## 2 Materials and Methods  
The experimental field (1230 m\({}^{2}\)) was located at the Paddy Crop Research Division, Department of Southern Area Crop Science, National Institute of Crop Science, Republic of Korea. The plots within the experiment were managed and fertilized as mentioned previously by [PERSON] et al. [18]. Briefly, the fertilization trial was initiated in 1967, and rice (_Oryza sativa_ cv. Hwayeong) was cultivated as a single crop. Out of several fertilization treatments, two different treatments with three replicate plots (10 m \(\times\) 10 m each) for each treatment arranged in a completely randomized manner were used in this study. The treatments were (1) inorganic NPK fertilized soil sample (\(-\)Compost) and (2) NPK amended with compost (10 tons-ha\({}^{-1}\).year\({}^{-1}\)) fertilized soil sample (+Compost). NPK fertilizers were applied as urea, fused superphosphate, and potassium chloride at the rate of 120, 80, and 80 kg-ha\({}^{-1}\) from 1967 to 1972. Since 1973, N, P, and K have been applied at a higher rate of 150, 100, and 100 kg-ha\({}^{-1}\), respectively. Compost was prepared by decomposing rice straw and cattle manure for a period of 6 months, and it contained 431, 19.8, 5.2, and 29.1 g-kg\({}^{-1}\) of total C, N, P, and K, respectively. A total of five individual subsamples (\(\sim\)20 cm depth) were collected from each of the three replicates of individual treatments in April 2016 and were pooled to make a composite sample (\(\sim\)100 g) for each replicate. Thus, six individual samples were collected. Soil samples were sieved (\(<\)2 mm) and stored in sterile bags and transported to the laboratory on ice. Soil DNA was extracted using 0.5 g of fresh soil sample by using a PowerSoil DNA Isolation Kit (Mo Bio Laboratories, Carlsbad, CA, USA), and DNA was stored at \(-\)20 \({}^{\circ}\)C for all downstream analysis. The 16S rRNA copy number was estimated using quantitative PCR (qPCR) with the primers 517F/1028R [19; 20] following conditions described in detail by [PERSON] et al. [18]. Briefly, qPCR amplification targeting the 16S rRNA gene of bacteria was performed using the primers 517F (5\({}^{\prime}\)-GCACGACGGCGTAA-3\({}^{\prime}\)) and 1028R (5\({}^{\prime}\)-CGACARCCATGCASCACCT-3\({}^{\prime}\)) with a Rotor-Gene(r) Q (Qiagen, Foster City, CA, USA) in 10 \(\mu\)L of reaction mixture containing 5 \(\mu\)L of Maxima SYBR Green Master Mix (Thermo Fisher Scientific Inc., Waltham, MA, USA), 0.4 \(\mu\)M of each of forward and reverse primers, 1 \(\mu\)L of template DNA, and 3.6 \(\mu\)L of sterile distilled water. The reaction conditions for the qPCR were as follows: 1 cycle at 95 \({}^{\circ}\)C for 10 min, 45 cycles of denaturation at 95 \({}^{\circ}\)C for 30 s, annealing at 60 \({}^{\circ}\)C for 40 s, and extension at 72 \({}^{\circ}\)C for 45 s. All sample and standard curve measurements were performed in triplicate, and negative controls were included in every qPCR run. For standard curve preparation, the 16S rRNA fragment from _Pseudomonas mendocina_ PC1 was amplified with the same primer pair under the same thermal conditions. Rotor-Gene Series Software v. 2.0.2 (Qiagen, Foster City, CA, USA) and LinRegPCRprogram v. 2017.0 (Academic Medical Centre, Amsterdam, Netherlands) [21] were used to analyze the obtained data. The qPCR standard curve efficiency was 1.866 \(\pm\) 0.031 (\(n\) = 12). Additionally, the amplification efficiency of each sample was considered for calculating the 16S rRNA gene copy numbers. The isolated DNA was subjected to high-throughput Illumina MiSeq sequencing at ChunLab, South Korea. The V3-V4 regions of 16S rRNA genes were targeted and amplified using the primers 341F (5'-TCGTCGGCAGCGTCAG ATGT GATAAGAGACAGCCTACGGNGGCWGGCAG-3', underlined sequences indicating the target) and 805R (5'-GTCTCGTGGCCTGAGAGGTATAAGAGACAGACTACHVGGTATCTAATCC-3'). The raw data obtained were analyzed using a Mothur pipeline v. 1.39.5 [22] similarly as performed in our previous studies [18; 23].