Smaller sized pieces produce a more effective mulch. Animal residue such as manure . Do not cover newly sown seeds with mulch. If the plants or trees are already established, just pile mulch around the bases of trees in 1 m diameters. Humus contains chemical and mineral substances in forms that plants can use immediately.
Humus is also the form of organic matter that most directly adds to a soil's productive properties.
Composting simply speeds the organic matter breakdown process that occurs over time in nature when the same materials pile up in layers on the soil surface as mulch. Composted organic matter can be placed in direct contact with plant roots as a soil amendment or bedding material. Compost improves soil properties just as mulch does just more immediately and extensively. Compost is really just partially decomposed mulch. Such soil resists compaction and erosion.