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Keywords:

  • carbon sequestration;
  • eddy covariance;
  • global change;
  • tillage practices

Abstract

Mitigating or slowing an increase in atmospheric carbon dioxide concentration ([CO2]) has been the focus of international efforts, most apparent with the development of the Kyoto Protocol. Sequestration of carbon (C) in agricultural soils is being advocated as a method to assist in meeting the demands of an international C credit system. The conversion of conventionally tilled agricultural lands to no till is widely accepted as having a large-scale sequestration potential. In this study, C flux measurements over a no-till corn/soybean agricultural ecosystem over 6 years were coupled with estimates of C release associated with agricultural practices to assess the net biome productivity (NBP) of this no-till ecosystem. Estimates of NBP were also calculated for the conventionally tilled corn/soybean ecosystem assuming net ecosystem exchange is C neutral. These measurements were scaled to the US as a whole to determine the sequestration potential of corn/soybean ecosystems, under current practices where 10% of agricultural land devoted to this ecosystem is no-tilled and under a hypothetical scenario where 100% of the land is not tilled. The estimates of this analysis show that current corn/soybean agriculture in the US releases ∼7.2 Tg C annually, with no-till sequestering ∼2.2 Tg and conventional-till releasing ∼9.4 Tg. The complete conversion of land area to no till might result in 21.7 Tg C sequestered annually, representing a net C flux difference of ∼29 Tg C. These results demonstrate that large-scale conversion to no-till practices, at least for the corn/soybean ecosystem, could potentially offset ca. 2% of annual US carbon emissions.