TECHNICAL FIELD
The present disclosure relates to sustained release fertilizers. More particularly, the present invention relates to a sustained release fertilizer comprising poly-phosphate linked with nitrogen and other nutrient(s). BACKGROUND OF THE DISCLOSURE
Fertilizers are mainly used was to provide nutrients to plants and to increase or sustain optimal crop yield. It is known that water-soluble phosphate can be converted to water insoluble phosphate after reaction with soil minerals, which can result in a decrease of phosphate availability. The forms of reaction products depend on phosphorous (P) sources and soil minerals. In general, Fe-Al-P minerals form in acidic soils containing Fe-Al-oxide minerals, whereas Ca-P minerals form in alkaline or calcareous soils. The phosphorous reaction process involves surface adsorption and/or precipitation. Research has been focused on modifying the physical characteristics of conventional water-soluble fertilizers to reduce phosphate fixation by soil, and thereby increase the phosphate efficiency for plant uptake.
Nitrogen use efficiency is usually low. Nitrogen derived firom fertilizers not taken up by plants may be lack of efficient nitrogen fixing bacteria or may be lost to the environment. In this case, it has the potential to become a pollutant of ground or surface waters or to contribute to the greenhouse effect. Thus, improving fertilizer use efficiency in terms of nutrient uptake and crop yield is important to fertilizer producers and users. Particularly, in case of macronutrients such as nitrogen and phosphate fertilizer, loss of applied fertilizers is already reported. DAP is used as a fertilizer. When applied as plant food, it temporarily increases the soil pH, but over a long term the treated ground becomes more acidic than before upon nitrification of the ammonium. It is incompatible with alkaline chemicals because its ammonium ion is more likely to convert to ammonia in a high-pH environment whereas urea is breakdown by soil harboring microbes by the process of denitrification and ammonification, releases much of the nitrogen present in the form gases which are unavailable to the plants.
Efforts to develop a sustained release fertilizer for nitrogen, phosphate and micronutrients, have been complicated by the formation of insoluble complexes of

micronutrient in the presence of phosphate fertilizer, and hence not immediately available for plants.
Thus, there is still a need in the art to develop a sustained release fertilizer that employs nitrogen and phosphate. SUMMARY OF THE DISCLOSURE
Accordingly, provided herein is a sustained release fertilizer comprising poly-phosphate linked with nitrogen and other nutrient(s); wherein the fertilizer is characterized by a structure of formula (I) and formula (II):

wherein,
Ri and R2 independently represents divalent or trivalent cation selected from the metal of group II, group III and group VIII of periodic table.
In another aspect, the present disclosure provides a water-soluble sustained release fertilizer to improve plant nutrient delivery.
In yet another aspect, the present disclosure provides a fertilizer having about neutral pH.
In yet another aspect, the present disclosure provides a process preparing the sustained release fertilizer; wherein the process comprises:
(a) solubilizing nutrient source in polyphosphoric acid to get a Solution;
(b) adding to the Solution of Step (a) a nitrogen containing macronutrient source; and
(c) neutralizing the reaction mixture of Step (b) to a pH of about 7 by adding ammonia to get a mixture containing the sustained release fertilizer.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
The features of the present disclosure will become fully apparent from the following description taken in conjunction with the accompanying figures. With the understanding that the figures depict only several embodiments in accordance with the disclosure and are not to be considered limiting of its scope, the disclosure will be described further through use of the accompanying figures:
FIG. 1 illustrates FTIR analysis of sustained release fertilizer according to one embodiment of the disclosure;
Fig 2: illustrates TGA analysis of sustained release fertilizer according to one embodiment of the disclosure;
Fig 3: illustrates nitrogen release rate profile of sustained release fertilizer according to one embodiment of the disclosure;
Fig 4: illustrates phosphate release rate profile of sustained release fertilizer according to one embodiment of the disclosure;
Fig 5: illustrates pH profile during release of nutrients of sustained release fertilizer according to one embodiment of the disclosure;
Fig 6: illustrates zinc release rate profile of sustained release fertilizer according to one embodiment of the disclosure;
Fig 7: illustrates iron release rate profile of sustained release fertilizer according to one embodiment of the disclosure; and
Fig 8: illustrates comparative release rate profile of nitrogen and phosphate of fertilizer according to one embodiment of the disclosure. DETAILED DESCRIPTION OF THE DISCLOSURE
Before the methods of the present disclosure are described in greater detail, it is to be understood that the methods are not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the methods will be limited only by the appended Claims.
Where a ränge of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit ofthat ränge and any other stated or intervening value

in that stated ränge, is encompassed within the methods. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the methods, subject to any specifically excluded limit in the stated ränge. Where the stated ränge includes one or both of the limits, ranges excluding either or both ofthose included limits are also included in the methods.
Certain ranges are presented herein with numerical values being preceded by the term "about." The term "about" is used herein to provide literal support for the exact number that it precedes, as well as a number that is near to or approximately the number that the term precedes. In determining whether a number is near to or approximately a specifically recited number, the near or approximating unrecited number may be a number which, in the context in which it is presented, provides the substantial equivalent of the specifically recited number.
Sustained release fertilizers containing poly-phosphate linked with nitrogen and other nutrient(s), demonstrate a more sustained release rate when compared to Standard nitrogen and/or phosphate fertilizers.
According an embodiment, the present disclosure provides a sustained release fertilizer comprising poly-phosphate linked with nitrogen and other nutrient(s); wherein the fertilizer is characterized by a structure of formula (I) and formula (II):

wherein,
Ri and R2 independently represents divalent or trivalent cation selected from the metal of group II, group III and group VIII of periodic table.
In yet another embodiment, the metal of group II is selected from a group comprising magnesium, calcium and a combination thereof.
In yet another embodiment, the metal of group III is selected from a group comprising boron and aluminium.
In yet another embodiment, the metal of group VIII is selected from a group comprising iron, nickel, copper, zinc and a combination thereof.
In yet another embodiment, the metal source may be from a group comprising metal oxide and micronutrient salt like metal carbonate.
The amounts of nutrients present within the sustained release fertilizer as described herein may vary as follows, where the listed amounts are weight percentages based on the weight of the fertilizer composition:

Nitrogen or nitrogen derivative (as nitrogen): about 6 wt. % - about 40
wt. %; and
phosphorus derivative (as P2O5): about 15 wt. % - about 65 wt. %.
In yet another embodiment, the fertilizer comprises nitrogen in an amount from about 10 wt. % - about 35 wt. % or about 15 wt. % - about 30 wt. % or about 15 wt. % -about 20 wt. %.
In yet another embodiment, the fertilizer comprises phosphate in an amount from about 20 wt. % - 60 wt. % or about 25 wt. % - 55 wt. % or about 35 wt. % - 55 wt. % or about 30 wt. % - 50 wt. % or about 35 wt. % - 45 wt. % or about 30 wt. % - 40 wt. %.
In yet another embodiment, the ratio of nitrogen to micronutrient is from about 1:10 to about 1:40. In certain embodiments, the ratio is about from about 1:15 to about 1:35 or from about 1:20 to about 1:30.
Depending on the process of preparation, the composition of the fertilizers may be controlled.
In certain embodiments, the fertilizer of the present disclosure may be used in a variety of ways such as soil application, seed coating, foliar spray and fertigation application.
The fertilizer of the present disclosure has about a neutral pH thereby making phosphate release at a neutral pH and preventing the possibility of crop burning.
In another embodiment, the present disclosure provides a process for preparing a sustained release fertilizer as provided herein; wherein the process comprises:
(a) solubilizing nutrient source in polyphosphoric acid to get a Solution;
(b) adding to the Solution of Step (a) a nitrogen containing macronutrient source; and
(c) neutralizing the reaction mixture of Step (b) by adding ammonia to get a mixture containing the sustained release fertilizer.
The process may further comprise separating the mixture of step (c) to get a residue and filtrate. The residue thus obtained was further dried to get the sustained release fertilizer as a solid. Further, the filtrate was concentrated to get the sustained release fertilizer as a solid.

The polyphosphoric acid used in step (a) is prepared by heating ortho-phosphoric acid at about 270°C. The nutrient source is selected from a group comprising nutrient oxide and nutrient salt. The solubilization of nutrient source in polyphosphoric acid is carried out at a predetermined temperature based on the nutrient being added. In certain embodiments, the temperature is about 5-150°C or about 20-120°C or about 110°C or about 10-25°C. The nutrient source being added may be one or more than one.
In step (b), after adding the nitrogen containing macronutrient source, the reaction mixture is stirred at a temperature of less than about 80°C until it dissolves to form a viscous liquid. The reaction was monitored by Thin Layer Chromatography (TLC). In certain embodiments, the reaction mixture is stirred at a temperature of about 50-70°C. In certain embodiments, the nitrogen containing macronutrient source may be selected from a group comprising urea, biuret, ammonia, methylurea and guanylurea. In certain embodiments, the nitrogen containing macronutrient source is urea.
The reaction mixture of step (c) is cooled to less than 30°C before adding ammonia to it. In certain embodiments, it is cooled to about 0-25°C or about 5-20°C or about 10-15°C. The neutralized reaction mixture may be further separated, according to its intended end use, to get a residue and filtrate. The obtained residue may be further dried, using methods known in the art, to get the sustained fertilizer as a solid. In certain embodiments, the residue may be dried at inert atmosphere. On the other hand, the filtrate may be concentrated, using methods known in the art, to get the sustained fertilizer as a solid. In certain embodiments, the filtrate is kept for air drying.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, preferred methods and materials are described. For the purposes of the present disclosure, the following terms are defined below.
The articles "a" and "an" are used herein to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element.

As used herein, the term "comprises" or "comprising" is generally used in the sense of include, that is to say permitting the presence of one or more features or components.
Link can include covalent bonds, ionic bonds, electrostatic bonds, Vander Waals bonds and hydrogen bonds.
As used herein, "nutrient" refers to both micronutrients and macronutrients. Non-limiting examples of nutrients include zinc, copper, manganese, boron, calcium, iron, calcium, magnesium, molybdenum, Silicon, selenium, phosphate, nitrogen, potassium and sulfur.
As used herein, "micronutrients" refer to elements required in small or trace amounts for plant growth. Non-limiting examples of micronutrients include molybdenum, nickel, copper, zinc, manganese, boron, iron and chloride.
As used herein, "macronutrients" refer to elements typically required in large amounts for plant growth. Non-limiting examples of macronutrients include sulfur, phosphorus, phosphate, magnesium, calcium, potassium, nitrogen, oxygen, carbon and hydrogen.
As used herein, "nutrient use efficiency fertilizer (NUE)" refers to the fertilizer products that can reduce nutrient loss to the environment while increasing the nutrient availability for the plant or crop.
The present disclosure is further described with reference to the following examples, which are only illustrative in nature and should not be construed to limit the scope of the present disclosure in any manner. Starting materials and reagents shown in the process can be obtained firom commercial sources or prepared based on procedures described in the literature. EXAMPLES EXAMPLE 1
2.27 moles of ortho-phosphoric acid heated at 270°C to prepare polyphosphoric acid. The temperature of the reaction mixture was reduced to 70°C. Then 0.038 moles of zinc oxide were added at a constant stirring tili a clear Solution was obtained. Further, 4 moles of urea were added to this Solution at the same temperature and continued stirring for 2 h. The reaction was monitored by TLC. The resultant mixture was cooled to 10-15°C and

neutralized with about 30% liquor ammonia with constant stirring in such a way that the temperature of the reaction mixture is not more than 30°C. Then the reaction mixture was filtered under vacuum at room temperature to obtain a residue (Product I) and filtrate (Product II) containing the Compounds of formula (I) and (II). The residue was further dried in a hot air oven at 50°C. The filtrate was concentrated under reduced pressure and kept for air drying to obtain solid. The compositional analysis of Product I and II were depicted in table 1 below.
EXAMPLE 2
To the polyphosphate as prepared in example 1, 0.5 moles of ferne oxide and 2 moles of ZnO were added at constant stirring and heated at 110°C tili a clear Solution was obtained. The temperature of the reaction mixture was reduced to 70°C and urea (4 moles) was added to this Solution at the same temperature and continued stirring for 2 h. The reaction was monitored by TLC. The resultant mixture was cooled to 10-15°C and neutralized with about 30% liquor ammonia with constant stirring in such a way that the temperature of the reaction mixture is not more than 30°C. The reaction mass was filtered under reduced pressure to obtain the residue (Product III) and filtrate (Product IV) containing the Compounds of formula (I) and (II). The residue was further dried at inert atmosphere and filtrate was concentrated and kept for air drying to obtain solid. The compositional analysis of Product III and IV were depicted in table 2 below.

EXAMPLE 3
To the polyphosphate as prepared in example 1, 0.5 moles of ferric oxide at constant stirring was added and heated at 110°C tili a clear Solution was obtained. The temperature of the reaction mixture was reduced to 70°C and urea (4 moles) was added and continued stirring for 2 h. The reaction was monitored by TLC. The resultant mixture was cooled to 10-15°C and neutralized with about 30% liquor ammonia with constant stirring in such a way that the temperature of the reaction mixture is not more than 30°C. The reaction mass was filtered under reduced pressure to obtain a residue (Product V) and filtrate (Product VI) containing the Compounds of formula (I) and (II). The residue was further dried at inert atmosphere and filtrate was concentrated and kept for air drying to obtain solid. The compositional analysis of Product V and VI were depicted in table 3 below.

To the polyphosphate as prepared in example 1 were added 2 moles of zinc oxide and 0.3 moles of calcium oxide at constant stirring and heated at 110°C tili a clear Solution was obtained. The temperature of the reaction mixture was reduced to 70°C and urea (4 moles) was added to this Solution at the same temperature and continued stirring for 2 h. The reaction was monitored by TLC. The resultant mixture was cooled to 10-15°C and neutralized with about 30% liquor ammonia with constant stirring in such a way that the temperature of the reaction mixture is not more than 30°C. The reaction mass was filtered under reduced pressure to obtain the residue (Product VII). The residue was further dried at inert atmosphere. The compositional analysis of Product VII was depicted in table 4 below.
Characterization of products I - VII having a general structure of formula (I) or (II) Product I:
As seen from Fig. 1A, absorption band at 3198 cm"1 corresponds to O-H stretching Vibration of Product I, peaks observed at 1206 cm"1 and 954 cm _1 correspond to stretching vibrations of P=0 and P-0-(H). Vibrations at 1623 cm"1 correspond to bending vibrations of free O-H and bending vibrations of N-H (amide II). Peak at 1715 cm"1 corresponds to C=0 (amide). The peak observed at 553 cm"1 may correspond to group of N-C-N, the peak appearing at 1402 cm"1 corresponds to stretching Vibration of C-N (amide). The peak appearing at 1120 cm"1 is attributed to the stretching vibrations of P-O-P. Absorption peaks appearing at 2209 cm"1 and 1941 cm"1 can be due to the stretching Vibration of POO" and (P) ON.

Product II:
As seen from Fig. 1B, FTIR of product II showed an absorption band at 3441 cm"1 corresponding to O-H stretching vibrations. Peaks observed at 1284 cm"1 and 908 cm _1 correspond to the stretching vibrations of P=0 and P-0-(H), respectively. Vibrations at 1631 cm"1 correspond to bending vibrations of free O-H and bending vibrations of N-H (amide II) and at 1679 cm"1 corresponds to C=0 (amide). The peak observed at 558 cm"1 may correspond to N-C-N. Peak appearing at 1462 cm"1 corresponds to the stretching Vibration of the group of C-N (amide). The peak appearing at 1096 cm"1 is attributed to the stretching vibrations of P-O-P. Product III:
As seen from Fig. IC, FTIR of product III showed an absorption band at 2800 cm"1 corresponding to O-H stretching vibrations. Peaks observed at 1196 cm"1 and 945 cm _1 correspond to the stretching vibrations of P=0 and P-O-(H) respectively. Vibrations at 1672 cm"1 corresponds to bending vibrations of free O-H and bending vibrations of N-H (amide II) and 1513 cm"1 peak corresponds to C=0 (amide). The peak appearing at 1404 cm"1 correspond to the stretching Vibration of C-N (amide). The peak appearing at 1018 cm"1 is attributed to the stretching vibrations of P-O-P. Absorption peaks appearing at 2200 cm"1 and 1940 cm"1 can be due to the stretching Vibration of POO'and (P) O-N. Product IV:
As seen from Fig. 1D, FTIR of product IV showed an absorption band at 3186 cm"1 corresponding to O-H stretching vibrations. Peaks observed at 946 cm"1 corresponds the stretching vibrations of P=0 and P-0-(H), respectively, Vibrations at 1626 cm"1 correspond to bending vibrations of free O-H and bending vibrations of N-H (amide II). The peak appearing at 1444 cm"1 correspond to the stretching Vibration of the group of C-N (amide). The peak appearing at 1038 cm"1 is attributed to the stretching vibrations of P-O-P.
PRODUCT V:
As seen from Fig. IE, FTIR of product V showed an absorption band at 2795 cm"1 corresponding to O-H stretching vibrations Peaks observed at 1204 cm"1 and 954 cm _1 correspond to the stretching vibrations of P=0 and P-O-(H). Vibrations at 1672 cm"1 correspond to bending vibrations of free O-H and bending vibrations of N-H (amide II).

Peak at 1739 cm"1 corresponds to C=0 (amide). The peak appearing at 1403 cm"1 correspond to the stretching Vibration of the group of C-N (amide). The peak appearing at 1165 cm"1 is attributed to the stretching vibrations of P-O-P. Absorption peaks appearing at 2247 cm"1 and 1939 cm"1 can be due to the stretching Vibration of POO" and (P)-O-N. PRODUCT VI:
As seen from Fig. 1F, FTIR of product VI showed an absorption band at 3431 cm"1 corresponding to O-H stretching vibrations Peaks observed at 1326 cm"1 and 965 cm"1 correspond to the stretching vibrations of P=0 and P-O-(H) respectively. Vibrations at 1674 cm"1 correspond to bending vibrations of free O-H and bending vibrations of N-H (amide II) and at 1679 cm"1 corresponds to C=0 (amide). The peak appearing at 14434 cm"1 correspond to stretching Vibration of C-N (amide). The peak appearing at 1018 cm-1 is attributed to the stretching vibrations of P-O-P. PRODUCT VII:
As seen from Fig. IG, FTIR of product VII showed an absorption band at 3357 cm"1 corresponding to O-H stretching vibrations Peaks observed at 1206 cm"1 and 962 cm"1 correspond to the stretching vibrations of P=0 and P-O-(H) respectively. Vibrations at 1632 cm"1 correspond to bending vibrations of free O-H and bending vibrations of N-H (amide II). Peaks observed at 1632 and 1666 cm-1 correspond to C=0 (amide). The peak observed at 561 cm"1 may correspond to N-C-N. The peak appearing at 1403 cm"1 corresponds to stretching Vibration of C-N (amide). The peak appearing at 1120 cm"1 is attributed to the stretching vibrations of P-O-P. The peak appearing at 1633 cm"1 corresponds to the C=C. THERMO GRAVIMETRIC ANALYSIS:
As shown in Fig. 2A, thermal stability of product I examined in the temperature ranging from 25°C to 800°C at a rate of 10.00°C/min under a nitrogen atmosphere. In the first stage (temperature ranging between 25°C to 60°C), where the loss is due to the evaporation of moisture, a weight loss of 2.740 % is observed. The higher weight loss is a result in an increase in water content in the material following derivation. The second decomposition stage is the pyrolysis and the evolution of combustible gases and started to decompose at 60°C with a weight loss of 10.473 %. The greater thermal stability is

evident from the differential thermogravimetry (DTG) curve where the decomposition curve was obtained at 625.50°C.
As shown in Fig. 2B, thermal stability of product II examined in the temperature ranging from 25°C to 800°C at a rate of 10.00°C/min under nitrogen atmosphere and sample decompositions involve 2 stages. In the first stage (temperature ranging between 25°C to 65°C), where the loss is due to the evaporation of moisture, a weight loss of 4.738 % was observed. The higher weight loss is a result in an increase in water content in the material following derivation. The second decomposition stage is due to the pyrolysis and the evolution of combustible gases. The product II started to decompose at 65°C with a weight loss of 26.2 %. The greater thermal stability is evident from the DTG curve where the decomposition curve is obtained at 625.58°C.
As shown in Fig. 2C, thermal stability of product III examined in the temperature ranging from 40°C to 900°C at a rate of 5.00°C/min under a nitrogen atmosphere and sample decomposition involve many stages. In the first stage (temperature ranging between 40°C to 60°C), where the loss is due to the evaporation of moisture, a weight loss of 34.44 % is observed. The second decomposition stage is due to pyrolysis and the evolution of combustible gases. The product III started to decompose at 60°C with a weight loss of 6.914 %. The greater thermal stability is evident from the DTG curve where the decomposition curve is obtained at 799.48°C.
As shown in Fig. 2D, thermal stability of product IV examined in the temperature ranging from 40°C to 899 °C at a rate of 5.00°C/min under a nitrogen atmosphere and sample decomposition involve 2 stages. In the first stage (temperature ränge between 40°C to 60°C), where the loss is due to the evaporation of moisture, a weight loss of 2.606 % is observed. The second decomposition stage is due to the pyrolysis and the evolution of combustible gases. The product IV started to decompose at 60°C with a weight loss of 29.41%. The greater thermal stability is evident from the DTG curve where the decomposition curve is obtained at 899.48°C.
As shown in Fig. 2E, thermal stability of product V examined in the temperature ranging from 40°C to 900 °C at a rate of 5.00°C/min under a nitrogen atmosphere and sample decomposition involve many stages. In the first stage (temperature ränge between 46°C to 59.91°C), where the loss is due to the evaporation of moisture, a weight loss of

0.06838 % is observed. The second decomposition stage is expected due to the pyrolysis and the evolution of combustible gases. The product V started to decompose at 59.91°C with a weight loss of 10.473 %. The greater thermal stability is evident from the DTG curve where the decomposition curve is obtained at 616.24°C.
As shown in Fig. 2F, thermal stability of product VI examined in the temperature ranging from 40°C to 900°C at a rate of 5.00°C/min under a nitrogen atmosphere and sample decomposition involves many stages. In the first stage (temperature ränge between 54.49°C to 70.06°C), where the loss is due to the evaporation of moisture, a weight loss of 0.3109 % is observed. The second decomposition stage is due to the pyrolysis and the evolution of combustible gases. The product VI started to decompose at 70.06°C that a weight loss of 26.2% is observed. The greater thermal stability is evident from the DTG curve where the decomposition curve is obtained at 625.58°C.
As shown in Fig. 2G, thermal stability of product VII examined in the temperature ranging from 25°C to 800°C at a rate of 10.00°C/min under a nitrogen atmosphere and sample decomposition involves many stages. In the first stage (temperature ränge between 25°C to 85°C), where the loss is due to the evaporation of moisture, a weight loss of 3.984 % is observed. The second decomposition stage is due to the pyrolysis and the evolution of combustible gases. At this stage, product VII started to decompose at 87°C with a weight loss of 9.2 %. The greater thermal stability is evident from the DTG curve where the decomposition curve is obtained at 704.67°C. NUTRIENT RELEASE STUDY
Leaching columns used to quantify the release of macronutrient such as nitrogen and phosphate over time. Acid treated neutralized soil sample of 2 mm packed in a tubulär column of approximately 5 x 50 cm) and column is attached with tubing from the bottom to collect the leachate. Immediately, after adding fertilizer on top of the column, water was added at a constant rate so that the top of column remains moistened. Samples collected at different interval and analyzed. NITROGEN RELEASE PROFILE
As shown in Fig. 3A, Product I showed steady State release of nitrogen up to 168 h (7days), where still 35% nitrogen is present in the Compound and showed the extended release of nitrogen over a period of time.

As shown in Fig. 3B, Product II showed steady State release of nitrogen up to 264 h (11 days) where still 22 % nitrogen present in the Compound and showed the extended release of nitrogen over a period of time.
As shown in Fig. 3C, Product III showed steady release of nearly 93% nitrogen up to 144 h (6 days).
As shown in Fig. 3D, Product IV showed steady State release of nearly 58% nitrogen up to 240 h (10 days) and remaining nitrogen was continuously released in time dependent manner.
As shown in Fig. 3E, Product V showed steady State release of nearly 79% nitrogen up to 240 h (10 days) whereas nearly 21% of remaining nitrogen was released in time dependent manner.
As shown in Fig. 3F, product VI showed steady State release of nearly 93% nitrogen up to 240 h (10 days) whereas nearly 17% nitrogen was released in time dependent manner.
As shown in Fig. 3G, product VII showed steady State release of nitrogen for nearly 432 h (18 days). PHOSPHATE RELEASE PROFILE (FIGURE 4):
As shown in Fig. 4A and 4B, Products I and II showed the release of phosphate for nearly 192 h (8 days) and 216 h (9 days) respectively. In both the cases approximately 95%) phosphate released in a steady State manner.
As shown in Fig. 4C and 4D, Products III and IV showed State release of phosphate for nearly 144 h (6 days) and 72 h (3 days). In both the cases, approximately 98%) and 96% phosphate released in a steady State manner.
As shown in Fig. 4E and 4F, Products V and VI showed steady State release of phosphate for nearly 3 days. In both the cases, approximately 97% and 89% phosphate released in a steady State manner.
As shown in Fig. 4G, Product VII showed continuous release of phosphate for at least for 4 days while nearly 20% remained in the Compound. pH PROFILE:

As shown in Fig. 5A-5G, Products I to VII during release of nutrients the pH become neutral or near neutral during the study to prevent the possibility of plants or crops burning by the process known in an acidic and un-buffered soil condition.
ZINC RELEASE PROFILE:
As shown in Fig. 6A and 6B, Product I and II released nearly 80% and 40% zinc respectively, in a steady State manner.
As shown in Fig. 6C and 6D, Product III released nearly 97.5% zinc released in 72 h (3 days) whereas Products IV released nearly 91 % of zinc in 168 h (7 days) in a steady State manner.
As shown in Fig. 6E, Product VII released nearly 25% zinc in a continuous manner while 75% zinc is in the Compound over 3 days. IRON RELEASE PROFILE (FIGURE 7):
As shown in Fig. 7A-7D, Products III to VI released nearly 90% iron in 72 h (3 days).
COMPARATIVE ANALYSIS OF NUTRIENT RELEASE WITH PAP AND UREA FOR PHOSPHATE AND NITROGEN RELEASE:
As seen in Fig. 8A, the nitrogen release of product I is 3 times slower than urea and 1.5 times slower than DAP. Similarly, the nitrogen release of product II is 4 times slower than urea and 2 times slower than DAP.
As seen in Fig. 8B, the phosphorous release of product I is 2 times faster than DAP. Similarly, the phosphorous release of product II is 15 times faster than DAP.
The results clearly demonstrated that the present disclosure surprisingly found the uses of macronutrient and micronutrients with organic matter to develop novel products which is sustained release of nutrients over a period of time and providing a Solution by employing micronutrients which are not precipitating even in the presence of phosphate. Organic matter present in the products capable of providing bonding with the nutrients in presence of phosphate in the form of polyphosphate and during the release of nutrients pH of the products remain neutral which is the additional benefit over the known products such as urea or DAP and therefore soil remain fertile without addition of any

base material which usually found in most of the agriculture soil after application the soil become acidic.
It is well known that in presence of phosphate, most of the soil applied micronutrients are immobilized either with phosphate which are usually not available to plants, whereas the products of the present disclosure showed the mobility of the micronutrients even in the presence of phosphate, calcium or soil and therefore easily available to the plants. Advantages of the present invention
1. The fertilizer of the present disclosure provides nutrients for extended period of time compared to individual nitrogen and/or phosphate fertilizers or any known fertilizers and found to provide better growth and yields in plants when used in a variety of ways such as seed coating, foliar and soil applications.
2. The fertilizer of the present disclosure in solid complex form, containing macronutrients and essential minerals are completely soluble in water and release the nutrients present therein in a sustained manner which makes the fertilizers high use efficiency fertilizers. This soluble Compound can be used for foliar application, and can be conventionally admixed to Solution to improve the retention of the products for longer duration of time for adsorption and translocation inside the leaf for cellular activities.
3. The fertilizer of the present disclosure is precipitate free, and water soluble which provides nutrients to the plants for an extended period of time.
4. The fertilizer of the present disclosure has neutral or near neutral pH to protect the plants from acid burns.
5. The fertilizer of the present disclosure provides higher ratio of nitrogen and phosphate and the presence of phosphate not hindered the uptake of trace elements present in the fertilizer of the present disclosure.
Although the foregoing disclosure has been described in some detail by way of illustration and examples for purposes of clarity of understanding, it is readily apparent to those of ordinary skill in the art in light of the teachings of this disclosure that certain

changes and modifications may be made thereto without departing from the spirit or scope of the appended claims.
Accordingly, the preceding merely illustrates the principles of the disclosure. It will be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the disclosure and are included within its spirit and scope. Furthermore, all examples and conditional language recited herein are principally intended to aid the reader in understanding the principles of the disclosure and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all Statements herein reciting principles, aspects, and embodiments of the disclosure as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents and equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. The scope of the present disclosure, therefore, is not intended to be limited to the exemplary embodiments shown and described herein. Rather, the scope and spirit of present disclosure is embodied by the appended claims.

WE CLAIM:
1. A sustained release fertilizer comprising poly-phosphate linked with nitrogen and
other nutrient(s); wherein the sustained release fertilizer is characterized by a structure of formula (I) and formula (II):

wherein,
Ri and R2 independently represents divalent or trivalent cation selected from the metal of group II, group III and group VIII of periodic table.
2. The sustained release fertilizer as claimed in claim 1, wherein the metal of group
II is selected from a group comprising magnesium, calcium and a combination thereof.
3. The sustained release fertilizer as claimed in claim 1, wherein the metal of group
III is aluminium.
4. The sustained release fertilizer as claimed in claim 1, wherein the metal of group VIII is selected from a group comprising iron, nickel, copper, zinc and a combination thereof.
5. The sustained release fertilizer as claimed in claim 1, wherein the fertilizer comprises at least one nutrient from the nutrients listed below:
nitrogen derivative (as nitrogen): about 6 wt. % - about 40 wt. %; and phosphorus derivative (as P2O5): about 15 wt. % - about 65 wt. %.
6. The sustained release fertilizer as claimed in claim 5, wherein the nitrogen
derivative (as nitrogen) is present in an amount from about 15 wt. % - about 30 wt. %.

7. The sustained release fertilizer as claimed in claim 5, wherein phosphorus derivative (as P2O5) is present in an amount from about 35 wt. % - about 55 wt. %.
8. The sustained release fertilizer as claimed in claim 1, wherein ratio of nitrogen to micronutrient is from about 1:10 to about 1:40.
9. The sustained release fertilizer as claimed in claim 1, wherein pH of the fertilizer is about neutral pH.
10. A process for preparing a sustained release fertilizer as claimed in claim 1; wherein the process comprises:

(a) solubilizing nutrient source in polyphosphoric acid to get a Solution;
(b) adding to the Solution of Step (b) a nitrogen containing macronutrient source; and
(c) neutralizing the reaction mixture of Step (b) by adding ammonia to get a mixture containing the sustained release fertilizer.

11. The process as claimed in claim 10, may further comprise separating the mixture of step (c) to get a residue and filtrate.
12. The process as claimed in claim 11, wherein the residue was dried to get the sustained release fertilizer as a solid.
13. The process as claimed in claim 11, wherein the filtrate was concentrated to get the sustained release fertilizer as a solid.
14. The process as claimed in claim 10, wherein the nutrient source in step (a) is selected from a group comprising nutrient oxide, nutrient salt and a combination thereof.
15. The process as claimed in claim 10, wherein the solubilization of nutrient source in polyphosphoric acid is carried out at a temperature of about 5-150°C.
16. The process as claimed in claim 10, wherein step (b) takes place at a temperature of less than about 80°C.
17. The process as claimed in claim 16, wherein the temperature is about 50-70°C.
18. The process as claimed in claim 10, wherein nitrogen containing macronutrient source in step (b) is selected from a group comprising urea, biuret, ammonia, methylurea and guanylurea.
19. The process as claimed in claim 18, wherein the nitrogen containing macronutrient source is urea.

20. The process as claimed in claim 10, wherein neutralization is carried out at a temperature of less than about 30°C, preferably 0-25°C.
21. A sustained release fertilizer obtained by the process as claimed in any of the Claims 10-20.