Soil improver is a term used to describe materials that are added to soil to improve its fertility and structure. Two common soil improvers are HUMUS and peatmoss. HUMUS is a dark, organic material that is formed when plant and animal matter decomposes. It helps to improve the water-holding capacity of soil, as well as its nutrient content. Peatmoss is a type of moss that is found in wetlands and bogs. It is often used as a soil amendment because it helps to improve soil drainage and aeration, as well as increase the soil's ability to retain nutrients.