To promote the use of methane fermentation technology in the treatment of organic by-products, methods for using the effluent produced by the digestion processes (i.e., the digested liquid) need to be developed. Application to agricultural fields is one potential use of this liquid. We investigated the effects of the method and application rate of digested liquid on plant growth and N_2O emission from the soil surface. Using komatsuna as a test plant in an upland field, we found that disturbing the soil immediately after surface application of digested liquid promoted plant growth, and the availability of nutrients from the digested liquid was similar to that from chemical fertilizer. Plant growth increased with digested liquid application rates up to 7.8L m^<-2> (24g-N m^<-2>) and remained constant at higher levels up to the maximum rate examined of 15.6L m^<-2>. Emission of N_2O increased with the amount of digested liquid applied, and the ratio of N emitted to N applied also increased. Omission of soil-surface disturbance following the surface application of digested liquid reduced both plant growth and emission of N_2O. This was presumably because disturbance restrained the ammonia volatilization by which N included in the applied digested liquid was lost. Placing 5cm of soil over the soil surface after digested liquid application was not as effective as disturbance in promoting plant growth or reducing N_2O emission.