Humification leads to:

The correct option is Accumulation of humus.

Humification is a key stage in the process of decomposition of organic matter in the soil.
During decomposition, dead plant and animal remains are broken down by soil microorganisms. This process involves two main sequential steps: humification and mineralization.

Humification leads to the accumulation of a dark-coloured, amorphous substance called humus in the soil.
Humus is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. Because it is colloidal in nature, it also serves as a reservoir of nutrients, thereby improving soil fertility and structure rather than causing erosion or salt accumulation.