The response of soil physical quality parameters to a perennial grain crop

Abstract

Soil physical quality is paramount for root growth, water and air movement, and for its subsequent effects on chemical and biological processes in the soil. Management practices and their legacies can impact soil physical quality, and perennial grain cropping has been proposed as a solution to maintain or improve soil physical quality in agroecosystems due to their provision of year-round ground cover and increased root growth. An alfalfa-brome perennial forage crop, a perennial rye crop (Secale cereale L. x S. montanum L.), and an annual rye crop (S. cereale L.) were evaluated at two sites in Central Alberta with contrasting management histories (Edmonton and Breton) over 3 years to determine the effects on soil physical and hydraulic properties. Compared to the annual crop, the perennial forage crop reduced the bulk density of the uppermost soil depth sampled (5–10 cm depth increment) (p < 0.05) at the Edmonton site and increased soil macroporosity (p < 0.05) and pore connectivity (p < 0.05) in the deeper subsurface soil layer (25–30 cm depth increment) at both sites. While moderate improvements in soil physical and hydraulic properties manifested under the perennial rye crop when compared to the annual rye crop, they did not do so to the extent of the perennial forage crop. We attribute this to the inclusion of tap-rooted alfalfa in the perennial forage, and the overarching beneficial influence of root mass density on soil properties. Root mass density from highest to lowest consistently ranked as perennial forage > perennial rye > annual rye for both sites. Root mass density was negatively correlated with bulk density at both Breton (r = −0.77, p < 0.05) and Edmonton (r = −0.69, p < 0.05) sites. Furthermore, at Breton, root mass density positively correlated with macroporosity (r = 0.88, p < 0.01). Notably, the perennial rye crop enhanced soil carbon mass density relative to the annual rye crop in the clayey topsoil of the Edmonton site (p < 0.05), but treatment effects were muted at the Breton site due to the influence of previous land use. Despite moderate improvements in soil physical quality, our results suggest that 3 years of perennial rye monocropping falls short of the major improvements seen under a perennial alfalfa-brome forage crop over the same timeframe.