Olsen's P could be a good index of P availability in acid soil, if the crop to be grown is lowland rice cop.

Thanks a lot, Mr. Prakash Chandra Srivastava.

Do you know the studies about using Olsen'P on acid soils?

Please see the papers on Internet. One such paper is : Open J Soil Sci. 3: 115-122. (2013).

regard,

P C Srivastava

 Olsen It is applicable to soils that are mildly acidic to alkaline pH ,mostli for high pH

But you can use the  Mehlich 3 and AL -method

 Yes it is true Mr. Parkash,  Olsen's P could be a good index of P availability in acid soil, if the crop to be grown is lowland rice cop.

Dear colleagues ,good discussion on Olsen's method use in acid soils or acid sulphate soils.Olsen method can safely be used in neutral,alkaline and calcareous soils.I find in literature the use of Olsen's method in solis upto a pH of 6.0.In soils below pH 5.5 the olsen method is not recommened .In acid sulphate soils the pH normally does not increase beyond 5.5(or 5.0) even under  waterlogged conditions.In aerated/aerobic acid sulphate soils pH drops to 3.5.We have to see the chemistry of soil and nature of P compound  in soil before going for Olsen, Bray or other tests.The acidic Bray and Mehlich1 extractants dissolve Al- and Fe-phosphates,while Olsen extractant removes dissolved and adsorped P on calcium carbonate and on Fe-oxide surfaces.Bray and Mehlich3 methods are for noncalcareous soils,whereas the Olsen is meant for non-acid soils,(even though used in soils upto pH 6.0).

Fully agree with Annangi Subba Rao. Olsen is not appropriate for acaid soils. In central Africa (Cameroon) we used Mehlich-3 and we did have nice results with.

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Do not use Olsen in acid soils the results could be underestimated  I agree with Annangi Subba Rao

The soil pH is very important in selecting extractants for soil P extraction. olsen method is more efficient in extracting soilPin alkaline soil than Bray P1 and Bray P 2 extractants. Hence ,there is need for correlation studies in soil testing  programme between soil P  and P uptake in test crop under different extractants used .Please note  that the choice of inappropriate extractant for soil P will affect determination of soil P critical level during soil calibration studies and the amount of P  fertilizer  to recommend  for crop growth.This is the main reason of over or under fertilisation of soil leading to luxury consumption by crops or resulting to nutrient antagonism

Olsen P is used in neutral and alkaline soils in order to determine easily soluble Ca-phosphates.  The P in alkaline soils is usually in the form of Ca-phosphates.  The Olsen P extracting solution is buffered at pH 8.5.  At that pH, free Ca is precipitated as CaCO3 which has lower solubility than many of the more soluble Ca-P's.  the removal of free Ca from solution by precipitation causes P linked Ca to come into solution thereby releasing the P into solution which can then be determined as ortho-phosphate.

In highly acid soils (pH < 5.5), the buffering of the NaHCO3 in overcome by the high acidity and the extracting solution then loses its efficacy to extract the P and in essence, you are determining water soluble-P.

In highly acid soils (pH

I am agree with Annangi Subba Rao, I found better correlation between P-Fractions in tea acid soils with Bray-1 and mehrich-3, instead of Olsen P.