These tests must be calibrated for the particular soil type by plant response to learn the sufficient test concentration

Please check these researchgate links and PDF attachments for said query.

https://www.researchgate.net/publication/232985043_Universal_soil_extractants_Their_composition_and_use

https://www.researchgate.net/publication/202860289_Soil-phosphorus_extraction_methodologies_A_review

Article Universal soil extractants: Their composition and use

Article Soil-phosphorus extraction methodologies: A review

Please check this PDF attachment also.

These tests must be calibrated for the particular soil type by plant response to learn the sufficient test concentration

 Good article on M3 extractant for mine soils

Should we consider olsen's extractant as the universal extractant for P in all type of soil?

No , in majority of cases , we use  Brays method fro acid soils and Olsen  for alkaline soils . So far , we havent come across with such extractant...? i agree with Paul, we need calibration first with soil test -crop response as basic premise of such concept

Probably, Olsen (NaHCO3 0.5M) is the most widely method in P extraction for ROUTINE fertility purposes, although it was initially proposed for neutral and alkaline soils.

In all our experiments with plants, with acid, or neutral, or alkaline, or volcanic (and so on) soils, Olsen extraction shows to be the more consistent method.

Thanks Dr. João Coutinho for clarification on Olsen extractant

Dear Dr. Naik,

Although Olsen et al. (1954) originally developed 0.5 M Sodium Bicarbonate (pH 8.5) extraction method to correlate crop response to fertilizer in calcareous soils, it has been found applicable to soils that are mildly acidic to alkaline pH. Having worked for more than one decade in the acidic soil region of India, my personal experience is: Olsen extractant gives satisfactory measures of P availability and correlation with crop response in acidic soils of pH range 5.5 to 6.0.

Thanks Dr. Kundu

I agree with Dr. Kundu Sir. I am working with acid soils of eastern region of India and getting good results with Olsen compared to Bray.

 Dear colleagues, good discussion on univeral extractant and Olsen's reagent.As I understand, the universal extractant should not only  be used in a wide range of soil conditions but it should also be used for analysis of macronutrients ,micronutrients and pollutant elements.Now the universal reagents and multinutrient extractants are equated together.Univeral soil extract is a reagent that can be used to extract more than one class of elements,and/or ions from a soil.Normally ,the extractant in a single step removes P as well as the major cations like K,Ca and Mg and micro nutrients,B,Cu,Fe,Mn,Zn,the heavy metals As,Se,Pb etc. and ions such as NO3,NH4 and SO4.The details are available in the paper mentioned by Arvind Singh(Jones !990).Another good paper is by Van Raij(1994).New diagnostic technologies,universal soil extractants.Commun.Soil Sci.Plant.Anal.25,799-816.The important  univeral/multinrient extractants are Mehlich no.3(used in acid to alkaline and organic soils,AB-DTPA (recommened for alkaline soils and is to some  extent tested in India) and Wolf-Morgan reagent(acid mineral and organic soils).Apartment from these ,0,01M CaCl2  was also tested as a univeral soil test.

Dear Dr. Naik,

I suppose, that would be helpful for you to get acquainted with the materials of John E. Sawyer and Antonio P. Mallarino, presented at the 19th Annual Crop Pest Management Short Course, University of Minnesota, November 22, 1999, St. Paul, MN., titled: “Differentiating and Understanding the Mehlich 3, Bray, and Olsen Soil Phosphorus Tests”

http://www.agronext.iastate.edu/soilfertility/presentations/mbotest.pdf

http://www.agronext.iastate.edu/soilfertility/info/mnconf11_22_99.pd

 Yours faithfully

The references attached by Dr.Zenon provide a good account of comparison of Olsen ,Bray and Mehlich 3 methods.It appeared that the Mehlich 3 method has an edge over Olsen or Bray methods in all types of soils.While Bray's method may not fare well above pH 7.4,Olsen's can not do well below pH 5.5.To my knowledge the Mehlich 3 method has  not been evaluated well under Indian conditions.

Dear Sushanta,

Have you thought of using ion exchange membranes? these serve as a good sink for P and all you need to do after P has been absorbed into these membranes is elute with the acid which will extract P from the membranes. They also work well across all pH ranges. 

Thanks Dr Zenon Hamkalo, Dr. Annangi Subba Rao and Dr. Dimpho Elvis Elephant for sharing your valuable information on the above topic.

In organic soil nutrient pools are different. so conventional extarctants are not suitable for the size of contributing nutrient pools. Under this background,biologically elaborated organic acids for inorganic insoluble P and basic EDTA for mineralizable P may be good extarctants.

 Dr.Saha,Can you elaborate your second sentence further? Organic acids can solubilize or mobilize inorganic P but how EDTA mineralize organic P?Potentially mineralizable N can be estimated by aerobic or anaerobic incubation method.P can also be similarly estimated with some associated problems(refixation of the mineralized P and also a small amount). In Mehlich 3 extractant P is solubilized by different mechanisms.Acidity of the two acids,nitric and acetic,increases the solubility of iron and aluminum phosphates and extracts a portion of calcium phosphate.Fluoride serves to complex aluminium cations that potentially bind with phosphates thereby increasing the quantity of orthophosphate in solution.The purpose of acetic acid is to keep the solution buffered below pH 2.9 to prevent calcium fluoride from precipitating.Ammonium exchange with K,Ca,Mg and EDTA chelates Fe,Mn,Zn and Cu.Full details of the method are available in the following paper/manuscript available online.

Mehlich 3 extraction for Macro-and Micronutrients  by Zhang,H.,Hardy,D.,Mylavarapu,R. and Wang,J. ( Manuscript).

Not only EDTA. It is Basic EDTA, ie. (M)  NaOH +EDTA. This extarctant can extarct easily mineralizable organic N &P pools which contributes in plant nutrition in organic system.

Mr.Saha,Can you give reference to the method you are referring to? I know the NaOH-EDTA can extract the organic P but it is not mineralizable P.The familiar Bowman and Moir( 1993) method  involves the use of 0.25 M NaOH+0.05 M Na2EDTA in a soil to solution ratio of 1:50,extraction for 2 hours at 85o C without shaking, followed by persulphate oxidation.This method is not suitable for routine estimation of plant -available soil P..This method formed the basis for determination of a range of organic P compounds including monoesters,DNA , pyrophosphates etc.using 31P NMR spectroscopy. The NaOH can serve as humic acid solvent.The EDTA chelates metal cations and increases the solubility of P bound via cationic bridges.Inorganic P can be estimated before the persulphate oxidation.Total P-inorganic P gives the organic P.

I am trying to develop soil testing protocol for organic farming. Different fractions of basic EDTA extarctable P with graded strength of NaOH and their dynamic (rate constant, half-life and mean residential period ) were monitored to find out the fraction with higher rate constant. That fraction may contribute in plant nutrition.

Dr Saha

Dr.Saha,best of luck.