The term 'soil layer' refers to the different layers of soil that can be found in the ground. The two most common soil layers are LOAM and solum. LOAM is a type of soil composed of clay, sand, silt, and organic matter. It is known for its ability to retain moisture and nutrients, making it ideal for growing plants. Solum is a deeper layer of soil that is composed of mineral particles and organic matter. It is usually darker in color than LOAM and is more resistant to erosion. Both LOAM and solum are important components of healthy soil and are essential for plant growth.