Resumen
In Japan, it is important to recycle the nutrients in manure for forage production because most dairy cattle are fed inside, mainly with imported grain and home-grown roughage. To understand the overall effect of manure use on grassland on the net greenhouse gas (GHG) emission and GHG intensity of herbage production systems, the integrated evaluation of emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) is essential. The objective of this study was to compare the net GHG emissions (expressed in CO2-eq ha−1 y−1) and GHG intensity (expressed in CO2-eq Mg–1 dry matter yield) of herbage production based on manure slurry + synthetic fertilizer (slurry system) with that based on farmyard manure + synthetic fertilizer (FYM system). Calculations of net GHG emissions and GHG intensity took into account the net ecosystem carbon balance (NECB) in grassland, the CH4 and N2O emissions from grassland, and GHG emissions related to cattle waste management, synthetic fertilizer manufacture, and fuel consumption for grassland management based on literature data from previous studies. The net GHG emissions and GHG intensity were 36% (6.9 Mg CO2-eq ha−1 y−1) and 41% (0.89 Mg CO2-eq Mg−1), respectively, lower in the FYM system.