2.4 Statistical analysis
The data were expressed as mean ± 1 SE. The treatments were run for a one-way ANOVA using the software of R version 3.5.2. Redundancy analysis (RDA) was implemented with the vegan package in the software R. The EMF was as a uniteless index that usually combines soil characters and plant performance indexes, such as soil fertility, N cycling and plant productivity. Here, we examined 17 indexes including soil pH, EC, ESP, available nitrogen (AN), total nitrogen (TN), soil organic matter (SOM), catalase activity, urease activity, sucrose activity, and plant coarse protein, fat, coarse fiber, ash, K+, Na+, Ca2+, Mg2+concentrations under different N addition rates. The averaging-based EMF measure was applied on Z-score transformed data to calculate the EMF value into a single index. The EMF of different treatments was compared through one-way ANOVA analysis followed by the Duncan’s test. The relationship between EMF and N addition rates was best fitted by quadratic equation model, with the highest determinate coefficient. Other figures in this article were manufactured by Origin Pro 8.0 (Microcal, Malvern, England).