CA2146359C - Slow release fertilizer and active synthetic soil - Google Patents

Abstract

A synthetic soil/fertilizer for horticultural application having all the agronutrients essential for plant growth is disclosed. The soil comprises a synthetic apatite fertilizer having sulfur, magnesium and micronutrients dispersed in a calcium phosphate matrix, a zeolite cation exchange medium saturated with a charge of potassium and nitrogen cations, and an optional pH buffer.
Moisture dissolves the apatite and mobilizes the nutrient elements from the apatite matrix and the zeolite charge sites.

Description

~. 214635 I
SLOW RELEASE FERTILIZER AND
ACTIVE SYNTHETIC SOIL
Origin of the Invention The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
Field of the Invention The present invention relates to an active synthetic soil for horticulture. More particularly the present invention relates to an active synthetic soil made from synthetic apatite and natural zeolite having a complete spectrum of agronutrients necessary for plant growth.
Background of the Invention Synthetic soils for horticulture (i. e., solid substrates for plant support) include two general categories-inert and active. Inert substrates are commonly used in nutriculture (e. g., hydroponics) and are designed to provide mechanical support, proper root aeration and drainage. Quartz sand is a good example of an inert soil. Plant nutrients are added separately as, for example, liquid fertilizers such as Hoagland's solution. Soils which are defined as "active" have the ability to provide nutrient retention and release (i. e., incorporate fertilizing capability) in addition to the other primary soil functions of the above mentioned inert soils.
It is known that nutrient retaining activity in natural soils is due to the presence of organic matter and clay components. Such components have charge sites suitable for ion exchange. Prior to release, the nutrient elements are held at the charge sites as "exchange ions."
Recent introduction of ion exchange media (that are not normally found in natural soils) having a high exchange ion holding capacity have made feasible the development of active synthetic soil-fertilizers which can supply plant nutrients over a long period of time.
Mineral zeolites have been found to be a class of very useful ion exchange media. Many natural species are prevalent and numerous synthetic species have been made in the laboratory. Zeolites are hydrated aluminosilicates of alkali and alkaline-earth rations that possess infinite, three-dimensional crystal structures (i.e., 2~463~9 '~O 94/0889b ~ f ~ PCT/US93/09906 tektosilicates). The primary building units of the zeolite crystal structure are (AI,Si)04 tetrahedra. When A13+ and sometimes Fe3+ substitute for Si4+ in the central ration position of the tetrahedron, a net-negative charge is generated. This negative charge is counterbalanced primarily by monovalent and divalent "exchange rations." Zeolites have shown the ability to exchange most of their constituent exchange rations as well as hydrateldehydrate without major changes in the structural framework. Most zeolites have large channels andlor cages that allow exchange rations easy access to charge sites and provide unique ration selectivity.
The use of zeolites as a major soil component has a relatively recent past. U. S. Patent 4,337,078 to Petrov et al. describes the use of a natural zeolite clinoptilolite with vermiculite and peat in a synthetic soil. The term zeoponics has been coined to describe synthetic soils containing zeolites in horticulture.
Agronomists and botanists have long recognized the vital function of sixteen nutrients needed by growing plants including the trace elements or micronutrients - zinc, chlorine, iron, manganese, copper, molybdenum and boron. It is also known that the optimal spectrum and concentration of micronutrients in a particular soil can vary depending on the plants being grown, soil properties, climate, and the stage of the plant growth cycle.
While most natural soils contain micronutrients at least to some extent and the overall need is small, depletion can occur with intensive agricultural activity. Even when the soil concentration is putatively adequate, other factors can prevent micronutrient uptake by the plant.
Since micronutrients must be available as soluble ions, such ions can be immobilized in low solubility alkaline soils andlor can be trapped on clays or organic materials as insoluble complexes.
It has been common practice to supplement phosphorus-impoverished soil by using a mineral fertilizers such as rock phosphate or natural apatite Such minerals, however, do not supply the required micronutrients and can contain toxic elements such as fluorine and ' cadmium.
Rock phosphate as mined is relatively insoluble in water.
TherEfore, the raw product is generally pretreated to enhance phosphate solubility prior to use. Such processes, however, are considered too expensive for farmers in underdeveloped nations. Yet, fertilizer use is necessary to promote economic development.
Summary of the Invention The present invention provides a synthetic soil and fertilizer composition for horticulture which contains an entire spectrum of nutrients essential for plant growth. The soil combines a ration exchange medium charged with ammonium and potassium exchange rations and an apatite composition ~ comprising magnesium, sulfur and plant micronutrients. The apatite is preferably synthetic which, unlike natural varieties is essentially free of toxic elements. The presence of moisture mobilizes the plant nutrients at a slow, steady rate. In addition, the nutrient release rate can be closely tailored to the horticultural requirements. These features and others offer potential for use in lunar and other agriculture applications.
In one embodiment, the present invention provides a slow release fertilizer. The fertilizer is made from apatite comprising a matrix of calcium phosphate having a dispersion of one or more agronutrients and a cationic exchange medium having a charge of one or more agronutrients. The apatite and cationic exchange medium are preferably essentially free of agrotoxins, such as, for example, fluorine, cadmium and sodium, in amounts detrimental to the growth of most plants. Agronutrients include, for example, potassium, ammonium-nitrogen, magnesium, sulfur, zinc, chlorine, iron, manganese, copper, molybdenum and/or boron. The fertilizer can further include a pH
buffer to maintain a pH balance of from about 5.5 to about 7. The cationic exchange medium can comprise natural or synthetic zeolite, phyllosilicate or a combination thereof including clinoptilolite, chabazite, mordenite, phillipsite, Linde type A, Linde type X, vermiculite, smectite or a combination thereof.
The ration exchange medium has a ration exchange capacity (CEC) of at least 50 cmolclkg, preferably at least 100 cmolclkg, and more preferably ~at least 150 cmolclkg. The ration exchange medium preferably has a charge of ammonium and potassium ions at a weight ratio of from about 1 to about 5:1 of ammonium:potassium. The fertilizer preferably comprises from about 5 to about 100 parts by weight of the synthetic apatite per 100 parts by weight of the cationic exchange medium.
In a preferred embodiment, the apatite of the fertilizer has a generally uniform composition and corresponds to the formula:
(~a5-xm/2 Mx)((P~4)3-yq/3 Qy)((~H)1-zXz) AMENDED SHEET

wherein M is a ration containing an element selected from potassium, zinc, iron, manganese, magnesium, or copper or a combination thereof; wherein m is the molar average valence of M according to the equation m = (Emixi)/(Exi) where each mi is the valence of an itn ration comprising M and xi is the relative molar proportion of the ~ ration; wherein Q is an anion of carbonate, silicate or containing an element selected from boron, molybdenum, or sulfur, or a combination thereof; wherein q is the molar average valence of Q according to the equation q = (Eqiyi)l(Eyi) where each qi is the valence of an ltn anion comprising Q and yi is the relative molar proportion of the ~tnanion; wherein X is chloride, fluoride or a combination thereof; and wherein x has a value of 0 -0.82, y has a value of 0 - 0.76, and z has a value of 0 - 0.15, provided that at least one of x and y are greater than zero and the amount of fluoride does not exceed 3000 ppm by weight, and also provided that when x is zero Q includes an anion of boron, rr~alybdenum andlor sulfur. Preferably Mx has the formula:
~ KxKMgxMgFexFeZnxZnMnxMnCuxCu wherein xK S 0.205; xMg <_ 0.412; xFe S 0.144; xZn S 0.0123; xMn S 0.044; xCu <_ 0.0038; x = xK + xMg + xFe + xZn + xMn + xCu~ and wherein x > 0. More preferably, 0.051 S xK S 0.?_~~5; 0.165 S xMg S 0.412; 0.0359 S xFe S 0.144;
0.006 _< xzn <_ 0.0123; 0.018 S xMn S 0.044; and 0.0016 S xCu S 0.0038.
Especially, 0.102 S xK <_ 0. ~i 54; 0.247 S xMg S 0.33; 0.072 S xFe S 0.108;
0.0061 S xzn S 0.0092; 0.018 S xMn S 0.036; and 0.0025 S xCu S 0.0032. Qy preferably has the formu!~::
(C03)yC{Si04)ySi(Mo04)yMo (B03)yB (S04)yS
wherein yC has a value up to about 0.5, y ,i has a value up to about 0.218, YMo has a value up to about 0.000052, yB has a value up to about 0.0093, and yS
has a value up to about 0.25; and wherein y = yC + YSi +YMo + YB + YS, and {YMo + YB + YS) > 0. More preferably, 0.00002 <_ yMo <_ 0.000042; 0.00185 S
yg <_ 0.00741; and 0.125 <_ yS <_ 0.25. Especially, 0.000021 s yMo S
0.0000313; 0.0037 <_ yg _< 0.0056; and 0.156 S yS S 0.219. Where the solubility control agent is carbonate, preferably 0.0668 <_ yC S 0.334, and especially 0.134 S yC 50.2; and where it is silicate, preferably 0.0435 5 ySi <_ 0.131, and especially 0.0653 <_ ySi <_ 0.109. Xz preferably has the formula:
CIzCI FZF

_ _ __ wherein zCl has a value up to about 0.071, zF has a value less than about 0.08, and z = zCl + zF. More preferably, 0.0283 S zCl s 0.071; and zF S 0.008.
Especially, 0.0565 5 zCl S 0.064; and zF S 0.00008.
In a particularly preferred embodiment, the apatite of the fertilizer in the present invention is an agronutrient-substituted hydroxylapatlte of the formula:
(Ca5-xmI2KxKMgxMgFexFe~xZnMnxMnCuxCu) I(P04)3-yql3 (C03)yC(Si04)ySi(Mo04)yMo (B03)yB (S04)yS]I(OH)1-z CIzCIFzF) wherein m is the molar average valence of the potassium, magnesium, iron, zinc, manganese and copper rations according to the equation:
m = (xK + 2xMg+2xFe+2xZn+2xMn+?.xCu)~x wherein q is the molar average valence of the anions C03, Si04, Mo04, B03 and S04 according to the equation:
q = (2YC + 4YSi +2YMo + 3YB + 2YS)~Y
wherein x = xK + xMg + xFe + xZn + xMn + xCu, Y = YC + YSi +YMo + YB + YS.
z = zCl + zF, and at least one of x, yMo, yg and yS is greater than zero; and wherein xK S 0.21; xMg S 0.41; xFe 5 0.14; xZn s 0.012; xMn S 0.044; xCu s 0.0038; yC S 0.5; ySi 5 0.218; yMo S 0.000052; yg S 0.0093; yS S 0.25; zCl 5 0.071; and zF _< 0.08. Preferably, 0.051 s xK s 0.205; 0.165 5 xMg S 0.412;
0.0359 S xFe 5 0.144; 0.006 5 x~ 5 0.0123; 0.018 s xMn 5 0.044; 0.0016 5 xCu S 0.0038; 0.00002 5 yMo 5 0.000042; 0.00185 S yg 5 0.00741; 0.125 S yS
5 0.25; 0.0283 S zCl S 0.071; and zF 5 0.008. Especially, 0.102 5 xK S 0.154;
0.247 5 xMg s 0.33; 0.072 5 xFe < 0.108; 0.0061 S x~ S 0.0092; 0.018 S xMn s 0.036; 0.0025 s xCu S 0.0032; 0.000021 S yMo S 0.0000313; 0.0037 S yB s 0.0056; 0.157 S yS S 0.219; 0.0565 S zCl S 0.064; and zF S 0.00008.
* *
AfIA~f~ED SHEET

~214G359 WO 94/08896 ~ PCT/US93/09906 In another embodiment, the present invention provides a horticultural method: In one step, a botanical species is planted in a sufficient amount of the fertilizer composition described above. In another step, the fertilizer is contacted with moisture to mobilize the agronutrients.
In a further embodiment, the present invention provides a method of making an active synthetic fertilizer. In one step, a synthetic apatite is prepared by admixing in an aqueous medium from about 1.0 to about 1.6 moles per liter of a soluble ionic calcium compound and a solution mixture comprising from about 0.5 to about 0.8 moles per liter of a soluble ionic phosphate compound and an agronomic amount of, one or more soluble agronutrients selected from magnesium, zinc, sulfur, chlorine, iron, manganese, copper, molybdenum and boron to form a crystalline calcium phosphate precipitate having agronutrients dispersed therein. The precipitate is recovered, dried and suitably granulated. As another step, individual zeolite portions are charged with ammonium and potassium rations to displace native rations. The precipitate is blended with the charged zeolites at a proportion of from about 5 to about 100 part by weight of the precipitate per 100 parts by weight of the ammonium and potassium charged zeolites. The weight ratio of ammonium charged zeolite to potassium charged zeolite is from about 1 to about 5:1. The zeolite is preferably clinoptilotite. The fertilizer blend preferably includes from 0 to about 10 parts by weight of a pH buffer per 100 parts by weight of the ammonium and potassium charged zeolites.
Brief Description of the Figure The Figure shows diffractographs with peak spacing for three different synthetic apatite compositions of the present invention. The diffractographs indicate that the present synthetic apatite has a crystalline structure similar to naturally occurring hydroxyapatite and carbonate hydroxyapatite.
Detailed Description of the Invention An entire spectn.im of essential agronomic nutrients including .
nitrogen, potassium, magnesium, sulfur and micronutrients are incorporated into an active synthetic soil for horticulture. Upon contact by moisture, the nutrients are slowly released, as required, for plant use.

214~3~9 In addition, a fertilization rate can be controlled and the soil tailored to horticultural needs.
The major component of the synthetic soil composition is a synthetic apatite fertilizer. The apatite has a calcium phosphate matrix ' 5 which is at least slightly soluble in water. Water solubility is necessary to give mobility to nutrient elements contained in the apatite matrix.
Examples of suitable calcium phosphates include dicalcium orthophosphate (CaHP04), monocalcium orthophosphate (Ca(H2P04)2), tricalcium orthophosphate (Ca3(P04)2), hydrates thereof and calcium pyrophosphate pentahydrate (Ca2P207~5H20).
Preferably, from about 30 to about 50 parts by weight phosphorus are used per 100 parts calcium, and more preferably, from about 40 to about 45 parts by weight phosphorus per 100 parts calcium.
One or more essential agronomic nutrients besides calcium and phosphorus are dispersed within the crystal structure of the synthetic apatite. Essential agronomic nutrients (agronutrients) in addition to calcium and phosphorus, include potassium, nitrogen, magnesium, sulfur, zinc, chlorine, iron, manganese, copper, molybdenum and boron.
The latter seven elements (zinc, chlorine, iron, manganese, copper, molybdenum and boron) are generally referred to as micronutrients and are needed by plants in lower amounts than the other essential agronutrients.
Agronutrients are provided in the present composition as water soluble inorganic (ionic) compounds. The inorganic compounds should not have acute toxicity (e. g. cyanide salts), or other undesirable properties and should be free of excessive amounts of agrotoxins including unwanted elements and organic toxins. Undesirable elements typically include most heavy metals such as lead, cadmium, mercury, and the like, and other elements such as fluorine, sodium, arsenic, antimony, selenium, tin, and the like. The synthetic apatite can, however, contain a relatively small amount of any of these toxins below a toxic level for plants and, where appropriate, grazing animals. For example, natural apatite contains about 6 percent fluorine and has only limited potential as a soil supplement because of the fluorine toxicity, particularly to grazing animals such as sheep which can ingest the fluorine, e.g. by licking the soil containing the supplement. Prior art phosphatic fertilizers, in contrast, can contain about 3000 ppm fluorine, whereas natural soils average about 300 ppm and plants typically 214f 3~9 WO 94/08846 - ~ PCT/US93/09906 contain about 3 ppm fluorine. Thus, the present synthetic apatite composition should generally contain no more than 10 parts fluorine per 100 parts calcium, by weight, but preferably contains no more than 3000 ppm fluorine, more preferably no more than 300 ppm, and especially no more than 3 ppm. Tolerance levels of specific plants and animals for other agrotoxins can be found in the literature or determined empirically.
The amount of agrotoxins in the synthetic apatite should be less than an amount which would result in release into the environment of the agrotoxins in excess of a given tolerance level.
Examples of suitable water soluble compounds of agronutrients used in the preparation of the synthetic apatite include potassium compounds such as potassium chloride, potassium nitrate, potassium nitrite, potassium sulfate, and potassium phosphate; magnesium compounds such as magnesium nitrate, magnesium chloride, magnesi~rm nitrite, magnesium chlorate, magnesium perchlorate and hydrates thereof; sulfur compounds such as sodium sulfate, ammonium sulfate, potassium sulfate, and hydrates thereof; zinc compounds such as zinc chloride, zinc nitrate, zinc nitrite, zinc sulfate and hydrates thereof; chlorine compounds such as sodium chloride, potassium chloride, ammonium chloride; iron compounds such as ferric nitrate, ferrous ~ nitrate, ferrous nitrite, ferric nitrite, ferric chloride, ferrous chloride, ferric sulfate, ferrous sulfate and hydrates thereof; manganese compounds such as manganese(II) nitrate, manganese(II) nitrite, manganese dichloride, manganese(II) sulfate and hydrates thereof;
copper compounds such as copper(II) chloride, copper(III) chloride, copper(II) nitrate, copper(II) nitrite and hydrates thereof; molybdenum compounds such as ammonium paramolybdate, ammonium permolybdate, sodium trimolybdate, sodium tetramolybdate, sodium paramolybdate, sodium octamolybdate, potassium molybdate and hydrates thereof; and boron compounds such as sodium tetraborate, sodium metaborate, potassium tetraborate, potassium metaborate, ammonium tetraborate, hydrates thereof and orthoboric acid. The preferred, more preferred and optimum amounts of the agronomic ' nutrient elements per 100 parts calcium in the synthetic apatite, are set forth in Table 1.

Table 1 AgronutrientPreferred More Optimum Element Amount Preferred Amount (parts Amount (parts by (parts by Weight) by weight) wei ht Ca 100 100 100 S 0-4 2-4 2.5-3.5 Zn 0-0.4 0.2-0.4 0.08-0.3 CI 0-1.25 0.5-1.25 0.1-0.13 Fe 0-4 1-4 2-3 Mn 0-1.2 0.5-1.2 0.5-1 Cu 0-0.12 0.05-0.12 0.08-0.1 Mo 0-0.0025 0.001-0.0020.001-0.0015 B 0-0.05 0.01-0.04 0.02-0.03 The synthetic apatite composition can also comprise a silicon and/or carbonate solubility control agent dispersed in the apatite matrix. The solubility control agent increases or decreases the water solubility and permits enhanced control over the rate at which nutrient elements are released. The effect of carbonate content on natural apatites is described in several publications including Caro, J., Journal of Agricultural Food Chemistry, 4:684-687, 1956; McClellan, G., American Mineralogist, 54:1374-1391, 1969; and Lehr R., National Fertilizer Development Center Bulletin, Y-43, Vol. 8 published by the Tennessee Valley Authority, Muscle Shoals, Alabama.
The solubility control agent is provided in the synthetic apatite composition as a water soluble inorganic or organic compound. Examples of suitable water soluble carbonate compounds include sodium carbonate, sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, potassium carbonate and potassium bicarbonate.
Examples of water soluble silicon compounds include inorganic silicates such as sodium silicate, sodium disilicate, sodium metasilicate, sodium orthosilicate, potassium disilicate, potassium metasilicate, potassium hydrogen disilicate, ammonium silicate, and hydrates thereof, and organic silicates such as ethyl orthosilicate and propyl orthosilicate.
A solubility control agent can comprise from 0 to about 15 parts by weight per 100 parts calcium. A carbonate agent is preferably used in an amount of 0 to about 15 parts by weight per 100 parts calcium, _~~463~9 '~'VO 94/08896 ~ PGT/US93/09906 , more preferably from about 2 to about 10 parts by weight and optimally from about 4 to about 6 parts by weight. A silicon agent is preferably used in an amount of 0 to about 10 parts by weight per 100 parts calcium, more preferably from about 2 to about 6 parts by weight and optimally from about 3 to about 5 parts by weight.
The present synthetic apatite composition can optionally include a binder agent to assist processing of the calcium phosphate into pellet form. Examples of such processing aid binders include calcium-lignosulfonate, cellulose, and the like. The binder comprises from 0 to 70 about 10 percent by weight or more of the synthetic apatite.
The present synthetic apatite composition is the precipitated product of a water soluble calcium compound and a water soluble phosphate mixture comprising a water soluble phosphate compound and one or more water soluble agronutrients. The resulting product has nutrient elements incorporated into the structure of the calcium phosphate matrix.
The second component of the present synthetic soil is a cationic exchange medium saturated with a charge of exchange rations of one or more agronutrients. Suitable cationic exchange media have a ration exchange capacity (CEC) greater than about 50 cmolclkg. Cationic exchange media preferably have a CEC of at least about 100 cmolclkg, but more preferably at least about 150 cmolclkg. In addition, suitable cationic exchange media are substantially chemically inert, have low solubility in water and are essentially free of elements toxic to plant growth.
A most preferred class of suitable cationic exchange media are mineral zeolites. Zeolites as mentioned previously are hydrated aluminosilicates of alkali and alkaline-earth rations that possess infinite, three-dimensional crystal tetrahedral structures. ~ Natural zeolites are a common mineral matter widely found in a relatively pure state.
Synthetic zeolites have also been manufactured. Zeolites generally have a theoretical CEC of from about 200 cmolc/kg to about 600 cmolclkg or more for some synthetically produced varieties. ' Representative examples of common natural zeolites include clinoptilolite (Na3,K3){AIgSi30072}~24H20, chabazite (Na2,Ca)6{AI12Si24072}~40H20, mordentite Nag{AIgSi300g6}~24H20, phillipsite (Na,K)5{AI5Si11032}~20H20, and the like.

Representative examples of synthetic zeolites include Linde Type - A Nag6{AIg6Sigg0384}~216H20, Linde Type X
Na86{AI86Si106~384}~2~H20, and the like.
Due to desirable sand-like mechanical properties, a high degree of internal tunneling for favorable nutrient retention capacity and relative abundance in nature, a most preferred natural zeolite is clinoptilolite which is widely found in a relatively pure state. Clinoptilolite has been found to have good drainage and water holding characteristics, and a high theoretical ration exchange capacity of about 200 cmolclkg.
Clinoptilolite also has a high affinity for NH4+ and the ability to hold the ion internally away from nitrifying bacteria. Hence nitrification rates are slow and the amount of leached N is low. Clinoptilolite is commercially available as sand-sized particles.
While zeolites are preferred cationic exchange media, other types can be used. Examples of other natural mineral exchange media are phyllosilicate clays such as vermiculite and smectite. Ion exchange resins can also be used though more expensive. For convenience of illustration, the cationic exchange medium will be referred to hereinbelow as the preferred but non-limiting zeolite embodiment.
The zeolite in the present synthetic soil is wholly or partially saturated with a charge of exchange rations of one or more agronomic nutrients so that existing native rations such as Na~ are replaced with the desired agronutrient rations. Applicable agronutrients which can be charged on the zeolite generally include potassium, ammonium, manganese(II), zinc, iron(II), copper(II), calcium and magnesium.
Selectivity (i. e. retention capacity) of exchange rations can vary depending on the type and variety of the ration exchange medium in question. However, as a rule of thumb, the adsorption selectivity in clinoptilolite favors monovalent exchange rations over divalent rations and among these, ion selectivity generally decreases with increasing ion hydration radius. For a clinoptilolite sample mined in the Wyoming region, selectivity for agronutrients and sodium was determined as follows: potassium > ammonium » sodium > manganese(II) -copper(II) = iron(II) > zinc > calcium > magnesium.
In the practice of the prESent invention, the zeolite is preferably saturated with ammonium and potassium rations (totally replacing native rations) at a weight ratio of from about 1 to about 5:1 of ammonium:potassium. As used herein, agronomic nutrients saturated - 2~.45~59 .

on the zeolite will be referred to by the preferred but non-limiting potassium and ammonium embodiment.
The present soil comprises from about 5 to about 100 parts of the synthetic apatite per 100 parts by weight of the K+, NH4+ saturated 5 zeolite.
A third optional but preferred component of the present soil composition is a pH buffer to maintain a soil pH in the range of from about 5.5 to about 7. Examples of suitable pH buffers include weak acids (e. g., humic acid). The pH buffer is used at from about 0 to about 10 10 parts per 100 parts by weight of the K+, NH4+ saturated zeolite.
The synthetic apatite is conveniently made, for example, by preparing two or more aqueous stock solutions containing the appropriate compounds and mixing the stock solutions together. An inorganic replacement reaction occurs in the solution mixture to produce a precipitate. The precipitate can be recovered, e. g. by filtration, and dried.
A first stock solution is made by dissolving a suitable quantity of the water soluble calcium compound in a neutral or basic aqueous medium. Examples of suitable calcium compounds include calcium nitrate, calcium nitrite, calcium chloride, calcium chlorate, hydrates thereof, and the like. Calcium nitrate tetrahydrate is a preferred compound. The first solution preferably includes the calcium compound in an amount of from about 1.0 to about 1.6 moles per liter.
A second stock solution is prepared by dissolving a suitable quantity of the soluble phosphate compound and suitable quantities of the soluble anionic nutrient compounds) in a neutral or basic aqueous medium. Examples of suitable soluble phosphate compounds include ammonium orthophosphate-mono-H, ammonium orthophosphate-di-H, ammonium orthophosphate, ammonium hypophosphate and the like.
The second solution preferably includes the phosphate compound in an amount of from about 0.5 to about 0.8 moles per liter. The amount of anionic nutrient compounds) in the second solution will depend on the desired concentration in the synthetic apatite end product which, in tum, ' will depend on the agronomic application. Generally, the second stock solution can include one or more anionic nutrient compounds each in an amount of from about 0.002 to about 0.4 moles per liter.
A third stock solution is prepared, where appropriate, by dissolving a suitable quantity of the soluble cationic nutrient z~~~3~s compounds) in a neutral or basic aqueous medium. The quantity of the cationic nutrient compounds) in the third solution will again depend on the desired concentration in the synthetic apatite end product which, in tum, will depend on the agronomic application. Generally, the third solution includes one or more cationic nutrient compounds, each in an amount of from about 0.05 to about 5 moles per liter.
The optional silicon andlor carbonate solubility control agent can be added to the second (anionic) stock solution in an amount of from about 0.002 to about 0.4 moles per liter.
When preparing the above stock solutions, it is desirable to avoid mixing salts together which can undergo unwanted inorganic replacement reactions in the stock solutions. Therefore, ionic compounds having a desired component element in the anion are held in solution separately from ionic compounds having a desired component element in the ration. Liquid organic compounds (e. g. ethyl orthosilicate), however, can be added to any of the stock solutions or added separately before or after the stock solutions are mixed together.
A preferred basic aqueous medium comprises a solution of from about 18 to about 30 percent by weight of ammonium hydroxide in deionized water. A preferred neutral aqueous medium comprises deionized water.
Typically, the third stock solution is mixed with the second stock solution and the combined solution is then mixed with the first stock solution. The resulting mixture is then maintained at ordinary temperature and pressure for a sufficient time period for the crystalline precipitate to form.
The precipitate is recovered by ordinary means, such as, for example, by decanting the supernatant and filtering in a Buchner funnel.
The precipitate is preferably washed with deionized water.
The washed precipitate can be dried at room temperature.
Preferably, however the precipitate is dried at a temperature ranging from about 200°C to about 600°C for a time period of from about 2 to ' about 20 hours in drying equipment such as an oven, wherein the temperature is preferably boosted in steps of 200°C after 2 hour intervals. The drying procedure can simultaneously dry the precipitate and dehydrate or partially dehydrate the calcium phosphate endproduct.
Solubility is also partially dependent on the degree of hydration of the calcium phosphate crystals, i. e., crystal size and degree of crystallinity.

2I4G3~ 9 WO 94/08896 ~ PGT/US93/09906 Since solubility is reduced by dehydration, the drying procedure specified can be used to adjust the solubility of the final product. The actual drying procedure used is not particularly critical so long as care is exercised in obtaining the desired degree of dehydration. The dried precipitate is preferably cooled in a low humidity environment.
The precipitate can be crushed, granulated or pelletized by conventional means to produce a suitable particle size for use in soil treatment. Binding agents can be used to assist the formation of a relatively consistent granulation particle size and avoid the production of fines. Preferably, non-reactive binders are used.
As indicated above, the type of nutrient elements incorporated into the calcium phosphate crystal structure can vary from a single nutrient element to all seven micronutrients as well as potassium, sulfur and magnesium. The quantity of each nutrient element incorporated can be specified based on the agronomic factors involved.
Prior to use, native rations of the zeolite exchange medium are replaced with rations of agronutrients, preferably NH4+, K+ as mentioned above. Various methods can be employed. Generally, zeolite particles having a size from about 50 mm to about 1000 mm are preferably divided into individual portions for each agronutrient used.
Each portion is then preferably individually charged with the desired agronutrient until saturation. The agronutrient charge is conveniently provided by a sufFiciently concentrated (e. g., 1 M) aqueous solution of an ionic compound such as a chloride, nitrate, sulfate, and the like of the agronutrient. Typically, the zeolite and nutrient solution are contacted at a suitable weight ratio, such as, for example, from about 1:2 to about 1:5 zeolite:nutrient solution. To ensure that the exchange sites of the zeolite are saturated with the agronutrient, the mixture is preferably agitated in a suitable vessel for a period of time such as 24 hours, the solution is decanted, and the zeolite is washed an additional two times with the appropriate solution. Afterward, the supernatant is decanted and the zeolite is washed with deionized water to remove excess nutrient solution. The wash supernatant can be tested with an indicator compound to determine the presence of excess solution in the zeolite.
Silver nitrate, for example, is a good indicator for chloride ions.
After each portion of the zeolite is saturated with the desired agronutrient charge and excess solution is removed, the saturated zeolites are dried in an oven, for example, at a temperature on the order . 2146359 of 105°C for a time period on the order of 24 hours. Once dried, the synthetic apatite and various saturated zeolite components can be dry blended in suitable equipment at a desired ratio.

When the instant synthetic soil comes in contact with moisture, ' 5 nutrient elements become mobilized as the apatite is dissolved.
As a first step, nutrients dispersed in the apatite matrix (magnesium, sulfur and micronutrients in addition to phosphorus and calcium) are slowly released as dissolution proceeds. Calcium ion production is adsorbed by the zeolite which acts as a Ca2+ sink. Removal of Ca2+
from the solution phase shifts the equilibrium towards increased apatite dissolution and phosphate fertilization in the soil. Adsorbed calcium ions compete with the K+ and NH4+ ion charge at zeolite exchange sites causing the release of K+ and NH4+ into the soil. The pH buffer maintains a mildly acidic soil pH to further assist the rate of apatite dissolution and nutrient release.

Desired apatite solubility and nutrient release rate are usually determined empirically based on type of plant being grown, growth cycle requirements, and the like agronomic factors.

The present fertilizing soil can be used in conventional agronomic applications by direct addition by conventional means to a suitably prepared field but is preferably used in horticultural applications such as zeoponics and hydroponics.

The present synthetic soil has potential for lunar applications since zeolite synthesis from minerals found on the moon is thought to be feasible. Furthermore, plant-essential elements occur in trace quantities in lunar rock and can be extracted.

To conduct a zeoponics culture, for example, a suitable greenhouse or culture environment has the present synthetic soil and fertilizer appropriately blended and spread to a sufficient depth to support the root structure of seedlings planted therein.
The soil is kept moist to fertilize the plants.

The present invention is further illustrated by the following examples:

Examples 1-3 Three synthetic apatite compositions having nutrient elements incorporated into the crystalline structure were synthesized by an inorganic replacement reaction to simulate a naturally occurring ~~~fi3~9 hydroxyapatite mineral. Initially, three stock solutions (A, B and C) were prepared using laboratory reagent grade chemicals. Each reaction was run using 500 ml of stock solutions A and B and 20 ml of stock solution C. The composition of the solutions is shown in Table 2.
Table 2 Compound Concmtratim (grams) Ex le 1 Exa (e Ex le 3 Solution A (0.5 liters 20 rrt X
NH OH in deionized water) Calcium nitrate 141.52 141.52 141.52 tetrahydrate (Ce(N ) '4H 0) Solution B (0.5 Liters 20 xt X
NH OH in deionized water) Ammonium orthophosphate-43.32 43.32 43.32 mono-N

((NH ) HPO ) Mmbnium carbonate 11.93 11.93 ((NH ) ) Ammonium chloride 1.011 1.011 1.011 ((NH )Cl) Orthoboric acid 0.779 0.779 0.779 (H BO ) Amaonium paramolybdate0.00098 0.00098 0.00098 ((NH ) N '4H 0) Ammonium sulfate 2.4974 2.4974 2.4974 NH ) SO ) Solution C (20 ml deionized water) Nagneaium nitrate 13.499 3.374 12.972 (Ng(Jl ) ) Iron(IL) nitrate 3.627 3.627 3.627 hexahydrate (Fe(N ) '6H 0) lianganese(11) sulfate0.5408 0.5408 0.5408 monohydrate (llnSO ' H 0 ) Zinc nitrate 0.5652 0.5652 0.5652 (zn(N ) ) Copper(II) nitrate 0.1464 0.1464 0.1464 2.5hydrate (Cu(N ) )'2.5H 0) Other additive (ml) Ethyl orthosilicate- S -After stock solutions A, B and C were prepared, solution C was quickly added to solution B and vigorously mixed for several seconds.
This combined solution (B and C) was then added to solution A. In Example 2, the ethyl orthosilicate liquid was also added to solution A
concurrently with solutions B and C. In all the examples the final mixture was vigorously stirred for 5 minutes and then allowed to stand for 18 hours to precipitate the calcium phosphate product. The clear supernatant was decanted and disposed of. The precipitate was washed 4 times with 3 liters of deionized water each washing. The precipitate was filtered using a Biichner funnel and Whatman #41 filter ' S paper, and washed again with an additional 500 ml of deionized water.
The precipitate was removed from the filter paper and placed into a ' glass beaker for drying. The precipitate was dried in an oven at 200°C
for 17 hours, lightly crushed in an agate mortar and stored in a desiccator.
10 The three synthetic materials were characterized by powder x-ray diffraction and by electron microprobe analysis. The Figure shows diffractographs of the compositions. The peaks (d-spacing) correspond to peaks for natural hydroxyapatites. Peak width was narrow suggesting that individual crystals have a width of from about 200-500 angstroms.
15 The chemical analysis of the composition is shown in Table 3.
Table 3 Cortponent Frectton (X) Ex le Exa le Ex le 3 Ua 0 0 0 0 S 0.439 0.139 2.584 Ca0 46.165 47.789 45.211 P 33.461 35.205 36.116 Fe 1.001 1.217 1.175 M 2.839 0.700 2.562 S1 - 0.9838 OH 3.163 3.265 3.401 C 6.T 5.7 -Nn 2028 2468 2635 Cu 38 75 T9 Cl 350 140 100 2n 303 849 587 ..-1237 ppm 768 pp" 716 ~, - ~

Examples 4-12 In the following examples, the apatite compositions prepared in Examples 1-3 were contacted with deionized water to determine the equilibrium ion concentration after dissolution. At the end of each run, pH and the ion concentrations of the various elements were measured.
Concentrations of manganese, iron, copper and zinc ions were determined using DTPA chelating agent (pH=7.3). The procedure _21~~3~9 ~v .

consisted of placing a 0.5 g sample of the synthetic apatite composition in a covered glass bottle containing 80 ml of deionized water. The bottles and samples were placed in an environmentally controlled reciprocal shaker at a setting of 100 rpm and shaken for 96 hours. The temperature was held at 25°C. Results are given in Table 4.
Table 4 Ex. Sale pH Element No. Concrntration mg/l mg/kg ~/l P Ca Ng S Mn* Fe* Cu' 2ntB Mo Cl 4 1 8.701.3313.629.85.6 121 244 6 31 4.4 <0.020.6 5 1 8.701.3013.638.86.0 118 249 b 29 4.4 <0.021.7 6 1 8.701.3013.539.65.8 118 250 6 29 4.3 <0.021.1 7 2 8.130.1715.23.682.4 152 250 7 5b 1.9 <0.022.3 8 2 8.160.2214.83.272.7 163 302 7 59 1.9 <0.02t.b 9 2 8.160.1T14.13.222.3 152 246 7 5b 1.9 <0.023.1 3 7.002.9510.32.6717.8 160 402 10 57 0.8 <0.020.4 11 3 6.953.8010.32.T5t7.6 158 40b 10 55 0.8 <0.020.4 12 3 7.123.4510.02.7117.6 158 408 10 55 0.8 <0.020.5 * DTPA extractable, pH=7.3.
Example 40 In the following examples, the apatite compositions 10 prepared in Examples 1-3 were contacted with an aqueous medium wherein the pH was varied between 5 and 7 to determine the equilibrium ion concentration after dissolution. The procedure was similar to Examples 4-12 except that a 0.5 M sodium acetate solutions buffered with acetic acid to the desired pH were used instead of deionized water. Results are given in Table 5. As expected, the synthetic apatite dissolved to a greater extent in a more acidic medium.

214G3~9 Table 5 Ex. Sample pH Element Ho. Concentration Ca Ng 13 1 8.00 116.1 51.8 14 1 8.06 99.8 48.0 15 1 8.11 98.5 46.6 16 1 6.30 314.7 70.0 17 1 6.31 310.5 66.0 18 1 6.31 310.5 66.0 19 1 5.08 1216 82.8 20 1 5.08 1384 82.6 21 1 5.08 1244 84.6 22 2 7.91 74.0 9.2 23 2 7.92 73.7 9.0 24 2 7.92 73.4 9.1 25 2 6.25 287.0 15.7 2b 2 6.25 282.8 15.4 27 2 6.25 287.0 15.8 28 2 5.07 1098 20.7 29 2 5.07 1056 20.5 30 2 5.07 1098 20.6 31 3 7.56 37.2 36.3 32 3 7.56 38.5 35.6 33 3 7.55 37.9 37.9 34 3 6.15 189.5 53.8 35 3 6.15 187.9 54.0 36 3 6.15 191.1 54.2 37 3 5.05 988 77.4 38 3 5.05 975 74.0 39 3 5.05 975 74.6

Claims (50)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for preparing a slow-release synthetic apatite fertilizer, comprising the steps of:
(1) preparing an aqueous calcium solution from a soluble ionic calcium compound;
(2) preparing an aqueous phosphate solution from a soluble ionic phosphate compound, optionally with an anionic agronutrient selected from sulfate, chloride, molybdate, borate, and combinations thereof, from a soluble ionic compound containing the anionic agronutrient;
(3) optionally preparing an aqueous solution of cationic agronutrients selected from potassium, magnesium, zinc, iron, manganese, copper, and combinations thereof, from a soluble ionic compound containing the cationic agronutrient;
(4) mixing the calcium solution, phosphate solution and any cationic agronutrient solution together and forming an apatite precipitate by inorganic replacement reaction; and (5) recovering the precipitate with a crystalline hydroxylapatite structure essentially free of agrotoxins and having at least one agronutrient structurally dispersed therein selected from sulfate, borate, molybdate, potassium, magnesium, zinc, iron, manganese, copper, or a combination thereof.

2. The method of claim 1, wherein the cationic agronutrient solution is prepared, and the mixing step comprises sequentially mixing the phosphate solution with the cationic solution and then mixing the resulting phosphate-cationic agronutrient solution with the calcium solution.

3. The method of claim 1, wherein the calcium solution comprises from about 1.0 to about 1.6 moles per liter calcium, the phosphate solution comprises from about 0.5 to about 0.8 moles per liter phosphate and from about 0.002 to about 0.4 moles per liter of sulfate, molybdate, borate, or a combination thereof, and the cationic agronutrient solution is prepared and comprises from about 0.05 to about 5 moles per liter of potassium, magnesium, zinc, iron, manganese, copper, or a combination thereof.

4. The method of claim 1, wherein the calcium solution comprises 1.0 - 1.6 molar calcium, the phosphate solution comprises 0.5 - 0.8 molar phosphate and 0.002 - 0.4 molar sulfate, molybdate, chloride and borate, and the cationic agronutrient solution is prepared and comprises 0.05 - 5 molar potassium, magnesium, zinc, iron, manganese and copper.

5. The method of claim 1, comprising dehydrating the precipitate at a temperature from about 200°C to about 600°C to control the solubility of the synthetic apatite.

6. The method of claim 1, wherein the calcium compound comprises calcium nitrate, calcium nitrite, calcium chloride, calcium chlorate or a hydrate thereof and the phosphate compound comprises ammonium orthophosphate-mono-H, ammonium orthophosphate-di-H, ammonium orthophosphate, ammonium hypophosphate, hydrazine orthophosphate or hydrazine hypophosphate.

7. The method of claim 1, wherein the cationic agronutrient solution is prepared; the magnesium compound is selected from magnesium nitrate, magnesium chloride, magnesium nitrite, magnesium chlorate, magnesium perchlorate and hydrates thereof; the sulfate compound is selected from sodium sulfate, ammonium sulfate, potassium sulfate, ammonium bisulfate, ammonium sulfite, ammonium bisulfate and hydrates thereof; the zinc compound is selected from zinc chloride, zinc nitrate, zinc nitrite, zinc sulfate and hydrates thereof; the chloride compound is selected from sodium chloride, potassium chloride, ammonium chloride, ammonium chlorate and ammonium perchlorate; the iron compound is selected from ferric nitrate, ferrous nitrate, ferrous nitrite, ferric nitrite, ferric chloride, ferrous chloride, ferric sulfate, ferrous sulfate and hydrates thereof; the manganese compound is selected from potassium permanganate, potassium manganate, manganese(II) nitrate, manganese(II) nitrite, manganese dichloride, manganese(II) sulfate and hydrates thereof; the copper compound is selected from copper(II) chloride, copper(III) chloride, copper(II) nitrate, copper(II) nitrite and hydrates thereof; the molybdate compound is selected from ammonium paramolybdate, ammonium permolybdate, sodium trimolybdate, sodium tetramolybdate, sodium paramolybdate, sodium octamolybdate, potassium molybdate and hydrates thereof; and the borate compound is selected from sodium tetraborate, sodium metaborate, potassium tetraborate, potassium metaborate, ammonium tetraborate, ammonium peroxyborate, hydrates thereof and orthoboric acid.

8. The method of claim 1, wherein the mixing step includes mixing the said solutions together with a solution of at least one water soluble solubility control agent selected from silicon and carbonate:

9. The method of claim 8, wherein the carbonate compound is selected from sodium carbonate, sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, potassium carbonate and potassium bicarbonate; or the silicon compound is selected from sodium silicate, sodium disilicate, sodium metasilicate, sodium orthosilicate, potassium disilicate, potassium metasilicate, potassium hydrogen disilicate, ammonium silicate, hydrates thereof and ethyl orthosilicate.

10. A slow-release fertilizer, comprising:
one or more agronutrients structurally dispersed in a crystalline matrix of hydroxylapatite essentially free of agrotoxins and prepared by the method of any of claims 1-9.

11. The fertilizer of claim 10, comprising per 100 parts calcium by weight:
from about 30 parts to about 50 parts phosphorous ;
magnesium up to 5 parts;
sulfur up to 4 parts;
zinc up to 0.4 parts;
chlorine up to 1.25 parts;
iron up to 4 parts;
manganese up to 1.2 parts;
copper up to 0.12 parts;
molybdenum up to 0.0025 parts; and boron up to 0.05 parts.

12. The fertilizer of claim 10, comprising per 100 parts calcium by weight:
40 - 45 parts phosphorous;
1 - 4 parts potassium;
2 - 5 parts magnesium;
2 - 4 parts sulfur;
0.2 - 0.4 parts zinc;
0.5 - 1.25 parts chlorine;
1 - 4 parts iron;

0.5 - 1.2 parts manganese;
0.05 - 0.12 parts copper;
0.001 - 0.002 parts molybdenum; and 0.01 - 0.04 parts boron.

13. The fertilizer of claim 10, comprising per 100 parts calcium by weight:
40 - 42 parts phosphorous;
2 - 3 parts potassium;
3 - 4 parts magnesium;
2.5 - 3.5 parts sulfur;
0.08 - 0.3 parts zinc;
1.0 - 1.13 parts chlorine;
2 - 3 parts iron;
0.5 - 1 parts manganese;
0.08 - 0.1 parts copper;
0.001 - 0.0015 parts molybdenum; and 0.02 - 0.03 parts boron.

14. The fertilizer of claim 10, comprising from about 2 to about 10 parts silicon agent per 100 parts calcium.

15. The fertilizer of claim 10, comprising from about 2 to about 15 parts carbonate agent per 100 parts calcium.

16. The fertilizer of claim 10, comprising not more than 10 parts fluorine per parts calcium by weight.

17. The fertilizer of claim 10, comprising not more than 3000 ppm fluorine.

18. An agronutrient-substituted hydroxylapatite of generally uniform composition having the formula:
(Ca5-xm/2 M x)((PO4)3-yq/3 Q y)OH)1-z X z) wherein M is a cation containing an element selected from potassium, zinc, iron, manganese, magnesium, or copper, or a combination thereof;
wherein m is the molar average valence of M according to the equation m =
(.SIGMA.m i x i)/(.SIGMA.x i) where each m i is the valence of an ith cation comprising M
and x i is the relative molar proportion of the ith cation;
wherein Q is an anion of carbonate, silicate or containing an element selected from boron, molybdenum, or sulfur, or a combination thereof;

wherein q is the molar average valence of Q according to the equation q =
(.SIGMA.q i y i)/(.SIGMA.y i) where each q i is the valence of an ith anion comprising Q
and y i is the relative molar proportion of the ith anion;
wherein X is chloride, fluoride or a combination thereof; and wherein x has a value of 0 - 0.82, y has a value of 0 - 0.76, and z has a value of 0 - 0.15, provided that at least one of x and y are greater than zero and the amount of fluoride does not exceed 3000 ppm by weight, and when x is zero Q includes an anion of boron, molybdenum, or sulfur, or a combination thereof.

19. The hydroxylapatite of claim 18, wherein M x has the formula:
K xK Mg x Mg Fe x Fe Zn x Zn Mn x Mn Cu x Cu wherein: x K <= 0.205;
x Mg <= 0.412;
x Fe <= 0.144;
x Zn <= 0.0123;
x Mn <= 0.044;
x Cu <= 0.0038;
x = x K + x Mg + x Fe + x Zn + x Mn + x Cu; and x > 0.

20. The hydroxylapatite of claim 19, wherein:
0.051 <= x K <= 0.205;
0.165 <= x Mg <= 0.412;
0.0359 <= x Fe <= 0.144;
0.006 <= x Zn <= 0.0123;
0.018 <= x Mn <= 0.044; and 0.0016 <= x Cu <= 0.0038.

21. The hydroxylapatite of claim 19, wherein:
0.102 <= x K <= 0.154;
0.247 <= x Mg <= 0.33;
0.072 <= x Fe <= 0.108;
0.0061 <= x Zn <= 0.0092;
0.018 <= x Mn <= 0.036; and 0.0025 <= x Cu <= 0.0032.

22. The hydroxylapatite of claim 18, wherein Q y has the formula:
(CO3)yC(SiO4)ySi(MoO4)yMo (BO3)yB (SO4)yS

wherein y C has a value up to 0.5, y Si has a value up to 0.218, y Mo has a value up to 0.000052, y B has a value up to 0.0093, and y S has a value up to 0.25; and wherein y = y C + Y Si + y Mo + y B + y S, and (y Mo + y B + y S) > 0.

23. The hydroxylapatite of claim 22, wherein:
0.00002 <= y Mo <= 0.000042;
0.00185 <= y B <= 0.00741; and 0.125 <= y S <= 0.25.

24. The hydroxylapatite of claim 22, wherein:
0.000021 <= y Mo <= 0.0000313;
0.0037 <= y B <= 0.0056; and 0.156 <= y S <= 0.219.

25. The hydroxylapatite of claim 23, wherein:
0.0668 <= y C <= 0.334; or 0.0435 <= y Si <= 0.131.

26. The hydroxylapatite of claim 24, wherein:
0.134 <= y C <= 0.2; or 0.0653 <= y Si <= 0.109.

27. The hydroxylapatite of claim 18, wherein X Z has the formula:

Cl z Cl F zF

wherein z Cl has a value up to 0.071, zF has a value less than about 0.08, and z = z Cl + z F.

28. The hydroxylapatite of claim 27, wherein:
0.0283 <= z Cl <= 0.071; and zF <= 0.008.

29. The hydroxylapatite of claim 27, wherein 0.0565 <= z Cl <= 0.064; and z F <= 0.00008.

30. An agronutrient-substituted hydroxylapatite of the formula:
[Ca5-xm/2K xK Mg xMg Fe xFe Zn xZn Mn xMn Cu xCu][(PO4)3-yq/3 (CO3)yC(S i O4)ySi(MoO4)yMo (BO3)yB (SO4)yS][(OH)1-z Cl zCI F zF]
wherein m is the molar average valence of the potassium, magnesium, iron, zinc, manganese and copper cations according to the equation:
m=(x K+2x Mg+2x Fe+2x Zn+2x Mn+2x Cu)/x wherein q is the molar average valence of the anions CO3, SiO4, MoO4, BO3 and SO4 according to the equation:

q = (2y C + 4y Si +2y Mo + 3y B + 2y S)/y wherein x = x K + x Mg + x Fe + x Zn + x Mn + x Cu, y = y C + y Si + y Mo + y B + y S. z = z Cl + z F, and at least one of x, y Mo, y B and y S is greater than zero; and wherein: x K <= 0.21;
x Mg <= 0.41;
x Fe <= 0.14;
x Zn <= 0.012;
x Mn <= 0.044;
x Cu <= 0.0038;
y C <= 0.5;
y Si <= 0.218;
y Mo <= 0.000052;
y B <= 0.0093;
y S <= 0.25;
z Cl <= 0.071; and z F <= 0.08.

31. The hydroxylapatite of claim 30, wherein:
0.051 <= x K <= 0.205;
0.165 <= x Mg <= 0.412;
0.0359 <= x Fe <= 0.144;
0.006 <= x Zn <= 0.0123;
0.018 <= x Mn <= 0.044;
0.0016 <= x Cu <= 0.0038;
0.00002 <= y Mo <= 0.000042;
0.00185 <= y B <= 0.00741;
0.125 <= y S <= 0.25;
0.0283 <= z Cl <= 0.071; and z F <= 0.008.

32. The hydroxylapatite of claim 30, wherein:
0.102 <= x K <= 0.154;
0.247 <= x Mg <= 0.33;
0.072 <= x Fe <= 0.108;
0.006 <= x Zn <= 0.009;
0.018 <= x Mn <= 0.036;
0.0025 <= x Cu <= 0.0032;
0.000021 <= y Mo <= 0.0000313;
0.0037 <= y B <= 0.0056;

0.157 <= y S <= 0.219;
0.0565 <= z Cl <= 0.064; and z F <= 0.00008.

33. The hydroxylapatite of claim 31, wherein:
0.0668 <= y C <= 0.334; or 0.0435 <= y Si <= 0.131.

34. The hydroxylapatite of claim 32, wherein:
0.134 <= y C <= 0.2; or 0.0653 <= y Si <= 0.109.

35. The method of any of claims 1-9, further comprising the steps of:
(6) exchanging ammonium and potassium rations onto a cationic exchange medium; and (7) blending from about 5 to about 100 parts by weight of the precipitate from step (5) with 100 parts by weight of the cationic exchange medium from step (6).

36. A fertilizer, comprising:
an admixture of agronutrient-substituted hydroxylapatite and cationic exchange medium obtained as the product from the blending step of claim 35.

37. The fertilizer of claim 36, further comprising a pH buffer.

38. The fertilizer of claim 36, wherein the cationic exchange medium comprises natural or synthetic zeolite, phyllosilicate or a combination thereof.

39. The fertilizer of claim 36, wherein the cationic exchange medium is selected from clinoptilolite, chabazite, mordenite, phillipsite, Linde type A, Linde type X, vermiculite, smectite or a combination thereof.

40. The fertilizer of claim 36, wherein said cationic exchange medium has a ration exchange capacity of at least 50 cmol c/kg.

41. The fertilizer of claim 36, wherein said cationic exchange medium has a ration exchange capacity of at least 100 cmol c/kg.

42. The fertilizer of claim 36, wherein said cationic exchange medium has a ration exchange capacity of at least 150 cmol c/kg.

43. The fertilizer of claim 36, wherein the agronutrients in the ration exchange medium comprise ammonium and potassium at a weight ratio of from about 1 to about 5:1 of ammonium:potassium.

44. The fertilizer of claim 37, wherein said buffer maintains a soil pH of from about 5.5 to about 7.

45. The fertilizer of claim 37, comprising from 0 to about 10 parts by weight of a pH buffer per 100 parts by weight of the ammonium and potassium charged zeolite.

46. An active synthetic soil, comprising in admixture:
the agronutrient-substituted hydroxylapatite of any of claims 18-34; and .
a cationic exchange medium saturated with a charge of ammonium and potassium at a weight ratio of ammonium:potassium of from about 1:1 to about 5:1.

47, The method of any one of claims 1-9, further comprising the steps of:
(6) placing a fertilizing amount of the precipitate from step (5) adjacent a plant root system; and (7) contacting the precipitate from step (6) with moisture to release the agronutrients.

48. The method of claim 35, further comprising the steps of:
(8) placing a fertilizing amount of the blend from set (7) adjacent a plant root system; and (9) contacting the blend from step (8) with moisture to release the agronutrients.

49. The method of any one of claims 1-9, further comprising the steps of:
(6) circulating a hydroponics solution through a bed of the precipitate from step (5) to replenish the concentration of agronutrients in the hydroponics solution; and (7) contacting a root structure of a plant with the hydroponics solution.

50. The method of claim 35, further comprising the steps of:
(8) circulating a hydroponics solution through a bed of the blend from step (7) to replenish the concentration of agronutrients in the hydroponics solution; and (9) contacting a root structure of a plant with the hydroponics solution from step (8).