# Classification Models for Nitrogen Concentration in Hop Leaves Using Digital Image Processing
## 2 Materials and Methods
### Experimental Characterization  
The experiment began in January 2022. Cascade hop plants were arranged in four rows oriented north-south, with each row containing 25 plants spaced 0.8 m apart, and 1 m between rows, totaling 100 plants grown in Red Latosol soil. The chemical and physical characteristics of the experimental soil were analyzed and are presented in Tables 1 and 2, respectively.  
The lateral rows were considered border rows, while the inner rows were longitudinally divided into 6 treatment groups (T0 to T5), with 4 plants per group, totaling  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \multirow{2}{*}{**Depth (m)**} & **pH** & **OM** & **V** & **AI3\({}^{\star}\)** & **H + AI** & **K** & **Ca** & **Mg** & **CEC** \\ \cline{2-10}  & **CaCl\({}_{2}\)** & **g/dm3** & \% & & & & **mmol\({}_{c}\)/dm3** & & & \\ \hline
0–0.20 & 5.6 & 17 & 74 & 0 & 23 & 1.1 & 51 & 12 & 87 \\
0.20–0.40 & 4.9 & 12 & 52 & 0 & 38 & 1.4 & 32 & 8 & 79 \\ \hline \multirow{2}{*}{**Depth (m)**} & **P resin** & **S** & **B** & **Cu** & **Fe** & **Mn** & **Zn** \\ \cline{2-10}  & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} \\ \cline{2-10}  & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} \\ \hline
0–0.2 & 309 & 9 & 0.22 & 6.3 & 72 & 7.3 & 24.9 \\
0.2–0.4 & 173 & 12 & 0.26 & 4.1 & 52 & 4.2 & 11.5 \\ \hline \end{tabular}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Soil Texture**} & **Sand** & **Silt** & **Clay** \\ \cline{2-10}  & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} \\ \cline{2-10}  & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} \\ \hline Medium & 631 & 98 & 271 \\ \hline \end{tabular}
\end{table}
Table 1: Chemical properties of the experimental soil.  
24 experimental plants. Each treatment group received a different dosage of nitrogen in the form of urea.  
The optimal nitrogen dose (11 g of nitrogen per plant) was determined via local soil analysis and based on the recommendations of [PERSON] et al. [5]. To create varying conditions of both nitrogen deficiency and excess, two treatment groups received nitrogen dosages lower than the optimal amount, two groups received higher than optimal dosages, one group received the optimal dosage, and one group served as the control. Thus, the 24 experimental plants were distributed across the six treatments groups as follows: T0 (no nitrogen added), T1 (25% of the optimal nitrogen dose), T2 (50%), T3 (100%), T4 (150%), and T5 (200% of the optimal level). These specific percentages are commonly used in nitrogen nutrition experiments in the literature [25; 26]. Other factors such as training, irrigation, soil composition, ventilation, and radiation were controlled and standardized.  
Maintenance fertilization was applied equally to all treatments and borders following the recommendations of [PERSON] et al. [5], and 50 g/plant of NPK 10-10-10 was applied once a month.