INCRI~E OF SOIL STRENGTH OVER TIME IN A US SOL'THEASTERN COAST At PLAIN LOAMY SAND

With rising energy costs, fuel-consumptive soil management practi-ces, such as deep tillage, need to be reassessed to detern1ine whether they need to be perforn1ed 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. Mter 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