Water repellent soil is as it sounds. Repels water droplets. It’s also known as hydrophobic. Which is to repel or fail to mix with water. The following video shows exactly what hydrophobic soils look like.
As the video shows, once the water is sprayed or poured onto the soil, it just runs off. It is dry. It happens because the soil is old, has been left alone for too long. Had no added nutrients for a long time. Or it is nutrient poor.
What are some associate problems?
As drainage is an issue, the plants in water-repellent soils will die and the soil may become baron. Run off on high areas can cause over watering on other parts of the garden or flooding. Any top soil will be lost in the move. Nutrient loss and leaching are also worth considering. The water at root level will decrease and can cause death to the plant. It is also not good for the environment.
How can you fix the problem?
Wetting agents can help but it really is a temporary solution. Also, it is also a good idea to avoid using wetting agents derived from petroleum and alcohol as these can be detrimental to plants, including death. They also should definitely not be used in organic gardens. However, there are other plant derived wetting agents which have been proven to aid water saturation. Some gels are also known to increase water capacity, but these will ultimately dry out and may leave the soil in a worse state than before.
Wetting agents should be added to the soil when a plant is being planted in hydrophobic soil. This will hopefully be enough to give the plant a good start in growth.
However, what really helps a hydrophobic soil is to add nutrients that are depleted in it. Compost, green compost and animal manure with lots of organic matter will add the nutrients to break down to form humus. Humus works like a sponge, soaking in water and holds it to release it gradually to the plants needing it. Humus also is the home of micro-organisms which are the ultimate wetting agents. Humus also increases aeration in clay soils as it opens them up.