Impacts of pellet pH on nitrous oxide emission rates from cattle manure compost pellets

2016-11-02T11:52:53Z (GMT) by Tsuyoshi Yamane Hideo Kubotera
<p>Previous reports indicated that the emission of nitrous oxide (N<sub>2</sub>O) when manure compost pellets (MCP) were applied to soil was greater than when ordinary manure compost or inorganic fertilizer was applied, but that applying pellets of nitrogen-enriched manure compost, a by-product of deodorizing manure during composting, resulted in N<sub>2</sub>O emission rates less than those from MCPs. To investigate the mechanism by which N<sub>2</sub>O emission rates and cumulative emissions were reduced in nitrogen-enriched manure composts pellets (N+MCP), we studied the impact of pellet pH on N<sub>2</sub>O emission, because pH is different between MCP (pH 8.6) and N+MCP (pH 5.3). In an incubation experiment, the pH of pellets was adjusted to five levels (5.3, 6.0, 7.0, 8.0 and 8.6) with acid or alkaline solutions, and the pellets were incubated without soil in a beaker at 30°C for 90 d (MCP) or 42 d (N+MCP). A large peak in N<sub>2</sub>O emission rate was observed soon after beginning the incubation (within 1–3 d) in the neutral and alkaline treatments for both MCP and N+MCP, and these peaks corresponded to a rise in the pellet nitrite contents. Thus, this N<sub>2</sub>O emission peak might have been generated by the denitrification of nitrite in the pellets. In the acid treatments of MCP, the N<sub>2</sub>O emission was distributed more in the later incubation period (14–90 d), when the reduction of nitrate in MCP occurred. This led to a significant increase in cumulative N<sub>2</sub>O emission as compared with the alkaline treatments for MCP. Regarding the mechanism by which N<sub>2</sub>O emission was reduced in N+MCP, although larger cumulative N<sub>2</sub>O emission rates in the earlier stage (0–14 d for MCP and 0–7 d for N+MCP) were observed when the pellet pH was adjusted close to 7.0, lowering the pH of MCP to 5.3 (the pH of N+MCP) did not demonstrate a significant decrease in cumulative N<sub>2</sub>O emission as compared with the original pH treatment (pH 8.6). These results indicate that pellet pH might not relate directly to the mechanism by which N<sub>2</sub>O emission was reduced in N+MCP.</p>