Description:FIELD OF THE INVENTION
The present invention relates to a rapid method for determining available phosphorus in soil. The present invention also relates to the kit for the determination of available phosphorus in soil. The method of the present invention is user friendly, environment friendly and cost effective.

BACKGROUND OF THE INVENTION
Phosphorus is an essential nutrient for plant growth and is one of the three primary macronutrients, along with nitrogen and potassium. It plays a crucial role in various plant processes such as energy transfer, cell division, and DNA synthesis. Phosphorus is commonly found in soil as inorganic phosphates, which are derived from natural mineral deposits and fertilizer applications.
The availability of phosphorus in soil depends on several factors, including soil pH, organic matter content, and the presence of minerals that can bind phosphates and make them less available to plants. In general, soil pH between 6.0 and 7.5 is optimal for phosphorus availability. However, in highly acidic soils (pH below 6.0), aluminium and iron can bind with phosphates and make them unavailable to plants. In alkaline soils (pH above 7.5), calcium can also bind with phosphates, reducing their availability. To ensure adequate phosphorus levels in the soil, farmers and gardeners often add phosphorus-containing fertilizers, such as monoammonium phosphate or diammonium phosphate. However, it's important to be mindful of applying too much phosphorus, as this can lead to excess levels in the soil and potentially harm the environment by promoting the growth of harmful algae in waterways.
Phosphorus testing in soil is used to determine the amount of available phosphorus in soil, which is an essential nutrient for plant growth. Phosphorus is a critical component of DNA, RNA, ATP, and various other cellular molecules, and is needed in relatively small amounts by plants. The precision measurement of available phosphorus provides information for proper fertilizer management and soil fertility.
There are several methods for testing soil phosphorus, including:
Chemical extraction methods: Chemical extraction methods, such as the Bray-1 or Mehlich-3 tests, which involve extracting the soil with a solution that dissolves the available phosphorus. The extracted solution is then analyzed to determine the concentration of phosphorus. The chemical extraction methods are expensive, require more time and use liquid chemicals, thereby making the extraction methods inconvenient for users.

Plant-based methods: Plant-based methods, such as the P-index or critical value approach, involve growing crops in the soil and measuring the concentration of phosphorus in the plant tissue. However, these are basic methods for qualitative tests and therefore, there is no precision testing.

Colorimetric methods: Colorimetric methods involve adding a reagent to a soil sample, which reacts with the available phosphorus to produce a color change. The color change is then compared to a standard to determine the concentration of phosphorus. These methods employ chemicals which are not stable, therefore, tests have to be conducted immediately. This also leads to wastage of chemicals.
The availability of phosphorus in soil depends on several factors, including soil pH, organic matter content, and the presence of minerals that can bind phosphates and make them less available to plants. In general, soil pH between 6.0 and 7.5 is optimal for phosphorus availability. However, in highly acidic soils (pH below 6.0), aluminium and iron can bind with phosphates and make them unavailable to plants. In alkaline soils (pH above 7.5), calcium can also bind with phosphates, reducing their availability. To ensure adequate phosphorus levels in the soil, farmers and gardeners often add phosphorus-containing fertilizers, such as monoammonium phosphate or diammonium phosphate. However, it's important to be mindful of applying too much phosphorus, as this can lead to excess levels in the soil and potentially harm the environment by promoting the growth of harmful algae in waterways.
Many reagents are used for testing phosphorus in soil.
Molybdenum Blue Method uses ammonium molybdate and a reducing agent, such as ascorbic acid, to form a blue complex with phosphorus in the soil. The intensity of the blue color is proportional to the amount of phosphorus present.
The Ascorbic Acid Method uses ascorbic acid to reduce phosphorus in the soil, which can then be measured spectrophotometrically. This method is simple and inexpensive, but it can be affected by other reducing agents present in the soil.
The Bray Method uses a mixture of sulfuric and hydrochloric acids to extract phosphorus from the soil. The extracted phosphorus can then be measured colorimetrically using the ascorbic acid method or the molybdenum blue method.
Olsen Method is based on the reaction of phosphorus with ammonium molybdate, which forms a yellow complex that can be measured spectrophotometrically. This method is simple and widely used, but it may not be as accurate as other methods.
Calcium Hydroxide Method involves adding calcium hydroxide to the soil to release phosphorus, which can then be measured colorimetrically. This method is simple and inexpensive, but it may not be as accurate as other methods.
N.J. Barrow et al (1976) “Sodium bicarbonate as an extractant for soil phosphate effects of the buffering capacity of a soil for phosphate” discloses an index of the buffering capacity for phosphate of a group of soils obtained by measuring adsorption of phosphate from dilute solutions of calcium chloride. The effect of buffering capacity on the amount of phosphate initially displaced by solutions of sodium bicarbonate and on the amount of secondary adsorption from bicarbonate was then studied. These two effects were separated using a regression procedure in which the soil: solution ratio was the independent variable.
Further, the Olsen method for soil available phosphorus by FAO discloses that Phosphorus (P) exists in the soil as organic and inorganic forms. The inorganic P forms are more available for plant uptake than the other forms. Inorganic P forms are primarily mixtures of aluminium (Al-P), iron (Fe-P), and calcium (Ca-P) phosphates; the relative percentages between these three forms are a function of soil pH, with higher percentages of Al-P and Fe-P in acid soils, and higher percentages of Ca-P in neutral to alkaline soils (Jones, 2001). It discloses soil analysis of P: a) total analysis and b) fractional analysis. The P-Olsen corresponds to the second group. The fractions of this element present in the soil must be related to the response of plants to the application of a phosphate fertilizer. There are numerous methods for extracting P fractions with different sets of generated values. However, these only have meaning when they are associated with the response of the plants. In the Olsen method, phosphorus is extracted using a 0.5 M NaHCO3 solution adjusted at a pH of 8.5.
In view of the above drawbacks, there is a requirement of testing method of available phosphorus which is user friendly, time effective, cost effective and environment friendly.

OBJECT AND SUMMARY OF THE INVENTION
To obviate the drawbacks in the existing state of the art, the main object of the present invention is to provide a rapid method for determining available phosphorus in soil.
Another object of the present invention is to provide a kit for the determination of available phosphorus in soil.
Yet another object of the present invention is to provide a rapid, user friendly, environment friendly and cost effective method and a kit for determining available phosphorus in soil.

Accordingly, in an aspect of the present disclosure, there is provided a rapid method for determining available phosphorus in soil, said method comprises extraction of available phosphorus from soil to obtain soil extract and then quantification of available phosphorus in the soil extract using test reagents. The method of the present invention is also referred to herein as “Powder Method”.
The method of the present invention comprises extraction of the soil phosphorus with a universal extractant in specific ratio to obtain soil extract. The soil extract is then treated with the reagents of the present invention and determination of available phosphorus in soil is done on the basis of colour developed using a colorimeter device.
The reagents of the present invention are in powder form and stable for up to 3 months, thus facilitating easy handling, avoiding wastage and making the method of available phosphorus determination cost-effective.
In another aspect of the present disclosure, there is provided a kit for rapid determination of available phosphorus in soil.
These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF DRAWINGS
In order to more clearly illustrate the technical solution of the present invention, the drawings used in the description will be briefly introduced below. For a person skilled in the art, without inventive effort, further figures can be obtained from these figures.
Fig. 1 is a flow chart of the method for detecting the content of available phosphorus in soil in a sugarcane area provided by the invention.
Fig. 2 depicts spectra comparison of powder method and Olsen method.
Fig. 3 depicts the absorbance at red wavelength and the concentrations of potassium dihydrogen phosphate ranging from 0 to 0.8 ppm.
Fig. 4 shows validation data of powder method using Olsen’s method as standard.

DETAILED DESCRIPTION OF THE INVENTION WITH NON-LIMITING EMBODIMENTS, EXAMPLES AND ILLUSTRATIONS
Those skilled in the art will be aware that the present disclosure is subject to variations and modifications other than those specifically described. It is to be understood that the present disclosure includes all such variations and modifications. The disclosure also includes all such steps, features, compositions, and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any or more of such steps or features.

The terms “comprise” and “comprising” are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as “consists of only”.

Throughout this specification, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of element or steps but not the exclusion of any other element or step or group of element or steps.

Ratios, concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the
numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited.

In an embodiment of the present disclosure, there is provided a rapid method for determining available phosphorous in soil, the method comprises extraction of available phosphorus from soil to obtain soil extract and then qualification of phosphorus in the soil extract using test reagents. The quantitative determination of available phosphorus is carried out with spectroscopic method based on colour development. These methods are based on the principle that, in an acid molybdate (ammonium molybdate) solution containing orthophosphate ions, phosphomolybdate complex is formed, which can be reduced by ascorbic acid or other reducing agents (e.g. SnCl2) in the presence of potassium antimony tartrate to form a blue coloured heteropolymolybdic complex. Antimony accelerates the development of the blue colour and stabilizes it for up to 24 hours, and no interference of Si should be expected.

As shown in Figure 1, the method of the present invention comprises extraction of the soil phosphorus with a universal extractant in specific ratio. The ratio of soil: universal extractant ranges from 1:8 to 1:12 to obtain a clear filtrate, referred to as soil extract. The charcoal is added in the soil-extractant solution. The soil extractant solution is kept for a specific period of time to obtain clear filtrate of soil extract. The soil extract is then treated with the reagents of the present invention and determination of available phosphorus in soil is done on the basis of colour developed using a colorimeter device.

In an embodiment of the present disclosure, there is provided a universal extractant, comprising Sodium Sulphate, Sodium Hydrogen Carbonate and a buffer to maintain pH of the universal extractant.

In an embodiment of the present disclosure, the universal extractant comprises 0.374 M Sodium Sulphate, 0.45 M Sodium Hydrogen Carbonate (0.45 M) and an alkali to maintain the pH between 8 to 9. The universal extractant is mixed in distilled water q.s. to make a universal extractant solution.

In an embodiment of the present disclosure, the ratio of soil: universal extractant is 1:10.

In an embodiment of the present disclosure, the pH of universal extractant solution ranges between 8.2 to 8.7.

In an embodiment of the present disclosure, the alkali solution is preferably Sodium Hydroxide.

In an embodiment of the present disclosure, the specific period of time to keep soil extractant solution to obtain clear filtrate of soil extract ranges from 5 min to 15 min.

In an embodiment of the present disclosure, the test reagents comprises Powder A, Powder B and Powder C.

In an embodiment of the present disclosure, the Powder A comprises Boric Acid, Adipic acid, Potassium Hydrogen Sulphate and Potassium Antimony Tartrate; the Powder B comprises Ammonium Heptamolybdate Tetrahydrate and Sodium Metabisulphite; and the Powder C comprises Ascorbic acid and Sodium Chloride.
In a tenth embodiment, the Powder A comprises Boric Acid (0.2000g), Adipic acid (0.1124g), Potassium Hydrogen Sulphate (0.6845g) and Potassium Antimony Tartrate (0.0002g); the Powder B comprises Ammonium Heptamolybdate Tetrahydrate (0.0096g) and Sodium Metabisulphite (0.0187g); and the Powder C comprises Ascorbic acid (0.0084g) and Sodium Chloride (0.0592g).

In an embodiment of the present disclosure, the level of detection of available phosphorus is 0.02 ppm.

In an embodiment of the present disclosure, the level of quantification of available phosphorus is 0.06 ppm.

Accordingly, the rapid method for determining available phosphorus in soil of the present invention comprising the steps of extraction of available phosphorus from soil to obtain soil extract. The extraction comprises mixing soil and a universal extractant solution in a tube in specific ratio to obtain a solution of soil and universal extractant, wherein said universal extractant comprises Sodium Sulphate, Sodium Hydrogen Carbonate and an alkali. Charcoal is added in specific quantity and the resultant solution is shaken for 5 to 10 mins. The specific quantity of charcoal to be added ranges between 15% to 35% of the soil. In a specific non-limiting embodiment, the specific quantity of charcoal 20% of the soil.

The soil extract is treated with the reagents of the present invention. The soil extract is diluted by mixing with distilled water in a specific ratio. The specific ratio of soil extract and distilled water is 1:4. The reagents are added one by one in the diluted soil extract. The Powder A is added followed by Powder B, and then Powder C. Resultant solution is then kept still for 10 min. for colour development and reading is taken at red wavelength using LED based colorimeter.

In a non-limiting example, 1.5 g air-dry soil was weighed and transferred into a Tarson's tube. 15 mL of universal extractant solution and 0.3 g of charcoal was added to obtain soil-extractant solution. The soil-extractant solution was shaken for 10 min and then filtered using Whatman filtration paper no. 42. 2 ml clear filtrate was taken and made up the volume to 10 ml with distilled water. Powder A was added, and the tube was shaken till the powder dissolved. Powder B was added, and shook the tube till the powder dissolved. Powder C was added, and shook the tube till the powder dissolved. After 10 minutes, colour developed and readings were taken in an LED-based colorimeter device at red wavelength.

The UV spectral scans of the soil sample obtained from both the Powder Method of the present invention and Olsen’s Method were stacked as shown in Figure 2. The absorbance values plotted here are the mean of 5 repetitions from each method. It is clear that from both the methods, phosphorus is being detected at the appropriate wavelength i.e., around 880 nm. The present method shows good specificity despite the fact that a soil sample has been considered which contains a lot of variability and interferences.

Example 1: Linearity of Phosphorus Testing by the present invention:
Linearity is an important criterion for any analytical procedure as it shows the ability to obtain test results which are directly proportional to the concentration (amount) of analyte. The absorbance at red wavelength and the concentrations of potassium dihydrogen phosphate ranging from 0 to 0.8 ppm were found to have a linear relationship as shown in the Table 1 and Fig. 3. The absorbance values are actually the mean of three replicates. The curve was fitted using simple linear regression which gave the equation: Absorbance = 0.283 * [concentration of potassium dihydrogen phosphate] + 0.00232. The data of the linearity curve and parameters of the curve are shown in Tables 1 and 2 respectively.

Table 1: Data for the linearity curve of powder method
Concentration (ppm) Mean Absorbance ± SD^
0.0 0.0000 ± 0.0000
0.2 0.0653 ± 0.0002
0.4 0.1119 ± 0.0008
0.6 0.1700 ± 0.0015
0.8 0.2309 ± 0.0050
SD - Standard Deviation

Table 2: Parameters of the linearity curve
Slope Intercept Regression Coefficient (R2)
0.283 0.00232 0.998

Example 2: Accuracy of Phosphorus Testing by the present invention:
Accuracy becomes important for phosphorus content prediction as this leads to recommending the most appropriate fertiliser content for the farmers, which in turn avoids wastage of fertiliser. The accuracy of the method was estimated by calculating the root mean square error (RMSE), bias and standard error of prediction (SEP) (Table 3 and 4).

Table 3: Accuracy of Phosphorus Testing
SOIL Olsen’s Method Present Method Error Error Squared
1 27.59 24.25 -3.34 11.1556
2 33.89 32.4 -1.49 2.2201
3 36.3 35.56 -0.74 0.5476
4 32.63 29.85 -2.78 7.7284
5 15.11 14.03 -1.08 1.1664
6 9.09 9.86 0.77 0.5929
7 13.09 14.79 1.7 2.89
8 18.43 22.07 3.64 13.2496
9 27.38 30.6 3.22 10.3684
10 6.14 8.34 2.2 4.84
11 40.52 41.54 1.02 1.0404
12 17.87 18.43 0.56 0.3136
13 20.45 17.86 -2.59 6.7081
14 27.18 30.04 2.86 8.1796
15 14.88 13.56 -1.32 1.7424
16 25.01 28.96 3.95 15.6025
17 27.25 27.97 0.72 0.5184
18 10.76 11.11 0.35 0.1225
19 12.17 12.82 0.65 0.4225
20 12.79 14.7 1.91 3.6481
21 14.93 17.32 2.39 5.7121
22 17.18 21.55 4.37 19.0969
23 5.89 6.05 0.16 0.0256
24 9.04 10.28 1.24 1.5376
25 8.69 11.14 2.45 6.0025

RMSE measures the error of the powder method in predicting phosphorus content as compared to the standard method. Bias tells about the tendency of powder method to overestimate or underestimate the phosphorus content. SEP gives the error when the phosphorus content for the powder method is predicted using the regression line. These parameters as a whole provide an insight into how much deviation or error is shown in the powder method when compared to the standard method. This analysis has been performed on 25 soil samples collected from various parts of India. The formulae for calculating these parameters are as follows:

Table 4: Error statistics of powder method
Root Mean Square Error (RMSE) (ppm) Bias (ppm)
Methodical Error Standard Error of Prediction (SEP) (ppm)
±2.24 0.83 2.10

As evident from Table 4, the low values of RMSE, bias and SEP support the fact that the powder method produces results that do not vary much when compared to the standard method.
Recovery of both the methods - Olsen’s and Powder were compared in the Tables 5A and 5B below:
Table 5A: Powder Method Recovery
Added (ppm) Found ± SD RSD % Mean Recovery ± SD
0.2 0.1891 ± 0.0004 0.19 94.54 ± 0.18
0.4 0.4137 ± 0.0008 0.20 103.42 ± 0.21
0.6 0.5984 ± 0.0020 0.34 99.73 ± 0.34
0.8 0.7968 ± 0.0021 0.26 99.60 ± 0.26

Table 5B: Olsen Method Recovery
Added Found ± SD RSD % Mean Recovery ± SD
0.2 0.1967 ± 0.015 7.65 98.33 ± 7.52
0.4 0.391 ± 0.012 3.14 97.75 ± 3.07
0.6 0.595 ± 0.004 0.73 99.17 ± 0.73
0.8 0.805 ± 0.009 1.06 100.625 ± 1.07

Example 3: Precision of Phosphorus Testing by the present invention:
The precision of the method was analysed from data obtained over different days and by different analysts as shown in the Table 6:
Table 6: Precision of Phosphorus Testing by the present invention
Precision Added (ppm) Found ± SD (ppm) RSD% (coefficient of variance)
Inter-Day
Same Analyst (days 1 & 2) 0.2 0.211 ± 0.003 1.27
0.4 0.4168 ± 0.004 1.05
0.6 0.6167 ± 0.026 4.2
0.8 0.7788 ± 0.025 3.27
Inter-Day
Analysts 1 & 2 (days 1 & 2) 0.2 0.2145 ± 0.008 3.56
0.4 0.4008 ± 0.018 4.55
0.6 0.59545 ± 0.004 0.7
0.8 0.8018 ± 0.007 0.88
Intra-Day
Different tests (same analyst, day 1) 0.2 0.2086 ± 0.006 2.92
0.4 0.4289 ± 0.013 2.97
0.6 0.6262 ± 0.012 1.99
0.8 0.7597 ± 0.002 0.21

The limit of detection (LOD) of the present invention was found using the relation:
LOD = 3.3(σ/S)
where σ is the standard deviation of the y-intercept of the regression line and S is the slope of the analytical curve. The curve shown in the linearity section was used for these calculations.
The LOD was found to be 0.02 ppm.

The limit of quantification (LOQ) was found using the relation:

LOQ = 10(σ/S)
The LOQ was found to be 0.06 ppm.

Example 4: Range of Phosphorus Method of the present invention:
The concentration range used for this validation procedure was 0 ppm to 0.8 ppm of potassium dihydrogen phosphate (Fig. 4).

In an embodiment of the present disclosure, there is provided a kit for conducting test for determining available phosphorus in soil. The kit comprises universal extractant, reagents comprising pre-weighed sachets of Powder A, Powder B and Powder C. The universal extract comprises Sodium Sulphate, Sodium Hydrogen Carbonate and an alkali. The Powder A comprises Boric Acid, Adipic acid, Potassium Hydrogen Sulphate and Potassium Antimony Tartrate. The Powder B comprises Ammonium Heptamolybdate Tetrahydrate and Sodium Metabisulphite. The Powder C comprises Ascorbic acid and Sodium Chloride.

More specifically the kit comprises the universal extract comprising Sodium Sulphate (0.374 M), Sodium Hydrogen Carbonate (0.45 M) and Sodium Hydroxide; charcoal; the Powder A comprising Boric Acid (0.2000g), Adipic acid (0.1124g), Potassium Hydrogen Sulphate (0.6845g) and Potassium Antimony Tartrate (0.0002g); the Powder B comprises Ammonium Heptamolybdate Tetrahydrate (0.0096g) and Sodium Metabisulphite (0.0187g); the Powder C comprises Ascorbic acid (0.0084g) and Sodium Chloride (0.0592g); and distilled water.

The kit further comprises beaker, filter papers, measuring cylinder and a simple LED based colorimeter. The kit enables testing even on field with no help of qualified or trained personnel.

Advantages of the rapid method of the present invention for determining available phosphorus in soil:
- Existing methods such as Olsen’s method requires freshly prepared liquid test solutions. Handling liquid reagents is a hassle and dangerous. Reagents of present invention are in powder form, stable, and provided in easy-to-handle sachets.
- Existing methods use multiple reagents to obtain clear extract of soil, causing handling issues and increasing cost of the test methods. Present invention uses simpler reagents, i.e. Sodium Sulphate and Sodium Hydrogen Carbonate to obtain clear filtrate.
- Existing methods use reagents which are prepared in solution form just before the testing. Present invention provides ready to use reagents which are stable for up to 3 months.
- Reagents prepared are for multiple tests in the existing methods are when remains unutilised, leads to wastage and eventual environmental contamination. Kit of the present invention provides accurately pre-weighed sachets required for testing per sample, hence cause no or minimal waste.
- Existing methods take testing time of 2 hr 2.5 hr for testing the available phosphorus in soil extract, while the choice of reagents and ready to use powder form reduces the time for up to 35 min.
- Existing methods are tedious and require well trained laboratory personnel to conduct the test. Any person can conduct the test by the present method without any training.
- Existing methods require accurate lab apparatus and sophisticated instruments such as UV-Vis Spectrophotometer, thereby requiring huge operational cost. Present invention provides a kit comprising beaker, filter papers, measuring cylinder and a simple colorimeter, enabling testing even on field at a low cost.
, Claims:We claim:
1. A rapid method for determining available phosphorus in soil, said method comprising the steps of:
(i) extraction of available phosphorus from soil to obtain soil extract, said extraction comprises
(a) preparing a universal extract solution by mixing a universal extractant in distilled water, wherein said universal extractant comprises Sodium Sulphate, Sodium Hydrogen Carbonate and an alkali,
(b) mixing soil and the universal extractant solution in a tube in specific ratio to obtain a solution of soil and universal extractant,
(c) adding and mixing charcoal in the solution of step (a) in specific quantity and shaking the solution for specific period of time,
(d) filtering the solution of step (b) to obtain clear filtrate referred to as soil extract; and
(ii) quantification of available phosphorus in the soil extract using powdered test reagents, said quantification comprises the steps of
(a) diluting the soil extract by mixing with distil water in specific ratio to obtain diluted soil extract,
(b) adding a Powder A to the diluted soil extract of step (a), wherein said Powder A comprises Boric Acid, Adipic acid, Potassium Hydrogen Sulphate and Potassium Antimony Tartrate,
(c) adding a powder B to the diluted soil extract of step (b), wherein said Powder B comprises Ammonium Heptamolybdate Tetrahydrate and Sodium Metabisulphite,
(d) adding a Powder C to the diluted soil extract of step (c), wherein said Powder C comprises Ascorbic acid and Sodium Chloride,
(e) Keeping the diluted soil extract of step (d) for specific period of time for colour development,
(f) Measuring the reading of the coloured diluted soil extract of step (e) at red wavelength using LED based colorimeter,
(g) Calculating the available phosphorus using known formula,
wherein said method is time-efficient, cost-effective, user friendly showing level of detection of available phosphorus as 0.02 ppm and level of quantification of available phosphorus as 0.06 ppm.
2. The method as claimed in claim 1, wherein the universal extract comprises Sodium Sulphate (0.374 M), Sodium Hydrogen Carbonate (0.45 M) and Sodium Hydroxide.
3. The method as claimed in claim 1, wherein said Powder A comprises Boric Acid (0.2000g), Adipic acid (0.1124g), Potassium Hydrogen Sulphate (0.6845g) and Potassium Antimony Tartrate (0.0002g); said Powder B comprises Ammonium Heptamolybdate Tetrahydrate (0.0096g) and Sodium Metabisulphite (0.0187g); and said Powder C comprises Ascorbic acid (0.0084g) and Sodium Chloride (0.0592g).
4. The method as claimed in claim 1, wherein said specific ratio of soil and a universal extractant ranges from 1:8 to 1:12.
5. The method as claimed in claim 4, wherein said specific ratio of soil and a universal extractant ranges from 1:10.
6. The method as claimed in claim 1, wherein said specific quantity of the charcoal ranges between 15% to 35% of the soil.
7. The method as claimed in claim 1, wherein said alkali is Sodium Hydroxide.
8. The method as claimed in claim 1, wherein said specific period of time for shaking is 5 min to 10 min.
9. The method as claimed in claim 1, wherein said specific ratio of soil extract and distil water is 1:4.
10. The method as claimed in claim 1, wherein the specific period of time for colour development is 10 min.
11. A kit for determining available phosphorus in soil, said kit comprises
- A universal extractant, said universal extractant comprising Sodium Sulphate (0.374 M), Sodium Hydrogen Carbonate (0.45 M) and an alkali to maintain pH between 8 to 9,
- Powdered test reagents comprising Powder A, Powder B and Powder C, wherein the Powder A comprises Boric Acid, Adipic acid, Potassium Hydrogen Sulphate and Potassium Antimony Tartrate; the Powder B comprises Ammonium Heptamolybdate Tetrahydrate and Sodium Metabisulphite; and the Powder C comprises Ascorbic acid and Sodium Chloride,
- Charcoal, and
- distilled water.
12. The kit as claimed in claim 11, wherein said Powder A comprises Boric Acid (0.2000g), Adipic acid (0.1124g), Potassium Hydrogen Sulphate (0.6845g) and Potassium Antimony Tartrate (0.0002g); said Powder B comprises Ammonium Heptamolybdate Tetrahydrate (0.0096g) and Sodium Metabisulphite (0.0187g); and said Powder C comprises Ascorbic acid (0.0084g) and Sodium Chloride (0.0592g).
13. The kit as claimed in claim 11, wherein said alkali is Sodium Hydroxide.
14. The kit as claimed in claim 11, wherein said kit further comprises beaker, filter papers, measuring cylinder and a simple LED colorimeter.