Effect of biodegradable plastics on greenhouse gas emission and paddy rice growth under flooding conditions

Biodegradable plastics applied to soil stimulate the production of greenhouse gases and inhibit plant growth under aerobic conditions. This study aimed to examine the effects of biodegradable plastics on paddy rice growth and greenhouse gas emission under flooding conditions in pot experiments and also on greenhouse gas production under flooding conditions in an incubation experiment. Two series of pot experiments were conducted with rice (Oryza sativa). First series as immediate flooded and 2nd series as 2 weeks nonflooding before flooded, and both kept flooded until harvest. The following four kinds of materials were added to the sandy paddy soil, (1) nonwoven fabric sheets made of polylactic acid and polybutylene-succinate, (2) laminate sheets made of polybutylene adipate terephthalate and pulp, (3) cellulose filter paper, and (4) rice straw. Only soil was used as control. Methane (CH4) emission, measured by chamber method followed by gas chromatography, was significantly larger only in the cellulose treatment than the laminate treatment in the immediate flooded series, indicating that biodegradable plastics had no significant impact on CH4 emission from paddy rice soil. Rice growth and yield did not show significant difference among treatments in both series. Incubation experiment showed the largest CH4 production in cellulose-amended soil, followed by straw-amended and laminate amended soils, and least in fabric-amended soil, while CO2 did not show significant differences among treatments. We need further examination with different biodegradable plastics for a longer period that test used in this study.