15.3 Soil fertility is determined by soil structure and nutrient retention Topsoil usually Soil Layers contains sand. silt and clay. 3 0 Horizon(humus Fertile topsoil is a A Horizon (topsoil E Horizon (eluviation layer) mixture of at least four components I B Horizon(subsoil mineral particles water, ar, organIC C Horizon (regolith matter R Horizon(bedrock EnchantedLearning. com15.3 Soil fertility is determined by soil structure and nutrient retention • Topsoil usually contains sand, silt, and clay. • Fertile topsoil is a mixture of at least four components: mineral particles, water, air, organic matter