## 4 Discussion
### Soil Total Nitrogen, Hydrolyzable Organic Nitrogen Fractions, and Mineral Nitrogen
The higher contents of soil amino sugar-N is  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{2}{c}{**Crop Recovery of Applied N (kg kg\({}^{-1}\))**} & \multicolumn{2}{c}{**Agronomic Efficiency of Applied N (kg grain kg\({}^{-1}\))**} \\ \hline \multicolumn{3}{c}{**(Mean \(\pm\) Standard Error) kg ha\({}^{-1}\)**} \\ \hline \multicolumn{3}{c}{Second Crop} \\ \hline T1 & 32 b (\(\pm\)0.88) & 9 c (\(\pm\)0.88) \\ T2 & 52 a (\(\pm\)0.88) & 21 ab (\(\pm\)2.40) \\ T3 & 48 a (\(\pm\)1.45) & 24 a (\(\pm\)0.88) \\ T4 & 33 b (\(\pm\)0.88) & 16 b (\(\pm\)1.45) \\ T5 & 45 a (\(\pm\)1.45) & 24 a (\(\pm\)0.57) \\ T6 & 39 b (\(\pm\)0.88) & 20 balso related to microbial growth which is also responsible for the increased presence of glucosamine, muramic acid, and other amino sugars [32]. Amino sugars are more labile than other fractions of hydrolyzable N which influences the quantity of N that can be mineralized to supply the bulk of crop available N [30]. The elevated amounts of total hydrolyzable N, hydrolyzable NH\({}_{4}\)+, and (NH\({}_{4}\)+ + amino sugar)-N contents in T2-T6 (Figures 2-4) are important as amino acids affect mineralization levels by bacteria which are able to reduce amino acids into soil exchangeable NH\({}_{4}\)+ [33]. Higher amino acid-N were observed in the plots with rice straw compost or paddy husk compost suggesting that amino acid-N in the soil depends on the supply of organic matter [34]. The lower non-hydrolyzable N in the plots with inorganic fertilizers, CZ, and rice straw compost or paddy husk compost (Figure 7) was due to the higher hydrolyzable and amino based nitrogen (Figures 2-6). [PERSON] and [PERSON] [35] reported that the proportion of non-hydrolyzable N was relatively higher in unfertilized soils, whereas the application of organic fertilizers led to increased hydrolyzability of the organic N compounds and lower non-hydrolyzable N. The organic matter in the rice straw and paddy husk composts might have contributed substantially to the soil hydrolyzable N because this is supported by the higher contents of amino sugar-N and amino acid-N following application of T3, T4, T5, and T6, regardless of the cropping cycle. The remaining fractions of the N-containing molecules in the plots treated with T1 and T2 (first crop) are not quantified by hydrolysis procedures and are therefore considered to be part of an aggregate unidentified fraction of acid hydrolysates [36]. The unaccounted fraction of acid hydrolyses contributed to bias in the estimation of the decomposable hydrolyzable N fraction. This is because the soil organic N fractions can be replenished through depletion of the unknown organic N fraction or unhydrolyzable N [37]. Microbes will decompose organic N from the substrate provided by the organic matter of the rice straw and paddy husk composts for their growth and activities. Therefore, the quantity of substrate available from organic amendments has an impact on soil N availability because it causes higher exchangeable ammonium and available nitrate [24]. The absorption and retention capacity of CZ for ammonium released from urea, rice straw compost, and paddy husk compost enables adequate maintenance of N supply in the soil. A slow release of N might also be the reason for the higher soil exchangeable ammonium for T2-T6 compared with T0 and T1 (without CZ) for both crop cycles and available NO\({}_{3}\)- for the first crop (Figures 8 and 9). The lower available nitrate in the plots with the different treatment combinations consisting chemical fertilizers, CZ, rice straw compost or paddy husk compost (treatments T2, T3, T4, T5, and T6) for the second crop is related to the retention of ammonium ions by CZ, rice straw compost and paddy husk compost such that nitrifying bacteria could not readily and rapidly oxidize the ammonium ions.