CH4 and N2O emissions from different varieties of forage rice (Oryza sativa L.) treating liquid cattle waste Original Research Article

To evaluate global warming potential (GWP) on livestock waste treatment and biomass production in rice field, methane (CH4) and nitrous oxide (N2O) fluxes from forage rice fields planted with 4 different cultivars (Oryza sativa L. cv. Hamasari, Leafstar, Kusahonami and Takanari) were measured. Each of the cultivars were subjected either to basal fertilization alone (control plots) (84 kg N ha− 1), or to basal fertilization plus topdressing with liquid cattle waste or LCW (treatment plots) (567 kg N ha− 1). Liquid cattle waste application to the rice field resulted in peak CH4 fluxes ranging from 22.0 to 32.1 mg m− 1 h− 1 during flooded conditions and large N2O fluxes ranging from 526 to 8591 μg m− 1 h− 1 after midsummer drainage and final drainage. The GWP of the control plots was between 1358 and 3872 kg CO2eq ha− 1, while the treatment plots ranged between 4503 and 8426 kg CO2eq ha− 1 and more than 60% of the GWP was from the N2O emission in treatment plots. In both the control and treatment plots, the lowest GWPs per ton of above-ground biomass were found to be from the Leafstar cultivar, which had a higher aboveground biomass than other cultivars; 117 kg CO2eq t− 1 from the control and 257 kg CO2eq t− 1 from the treatment plots. Thus, both forage production and suitable disposal of the LCW may be able to be achieved concomitantly with lower levels of GWP by cultivation of Leafstar in our field.