Increase of soil strength over time in a US southeastern coastal plain loamy sand

With rising energy costs, fuel-consumptive soil management practices, such as deep tillage, need to be reassessed to determine whether they need to be performed every year or not. Between 1978 and 1996, conservation (nondisked) and conventional (disked) tillage treatments had been annually deep-tilled with noninversion subsoiling to break up a subsurface layer that had high soil strength, associated with the E horizon of a coastal loam sand. After 1996, treatments were split with half being deep-tilled until 2001, after which no treatments were deep-tilled, although surface tillage continued. By 1999, soybean (Glycine max L. Merr.) treatments in which deep tillage ceased in 1996 were significantly higher in cone index (as measured by a penetrometer) than were treatments that had been deep-tilled, suggesting that the effects of deep tillage lasted three years. By 2004, conventional treatments in which tillage ceased in 2001 had reconsolidated to the point that they were not different from conventional treatments where tillage had ceased in 1996. However, conservation tillage treatments were still significantly different, suggesting that conservation tillage can help buffer the effects of reconsolidation. Two competing trends could be observed. On the one hand, although reconsolidation might not be complete, soils with incomplete reconsolidation could be hard enough to reduce production. On the other hand, soils in which tillage ceased still showed the effects of deep tillage even after they reconsolidated to the point that they were statistically different from deep-tilled treatments.