2nd AFRILAB meeting Zoom platform, 30 September - 1 - 8 October (English) Mr. Musefa Redi Abegaz, Holeta Agricultural Research Center, Ethiopian Institute of Agricultural Research, Ethiopia

1. Experience
on
Establishment of National Proficiency Testing (PT) Provision
in the Scheme of Soil Analysis
Musefa Redi, Abegaz
(MSc. Soil Science)
Holeta Agricultural Research Center (HARC), Ethiopia
1

2. Outlines
▪ Introduction
▪ Design of Proficiency Testing Scheme
▪ Choice of Test Method
▪ Operation of Proficiency Testing Scheme
▪ Data Analysis and Evaluation of PT Results
▪ Reports
▪ Communication with Participants
▪ Confidentiality
▪ First Round PT for 8 Soil Labs
▪ Results and Statistical Evaluation

3. Introduction
➢ In Ethiopia, a lot of agricultural technologies to Ethiopian farmers
have been releasing since 50 years ago through agricultural research.
➢ Those research technologies were released based on data collected
from field and laboratory experiments.
➢ The soil laboratories is fundamental to such agricultural research
endeavors, involving:
✓ analysis of soils as a basis for soil characterization and classification,
✓ identifying plant nutrient constraints, and
✓ establishing criteria for fertilizer application and efficient nutrient
use,
▪ along with water, plant, and fertilizer analysis.

4. Introduction...
➢ For these purposes, currently, there are 68 soil laboratories
distributed over 35 cities in different parts of Ethiopia (Bakker et al., 2016).
Spatial distribution of soil laboratories over Ethiopia.
Source: Bakker et al., 2016

5. Introduction
➢ However, the data generated from the Ethiopian soil
laboratories are not reliable enough and need to improve
their analytical services quality (Bakker et al., 2016).
➢ Reliable and acceptable data could be generated when
laboratories
✓ fulfill ISO/ IES 17025 standard and
✓ gets an accreditation certificate.
➢ Consequently, since the last 5 years, very few soil laboratories
fulfills ISO/ IES 17025 requirements and able to get
accreditation certificate.

6. Introduction
➢ Among few accredited soil laboratories, Holeta Agricultural
Research Center (HARC) soil laboratory has been accredited
since 2014.
➢ One of the major reasons behind many soil laboratories were
not accredited is because of difficulty in proficiency testing
(PT) participation.
➢ ENAO, in compliance with ILAC rules, have a policy for
participation in PT activities
✓ laboratories need to demonstrate an evidence of
satisfactory participation

7. Introduction
➢ Proficiency testing is a significant component in the laboratory
accreditation process as it allows laboratories to monitor the
quality of their analytical results as stipulated in ISO/IEC 17025.
➢ There are a number of benefits to participating in PT, including
✓ monitoring and improving measurements,
✓ demonstrating analytical competence,
✓ developing and training analysts, and
✓ validation of methods and instruments.
➢ Furthermore, regular participation in a PT program provides an
external quality assurance.

8. Introduction
➢ Accordingly, those accredited soil laboratories have been
searching soil PT provider from outside the country due to the
absence of local soil PT provider.
➢ It is the fact that participating foreign PT provider demands a
hard currency that makes difficult for the developing country
✓ particularly Ethiopia that lucks hard currency.
➢ In general, fees for PTs from industrialized countries and
transportation costs are often high and Ethiopian soil
laboratories could not afford it.

9. Introduction
➢ Therefore, establishing a local/ national PT provider for
Ethiopian soil laboratories is mandatory to overcome such
situations:
In addition,
▪ it is cheaper and provides an opportunity for
networking between soil laboratories of Ethiopia.
➢ HARC soil laboratory has been selected to be soil PT provider
through ELA
✓ for interested soil laboratories of Ethiopia.
➢ Accordingly, the pilot PT provision was conducted for 8 soil labs
of EIAR during the first quarter of 2019.

10. Design of Proficiency Testing Scheme
1. Planning of PT scheme and preparation of PT items
➢ The soil will be representing different soil types exist in Ethiopia and sampled
from different parts of the country.
➢ The frequency of participation will be 4 times in a year i.e. every three
months.
➢ For the coming two years, no payment is expected from the participating
laboratories to encourage the participation.
➢ However, probably after two years and getting enough participants, some
payment procedure will be devised
✓ through discussion with participant laboratories and considering
National Agricultural Research System (NARS) rules and regulations.

11. Design…
➢ In each round, participating laboratories will receive 1 to 2
samples representing 1 to 2 soil types of Ethiopia.
✓ Each sample with 300 to 500 gram
✓ Then, results of each test items will be requested during
result submission to the PT provider.
➢ All 8 soil laboratories of EIAR will be necessarily participate in
each round.
➢ In addition, other interested soil laboratories will be
encouraged to participate

12. Design…
➢ Samples will be first sampled from agricultural fields
representing a homogeneous soil type.
✓ For example, sample from Vertisols, Nitisols, Cambisols, etc.
➢ Sampling depth: most plants (Crops) root depth of 0-20cm
➢ Care will be taken during sampling to avoid any heterogeneous
material other than the soil is mixed.
➢ Then, the sampled soil will be air dried in soil preparation room,
ground manually in a porcelain mortar and pestle and then
sieved by 0.5mm mesh size.

13. Design…
2. Homogeneity and stability studies
➢ Soil particles are difficult to mix and need repeated subsampling
to make homogeneous.
➢ Therefore, after grinding dried sample and sieved by 0.5mm
sieve size, the bulk sample will be divided in to sub samples by
using rotary sample divider.
➢ Each sample will be subjected to homogeneity and stability test
before dispatched to each participating laboratories.

14. Design…
➢ Homogeneity will be determined and guaranteed on samples
that are in the same status as before sending the samples to
participants
▪ Organic carbon analysis will be used during homogeneity test
➢ Stability test will also be performed in order to demonstrate
that the samples are stable for the maximum duration of the
analysis time of the participants.
➢ In general, appropriate statistical design will be followed for the
homogeneity and stability studies.

15. Choice of Test Method
➢ The test method used for analytical parameters will be the most soil test
methods used in Ethiopian soil laboratories.
No Analytical parameters Test method commonly used in
Ethiopian Soil Laboratories
Unit Decimal
digit
1 Moisture content Gravimetric (Oven drying @ 105oC) % 1
2 pH (1:2.5 soil to water) Potentiometric -- 2
3 pH (1:2.5 soil to 1N KCl) Potentiometric -- 2
4 Electrical conductivity (EC) Potentiometric µs/cm 2
5 Exchangeable Acidity KCl leaching and titration with 0.02N
NaOH
Meq/100g 2
6 Exchangeable Aluminum KCl leaching and titration with 0.02N
HCl
Meq/100g 2
7 Total Nitrogen Modified Kjeldhal % 2
8 Available Phosphorous Bray II extraction mg/kg 2
9 Available Phosphorous Olsen extraction mg/kg 2
10 Available Phosphorous Mehlich 3 mg/kg 2

16. Choice…
No. Analytical parameters Test method commonly used in Ethiopian Soil
Laboratories
Unit Decimal
digit
11 Total phosphorus Per chloric acid digestion and
spectrophotometer
mg/kg 2
12 Available Sulfur Turbidity and spectrophotometer mg/kg 2
13 Exchangeable Na and K Ammonium acetate extraction and FP/AAS
reading
Cmolc/ kg 2
14 Exchangeable Ca and Mg Ammonium acetate extraction and AAS reading Cmolc/ kg 2
15 Organic Carbon Walkley and Black wet digestion % 2
16 Organic Matter Loss on ignition (L.O.I) % 2
17 Cation exchange capacity NH4OAC (@ PH=7) extraction method Cmolc/ kg 2
18 Micronutrients (Fe, Cu,
Zn, Mn and Mo)
DTPA Extraction and AAS mg/kg 2
19 Heavy metals or Total
elemental analysis (Co,
Pb, Cd, Se, Cr, Ag, Ni, As,
Al, V and Sn)
Digestion and AAS mg/kg 2

17. Choice…
➢ All 8 soil laboratories of EIAR usually use the above mentioned
methods.
➢ However, other participating laboratories can use other
methods
▪ the method used will be given as an option and ordered
to be written in the other method (specify) column.
➢ During reporting the test result, each test parameters need to
be reported with:
✓ specific unit of measurement and number of significant
figures (number of decimals).

18. Operation of Proficiency Testing Scheme
Packaging, labeling, handling and storage, distribution of samples and Instructions for
participants
➢ Packaging: zipper plastic bag and waterproof card board
➢ Labeling: appropriate labeling and coding to ensure that PT samples are
identified and segregated from the time of preparation to distribution.
➢ Therefore, each laboratories will receive sample with unique code.
➢ Samples will be dispatched using a courier service Ethiopian Postal
service.
▪ Appropriate safety, transport requirements and environmental conditions for the
transport of PT items will be determined and communicated to the courier service
(Ethiopian Postal Service).

19. Operation…
➢ All participants’ laboratories will be instructed on how to store samples
(dry and room temperature area)
➢ A procedure to confirm the delivery of PT samples will be used.
➢ After analyzing, the test results need to be reported before the deadline.
▪ The dead line for reporting the PT results for 1st, 2nd, 3rd, and 4th round samples
will be March 1st, June 1st, September 1st and December 1st of every year,
respectively.
➢ In general, procedures for dispatch and receipt of PT samples will be
established.
➢ When the PT samples suspected inhomogeneity, instability, contaminated
or deteriorated safe disposal mechanism will be followed.

20. Data Analysis and Evaluation of Results
➢ The results of soil PT will be collected either E-mail or through FAX
or Ethiopian Postal services.
➢ After collecting the results, the data set will be evaluated by
defining a range within which the result is assessed as satisfactory.
➢ Consensus values from participating labs will be used as an assigned
value
➢ ISO 13528:2005 – Statistical methods for use in PT by inter
laboratory requirements concentrates on methods for evaluation
and assessment will be used for analyzing the results.

21. Data Analysis
➢ During analysis of the results, values differing too much from
mean are marked as outliers.
➢ Microsoft Excel software or self-programmed software for the
data processing will be used.
➢ All data will have a back-up to eliminate potential loss of
electronic data.
➢ Detail working instruction will be prepared to ensure the
validity of data entry, data transfer and statistical analysis.

22. Data Analysis…
➢ Participant’s performance will be evaluated by calculating Z-
scores: zi= (xi-xpt)/σ_pt.
➢ The following criteria will be used for the performance
assessment.
✓ Iz-scoreI ≤ 2.0: Satisfactory Performance
✓ 2.0 < Iz-scoreI < 3.0: Questionable Performance
✓ Iz-scoreI ≥ 3.0: Unsatisfactory Performance
➢ The evaluation will constitute variation between participants,
variation between methods/procedures, possible sources of error,
improvement suggestions, recommendations and general
comments.

23. Reports
➢ The performance of the labs will be reported (incorporating results
reported by all the participants) to them through different
mechanisms with maintaining confidentiality
➢ The report will enable the participating laboratories to compare the
performance of their method with that of other methods used.
➢ Reports will be sent to each participating laboratories within three
weeks after the deadline of each PT scheme.
➢ The final report: authorized by the PT coordinator

24. Communication with Participants
➢ English language will be used as a media for communication
between PT provider and participating laboratories.
➢ The PT coordinator/ manager will communicate all
participating labs through e-mail during sample dispatching,
to confirm they get the reports and possible corrective action
to improve the results.
➢ In the long run, the PT provider will establish an electronic
database and system (web portal or web based software) for
submitting test results and reports.

25. Confidentiality
➢ Each participating laboratories will have a unique lab code
throughout communication in sample delivery, reporting
performance and issue of certification
▪ The lab code is only used in order to keep confidentiality.
➢ Therefore, all information provided the participants treated as
confidential unless the participant has waived this confidentiality.
➢ When the results issued to an interested 3rd party (accreditation
body, a regulatory authority etc.) a participant will be notified in
writing.

26. First Round PT for 8 Soil Labs
➢ Preparation of PT sample
✓ Sampled from Nitisols from HARC station,
✓ Air dried and crushed with mortar and pestle,
✓ Sieved with 0.5mm mesh size,
✓ Manual sample division in to 8 parts with stepwise of a
small portion of the sample from bulk sample
➢ Finally, ready for homogeneity test

27. First Round PT…
➢ Test for homogeneity
❑ Test for homogeneity
Sample t value#1, xt,1 value#2, xt,2
1 1.87 1.79 1.83 0.0016 0.0032
2 1.79 1.99 1.89 0.01 0.02
3 1.95 1.75 1.85 0.01 0.02
4 1.79 1.95 1.87 0.0064 0.0128
5 1.87 1.87 1.87 0 0
6 1.83 1.75 1.79 0.0016 0.0032
7 1.71 1.91 1.81 0.01 0.02
8 1.87 1.91 1.89 0.0004 0.0008
Homogeneity check according to
ISO 13528, B.2 and B.3
© 2017 Dr. Michael Koch, Univ. Stuttgart
www.aqsbw.de
michael.koch@iswa.uni-stuttgart.de
The use of this EXCEL-sheet is free, as
long as the copyright statement is not
removed.

28. First Round PT…
➢ Test for Homogeneity: Ssam< 0.3 σ
➢ Then, samples were dispatched to each participating
laboratories with instruction
number of samples 8
number of replicates 2
General average 1.85
variance of sample averages 0.00137143 standard dev. of sample averages 0.0370328
within-sample variance 0.01 within-sample standard dev. 0.1
between-sample variance 0 between-sample standard dev. 0
Expected standard deviation for proficiency assessment spt 0.03
check value 0.009
Homogeneity OK

29. Results and Statistical Evaluation
➢ Results submitted by eight participant soil labs
➢ Possible root cause for corrective action??
Lab Code pH-H2O (1:2.5) OC (%) Bray II-P (mg Kg-1) Total N (%)
A 5.09 1.79 6.68 0.171
B 5.64 1.82 2.75 0.180
C 5.41 1.74 4.04 0.195
D 5.32 1.90 -- --
E 4.54 1.42 -- --
F 5.27 1.56 -- 0.140
G 5.18 1.86 21.57 0.195
H 5.92 1.51 1.33 0.103
Method
Potentiometric
(1:2.5 soil to water Ratio)
Walkley-Black Wet
Digestion Bray II Extractant Kjeldhal

30. Results and Statistical Evaluation
➢ OC (%) results of eight participant soil labs
labcode result 1 mean method# Z-score Assessment
A 1.79 1.79 1 0.8 s
B 1.82 1.82 1 1.0 s
C 1.74 1.74 1 0.3 s
D 1.9 1.9 1 1.7 s
E 1.42 1.42 1 -2.4 q
F 1.56 1.56 1 -1.2 s
G 1.86 1.86 1 1.3 s
H 1.51 1.51 1 -1.6 s

31. Results and Statistical Evaluation
➢ OC (%) results of eight participant soil labs
ref. value: 1.7 % PT provider
exp. uncertainty (95%): 0.3 % PT provider: HARC Soil Lab
limit for rel. std for assessm.: 7% Dep. XX
specified rel. std for
assessm.: 7% Street
assigned value using ZIP City
1 1. ref. value Country: Ethiopia
2. Alg A mean 1.7 %
± 0.3 % PT round
std for assessment using 1st round, 2020
1. specified value 0.119 %
2 2. Alg. A 7.00% limited
Statistical results:
number of data 8 data outside limits 1
number of valid data 8 data below limit 1
data above limit 0
Alg. A mean: 1.7 %
exp. uncertainty (95%): 0.17922108 % from Alg. A std
upper limit 1.938%
Alg. A std: 0.20276551 % lower limit 1.462%
Alg. A rel. std: 11.93%

32. Results and Statistical Evaluation
➢ OC (%) results of eight participant soil labs

33. Experience Visit
➢ PT coordinators (Musefa R. and Mihretu B.) Visited three
international PT providers from September 1-7, 2019.
✓ LANUV, Duisburg/Germany,
✓ WEPAL, Wageningen/The Netherlands and
✓ ISWA, Stuttgart/Germany
➢ Purpose: to organize a local proficiency test in Ethiopia.

34. The Way Forward
➢ Receiving the purchased rotary sample divider from the donner
➢ Purchase of certified reference soil sample (Assigned value)
➢ PT launching Workshop to gather most of Soil Labs of Ethiopia
✓ Awareness creation to get enough participant labs
➢ Conduct second round PT provision for more than 10 soil labs

35. Thank You!!!