2.5 | Statistical analysis
Data were subjected to analysis of variance (ANOVA) using the windows-based SPSS program (SPSS v19.0).The impacts of tillage management, straw management, and annual variation on SOC contents, wheat grain yields, and maize grain yields were tested using three-way ANOVAs. The effects of tillage and straw managements on plant-derived biomass and carbon, SOC stock, yield variations of both wheat and maize, and sustainable yield index of both wheat and maize were analyzed using two-way ANOVAs. Multiple comparisons were made for determining significant effects of treatments using the least significant difference (LSD) test with P < 0.05. Simple correlation coefficients and regression equations were developed to evaluate the relationships between grain yields and SOC stocks.
3 | RESULTS