Long-term plowing can create a hard layer in the soil called a plough pan, which blocks water and restricts root growth, reducing crop yield. Scientists used electrical resistivity and penetration resistance measurements to locate and assess plough pans in two fields with different tillage depths. They found that electrical resistivity tomography is a fast and efficient way to identify plough pans without invasive sampling. By combining resistivity and penetration data, they could pinpoint the position of compacted soil layers. The topsoil showed more variation than the subsoil, indicating a more uniform compacted layer below. To clearly see shallow plough pans, electrodes should be placed close together.