1. Separate the zones. Do not mix soils with different textures, slopes, management or crop performance. Each composite sample should represent a uniform zone.
2. Collect several subsamples. Cover each zone, use clean tools and containers, and keep a consistent depth. Agree the depth, number of sampling points and required amount with the laboratory for your crop and test.
3. Mix and label. Mix subsamples from the same zone and follow the laboratory’s storage and shipping instructions. Record the field, crop, depth and recent fertilisation; avoid unusual spots that do not represent the zone.
4. Interpret in context. A result is not a fertiliser recipe. Review the method, units, crop, irrigation water and field history with an adviser. Poor sampling can lead to wrong decisions even when the laboratory result is correct.
General information. Product and dose selection requires crop diagnosis and documentation for the specific formulation.