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Optimal manure management can maximize agronomic benefits and minimize environmental impacts. Field experiments were conducted in the Pacific Northwest (Vancouver, Canada) to determine how chicken and horse manures that were fall-applied to meet nitrogen crop demand affect soil ammonium (NH₄⁺) and nitrate (NO₃^−), apparent net mineralization (ANM) and nitrification (ANN), crop biomass and nutrient concentration, and fluxes of nitrous oxide (N₂O), carbon dioxide (CO₂), and methane (CH₄). Relative to horse manure, chicken manure increased soil NH₄⁺ by 60-fold, ANM by 2-fold, and ANN by 4-fold. Emissions of N₂O (+600%) and CO₂ (+45%) were greater and growing season CO₂ emissions (−40%) were lower after application of chicken than horse manure. Productivity of cover crop (+30%), legume cover crop (−25%), and squash cash crop (+20%) were affected by chicken relative to horse manure. Overall, fall-applied chicken manure increased yields, N availability, and environmental impacts relative to horse manure.