## 3 Results and Discussions
### Assessment of Litter Characteristics  
In this study, after the broiler rearing experiment, the litter was sampled to measure its moisture content, pH, TC, TN, and C/N. The measurement results are shown in Table 2.  
During broiler rearing, the NH\({}_{3}\) generation and emission mechanism is an extremely complex process. The moisture content and pH of litter, environmental temperature, wind speed, and the litter surface area affected the NH\({}_{3}\) generation and emission [27; 28; 29]. NH\({}_{3}\) mainly originates from the urease hydrolyzation of urea and uric acid, with a small quantity coming from the degradation of undigested protein. The reaction processes are shown in Formulas (1)-(3) [23; 29; 30]. Several enzymes and microorganisms participate in this process, and water and oxygen are essential. The balance relationship between NH\({}_{3}\)(I) and NH\({}_{4}\)+ in litter is affected by pH and temperature (T) (Formula (4)). A decrease in the litter pH can promote the transformation of NH\({}_{3}\) into NH\({}_{4}\)+ ion, thus inhibiting NH\({}_{3}\) generation and emission [31; 32; 33]. The balance between the NH\({}_{3}\)(I) and NH\({}_{3}\)(g) on the litter surface is affected by wind speed (V) and the litter surface area (A). The reaction process is shown in Formula (5). \[\text{C}_{5}\text{H}_{4}\text{O}_{3}\text{N}_{4}+1.5\text{O}_{2}+4\text{H}_{ 2}\text{O}\overset{\text{u}\text{e}\text{e}\text{e}\text{e}  
During this experiment, the litter moisture content in the waste-tea-litter group (59.3% \(\pm\) 1.3) was decreased by 13.7% when compared with the nonlitter group (73% \(\pm\) 4.2). An ideal litter material should feature high hygroscopicity, a reasonable drying time, and high fragility. The litter can quickly separate urine and manure in the excrement [34], thus blocking the NH\({}_{3}\)-generation process, because the surface area of fresh urine or slurry exposed to air greatly influences the NH\({}_{3}\) emissions. The urea and uric acid in manure is decomposed by urease to generate NH\({}_{3}\), while tea polyphenols can reduce the urease activity, thus decreasing the decomposition of urea and uric acid, and inhibiting NH\({}_{3}\) generation. Meanwhile, tea absorbs the urine in broiler litter, which reduces the contact between urea and urease and the contact between urine and air, and increases the NH\({}_{3}\) diffusion distance and transmission resistance, finally lowering NH\({}_{3}\) emissions [35]. The waste tea litter also decreases the moisture content in litter; decreased moisture content will lower the microorganism activity and weaken the decomposition of nitrogenous substances in litter, thus reducing NH\({}_{3}\) generation. [PERSON] et al. [36] found that when the moisture content in chicken litter was lower than 40%, NH\({}_{3}\) release was directly proportional to moisture content, and low moisture content inhibited microorganism growth; when the moisture content in chicken litter was higher than 60%, the microorganism activity in the anaerobic environment was inhibited, and the NH\({}_{3}\) release was inversely proportional to moisture content; when the moisture content in chicken litter was 40-60%, it was ideal for microorganism activity, and NH\({}_{3}\) release increased and then decreased as the moisture content rose; when the litter moisture content was lower than 10%, no NH\({}_{3}\) was produced. Therefore, during the poultry-rearing process, the litter's moisture content is often controlled at 25-35% to keep the poultry house dry. In this study, litter moisture content in the waste-tea-litter group was 59.3% \(\pm\) 1.3, though it reduced the moisture content of litter, but it still was slightly higher than expected. As shown in Formula (4), the litter pH value and temperature are also some of the main affecting factors in NH\({}_{3}\)(l) generation.