Effect of biogas slurry application on CH4 and N2O emissions, Cu and Zn uptakes by whole crop rice in a paddy field in Japan

Effects of 4-year consecutive application of biogas slurry (BS) at rates of 0 (NF), 100 (BS100) and 300 (BS300) kg nitrogen (N) ha(-1) on yield of whole crop rice (Oryza sativa L. var. Leaf Star) and environmental impacts were investigated in a field experiment in comparison with a conventional rate of chemical fertilizer CF100 (100 kg N ha(-1)). Average biomass production was comparable between BS100 (1.9 +/- 0.1 kg dry matter m(-2)) and CF100 (1.8 +/- 0.1 kg m(-2)) and significantly (P < 0.01) highest in BS300 (2.1 +/- 0.1 kg m(-2)). Four years' average methane (CH4) emissions during the growing periods were significantly (P < 0.05) highest in BS300 (43.7 +/- 18.4 g m(-2) season(-1)), followed by BS100 (32.0 +/- 3.0 g m(-2) season(-1)) and then NF (23.5 +/- 8.2 g m(-2) season(-1)) and CF100 (20.3 +/- 3.3 g m(-2) season(-1)), indicating that BS application may cause a potential risk of CH4 emission. There were no significant differences in copper (Cu) and zinc (Zn) uptakes by the rice plant between BS100 and CF100, but significantly higher Zn content was observed in the grain of BS300 in 2011, indicating a potential risk of higher heavy metal uptake in BS300. Compared with CF100, no significant higher accumulations of extractable and total forms of Cu and Zn in soil were observed from four years of consecutive BS application. This study revealed that the application of BS, generated from pig manure, to rice fields at the conventional rate (100 kg N ha(-1)) may be considered to substitute chemical fertilizer utilization without additional environmental impacts in greenhouse gas emission and heavy metal uptake.