Nitrogen (N) has been considered one of the vital elements to enhance agricultural productivity. However, excessive use of N fertilizer can deteriorate environmental quality, increasing ammonia (NH 3 ) and greenhouse gases (GHGs) emissions from agricultural ecosystems. The combined use of inorganic and organic fertilizers may improve nutrient holding capacity, which can potentially reduce N losses (NH 3 and N 2 O), resulting in high N use efficiency (NUE) and crop productivity. To investigate gaseous N losses and NUE in a maize (Zea mays L.) field experiment, four treatments for N fertilizers were laid out: NPK (urea), compost (compost), NPK+Compost (urea and compost), and control (no fertilizer) treatments. As compared to the control, seasonal NH 3 emissions significantly increased with all fertilization. In particular, combination of organic and inorganic fertilizers was effective on reducing N losses including NH 3 volatilizations and N 2 O emissions, showing ca. 16% and 47% reduction, respectively over sole NPK treatment even though the same amount of N was incorporated in all treatments except the control. Maize productivity was significantly improved by N fertilizations, but was the highest in the NPK+Compost treatment, showing no statistical difference with NPK treatment. The NUE was the highest in the NPK treatment (35%) and followed by NPK+Compost (27%), compost (11%), respectively. In conclusion, mixing of organic-inorganic fertilizers could be a reasonable countermeasure to reduce the loss of gaseous N and simultaneously maintain productivity and NUE in agricultural soils.

Long-term fertilizations of inorganic and organic fertilizers can affect microbial abundance and community structure in agricultural soils, particularly controlling the activities of methane (CH 4 ) microbes such as methanotrophs in the rice paddy soils. However, the effect of fertilizations on CH 4 oxidation potential and methanotrophic community remains unclear. In order to investigate the response of the soil bacterial community abundance, composition, and CH 4 oxidation potential under four different fertilization regimes (control, NPK, compost, and NPK + compost) in a 49-year old paddy field, the soil bacterial community abundance and structure including CH 4 -oxidizing microbes as well as the potential of CH 4 oxidation were investigated by assessing real time quantitative PCR (qPCR), Miseq illumina sequencing analysis based on 16S rRNA genes, and oxic in vitro slurry incubation, respectively. Long-term fertilizations changed significantly soil biochemical characteristics, mainly influencing carbon and nitrogen pools in rice paddy soils. CH 4 oxidation potential was stimulated by inorganic fertilizations, mainly increasing the relative abundance of the genus Methylosarcina probably due to increased N availability and soil pH in the soils. Our results showed inorganic fertilizations may enhance CH 4 oxidation potential by altering methanotrophic communities, which potentially mitigate CH 4 emissions in paddy ecosystems during the cultivation. However, additional research would be necessary for a better understanding of CH 4 dynamics in rice paddy soils under the long-term field conditions.