## 3 Results and Discussion
### Soil Inorganic Phosphorus Speciation  
The percentages of inorganic P distribution at 90 DAI following application of TSP, ERP, and CIRP are summarized in Figure 2. Approximately 80% of inorganic P was occupied by active P fractions such as Fe-P, Al-P, and Ca-P in both 90 DAI and 49 DAS (T0) of soil alone (T0) whose Fe-P was the highest. The fractionations of the inorganic P pools were in the order of Fe-P \(>\) Ca-P \(>\) Al-P \(>\) Occl-P \(>\) Red-P \(>\) Sol-P in 90 DAI, whereas Fe-P \(>\) Al-P \(>\) Ca-P \(>\) Occl-P \(>\) Red-P \(>\) Sol-P in 49 DAS. The dominance of Fe-P fraction of soil alone (T0) is related to a lower pH, higher content of Fe, and the weathering processes of soils. These results corroborated with some findings on Ultisols [41; 42] where Fe-P was the highest apart from indicating that the dynamics of P, in particular P sorption, in agricultural soils is governed by colloidal Fe surfaces when soil pH is lower than 4.5 [43; 44; 45; 34]. \begin{table}
\begin{tabular}{l c c c c c c c c c} \hline \hline  & & \multicolumn{2}{c}{**TSP**} & \multicolumn{3}{c}{**ERP**} & \multicolumn{3}{c}{**CIRP**} \\ \cline{2-10}
**Pi** & **T0** & **T1** & **T2** & **T0** & **E1** & **E2** & **T0** & **C1** & **C2** \\ \hline Sol-P & 0.1c & 309.5a & 146.6b & 0.1a’ & 0.1a’ & 0.1a’ & 0.1b” & 0.3a” & 0.1b” \\ (ppm) & \(\pm\)0.01 & \(\pm\)12.38 & \(\pm\)9.07 & \(\pm\)0.01 & \(\pm\)0.01 & \(\pm\)0.01 & \(\pm\)0.01 & \(\pm\)0.03 & \(\pm\)0.01 \\ Al-P & 3.6c & 1750.0a & 1103.3b & 3.6c’ & 42.6a’ & 30.2b’ & 3.4c” & 26.0b” & 41.9a” \\ (ppm) & \(\pm\)0.03 & \(\pm\)42.02 & \(\pm\)56.36 & \(\pm\)0.03 & \(\pm\)2.04 & \(\pm\)2.60 & \(\pm\)0.03 & \(\pm\)0.27 & \(\pm\)1.58 \\ Fe–P & 25.9c & 188.0a & 133b & 25.9a’ & 11.0b’ & 12.3b’ & 25.87c” & 234.1a” & 143.6b” \\ (ppm) & \(\pm\)0.9 & \(\pm\)2.1 & \(\pm\)12.5 & \(\pm\)0.89 & \(\pm\)0.75 & \(\pm\)0.13 & \(\pm\)0.89 & \(\pm\)10.66 & \(\pm\)4.79 \\ Ca–P & 4.91b & 108.1a & 105.3a & 4.91b’ & 2122.5a’ & 2090.8a’ & 4.91c” & 1217.0a” & 595.7b” \\ (ppm) & \(\pm\)0.1 & \(\pm\)1.3 & \(\pm\)6.6 & \(\pm\)0.1 & \(\pm\)90.6 & \(\pm\)102.6 & \(\pm\)0.08 & \(\pm\)40.08 & \(\pm\)31.38 \\ Red-P & 0.7 ab & 0.8 ab & 0.9a & 0.7c’ & 3.2a’ & 2.9b’ & 0.7c” & 2.3a” & 1.6b” \\ (ppm) & \(\pm\)0.04 & \(\pm\)0.07 & \(\pm\)0.07 & \(\pm\)0.04 & \(\pm\)0.10 & \(\pm\)0.02 & \(\pm\)0.04 & \(\pm\)0.08 & \(\pm\)0.05 \\ Occl-P & 2.7c & 10.7b & 12.5a & 2.7c’ & 56.7b’ & 79.1a’ & 2.71c” & 317.0a” & 169.6b” \\ (ppm) & \(\pm\)0.16 & \(\pm\)0.34 & \(\pm\)0.08 & \(\pm\)0.16 & \(\pm\)3.70 & \(\pm\)3.90 & \(\pm\)0.16 & \(\pm\)5.25 & \(\pm\)4.92 \\ \hline \hline \end{tabular}  
* Means within row with different letters indicate significant difference using [PERSON]’s test at \(p\leq 0.05\). The “\(\pm\)’ indicates standard error of quadruplicates. Sol-P is loosely soluble P, Al-P is aluminum bound P, Fe-P is iron bound P, Ca–P is calcium bound P, Red-P is reductant P, and Occl-P is occluded P. Pi—inorganic P.  
\end{table} 
Table 6: Inorganic phosphorus speciation of soil at ninety days after incubation. In general, the use of fertilizers in this incubation and pot trial regardless of P fertilizer type and rate altered the distribution of soil inorganic P differently. In the incubation trial, the TSP treatment at 90 DAI reduced the Fe-P fraction by six folds, whereas Al-P increased by seven folds (dominant inorganic P fraction) (Table 6 and Figure 2). This observation is, however, contrary to those of the soils with RPs as Ca-P was the dominant fraction regardless of the amount of RP. Application of ERP resulted in more than 90% Ca-P fraction, whereas CIRP showed 60% to 70% Ca-P regardless of the amount of RP used. The treatments with CZ (T2, E2, and C2) and fertilizer reduction showed a similar trend of those of the recommended rates of the fertilizers (T1, E1, and C1). At 49 DAS, T1 and T2 showed the highest Al-P fraction of 42% and 45%, respectively. The treatments with ERP (E1 and E2) showed 55% and 61%, respectively of Ca-P followed by Fe-P and Al-P. For CIRP, Fe-P dominated followed by Ca-P > Ocol-P > Al-P.