micro-organisms for extracting the phosphorus once the fertiliser has been broadcast, do not teach a lengthy factory "composting"- process.

The inventors' group has previously experienced problems when using plant material or animal by-products such as fish or marine material, manure or waste from meat and milk processing plants for their range of nutrients. Anaerobic conditions resulted in foul smelling odours during breakdown. Unintended contamination with micro-organisms pathogenic to animals or humans can occur particularly if manure or civic sewage is included. Any contamination can be a major health and safety concern to anyone coming in contact with the fertiliser. One particular problem that has been experienced in commercial production is contamination by Clostridium perfringens, a spore-forming anaerobe (widespread in the soil), some strains of which cause enterotoxaemia and "pulpy kidney" in sheep. The inventors have found in trials that aeration by intermittently turning piles of composting mixture with a mechanical shovel was inadequate and expensive. The time required for the composting process was prolonged, and resulted in odour problems due to the anaerobic breakdown of the organic nutrient in parts. Contamination by pathogenic micro-organisms occurred as a result of the incomplete composting. The mixing steps may have an adverse effect by re-inoculating the entire pile with pathogenic micro-organisms each time the pile was turned. Better aeration alone did not solve the problem.

Tsuru in US 6548288 describes a method for producing, in an aerated liquid process at a moderately raised temperature, a "high density antagonistic microbe base" fertiliser designed to improve the ecology of a soil under treatment. Many other patent specifications address similar goals. A number of publications relating to composting employ a raised temperature in order to minimise the content of potential pathogens.

DEFINITIONS

"Aerobic" as used herein refers to conditions sufficient for the growth of aerobic microorganisms (involving use of oxygen as electron acceptors, for example) while disadvantaging or preventing the growth of facultative and especially obligate anaerobes. An empirical measure of aerobic conditions is "at least 5% oxygen".

"Compost" as used herein refers to "a compound manure or combination" (OED) or "a mixture for fertilising land; esp. a composition of various substances (as muck, mould, lime, and stable manure) thoroughly mingled and decomposed, as in a compost heap. (Websters (1913)). A definition from the waste treatment industry is "aerobic thermophilic stabilisation".

"Organic" as used herein refers to carbon chemistry; compounds including carbon of biological origin, unless the term is used in relation to "organic foods" or "organic farming".

"Pathogenic micro-organism" as used herein refers to a micro-organism capable of causing or producing disease in animals and/or humans, as well as in plants. Examples of relevance include the faecal coliforms Escherischia coli, (some strains at least), Salmonella spp, faecal streptococci, or other faecal contaminants, spore-forming Bacillus spp and anaerobic Clostridia, or viruses. Faecal coliforms are dominant in^' some forms of waste such as pig manure or chicken litter which may be used as a nutrient source in a composting process. "Primary micro-organism" as used herein refers to any beneficial micro-organism such as 105 bacteria, or fungi that have the ability to break down and/or absorb the initial mixture of nutrient source and mineral substrate. This group includes thermophilic species or strains.

"Secondary micro-organism" as used herein refers to any beneficial micro-organism such as bacteria or fungi, less able to withstand the temperature during the initial composting period and which may be added subsequently.

110 'Thermophilic micro-organism" as used herein refers to any heat-tolerant micro-organism; such as bacteria, yeasts, or fungi regardless of whether the heat tolerance is a necessity for metabolism and growth, or merely a capability. For purposes of this specification, the term is used for the set of micro-organisms metabolically active around or above 40 to 65 deg C.

OBJECT

115 It is an object of this invention to provide a combination fertiliser or compost having both a biological and a mineral fertiliser component, or at least to provide the public with a useful choice.

STATEMENT OF INVENTION

In a first broad aspect the invention provides a compost based on a mineral or rock rich in at 120 least one selected element, wherein the compost includes (a) the rock, reduced to a fine particle size and at least partially digested, (b) a proportion of the at least one selected element converted by an aerobic composting process into a biologically available form, (c) at least some micro-organisms or remains thereof in the form of organic matter; the compost having a low water content.

125 In a related aspect the invention provides a compost based on a phosphate rock, wherein the rock has been reduced to a fine particle size and a proportion of the phosphate has been converted into a form available to plants (the remainder being potentially available at a time after application) by means of a controlled aerobic composting process in which added microorganisms, supported by added nutrients, extract and make biologically available an amount of

130 the phosphate from the reduced rock; at least some of which micro-organisms or remains thereof in the form of organic matter persist in the compost as organic matter; the composition having an about neutral pH and a low water content.

Preferably the compost is capable of continuing to make supplies of the at least one selected element available to plants after an application, as a result of continued activity of micro- 135 organisms upon the reduced rock.

Preferably the mixture is made by mixing together a nutrient source, at least one primary micro-organism, a porous material, and a mineral substrate (the reduced rock).

Preferably the nutrient source is a fish hydrolysate.

Preferably the fine particle size is defined as "over 90% of a sample passes through a 1 mm 140 mesh screen", although the duration of continued release of the at least one selected element after application of the compost may be extended by use of larger particle sizes.

In a first related aspect the micro-organisms include one or more types selected from a mesophilic group including some capability to extract the selected element from the reduced rock so that the compost includes means to continue to release the element after application.

145 In a second related aspect the micro-organisms include one or more types selected from a thermophilic group.

In a third related aspect the micro-organisms are obtained from soil samples.

In a fourth related aspect the micro-organisms are obtained from previous batches of compost.

Preferably the compost has a minimised amount of potential animal pathogens.

150 In a second broad aspect the compost includes up to about 3% by weight of available phosphate, up to about 5.5% of organic matter, and up to about 3% by weight of available nitrogen, and a low water content of between 5 and 10% by weight, so that the mixture has a friable sand-like structure.

In a first related aspect the fertiliser composition further includes a customised variety of added 155 minor and trace elements, held within the compost, so that the needs of a particular customer may be satisfied.

In a second related aspect, a plurality of seeds of a plant species, and a species of bacteria together capable of fixing nitrogen is mixed with the compost, so that the compost provides a soil with a sustainable nitrogen fixing capacity. For example, Rhizobium spp bacteria may be 160 included together with clover (Trifolium spp) seeds.

In a third broad aspect, the invention provides a method for making a compost based on a rock rich in at least one selected element, wherein the method includes the steps of reducing the rock to a specified particle size, mixing a supply of nutrients with the rock in order to create a mixture, mixing a first inoculum including a first set of selected aerobic micro- 165 organisms with the mixture, holding the mixture in a container for a period of time, under aerobic conditions, until an evolution of heat has slowed and the mixture has cooled below about 40 deg C, optionally adding a second inoculum including a second set of selected aerobic micro-organisms into the mixture, holding the mixture for a period of time, under aerobic conditions, until the second inoculum has become distributed through the mass and 170 acted upon the rock, and supplying the resulting compost to a customer.

Preferably the first set of added micro-organisms includes one or more types selected from the following thermophilic group: actinomycetes including Streptomyces, fungi including Zygomycetes, phosphate- and other mineral-fixing bacteria including Thiobacillus, selected archaebacteria, autotrophic bacteria including Glomus tenuis, aerobic composting bacteria 175 including Theobacillus, Alkaligenes, Azotobacter, and Pseudomonas, acidophiles and lactic-acid bacteria.

Preferably the second set of added micro-organisms include one or more types selected from the following mesophilic group: Actinomycetes spp, fungi including Aspergillus niger, Penicillium spp, Trichoderma viride, Gigaspora margarita, vesicular-arbuscular (V-A) mycorrhizae such as 180 Ectomycorrhiza, and bacteria including Rhizobium, and Pseudomonas spp.

Preferably the mixture has a low water content of less than 10% by weight, so that the mixture has a friable sand-like structure.

In a fourth broad aspect the invention provides a method for making a low-pathogen compost based on a mineral rock and added nutrients, wherein the mixture is permitted to reach a 185 temperature of at least 50 deg C for at least a period of several days, so that micro-organisms not capable of thriving at that temperature are preferentially eliminated and so that the processed mixture contains a minimised proportion of potential animal pathogens.

In a related aspect the invention provides a container for holding a compost during a composting process, wherein the container is thermally insulated and includes means for 190 aerating the compost by introduction of air from an air distribution means so that an aerobic environment is provided and so that self-heating is encouraged in order that a risk of holding potential pathogens is reduced.

In a first related aspect this invention provides a method for the production of a fertilising composition or compost, in which the temperature of the mixture during composting reaches 195 55°C or above and the moisture content is less than 10% by weight so that the mixture retains air spaces around particles and may be aerated.

In a second related aspect this invention provides a method for the production of a compost in which an added porous material is capable of being broken down by the at least one primary micro-organism during the period of time.

200 A preferred porous material is sawdust, and preferably the amount of the porous material added is about one part sawdust to eighteen parts by weight of mineral substrate.

PREFERRED EMBODIMENT

Further aspects of the present invention will become apparent from the following description 205 which is given by way of example only and with reference to the accompanying drawings.

DRAWINGS

Fig 1 : is a diagram showing a composting container in cross-section.

Fig 2: is a graph 200 of temperature against time for an example composting process. 201, the horizontal axis, is in days and 202 - the vertical axis - is in degrees Celsius.

210 Surprisingly, it has been found that a "composting" process can be applied to digestion of a rock substrate, instead of (as usual) to the rotting of plant material employing bacterial and fungal action over a period of time (about one month) in order to create a relatively slow- release fertiliser presenting the mineral and organic constituents in a form readily available to plants in soil. The material produced by the invention comprises a free-flowing powdery or

215 sandy material of 5% to 10% water content, a variety of dead or living micro-organisms and some secretions, at a pH of about 7 to 7.2 (sometimes pH 6.5 to 7.5, depending on the rock used). The micro-organisms have already begun to solubilise or digest the phosphate rock while being supported by a community of other micro-organisms that are converting the nutrients into cellular material. This composting process is closely controlled in the factory.

220 Aerobic and nearly dry conditions are deliberately maintained within a thermally insulated space, the temperature is allowed to rise and then fall during a period of significant microbial activity, and the material being composted is inoculated on at least one occasion with selected micro-organisms, some of which stay alive and enter the soil to be fertilised. The process may replace the acid treatment involved in manufacture of superphosphate fertiliser.

225 PHYSICAL CONTAINMENT

The inventors found that careful attention to the containment of the composting material was needed. In order to provide hot, aerobic composting conditions for bulk amounts of composition, a bin is constructed preferably from concrete (as shown in cross-sectional view in Fig 1) in a size capable of accepting a front-end loader or similar machinery. A concrete bin 230 with walls 101 and floor 110, is shown in cross-section, holding a composting composition 100. Preferred dimensions are about 18 metres long, 10 metres wide and 2 metres high. Deeper bins would press down on and compact the deeper layers. Shallower bins do not heat as well, and use up relatively more valuable factory floor space. Heat produced is retained with thermal insulation (such as polystyrene foam pads 102, 103) within the walls and floor of the bin, a

235 cover 112, and preferably can be supplemented such as by buried heating means especially at comers (see pipes 105, 109) because the composition in corners may otherwise not reach an intended temperature. The array of rods 111 may be taken to represent an "under-floor heating" installation option, or may simply comprise a section through steel reinforcing mesh (which could be heated by connection to a high-current, low-voltage source of electricity). The

240 required aerobic conditions are met, in this example, by pumping air through the composition 100. In general an air inter-outlet spacing of about 1 metre is found to be sufficient, especially with a modification to the mixture to be composted providing greater porosity (see below). The air may be heated or cooled and/or humidified as required. Thermal, oxygen, and humidity sensors are not shown, but close attention to process control is desirable.

245 Referring to Fig 1 in detail, two physical aeration methods are shown. To the left of the dotted line A-A, the first way to aerate the composition 100 is from suspended, perforated air pipes 107 (suspended perhaps from hook 108) is shown. A second way is shown to the right side of the dotted line A-A. Pipes 109 within the floor supply air to the composition through a matrix of holes 104..In both cases, air should pass through the entire mass of the composition 100

250 rather than forming open channels. Use of large-bore pipes, reasonable pressure, and small apertures makes the distribution system insensitive to variations of air resistance at any individual aperture. In the currently preferred process, the aerated composition is left to stand undisturbed for about a month until finally being removed for packaging and sale. No remixing or turning over treatment occurs prior to completion. See below under "Aeration".

255 During composting, there may be considerable growth of fungal hyphae within the composition.

It is relevant to state here that the preferred composition is always visually dry during composting. Less than 10% water by weight, more preferably less than 8% is used so that the physical appearance of the composition is a free-flowing powdery or sandy material. After a

260 time, growth of fungal hyphae through the mass tends to create friable lumps. It has been a surprising discovery by the inventors that the desired composting reaction proceeds best under those dry conditions. This may reflect the predominance of fungi in the process, and also facilitates aerobic conditions. Workers should guard against starting a batch with damp phosphate rock or watery nutrient mixtures because these may cause the water content to

265 exceed 10%, raising the risk of anaerobic microbial activity which is inefficient, smelly, wasteful of nitrogen (much of which is lost as ammonia) and promotes the survival of some pathogens. If the material cannot be dried before use, some dried bentonite (a clay) or the like may be added to take up some moisture. PHOSPHATE or other ROCK:

270 The preferred mineral substrate used is phosphate rock, a widely used commodity available through international trade. A hard North African rock, not a "reactive phosphate rock" includes about 15% P. This is suitable. The material is ground to a fine particle size typically such that 90% will pass through a 1 mm screen although use of a greater proportion of larger particles will result in a longer period of release after application. Phosphorus and nitrogen are

275 the macro-elements most in demand as fertilisers. Other suitable mineral substrates, (though not phosphate-rich) include: limestone, dolomite, zeolite, bentonite, serpentine, and volcanic rock.

MINOR AND TRACE ELEMENTS

Standard inorganic fertilisers usually offer a limited range of elements (selected from nitrogen,

280 phosphorus, potassium, magnesium, calcium, and sulphur). Standard organic fertilisers include urea (for nitrogen), blood and bone, chicken litter and the like for a wider spectrum of organic supplements. The present invention permits a wider range of inorganic elements to be supplied in slow-release form, bound as chelates such as with amino acids or together with organic compounds within living or dead micro-organisms. The organic material significantly improves

285 the Cation Exchange Capacity (CEC) of a soil, over time. The preferred nutrients used in this invention inherently contain some minor and trace elements and others can be added to the fertiliser of the invention, as is known in the art, in order to compensate for suspected or proven shortages in the soil to be fertilised. Trace elements may be added as required to the mineral substrate and/or the nutrient source in the form of inorganic compounds such as

290 sulphates, or as organic chelates available for all trade elements. The set of "trace elements"

(the need for which is indicated by soil, plant, or and animal assays) includes boron, copper, cobalt, manganese, iodine, magnesium, molybdenum, zinc, and selenium.

ADDED NUTRIENTS:

A source of microbial nutrients is used during composting because the rock phosphates as 295 supplied lack sufficient organic and nitrogenous materials, minor and trace elements for microbial metabolic processes to occur at the desired rates. An advantage is that most of the added nutrients are retained in the final mixed product as bio-available materials; nitrogen, for example is within living or dead micro-organisms or their secretions. Hence some of the original microbial nutrients become plant nutrients after application to the soil. Also, the 300 nutrients are fuel for the self-heating process that eliminates pathogens.

The inventors prefer a nitrogen-rich nutrient source, namely fishing industry by-products known as offal, fish hydrolysate or fish silage (guts, fins, heads and the like, non-food species, deteriorated catch, all of which is ordinarily considered inedible waste). This readily and cheaply available rich nutrient source otherwise presents a disposal problem. An advantage of 305 fish is that being cold-blooded, their by-products are not likely to be carry pathogenic microorganisms dangerous to people or farm animals, whereas animal-derived materials can be expected to include pathogenic micro-organisms that might be transferred to humans or other animals through contact with fertiliser made with such nutrients. Although preliminary sterilisation could be carried out, it may not be cost-effective.

310 The inventors prefer that the fish offal has a reasonably high solids content. They acidify ground, wet fish offal in a mixing vat in order to reach a pH of less than 3.7, preferably about 3.0 to 3.3 which will retard bacterial degradation although autolytic degradation by stomach enzymes may continue at this pH. A pH of less than 2 gives longer preservation. This requires addition of about 1 to 1.5% of concentrated sulphuric acid, its equivalent of hydrochloric acid,

315 or a mixture of formic and inorganic acid. The resulting slurry is herein termed "the nutrient".

MICROBIOLOGY

The first inoculation of selected micro-organisms into the compost initiates the composting process at a desired rate and with an intended mixed population of largely thermophilic and rock-attacking micro-organisms. The composting process will typically take four weeks to

320 produce the compost/fertiliser. As is common in composting, there is a substantial evolution of heat during nutrient breakdown within this process (see Fig 2). In the preferred method the heat is desired and is not normally dissipated. Thermophilic organisms are preferred as the first inoculate, to maintain microbial activity and the intended population during the high temperature phase. As can be seen from Fig 2, the mass typically remains at 55 degrees C or

325 above for about 10 days. A temperature of at least 50 deg C is preferred in order to (a) speed the composting process, which even with this temperature profile still lasts for about a month, and (b) to help to eliminate undesired pathogenic organisms. The inventors have identified 50 to 55 deg Celsius as an approximate composting temperature at or above which few pathogenic micro-organisms will survive the composting process. Within limits, a higher temperature is

330 more effective. Testing of the microbiological content of the compost showed that pathogens were destroyed in the fertilising composition within 24 hours at 60 deg C or within 1 hour at 70 deg C. However, the beneficial micro-organisms are also destroyed above 90 deg C. (Another advantage of thermophilic micro-organisms in this process is that their activity is much reduced after introduction into soils, where they will be at a competitive disadvantage as

335 compared to ordinary (mesothermic) soil bacteria).

It must be realised that some pathogenic micro-organisms may sporulate in adverse conditions. Also, it must be realised that persons receiving immune suppression therapy or who otherwise have a compromised immune system will be liable to infection by many of the fungi used in this invention.

340 Thermophilic bacteria and fungi occur in many soil sample isolates, though are more likely to be found in soil isolates from hot springs (or other volcanically heated ground). Some of those are known as the archaebacteria. Some soil fungi are inherently thermophilic. Inoculates taken from past batches of the same process, or isolated from the raw phosphate rock before use are also suitable sources. For (a non-limiting) example, a mixture of primary micro-organisms

345 may be selected from the group of: actinomycetes such as Streptomyces, fungi such as Zygomycetes, phosphate- and other mineral-fixing bacteria such as Thiobacillus and selected archaebacteria, autotrophic bacteria such as Glomus tenuis, aerobic composting thermophilic bacteria such as Theobacillus, Alkaligenes, Azotobacter, Pseudomonas, acidophiles, lactic-acid bacteria and the like. That list is given by way of example only: a range of other aerobic micro-

350 organisms could also be used separately or together as would be appreciated by a skilled addressee, indeed, an effective inoculate could be obtained and used without identifying the species within. Micro-organisms are known to exchange genetic material in nature.

Prior art composting techniques (using plant material) have avoided temperatures of much over 40 deg C because higher temperatures tend to destroy the non-thermophilic organisms 355 responsible for the composting action and would result in an aborted processing cycle.

The inventors prefer to inoculate the fertiliser with at least one secondary micro-organism after the initial peak of composting activity and after the temperature of the fertiliser had dropped to below about 50 deg C. Additional thermophilic micro-organisms (such as from the class Zygomycetes) may optionally be added in order to consume the nutrients released by the

360 breakdown of the nutrient source and mineral substrate. Additional nitrogen or phosphate- fixing micro-organisms may also be added to fix nutrients released by the composting process. This allows further breakdown of the nutrient and mineral substrates by selected microorganisms which would have been destroyed by the high temperatures during the earlier phase of composting. At least some of the secondary group will be carried into the soil treated by the

365 final composted fertiliser where, in addition to further decomposition of the phosphate rock by added micro-organisms, modification of the existing microbial ecology (such as the suppression of plant pathogens) may be desired.

Once the composting process slows and the temperature drops below 40°C, secondary microorganisms may be added in a similar manner in order to complete the composting process and 370 adsorb the nutrients released during composting. Such nutrients can then be gradually released to the plants once the fertiliser has been applied to the soil. Optionally, other lithotrophic and/or chemoautotrophic / lithotrophic micro-organisms are added in order to fix nitrogen, sulphur and iron and to aid in the utilisation of these materials once the fertiliser is applied to the soil. Mesophilic species suitable for use as secondary micro-organisms in the present 375 invention include: Aspergillus niger, Penicillium glaucum, P brevicale, and other R spp, Trichoderma viride, Actinomycetes, vesicular-arbuscular (V-A) mycorrhizae, Ectomycorrhiza, Gigaspora margarita, and other fungi, Rhizobium, Pseudomonas spp bacteria, Actinomycetes, and so forth.

Additional micro-organisms may also be added during the final stage of the composting process (at 206) in order to suppress plant pathogens once the fertiliser applied to the soil. It 380 will be appreciated that the ecological microbiology of soil is complex. (We have not considered protozoa, nor multicellular life such as nematodes or annelid worms in this specification). Fertilisers including micro-organisms provide a careful gardener or farmer with a good opportunity to modify the existing ecology of a soil both by altering substrates and also by inoculating relatively large numbers of selected microbial species.

385 (The above list of mesophilic organisms was given by way of non-limiting example. The inventors have contributed a soil treatment composition itself worth spreading for intrinsic fertiliser-type benefits that is also compatible with specific soil ecology modifiers such as (for example) US 6387146 Protzmann - a mycorrhizal fungus useful in symbiotic relationships, and US 6074451 Goda, a Pseudomonas species for controlling the common scab of potato).

390 One useful source of secondary micro-organisms comprises a proportion of a previous fertilising composition, used as a starter culture to inoculate each new fertilising composition. The composition of the fertilising composition as sold is monitored by semiquantitative (serial dilution plates) microbiology in case undesired micro-organisms should appear. The manufacturers would also store reserve supplies of approved inoculates.

395 AERATION

An aerobic composting environment is highly desired. The growth of beneficial microorganisms is favoured, efficient composting occurs without odours, and anaerobic pathogens such as many Clostridia spp are strongly discouraged. Two improvements are used; preferably together, on the substantially dry mixture during the composting process. The first is to

400 provide forced-air ventilation for example as previously described with reference to Fig 1. The flow rate and pressure should be sufficient to provide a gentle current of air. The air may be heated in order to speed the onset of the composting process, and to help ensure that the entire mass, even in comers and around air inlets, reaches at least a desired temperature (such as 55 deg C). Temperature may be monitored by a thermometer built into a long probe and

405 directed manually into the heap, or by use of an automated monitoring system. To date we have not used a probe to sense anaerobic areas directly, although an oxygen electrode could be built into a probe. A smell of ammonia is another sign of anaerobic fermentation. We find that aeration through pipes is cheaper and far better for providing an aerobic environment than previous methods which involved turning the piles of fertiliser occasionally with a mechanical 410 shovel.

Inoculates may be introduced via the aeration system and dispersed under positive pressure into the fertilising composition, or they may be dispensed by hand using a backpack sprayer and a lance. The moisture content of the composition can be monitored and changed if necessary by controllably humidifying the incoming air.

415 The second improvement related to aeration is the use of "porosity-enhancing" additives that physically modify the density and structure of the composition. Finer ground rock restricts the ability of air to diffuse through the composition, significantly so for the preferred fineness grade. A preferred porosity enhancing additive is dry sawdust, preferably taken from un-treated wood in order to avoid introduction of toxic chemicals into the food chain. This material

420 immediately serves to lighten and to break up the composition, but later the sawdust (comprised of cellulose, lignin, and xylans) becomes digested by fungal action and is substantially invisible in a final product. The digested sawdust will leave voids within the undisturbed, dry composition.

One preferred proportion of sawdust is about one part of sawdust to 18 parts of mineral (both 425 by weight). Other proportions may be used depending on specific conditions and on the nature of the composition and of the sawdust or analogous substance. Any sawdust is an advantage. Too much may distort the balance of micro-organisms in the final product or lower the rated concentration of available phosphorus. Some sawdusts or barks may contain natural substances deleterious to the desired microbial ecology.

430 EXAMPLE 1

Figure 2 illustrates a temperature: time curve for a typical composting process as used in the present invention for the production of a fertilising composition, including a high-temperature composting sequence and aerobic conditions. The conditions were as follows:

A quantity (900 kg) of dry rock phosphate was ground or otherwise broken down to a desired 435 particle size and mixed with about 50 kg of untreated sawdust (a ratio of about one part sawdust to 18 parts of rock phosphate), in order to provide the mineral substrate.

50 litres of liquid fish based by-product, prepared as previously described was used as a nutrient. The acidic nutrient becomes neutralised on mixing with the ground rock. Approximately 10 litres of primary micro-organism inoculant (as previously described) was 440 dripped onto the rock/nutrient mixture as it passed along a conveyer. That mixture was then mixed well with the porosity modifier (sawdust) and the resulting composition was placed into insulated concrete fertiliser bins. (See point 203 on the graph of Fig 2). Note that the water content is about five to ten per cent, which is unusually low for a composting process. During composting and afterwards, the product is a flowable powdery material, compatible with

445 normal fertiliser spreading machinery and compatible with diffusion of air through the mixture.

The composting process will typically take four weeks to produce the fertilising composition. When the composition drops to 40 deg C or below ,or at other times, additional thermophilic micro-organisms may be added as previously described in this section. Optionally, yet further lithotrophic and/or chemoautotrophic / lithotrophic micro-organisms are added in order to fix 450 nitrogen, sulphur and iron and to aid in the utilisation of these materials once the fertiliser is applied to the soil. Additional mesophilic micro-organisms may also be added in order to suppress plant pathogens once the fertiliser applied to the soil. The neutral, dry nature of the composted mineral fertiliser is compatible with such additions.

The composition of the product according to the invention is typically (by weight):

455 Water 5-10%, Total Phosphorus 11-14%, Plant-available Phosphorus about 3%, Organic material up to about 6%, Nitrogen up to about 3%, Calcium about 35%, pH 6.5 - 7.2. All the phosphorus will be released over about one year after application, assuming healthy soil. A flowable brown powdery to sandy material, compatible with normal fertiliser spreading machinery. Tendency to form loosely adherent lumps if stored, owing to continual fungal

460 activity. (Shelf life has not been tested). These values depend on the original rock as well as the process and the balance of organisms present, as will be realised by one skilled in the art. The mass or organic material appears to have increased slightly over that originally included, suggesting some carbon fixation has occurred.

VARIATIONS

465 The greatest variability in relation to use of this invention relates to the very wide selections and balanced groupings of micro-biological forms that may be added in varying quantities to the composition, during or after the composting process. Some of these may be genetically engineered organisms, such as to provide desired thermophilic characteristics in addition to a gene product active in a desired aspect of fertiliser bio-availability. Some will be selected or

470 modified in order to modify the soil ecology of a target soil for a particular purpose. On the other hand perfectly good organisms may appear within any soil isolate, as a result of gene swapping occurring naturally between existing strains of micro-organisms. Over-reliance on species identification may be a fallacy.

The neutral pH of the dry product permits addition of materials such as living plant seeds and 475 clover seeds with Rhizobium spp (an example of a symbiotic group providing long-term self- sustainable nitrogen fixation). The dry state of the composition does not stimulate seed germi- nation and the neutral pH does not reduce viability of the seeds.

In relation to nutrients, in some situations there may be a requirement to partially or completely substitute other aquatic-derived material such as seaweed, or other animal by- 480 products such as manure, waste from meat and/or milk processing plants, used litter, waste food, waste from animal processing plants or civic sewage, for the preferred fish offal/hydro- lysate.

Materials other than sawdust may be added in order to facilitate aeration, such as chopped straw, finely chopped cardboard, waste paper, wood chips, bark, and wood shavings.

485 Mineral materials that may be used instead of, in addition to, or as well as phosphate rock includes feldspar (for potassium), bentonite (for water absorbtion), zeolites (for chelation), dolomite, lime, granite, serpentine, or volcanic rocks.

An aeration process involving mechanical agitation of the material (see for example PCT/FRO 1/02402 Chenu) may be used but the elongated shapes of the storage bins involved 490 may prevent the evolution of sufficient heat and the infrequent aeration may lead to anaerobic fermentation.

Details of the composting process as described herein are dependent on the volume of fertiliser manufactured, the type, concentration, and pH of the nutrient source, and the nature, type, and particle size of the mineral substrate, the composition and concentration of the 495 micro-organisms, the thermal insulation efficiency (R value) of the bins and any extra heating, as well as the ambient temperature, efficiency of oxygenation, moisture content and so forth, as will be realised by a person skilled in the art.

INDUSTRIAL APPLICABILITY and ADVANTAGES

1. The procedure has a competitive cost, in production volumes. For example, a price "on the 500 ground" per kg is expected to be about NZD 2.30 whereas conventional superphosphate is about NZD 2.00 - 2.15 per kg yet has less available phosphate in the long term, no organic materials or nitrogen, and some disadvantages. The product is a "high-test fertiliser". ^•

2. The product as sold includes soluble phosphates, and micro-organisms adapted to further solubilise and distribute phosphate from the phosphate rock substrate even after application;

505 the release occurring relatively steadily over an extended period typically one year, assuming a healthy soil with microbial activity..

3. The product as sold is a flowable powder or granular brown material, and typically the pH is 7 to 7.2 - perhaps 6.5 to 7.5 with some rock types.

4. Although the product as sold includes micro-organisms and has been through a composting 510 type procedure, the proportion of potentially dangerous (pathogenic) organisms within the product has been deliberately minimised by (a) direct effects of the high temperature used, (b) competition with thermophilic organisms during the high temperature phase, and (c) effective aeration during the composting type procedure.

5. The product as sold includes a soil inoculum capable of modifying the ecology of a target 515 soil including for example mycorrhizae. (If this was not desired the product may be sterilised before use).

6. The product as sold includes minor and/or trace elements; the release of which occurs relatively steadily over an extended period from the cells or remains of the micro-organisms included.

520 Finally, it will be understood that the scope of this invention as described and/or illustrated herein is not limited to the specified embodiments. Those of skill will appreciate that various modifications, additions, known equivalents, and substitutions are possible without departing from the scope and spirit of the invention as set forth in the following claims.

Claims

525 1. A compost based on a mineral or rock rich in at least one selected element, characterised in that the the compost includes (a) the rock, reduced to a fine particle size and at least partially digested, (b) a proportion of the at least one selected element converted by an aerobic process into a biologically available form, (c) at least some micro-organisms or remains thereof in the form of organic matter; the compost having a low water content.

530 2. A compost based on a phosphate rock, characterised in that the rock has been reduced to a fine particle size and a proportion of the phosphate has been converted into a form available to plants (the remainder being potentially available at a time after application) by means of a controlled aerobic composting process in which added micro-organisms, supported by added nutrients, extract and make biologically available an amount of the

535 phosphate from the reduced rock; at least some of which micro-organisms or remains thereof in the form of organic matter persist in the compost as organic matter; the composition having an about neutral pH and a low water content.

3. A compost as claimed in claim 2, characterised in that the compost includes up to about about 3% by weight of available phosphate, up to about 5% organic matter, up to about 3%

540 by weight of available nitrogen, and a low water content of between 5 and 10% by weight, so that the mixture has a friable sand-like structure.

4. A compost as claimed in claim 3, characterised in that the compost is capable of continuing to release the at least one selected element after an application, as a result of continued activity of micro-organisms upon the reduced rock.

545 5. A compost as claimed in claim 4, characterised in that the duration of continued release of the at least one selected element after application may be in part determined by control of the particle size of the rock.

6. A compost as claimed in claim 4, further characterised in that a plurality of seeds of a plant species, and a species of bacteria together capable of fixing nitrogen are included with the

550 compost, so that after application the compost also provides an environment with a sustainable nitrogen fixing capacity.

7. A compost as claimed in claim 4 characterised in that the fertiliser composition further includes a customised variety of added minor and trace elements, held within the compost, so that the needs of a particular customer may be satisfied.

555 8. A container for holding a compost as claimed in claim 1 during a composting process, characterised in that the container is thermally insulated and includes means for aerating the compost by introduction of air from an air distribution means so that an aerobic environment is provided and so that self-heating is encouraged in order that a risk of holding potential pathogens is reduced.

560 9. A compost as claimed in claim 2 characterised in that the temperature of the compost was raised to a temperature of at least 50 deg C for at least a temperature-related minimum time, so that mesophilic micro-organisms are preferentially eliminated and so that the processed mixture contains a minimised proportion of potential animal pathogens.

10. A method for making a compost based on a rock rich in at least one selected element, 565 characterised in that the method includes the steps of

(a) reducing the rock to a specified particle size,

(b) mixing a supply of nutrients with the rock in order to create a mixture,

(c) mixing a first inoculum including a first set of selected aerobic micro-organisms with the mixture,

570 (d) holding the mixture in a container for a period of time, under aerobic conditions, until an evolution of heat has slowed and the mixture has cooled below about 40 deg C,

(e) optionally adding a second inoculum including a second set of selected aerobic microorganisms into the mixture,

(f) holding the mixture for a period of time, under aerobic conditions, until the second 575 inoculum has become distributed through the mass and acted upon the rock, and

(g) supply the resulting compost to a customer.

11. A compost as claimed in claim 10, characterised in that the first set of added microorganisms includes one or more types selected from the following thermophilic group: actinomycetes including Streptomyces, fungi including Zygomycetes, phosphate- and other

580 mineral-fixing bacteria including Thiobacillus, selected archaebacteria, autotrophic bacteria including Glomus tenuis, aerobic composting bacteria including Theobacillus, Alkaligenes, Azotobacter, and Pseudomonas, acidophiles and lactic-acid bacteria.

12. A compost as claimed in claim 10, characterised in that the second set of added microorganisms include one or more types selected from the following mesophilic group:

585 Actinomycetes spp, fungi including Aspergillus niger, Penicillium spp, Trichoderma viride, Gigaspora margarita, vesicular-arbuscular (V-A) mycorrhizae such as Ectomycorrhiza, and bacteria including Rhizobium, and Pseudomonas spp.

13. A method as claimed in claim 10 characterised in that a proportion of a pore-forming material is mixed with the mixture, so that the mixture is more easily aerated by a forced

590 flow of air through the mixture.

14. A method as claimed in claim 13 characterised in that the pore-forming material is capable of being digested by micro-organisms included within the mixture.