The high organic matter content typical of grasslands is primarily due to what feature?

• A. Frequent tillage
• B. High rainfall
• C. Extensive root systems
• D. Long-term droughts

Answer: (C)

Extensive fibrous root systems are the primary source of soil organic matter in grasslands. Grasses invest a large portion of their carbon below ground, with dense, fine roots that turn over continually. Each cycle of root growth and death adds carbon-rich material to the soil, feeding microbes and helping form stable organic matter and soil structure. This steady below-ground input builds up organic matter over time far more than aboveground litter alone, which is often eaten or decomposed more quickly.

Frequent tillage would disrupt and oxidize organic matter, reducing its accumulation; while rainfall and drought affect how much biomass is produced, they don’t by themselves explain why grassland soils become rich in organic matter—the continual root turnover is the decisive factor.