## 2 Materials and Methods  
### Study Materials  
Shoots of annual willow were sourced from the plantation of the Experimental Station of the Institute of Agriculture, Warsaw University of Life Sciences located in Skierniewice, Poland. The plantation is located on soil classified as IVa valuation class. Characterisation of the collected willow shoots was conducted by measuring 50 randomly selected samples. The parameters assessed included whole plant weight, leaf weight, stem weight, centre of gravity of the shoot, shoot length, and stem diameter at heights of 0, 150, 500, 750, 1000, 1250, 1500 and 2000 mm. The measurements were performed using an electronic balance WLC 6/A2 with an accuracy of 0.1 g, a digital calliper, type MAUa-E24F, with a range of 0-150 mm and an accuracy of 0.01 mm, and a 3 m tape measure with an accuracy of 1 mm. The results are summarised in Tables 1 and 2.  
Five levels of willow shoot moisture content were evaluated. The average moisture content of the fresh sample was determined using the oven-drying method in accordance  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Plant No.** & **Unit** & **Geometric Mean** & **Median** & **Min \({}^{\star}\)** & **Max \({}^{\star}\)** & **Deviation** & **CV \({}^{\star}\)** \\ \hline Whole plant weight & g & 254.45 & 237.6 & 119.7 & 448.8 & 80.99 & 31.83 \\ \hline Leaf weight & g & 60.99 & 54.65 & 4.80 & 132.6 & 29.09 & 47.69 \\ \hline Stem weight & g & 80.34 & 72.70 & 7.10 & 210.6 & 49.34 & 61.41 \\ \hline Basal shoot weight & g & 152.89 & 142.75 & 89.50 & 248.0 & 36.16 & 23.65 \\ \hline Centre of gravity of the shoot & mm & 1159.1 & 1155.0 & 770.0 & 1380.0 & 133.52 & 11.52 \\ \hline Shoot length & mm & 2301.0 & 2295.0 & 1900.0 & 2670.0 & 237.44 & 10.32 \\ \hline \end{tabular} \({}^{\star}\) CV—Coefficient of variation; Min—Minimum value; Max—Maximum value.  
\end{table}
Table 1: Parameters of the willow shoots analysed in the study.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Stem Diameter at Height of:** & **Unit** & **Geometric Mean** & **Median** & **Min \({}^{\star}\)** & **Max \({}^{\star}\)** & **Deviation** & **CV \({}^{\star}\)** \\ \hline
0 & mm & 14.82 & 14.67 & 11.86 & 19.25 & 1.74 & 11.77 \\ \hline
150 & mm & 14.14 & 13.79 & 11.59 & 18.5 & 1.71 & 12.06 \\ \hline
500 & mm & 12.98 & 12.745 & 10.19 & 16.64 & 1.53 & 11.77 \\ \hline
750 & mm & 12.20 with ASABE Standard S358 [62; 63]. The samples were dried in an SLW 115 TOP laboratory drying oven at a temperature of 103 \(\pm\) 0.4 \({}^{\circ}\)C for 24 h. They were weighed on a WLC 0.6/A1 electronic balance with an accuracy of 0.01 g. The moisture content was calculated using the following formula:  
\[MC=\frac{m_{w}-m_{s}}{m_{w}}\times 100\% \tag{1}\]  
where:  
_MC_--moisture content of the fresh sample, %;  
_mw_--weight of the fresh sample, g;  
_mts_--weight of the sample after drying, g.  
The highest moisture content was observed in samples collected immediately after harvesting. The next three levels of moisture were obtained through natural drying of the stems, while the lowest level was achieved by forced semi-drying. This process resulted in five moisture levels: 46.30 \(\pm\) 0.55%, 37.05 \(\pm\) 0.61%, 25.43 \(\pm\) 1.07%, 15.21 \(\pm\) 0.16%, and 1.35 \(\pm\) 0.64%, which were used for subsequent analyses.