Variable rate precision application of feedlot cattle manure mitigates soil greenhouse gas emissions

• Constant and variable manure rates impact GHG emissions within commercial silage barley fields. • Landscape position and its catchment area size impacted N 2 O, CH 4 , and CO 2 emissions. • Phosphorus-limited crop growth increased yield- and value-scaled N 2 O, CH 4 , and CO 2 emissions. • Solid cattle manure did not influence ecosystem respiration or the CO 2 -equivalent emissions. • Variable rate manure application reduced N 2 O emissions and increased CH 4 sink strength. Solid cattle manure amendments provide a low-cost alternative nutrient source to inorganic fertilizers, while providing a carbon input to the soil. The augmented soil organic carbon levels, however, may be largely offset by manure-related greenhouse gas (GHG) emissions. Soil nitrous oxide (N 2 O), methane (CH 4 ), and carbon dioxide (CO 2 ) emissions were measured at the landscape-scale in a Canadian prairie agricultural field supporting silage barley ( Hordeum vulgare L.) production. Manure was applied to meet barley P requirements, while total N rate was supplemented using anhydrous ammonia. A non-manured control (NMC) also was included, to calculate N 2 O emission factors. The NMC zone consisted of an annual application of anhydrous ammonia at 80 kg N ha −1 . In addition to solid cattle manure at a constant (CRM; 45 Mg ha −1 ) or variable (VRM; 0–72 Mg ha −1 ) rate, the manured treatment zones also received 80 kg N ha −1 of anhydrous ammonia. The VRM treatment included set-backs from the watershed basin centers in ephemeral wetlands that did not receive solid cattle manure. Gas samples were collected using chamber-based methodology, with chambers installed at 130 locations across six watershed basins (n = 2 per zone) during 2019–2021. Cumulative N 2 O emissions were 76 % (CRM) and 62 % (VRM) higher following manure addition. The normalized N 2 O emissions for CRM were 24 % greater than VRM and NMC, with CRM having 31 % larger manure-induced N 2 O emissions than VRM. Though all soils were net CH 4 sinks, manure application reduced CH 4 consumption by 33 % (CRM) and 25 % (VRM) compared with the NMC. Manure addition did not impact cumulative CO 2 emissions. Although VRM application mitigated manure-related GHG emissions, enhanced GHG intensity following manure addition highlights the importance of ensuring balanced soil fertility, to support optimal crop growth and maximize yield-scaled GHG performance metrics in manured landscapes.