CHANGES IN CARBON CONTENT OF A NORFOLK LOAMY SAND AFTER 14 YEARS OF CONSERVATION OR CONVENTIONAL TILLAGE

Soil carbon (C) management is vital for sandy southeastern Coastal Pla in (SCP) soils that are naturally low in C. A long-term investigation began in 1979 to determine if conservation tillage would increase the C content of a Norfolk loamy sand (Typic Kandiudult) with a cropping s ystem that included corn (Zea mays L.) cotton (Gossypium hirsutum L.) soybean [Glycine max (L.) Merr.], and wheat (Triticum aestivum L.). Pl ots were 60 m (196.8 ft) long and 23 m (75.5 ft) wide with five replic ations Before modern conservation tillage technology was available, in creasing soil C was believed to be nearly impossible under row crop pr oduction, particularly if cotton and soybean were part of the rotation . Tillage (conventional vs. conservation) war the main plot treatment. At the beginning of the experiment, C contents were not significantly different. In years 9 to 14, the mean C content of the 0- to 5-cm (0- to 2-in) depth for conservation tillage war nearly double that for co nventional tillage: 12.0 vs 7.2 g kg(-1) (1.2 and 0.72%) (P less than or equal to 0.05). The r(2) of C content vs time over the 14 years was 0.44 for the 0- to 5-cm layer of the conservation tillage plots. The slope was 0.61 g kg(-1) yr(-1) (0.06%) and the probability that the sl ope was zero was < 0.001. A smaller slope increase of 0.17 g kg(-1) yr (-1) (0.017%) also existed for conservation tillage at the 5- to 10-cm (2.0- to 3.9-in) depth. The C content was not consistently different between tillage treatments below the 15-cm (5.9-in) depth. Improved eq uipment, management and soil quality allowed conservation tillage plot s to produce greater yields during years 9 to 14. Long-term conservati on tillage of row crops appears to be a viable method of increasing th e C content of sandy SCP soil even when soybean and cotton are part of the rotation.