What commonly forms in soils repeatedly plowed at the same depth?

• A. Erosion rill
• B. Leached horizon
• C. Hardpan or plowpan
• D. Soil crust

Answer: (C)

When soil is tilled to the same depth over and over, a dense, compacted layer forms just below the cultivated zone. This is called a plowpan (or hardpan). The repeated disturbance and the weight of farming traffic squeeze the loosened material, expelling air and allowing fine particles and clays to rearrange and cement together, which reduces pore space and permeability. That compact layer becomes harder for roots to penetrate and for water to move through, limiting root growth and drainage. To prevent or break it up, farmers may vary tillage depth, use subsoiling or deep ripping to fracture below the pan, reduce traffic on wet soil, and add organic matter to improve soil structure.