Which of the following is not considered organic matter when added to soil?

Lime is not considered organic matter when added to soil because it is a mineral that primarily consists of calcium carbonate or calcium oxide, which does not decompose like organic materials. Organic matter refers to the remnants of once-living organisms, which can contribute nutrients to the soil as they break down.

In contrast, peat, manure, and leaf mold are all derived from organic sources. Peat is partially decomposed plant material that accumulates in wetland areas, manure is the waste produced by animals that is rich in nutrients, and leaf mold is made from decomposed leaves. These organic materials improve soil structure, water retention, and provide essential nutrients for plant growth. Therefore, the inclusion of lime in soil relates more to its role in altering pH rather than contributing to the organic content of the soil.