A compacted layer may develop in some, but not all plowed soils. Often located just below tillage depth, it is slightly darker in color than the soil above. Plowing at the same depth year after year encourages its formation and it becomes an effective barrier against water movement and root growth. These layers can be destroyed mechanically by the use of subsoilers, deep-set chisel plows, or by plowing at variable depths. However, these remedies are temporary unless soil management practices change so that roots and earthworms can effectively penetrate compacted layers.
Compacted layers are severe in tomato production areas.
Discs Discs used as primary tillage implements on sandy soils can form a disc pan below tillage depth. Disc pans often limit crop growth particularly on sandy knolls. The pan can be removed by setting the shanks on a chisel plow or a heavy field cultivator to operate below the pan depth. The seedbed zone on the top of ridges is 8 to 12 cm in thickness. The soil aggregates in this zone are generally fine to medium in size and increase in size beneath this layer.