2.4. Statistical analysis
Data Processing System (DPS) was applied to perform statistical
analyses. A three-way analysis of
variance (ANOVA) together with Tukey’s test was carried out to analyze
the effects of experimental years
(four levels: 2015, 2016, 2017 and 2018), soil depths (four levels:
0-20, 20-40, 40-60, and 60-80 cm), and straw interlayers (four levels:
0, 6, 12, and 18 Mg ha-1) on SOC and TN contents, and
soil C:N ratio. SOC content was significantly influenced by the
interaction among these three factors. Therefore, a two-way ANOVA was
performed to compare the effects of soil depths and straw interlayers on
soil parameters in each year, and another two-way ANOVA was performed to
examine the influences of experimental years and straw interlayers on
soil parameters in each soil layer. When significant interactions were
observed between experimental years / soil depths and straw interlayers,
one-way ANOVA was conducted between straw interlayers in the same
experimental year / soil depth. The Pearson’s correlation coefficients
between SOC / TN and soil salinity / crop yield were calculated using
IBM SPSS Statistics 20.0 (SPSS Inc., ILZZ, USA). Figures were plotted
with Origin 2020.