## 4 Discussion
### Proximate Composition
In the third term, there was a significant decrease in the protein content, on average by about 3%, compared to the earlier term. [PERSON] and [PERSON] [28] observed a similar downward trend in protein content as plants matured in the leaves of the red mustard (Brassica juncea). On the 70 th day of vegetation, they contained 24.68% of protein, while on the 85 th day it was 23.68%, and on the 130 th day only 17.64%. In our research, the double-improved Warta cultivar, with an average content of 36.28% DM, was the richest in protein. It was also found that individual cultivars reacted slightly differently in terms of the content of this component to the date of harvest (Table 1). Similarly, [PERSON] et al. [12] noted the higher protein content in the meal of seeds of the Warta cultivar (43.1%) compared to the Bamberka cultivar (42%), presenting two-year results from 12 field experiments. Usually, for mustard seeds, the protein content, according to different authors, is 30-36.8% [48; 49]. [PERSON] [26] points out that, similarly to the presented results, differences in protein content in total white mustard seeds were conditioned by the cultivar factor. It is well known that white mustard seeds are a rich source of fat and, according to various authors, its content usually ranges from 29% [48] to 31.78% [49]. The literature indicates slight differences in the fat content between the seeds of the varieties used in the experiment: Borowska 25.60-27.56%, Bamberka 28.9-31.4% [12; 50; 51; 52]. [PERSON] [26] emphasizes that differences in protein content in white mustard seeds depend on the genotype used. However, there is insufficient scientific literature on the fat content of the green parts of white mustard. In the presented results, the fat content in mustard plants ranged from 0.82-2.76% DM. [PERSON] et al. [27], using monthly plants of two cultivars of red mustard, indicating the content of crude lipids in one of the tested plants in the range of 0.42-0.59%,while in the other 0.40-0.61%. In turn, [PERSON] et al. [43] in mustard leaves obtained 0.47 g of fat from 140 g of fresh mass of leaves used for research. On the other hand, research by [PERSON] et al. [47] showed the content of fat in fresh _Brassica juncea_ plants in the range of 0.2-0.7%, which gives more than 3% of fat in dry mass--more than the tested varieties of white mustard, where the highest determined fat content was 2.76% DM. In the presented results of our own research, statistically significant differences in fat content between varieties of white mustard were found. The Warta cultivar was characterized by a lower fat content in the green parts of the plant: on average, 1.01% DM compared to the Bamberka and Borowska varieties, 1.77 and 1.90 DM, respectively. On the contrary, in the seeds, [PERSON] et al. [12] indicate a higher oil content in the seeds of the Warta cultivar (32.5%) compared to the Bamberka cultivar (31.4%), presenting two-year results from 12 field experiments: The third harvest, on average, 1.17 DM compared to the second harvest. This may explain the fact that [PERSON] et al. [53], in experiments conducted with the use of black mustard biomass, obtained a higher crude fat content of 2.66 and 2.62% DM. The aim of these studies was to use the crop for fodder, so older plants were probably used in this experiment. It should also be emphasized that the total lipid content decreases in stressed plants with increasing triacylglycerol levels [54]. The content of total carbohydrates in the dry matter of plants significantly increased with the development of plants. During the first harvest, the mustard plants contained an average of 50.81 DM, total carbohydrates and a week later by 1.92% more, and after two weeks by 6.31% DM, compared to the first harvest. However, the reaction to the date of harvesting of individual varieties was slightly different, because the Borowska cultivar reached the highest carbohydrate content during the second harvest: on average 56.82% DM.