Effect of dairy manure type and supplemental synthetic fertilizer on methane and nitrous oxide emissions from a grassland in Nasu, Japan

Abstract

We investigated the effects of different types of manure on greenhouse gas (GHG) emissions from grassland for 2 years using a closed chamber method to measure methane (CH4) and nitrous oxide (N2O) fluxes from plots that received no nitrogen (“-N” plots), dairy cattle slurry plus synthetic N fertilizers (“slurry” plots) and farmyard manure plus synthetic N fertilizers (“FYM” plots). The application rates of slurry (65.8 to 66.4 Mg ha-1y-1) or FYM (36.5 to 39.2 Mg ha-1 y-1) were determined so that the annual potassium supply from slurry or FYM roughly covered the annual potassium requirement for forage grass production. Supplemental ammonium sulfate and superphosphate were applied to cover the annual N and phosphorus (P) requirements. Sharp peaks of CH4 flux were observed shortly after slurry applications, whereas CH4 fluxes only slightly increased following FYM applications. The annual CH4 emissions from -N, slurry, and FYM plots ranged from -1.17 to -1.16, 0.21 to 1.84 and -1.67 to -0.27 kg CH4-C ha-1 y-1, respectively. The CH4 emissions from slurry plots tended to be greater than those from -N (P = 0.066) and FYM plots (P = 0.097). No significant difference was observed between -N and FYM plots (P = 0.973). The annual N2O emissions from -N, slurry, and FYM plots ranged from 0.35 to 0.81, 1.77 to 7.58 and 2.24 to 7.59 kg N2O-N ha-1 y-1, respectively. The N2O emissions in the first year were greater than those in the second year (P = 0.012). The N2O emissions in slurry and farmyard manure (FYM) plots tended to be greater than those in -N plots (P = 0.076, P = 0.059). No significant difference was observed between slurry and FYM plots (P = 0.989). Both the cumulative precipitation following fertilization and soil moisture content at time of fertilization substantially affected the interannual differences in N2O emissions. In terms of carbon dioxide equivalents (CO2-eq), the N2O emissions (0.83 to 3.55 Mg CO2-eq ha-1 y-1) were substantial in comparison to the CH4 emissions (-0.06 to 0.06 Mg CO2-eq ha-1 y-1). These results collectively suggest that the types of manure, from different storage conditions, had little impact on annual GHG emissions under optimized fertility management. Environmental factors had much greater impact.