Carbon and nitrogen storage by deep-rooted tall fescue ( Lolium arundinaceum) in the surface and subsurface soil of a fine sandy loam in eastern Canada

Compared to annual crops, the use of deep-rooted vegetation, such as perennial grasses, in agricultural systems can increase soil organic C (SOC) storage deep within the soil profile. However, this potential increase could be adversely influenced by physical limitations in the soil profile. Tall fescue ( Lolium arundinaceum Schreb.) was grown for 7 years after a long-term tillage experiment on a fine sandy loam (Orthic Podzol) in Prince Edward Island which had naturally compacted subsoil. Soil samples from the 0–60 cm soil depth (divided into five depth increments) were collected periodically from 2000 to 2007 to evaluate the potential for tall fescue to increase SOC and total N (TN) storage and depth distribution in the soil profile, especially in subsurface soil layers. Light fraction C (LF-C) and particulate organic matter C (POM-C) were also evaluated as indicators of SOC change in the soil profile. Annual tall fescue biomass yield (>7 Mg dry matter ha −1) was above regional norms, but rooting depth (70–90 cm) was relatively shallow. Comparison of the 2000 and 2007 data showed that tall fescue increased SOC and TN in the 0–10 and 40–60 cm soil depths. Over the 0–60 cm soil depth, SOC content increased by 23% and TN by 34%. Use of the equivalent soil mass approach, to adjust for soil bulk density increases over the 7-year period, reduced the SOC gain to 17% (increase of 12.8 Mg C ha −1). This SOC increase corresponded with standard decomposition calculations based on plant biomass inputs. Both LF-C and POM-C indicated that tall fescue increased SOC down the soil profile. This research demonstrates the important role that plant roots which play in SOC storage deep within the soil profile, even when soil profile conditions may adversely influence rooting depth.