## 1 Introduction  
The United Nations Environment Program (UNEP) announced in 2021 that agriculture is responsible for 40% of anthropogenic methane (CH\({}_{4}\)) emissions, with enteric fermentation and manure management accounting for 32% of the emissions and rice cultivation accounting for 8% [1]. Countries worldwide agree with the claim that CH\({}_{4}\) emissions and carbon dioxide (CO\({}_{2}\)) must be reduced to improve global warming [1]. The number of countries that have endorsed the Global Methane Pledge (GMP) to curtail CH\({}_{4}\) emissions--known for their amplified impact on global warming--by 30% before 2030 has risen to 151 [2]. However, to accurately calculate the amount of CH\({}_{4}\) reduction, actual data on emission sources and emissions in various manure management environments are required. The slurry pit stores slurry-type manure generated in slattled-floor pig houses for a certain period and then discharges it outside [3; 4; 5; 6]. Stored pig slurry generally induces biochemical reactions depending on aerobic and anaerobic conditions resulting from pig house management [3; 7; 8; 9]. Greenhouse gases such as CH\({}_{4}\), CO\({}_{2}\), and nitrova oxide (N\({}_{2}\)O) can be emitted due to biochemical reactions, and studies have been conducted on greenhouse gas emissions from pig slurry pits under various environmental conditions [10; 11; 12]. During storage of the raw pig slurry, CH\({}_{4}\) and CO\({}_{2}\) emissions were reported to range from 5 to 75 g\(\cdot\)m\({}^{-3}\cdot\)d\({}^{-1}\) and 50 to 300 g\(\cdot\)m\({}^{-3}\cdot\)d\({}^{-1}\), respectively [12; 13; 14]. N\({}_{2}\)O emissions occurred at negligible levels [14; 15; 16; 17]. Various studies have been conducted to reduce greenhouse gas emissions from these pig slurry pits in terms of diet manipulation, housing system, and manure management, such as the use of feed additives [18], the use of cover agents [12; 19], the acidification of manure [17; 20], and the formation of aerobic conditions in the slurry [8]. In particular, for acidification, chemical amendments such as sulfuric acid and citric acid and organic-based compounds such as humic substances (HS) were used [21; 22; 23]. HS is composed mainly of humic acid, fulvic acid, and humin and is usually associated with acidification [24]. However, according to a recent study, the abundant electron transport function derived from the molecular structure of HS causes a biochemical reaction to inhibit hydrolysis and methanogenesis [25; 26; 27; 28]. Peat moss contains such HS, and the contents of HS in peat moss have been reported as 76% humin, 18% humic acid, and 3% fulvic acid based on the total organic matter content [29]. When peat moss was used for feeding livestock, there were positive effects, such as promoting digestion and improving growth rate [24]. Feeding of HS improved broiler productivity by about 7% compared with the control, which was estimated to be due to increased absorption of nitrogen, phosphorus, and other nutrients according to chelating properties [30]. Several studies have shown that feed efficiency is improved when HS is fed as feed additives to livestock, especially in poultry and pigs [30; 31; 32; 33; 34]. The reasons for the increase in feed efficiency include the maintenance of intestinal microbial activity, improvement of animal gut health such as antibacterial activity [35; 36; 37], modification of protein digestibility [37], and activation of pancreatic enzymatic activity [35]. However, the prior studies mentioned above focus only on the utilization of HS themselves or on the effect of peat moss on the physiological changes of livestock. There is no well-known study on the relationship between pig manure generated after feeding peat moss as a feed additive and CH\({}_{4}\) and CO\({}_{2}\) released during the storage period. Using peat moss as a feed additive for livestock could potentially lead to a decrease in the organic matter content of manure due to improved feed efficiency [35; 36; 37].