CR-21 Landscapes and Irrigation Practice Test 2026 – Your All-In-One Guide to Exam Success!

Humus, the stable organic matter in soil, acts like a sponge. Its porous, crumbly structure creates long-lasting pore spaces that hold onto water and release it slowly to plant roots, boosting the soil’s water-holding capacity. This moisture-retaining quality is the most direct and impactful effect humus has on soil, helping plants stay hydrated between rainfall events. While humus does contribute nutrients over time and can darken soil color, these effects are secondary to its role in retaining water. Air porosity can improve as organic matter helps form aggregates, but the primary association of humus among these properties is its ability to retain water.