## 3 Results
### Effect of pH on Ammonia Volatilization  
Comparing the data in Table 1, we find that a and b in the linear equation of ammonia volatilization (Y) and ammonium concentration (C) after ammonium bicarbonate and diammonium phosphate treatment both increased with the increase of pH when under the condition of the same temperature. This indicates that a and b are related to the pH of the solution. We used a binary quadratic equation model to fit the correlation between CIF and pH at the same temperature, while we used a binary equation model to fit their correlation with the IAVFs, and the results are shown in Table 3. As shown in Table 3, the coefficient of determination (\(R^{2}\)) of the CIF, IVAFs, and pH were all higher than 0.9, except for ammonium bicarbonate treated at 15 \({}^{\circ}\)C, which indicates that these equations can well expound the relationships between them. From Table 3, we find that the apex of the fitting equation of the CIF value was concentrated between pH 7.1 and 7.3, which means that the value of the CIF increases rapidly with the increase of pH when the solution is alkaline. This indicates that the effect of pH is significantly greater than that of temperature on ammonia volatilization. Further analysis showed that the value of \(\varepsilon\) increases gradually with increasing temperature, which indicates that the changing rate of \(\Delta pH/\Delta a\) increases rapidly as the temperature increases. From the fitting equation of the IVAFs value, we found that when the ambient temperature was low (15 \({}^{\circ}\)C and 20 \({}^{\circ}\)C), the coefficient \(\eta\) of SAB, which is the effect strength of pH on the IVAFs, was lower than that of SDP. When the temperature rose to 25 \({}^{\circ}\)C and 30 \({}^{\circ}\)C, the values of \(\eta\) of these two fertilizer solutions were contrary to the values under a low temperature. These results show that the pH plays an important role in the ammonia volatilization trend of SDP in a low ambient temperature. However, the impact of SAB is even greater at a high temperature. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Fertilizer**} & \multirow{2}{*}{**pH**} & \multicolumn{4}{c}{**Regression Equation**} \\ \cline{3-6}  & & **Value of \(a\)** & \(R^{2}\) & **Value of \(b\)** & \(R^{2}\) \\ \hline \multirow{4}{*}{SAB} & 7.0 & \(=\)0.0005T \(-\) 0.0042 & 0.9792 & \(=\)0.0053T \(-\) 0.0029 & 0.6763 \\  & 7.5 & \(=\)0.0013T \(-\) 0.0134 & 0.9716 & \(=\)0.0106T \(-\) 0.0204 & 0.8502 \\  & 8.0 & \(=\)0.0049T \(-\) 0.0555 & 0.9381 & \(=\)0.0200T \(-\) 0.1020 & 0.9837 \\  & 8.5 & \(=\)0.0104T \(-\) 0.0799 & 0.9625 & \(=\)0.0397T \(-\) 0.4147 & 0.9326 \\ \hline \multirow{4}{*}{SDP} & 7.0 & \(=\)0.0004T \(-\) 0.00492 & 0.9625 & \(=\)0.0055T \(-\) 0.0521 & 0.4384 \\  & 7.5 & \(=\)0.0016T \(-\) 0.02025 & 0.8546 & \(=\)0.0118T \(-\) 0.1273 & 0.9258 \\ \cline{1-1}  & 8.0 & \(=\)0.0041T \(-\) 0.05713 & 0.8409 & \(=\)0.0230T \(-\) 0.1994 & 0.9940 \\ \cline{1-1}  & 8.5 & \(=\)0.0105T \(-\) 0.11673 & 0.9423 & \(=\)0.0274T \(-\) 0.1940 & 0.9042 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The regression equations between temperature and the values of \(a\) and \(b\). (\(a=\)\(\tau\)T \(+\)\(\beta\), \(b=\gamma\)T \(+\)\(\delta\)).