Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2006
Publication Date: 3/12/2007
Citation: Novak, J.M., Bauer, P.J., Hunt, P.G. 2007. Carbon dynamics under long-term conservation and disk tillage management in a Norfolk loamy sand. Soil Science Society of America Journal 7l(1):453-456.
Interpretive Summary: The concentration of carbon dioxide in the atmosphere has been increasing and scientists have been exploring methods to reduce its concentration. Because soils hold more carbon than the atmosphere, it is an important carbon storehouse, soil scientists have been studying tillage methods that can reduce crop residue decomposition rates, thereby trapping more soil carbon. Our research has been focused on examining the long-term (24 yrs) effects of tillage on soil carbon levels in a sandy, coastal plain soil. We measured soil carbon levels in plots that were tilled using conventional and conservation tillage practices. We found that soil carbon levels under conservation tillage, where the plant residue is mainly left on the soil surface, had higher levels compared to conventional systems. Lower soil carbon contents occurred under conventional tillage systems because plant residues were mixed into the soil, which accelerated decomposition and carbon dioxide production. The soil carbon levels under conservation tillage after 24 yrs, however, had reached a plateau. Our results showed the importance of using conservation tillage as a countermeasure to reduce carbon dioxide production by sequestering more soil carbon. Unfortunately, the soil after time can reach a saturation level, where no additional carbon can be sequestered.
Technical Abstract: Conservation tillage (CnT) and crop management practices in short-term field experiments (5-15 yrs) have produced substantial increases in soil organic carbon (SOC) concentrations. Because it may take a few decades for C inputs vs. outputs to reach a steady state, short-term studies can potentially underestimate a soil's capacity to store organic carbon (OC). Questions remain as to the long-term (15 to 50 yrs) effects of management practices on SOC levels. Our objective was to ascertain the effect of long-term (24 yrs) conservation tillage and conventional (CvT) tillage management on C sequestration in plots containing a Norfolk loamy sand soil (Fine-loamy, siliceous, thermic, Typic Kandiudults). Between 1994 and 2003, the plots were under a 2-yr crop rotation of corn (Zea mays L.), soybean (Glycine max L.), or cotton (Gossypium hirsutum L.), and winter wheat (Triticum aestivum L.). CnT plots (n = 10) were subsoiled while CvT plots (n = 10) were subsoiled and surface harrowed. SOC was measured in soil cores (90 cm deep) and expressed on a g/kg and a Mg/ha basis. The mean SOC concentration (as g/kg) in the 0- to 5-cm depth of the CnT plots was significantly higher than in the CvT plots. No difference in SOC concentration was found at greater depths. Slopes from the regression equations between the annual mean SOC contents (as g/kg) in the 0- to 5-cm depth vs. yr were equal to zero indicating that the SOC contents were at a saturation phase of equilibrium. When the SOC contents were expressed on a Mg/ha basis, OC sequestered at 0- to 5-cm depth under CnT was 15.3 Mg/ha while only 6.8 Mg/ha was sequestered in soils under CvT. Although CnT effectively increased SOC levels, these tillage plots have reached steady-state OC equilibria. Additional augments in C sequestration may be possible, but will require significant shifts in current crop or soil management practices.