Soils were collected from all 21 DIRT plots on June 13, 2000.  Oea and 0-10 cm mineral soil samples were taken from three locations in each plot (no Oea from OA-less plots 5, 7, and 21).  Where possible, two sampling sites (reps A and B) were located near the zero tension lysimeter and the third (C) located on the opposite side of the plot.  All samples were taken close to the plot border.

O horizon: Each sample consisted of a 3” x 3” square of Oea material cut from the forest floor of each plot.   The O/A boundary was interpreted differently among the four persons collecting soils, resulting in the inclusion of mineral soil in some Oea samples.  The excess mineral soil was removed before sieveing and the mass data were corrected for this.

Mineral horizon: Mineral 0-10 cm cores were taken directly beneath the locations from which O samples were collected. Cores were taken with a 1” diameter Oakfield corer, and measured 10 cm in length by 4.8 cm in diameter. Some compaction of the soil may have occurred during coring, possibly affecting bulk density values.

Fresh weights were recorded for all samples, and subsamples were taken for moisture analysis at 50 and 105 degrees C.  The rest of the sieved material was air-dried in a greenhouse at 40-60 degrees C to minimize C loss due to microbial respiration while drying.  All samples were ground with a mortar and pestle.    Subsamples of Oea soil were further ground in a ball mill at the Ecosystems Center and dried at 50 degrees (some dried at 40 degrees due to oven malfunction) prior to CHN analysis.