Why does it take longer for water to soak into dry dirt than wet dirt?

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I notice this when I’m watering plants around the house. If I haven’t watered a plant in a long time and the soil on top is hard and dry, when I go to water it the water will sit on top and take a while to absorb down into the dirt. But if a plant was watered more recently and still has some damp soil on top, the water will absorb a lot quicker.

Why is that?

In: Chemistry

Soil that has been dried out, in weather or lack of watering takes on hydrophobic (does not like water) properties. That takes it a lot longer to absorb the water.

The main particles in healthy soil are decomposed organic ingredients. These are natural ingredients that were once living organisms.

Soil that is moist has more of a water absorption tendency and can easily be watered again.

You should try adding compost or manure to keep your soil moist with as much water retention so you only need to top up every once in a while.

When water gets absorbed into soil it slides into cracks between the particles. When soil dries out, the particles get closer and closer together, which is why the volume of dry soil is less than wet soil. It takes a while for the water to work its way back into these cracks whereas with wet soil the cracks are there already it just needs to slip in and widen them