While researching surface tension, the topic of soil water retention came up, and it seems that soil with high water retention is characterized by a soil state called an aggregate structure. An aggregate is a state in which large and small ball-shaped lumps of soil are mixed together in a balanced manner, with plenty of gaps. It has a good balance of water retention and drainage, which are difficult to achieve, and is excellent in breathability and fertilizer retention, so plants grow well.
https://www.shinshu-u.ac.jp/faculty/science/quest/sp/research/post-54.php
There are tiny passages within the aggregates, and slightly wider passages between the aggregates, so excess water flows downwards due to gravity, while water held in place by surface tension is retained between the aggregates. Water circulates finely up, down, left and right within a certain range, distributing water and nutrients evenly between the upper and lower layers. When the roots absorb water and the water level decreases, this circulation immediately replenishes water. Aggregates are amazing.
https://www.ruralnet.or.jp/syutyo/2001/200110.htm
To create soil aggregates, a kind of glue is needed to hold the soil together, and there is a theory that the glue is made up of rotting roots, bacteria in the soil, and mucus produced by small animals. Earthworms are a representative organism that creates these aggregates, and the glue they produce is water-resistant and durable. Earthworms are ecosystem engineers that break down fallen leaves and other materials to produce high-quality aggregates that contain many microorganisms.
https://www.hotoku-co.jp/mimizutarou/mimizufundo
Microorganisms in soil are not always active, and go into a dormant state when separated from organic matter and other resources. Earthworms ingest dormant microorganisms into their bodies, and the organic matter they ingest awakens the microorganisms and promotes decomposition. Earthworms are amazing. The polyphenols contained in fallen leaves are toxic to other organisms and cannot be eaten, but earthworms seem to be resistant to these polyphenols. Earthworms are amazing.
https://www.brh.co.jp/publication/journal/063/research_1
When I was researching earthworms, I realized how amazing they are. Because earthworms have gaps in them, it is easy for plants to grow their roots, and many microorganisms can live in the gaps. They are like the soil itself, enriching the ecosystem. Earthworms are amazing. The ecosystem of the earth is amazing.
