Short-term legacy effects of feedlot manure amendments on surface soil CO2 efflux under irrigated silage barley in Southern Alberta

The short-term legacy effects following long-term (17 yr) feedlot manure application on CO2 efflux for a surface soil (clay loam) were studied over 2 yr (2016-2017) on a Dark Brown Chernozem in southern Alberta. The five treatments were stockpiled (SM) or composted (CM) manure with either straw (ST) or wood-chips (WD) bedding applied at 77 Mg center dot ha-1 (dry wt.) and an unamended control (CON). Surface soil efflux was measured during the growing season of the 2 yr using the dynamic, closed-chamber method. Ancillary measurements (soil water and temperature, total carbon, bulk density) were also obtained. Soil CO2 efflux was similar (P 0.05) among the four amended treatments in the first (0.63-0.86 g center dot m-2 center dot h-1) and second (0.40-0.46 g center dot m-2 center dot h-1) years. However, soil CO2 efflux was significantly greater for amended than unamended treatments by 54-110% in the first year (CON = 0.41 g center dot m-2 center dot h-1) and by 33-53% in the second year (CON = 0.30 g center dot m-2 center dot h-1). Soil CO2 efflux was similar for SM and CM in both years and was significantly greater for WD than ST bedding in the first but not second year. Weak positive correlations (r < 0.39) occurred between soil CO2 efflux and total soil C, water-filled pore space (WFPS), and soil temperature. Overall, our findings suggested that legacy effects of manure may persist for 1-2 yr following discontinued applications, but are mostly restricted to greater soil CO2 efflux for amended than unamended soils.