DIRT plot soils were sampled from November 18 to December 2, 1991. 15 x 15 cm templates were used to collect Oe+Oa organic horizon samples (referred to as "Oea"). Three Oea samples were taken from each plot (except in OA-less plots). Three 0-10 cm and three 10-15 cm mineral soil samples were also taken from each plot, from directly underneath each Oea sample. The mineral soil cores measured 5.1 cm by 15 cm length.

Sample processing: Mineral soil cores were divided into 0-10 cm and 10-15 cm portions. The 10-15 cm samples were not processed further. After total fresh sample weights were recorded, each 0-10 cm mineral core was passed through a 5.6 mm sieve. A subsample of sieved material was analyzed for moisture content after oven-drying at 105 °C. Oea samples were also passed through a 5.6 mm sieve. Material >5.6 mm was added back to subsamples of sieved material which were then analyzed for moisture content (105°C). Material from Oea samples and 0-10 cm cores was subsequently incubated in a laboratory study in which CO₂ efflux and release of NH₄⁺ and NO₃^- were measured over time. Samples were also analyzed for pH, %C, %N, ¹⁵N, ¹³C. Root mass was also measured.   Bulk density of the Oea and 0-10 cm cores was calculated on a mass per unit area basis (Mg/ha) because volume data for >5.6 mm material were not available.