Regulations 12 and 13
SCHEDULE 5N.I.Soil test for Phosphorus
1. Reference to the results of a soil test is a reference to the results of an analysis of a soil sample carried out by a soil testing laboratory competent to analyse soils for phosphorus. Each analysis, provided by the competent laboratory, will require a UKAS accreditation or (National equivalent) statement.N.I.
2. The taking of soil samples and the analysis for phosphorus shall be carried out in accordance with the procedures below.N.I.
Soil sampling procedureN.I.
3. Area to sample: The size of the area from which one sample can be taken varies but shall not be more than four hectares. Generally one sample shall be collected from each field. Within one field, areas which are not uniform for crop growth and areas which have been cropped or fertilised differently shall be sampled separately.
4. Time of sampling: Sampling every fourth year shall be satisfactory as a basis for phosphorus fertiliser recommendations. A field shall not be sampled for phosphorus until at least three months after the last application of any fertiliser (organic or chemical) containing this nutrient.N.I.
5. Depth of sampling: Grassland shall be sampled to a depth of 75 millimetres and arable land to a depth of 150 millimetres.N.I.
6. Method of sampling: A soil sample shall be made up by bulking at least 25 sub-samples taken from the area to be sampled. The sub-sampling points shall be selected systematically to give an even distribution over the whole sampling area. This distribution shall be achieved by following the pattern of a letter “W” and taking sub-samples at regularly spaced intervals. Taking sub-samples from headland, dung and urine patches, areas where stock gather or other unusual features shall be avoided. Each sub-sample shall be taken using a soil auger which takes an even core of soil throughout the sampling depth. The soil sample shall be stored in a clean, labelled plastic bag.N.I.
Soil analysis for phosphorusN.I.
7. The soil test for phosphorus shall be carried out after the soil sample has been air-dried and ground.
8. Air-drying and grinding soil: The entire soil sample shall be dried to constant weight in an oven with a current of air at a temperature not exceeding 30 °C. Then the whole of the air-dried sample, excluding stones and fibrous material from roots, shall be ground to pass a two millimetre sieve.N.I.
9. Soil analysis for Olsen extractable phosphorus: The measure of phosphorus which is available for crop growth shall be given by the amount extracted from soil at 20 ± 1 °C with a sodium bicarbonate solution of pH 8.5. Details of the analytical procedure are given in The Analysis of Agricultural Materials, Third Edition, pp183-185, Ministry of Agriculture, Fisheries and Food reference Book 427, 1986. Olsen extractable phosphorus results are expressed as milligrammes phosphorus per litre (mg P/l) of soil, rounded to the nearest whole number.N.I.
10. Classification of soil analysis results into indices: The Olsen extractable phosphorus concentration in soil is classified into an index according to the following scale.N.I.
| Soil phosphorus index | Olsen extractable phosphorus (P) (mg P/l) |
|---|---|
| 0 | 0 – 9 |
| 1 | 10 – 15 |
| 2- | 16 – 20 |
| 2+ | 21 – 25 |
| 3 | 26 – 45 |
| 4 | 46 – 70 |