The Effect of Earthworm (Lumbricus terrestris L.) Population Density and Soil Water Content Interactions on Nitrous Oxide Emissions from Agricultural Soils
Earthworms may have an influence on the production of , a greenhouse gas, as a result of the ideal environment contained in their gut and casts for denitrifier bacteria. The objective of this study was to determine the relationship between earthworm (Lumbricus terrestris L.) population density, soil water content and emissions in a controlled greenhouse experiment based on population densities (90 to 270 individuals ) found at the Guelph Agroforestry Research Station (GARS) from 1997 to 1998. An experiment conducted at considerably higher than normal densities of earthworms revealed a significant relationship between earthworm density, soil water content and emissions, with mean emissions increasing to 43.5？ g at 30 earthworms 0.0333？ at 35% soil water content. However, a second experiment, based on the density of earthworms at GARS, found no significant difference in emissions (5.49 to 6.99？g ) aa a result of density and 31% soil water content. 1. Introduction The presence of earthworms can be seen as an added benefit to many agricultural systems since earthworms contribute greatly to the overall physical properties of agricultural soils [1]. Previous studies in sole cropping systems have focused on the ability of earthworms to facilitate soil mixing and the decomposition of organic matter, which is especially important in agricultural systems [2–4]. Earthworms also affect soil properties, by increasing soil porosity and decreasing bulk density and through bioturbation and cast deposition on the soil surface [1]. Earthworm activity stimulates mineralization of N in residues, which promotes the availability for plants and microorganisms of inorganic forms of N from plant material [1, 5]. However, increased earthworm population might increase the production of nitrous oxide (N2O) emissions from agricultural soils. Over 50% of in situ N2O emissions, in some soils, could be a result of earthworm activity [6]. Recent research suggests that, globally, earthworms could be producing up to ？kg of N2O annually [6]. Conventional agricultural practices, which aim to encourage earthworm populations due to their positive influence on soil properties are the highest anthropogenic sources of N2O emissions. On a global scale, annual emissions of N2O were 16.2？Tg in 2004 [7], and as a result, earthworms could be responsible for nearly 2% of global emissions. One reason for this is that the earthworm gut is an ideal environment for denitrification [8–10]. Using microsensors, Horn et al. [9] determined that the earthworm gut is anoxic and contains copious carbon
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