What is the primary characteristic of humus?

It undergoes decomposition at an extremely slow rate.

The correct answer is a) It undergoes decomposition at an extremely slow rate.

The primary characteristic of humus is that it undergoes decomposition at an extremely slow rate. Humus is a highly decomposed organic material that forms during the process of decomposition. It is the end product of the breakdown of organic matter by microbial and enzymatic activity.

Unlike less decomposed organic matter, which is more readily broken down by microorganisms, humus is highly resistant to further microbial action. Its resistance to decomposition is due to its complex molecular structure and chemical composition, which make it difficult for microbes to break down.

Humus is known for its stability and long-term persistence in the soil. It decomposes at an extremely slow rate, often taking decades or even centuries to undergo significant changes. This slow decomposition rate allows humus to serve as a long-term reservoir of organic matter and nutrients in the soil.

Humus also possesses other important characteristics. It is colloidal in nature, meaning it forms small particles that have a large surface area, which enhances its ability to retain water and nutrients. However, it is not highly soluble in water (option b). Humus is not primarily broken down easily by microbial action (option c), but rather it is microbially resistant. While humus does contain nutrients, it is not specifically rich in nitrogen and water-soluble substances (option d). Its nutrient content varies depending on the composition of the original organic matter from which it formed.

In summary, the primary characteristic of humus is its slow decomposition rate, making it highly stable and resistant to further microbial breakdown.