Agronomists' study involves the study of soils and SOIL. Soils are a complex mixture of minerals, organic matter, gases, liquids, and organisms that together support life. SOIL is the uppermost layer of the Earth's surface, consisting of rock and mineral particles mixed with organic matter. Agronomists use their knowledge of soils and SOIL to help farmers and gardeners improve crop yields, reduce SOIL erosion, and increase SOIL fertility.