Question

what is the rotten dead matter in soil

Answer 1

 Rotting Wood and how it affects the EnvironmentRotting wood and your gardenRotting logs are a very common feature of wild ecosystems. Rotting logs recycles nutrients back into the soil and provides a healthy habitat for a wide range of insects, plants, and animals. Rotting log provides homes for small mammals, insects, worms, and spiders. The rich, organic soil provides a unique habitat for fungi, tree seedlings, wildflowers, mosses, and ferns.Help your garden by leaving a few logs to rot in an unobtrusive area.How long does it take for a tree to decay?The time it takes a tree to rot depends on the species, the various fungi that move in, the moisture content, the geographic location, and the size of the tree. 

A red cedar tree may take a century to completely decompose. Pacific silver fir will totally decay in about 50 years.

Answer 2

Rotten dead matter in soils are decomposed by various micro-organisms like bacteria. They decompose the organic matters into simpler molecules. Different types of matter take different time to decompose. For example: bones take much more time compared to leaves or flesh to decompose. After long time, it becomes humus.