What is the purpose of Humus?

• A. To Replace Sulfur
• B. To Aid in Compaction
• C. To Increase Water Retention
• D. To Decrease Water Retention

Answer: (C)

Humus is the dark, decomposed organic matter in soil. Its main role is to increase the soil’s water-holding capacity. It acts like a sponge, absorbing and retaining moisture so plant roots can access water during dry periods. Beyond that, humus improves soil structure by helping form stable aggregates, which enhances porosity, drainage, and nutrient retention over time. Among the options, increasing water retention best matches humus’s primary function. It does not replace sulfur, it doesn’t aid compaction, and it certainly doesn’t decrease water retention—in fact, it helps soils hold more water.