Mull humus is characterized by

Options

A. Nutrient deficiency
B. Layered composition
C. `Ca^(+2)` deficiency
D. Rich bacterial growth

Answer

### Step-by-Step Solution:

1. **Understanding Mull Humus**: Mull humus is a specific type of humus that is typically found in grassland ecosystems. It is important to recognize its significance in soil health and fertility.

2. **Characteristics of Mull Humus**:
- **Nutrient Deficiency**: Mull humus is generally not characterized by nutrient deficiency; rather, it is known for its nutrient-rich composition.
- **Layered Composition**: While humus can have a layered appearance, this is not a defining characteristic of mull humus specifically.
- **Calcium Ion Deficiency**: Mull humus is not characterized by calcium ion deficiency; in fact, it tends to have a balanced nutrient profile.
- **Rich Bacterial Growth**: Mull humus is characterized by rich bacterial growth, indicating high biological activity. This is a key feature that distinguishes it from other types of humus.

3. **Conclusion**: Based on the characteristics discussed, the defining feature of mull humus is its rich bacterial growth, making it biologically very active.

4. **Final Answer**: Mull humus is characterized by rich bacterial growth.