# Changes in Soil Chemical Properties Due to Long-Term
## 3 Results  
Long-term compost fertilization either as compost alone (Com) or a combination of compost and inorganic fertilizers (NPKCom) changed the soil chemical properties of paddy fields (Tables 1 and 2). The ANOVA results showed that there are significant mean differences in the soil chemical properties across treatments, especially for pH, OM, TN, P, K, Ca and DOC. Some of the changes in chemical properties include a significant increase in organic matter (OM) content, total nitrogen (TN), phosphorus (P), and potassium (K)in both Com and NPKCom treatments. The nutrients Ca2+ and Mg2+ were observed to be significantly higher in the NPKCom treatment, while dissolved organic carbon (DOC) is significantly higher in the Com treatment. The pH in NPKCom has also become significantly less acidic than in the Com treatment, but not significantly different than the unfertilized control. Using quantitative Real-Time PCR (qPCR), the absolute abundance of _mcrA_ and _pmoA_ genes was quantified in the paddy soils fertilized with compost and NPK+Compost. There is more than a three-fold statistically significant increase in the abundance of _mcrA_ genes in the Com and NPKCom treatments (Table 2), which ranged from 1.23 \(\times\) 10\({}^{6}\) to 3.47 \(\times\) 10\({}^{6}\) copy number g\({}^{-1}\) dry soil. The _pmoA_ gene abundance also increased significantly by 2.61-fold (4.31 \(\times\) 10\({}^{6}\) copy number g\({}^{-1}\) dry soil) and 2.47-fold (4.08 \(\times\) 10\({}^{6}\) copy number g\({}^{-1}\) dry soil) in compost and NPK+Compost-fertilized paddy fields, respectively, compared to the unfertilized control (1.65 \(\times\) 10\({}^{6}\) copy number g\({}^{-1}\) dry soil). The correlation matrix (Table S2) showed that correlations exist between the gene abundance and the soil chemical properties. There is a positive and significant correlation of the _mcrA_ gene abundance with that of the _pmoA_ gene abundance. The abundance of the _mcrA_ gene is positively and significantly correlated to organic matter (OM), total nitrogen (TN), potassium (K), calcium (Ca), and DOC. These correlations for the _mcrA_ gene abundance and the soil chemical properties were also observed at the level of the individual treatments. Overall, for the _pmoA_ gene abundance, it is positively correlated with OM, TN, P, K and DOC; however, these correlations were not clearly observed at the level of each treatment. The principal component analysis showed the overall effect of the fertilization treatment on the soil chemical properties and the gene abundance of methane-related functional genes as well as the variability that exists (Table 3). Principal components (PC) 1, 2 and 3 have eigenvalues greater than 1 (6.851, 1.859 and 1.144, respectively). PC1, PC2 and PC3 have component loadings of 0.6228, 0.1690 and 0.1040, respectively, with a cumulative loading of 89.57%. For each of the individual loading factors, TN and K almost equally \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multirow{2}{*}{**DF**} & **Sum of** & **Mean** & **F Value** & **Pr \textgreater{} F** & **Number of** \\  & & **Squares** & **Square** & **F Value** & **Observations** \\ \hline pH & 4 & 0.529 & 0.132 & 7.91 & 0.0350 & 9 \\ EC & 4 & 0.196 & 0.049 & 0.15 & 0.9513 & 9 \\ OM & 4 & 1.149 & 0.287 & 15.41 & 0.0107 & 9 \\ TN & 4 & 0.009 & 0.002 & 43.01 & 0.0015 & 9 \\ P\({}_{2}\)O\({}_{5}\) & 4 & 20640 & 5160 & 55.52 & 0.0009 & 9 \\ K & 4 & 0.298 & 0.075 & 43.16 & 0.0015 & 9 \\ Ca & 4 & 4.989 & 1.247 & 6.58 & 0.0476 & 9 \\ Mg & 4 & 0.662 & 0.167 & 3.95 & 0.1060 & 9 \\ DOC & 4 & 3926 & 981.5 & 6.89 & 0.0441 & 9 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: ANOVA summary table for the soil chemical parameters in paddy fields under long-term compost fertilization.