WO2017168446A1 - Metal oxide based soil conditioner - Google Patents

Abstract

Metal oxide based soil conditioners comprising nano iron oxalate capped metal oxide(s)(Fe, Mn, Cu) are capable of enhancing the iron availability to plants from soil without increasing soil acidity and hindering phosphorous availability in soil in comparison to conventional iron fertilizers. The said iron oxalate capped metal5 oxides also enhance the nitrogen and phosphorus availability in such treated soil. Moreover iron oxalate capped metal oxide nanomaterials comprising Fe sourced from iron salt other than Mohr salt shows atleast four folds enhanced Fe release capability in soil with respect to the nanomaterials with Fe sourced from Mohr salt. Metal oxide based soil conditioner is a reaction product of iron10 salts other than Mohr's salt, and oxalic acid followed by reduction with Sodium Borohydride, and optionally other metal salts at elevated temperature

Description

TITLE: METAL OXI DE BASED SOI L CONDITIONER Fl ELD OF THE I NVENTI ON

The present invention relates to nano metal oxide based soil conditioners. More specifically, the present invention relates to nano metal oxide based soil conditioners comprising iron oxalate capped metal oxide(s). Advantageously the said soil conditioners are capable of enhancing the iron availability to plants from soil without increasing soil acidity and hindering phosphorous availability in soil. Further, the iron oxalate capped metal oxides of the present invention is directed to increase the nitrogen and phosphorus availability in such treated soil Moreover the present invention provides an industrially scalable process for the production of environmentally safe iron oxalate capped metal (Fe, Mn, and Cu) oxide nanomaterials as solid conditioners.

BACKGROUND ART

Assimilation of iron from soil by plants is significantly low especially in arid regions where the soil pH varies from neutral to alkaline. Ferrous ion readily oxidizes to plant unavailable ferric (Fe³⁺) when soil pH is greater than 5.3. [Morgan, B., Lahav, O., 2007, Chemosphere, 68(11), 2080-2084]. Crop production in such soils is severely hindered as iron readily forms insoluble ferric oxides [Robinson, N. J.,et. al.1999, Nature, 397, 694] . Phosphorous bioavailability from soils is also dependent on the redox conditions and the nature of organic matter in soil [Zhou, D. M., et. al., 2012, Soil sediment contam. 21, 101-114]. Iron salts such as Ferrous Sulphate has routinely been used to treat soil to enhance phosphorous availability by lowering the soil pH [Weng, L, et.al. , 2012, J Environ Qual. 41(3), 628-35]. Chelated iron (Fe-EDTA or Fe-EDDHA) is an effective correction measure to avoid Fe/P disorders in soil [Liu, G., Hanlon, E., Li, Y., 2012. Understanding and applying chelated fertilizers effectively based on soil pH. HS1208 series of Horticultural Sciences Department, UF/IFAS extension, University of Florida]. However, EDTA containing soil conditioners/fertilizers are expensive and have limited use only in calcareous soils. Further they are prone to leaching losses and their use has been questioned due to possible negative effects on the environment

Pratihar et al. (2014, RSC Adv. 4, 33446-33456) describes the preparation of iron(oxalate) capped Fe(0) [ Fe(ox)-Fe(0)] nanomaterial for improving the ion content of the soil . The publication teaches said nanoparticle sourced from Mohr's salt, NH₄)₂S0₄.FeS0₄. 6H₂0 by sodium borohydride (NaBH₄) reduction in the presence of oxalic acid at room temperature in water The synthesized [ Fe(ox)-Fe(0)] nanomaterial is capable of producing iron oxalate capped Fe₃0₄ [Fe(ox)-Fe₃0₄] from the aerial oxidation of Fe(0) at room temperature. The iron content and iron release profile of [Fe(ox)-Fe₃0₄] material is found to be 19% and 58 mg L^"1 respectively. However, inspite of such generation of nanomaterial is capable of producing iron oxalate capped Fe₃0₄ [Fe(ox)-Fe₃0₄], the process was found to have severe limitations in large scale production due to cost implications and process limitations. Moreover, the iron content and iron release profile of [Fe(ox)-Fe₃0₄] material is found to be only 19% and 58 mg L^"1 respectively. Also, this prior art process suffers from the following shortcomings and hence is not appropriate for scale up and commercial production:

(a) The yield and iron content in the material and iron release profile is poor and therefore not appropriate for application as soil conditioner.

(b) The process is not cost effectiveness.

(c) The scale up is cumbersome.

Therefore, cost effective and commercially scalable processes for the production of iron oxalate capped (Fe₃0₄) iron oxide with the desirable iron release profile continued to reamin a challenge in the related art.

OBJECTS OF THE I NVENTI ON The basic object of the present invention is thus directed to provide nano metal oxide based soil conditioner which would be simple and cost-effectiveto enhance iron availability to plants from soil.

Another object of the present invention is to provide the said metal oxide based soil conditioner for sustained availability of Fe, Mn, and Cu in the soil for plant assimilation.

Another object of the present invention is to provide iron oxalate capped metal oxides to increase the nitrogen and phosphorus availability in treated soils.

Another object of the present invention is to enhance iron availability to the plants without hindering phosphorous availability in soil.

Another object of the present invention is to provide Fe as a micronutrient without increasing soil acidity.

Another object of the present invention is to enhance crop growth and yield under field condition using in the said metal oxide based soil conditioner of the present invention.

Another object of the present invention is to provide for method of treatment of soil with the said metal oxide based soil conditioner to enhance growth and favourable production of plants including the enhancement of expression of GS1 and GOGAT genes that are responsible for primary nitrogen assimilation in plants.

SUMMARY OF I NVENTI ON

Thus according to the basic aspect of the present invention there is provided metal oxide based soil conditioner comprising nano iron oxalate capped metal oxide(s) wherein the nano iron oxalate capped metal(s) oxide comprise selectively (i) Fe(Ox)-Fe₃0₄ with Fe sourced from Fe salts other than Mohr salt with atleast four folds enhanced Fe release capability in soil with respect to Fe(Ox)- Fe₃0₄ with Fe sourced from Mohr salt and (ii) mixed metal oxides selected from Fe(ox) Fe-MnO_x and Fe(ox) Fe-CuO_x involving said Fe(Ox)- Fe₃0₄with Fe sourcedfrom Fe salts other than Mohr salt.

In accordance with another aspect of the present invention there is provided metal oxide based soil conditioner which is a reaction product of iron salts other than Mohr's salt, oxalic acid followed by reduction with Sodium Borohydride, and optionally other metal salts at elevated temperature providing said caped metal oxide with its said selective Fe source with or without other metal micronutrients favouring enhancing sustained availability of metal micronutrients, N, P for plant assimilation and stabilisation in pH of treated soil in the range of 5.0 to 6.0.

In accordance with another aspect the present invention there is provided metal oxide based soil conditioner wherein the ratio of iron oxalate to Fe₃0₄ are in the range from 1:0.1 to 1:1.

In another aspect the present invention provides metal oxide based soil conditioner comprising porous structure connected with nano ribbon like structures with uniform particle size in the range of 2-16 nm and average particle size in the range of 9 to 32 nm.

In a further aspect the present invention provides metal oxide based soil conditioner wherein the aspect ratio of the particles of Fe(ox)-Fe304 is 15-20, Fe(ox)Fe-MnOx is 1 - 4 and Fe(ox) Fe-CuOx is 10-15.

In a still further aspect, the present invention provides metal oxide based soil conditioner wherein surface area, pore radius and pore volume of the particles are as hereunder:

Pore Radius (A) 17.1 to 18.3 17.8 to 19.2 15.5 to 16.26

Pore Volume (ccg ¹) 0.061 to 0.072 0.123 to 0.141 0.076 to 0.092

Another aspect of the present invention provides mMetal oxide based soil conditioner further characterised by: i) The XRD pattern of Fe(ox)-Fe304, Fe(ox) Fe-CuOx, and Fe(ox) Fe-MnOx showing presence of orthorhombic iron oxalate and magnetite Fe304; orthorhombic Fe(C204), 2H20, Fe304, and CuO; and orthorhombic Fe(C204).2H20, Fe304, and MnO; ii) FT-IR having peaks of 1685, 1412, and 563 cm-1 for Fe(ox)-Fe304, 1691, 1360, 1319 and 502 cm-1. for Fe(ox) Fe-MnOx and 1672 and 495 cm-1 for Fe(ox) Fe-CuOx indicating presence of Oxalate; iii) SEM and TEM showing material as porous connected with nano ribbon like structures; iv) EDS showing the presence of Carbon 17.54%, oxygen 56.06% and iron 26.4% in Fe(ox)-Fe304, Carbon 13.52%, oxygen 63.0%, iron 19.3%, and copper 4.13% in Fe(ox)Fe-CuOx Carbon 16.1%, oxygen 58.4%, iron 20.7%, and manganese 4.73% in Fe(ox) Fe-MnOx ; v) BET showing pore radius of 18.432 for Fe(ox)-Fe304, 19.283 for Fe(ox)Fe- CuOx and 16.363 for Fe(ox) Fe-MnOx and pore volume of 0.071 for Fe(ox)- Fe304, 0.092 for Fe(ox) Fe-CuOx and 0.141 for Fe(ox) Fe-MnOx. Yet another aspect of the present invention provides metal oxide based soil conditioners wherein soils treated with

(I) Fe(Ox)-Fe₃0₄ i. enhances Fe availability by 10.0 -14.0 mg kg^"1 in 5 to 90 days. ii. increases N and P availability in soil from 1.3 % to 7.5 % and 50 mg kg-1 to 110 mg kg^"1. iii. enhances activity of soil enzymes urease and Phosphatase from 19.0 to 32.0 μg g-1 and 13.0 to 27.0 μg g^"1 respectively;

(II) Fe(ox)Fe-MnOx i. enhances Fe availability by 10.0 - 14.5 mg kg^"1 in 5 to 90 days and Mn content increases by 35.0 - 40.0 mg kg^"1 in 5 to 90 days; ii. increases N and P availability in soil from 1.3 % to 5.3 % and 46 mg kg-1 to 90 mg kg-1 iii. enhances activity of soil enzymes urease and Phosphatase from 18.0 to 27.0 μg g-1 and 11.0 to 21.0 μg g-1 respectively. and

(III) Fe(ox)Fe-CuOx i. enhances Fe availability increases by 6 -10 mg kg^"1 in 5 to 90 days and Cu content increases by 85 - 90 mg kg^"1 in 5 to 90 days; ii. increases N and P availability in soil from 1.3 % to 5.0 % and 45 mg kg^"1 to 80 mg kg^"1 respectively iii. enhances activity of soil enzymes urease and phosphatase from 17.0 to 25.0 μg g-1 and 10.0 to 20.0 μg g-1 respectively.

In a further aspect, the present invention relates to metal oxide based soil conditioner when used for treatment of soil enhances the Fe availability in the range of 19 to 29 %. Yet another aspect of the present invention provides metal oxide based soil conditioners which significantly reduces the bulk density of soil treated by the said metal oxides at least by 7%.

In a further aspect, the present invention provides metal oxide based soil conditioner wherein soils treated with the said metal oxides increase tomato yields at least by 80 to 90% as compared to FeS04 and 70 to 80 % as compared to Fe-EDTA with concomitant increase in carotenoid and chlorophyll content at least by 85 to 90% and 90 to 95%, respectively as compared to soil conventionally treated with Ferrous Sulphate and Fe-EDTA. In yet another aspect the present invention provides metal oxide based soil conditioner wherein the soils treated with the said metal(s) oxide enhances the expression of GS1 and GOGAT genes in tomato as compared to conventional Fe- EDTA treated soils.

Another aspect of the present invention provides use of Metal oxide based soil conditioner as claimed in anyone of the preceding claims for conditioning soil including selectively one or more of : i) stabilising soil pH, ii) increasing iron availability in soil without increasing the acidity, iii) reduction of soil bulk density, iv) increasing N and P availability in soil ; v) enhancing activity of soil enzymes such as urease and phosphatise.

A further aspect of the present invention provides a process for enriched availability of plant nutrients in soil for enhanced plant growth comprising treating the soil with nano metal oxide based soil conditioners of the present invention.

A still further aspect of the present invention provides a process comprising steps of: (i) preparing the field by light secondary ploughing followed by levelling of the soil surface prior to planting;

(ii) transplanting nursery raised seedlings;

(iii) treating @ 2 to 10 kg ha^"1 the root zone of the transplanted seedlings with nano metal oxide soil conditioners dispersed in aqueous solution after 2 to 3 days after transplantation of tomato seedlings.

(iv) applying NPK after the incorporation of the nano metal oxide based soil conditioners

(v) carrying out routine agricultural practices such as weeding, cleaning, pest control measures, and harvesting .

In yet another aspect the present invention provides a process for treating soil for tomato cultivation with said soil conditioners selected from one or more of [Fe(ox)-Fe304, Fe(ox)Fe-MnOx, and Fe(ox) Fe-CuOx] for enhanced conditioning of soil as compared to Fe-EDTA and control including i. Fe(ox)Fe-MnOx treatment for raising the expression of GOGAT genes in tomato by 0.12 units as compared to Fe-EDTA treatment. ii. Fe(ox)-Fe304 treatment for raising the expression of GOGAT genes by 0.05 unit as compared to Fe-EDTA . iii. Fe(ox) Fe-CuOx and Fe(ox)-Fe304 treatment for raising the xpression of GS1 gene by 0.23 and 0.19 units respectively as compared to Fe-EDTA treatment.

Another aspect of the present invention provides for a process for manufacture of the said metal oxide based soil conditioner comprising steps of:

(i) reacting ferrous salts other than Mohr salt and oxalic acid in aqueous reaction medium at room temperature;

(ii) reduction with Sodium Borohydride to obtain Fe(ox)-Fe(0); (iii) optionally for providing mixed metal oxide , insitu reacting formed Fe(ox)- Fe(0) with metal salts to produce the mixed metal oxides at elevated temperature;

(iv) separating and drying the product; In a further aspect the present invention provides for a process wherein the molar ratio of ferrous salt : oxalate is in the range of 0.3 to 3, and said optional step for providing mixed metal oxide comprise further reacting with copper sulphate and potassium permanganate for the preparation of Fe(ox) Fe-CuOx and Fe(ox)Fe-MnOx respectively and wherein the molar ratio of ferrous salt : copper in mixed Fe(ox) Fe-CuOx is 0.5 to 3, and molar ratio of ferrous salt : manganese in mixed nano Fe(ox)Fe-MnOx is in the range of 0.5 to 3.

The details of the invention, its objects and advantages are explained hereunder in greater detail in relation to the following non-limiting exemplary illustrations as per the accompanying figures: BRI EF DESCRI PTI ON OF ACCOMPANYI NG Fl GURES

Fig.1 XRD of prepared materials: (a)Fe(ox)-Fe(0); (b)Fe(ox)-Fe₃0₄;

(c)Fe(ox)Fe-CuO_x; (d) Fe(ox) Fe-MnO_x.

Fig. 2. Comparative FT-IR of prepared materials: (a) Fe(ox)-Fe(0)and Fe(ox)- Fe₃0₄ with Iron oxalate complex; (b) FT-IR spectrum of Fe(ox) Fe-CuO_x and Fe(ox)Fe-MnO_x.

Fig. 3. (a) and (b) HR-SEM and EDS of Fe(ox)-Fe₃0₄ nanomaterial; (c) and (d) HR-TEM of Fe(ox)-Fe(0) nanomaterial and of Fe(ox)-Fe₃0₄ nanomaterial.

Fig.4. (a) HR-SEM and (b) HR-TEM of Fe(ox) Fe-CuO_x; (c) HR-SEM and (d) HR- TEM of Fe(ox)Fe-MnO_x. Fig. 5. Partcle size distribution of Fe(ox)-Fe(0), Fe(ox)-Fe₃0₄, Fe(ox) Fe-CuO_x, and Fe(ox) Fe-MnO_x from HR-TEM image.

Fig.6. EDS Analysis: (a) Fe(ox) Fe-CuO_x ; (b) Fe(ox) Fe-MnO_x. Figure 7(a) . Effects on pH, BD and Fe content in soil. Figure 7(b). Effects on Mn and Cu content in soil.

Figure 8. Effects on Total N, available P, urease and phosphatase activity in soil.

Figure 9: Changes in phosphate & Fe availability and pH status with time Figure 10:RT-PCR using GS1 and GOGAT gene-specific primers where gapdh served as an internal control. T1 = Control, T2= Fe(ox) - Fe₃0_4! T3= Fe(ox)Fe- Μηθχ, T4= Fe(ox)Fe-CuO_x, T5= Fe-EDTA

Detailed description of the invention According to the basic aspect the present advancement resides in the surprising finding that soil treated with iron oxalate capped nano metallic oxides of the present invention are unexpectedly and significantly capable of enhancing the iron, manganese, and copper availability to plants from treated soil. Further, the N and P availability in such treated soil also significantly increased in soils treated with nano metal oxide based soil conditioners of the present invention.

In prior art the preparation of orthorhombic iron(oxalate) capped Fe(0) [Fe(ox)- Fe(0)] nanomaterial was done by using sodium borohydride (NaBH₄) reduction of Mohr's salt, (NH^SC .FeSC . 6H₂0 in the presence of oxalic acid at room temperature in water [Pegu, R., Majumdar, K.J., Talukdar, D. J., Pratihar, S., 2014, RSC Adv.4, 33446-33456] .This prior art process suffers from the following short comings and hence is not appropriate for scale up and commercial production: i. The yield and iron content in the material and iron release profile is poor and therefore not appropriate for application as soil conditioner.

ii. The process is not cost effectiveness,

iii. The scale up is cumbersome. The present invention overcomes the problems of the prior art and provides a commercially scalable process for the preparation nano metal oxide based soil conditioners of the present invention.

In one embodiment of the present invention the Fe(ox) containing metal(s) oxide nanomaterial is prepared as per the scheme depicted below:

_Clirm„_c . .,. Water Yellow NaBH_{4 B)ack}

i-errcus sail * oxanc acia _rt stirr. Solution Solution Material

Fe(ox]hFe(G)

Any ferrous salt may be used. However ferrous sulphate is preferred.

The iron content of [ Fe(ox)-Fe₃0₄] material prepared from FeS0₄ is higher than (28.6%) the previously prepared material (19.2%) from Mohr salt [prior art route] .

In terms of overall yield, Fe(ox) containing metal(s) oxide nanomaterial is found to be high yielding (84%) compared to Mohr salt method (63%) [prior art route]. The overall yield of [ Fe(ox)- Fe₃0₄] nanomaterial synthesized from other ferrous salts such as FeCI₂.4H₂0 and Fe(N0₃)2.9H₂0 is 75 % and 71%, respectively.

The iron content of [Fe(ox)-Fe₃0₄] nanomaterial prepared from FeCI₂.4H₂0 and Fe(N0₃)₂is 23.5 % and 24.1%, respectively.

The release of Fe from the nano metal oxide based soil conditioners of the present invention exhibits 5 fold increase in Fe release (286.8 mg L^"1) as compared to the Fe release (58 mg L^"1) from Fe(ox)-Fe₃0₄ prepared from Mohr salt observed in prior art.

In another embodimentFe(ox)Fe-CuO_x nanomaterial is prepared as per the

following scheme:

p I* Water Yellow NaBHe Black GUSO Brown herrous salt + oxalic acid _rt, stirr.' Solution Solution' Material Solution' Material

Fe(ox)Fe-GuQ_x

In yet another embodiment of the invention Fe(ox)Fe-MnO_x nanomaterial is

prepared as per the following scheme:

c .. .. . , Water„ Yelld* MaBH₄ Black MnQ₄ Black rerrous salt^♦ oxalic acia ^ stirr. solution Solution Material Solution Material

Feiox}Fe~MnQ_x The process of the present invention includes the reaction of ferrous salt and oxalic acid in aqueous medium at room temperature followed by reduction with Sodium Borohydride to obtain Fe(ox)-Fe(0). For the preparation of the mixed metal oxide systems the Fe(ox)-Fe(0) material is in situ reacted with Copper sulphate (if the Fe(ox) Fe-CuO_x is required) or with Potassium Permanganate solution (if the Fe(ox)Fe-MnO_x is required).

The product is separated and dried at about 80°C. This preparation does not involve any high temperature calcination.

The amount of oxalic acid and iron in the synthesized [ Fe(ox) -Fe₃0₄] nanomaterial was determined by titration of potassium permanganate solution (KMn0₄) and spectrophotometric determination of iron by reacting with o- phenanthroline. The ratio between oxalate and iron in nano [Fe(ox)-Fe₃0₄] obtained from ferrous sulphate is higher than (1:3) the material (1:5) obtained from mohr's salt. The ratio of iron oxalate and Fe₃0₄ of nano [ Fe(ox)-Fe₃0₄] material prepared from FeS0₄ is lower than (1:0.7) the previously prepared material (1 : 1.3) from Mohr salt. The present invention and the process and the nanomaterials obtained thereof is now illustrated with following non-limiting examples.

Example I : Synthesis of the Fe(ox) capped metal(s) oxide nanomaterial a) Preparation of Fe(ox)-Fe₃0₄ nanomaterial

In a typical procedure as explained in Scheme 1, 34.7 g of FeS0₄.6H₂0 and 9.45 g of oxalic acid was added in 400 ml of distilled water to prepare a solution in a 1L beaker and stirred for 20 minutes. Then, a solution of 30 g of NaBH₄ was prepared in 100 ml distilled water and added drop wise in the earlier prepared solution under vigorous stirring. During the addition, the color of the solution slowly turns into yellow then green and finally black iron nanoparticles began to appear in the solution. After the completion of the reaction, the reaction mixture was kept under stirring at room temperature for 14 h. During this, black colour solution slowly turns into yellow-brown and finally brown color material was collected in 42 g amount after centrifuging and oven drying at 80°C for 8 h. The same material could be synthesized from other ferrous salts like; FeCI₂.4H₂0 and Fe(N0₃)₂.9H₂0 with 35g and 38g, respectively.

Elemental Analysis of samples

The volume of oxalic acid consumed during the course of the reaction, i.e., the amount of oxalic acid binding with the formed nanoparticles is determined by titrating against aqueous solution of potassium permanganate solution (KMn0₄). The amount of iron in the oxalate capped nanomaterial was determined by reacting iron(ll) with o-phenanthroline to form an orange-red complex, which was monitored with UV-vis spectrum. The ratio between oxalate and iron in nano [Fe(ox)-Fe₃0₄] obtained from ferrous sulphate is higher than (1:3) the material (1:5) obtained from mohr's salt. The ratio of iron oxalate and Fe₃0₄ of nano [Fe(ox)-Fe₃0₄] material prepared from FeS0₄ is lower than (1:0.7) the previously prepared material (1:1.3) from Mohr salt. b) Process for the preparation of Fe(ox) -Fe-CuO_x nanomaterial

According to the process as explained in Scheme 2 , 34.7 g of FeS0₄. 6H₂0 and 9.45 g of oxalic acid was mixed in 400 ml of distilled water in a 1L beaker and stirred for 20 minutes to prepare a homogeneous solution. Then, drop wise addition of earlier prepared NaBH₄ solution (30 g NaBH₄ in 100 ml distilled water) under vigorous stirring turns the solution color from yellow to green and finally black iron nanoparticles began to appear in the solution. After the completion of the reaction, CuS0₄ solution (25 g of CuS0₄.5H₂0 dissolved in 100 ml of distilled water) was added to the reaction mixture and stirred at room temperature for 45 minute. After that, the reaction mixture was kept at 80°C under stirring for 12 h to produce yellow-brown color nanomaterial, which was centrifuged from the reaction mixture, washed with distilled water for several times to remove un- reacted metal salt and dried in oven at 80 °C for 8 h. Finally, 47 g yellow-brown Fe(ox) Fe-CuO_x nanomaterial was collected from the reaction. The similar procedure may be applied to synthesize the said material from other ferrous salts like; FeCI₂.4H₂0 and Fe(N0₃)₂.9H₂0 with 42g and 40g yield, respectively.

c) Process for the preparation of Fe(ox)-Fe-MnO_x nanomaterial

According to the process as explained in Scheme 3 For the synthesis of Fe(ox)Fe- Μηθχ, 16 g of KMn0₄ was dissolved in 100 ml of distilled water and added to the reaction mixture, after the immediate formation of black colour Fe(ox)-Fe(0) nanomaterial and stirred at room temperature for 45 minute. After that, the reaction mixture was kept at 80°C under stirring for 12 h to produce black color material, which was centrifuged, washed several times with distilled water to remove un-reacted metal salt and collected after keeping it in oven at 80°C for 8 h. Finally, 45 g black material was collected from the reaction. The said procedure may be applied for other ferrous salts like; FeCI₂.4H₂0 and Fe(N0₃)₂.9H₂0 to synthesize nano Fe(ox)-Fe-MnO_x with 38g and 41g yield, respectively.

Example 11 : Characterization of synthesisedmetal oxide based

nanomaterial i) Powder XRD analysis

The XRD of the prepared material [ Fe(ox)-Fe(0)] shows the presence of orthorhombic Fe(C₂0₄). 2H₂0 (Fig. 1a). As the peaks for Fe(ox) and Fe(0) overlap, it is difficult to detect them separately. However, [ Fe(ox)-Fe(0)] (the black material) reduces methylene blue to its corresponding leuco methylene blue and after this reaction, the black material transforms into brown material because of the oxidation of Fe(0) to its corresponding oxide. The XRD pattern of oxidized material shows the presence of both orthorhombic iron oxalate and magnetite Fe₃0₄ ( Fig.1 b) [Aragon, M. J., et.al. , 2008, Inorg. Chem. 47, 10366- 10371]. The XRD of [ Fe(ox) Fe-CuO_x] material shows the presence of orthorhombic Fe(C₂0₄), 2H₂0, Fe₃0₄, and CuO (Fig. 1c). XRD of the Fe(ox)Fe- MnO_x material show the presence of orthorhombic Fe(C₂0₄).2H₂0, Fe₃0₄, and MnO (Fig. 1d). ii) FT-I R analysis

The FT-IR of the prepared materials are shown in Fig. 2. Ferrous Oxalate [Fe(C₂0₄). 2H₂0] shows two peaks at 1640 and 1362 cm^"1 for typical metal carboxylate, in which oxalic acid acts as a bidentate ligand. The other two peaks at 1320, 820 cm^"1 are due to the C-0 and C-C stretching vibration of coordinated oxalate in Fe(C₂0₄).2H₂0. The comparative FT-IR of the prepared [ Fe(ox)-Fe(0)] and Fe(C₂0₄). 2H₂0 clearly shows the presence of iron oxalate in synthesized [Fe(ox)-Fe(0)]. FT-IR of [ Fe(ox)-Fe₃0₄] material showed two peaks at 1412 and 1655 cm^"1 due to the oxalate coordination to metal oxide and another two peaks at 415 and 563 cm^"1 due to Fe-0 symmetric bending vibration and Fe-O-Fe. The prepared [ Fe(ox) Fe-CuO_x] material showed peaks at 502, 819, 1319, 1360, and 1691 cm^"1. The FT-IR spectrum of [ Fe(ox) Fe-MnO_x] material shows the presence of oxalate (Fig.2).

Mi) Morphology and Elemental Analysis

The HR-TEM as represented in Figs. 3 and 4 of Fe(ox)-Fe(0) characterises the material as porous connected with several nano ribbon like structure, which are similar to the HR-TEM of Fe(ox)-Fe₃0₄. The SEM of Fe(ox) Fe-CuO_xand Fe(ox)Fe- MnO_x also shows porous structures. Fig. 5 presents the particle size distribution profile of all the synthesized materials from HR-TEM images using Image J software. The materials exhibit uniform particle size having narrow distribution in the range of 2-16 nm. The profiles are fitted with Gaussian distribution to obtain the average particle size. The average particle size of Fe(ox)-Fe(0) and Fe(ox)- Fe₃0₄ are found to be 39 and 32 nm respectively. On the other hand, the average particle size are 12 and 9 nm respectively in Fe(ox) Fe-CuO_x and Fe(ox) Fe-MnO_x material. It is worthwhile to mention that the aspect ratio of Fe(ox)-Fe(0) and Fe(ox)-Fe₃0₄ materials (19 and 17) is greater than the Fe(ox) Fe-CuO_x and Fe(ox)Fe-MnO_x (11 and 2) materials.

Energy Dispersive Spectroscopic Analysis (EDS) of a selected region of the Fe(ox)-Fe₃0₄ nano material shows the material to contain carbon (17.54%), oxygen (56.06%) and iron (26.4 %). Quantitative analysis of Fe done on Fe(ox)- Fe₃0₄ using UV-VIS titration method with 1 ,1 O-phenanthroline after digesting the sample with HCI shows 28.6 wt% Fe in the sample.

Fig. 6 presents the EDS analysis of Fe(ox) Fe-CuO_x and Fe(ox) Fe-MnO_x which is consistent with respect to the wt % of carbon, oxygen, iron, Cu and Mn in the prepared materials. iv) Surface area analysis:

Table 1 presents the results of BET Analysis of prepared materials. These textural characteristics are consistent with the results of HR-SEM and HR-TEM.

Example-Ill: Improvement in Soil Quality using Fe(ox)-Fe30₄, Fe(ox)Fe-CuO_x, and Fe(ox)Fe-MnO_x

The effect of the prepared nano materials was tested to assess the enhancement of Fe and P availability in soil. Fe-EDTA was used as a control against which all the enhancements were monitored. The Fe content of the materials used for these experiments is given in Table 2. Prior to soil application, the released profile of the prior art product (Mohr salt mediated) and product of the present invention (FeS0₄ mediated) were measured in aqueous (deionized water) solution. The release of Fe from the material prepared via FeS0₄ (286.8 mg L^"1) was more than 5 folds higher than the product prepared via the prior art Mohr salt mediated process (58 mg L^"1) (Table 2a). The soil sample used was a typical alluvial soil whose characteristics are given in Table 3. Table 2: Fe content in prepared nanomaterials and Fe-EDTA

Treatments Fe (wt %)

Fe(ox)-Fe₃0₄ 28.68±0.16

Fe(ox)Fe-MnO_x 20.1±0.15

Fe(ox) Fe-CuO_x 19.01±0.07

Fe- EDTA 3.58±0.09

Table 2a: Fe release from the two preparation pathways [Mohr salt (prior art) and FeS0₄ ( present invention)] of Fe(ox)-Fe₃0₄ in aqueous solution

Pathways Fe release (mg L^"1)

Ferrous sulphate

(present

invention) 286.8±22.14

Mohr salt (prior

art) 58±5.43

Table 3: Characteristics of the soil sample used

Soil Characteristics mean± stdev

pH 5.5±0.1

Avl P (mg kg^"1) 44.08± 1.3

Phosphatase ( ig 7.85±0.2

TKN 1.23±0.14

Urease (ig g^"1 h^"1) 16±0.3

1.42±0.02

Bulk density (g cc^" )

Fe (mg kg ¹) 142.6± 1.2 Mn (mg kg ¹) 57.7± 1.1

Cu (mg kg ¹) 9.15±0.5

The soil samples were incubated with Fe(ox) - Fe₃0₄, Fe(ox) Fe-CuO_x and Fe(ox)Fe- MnO_x @ 10 mg kg^"1. Soil samples were also incubated with 3% FeS0₄ and 10 mg kg^"1 Fe-EDTA respectively which were used as controls. The study was conducted for 90 days. The soil pH increased by from 5.5 to 5.7as compared to the initial value (5.5±0.1) under 10 mg kg^"1 Fe(ox)- Fe₃0₄ in 90 days (Fig. 7a). The soil pH also was 5.55±0.09 and 5.58±0.02 under 10 mg kg^"1 application of Fe(ox) Fe-CuO_x and Fe(ox) Fe-MnO_x respectively. On the other hand, soil pH was reduced by 1.27 times from 5.5±0.1 to 4.3±0.2 after 90 day due to application of FeS0₄. Following are the observations of Fe availability in the soil following the treatment with the prepared materials:

(a) Fe content in the soil was 142.6± 1.2 mg kg^"1.

(b) During the early stage of the study (5-45 day) Fe availability in soil increased from 168.95±2.5 mg kg^"1 to 196.95±2.8 mg kg^"1 in the FeS0₄ treated soil, which significantly reduced to 174.9±2.6 mg kg^"1 during the later stage (45 to 90 days).

(c) Fe availability in soil under Fe(ox)-Fe₃0₄treatment was lower (171.45±2.2 mg kg^"1) than FeS0₄ treatment at the end of the first 45 days, which increased significantly to 178.77±2.5 mg kg^"1 in 90 days after the treatment. This was the highest among all the treatments in regard to Fe availability in soil at the end of the study period (P=0.000, LSD=0.48) (Fig. 7a). [i.e. Fe availability is enhanced by 10.0 -14.0 mg kg^"1 in 5 to 90 days]

(d) Fe availability increased in soil treated with Fe(ox) Fe-MnO_x and Fe(ox)Fe- CuO_x application at the end of the first 45 days, but the availability of Fe reduced at the end of 90 days. [The enhancement of Fe availability by

Fe(ox)Fe-MnO_x is 10.0 - 14.5 mg kg^"1 in 5 to 90 days and by Fe(ox) Fe-CuO_x is 6 -10 mg kg^"1 in 5 to 90 days respectively ] These results demonstrate the superiority of the prepared Fe(ox)capped metal oxide nano materials with respect to Fe nutrition in soil over the conventional Fe fertilizers (FeS0₄ and Fe-EDTA).

Following are the observations on the available Mn and Cu on treatment with Fe(ox)Fe-MnO_x and Fe(ox) Fe-CuO_x:

• Mn content in the soil increased from 81.39±1.5 mg kg^"1 to 154.45±4.2 mg kg^"1 during 45 days due to application of Fe(ox)Fe- MnO_x and then decreased to 119+3.6 mg kg^"1 during 90 days (Fig. 7b). [Mn content increases by 35.0 - 40.0 mg kg- 1 in 5 to 90 days] · Cu content increased in the soil from 13.15+ 1.1 mg kg^"1 to

106.87±1.8 mg kg^"1 (45 days) but decreased later on to 98.8+1.1 mg kg^"1 due to application of Fe(ox) Fe-CuO_x @ 10 mg kg^"1, [i.e Cu content increases by 85 - 90 mg kg- 1 in 5 to 90 days]

• As compared to the starting soil characteristics (table 3), Mn availability increased by 2.06 folds due to application of Fe(ox)Fe-

MnO_x in soil, while, the Cu availability enhanced by 10.7 folds through soil incorporation of Fe(ox) Fe-CuO_x @ 10 mg kg^"1 (Fig.7 b).

Further, incorporation of Fe(ox)-Fe₃0₄ in soil resulted into substantial reduction of soil bulk density (BD) from 1.38±0.03 g cc^"1 to 1.29±0.03 g cc^"1 over 90 day. This indicates the improvement of soil porosity due to incorporation of Fe(ox)-Fe₃0₄. Soil BD also reduced from 1.40±0.03 g cc^"1 to 1.33±0.02 g cc^"1 under Fe (ox)-MnO_x (Fig 7a).

Following are the observations on the available N and Pon treatment with Fe(ox)- Fe₃0₄, Fe(ox)Fe-MnO_x and Fe(ox) Fe-CuO_x:

• N and P availability in soil significantly increased from 1.34+ 0.11 % to 7.38±0.5 % and 49.64±0.8 mg kg^"1 to 105.54±1 mg kg^"1 due to application of Fe(ox)-Fe₃0₄ (P= 0.000). • P availability reduced from 44.15± 1.1 mg kg^"1 to 40.12± 1.1 mg kg^"1 in soil due to 3% FeS0₄ application.

• Availability of N and P was also higher in Fe(ox)Fe-MnO_x and Fe(ox) Fe-CuO_x treated soil as compared to FeS0₄ (Fig.8). · Activity of important soil enzymes (urease and phosphatase) was enhanced due to incorporation of Fe(ox)-Fe₃0₄, Fe(ox) Fe-CuO_x, and Fe(ox) Fe-MnO_x@ 10 mg kg^"1 in soil. Urease activity in soil under Fe(ox)-Fe₃0₄ treatment increased by 2.0 fold as compared the basic value (Table 3) . · Phosphatase activity was also significantly higher under Fe(ox)-Fe₃0₄ treatment (27.50±0.40 μg g^"1 h^"1) as compared to Fe(ox) Fe-CuO_x (22.01±0.10 μg g^"1 h^"1), Fe(ox) Fe-MnO_x (21.20±0.05 μg g^"1 h^"1), Fe- EDTA (8.56±0.10 μg g^"1 h^"1), and the control (8.86±0.50 μg g^"1 h^"1) (P= 0.000). The detailed results are shown in figure 7 (a and b) and figure 8 respectively.

These results clearly demonstrate the positive impact on soil health when soil is treated with the prepared materials of the present invention.

Example IV: Demonstration of the effect of Fe(ox) -Fe₃0₄, Fe(ox)Fe- MnO_x, and Fe(ox) Fe-CuO_x to maintain balance in soil pH and P availability in treated soils.

In one experiment, equal amount of Fe(ox)-Fe₃0₄ and FeS0₄ were added separately in six aqueous solutions of different pH (pH 4, 5, 6, 7, 8 and 8.5).

Table 4: Effects of the Fe(ox)-Fe₃0₄ on pH with time

Fe(ox)-

Fe(ox)-Fe304 FeS0₄ Fe₃0₄ FeS0₄ Fe(ox)-Fe₃0₄ FeS0₄

PH

range 12hrs 12hrs 24 hrs 24 hrs 48 hrs 48 hrs pH4 5.05±0.03 4.3±0.02 6.02±0.03 4.3±0.02 6.78±0.03 4.3±0.02 pH5 5.72±0.03 4.8±0.02 6.18±0.03 5±0.04 6.56±0.02 5.1±0.03 pH6 6.38±0.02 5.2±0.02 6.77±0.02 5.2±0.02 6.97±0.02 5.4±0.02 pH7 7.3±0.02 5.0±0.03 7.3±0.02 5.2±0.02 7.2±0.02 5.5±0.02 pH8 8.18±0.02 4.8±0.02 8.15±0.02 5.2±0.02 8.21±0.02 5.4±0.02 pH 8.5 8.58±0.02 5.5±0.02 8.6±0.02 5.2±0.02 8.64±0.02 5.2±0.02

Following are the observations:

• pH of the acidic solutions shifted (pH: 4 shifted to 6.78 ±0.03 and 5 shifted to 6.56±0.02) towards neutral pH within 48^th hours in the presence of Fe(ox)-Fe₃0₄ (Table 4).

• pH 6 increased to 6.97±0.02 and pH 7 increased to only 7.2±0.02 in presence of Fe(ox)-Fe₃0₄ in solution.

• pH of the alkaline solutions (pH: 8 and 8.5) did not increase in the presence of Fe(ox)-Fe₃0₄ in the solution. · FeS0₄ addition to low pH solutions (pH: 4 and 5) did not change the pH considerably (pH: 4 changed to 4.3±0.02 and 5 changed to 5.1±0.03);

pH of the weakly acid, neutral and alkaline solutions (pH 6, 7, 8, and 8.5) noticeably shifted towards high acidity (pH: 6 reduced to 5.4±0.02; 7 reduced to 5.5±0.02; 8.5 reduced to 5.2±0.02) on addition of FeS0₄ to the solutions (Table 4).

In another experiment, equal amount of Fe(ox)-Fe₃0₄, Fe(ox) Fe-CuO_x, Fe(ox)Fe- MnO_x , Fe-EDTA and FeS0₄ along with one easily soluble salt of phosphorus (KH₂P0₄) were separately dissolved in deionized water in Erienmeyer flasks. All the flasks were then subjected to gentle shaking (120 rpm) in a mechanical shaker for 21 days.

Figure 9 presents the results of these experiments. The observations are as follows:

• phosphate release from KH₂P0₄ significantly enhanced from 94.13±2.3 mgL^"1 to 95.98±2.5 mgL^"1 after 21 days in presence of Fe(ox)-Fe₃0₄ followed by Fe(ox) Fe-MnO_x and Fe(ox) Fe-CuO_x (from 84.45±2.8mg L^"1 to 86.54±2.2 mg L^"1 and 16.07±1.1mg L^"1 to 45.07±1.08 mgL^"1) (P=0.000).

• phosphate release reduced in presence of FeS0₄ from 39.2±2.9 mg L^{" 1} to 5.42± 1.9 mg L^"1 at an early stage of the studyand did not change further. Fe availability was higher in presence of FeS0₄ as compared to other compounds throughout the study period (Fig. 9) (at 24 hours=308.58±7.5 mg L^"1 and at 21 day= 347.28± 6.8 mg L^"1).

• Fe availability gradually increased with time in Fe(ox)-Fe₃0₄ containing solution and was 268.53±6.4 mg L^"1 after 21 days. The increase was about 3.87 folds (Fig. 9). Similar trend of slow release of Fe was also observed in presence of Fe(ox)Fe-MnO_x and Fe(ox)Fe- CuO_x . These results thus clearly indicate that Fe(ox)-Fe₃0₄, Fe(ox)Fe- CuO_x and Fe(ox) Fe-MnO_x are capable of correcting soil acidity and thereby induce bioavailability of phosphorus in soil.

Example V: Field Trials of soil treated with Fe(ox) -Fe₃0₄, Fe(ox) Fe-MnO_x and Fe(ox) Fe-CuO_x and their impact on crop productivity

The Fe(ox)- Fe₃0₄, Fe(ox) Fe-MnO_x and Fe(ox) Fe-CuO_x were field tested on tomato. Three doses of three prepared compounds were selected for the study and compared with FeS0₄ @ 20 kg ha^"1 (recommended dose) used as control. All other agronomic management practices such as seed treatment, land preparation, fertilizer (NPK) application, and intercultural operation and pest control measures were uniformly conducted for all the treatments following the package of practice recommended by the Department of Agriculture, Govt, of Assam. The study was conducted in a randomized block design with four replicates.

Following are the results of the field trials:

• Chlorophyll content in tomato leaves was significantly high when Fe(ox)- Fe₃0₄ was applied as 2 kg ha^"1 (48.59± 0.13 mg g^"1). • The 10 kg ha^"1 dose for Fe(ox)-Fe₃0₄ also showed good chlorophyll content (47.65± 0.52 mg g^"1).

• Carotenoid content in tomato was significantly high under 5 kg ha^"1 dose of Fe(ox)-Fe₃0₄ (10.26± 0.33 mg g^"1). In addition Fe(ox)-Fe₃0₄ @ 2 and 10 kg ha^"1 also attributed high carotenoid content in tomato (7.43±0.18 and 8.61±0.05 mg g^"1) respectively (table 5).

• Maximum yield of tomato was obtained under 2 kg ha^"1 (41.67+ 1.11 ton ha^"1) followed by 5 kg ha^"1 (38.33±0.68 ton ha^"1) application of Fe(ox)- Fe₃0₄ compound (table 6), which are almost 2.49 and 2.29 folds higher than the yield obtained with 20 kg ha^"1 of FeS0₄ (16.7±0.2 ton ha^"1) application.

• Tomato yield under 2 kg ha^"1 application of Fe(ox)-Fe₃0₄ was significantly higher than the yield under 10 kg ha^"1 Fe-EDTA (20.8±0.2 ton ha^"1) application. · Tomato yield under application of Fe(ox)Fe-MnO_x and Fe(ox) Fe-CuO_x treated plots were significantly higher than Fe-EDTA or FeS0₄ treated plots (P= 0.000, LSD=0.333).

Table 5: Representation of Chlorophyll and carotenoid data in various doses of synthesized compounds in field trial

Treatment Chlorophyll Carotenoid

(mg Chi g^"1 fresh (mg carotenoid g tissue) leaf)

Control 23.65±0.42 3.33±0.21

Fe(ox)-Fe₃0₄ ^@ 10 kg ha^"1 47.65±0.52 8.61±0.05

Fe(ox)-Fe₃0₄ @ 5 kg ha^"1 38.19+0.15 10.26±0.33

Fe(ox)-Fe₃0₄ @ 2 kg ha^"1 48.59±0.13 7.43±0.18

Fe(ox)Fe-MnO_x @ 10 kg ha^"1 22.34±0.01 4.78±0.01

Fe(ox)Fe-MnO_x @ 5 kg ha^"1 34±0.07 7.05±0.05

Fe(ox)Fe-MnO_x @ 2 kg ha^"1 17.82+0.01 5.21+0.01 Fe(ox)Fe-CuO_x @ 10 kg ha^"1 24.75±0.01 4.63±0.01

Fe(ox)Fe-CuO_x @ 5 kg ha^"1 29.83±0.03 6.65±0.03

Fe(ox)Fe-CuO_x @ 2 kg ha^"1 24.34±0.02 6.95±0.01

Fe-EDTA @ 10 kg ha^"1 13.0+0.2 2.8±0.04

Fe-EDTA @ 5 kg ha^"1 15.1+0.3 3.4±0.03

Fe-EDTA @ 2 kg ha^"1 17.0+0.3 2.7±0.03

FeS0₄ @ 20 kg ha^"1 16.14+0.01 4.55±0.01

P value 0.00 0.00

LSD 0.15 0.13

Table 6: Representation of yield data after harvest in field trial

Treatment Yield (ton ha^"1)

Control 20±0.56

Fe(ox)-Fe₃0₄ @ 10 kg ha^"1 30.67+1.02

Fe(ox)-Fe₃0₄ @ 5 kg ha^"1 38.33±0.68

Fe(ox)-Fe₃0₄ @ 2 kg ha^"1 41.67+1.11

Fe(ox)Fe-MnO_x @ 10 kg ha^"1 18+0.2

Fe(ox)Fe-MnO_x @ 5 kg ha^"1 20.5±0.4

Fe(ox)Fe-MnO_x @ 2 kg ha^"1 21.4+0.3

Fe(ox)Fe-CuO_x @ 10 kg ha^"1 21+0.5

Fe(ox)Fe-CuO_x @ 5 kg ha^"1 21.5+0.3

Fe(ox)Fe-CuO_x @ 2 kg ha^"1 22±0.4

Fe-EDTA @ 10 kg ha^"1 20.8±0.2

Fe-EDTA @ 5 kg ha^"1 20.1+0.3

Fe-EDTA @ 2 kg ha^"1 20.0±0.2

FeS0₄ @ 20 kg ha^"1 16.7+0.2

P value 0.00

LSD 0.333 Example VI : Enhancement of the Expression GS1 and GOGAT Genes responsible for increased nitrogen uptake by plants treated with Fe-ox capped metal oxide nanomaterials

The effect of the Fe-ox capped metal oxide nanomaterialsof the present invention on the physiological metabolism of the treated tomato plants and one of the most vital nutrient mediated metabolic pathways (i.e., Nitrogen assimilation pathway) was targeted. The expression of GS1 and GOGAT genes essential in nitrogen assimilation in tomato leaves [treated with Fe(ox)-Fe₃0_4i Fe(ox) Fe-MnO_x and Fe(ox) Fe-CuO_x] was evaluated in comparison with control and Fe-EDTA treated plants (Fig. 10). The Fe-EDTAwas taken as positive control because it is a well known eco-friendly and effective iron fertilizer. The expressions of GS1 and GOGAT genes were assessed against a house keeping gene gapdh which are constitutive genes for the maintenance of basic cellular function; and they express in all cells of any organism under normal conditions (Kon Butte et al., 2001).

The results clearly showed that the expression of GS1 and GOGAT genes were significantly elevated in tomato treated with the said nanomaterials of the present invention : [Fe(ox)-Fe₃0_4i Fe(ox) Fe-MnO_x, and Fe(ox) Fe-CuO_x] as compared to Fe-EDTA and control. The GOGAT gene expression in tomato was higher by 0.12 unit under Fe(ox)Fe- MnO_x (T3) than Fe-EDTA (T5) treatment which was statistically significant (Fig. 10 A). The gene expression was also significantly higher by 0.05 unit under Fe(ox)-Fe₃0₄ (T2) than Fe-EDTA (T5).

Since the activity of GOGAT is highly dependent on iron containing protein Ferredoxin; the improved iron uptake in plants treated with the nanomaterials of the present invention probably activated ferredoxin, thereby, elevated GOGAT expression.

On the other hand, the expression of GS1 gene was higher by 0.23 and 0.19 units under Fe(ox) Fe-CuO_x and Fe(ox)-Fe₃0₄ (T4 and T2) respectively as compared to Fe-EDTA (T5) treatment. (Fig 10B) Thus the above demonstrates surprisingly and unexpectedly the advancement related to metal oxide based soil conditioners comprising metal(s) oxide nanomaterials which is iron oxalate capped- nano metal oxide. The said nanomaterials as exemplified above according to the advancement Fe(ox)- Fe₃0₄, Fe(ox) Fe-MnO_x and Fe(ox) Fe-CuO_x not only enhance the Fe availability in the soil for the assimilation by plants, but also positively impacts the N and P availability, improves phosphate release, controls pH of soil, reduces the bulk density of the soil thereby improving porosity as compared to conventional Ferrous Sulphate or Fe-EDTA treated soils. Further field trials have demonstrated that soils treated with Fe(ox)-Fe₃0₄, Fe(ox)Fe-MnO_x and Fe(ox) Fe-CuO_x substantially improve the yields for example of tomato with concomitant increase in their carotenoid and chlorophyll content, almost doubled the activity of soil enzymes including urease and phosphatase. They have been found to enhance the expression of GS1 and GOGAT genes in treated plants therebycontrolling the major enzymesGlutamine synthetase (GS) and glutamate synthase (GOGAT) involved in biochemical pathway of nitrogen assimilation.

It is thus possible by way of the present invention to provide novel soil conditioners comprising capped metal oxide nanomaterials which enhance the iron availability to the plants along with improved nitrogen and phosphorus availability to the plants over the conventional Fe fertilizers or soil conditioners. The said iorn oxalate capped metal oxide nanomaterials also activate genes for nitrogen assimilation, have positive impact on the soil health and maintain balance in soil pH. Hence the application of the said nanomaterials improves the crop yields significantly.

Claims

We claim :

1. Metal oxide based soil conditioner comprising nano iron oxalate capped metal oxide(s) wherein the nano iron oxalate capped metal(s) oxide comprise selectively (i) Fe(Ox)-Fe304withFe sourced from Fe salts other than Mohr salt with atleast four folds enhanced Fe release capability in soil with respect to Fe(Ox)-Fe304with Fe sourced from Mohr salt and (ii) mixed metal oxides selected from Fe(ox) Fe-MnOx and Fe(ox) Fe-CuOxinvolving said Fe(Ox)- Fe304with Fe sourcedfrom Fe salts other than Mohr salt.

2. Metal oxide based soil conditioner as claimed in claim 1 which is a reaction product of iron salts other than Mohr's salt, oxalic acid followed by reduction with

Sodium Borohydride, and optionally other metal salts at elevated temperature providingsaid caped metal oxide with its said selective Fe source with or without other metal micronutrients favouringenhancing sustained availability of metal micronutrients, N, P for plant assimilation and stabilisation in pH of treated soil in the range of 5.0 to 6.0.

3. Metal oxide based soil conditioner as claimed in anyone of claims 1or 2 wherein the ratio of iron oxalate to Fe₃0₄ are in the range from 1:0.1 to 1:1.

4. Metal oxide based soil conditioner as claimed in anyone of claims 1 to 3 comprising porous structure connected with nano ribbon like structures with uniform particle size in the range of 2-16 nm and average particle size in the range of 9 to 32 nm.

5. Metal oxide based soil conditioner as claimed in anyone of claims 1 to 4 wherein the aspect ratio of the particles of Fe(ox)-Fe304 is 15-20, Fe(ox)Fe- MnO_x is 1 to 4 and Fe(ox) Fe-CuO_x is 10-15. 6. Metal oxide based soil conditioner as claimed in anyone of claims 1 to 5 wherein surface area, pore radius and pore volume of the particles are as hereunder: Table 1. Surface area, pore radius, pore volume of the prepared materials

Characteristics Fe(ox)- Fe₃0₄ Fe(ox) Fe-MnO_x Fe(ox) Fe-CuO_x surface area 53.0 to 55.7 76.1 to 79.2 152.1 to 155.

6

Pore Radius (A) 17.1 to 18.3 17.8 to 19.2 15.5 to 16.26

Pore Volume (ccg ¹) 0.061 to 0.072 0.123 to 0.141 0.076 to 0.092

7. Metal oxide based soil conditioner as claimed in anyone of claims 1 to 6 further characterised by i) The XRD pattern of Fe(ox)-Fe304, Fe(ox) Fe-CuOx, and Fe(ox) Fe-MnOx showing presence of orthorhombic iron oxalate and magnetite Fe304; orthorhombic Fe(C204), 2H20, Fe304, and CuO; and orthorhombic Fe(C204).2H20, Fe304, and MnO; ii) FT-IR having peaks of 1685, 1412, and 563 cm-1 for Fe(ox)-Fe304, 1691, 1360, 1319 and 502 cm-1. for Fe(ox) Fe-MnOx and 1672 and 495 cm-1 for Fe(ox) Fe-CuOx indicating presence of Oxalate; iii) SEM and TEM showing material as porous connected with nano ribbon like structures; iv) EDS showing the presence of Carbon 17.54%, oxygen 56.06% and iron 26.4% in Fe(ox)-Fe304, Carbon 13.52%, oxygen 63.0%, iron 19.3%, and copper 4.13% in Fe(ox)Fe-CuOx Carbon 16.1%, oxygen 58.4%, iron 20.7%, and manganese 4.73% in Fe(ox) Fe-MnOx ; v) BET showing pore radius of 18.432 for Fe(ox) - Fe304, 19.283 for Fe(ox)Fe- CuOx and 16.363 for Fe(ox) Fe-MnOx and pore volume of 0.071 for Fe(ox)- Fe304, 0.092 for Fe(ox) Fe-CuOx and 0.141 for Fe(ox) Fe-MnOx.

8. Metal oxide based soil conditioner as claimed in any of the preceding claims wherein soils treated with (I) Fe(Ox)-Fe₃0₄ i. enhances Fe availability by 10.0 -14.0 mg kg^"1 in 5 to 90 days ii. increases N and P availability in soil from 1.3 % to 7.5 % and 50 mg kg - 1 to 110 mg kg- 1 iii. enhances activity of soil enzymes urease and Phosphatase from 19.0 to

32.0 μg g-1 and 13.0 to 27.0 μg g^"1 respectively;

(II) Fe(ox)Fe-MnOx enhances Fe availability by 10.0 - 14.5 mg kg- 1 in 5 to 90 days and Mn content increases by 35.0 - 40.0 mg kg- 1 in 5 to 90 days; v. increases N and P availability in soil from 1.3 % to 5.3 % and 46 mg kg - 1 to 90 mg kg- 1 vi. enhances activity of soil enzymes urease and Phosphatase from 18.0 to 27.0 μg g-1 and 11.0 to 21.0 μg g-1 respectively. and

(Ill) Fe(ox)Fe-CuOx iv. enhances Fe availability increases by 6 -10 mg kg- 1 in 5 to 90 days and Cu content increases by 85 - 90 mg kg- 1 in 5 to 90 days; v. increases N and P availability in soil from 1.3 % to 5.0 % and 45 mg kg - 1 to 80 mg kg- 1 respectively enhances activity of soil enzymes urease and phosphatase from 17.0 to 25.0 μg g-1 and 10.0 to 20.0 μg g-1 respectively.

9. Metal oxide based soil conditioner as claimed in anyone of the preceding claims when used for treatment of soil enhances the Fe availability in the range of 19 to 29 %.

10. Metal oxide based soil conditioner as claimed in anyone of preceding claims significantly reduces the bulk density of treated soil at least by 7%.

11. Metal oxide based soil conditioner as claimed in any of the preceding claims wherein soils treated with the said metal oxides increase tomato yields at least by 80 to 90% as compared to FeS04 and 70 to 80 % as compared to Fe-EDTA with concomitant increase in carotenoid and chlorophyll content at least by 85 to 90% and 90 to 95%, respectively as compared to soil conventionally treated with Ferrous Sulphate and Fe-EDTA.

12. Metal oxide based soil conditioner as claimed in any of the preceding claims wherein the soils treated with the said metal(s) oxide enhances the

expression of GS1 and GOGAT genes in tomato as compared to conventional Fe-EDTA treated soils.

13. Use of Metal oxide based soil conditioner as claimed in anyone of the

preceding claims for conditioning soil including selectively one or more of : i) stabilising soil pH, ii) increasing iron availability in soil without increasing the acidity, iii) reduction of soil bulk density, iv) increasing N and P availability in soil ; v) enhancing activity of soil enzymes such as urease and phosphatase .

14. A process for enriched availability of plant nutrients in soil for enhanced plant growth comprising treating the soil with nano metal oxide based soil conditioners as claimed in anyone of preceding claims 1 to 12.

15. A process as claimed in claim 15 comprising steps of: (i) preparing the field by light secondary ploughing followed by levelling of the soil surface prior to planting ;

(ii) transplanting nursery raised seedlings ;

(iii) treating @ 2 to 10 kg ha^"1 the root zone of the transplanted seedlings with nano metal oxide soil conditioners dispersed in aqueous solution after 2 to 3 days after transplantation of tomato seedlings;

(iv) applying NPK after the incorporation of the nano metal oxide based soil conditioners;

(v) carrying out routine agricultural practices such as weeding, cleaning, pest control measures, and harvesting .

16. A process as claimed in anyone of preceding claims for treating soil for tomato cultivation with said soil conditioners selected from one or more of [ Fe(ox)-Fe304, Fe(ox) Fe-MnOx, and Fe(ox) Fe-CuOx] for enhanced conditioning of soil as compared to Fe-EDTA and control including: i. Fe(ox)Fe-MnOx treatment for raising the expression of GOGAT genes in tomato by 0.12 units as compared to Fe-EDTA treatment

ii. Fe(ox)-Fe304 treatment for raising the expression of GOGAT genes by 0.05 unit as compared to Fe-EDTA

iii. Fe(ox) Fe-CuOx and Fe(ox)-Fe304 treatment for raising the the

expression of GS1 gene by 0.23 and 0.19 units respectively as compared to as compared to Fe-EDTA treatment.

17. A process for manufacture of metal oxide based soil conditioner as claimed in anyone of preceding claims 1 to 12 comprising steps of:

(i) reacting ferrous salts other than Mohr salt and oxalic acid in aqueous reaction medium at room temperature; (ii) reduction with Sodium

Borohydride to obtain Fe(ox)-Fe(0); (iii) optionally for providing mixed metal oxide , i nsitu reacting formed Fe(ox)-Fe(0) with metal salts to produce the mixed metal oxides at elevated temperature;

(iv) separating and drying the product; 18. A process as claimed in claim 17 wherein the molar ratio of ferrous salt : oxalate is in the range of 0.3 to 3, and said optional step for providing mixed metal oxide comprise further reacting with copper sulphate and potassium permanganate for the preparation of Fe(ox) Fe-CuO_x and Fe(ox) Fe-MnO_x respectively and wherein the molar ratio of ferrous salt : copper in mixed Fe(ox) Fe-CuO_x is 0.5 to 3, and molar ratio of ferrous salt : manganese in mixed nano Fe(ox) Fe-MnO_x is in the range of 0.5 to 3.