What is humus? How is it formed?

Explanation

### Step-by-Step Solution

**Step 1: Definition of Humus**
Humus is a dark, organic material found in the soil. It is the topmost layer of soil, known as the O-horizon, which is rich in organic matter.

**Step 2: Importance of Humus**
Humus plays a crucial role in soil health as it provides essential nutrients to the soil, which are vital for plant growth. It improves soil structure, water retention, and fertility.

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