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Organic carbon convergence in diverse soils toward steady state: A 21-year field bioassay

Yanni, S.F., Janzen, H.H., Gregorich, E.G., Ellert, B.H., Larney, F.J., Olson, B.M., Zvomuya, F. (2016). Organic carbon convergence in diverse soils toward steady state: A 21-year field bioassay, 80(6), 1653-1662. http://dx.doi.org/10.2136/sssaj2016.07.0214

Abstract

© Soil Science Society of America. The response of soil organic matter (SOM) to an abrupt change in environment and management was studied in a long-term field bioassay. Thirty-six soils, with a wide range of SOM reflecting large differences in management, climate, and ecological histories, were selected and transported to a common site at Lethbridge, Alberta, Canada. The experiment included control and N-fertilized treatment plots. The plots were seeded annually to spring wheat and managed under no-till rain-fed conditions, with annual removal of aboveground residues. The soils were sampled every 7 yr and analyzed for organic C (OC), total N (TN), and light fraction C (LF-C) and N (LF-N). Most of the soils lost OC and TN over 21 yr, and the amount of loss was highly related to the original contents (9-74 g C ka-1, 1.4-6.4 g N ka-1). Similarly, LF-C and LF-N, indices of labile OM, declined in most soils, but the rate of loss was faster than for OC. In a few soils, SOM slowly increased from initially low levels. The soils seem to be progressing toward a steady state, although complete convergence of OC and TN may not occur for a century or longer based on an exponential model. Labile OM may converge within a few decades, so that these soils, conceivably, will still have widely different OC and TN but similar labile SOM, with possible implications for soil health. Our findings demonstrate the value of long-term field bioassays for improved understanding of SOM dynamics in response to management and climate change.

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