Humus is a complex organic substance that is formed by the decomposition of dead plant and animal matter. It is an essential component of healthy soils because it helps to improve soil structure, retain moisture, and provide nutrients for plants. However, humus is not a static substance, and it can be affected by a variety of factors, including microbial activity.

Why Humus is not Good for Plant Growth?

Humus is not good for plant growth because it does not contain all of the necessary nutrients that plants need to survive and thrive. While humus does contain some nutrients, such as nitrogen, phosphorus, and potassium, it is not a complete fertilizer. In addition, the nutrients in humus are not always readily available to plants, as they may be bound up in complex organic molecules that must be broken down by soil microbes before they can be used by plants.

Why Humus is not Resistant to Microbial Action?

Humus is not resistant to microbial action because it is made up of organic matter that is highly susceptible to decomposition by microorganisms. In fact, the process of humus formation is largely driven by the activities of soil microbes, which break down complex organic molecules into simpler compounds that can be used by plants. Without microbial activity, humus would not be formed, and soils would be much less fertile.

Why Humus is Reservoir of Nutrients?

Humus is a reservoir of nutrients because it contains a variety of organic compounds that can be broken down by soil microbes to release essential nutrients for plant growth. In addition, humus helps to retain nutrients in the soil by binding them to organic matter and preventing them from being washed away by rainfall or irrigation. This means that soils rich in humus are able to provide a steady supply of nutrients to plants over time, even in the face of environmental stresses such as drought or nutrient depletion.

Conclusion:

In conclusion, humus is an important component of healthy soils, but it is not a complete fertilizer and it is not resistant to microbial action. However, it does serve as a reservoir of nutrients and helps to improve soil structure and moisture retention, making it an essential component of sustainable agriculture.

If we see comparatively others option are not answers so it is d but at some point you cannot even say it that d is option coz it is not wrong also