Nearly 80 percent of the compaction caused by wheel traffic occurs on the first pass. This is the basis for suggesting the same track be used for repeated passes (controlled traffic).
One rule-of-thumb suggests that compaction will occur to an 8 to 10 inch depth from axle weights less than five tons. However, some 6-row combines have 10 tons on the front axle with a full grain tank and tricycle fertilizer spreaders may carry 14 tons on the rear axle. Therefore, significant compaction can occur below the 10-inch depth and tillage and frost action may not be able to relieve the effect.
The severity of loads and pressures in the subsoil is evident from the breakage of large drain tile by excessive loads. A liquid manure spreader with a 1650 pound moving load per wheel will exceed the strength of a 15-inch special quality concrete drain tile in a trench 24 inches wide with a flat bottom and 36 inches of soil cover. The tile will be safe for the example load if the trench bottom is shaped to fit the tile rather than left flat. The problem is less severe with small diameter laterals than with large mains.
Most effects of compaction are detrimental. However, in some cases slight compaction near seeds can aid germination and improve plant growth in times of low soil moisture caused by low rainfall or low water-holding capacity soils. In Ohio, soil compaction usually has a net negative effect.