A Multi-Site Decadal-Duration Litter Decay Study: Problems and Prospects.

Long-term maintenance of soil organic matter depends ultimately on replenishment with plant litter, and the rate of its decay. All our models – whether conceptual or mathematical – depend on understanding how quickly the annual cohorts of litter decompose, and where its remaining C hides in the soil. One way to study these questions is by labeling plant residues with C isotopes, and following the fate of these residues through the long years. In 2007, we established such a study, by incorporating ¹³C-enriched barley residue (~10 atom% ¹³C) in the surface soil (10 cm) at 10 sites across Canada. At five of the sites an additional, surface-placed application treatment was applied. Since then, other sites have been established to expand the range of climates and soil types and include Scotland, California, New Zealand and Inuvik, Northwest Territories, Canada.

Planning and implementing such studies, with an intended lifespan of about 2 decades, pose some logistical challenges such as: producing uniformly-labelled plant residues, applying those residues to soils in the field without artifact, maintaining uniform/consistent management of the experimental plots, ensuring the long-term survival of sites, and sampling and archiving soils with future analyses in mind. Inevitably, such experiments involve simplifying assumptions and compromises which should not be overlooked. Still, if carefully managed and interpreted, they provide data and samples that may not be available from any other approach.

In this paper we describe our rationale for establishing this study, the protocol used for pulse labeling the barley residue, the experimental plot layout, management and maintenance, and the protocols for gas and soil sample collection and analysis.