🌱 Sampling of soil for chemical and agricultural analysis — PN-R-04031

Environment PN-R-04031

Overview

STATUS (state of the PKN card on 22.09.2026). PN-R-04031:1997 is CURRENT — the card contains no withdrawal note and no "Replaced by" row. Publication 28-11-1997, 5 pages, ICS 13.080.05, technical body KT 90 (Soil Cultivation and Horticulture), sector SRZ (Food, Agriculture and Forestry). We draw attention to the letter of the series: this is a standard of the R series (agriculture), not Z (protection of the environment and health), and the technical sector confirms this.

THE MOST IMPORTANT DISTINCTION: NUTRIENT STATUS IS NOT CONTAMINATION. The standard is entitled "Chemical and agricultural analysis of soil", and its scope covers the sampling of the TOP layer of mineral arable soils, organic soils and permanent grassland FOR CHEMICAL AND AGRICULTURAL ANALYSES — that is, for assessing the soil reaction (pH) and the supply of nutrients in the soil, for fertiliser recommendations and liming. Its whole way of averaging is designed for this: 20 probings spread over a field of up to 4 ha, mixed into one sample, give a good AVERAGE value for a piece of land that is agrotechnically homogeneous. With soil contamination the same procedure works against its intention. Contamination usually takes the form of a hot spot or a patch, not an even background — averaging 20 probings dilutes it to a value that may not exceed any threshold, even though in one place the concentration is many times higher. THE SAMPLING DESIGN IS MORE IMPORTANT HERE THAN THE LABORATORY: the same analyst, the same instrument and the same determination method will give a different result with a different sampling plan. THIS IS CONFIRMED BY A LEGAL ACT, NOT ONLY BY OUR ASSESSMENT. The Regulation of the Minister of the Environment of 1 September 2016 on the method of assessing the contamination of the earth's surface (Journal of Laws 2016 item 1395) has an annex "Reference methodologies for testing the contamination of soil and earth". In its point 1, under the item "Sampling in the field, preservation, storage, transport and preparation for laboratory analysis", the reference methodologies are listed exhaustively: PN-ISO 10381-1, PN-ISO 10381-2, PN-ISO 10381-3 and PN-ISO 10381-4 OR PN-ISO 10381-5. PN-R-04031 DOES NOT APPEAR IN THIS ACT EVEN ONCE — we checked this on the whole text (reading of 22.09.2026), and the amendment of 31 October 2024 (Journal of Laws 2024 item 1657) does not change this part of the annex, which we also checked. In the assessment of contamination of the earth's surface the agricultural standard is therefore not a reference sampling methodology; the PN-ISO 10381 series is. At the same time the act does not close the way to other methodologies: § 11 para. 2 provides that the tests referred to in § 9 and § 10 "prowadzi się w oparciu o referencyjne metodyki wykonywania badań właściwości oraz zanieczyszczenia gleby i ziemi lub inne metodyki, o których mowa w art. 12 ust. 2 ustawy z dnia 27 kwietnia 2001 r. - Prawo ochrony środowiska" [are carried out on the basis of the reference methodologies for testing the properties and contamination of soil and earth or other methodologies referred to in Article 12(2) of the Act of 27 April 2001 — Environmental Protection Law] (text of the act from ELI, reading of 23.09.2026; the 2024 amendment changes §§ 3, 4, 8, 9, 10, 13 and Annex No. 1, and does not touch § 11 or the annex with the methodologies). Whether PN-R-04031 can be such another methodology — WE HAVE NOT ESTABLISHED: we did not read Article 12(2) of the Act. This takes nothing away from PN-R-04031 — it simply separates the purposes. A NOTE THAT THE LEGAL ACT DOES NOT CONTAIN, BUT WHICH CHANGES THE READER'S SITUATION: THE WHOLE PN-ISO 10381 SERIES HAS BEEN WITHDRAWN BY PKN within the last year. We checked the cards of all five parts, one by one (reading of 22.09.2026): part 1 — withdrawn 20-11-2024; parts 2, 3 and 4 — 12-03-2025; part 5 — 24-11-2025. NONE of the cards indicates a replacing document. This means a situation that the laboratory has to resolve on its own: the regulation indicates these standards as the ONLY reference methodologies for sampling in the assessment of contamination of the earth's surface (the list is closed, it contains no alternative), and PKN has withdrawn them all. Withdrawal by PKN does not remove a standard from a legal act — until the list is amended, it is these withdrawn standards that are the reference methodology. This is exactly the reverse of the situation with PN-R-04031, which is CURRENT and absent from the act. WHAT WE HAVE NOT ESTABLISHED: whether work on amending the list is under way and whether PKN intends to introduce a replacing series (ISO replaced the 10381 series with the ISO 18400 series, but we did not check its introduction into the PN collection). A measurement on the accreditation scopes shows that the transition is only beginning: citations of the 10381 series alone — 69 entries, joint citations of 10381 with ISO 18400 — ONE entry, citations of ISO 18400 alone — zero.

This can also be seen in the accreditation scopes: PN-R-04031:1997 appears in them most often not on its own, but TOGETHER with PN-ISO 10381-4:2007 (guidance on sampling from natural, near-natural and cultivated sites) and PN-ISO 10381-5:2009 (investigation of soil contamination of urban and industrial sites), and some laboratories add ISO 18400-205. Laboratories thus add documents covering what the agricultural standard does not cover. A citation of PN-R-04031 alone in a scope row does not settle whether nutrient status or contamination was tested — and the difference is fundamental for the reader of the report.

WHAT THE STANDARD SETS — THE NUMBERS AND THEIR DIRECTION. For each of these numbers we state in which direction the limit works, because the three numbers of this entry have two opposite directions and the value alone does not carry this. • 4 ha is the MAXIMUM area per one final sample, not a recommended size: a larger field must be divided, a smaller one may be tested as a whole. • 20 (mineral arable soils) and 40 (organic soils and permanent grassland) are the MAXIMUM numbers of primary samples making up the final sample — the wording is "up to 20" and "up to 40". • 0.5 kg is the MINIMUM mass of the final sample — a smaller one must not be submitted for testing. • 0–20 cm is the layer from which the primary samples are taken: the top arable layer. The twice as large number of probings for organic soils and grassland is not caution for good measure — these soils are more varied within one field, so more points are needed for the same reliability of the average.

HOMOGENEITY THAT MUST BE TWOFOLD. The final sample is to represent an area with similar NATURAL conditions (type, kind and textural class of the soil, landform) AND AGROTECHNICAL conditions (previous crop, crop, fertilisation). Both conditions must be met at once: a piece of field that is homogeneous in terms of soil, on which two different crops stood last year and which was fertilised differently, is not one sampling unit. A further rule says this separately: the final sample is prepared separately for each crop.

REPRESENTATIVENESS IS DECIDED BEFORE SAMPLING, NOT DURING IT — AND THIS CANNOT BE SEEN FROM THE NUMBERS. This is a difference that is easy to overlook, because the standard gives numbers (up to 20 probings, up to 4 ha, 0.5 kg) and they look like a sufficient condition. They are not. The condition is the CHOICE OF AREA: if the delimited unit covers two different soil textural classes or two different ways of fertilisation, the bulk sample is unrepresentative from the first probing — and no number of samplings will fix this, because things are then averaged that must not be averaged. This is the opposite of standards in which representativeness is built by the number and distribution of samplings: there an error in the plan can partly be made up for by a larger number of points, here it cannot. The practical consequence for the report: next to the number of primary samples, it must be recorded on what basis the area was considered homogeneous — because it is this second piece of information that decides the value of the result.

WHAT MUST NOT BE SAMPLED — EXCLUSIONS. Samples are not taken: in a strip of up to 5 m from the edge of the field, at sites of former stacks and clamps, in ditches, furrows, molehills and gravel patches, and in depressions and on sharp elevations of the terrain. These places are chemically atypical, and drawn into the average sample they would falsify it. From depressions and elevations, however, ADDITIONAL samples may be taken — that is, separate ones, not added to the bulk sample.

WHEN TO SAMPLE. The most suitable period is spring or autumn BEFORE fertilisers are applied. Sampling should be avoided immediately after the application of mineral fertilisers, after organic fertilisation and during excessive drought or excessive soil moisture. The reason is the same in all cases: freshly applied fertiliser or extreme moisture describes a momentary state of the field, not its nutrient supply, which the test is meant to measure.

THE SAMPLING OPERATION AND DOCUMENTATION. Before sampling, an outline on a geodetic base map or an accurate sketch of the area is prepared, and the points where primary samples are taken are marked on the sketch and numbered — a sample without this sketch is not assigned to a place. Primary samples are taken with a soil probe or another instrument ensuring representative sampling from the 0–20 cm layer, distributing the points over the field according to one of the patterns (diagonals in the shape of the letter X, a zigzag in the shape of the letter W, or the perimeter); on freshly ploughed land the sampling spot must first be trodden down. The probe is set vertically, pushed in to the stop marked by the limiting crossbar, given a full turn and pulled out, and the contents of its chamber are transferred to the container. After all the primary samples have been collected, the whole is mixed, and only from this is the packaging of the final sample filled, durably labelled and secured for transport. It is recommended that the direction of taking primary samples be PERPENDICULAR to the direction of the agrotechnical operations — otherwise the whole sampling line may fall into one fertiliser strip, and the average ceases to be an average.

WHAT WE DO NOT GIVE. We did not have the text of PN-R-04031:1997 — the standard is sold for a fee. The scope, title and publication data come from the PKN catalogue card, and the detailed sampling rules from an instruction prepared on the basis of this standard and published by the Institute of Soil Science and Plant Cultivation — State Research Institute (IUNG-PIB), where the reference to PN-R-04031:1997 is given directly in the title. We did not check whether the instruction reproduces the standard in full or whether it supplements it at any point — this is a gap, not a feature of the entry. Nor do we give requirements concerning the preparation of the sample in the laboratory (drying, sieving), because the card only shows that the standard covers "sampling and preparation of samples", and we did not have the content of this part.

Method principle

The area of the land is divided into units with similar natural conditions (type, kind and textural class of the soil, landform) and agrotechnical conditions (previous crop, crop, fertilisation), each of which has no more than 4 ha and a separate crop. From each unit, primary samples are taken with a soil probe from the 0–20 cm layer — up to 20 from mineral arable soils, up to 40 from organic soils and permanent grassland — distributed according to the X, W or perimeter pattern, perpendicular to the direction of the agrotechnical operations, omitting the edges of the field, sites of former stacks and clamps, ditches, furrows, molehills and gravel patches. The primary samples are mixed and the mixture forms a final sample with a mass of not less than 0.5 kg, durably labelled and assigned to the points marked on the sketch of the area.

Applications

• Sampling of soil for the assessment of soil reaction and nutrient supply — fertiliser recommendations and liming
• Testing of mineral arable soils, organic soils and permanent grassland, as well as horticultural substrates
• Sampling for chemical and physical soil tests in the accreditation scopes of laboratories — usually together with PN-ISO 10381-4 and PN-ISO 10381-5
• Deciding whether a given row of an accreditation scope concerns the assessment of nutrient status or a soil contamination test

Key parameters

Standard

Standard number

PN-R-04031:1997 (wersja polska)

Title (PL)

Analiza chemiczno-rolnicza gleby — Pobieranie próbek

Title (EN)

Chemical and agricultural analysis of soil — Sampling

Step-by-step procedure

1. Preparing an outline or sketch

   Before starting sampling, prepare an outline on a geodetic base map or an accurate sketch of the area of agricultural land from which the samples are to be taken. A NOTE ON THE WHOLE PROCEDURE: we reproduce the following steps after the IUNG-PIB instruction prepared on the basis of this standard — we did not have the text of the standard itself, so we cannot state whether the instruction renders it in full.

2. Dividing into sampling units

   Delimit areas with similar natural conditions (type, kind and textural class of the soil, landform) and agrotechnical conditions (previous crop, crop, fertilisation). The area per one final sample must not exceed 4 ha. Prepare a separate final sample for each crop.

3. Choosing the pattern and direction of sampling

   Distribute the sampling points according to one of the patterns: diagonals (X), zigzag (W) or perimeter. The direction of taking primary samples is to be PERPENDICULAR to the direction of the agrotechnical operations — otherwise the whole sampling line may fall into one fertiliser strip.

4. Marking the points on the sketch

   Mark the points where primary samples are taken on an accurately made sketch and give them consecutive numbers.

5. Taking primary samples

   Take up to 20 primary samples from mineral arable soils or up to 40 from organic soils and permanent grassland, from the 0–20 cm layer. At the sampling spot, tread down freshly ploughed land; set the probe vertically to the soil surface, push it in to the stop at the height of the limiting crossbar, give it a full turn, pull it out and transfer the contents of the chamber to the container.

6. Omitting atypical places

   Do not take samples in a strip of up to 5 m from the edge of the field, at sites of former stacks and clamps, in ditches, furrows, molehills and gravel patches, or in depressions and on sharp elevations of the terrain. From depressions and elevations, take ADDITIONAL samples if necessary — separate ones, not added to the bulk sample.

7. Forming the final sample

   After all the primary samples have been taken, mix the whole thoroughly, and only from the mixture fill the packaging of the final sample. The mass of the final sample must not be less than 0.5 kg.

8. Labelling and securing

   Label the packaging durably and secure it so that it is not damaged in transport. Attach the sketch with the numbering of the points to the sample — without it the result cannot be related to the place.

9. Choosing the time

   Sample in spring or autumn before fertilisers are applied. Avoid sampling immediately after the application of mineral fertilisers, after organic fertilisation and during excessive drought or excessive soil moisture.

10. Checking whether the purpose of the test corresponds to the standard

    If the test concerns soil contamination rather than its nutrient status, the sampling plan from this standard alone is insufficient: averaging 20 probings over 4 ha dilutes a contamination hot spot. Apply the documents appropriate for such a purpose (PN-ISO 10381-5, ISO 18400-205) — this is also what most laboratories that cite this standard in their accreditation scope do.

Required equipment and apparatus

Health and safety (OHS)

• Work in agricultural terrain — protection against operations carried out earlier on the field (plant protection products, fertilisers) and observance of the pre-harvest interval given by the farmer apply
• When sampling from potentially contaminated sites, a hazard assessment is required before entering the site — the agricultural standard contains no guidance for such conditions
• A soil probe pushed in to the stop risks injury on hitting a stone or a cable — check the routing of underground installations before starting sampling
• A sample without a sketch with the numbering of the points is not evidence — a result related to the wrong place is worse than no result
• Report the result with the information for what purpose the sample was taken: averaging suitable for assessing nutrient status is NOT suitable for detecting contamination hot spots

Frequently asked questions