Figure 1.
Conventional rice plantations used in this study.

Figure 1.
Conventional rice plantations used in this study.

Figure 2.
The WSC, HWSC, and DOC (a), POXC (b), and SOC (c) at different soil depths. Note: differences in soil depth across the latter means are significant (p < 0.05). The lines above the bars represent the standard error. SOC = soil organic carbon; POXC = permanganate oxidizable carbon; HWSC = hot water-soluble carbon; DOC = dissolved organic carbon.

Figure 2.
The WSC, HWSC, and DOC (a), POXC (b), and SOC (c) at different soil depths. Note: differences in soil depth across the latter means are significant (p < 0.05). The lines above the bars represent the standard error. SOC = soil organic carbon; POXC = permanganate oxidizable carbon; HWSC = hot water-soluble carbon; DOC = dissolved organic carbon.

Figure 3.
The fractionation of inorganic phosphorus in conventional paddy soil at specific soil depths between 0?5 and 10?15 cm. Note: There were substantial differences between the selected soil depths (0?5 and 10?15 cm) between the small case and bar (p < 0.05). The lines above the bars represent the standard error. P? solution was extracted using 0.1 M NH4Cl; Al?P was extracted using 0.5 M NH4F; and Fe?P was extracted using 0.1 M NaOH. Red?So?P = Reductant soluble P, which was extracted using a mixture of Na3C3H6O7, NaHCO3, and Na2S2O4. Ca?P was extracted using 0.25 M H2SO4.

Figure 3.
The fractionation of inorganic phosphorus in conventional paddy soil at specific soil depths between 0?5 and 10?15 cm. Note: There were substantial differences between the selected soil depths (0?5 and 10?15 cm) between the small case and bar (p < 0.05). The lines above the bars represent the standard error. P? solution was extracted using 0.1 M NH4Cl; Al?P was extracted using 0.5 M NH4F; and Fe?P was extracted using 0.1 M NaOH. Red?So?P = Reductant soluble P, which was extracted using a mixture of Na3C3H6O7, NaHCO3, and Na2S2O4. Ca?P was extracted using 0.25 M H2SO4.

Figure 4.
Physiochemical properties of paddy soil at various soil depths; CEC and Avai. P (a), soil pH (b), clay and silt (c), and DOC/Avai. P ratio (d). Note: There were substantial differences between the selected soil depths (0–5 and 10–15 cm), as shown by the differences in the latter (p < 0.05). The lines above the bars represent the standard error. CEC = cation exchange capacity (1 N NH4OAC pH = 7), where P is available phosphorus assessed using the Bray II method; pH = soil pH (1:1 H2O); clay and silt are percentages of clay and silt content; and DOC/P is the ratio of DOC to P.

Figure 4.
Physiochemical properties of paddy soil at various soil depths; CEC and Avai. P (a), soil pH (b), clay and silt (c), and DOC/Avai. P ratio (d). Note: There were substantial differences between the selected soil depths (0–5 and 10–15 cm), as shown by the differences in the latter (p < 0.05). The lines above the bars represent the standard error. CEC = cation exchange capacity (1 N NH4OAC pH = 7), where P is available phosphorus assessed using the Bray II method; pH = soil pH (1:1 H2O); clay and silt are percentages of clay and silt content; and DOC/P is the ratio of DOC to P.

Figure 5.
The correlation coefficient between the physiological soil properties and inorganic phosphorus fractions and the labile carbon fractions and soil carbon content determined using principal component analysis. Note: ? p < 0.05, ?? p < 0.01, and ??? p < 0.001. Solution–P was extracted using 0.1 M NH4Cl; Al–P was extracted using 0.5 M NH4F; and Fe–P was extracted using 0.1 M NaOH. Re.So.P = Reductant soluble P, which was extracted using a mixture of Na3C3H6O7, NaHCO3, and Na2S2O4; and Ca–P was extracted using 0.25 M H2SO4. SOC, soil organic carbon; WSC, water-soluble carbon; HWSC, hot water-soluble carbon; DOC, dissolved organic carbon; POXC, permanganate oxidizable carbon; Avai. P, available phosphorus; pH, soil pH; CEC, cation exchange capacity; clay and silt, percentages of clay and silt.

Figure 5.
The correlation coefficient between the physiological soil properties and inorganic phosphorus fractions and the labile carbon fractions and soil carbon content determined using principal component analysis. Note: ? p < 0.05, ?? p < 0.01, and ??? p < 0.001. Solution–P was extracted using 0.1 M NH4Cl; Al–P was extracted using 0.5 M NH4F; and Fe–P was extracted using 0.1 M NaOH. Re.So.P = Reductant soluble P, which was extracted using a mixture of Na3C3H6O7, NaHCO3, and Na2S2O4; and Ca–P was extracted using 0.25 M H2SO4. SOC, soil organic carbon; WSC, water-soluble carbon; HWSC, hot water-soluble carbon; DOC, dissolved organic carbon; POXC, permanganate oxidizable carbon; Avai. P, available phosphorus; pH, soil pH; CEC, cation exchange capacity; clay and silt, percentages of clay and silt.

Figure 6.
The principal correlation analysis of soil properties and inorganic phosphorus fractions at differing soil depths: 0–5 cm (a) and 10–15 cm (b). Note: Solution–P was extracted using 0.1 M NH4Cl; Al–P was extracted using 0.5 M NH4F; and Fe–P was extracted using 0.1 M NaOH. Re.So.P = Reductant soluble P, which was extracted using a mixture of Na3C3H6O7, NaHCO3, and Na2S2O4; and Ca–P was extracted using 0.25 M H2SO4. SOC, soil organic carbon; WSC, water-soluble carbon; HWSC, hot water-soluble carbon; DOC, dissolved organic carbon; POXC, permanganate oxidizable carbon; Avai. P, available phosphorus; pH, soil pH; CEC, cation exchange capacity; clay and silt, percentages of clay and silt.

Figure 6.
The principal correlation analysis of soil properties and inorganic phosphorus fractions at differing soil depths: 0–5 cm (a) and 10–15 cm (b). Note: Solution–P was extracted using 0.1 M NH4Cl; Al–P was extracted using 0.5 M NH4F; and Fe–P was extracted using 0.1 M NaOH. Re.So.P = Reductant soluble P, which was extracted using a mixture of Na3C3H6O7, NaHCO3, and Na2S2O4; and Ca–P was extracted using 0.25 M H2SO4. SOC, soil organic carbon; WSC, water-soluble carbon; HWSC, hot water-soluble carbon; DOC, dissolved organic carbon; POXC, permanganate oxidizable carbon; Avai. P, available phosphorus; pH, soil pH; CEC, cation exchange capacity; clay and silt, percentages of clay and silt.

Figure 7.
The correlation coefficient between soil properties, SOC, and the labile organic carbon fraction at various soil depths. Note: ? p < 0.05, ?? p < 0.01, and ??? p < 0.001. SOC, soil organic carbon; WSC, water-soluble carbon; HWSC, hot water-soluble carbon; DOC, dissolved organic carbon; POXC, permanganate oxidizable carbon; P, available phosphorus; pH, soil pH; CEC, cation exchange capacity; clay and silt, percentages of clay and silt.

Figure 7.
The correlation coefficient between soil properties, SOC, and the labile organic carbon fraction at various soil depths. Note: ? p < 0.05, ?? p < 0.01, and ??? p < 0.001. SOC, soil organic carbon; WSC, water-soluble carbon; HWSC, hot water-soluble carbon; DOC, dissolved organic carbon; POXC, permanganate oxidizable carbon; P, available phosphorus; pH, soil pH; CEC, cation exchange capacity; clay and silt, percentages of clay and silt.

Figure 8.
The effect of long-term synthetic fertilization on the changes in SOC and C dynamics in the paddy soil. Note: The numbers in the boxes indicate the relationships between the correlation coefficients of the indicators. Solution–P was extracted using 0.1 M NH4Cl; Al–P was extracted using 0.5 M NH4F; and Fe–P was extracted using 0.1 M NaOH. Re.So.P = Reductant soluble P, which was extracted using a mixture of Na3C3H6O7, NaHCO3, and Na2S2O4; and Ca-P was extracted using 0.25 M H2SO4. SOC, soil organic carbon; WSC, water-soluble carbon; HWSC, hot water-soluble carbon; DOC, dissolved organic carbon; POXC, permanganate oxidizable carbon; Avai. P, available phosphorus; pH, soil pH; CEC, cation exchange capacity; clay and silt, percentages of clay and silt. The numbers in the green boxes varied between the datasets 0–5 and 10–15 cm, while the numbers in the orange boxes came from a 0–30 cm soil depth dataset. Note: ? p < 0.05, ?? p < 0.01, and ??? p < 0.001.

Figure 8.
The effect of long-term synthetic fertilization on the changes in SOC and C dynamics in the paddy soil. Note: The numbers in the boxes indicate the relationships between the correlation coefficients of the indicators. Solution–P was extracted using 0.1 M NH4Cl; Al–P was extracted using 0.5 M NH4F; and Fe–P was extracted using 0.1 M NaOH. Re.So.P = Reductant soluble P, which was extracted using a mixture of Na3C3H6O7, NaHCO3, and Na2S2O4; and Ca-P was extracted using 0.25 M H2SO4. SOC, soil organic carbon; WSC, water-soluble carbon; HWSC, hot water-soluble carbon; DOC, dissolved organic carbon; POXC, permanganate oxidizable carbon; Avai. P, available phosphorus; pH, soil pH; CEC, cation exchange capacity; clay and silt, percentages of clay and silt. The numbers in the green boxes varied between the datasets 0–5 and 10–15 cm, while the numbers in the orange boxes came from a 0–30 cm soil depth dataset. Note: ? p < 0.05, ?? p < 0.01, and ??? p < 0.001.