Our method of pH determination was based on the method published in: Methods of Soil Analysis. Part 3: Chemical Methods. 1996. Published by Soil Science Society of America, Inc., and American Society of Agronomy, Inc. Madison, WI, USA.

We modified that method as follows:

1. Soils were mixed with 0.01M CaCl₂ instead of water.
2. We used a 2:1 liquid:soil ratio for mineral soils and a 4:1 ratio for organic soils.

Measurements were made using air-dry soil.

pH was measured on replicate soil cores at each depth in each plot for Bousson Forest 1996 soils and for Univ. of Wisconsin Arboretum 1997 soils. Only one sample per depth per plot was measured for pH for the Harvard Forest 1991 and 1995 soils.

Where replicate samples were measured, the average pH of the replicates and the standard error are given.

Avg = mean pH by treatment
se = + 1 standard error of the mean, calculated as: [standard deviation (sample) of the mean /square root of n]
n = number of samples
trt = treatment (if given)
blk = block (if given)