The study looked at how salt and water move in soil when groundwater is close to the surface. They found that as water moves up from below, it brings salt with it, leading to salt buildup in the topsoil. The rate of salt buildup depends on how much water is moving and the type of salt in the soil. When the groundwater is far from the surface, water flow decreases. If there are clay layers in the soil, water flow decreases even more, reducing salt buildup. Rain or irrigation can also help prevent salt buildup in the topsoil.