Quantitative Guidelines for Establishing and Operating Soil Archives

Soil archives are widely recognized as important, but there is limited information available on the basic elements of archive design, such as how much material to archive, which sites and horizons to prioritize, and the most effective way to promote an archive. Here I address these gaps based on 6 yr of operating the National Ecological Observatory Network's (NEON) Megapit Soil Archive, which has provided over 1500 samples to researchers. Active outreach by NEON staff was the most effective way of raising awareness of the archive among the user community. On average, 14.6 +/- 4.3 g soil was sent to requesters per sample per year, with soils from A horizons and intensively studied sites consumed fastest. Based on these consumption rates and depending on soil horizon and site type, archiving between 22.3 and 39.9 g soil for each year of a sample's desired lifespan would be sufficient to ensure that it is not exhausted earlier than expected with >= 89% confidence. Similarly, 500 g of archived soil would be sufficient for the vast majority of samples to last at least 12 to 22 yr, depending on horizon and site type. A simple equation is proposed, and parameterized using NEON data, to determine the quantity of soil necessary to archive if the desired sample lifespan is known. Setting a desired lifespan can inform archive management decisions, such as the number of requests to approve and whether to increase or decrease the allocation of resources to raising awareness of the archive.