How do humus levels indicate soil's organic content?

Humus levels indicate soil's organic content as they represent the stable, decomposed organic matter in the soil.

Humus is the end product of the decomposition process of organic matter, such as plant and animal materials, by soil microorganisms. It is a complex, stable substance that is resistant to further decomposition and is rich in carbon and other nutrients. Therefore, the level of humus in the soil is a direct indicator of the soil's organic content.

The organic content of soil is crucial for its fertility and overall health. Organic matter contributes to the soil's structure, water-holding capacity, nutrient availability, and microbial activity. It also plays a significant role in the soil's ability to sequester carbon, which has implications for climate change.

Humus levels can be determined through various methods. One common method is the loss-on-ignition (LOI) method, which involves heating a soil sample to a high temperature (usually around 550°C) and measuring the weight loss. The weight loss represents the organic matter that has been burned off, and thus gives an indication of the humus level.

Another method is the Walkley-Black method, which involves oxidising the organic matter in a soil sample with a strong chemical oxidant, and then measuring the amount of oxidant consumed. This gives a measure of the organic carbon content of the soil, which can be used to estimate the humus level.

It's important to note that while humus levels give an indication of the soil's organic content, they don't provide a complete picture of the soil's fertility or health. Other factors, such as the soil's physical properties (e.g. texture, structure), chemical properties (e.g. pH, nutrient levels), and biological properties (e.g. microbial activity), also play a crucial role. Therefore, a comprehensive soil analysis should take into account all of these factors.