Submitted to: Extension Reports
Publication Type: Other
Publication Acceptance Date: 4/27/2005
Publication Date: 5/1/2005
Citation: Novak, J.M. 2005. Soil organic carbon in long-term tillage plots has reached a plateau. North Carolina Soil Quality Newsletter. 8(1):1-2.
Technical Abstract: Past agricultural management activities have contributed to soil organic carbon (SOC) losses, which can reduce soil productivity, rainfall infiltration, and soil pesticide retention. Fortunately, SOC can be increased using conservation tillage and crop management systems, which sequester more SOC than conventional systems. In the Southeastern USA Coastal Plain, it takes between 5 to 10 yrs of managing soils with conservation practices to significantly increase SOC contents above levels occurring in soils under conventional tillage management. Information is sparse showing the long-term effects (> 20 yrs) of tillage and crop management on SOC levels. The long-term (1979 to 2003, or 23 yrs) effects of conservation and conventional tillage management on SOC sequestration in a Norfolk soil (Fine-loamy, siliceous, thermic, Typic Kandiudults) were monitored in plots in a 2-yr rotation with corn (Zea mays), winter wheat [(Triticum aestivum (L.)], soybean [Glycine max (L.) Merr.], and cotton [Gossypium hirsutum (L.)], in the South Carolina Coastal Plain region. The conservation tillage plots (n = 10) were deep-tilled, while conventional plots (n = 10) were deep-tilled and surface disked. After 23 yrs, the mean SOC contents (as g/kg) in the 0- to 5-cm depth of the conservation tillage plots were significantly different than the conventional system. No differences in SOC were found at greater depths. Additionally, the annual mean SOC contents in the 0- to 5-cm depth were at a maximum after 15 yrs of management and did not significantly change under either tillage systems between 1993 and 2003. This implies that the soils, under this tillage and crop management scheme, were at C saturation. Results from this study showed that SOC accumulation reaches a saturation limit, which ultimately governs the soil C sink limit.