2.4 |Biomass sampling and analysis
The aboveground biomass including grain, straw, and stubble, were recorded from 2008 through 2016. At maturity, biomass samples of wheat and maize were manually collected in the center of each plot from two separate 10-m2 areas (2 rows × 10 m) for maize, and from two separate 2-m2 areas (1 m × 2 m) for wheat, respectively. After air-drying, portions of biomass samples were oven-dried at 65℃ for biomass determination.
The root biomass of wheat and maize were estimated by 22% and 23% of aboveground biomass, respectively (Kong et al., 2005). The plant-derived C content was 40% of both wheat and maize (Johnson et al., 2006).
Grain yield stability of wheat and maize was calculated for the treatments by the yield variability(YV%, Xu et al., 2019):
\begin{equation} YV=\frac{Y_{\text{std}}}{Y_{m}}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (1)\backslash n\nonumber \\ \end{equation}
The sustainable yield index (SYI) of wheat and maize was evaluated for the treatments accounting for all the 8-years’ grain yields (Ghosh et al., 2012):
\begin{equation} SYI=\frac{{Y_{m}-Y}_{\text{std}}}{Y_{\max}}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (2)\backslash n\nonumber \\ \end{equation}