Reduced nitrous oxide emissions from andosol upland field applied with nitrogen-enriched cattle manure compost pellets

Manure compost pellets (MCP) are cylindrically shaped manure composts. Their physical characteristics greatly facilitate handling in transportation, spreading by machine, and storage, but emissions of nitrous oxide (N2O) are much larger after soils are amended with MCP versus non-pelleted manure composts (MC) and nitrogen fertilizers. Emissions of N2O have been reported to be lower, however, when soils are amended with pellets of nitrogen-enriched manure composts, which are byproducts of compost deodorization, than with MCP. The objective of this study was to confirm the reduction of N2O emissions from soils amended with nitrogen-enriched manure compost pellets (N+MCP) and to assess the environmental conditions that affect N2O emissions by conducting field experiments where cabbage was cultivated through five cropping seasons. During two cropping seasons when soil temperatures at the time of pellet application were relatively high (24–29°C), cumulative emissions of N2O from the N+MCP treatment were significantly reduced (by 66–75%) relative to those from the MCP treatment, and the initial peak of N2O emissions from the MCP treatment was very large compared to the peak from the N+MCP treatment. During the other three cropping seasons, when soil temperatures at the time of pellet application were relatively low (7–18°C), the reduction of N2O emissions from the N+MCP treatment compared to the MCP treatment was less (42% reduction) or none. These results suggested that the environmental conditions at the time of pellet application (e.g. soil temperature) were important determinants of N2O emissions from soils amended with MCP and of the reduction of N2O emissions from soils amended with N+MCP. The effect of adding urea to manure compost pellets (U+MCP) to reduce N2O emissions was explored using urea-added pellets with the same total nitrogen content as the N+MCP (4% of dry material) during the final two cropping seasons. Total N2O emissions from the U+MCP treatment were 33–52% lower than from the MCP treatment, but the reductions of N2O emissions were less than those from the N+MCP treatment. Total N2O emissions from soils amended with N+MCP or U+MCP were not significantly different from soils amended with non-pelleted MC throughout this study.