Final answer:
Mulch is the correct answer as it is the organic material, like straw or compost, spread on the soil to enrich it, conserve moisture, and inhibit weeds. Humus, silt, and loam are all components of soil but do not serve the specific purpose of mulch.
Step-by-step explanation:
The organic material such as straw or compost used on the ground around plants to enrich the soil is known as mulch. Mulching helps to keep the soil moist, reduces weed growth, and improves soil quality. Mulch can be made of various organic materials including straw, leaves, wood chips, and compost. It not only protects the soil from erosion but also provides essential nutrients as it breaks down. This provides a favorable environment for earthworms and other beneficial organisms.
Humus is the organic material of soil, made of microorganisms, dead animals, and plants in varying stages of decay, and it improves soil structure and provides water and minerals. Silt is composed of soil particles between 0.002 and 0.1 mm in size, whereas loam is a mixture of sand, silt, and humus with no dominant particle size, which makes it an ideal plant-growing medium due to its nutrient content and good drainage.