The Effects of Aging on pH in Forest Soil Samples

pH measurements are the backbone of chemical soil analyses. Measuring pH is a simple and fast method of elucidating the general chemical properties of a particular soil. pH affects the cation exchange capacity of soils and, thus, the nutrient availability of necessary plant resources. The goal of this paper is to showcase a repeated analysis of forest soil pH from 2002 and 2020. Research samples often stay in laboratory storage for long periods of time. In some instances, there is a backlog of analyses that can affect when soil samples can by tested. Regarding long-term monitoring studies, the best method of sample comparison is rerunning old samples when new samples come into the lab for analysis. In these scenarios, it is imperative that researchers can be confident that their results are accurate with respect to the sample’s properties on the day it was collected. To this end, this research project aims to determine if there is a change in sample measurement results over time. Using B horizon samples from the Vermont Monitoring Cooperative 200-Year Soil Monitoring Study, pH data measured in 2002 was compared to pH data collected in 2020. The B horizon was chosen because it was thought to be the most likely to show changes over time and be unaffected by organic horizon development. The soil from the same exact samples were analyzed to determine if there is a significant change in pH after long periods of storage. Using a two-sided paired t-test, there was determined to be a statistically significant difference in measured pH from 2002 to 2020 (t(36) = -4.27, p \u3c 0.001. In addition to storage effects, B horizon cation sample measurements were also compared from each year of the study to determine possible changes in the soils in the field. There were statistically significant changes in the means of aluminum, calcium, potassium, magnesium, and manganese among years. These differences over the first 15 years will need to be borne out by further sampling and reanalysis. Overall, the recommendation is to analyze soils as soon as feasible after sampling to avoid any changes during storage