# Sloping Farmlands Conversion to Mixed Forest Improves Soil Carbon Pool on the Loess Plateau
## 3 Results  
### SOC and Soil N and P Nutrients in Different Vegetation Restoration Types  
All studied vegetation restoration types significantly increased SOC, LOC, NLOC, TN, TP, AN and AP compared with sloping farmland (\(p<0.05\)) (Figures 2 and 3). Among the four vegetation restoration types, i.e., grasslands, shrublands, forestlands and mixed forests, the mixed forests had the largest effect on SOC. The SOC in the mixed forests increased by 6.45 g kg\({}^{-1}\) after 30 years of farmland conversion to mixed forests (Figure 2). In addition, vegetation restoration decreased soil pH and BD (Table 2). The soil silt and clay contents also increased overall after vegetation restoration (Table 1).  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Land Use Types**} & \multirow{2}{*}{\begin{tabular}{c} **Slope** \\ **(\({}^{\circ}\))** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Altitude** \\ **(m)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **BD** \\ **(g cm\({}^{-3}\))** \\ \end{tabular} } & \multicolumn{2}{c}{**Soil Fractions (\%)**} & \multicolumn{2}{c}{**Primary**} \\  & & & & **(g cm\({}^{-3}\))** & **Sand** & **Silt** & **Clay** & **Undergrowth** \\  & & & & **(0-0.2 mm)** & **(0.2-0.002 mm)** & **Vegetations** \\ \hline SF (Farmlands) & 20–22 & 1165–1178 & 8.7 \(\pm\) 0.2 a & 1.27 \(\pm\) 0.12 a & 82.1 \(\pm\) 0.2 & 14.8 \(\pm\) 0.1 c & 3.1 \(\pm\) 0.1 c & _Setaria thaliana_ \\ GL (Grasslands) & 20–23 & 1189–1202 & 8.7 \(\pm\) 0.1 a & 1.18 \(\pm\) 0.12 bc & 81.1 \(\pm\) 0.4 & 15.9 \(\pm\) 0.3 b & 3.0 \(\pm\) 0.2 c & _Attennisia sacorum_ \\ SL (Shrublands) & 24–27 & 1039–1089 & 8.7 \(\pm\) 0.1 a & 1.19 \(\pm\) 0.12 b & 82.1 \(\pm\) 0.3 & 14.6 \(\pm\) 0.5 c & 3.3 \(\pm\) 0.2 c & _Attennisia sacorum_ \\ FL (Forestlands) & 22–25 & 1119–1234 & 8.7 \(\pm\) 0.1 a & 1.08 \(\pm\) 0.12 d & 78.6 \(\pm\) 0.3 & 17.7 \(\pm\) 0.4 a & 3.7 \(\pm\) 0.1 a & _Sigton buropean_ \\ MF (Mixed forests) & 23–27 & 1087–1165 & 8.6 \(\pm\) 0.1 b & 1.15 \(\pm\) 0.12 c & 80.8 \(\pm\) 0.3 & 16.0 \(\pm\) 0.2 b & 3.2 \(\pm\) 0.1 b & _Attennisia sacorum_ \\ \hline \hline \end{tabular}
\end{table}
Table 1: Information of geographical characteristics and soil physical properties in the five land use types. Note: SF, Sloping farmland; GL, Grassland; SL, shrubland of _Cangana korsthinskii_; FL, forestlands of _Robinia pseudoacacia_; ML, mixed forests of _Robinia pseudoacacia_ + _Cangana korsthinski_. pH, soil pH; BD, soil bulk density. Different lower-case letters mean significant differences in different land use types at 0.05 level (\(p<0.05\)). Data of soil physical properties are Means \(\pm\) SE. \(n=3\). All plots of the five land use types were located in the hill-slope, loess-derived soil and north-faced slope.  
Figure 2: Soil organic carbon (SOC, (**a**)), soil labile organic carbon (LSOC, (**b**)) and Non-labile organic carbon (NLSOC, (**c**)) in different vegetation restoration types. Note: SF, Sloping farmland; GL, Grassland; SL, shrubland of _Caragana korslinskii_; FL, forestlands of _Robinia pseudoaacia_; ML, mixed forests of _Robinia pseudoaacia_ + _Caragana korslinski_. Different lower-case letters above the error bars indicate significant differences in different land use types at 0.05 level (\(p<0.05\)). Data are Means \(\pm\) SE, \(n=3\).