Nitrous oxide emissions after application of cattle-manure-based pellet of different pH levels to an Andosol upland field

The pH of manure pellet fertilizer can affect the nitrous oxide (N2O) emission from soil, although its effectiveness and the relative mechanisms are not well understood. This study aims to quantify the effect of cattle-manure-based pellet pH on N2O emissions from an Andosol field. The field experiment consisted of four treatments: chemical (mineral) fertilizer (CF), cattle-manure-based pellet fertilizer of pH 5.6 (OP), cattle-manure-based pellet fertilizer of pH 7.1 (NP), and cattle-manure-based pellet fertilizer of pH 10.1 (AP). Cumulative N2O emission over the 365 days in the OP and NP treatments was 59.4% and 49.3% lower than that in the AP treatment, respectively, but the cumulative N2O emissions were statistically significant only between the OP and AP treatments. Moreover, cumulative N2O emission in the pellet fertilizer treatments during the peak period after fertilization in the autumn and spring cropping seasons (total 70 days) increased with increasing pellet pH. In the pellet fertilizer treatments, soil nitrification potential, soil N2O production rate, and total denitrification rate of soil also clearly increased with the increase of pellet pH. Therefore, slightly acidic pellet pH (OP treatment) may have inhibited the microbial N2O production processes in comparison to the neutral pellet pH (NP treatment), but alkaline pellet pH (AP treatment) could have stimulated the microbial N2O production processes than the neutral pellet pH. These results suggested that increased N2O emission with an increase in pellet pH may be attributed to a change in the N2O production rate via nitrification and denitrification.