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}