## 3 Results and Discussions
### Measurement of NH\({}_{3}\) and CO\({}_{2}\) Levels  
The changing trend in daily concentrations of NH\({}_{3}\) and CO\({}_{2}\) during the experiment is shown in Figure 3.  
The emissions of each gas showed a significant difference (\(p<0.05\)) between the waste-tea-litter group and the nonlitter group. As shown in Figure 3a, NH\({}_{3}\) concentrations in the nonlitter broiler group and the waste-tea-litter broiler group were increased sharply and increased slightly in the early stage of the experiment (2-3 days), respectively, and both were maintained as stable in the middle and later stages. Namely, in two conditions, the NH\({}_{3}\) concentrations tended to rise at first and became stable later, and the NH\({}_{3}\) concentrations in the nonlitter group were higher than in the waste-tea-litter group. As shown in Figure 3b, the daily average emission concentration of CO\({}_{2}\) in the waste-tea-litter group (713 \(\pm\) 69 ppm) was significantly lower than that in the nonlitter group (797 \(\pm\) 107 ppm). The highest NH\({}_{3}\) emission concentration in the non-litter group was 19 ppm, and the respective value was only 2.2 ppm in the waste-tea-litter group. Therefore, waste tea litter could lower the NH\({}_{3}\) and CO\({}_{2}\) emissions during the broiler rearing process. As reported [21], the NH\({}_{3}\) concentration in the air of broiler house should be lower than 25 ppm. When the concentration was higher than 75 ppm, the broiler production performance was reduced greatly; when it was higher than 50 ppm, both daily average feed intake and weight gain were decreased [22]. As shown in Table 1 and Figure 3, the maximum NH\({}_{3}\) concentration was 19 ppm in this experiment, not more than 25 ppm; and the emissions of NH\({}_{3}\) and CO\({}_{2}\) had almost no effect on the broilers' growth performance. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{3}{*}{Days} & \multicolumn{6}{c}{**Growth Parameters**} \\ \cline{2-9}  & \multicolumn{2}{c}{**Average Daily Weight/g**} & \multicolumn{2}{c}{**Average Daily Excretion/g**} & \multicolumn{2}{c}{**Average Daily Feed Intake/g**} & \multicolumn{2}{c}{**Average Daily Water Intake/g**} \\  & **Non-Bedding** & **Waste Tea** & **Non-Bedding** & **Waste Tea** & **Non-Bedding** & **Waste Tea** & **Non-Bedding** & **Waste Tea** \\  & **Materials** & **Litter** & **Materials** & **Litter** & **Materials** & **Litter** & **Materials** & **Litter** \\ \hline
1 & 1861 & 1964 & 78 & 181 & 113 & 118 & 239 & 229 \\
2 & 1958 & 1945 & 184 & 125 & 119 & 118 & 237 & 238 \\
3 & 1963 & 1944 & 172 & 138 & 121 & 120 & 260 & 238 \\
4 & 1964 & 1992 & 115 & 112 & 121 & 118 & 254 & 238 \\
5 & 1955 & 1946 & 110 & 209 & 126 & 121 & 238 & 239 \\
6 & 1980 & 1962 & 128 & 114 & 121 & 120 & 240 & 238 \\
7 & 1991 & 1949 & 46 & 111 & 122 & 120 & 246 & 239 \\ Notability & & & & & & & & \\ analysis & & NS (\(p=0.815\)) & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Effect of non-bedding materials and waste tea litter on growth parameters of broilers. Figure 3: The daily concentration of NH\({}_{3}\) (**a**) and CO\({}_{2}\) (**b**) in the chambers in rearing conditions without litter and with waste tea litter. NH\({}_{3}\) is mainly produced by microorganisms' decomposition of nitrogenous substances in litter, and the emission of NH\({}_{3}\) is related to the surface area of litter exposed to air [23; 24] and the accumulation time [25]. In general, the smaller the exposed surface area of the litter or the slurry, the lower the NH\({}_{3}\) release [26].