turnedunder

Turned-under is a term used in agriculture and horticulture to describe the practice of burying plant material, such as crop residues or cover crops, by mechanically turning the soil over. The material is incorporated into the topsoil to decompose, release nutrients, and improve soil structure. The concept is closely linked to residue management and green manuring within crop rotations.

In practice, turned-under can be achieved with various tillage tools, including plows, disks, and harrows. Timing and depth vary with goals: residues may be incorporated after harvest to reduce left-over debris, or green manures and cover crops may be turned under before planting to add organic matter and nutrients. Shallow incorporation preserves surface residues where desired, while deeper incorporation can mix organic matter more uniformly into the soil profile.

Benefits commonly associated with turned-under include increased soil organic matter, improved soil structure and aeration, and enhanced microbial activity. When leguminous cover crops are used, nitrogen can be added to the soil as they decompose. Turned-under residues can also help suppress weeds and reduce pest habitat. However, risks include erosion if performed on exposed ground, potential nutrient immobilization during decomposition, and disruption of surface soil life. It may also lead to higher energy use and greenhouse gas emissions compared with no-till approaches.

Turned-under is often contrasted with no-till or reduced-till systems, which leave residues on the surface rather than burying them.