Akira Miyata

Mitigation Effect of Farmyard Manure Application on Greenhouse Gas Emissions from Managed Grasslands in Japan

Applying manure can lead to decrease of chemical nitrogen (N) fertilizer use and increase of soil carbon (C) sequestration. The effect of manure application on net ecosystem C balance (NECB), methane (CH4) and nitrous oxide (N2O) emissions and global warming potential (GWP) was examined at four managed grasslands on Andosols in different climatic regions in Japan for 3 years. At adjoining manure and fertilizer plots in each site, net ecosystem exchange (NEE) and CH4 and N2O fluxes were measured by the eddy covariance method and dark chamber methods, respectively. Manure application decreased fertilizer N application rate in manure plot to 65–88 % in fertilizer plot. NECB (= NEE−C applied in manure + harvested C) was higher in fertilizer plot (1.9 ± 0.9 MgC ha−1 year−1) than in manure plot (−1.8 ± 1.8 MgC ha−1 year−1), indicating that the soils in fertilizer plots lost C. There was no significant difference in harvested C between fertilizer and manure plots (4.3 ± 0.8 and 4.1 ± 0.6 MgC ha−1 year−1, respectively). NEE showed more CO2 uptake in fertilizer plots (−2.4 ± 1.1 MgC ha−1 year−1) than in manure plots (−1.6 ± 0.7 MgC ha−1 year−1), but manure application could compensate for the shortage in NEE. CH4 emission was close to zero, while the N2O emission was greater in manure plots (6.2 ± 3.7 kgN ha−1 year−1) than in fertilizer plots (3.6 ± 3.2 kgN ha−1 year−1). The difference of GWP between manure and fertilizer plots showed a negative relationship with manure C application rate (y = −4.45 ln(x) + 2.84; R 2 = 0.85; p < 0.01), indicating that manure application rate more than 2 MgC ha−1 year−1 can mitigate global warming in the Japanese grasslands.