## 3 Results and Discussion
### Compost Characteristics
#### 3.1.3 Carbon Ratios (C:N and C:P)  
_C:N ratio_ is one of the main parameters (along with temperature, pH and moisture content) contributing to the efficiency of the composting process [74]. The C:N ratio of the tested composts was relatively low (\(>\)5.42\(\sim\)6.80) and slightly to moderately variable, as seen from the close coefficient of variation values (Table 3). Those results are not uncommon for compost from green wastes. The green materials (especially plant wastes) have lower C:N ratio than woody materials and animal wastes [66]. The low C:N ratio of the compost (i.e., insufficient carbon content) is not desirable because the microorganisms in the substrate use the available carbon and convert the excess nitrogen to NH\({}_{3}\) or NH\({}_{4}\)\({}^{+}\), the ultimate effect being nitrogen loss from the compost [67]. Many studies [5; 8; 9; 22; 25; 65] reported higher C:N ratios (8.69-14.9:1) for GW compost and for compost produced from the mixture of different green and biowastes than those in the present study. Higher C:N ratio values, varying within a wide range (13.5-79.0:1) and greater coefficient of variation (Cv = 44.6%), are also reported for GW used for composting [18].  
The C:N ratio is widely used for easier evaluation of the compost maturity, as it is a function of TOC and N that changes in organic materials during the composting process [67; 75]. Researchers' opinions for the optimal C:N ratio of compost determining its maturity are not unambiguous. Some consider that the ideal C:N ratio of well-matured compost should be below 10 [42], about 10 [76] or lower than 12 [77]; others offer larger ranges--10-15:1 [66; 78; 79], 15-20:1 [71], 10-25:1 [69] and 7.8-20.5:1 [12]. It is considered that C:N values lower than 20:1 are sufficient for N supply for plant growth [80]. Finally, it should be emphasized that there is no uniform, standardized limit of this parameter for compost maturity assessment accepted by the scientific community. The main reason is that the C:N ratio varies considerably in raw materials, and as a result often gives misleading information about compost maturity [9]. The results obtained raise the necessity of future research on green composts in relation to their C:N ratio.  
Compared to the C:N ratio, research data for the compost _C:P ratio_ in available literature are less numerous. The C:P ratio as an indicator of compost quality should not be underestimated, because the amount of phosphorus can be a limiting factor when that nutrient is deficient in the mixture [81]. C:P ratio in the organic matter determines whether mineralization reactions predominate over immobilization reactions, and in this regard, a critical C:P ratio of 200:1 has been proposed [82]. The results obtained were much lower than this value and were relatively close for both composts--16.7-19.3:1 (Cv = 8.18-10.8%). The C:P ratio of C2 was insignificantly higher compared to that of C1. Due to the lack of data in the available literature on the C:P ratio of GW compost, the comparison with other types of composts revealed that this ratio was significantly higher for compost made from garden waste (pruning remains (40-60%), leaf litter (20-30%), sewage sludge (0-10%) and biomass ash (0-20%)), at 56-155:1 [30]; and for compost prepared from municipal waste, at 45.6-95.0:1 (Cv = 22.0%) [83]. Future studies are needed to gather more information on this parameter as an indicator for GW compost quality assessment.