Short-term legacy effects of feedlot manure amendments on surface soil C[O.sub.2] efflux under irrigated silage barley in Southern Alberta

The short-term legacy effects following long-term (17 yr) feedlot manure application on C[O.sub.2] 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*[ha.sup.-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 C[O.sub.2] efflux was similar (P > 0.05) among the four amended treatments in the first (0.63-0.86 g*[m.sup.-2]*[h.sup.-1]) and second (0.40-0.46 g*[m.sup.-2]*[h.sup.-1]) years. However, soil C[O.sub.2] efflux was significantly greater for amended than unamended treatments by 54-110% in the first year (CON = 0.41 g*[m.sup.-2]*[h.sup.-1]) and by 33-53% in the second year (CON = 0.30 g*[m.sup.-2]*[h.sup.-1]). Soil C[O.sub.2] 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 [less than or equal to] 0.39) occurred between soil C[O.sub.2] 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 C[O.sub.2] efflux for amended than unamended soils.