Two multi-year field trials were conducted to elucidate the optimal application method of barnyard manure in non-tilled cropping systems of forage corn (Zea mays L.). In Trial 1, manure application rates ranging from 0 to 12 t/10 a in addition to a fixed amount of synthetic fertilizer were provided annually on the non-tilled soil surface over three-years. In the third year of non-tilled cropping, the plots applied with 6 and 9 t/10 a of manure exhibited significantly higher dry matter yields than those without manure application. Moreover, the plots applied with lower amount of manure showed higher nitrogen utilization efficiencies. In Trial 2, the non-tilled plots provided with a single application of 15 t/10 a manure tilled in the previous year resulted in higher dry matter yield than those in conventional tilled plots with 5 t/10 a/year manure over three years. Soil analysis also revealed that the non-tilled plot maintained more than 80 mg/kg an available nitrogen in the soil layer of 20-40 cm depth in the third year of non-till cropping. These findings indicate that surface application of 6-9 t/10 a/year of manure or tilling with 15 t/10 a of manure in the year before non-tillage effectively enhances the productivity of forage corn in continuous non-tilled cropping systems.