Why and How to Soil Sample

The Phosphorus Regulations became effective on 1 January 2007. These state that farmers must not apply any chemical fertiliser containing phosphorus unless there is a crop requirement. This can only be established through a soil test. With the current price of fertiliser, there is also a significant financial incentive to ensure that the type of fertiliser sown best meets the needs of the growing crop.

Area to sample: The size of the area from which one sample can be taken varies, but must not be more than 4 hectares. Generally one sample should 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, must be sampled separately.

Time of sampling: Sampling every 4th year is satisfactory as a basis for phosphorus fertiliser recommendations. A field must not be sampled for phosphorus until at least 3 months after the last application of any fertiliser (organic or chemical) containing phosphorus. Results from a previously taken soil sample taken is valid for a 4 year period from the date sampled.

Depth of sampling: Grassland must be sampled to a depth of 75 mm and arable land to a depth of 150 mm.

Method of sampling: Using a soil auger, a soil sample must be made up by bulking at least 25 sub-samples taken from the area to be sampled. The sub-sampling points must be selected systematically to give an even distribution over the whole sampling area. This distribution should be achieved by following the pattern of a letter “W” and taking sub-samples at regularly spaced intervals. Taking sub-samples from headlands, dung and urine patches, areas where stock gather or other unusual features must be avoided.

Analysis: Soil samples should only be analysed 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.

With good management of livestock manures most farms can eliminate chemical phosphorus with no loss to productivity due to the levels of phosphorus present in the soil. If you are considering applying any chemical fertiliser containing phosphorus this season, sample now before slurry is applied to establish the requirement – it may save you money!

For more information on soil sampling or to obtain a soil auger, please contact Countryside Management at your local DARD office.

Use an auger to take at least 25 soil samples