Eli5 How can dirt become hydrophobic?

Question

I saw a video about some plants that had become dehydrated because the soil had turned hydrophobic, and was wondering how and why it did that?

In: 11

Answer 1

Usually caused by a buildup of waxy compounds in the soil. Some plants like eucalyptus are quite waxy, and as they decompose the wax remains and builds up. It’s most common in sandy soils – the larger particle size (as compared to silt) means they have a smaller surface area, and are more likely to be fully coated by the wax.

Answer 2

THIS COMMENT EDITED AS PER QUESTIONS IN REPLIES

The topmost layer of soil is where most of the organic detritus is such as fallen leaves. When this stuff decomposes, the soil can get waxy – especially if the temperature is high enough to turn the wax to gas, such as from a wildfire.

Wax buildup is mitigated by most forms of life that till dirt, which is why compost doesn’t have a strong risk of making soil waxy, even though compost can get hot enough to spontaneously combust.

Sand is more susceptible than silt or clay, and there are detergent-like products that claim to help break up the wax to try to restore absorption.

Answer 3

THIS COMMENT EDITED AS PER QUESTIONS IN REPLIES

The topmost layer of soil is where most of the organic detritus is such as fallen leaves. When this stuff decomposes, the soil can get waxy – especially if the temperature is high enough to turn the wax to gas, such as from a wildfire.

Wax buildup is mitigated by most forms of life that till dirt, which is why compost doesn’t have a strong risk of making soil waxy, even though compost can get hot enough to spontaneously combust.

Sand is more susceptible than silt or clay, and there are detergent-like products that claim to help break up the wax to try to restore absorption.

Answer 4

Usually caused by a buildup of waxy compounds in the soil. Some plants like eucalyptus are quite waxy, and as they decompose the wax remains and builds up. It’s most common in sandy soils – the larger particle size (as compared to silt) means they have a smaller surface area, and are more likely to be fully coated by the wax.