3.1 Soil chemical and microbial properties
Temporal changes of soil chemical and microbial properties across all the treatments are presented in Table 4 and Figure 2, respectively. Compared with control treatment (CK), consecutive N fertilization significantly increased SOC, TN, MBC, MBN, CMR, NMR and PRN, whereas significantly decreased soil ECe. The effect of N fertilization rates on soil pH, CEC and AN was not significant across all the treatments. Soil AP showed temporal decrease trend since calcium superphosphate was applied as soil amendment and phosphorus fertilizer supply for single use prior to the first paddy rice season. Table 5 shows the Pearson correlation coefficient among the soil chemical and microbial properties. Soil ECe was negatively correlated with SOC, CEC, AP, MBC, MBN, CMR, NMR and PNR, and SOC showed positive correlation with CEC, TN, AN, MBC, MBN, CMR, NMR and PNR. Soil microbial properties were relevant to each other whereas the correlation between pH and other soil attributes was not significant. The two-way ANOVA results across all the treatments are also presented in Table 5. Cultivation time effect of treatments on ECe, pH, SOC, CEC, AP, MBC, MBN, CMR, NMR and PRN was observed, and the effect of N fertilization rates on SOC, TN, AN, AP, MBC, MBN and NMR was significant. Cultivation time and N fertilization rates had interactive effect on AN, MBC and NMR in this study.
Table 4
Table 5
Figure 2