# Nitrogen Budget of Short Rotation Forests Amended with Digestate in Highly Permeable Soils
## 3 Results and Discussion
### Components of the Soil N Budget
#### 3.1.5 Nitrogen Content in Woody and Herbaceous Biomass  
The total values of dry woody biomass estimated at the end of this experiment on 26 July 2011 were: 5.4, 6.4 and 8.3 t ha\({}^{-1}\), in A0, A1 and A2, respectively. The values show a low uptake of N by trees plantation at this stage: 19.9, 18.6 and 25.7 kg-N ha\({}^{-1}\), in A0, A1 and A2, respectively. Long-term studies have reported significant values of immobilized N in woody biomass [27], recorded values ranged from 110 to 300 kg-N ha\({}^{-1}\) in a nine-year poplar plantation.  
The values of total dry herbaceous biomass recorded from May 2010 to May 2011 in all the plots (Table 5) ranged from 6 to 13 t ha\({}^{-1}\) y\({}^{-1}\). In the three SRF plots from 30 June 2010 to 23 August 2010, there was a significant growth of Amaranthus sp., an invasive herbaceous species.  
The biomass values showed clear differences between the two control plots and the plots fertilized with digestate, and a clear and proportional effect of the fertilization was demonstrated. However, part or the whole N quantity has been removed (see Table 5). Unlike in the SRF system, where only Amaranthus sp. was removed, the above ground herbaceous vegetation in the permanent meadow was completely removed after moving.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Depth (cm)** & \multicolumn{6}{c}{**May 2010 (kg-N ha\({}^{-1}\))**} & \multicolumn{6}{c}{**May 2011 (kg-N ha\({}^{-1}\))**} \\ \hline  & **A0** & **A1** & **A2** & **P0** & **P1** & **P2** & **A0** & **A1** & **A2** & **P0** & **P1** & **P2** \\
0–30 & 39.1 & 41.3 & 40.7 & 50.2 & 51.1 & 53.7 & 36.9 & 26.7 & 25.6 & 19.9 & 22.4 & 30 \\
30–50 & 54.7 & 59.3 & 56.9 & 63.6 & 65.9 & 59.6 & 56.1 & 34.7 & 39.3 & 12.5 & 41.5 & 33.2 \\
50–80 & 60.5 & 68.1 & 65.1 & 64.8 & 63.4 & 69.1 & 53.1 & 49.5 & 59.8 & 9.6 & 41.8 & 47.4 \\
80–90 & 49.9 & 50.7 & 47.2 & 63.2 & 64.8 & 59.9 & 46.7 & 49.5 & 59.8 & 10.2 & 39.1 & 41.9 \\ TOT & 204.2 & 219.4 & 210 & 241.8 & 245.3 & 242.3 & 192.8 & 160.4 & 184.4 & 52.2 & 144.8 & 152.6 \\ \hline
**Depth(cm)** & \multicolumn{6}{c}{**Difference * (kg-N ha\({}^{-1}\))**} \\ \hline  & **A0** & **A1** & **A2** & **P0** & **P1** & **P2** \\
0–30 & \(-\)2.2 & \(-\)14.6 & \(-\)15.1 & \(-\)30.3 & \(-\)28.7 & \(-\)23.7 \\
30–50 & 1.4 & \(-\)24.6 & \(-\)17.6 & \(-\)51.1 & \(-\)24.4 & \(-\)26.4 \\
50–80 & \(-\)7.4 & \(-\)18.6 & \(-\)5.3 & \(-\)55.2 & \(-\)21.6 & \(-\)21.7 \\
80–90 & \(-\)3.2 & \(-\)1.2 & 12.6 & \(-\)53.0 & \(-\)25.7 & \(-\)18.0 \\ TOT & \(-\)11.4 & \(-\)59.0 & \(-\)25.4 & \(-\)189.6 & \(-\)100.4 & \(-\)89.8 \\ \hline \hline \end{tabular} \({}^{*}\) difference in N soil content between May 2010 and May 2011.  
\end{table}
Table 4: Concentration of N in soil.  
\begin{table}
\begin{tabular}{c c c} \hline  & **Dry Herbaceous** \\  & **Biomass (\(\mathbf{\text{th}}\) ha\({}^{-1}\) y\({}^{-1}\))** & **Available N (kg ha\({}^{-1}\) y\({}^{-1}\))** & **N Removed (kg ha\({}^{-1}\) y\({}^{-1}\))** \\ \hline
**A0** & 6 & 152 & 6 \\
**A1** & 9 & 218 & 24 \\
**A2** & 10 & 246 & 36 \\
**P0** & 8 & 0 & 188 \\
**P1** & 10 & 0 & 256 \\
**P2** & 13 & 0 & 340 \\ \hline \hline \end{tabular}
\end{table}
Table 5: N amount in herbaceous biomass.