**4. Discussion**

Our results clearly show that the weather course during the vegetation season is a primary factor affecting the performance of oat–vetch mixtures. Interestingly, oats had higher yields during the dry season, whereas vetch had higher yields during seasons classified as regular. Many authors emphasize that oats are more competitive toward companion species in mixtures during dry seasons [32–37]. In adverse weather conditions, such as rainfall shortage or inadequate rainfall distribution during vegetation and lack of radiation, the cereal component determines the cereal–legume mixture's yield [38].

We also showed that particular components of the mixture preferred different soil types; oat yielded better on a fertile Stagnic Luvisol. The vetch's yield parameters were better on a sandy Haplic Cambisol of a low N content. Moreover, vetch was performing better than oat in the following years of the experiment, when the rainfall distribution was variable. The balance between species is a key factor determining productivity of mixtures [39–41]. One of the managemen<sup>t</sup> factors that affect intercropped species' relative competitiveness and performance is N availability [35–37,42–44]. According to [45], the yield of cereal-legume mixtures grown on the poorer soils depends mainly on the cereal component and the species and sowing density of lupine do not have a significant impact on the yield of mixtures.

On the other hand, [44] showed that the mixtures of oats with yellow lupine and triticale with lupine yielded the best on the soil intended for rye cultivation. Other authors [42,46,47] underline that the legume component performs better in a situation of N deficiency, which may happen in the organic crop rotations. Cultivation of mixtures of oat and legumes is beneficial through the structure-forming action of the legume root system [48], increasing soil biodiversity and activating nutrients from compounds inaccessible to the root system of cereals [49].

In our research, oat cultivars significantly differentiated the yield, total protein content of oat grains and vetch seeds, as well as the vetch yield parameters, such as the 1000-seed mass. Similar results were obtained by [50], who found that in the oat–vetch mixture grown for fodder, the selection of oats cultivars and vetch species affected the crude protein content in the mixtures' biomass. However, [37] underlines that the N content in pea grain is lower in the mixture with cereal, compared to the pure sowing. The reverse situation was noted for the mixture's cereal component, in which N content in both grain and straw was higher [37].

Cultivation of crop mixtures, composed of at least two species, is a crucial element of proper agricultural technology, particularly in conventional farming, but mostly in the organic one [42,51,52]. The results of our study showed that the yielding and protein content of interspecies mixtures is the result of many natural and agrotechnical factors [7]. Therefore, the identification of yield variability of legume-cereal mixtures is particularly important and justified due to climate change, and more frequently occurring water shortage, as they are considered an important element of agricultural diversification [53].
