## 3 Results and Discussion
### Physicochemical Characterization
In addition to the C and N contents, the assessment of the chemistry bedding quality usually includes the determination of other nutrients of agronomic interest, such as phosphorus (P) and potassium (K). In CBP systems, C is supplied by adding organic material (sawdust and/or wood shavings, peanut, coffee husks, etc.). The amount of available C is consumed/reduced throughout the composting process, through the degradation of organic matter, in which organic C is converted into CO\({}_{2}\)[7; 13]. In the evaluated studies, the C content was very variable, with minimum and maximum values reported by [PERSON] et al. [5] and [PERSON] et al. [11] (5.8 and 47.1%, respectively--Table 3). Similar conditions of variation were obtained for the N content, which comes from the manure and urine of housed animals, and ranged from 0.3% [32] to 4.4% [5]--Table 3.  
In terms of the composting process, the assessment of C and N contents is usually performed using the ratio between them (C:N). According to [PERSON] et al. [53], the degradation of organic matter occurs more quickly when the C:N ratio is maintained between 25:1 and 30:1. For this reason, this first value is considered the lower desired C:N threshold for maintaining the active composting process [7; 13]. In most studies, the determined C:N ratio was less than 25:1 in at least one facility and/or evaluation period ([PERSON] et al. [30], [PERSON] et al. [19], [PERSON] et al. [11], [PERSON] et al. [5], [PERSON] and [PERSON] [32], [PERSON] et al. [4], and [PERSON] et al. [34]--Table 3). This is an indication that, in these situations, the low C content may have been a limiting factor for the decomposition activity, as it did not provide enough energy. The most challenging situation in terms of maintaining the composting process was observed in the study conducted by [PERSON] et al. [5], in which the C:N ratio ranged from 2.4 to 3.5. According to the authors, these values can be explained by the low frequency of bedding replacement on local, which occurred due to the low availability of bedding material. Such low C:N ratio values are a strong indication that the decomposing activity in this location was being inhibited, and that the bedding material should be changed [7; 54]. In studies conducted by [PERSON] et al. [30], [PERSON] et al. [11], [PERSON] et al. [19], [PERSON] et al. [4], and [PERSON] et al. [34], even though higher C:N ratios than those reported by [PERSON] et al. [5] were found, it appears that it would be advisable to change the bedding material. In these systems, the 15:1 ratio is considered the minimum recommended threshold for maintaining the active composting process and not reducing N availability (when applied to the soil as an organic fertilizer) [54; 55]. In the study conducted by [PERSON] et al. [29], in which the analyses were carried out after periods of eleven weeks from the beginning of the use of bedding materials, in fall and winter conditions, the prevalence of high C:N ratios (35:1 to 48:1) was observed for both materials used (sawdust and forest biomass). These results are an indication that there was an excess of C in the bedding [7], which was reflected in lower activity of decomposing microorganisms and, consequently, lower heat production (25.9 \(\pm\) 3.1 to 34.7 \(\pm\) 5.6). In cases like this, it may be necessary to add sources of N, such as animal manure (which has a C:N ratio between 15:1 and 19:1 [50; 56]) in order to increase the N content up to levels such that the composting process is not compromised by low protein synthesis of decomposing microorganisms [29]. It should be noted that if bedding turning is not effective in spatially homogenizing the material, regions with different C:N ratios may occur and, consequently, distinct levels of decomposition activity. Following what has already been reported for C and N, the P and K contents varied between studies.