Plant Residue Decay in Diverse Canadian Soils.

The decay of plant residues is tied to many ecosystem functions, affecting atmospheric CO₂, plant-available nutrients, microbial diversity, soil organic matter quality, among others. The rate of decay, in turn, is governed by a range of management, soil, and environmental variables, some of which may be changing in coming decades. To describe mathematically the importance of these variables across a broad scale, we established in 2007 a long-term study at 10 sites across the agricultural regions of Canada, spanning a range of climate and soil properties. At each site, barley straw enriched with ¹³C (10 atom%) was applied at 200 kg C m^-2 to soil microcosms (15 cm long, 10 cm diameter) inserted to 10 cm depth. All microcosms received additional unlabelled residue every fall (200 kg C m^-2) and ammonium nitrate every spring (40 kg N ha^-1).  Hourly soil temperature was logged throughout the year at each site, and soil water content was also monitored during the frost-free period at one of the sites (Ottawa). Four replicate microcosms were removed from each site about 0, 0.5, 1.0, 2.0, and 3.0 years after applying residue to estimate decay using isotopic analysis. At all sites, recovery of applied ¹³C initially declined quickly – roughly half of the ¹³C was lost within a year – but the rate of loss then slowed. After 3 years, the amount of applied ¹³C remaining ranged from 13 to 28%. Much of the difference in observed loss among sites was related to variation in soil temperature. These findings illustrate the differences in initial decay rates across diverse sites, but suggest that prediction of decay rate can be improved with a simple algorithm based on cumulative thermal units. Future research, involving additional sites in an international network, will explore ways of including mathematically also other variables such as soil moisture and clay content.

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 [EG1]Wording?

See more from this Division: SSSA Division: Soil Chemistry
See more from this Session: Climate Change Impacts on Soils: Understanding and Estimating the Extent and Rates of Reactions, Processes, Interactions and Feedbacks

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