Storage and disposal of digested effiuent of manure (DEM) produced by biogas plant is a challenge to beef producers because of the mitigation of environmental pollution. The DEM contains essential plant nutrients and to use DEM as a soil amendment for crop production is a practical method to solve the disposal problem. In 2 years of cropping with dwarf napiergrass as a perennial summer grass and Italian ryegrass as an annual winter grass, DEM revealed to be so effective fertilizer as chemicals to increase dry matter yield and forage quality, especially crude protein (CP) content and in vitro dry matter digestibility (IVDMD). The efficient use of DEM can be an agronomic-and economic-viable management practice for sustainable crop production in Miyazaki, southern Kyushu of Japan.