First lab managers’ meeting of the South-East Asia Laboratory NETwork (SEALNET 2.0) - Quality improvement in Asian soil laboratories: towards standardization and harmonization of soil analyses and their interpretation, Bogor, Indonesia, 20 - 24 November 2017.

1. Available phosphorus

2. P cycle Crop harvest
Plant residues
Animal manure
Bio solids
Organic P
- Microbial biomass
- Plant residue
- Humus
Atmospheric
deposition
P
Plant uptake
Leaching
Run off
Erosion
Primary
Minerals
Secondary compounds
CaP, FeP, MnP, AlP
Soil solution
phosphorus
HPO4
2-
, H2PO4
1-
Clay mineral
surfaces, Fe
and Al oxides,
carbonates

3. Soil phosphorus compounds in relation to soil pH.

4. • P extracted by
o Bray P1: 0.03 M ammonium fluoride + 0.025 M HCl
o Bray P2: 0.03 M ammonium fluoride + 0.1 M HCl
o Olsen-P: 0.5 M sodium bicarbonate pH 8.5
Methods used for measuring available P in some SEALNET labs

5. Bray-P: acidic, complexes Al, dissolves Ca-P
Olsen-P: alkaline, hydrolyses org C, reduces
soil solution Ca activity
Bray-P and Olsen-P may extract P from different sources
in different soils
Sorbed P
(attached to -O- groups
on clay mineral surfaces)
Mineral P
(apatites, fertiliser residues)
P
P P
P
Solution P
P
precipitation/
dissolutionsorption/
desorption
dissolution
Organic P
mineralisation
?

6. Methods used for measuring available P in some SEALNET labs
• Variations in extraction conditions for Bray P:
o Soil:extractant ratio: original 1:7; often 1:10
o Extraction time: original: 60 sec; often 5 min
o Separation: centrifuging; often filtering
• Variations in extraction conditions for Olsen-P:
o Separation: centrifuging; often filtering

7. Michaelson et al. (1987)
Can one soil P test value be converted to another soil P test
value?
Bray-P1 is correlated
with Mehlich-3P,
but slope varies with
soil type….

8. Can one soil P test value be converted to another soil P test
value?
Relationships between the P2O5 amounts extracted by Lancaster solution and six
solutions (Mehlich , Mehlich , Bray 1, Olsen; significant at p < 0.001.Ⅲ Ⅱ
Source: Kim et al. (2013)
For these soils,
Lancaster-P is
highly correlated
with Mehlich-P
and Bray-P, but
not Olsen-P.

9. Can one soil P test value be converted to another soil P test
value?
Sometimes ‘Yes’, sometimes ‘No’.
It depends on the similarity between the two soil P
extractants and the variation in properties (pH, clay content,
clay mineralogy) of the soils.

10. What critical factors will the SOP for soil P need to address?
• Extraction time- this is the elapsed time between
addition of extractant and the separation of
clear extractant from the soil sample.

11. Will these differences affect results?
• Extraction time (including extractant recovery time) for
Bray P1 and Bray P2 is critical
Time
Extracted P
Al-P, Ca-P
dissolution P
re-precipitation
Extraction Extractant recovery

12. What critical factors will the SOP for soil P need to address?
• Extraction time- this is the elapsed time between
addition of extractant and the separation of
clear extractant from the soil sample.
• Shaking method- vigorous orbital shaking may give
different results to gentle end-over-end shaking.
• Extraction temperature

13. Interpretation of available P in ASEAN region
Variation even in low-moderate-high categories
Units: P2O5 /kg?
Need to harmonise!Need to harmonise!

14. Thank you for your attention…