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The consequences of conversion from conventional agriculture to perennial grassland for soil carbon dynamics .
McLauchlan, Kendra*,1, Hobbie, Sarah1, 1 University of Minnesota, St. Paul, MN
ABSTRACT- Soil organic carbon (SOC) decreased dramatically after native grasslands in the U.S. were converted to agriculture in the early 20th century, and some have proposed managing the depleted soils of the northern Great Plains as a carbon sink. Although SOC is assumed to increase following the conversion of agricultural land back to perennial grassland, surprisingly few studies have documented SOC dynamics in the first few decades after grassland establishment. We sampled a chronosequence of former agricultural sites in western Minnesota that had been converted to perennial grassland at different times over the past 35 years to reconstruct the response of soil properties to this land use change. Specifically, we tested the hypothesis that active fractions of SOC would recover more quickly than total C pools. Contrary to our expectations, neither the pool size nor the turnover rate of mineralizable soil C in surface soils (determined using aerobic incubations) were correlated with length of time since agriculture. In contrast, total SOC and nitrogen in surface soils increased linearly over time. Our results suggest that time since grass establishment is an important determinant of total organic C, but factors other than field age are important in determining the partitioning of that C into active and passive fractions.
KEY WORDS: soil organic matter, land use change, grassland restoration, active carbon pool