## 3 Results and Discussion
### Dry Matter Yield (DMY)  
The DMY depended on the maize variety. The average DMY of the variety Magitop (FAO 270) was higher than that of the variety Delitop (FAO 240) regardless of the fertilizer dose. Both varieties differed in their reaction to fertilization. In terms of the average DMY of the variety Delitop, the highest-yielding variant fertilized with a dose of 200 kg N\(\cdot\)ha\({}^{-1}\) + PK differed by 4.7% from the variant fertilized with a dose of 120 kg N\(\cdot\)ha\({}^{-1}\) + PK and by 1.6% from the variant fertilized with a dose of 160 kg N\(\cdot\)ha\({}^{-1}\) + PK, i.e., by 1.0 t\(\cdot\)ha\({}^{-1}\) and 0.35 t\(\cdot\)ha\({}^{-1}\), respectively. There were smaller differences between the nitrogen fertilization variants applied to the variety Magitop, where the DMY increased by 1.4% (0.31 t\(\cdot\)ha\({}^{-1}\)) \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Years of Study**} & \multicolumn{4}{c}{**Fertilization Treatment**} & \multicolumn{2}{c}{**Variety**} \\ \cline{2-7}  & **120 kg** & **120 kg** & **160 kg** & **200 kg** & **Delitop** & **Magitop** \\  & **N\(\cdot\)ha\({}^{-1}\)** & **N\(\cdot\)ha\({}^{-1}\) + PK** & **N\(\cdot\)ha\({}^{-1}\) + PK** & **N\(\cdot\)ha\({}^{-1}\) + PK** & **N\(\cdot\)ha\({}^{-1}\) + PK** & **FAO 240** & **FAO 270** \\ \hline Year 1 & 20.00a & 21.47b & 21.93c & 22.16c & 20.87a & 21.91b \\ Year 2 & 20.42a & 21.91b & 22.28 bc & 22.53c & 21.30a & 22.27a \\ Mean from years & 20.21a & 21.69b & 22.11c & 22.35c & 21.09a & 22.09b \\ \hline \hline \end{tabular} a, b, c—means in the same rows with the same letter are not significantly different.  
\end{table} 
Table 4: DMY of maize biomass depending on the fertilization variant and variety (t\(\cdot\)ha\({}^{-1}\)). Figure 6: Boxplot of the DMY of two maize varieties during two study years. and 0.6% (0.13 t\(\cdot\)ha\({}^{-1}\)), respectively (Table 4). [PERSON] et al. [7] increased the dose of nitrogen fertilization from 120 to 160 kg\(\cdot\)ha\({}^{-1}\) and observed a significant increase in DMY. Moreover, increasing nitrogen doses applied by [PERSON] et al. [40] were effective to the level of 160 kg per ha and resulted in a DMY increase. Higher doses of nitrogen were ineffective in terms of yield. The level of nitrogen fertilization in the study by [PERSON] and [PERSON] [41] did not significantly influence the yield of fresh or dry matter of maize. The latter authors only observed that maize yield tended to increase when higher doses of nitrogen were applied. A comparison of the DMY of maize in the variant fertilized with a nitrogen dose of 120 kg N\(\cdot\)ha\({}^{-1}\) + PK and the control variant fertilized with the same dose of nitrogen, but without P and K, revealed interesting results. These fertilization variants of the variety Delittop differed in DMY by as much as 11.7% (2.22 t\(\cdot\)ha\({}^{-1}\)), whereas the variants of the variety Magittop differed only by 3.5% (0.75 t ha\({}^{-1}\)). The lack of P and K fertilization strongly differentiated DMY of the variety Delittop (Table 4, Figures 4-6). The results of the research on optimal nitrogen fertilization doses of maize grown for silage under Polish climate conditions are variable. [PERSON] [42] conducted a study on maize grown for silage and found that the optimal dose of nitrogen should be 140-150 kg\(\cdot\)ha\({}^{-1}\). According to [PERSON] [43], the optimal dose of nitrogen, calculated on the basis of the ratio of the DMY to N fertilization efficiency, is 150 kg\(\cdot\)ha\({}^{-1}\). According to various authors [7; 44; 45; 46], optimal doses of nitrogen applied to maize in the climatic and soil conditions of Poland ranged from 90 to 180 kg N\(\cdot\)ha\({}^{-1}\). Differences in the assessments of maize's response to nitrogen fertilization resulted from different cultivation purposes, different varieties, different plant density, and harvest time limiting the length of the growing season. [PERSON] et al. [47] noticed a high variation in the reaction of various maize varieties to nitrogen fertilization.