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Long-term effects of tillage and corn stalk return on the dynamics of old and new carbon pools.
Hooker, Beth*,1, Morris, Thomas1, Cardon, Zoe1, 1 University of Connecticut, Storrs, CT
ABSTRACT- The ability to increase pools of soil organic carbon (SOC) in agricultural ecosystems is of interest both for sequestering atmospheric CO2 in relatively long-lived soil pools, and for restoring organic matter pools that are important to soil "health." It has been well established that tillage and harvest management regimes can influence SOC in cropland, but long-term, continuous experiments are rare. Such experiments are essential for exploring processes whose results accrue slowly in soils. We are investigating the dynamics of old and new soil carbon pools using 13C analysis in corn fields established in 1972 at the UConn Research Farm. The plots have been under no-till (NT) or conventional till (CT) management, with silage corn (no residue returned annually) or grain corn (shoot residue returned annually), with three replicates. These plots are very unusual in long-term (>20 year) agricultural experiments because both tillage differences and differential aboveground C input practices are in place. Our data indicate that the relative half life of the relic C3-C (g C kg-1) is not influenced by tillage or C input levels in the upper 5 cm of the soil, though significantly more relic C3-C has been lost from the tilled, silage treatment in the 5-15 cm depth than from other treatments. After 30+ years of corn shoot return to the grain plots, the total amount of corn-derived C remaining in grain or silage treatments under NT or CT is similar, even though nearly four times as much C was applied to the grain plots. Our results indicate that there is a rapid cycling of the aboveground corn-derived C back to the atmosphere. This calls into question the potential for the annual return of biomass to substantially increase soil C storage over the long term.
Key words: agroecosystem, carbon sequestration