This document discusses soil testing proficiency certification programs run by ASPAC (Asia Pacific Soil and Plant Analysis Council). Around 50 soil tests can be certified through proficiency testing of 59 laboratories in Australia, New Zealand, Pacific Islands, and Southeast Asia. Laboratories test 12 soil samples per year and are certified for specific methods if they receive 4 or fewer demerit points total. The best and worst performing soil test methods based on robust coefficient of variation scores are also listed.

1. Value of a PT – a Case Study
Rob De Hayr

2. Soil Testing Proficiency
Approx. 50 tests certifiable
depending on test, 10-52
labs provided results
total of 59 labs, including
Australia, New Zealand,
all Pacific Islands and
some SE Asian

3. ASPAC proficiency certification
• In SoilChek each laboratory tests 12 soil samples
per year, consisting of 3 rounds of 4 samples each.
• The scoring system involves allocation of demerit
points for each sample on the basis of the z-score
result obtained from method specific statistical
analysis.
• Method specific certification is given when a
laboratory incurs no more than 4 demerit points for
the 12 samples.

4. • For each test method:
• 2 demerit points are allocated to a statistical
outlier (ASPAC Score >2 at the first iteration ), or if
no result submitted.
• 1 demerit point is allocated to a statistical
straggler (ASPAC Score >2 at the second
iteration).
• A maximum of 3 demerit points are accrued per
round, so that no single poor performing round
will incur a laboratory’s certification failure.
ASPAC proficiency certification

5. 0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
MedianRobustCV's Change in Lab Performance overTime (Soils)
2005-07 2009-11 2013-15

6. ASPAC soil proficiency performance
Best (Lowest Robust %CVs)
Soil Method %CV
Soil pH, 1:5 0.01 M CaCl2 (4B1) 1.8
Soil pH, 1:5 0.01 M CaCl2 (4B2) 1.8
Soil pH, 1:5 H2O (4A1) 2.2
Exch. Ca, NH4Cl (15A1) 3.7
EC, 1:5 water (3A1) 4.2
Total Org. C (6B1 + 6B2 +6B3) 5.4
Exch. Mg, NH4Cl (15A1) 6
Exch. K, NH4Cl (15A1) 6.5
Exch. Mg, NH4OAc (15D3) 7.6
Total N (pooled 7A1 + 7A2) 7.9

7. Worst (Highest Robust %CVs)
Soil Method %CV
Meh 3 Extr. Fe (18F1) 21.5
Meh 3 Extr P (18F1) 21.5
Meh 3 Extr Zn (18F1) 22
Water Sol. Cl Auto –Color. (5A2) 22.5
Meh 3 Extr S (18F1) 23
Bray – 1 Extr. P (9E1 + 9E2) 25
Meh 3 Extr Cu (18F1) 29
Water Sol. Cl Potent. (5A1) 35.5
Exch. Al KCl (15G1) 79.5
Meh 3 Extr B (18F1) 81.5
ASPAC soil proficiency performance

8. Thanks for your attention
https://asq.org/quality-resources/control-chart
Further Reading and resources
http://www.fao.org/3/w7295e/w7295e0a.htm#8.3.2%20co
ntrol%20chart%20of%20the%20mean%20(mean%20chart)