## 4 Discussion  
### Soil Total Nitrogen, Hydrolyzable Organic Nitrogen Fractions, and Mineral Nitrogen  
The higher retention of soil total N was possible because of the high CEC of the CZ (100 cmol\({}_{\rm c}\) kg\({}^{-1}\)), rice straw (86 cmol\({}_{\rm c}\) kg\({}^{-1}\)), and paddy husk (176 cmol\({}_{\rm c}\) kg\({}^{-1}\)) composts [10]. The higher soil total N in T2, T3, T4, T5, and T6 suggests that the use of CZ is effective in reducing N loss in soils, consistent with the findings of [PERSON] et al. [24] and [PERSON] et al. [25]. Nitrogen ions retention by CZ is due to its open-ringed structure consisting of small-sized molecules that physically protect NH\({}_{4}\)\({}^{+}\) ions against microbial nitrification [26]. The use of rice straw and paddy husk composts affected the retention of soil total N partly because their organic matter contents were 47% and 48.6%, respectively [11]. [PERSON] et al. [27] reported that the organic matter content of composts resulted in slower mineralization to NH\({}_{3}\) or NH\({}_{4}\)\({}^{+}\) and NO\({}_{3}\)\({}^{-}\). Hence, with time, organic N accumulation in soil is influenced by the increase in total soil organic matter following the application of composts [28]. Using inorganic fertilizers, CZ, rice straw, and paddy husk composts together contributed to soil N availability and this directly affected the maize crop productivity. For the organic N fractions in soil, the higher hydrolyzable organic N fractions could be partly due to the adequate supply of substrates from the CZ, rice straw, and paddy husk composts for microbial growth and other activities. The limited supply of substrates such as the low content of total N associated with T0 (soil only) and T1 (recommended chemical fertilization) resulted in lower total hydrolyzable N, hydrolyzable NH\({}_{4}\)-N and (NH\({}_{4}\)\({}^{+}\) + amino sugar)-N (Figures 2-4). The relatively low C/N ratios of rice straw (15) and paddy husk (17) composts (Table 2), which are considered ideal for increasing N availability in soil, might have also partly caused the higher contents of soil total hydrolyzable N, hydrolyzable NH\({}_{4}\)-N and (NH\({}_{4}\)\({}^{+}\) + amino sugar)-N in the plots treated with these composts. According to [PERSON] et al. [29], the C/N ratio of composts is a good indicator of N supply because composts having a C:N values ranging from 10 to 15 results in mineralization. In contrast, the addition of composts with C:N \(>\) 20 can induce soil microbial activities to decompose labile C, thus, causing immobilization of added inorganic N. The organic matter of rice straw and paddy husk composts are also sources of microorganisms to decompose soil organic matter. The lower content of soil amino sugar-N in T2, T3, and T6 for the second crop cycle was partly a result of the amino sugar-N in these soils being the primary source of soil N that can easily be mineralized, resulting in a decrease in amino sugar-N (Figure 5). The higher content of soil amino sugar-N in T5 for the second crop suggests that the accumulated amino sugar-N can be mineralized for subsequent crops (residual or carry-over effect). [PERSON] et al. [30] reported that the accumulation of amino sugar-N in soils after the organic amendment application is related to N carry-over from previous cropping cycles. [PERSON] [31] explains that the accumulation of soil amino sugar-N is due to the residue being decomposed by microbes whereby amino sugars are prominently present in cell wall materials generated by bacteria, fungi or actinomycetes.