Highfield, Rothamsted

On Highfield at the Rothamsted Research facility in Hertfordshire, UK, a continuous grass pasture plot went from 2.7% organic matter to 3.2% over 40 years, from 1949 to 1989. By contrast, the part of the pasture turned into arable ground lost carbon, going from 2.7% organic matter to 1.6% over the same period, a 41% loss.

See p. 42 of the Long Term Experiment publication by Rothamsted.