Which of the following is NOT one of the five soil-forming factors?

Soil-forming factors are the primary influences that lead to the development and characteristics of soil. These include parent material, climate, topography, and biological activity, among others. Each of these factors contributes to the formation and evolution of soil over time.

Parent material refers to the underlying geological material from which soil horizons develop. Climate affects soil development through temperature and precipitation, which influence the rate of weathering and organic matter decomposition. Topography influences drainage patterns and how water moves across the landscape, which can affect soil moisture levels.

Soil structure, on the other hand, describes the arrangement of soil particles into aggregates or clumps and is influenced by various factors, including biological activity and moisture content. While it is an important characteristic of soil, it is considered a result of the interaction of the soil-forming factors rather than a factor itself. Thus, when identifying the five soil-forming factors, soil structure does not belong in that classification as a fundamental cause of soil formation but rather describes a property that develops as a result of those factors.