How deep should I dig when taking a soil sample?

For most field crops, sample to the depth of the plough layer, which is about 15 cm or six inches. That is the zone where most crop roots feed, so it is what the lab needs. The method is to scrape off the surface litter, then dig a small V-shaped pit to 15 cm and take a thin vertical slice of soil down the side, so you get an even amount from top to bottom of that layer, not just the surface scrape and not a deep chunk. Two exceptions to know. For deep-rooted orchard and plantation crops, your KVK may advise a second, deeper sample as well. For very shallow-rooted vegetables the 15 cm depth is fine. The key error to avoid is taking only the top one or two centimetres, which over-reads surface dust and fertiliser, or digging a random deep hole. Keep the depth the same at all your sampling spots so the mixed sample is consistent.