## 4 Discussion  
Insights into the dynamic shifts in soil chemical properties and ecosystem functioning though changed microbial dynamics could be attained through studies involving the long-term fertilization of paddy fields. The current study evaluated the changes in soil edaphic factors along with the concurrent changes in gene abundances related to nitrogen cycling in rice paddy fields established through decades of fertilization amendment. Potential correlations that exist between changes in edaphic factors and the population size indicated by the copy number of nitrification and denitrification functional genes together with the overall soil variabilities that exist between different paddy field treatments were also assessed. Paddy Fields with Stable Soil Chemical Properties Rich in SOM and Nutrients Were Established by Long-Term Compost and NPK + Compost Fertilization  
The long-term input of a mixture of composed cattle manure and rice straw compost along with its combination with NPK chemical fertilizer in rice paddy fields significantly changed their soil chemical properties but have attained compositional stability over decades of long-term fertilization. The significant increase in chemical properties, SOM, TN, P, and K, could be attributed to a net accumulation, especially by SOM/SOC and TN [4; 19; 20; 21], under long-term fertilization. In addition, the increase in these nutrient contents could also be due to the increased input, as in the case of SOM through enhanced carbon input [22]. Paddy fields under long-term fertilization also showed higher carbon sequestration efficiency, leading to an increased SOM [23]. These changes in chemical properties were also observed in previous long-term fertilization studies [24; 25; 26; 27; 28]. Soil chemical stability was also observed in the current study. Stability was detected in terms of non-significant fluctuations in soil edaphic factors, especially chemical properties, during the continuous soil testing, at least during the fallow period. This soil chemical stability was observed in paddy fields amended with NPK + compost and compost. In contrast, paddy fields without any fertilization input showed significant fluctuations in their soil chemical properties from 2018 to 2021. The non-significant fluctuations in soil chemical properties could indicate some scenarios where the paddy fields may have attained a nutrient saturation level or have maintained nutrient input and loss particularly in the case of soil carbon and soil organic matter [29; 30]. It is more probable that the  
Figure 3: PCA score plot showing variability in soil chemical properties and copy number of functional genes associated to denitrification and nitrification observed in different paddy fields amended with long-term compost fertilization. nutrient input and loss has stabilized in paddy fields under long-term compost and NPK + compost application, since a higher input of organic matter into the paddy fields adds nutrients into the soil, particularly at the initial stages, but attains stability over decades of fertilizer amendment [21, 22]. In contrast, the soil chemical fluctuations occurring in the unfertilized lands could be due to natural nutrient cycling processes such as nitrogen fixation, phosphate solubilization, and organic compound mineralization, which are mainly affected by the cultivation of Hwayeong rice cultivar without additional nutrient input and are potentially greatly influenced by external environmental conditions. Soil Organic Matter, Total Nitrogen and Soil Nutrients Interact to Establish Abundances of Nitrigen Cycle Functional Genes and Their Implications  
As shown in the results of this study, long-term amendment with compost and a combination of compost and NPK have led to stable yet significantly higher nutrient content in and changed the chemical properties of the paddy fields. Concurrent to this is the altered microbial community, both in terms of abundance and potential composition, as indicated by molecular markers.