**3. Results**

Meteorological conditions during the growing season of spring cereals (2013–2015) were not very diverse (Table 3). Average air temperatures during these growing periods were similar. The highest amount of precipitation in the growing period occurred in 2013, while the lowest occurred in 2015. This did not affect the differences in grain yields of mixtures during the years of research. The tendency for lower yields of mixtures on the better soil in 2015 can be explained by lower rainfall in that year and more permeable granulometric composition of the soil. The lack of precipitation, especially in May and June, is the main reason for low yields of cereals in a given year. It can be assumed that the sum of precipitation from March to July within the range of 220–250 mm is sufficient to obtain a fairly high spring grain yield.


**Table 3.** Meteorological conditions in 2013–2015 compared to the long-term (1969–2005).

Significant differences in grain yield, protein yield, and net energy yield in grain (in MJ) were found among treatments. The percentage of cereal species in the grain yield of mixtures was uneven (Tables 4 and 5). On soils of Albic Luvisols, barley exhibited a higher share in the yield (as compared to other components), which was followed by covered oats. On the Haplic Arenosols, the highest percentage in the yield was observed for covered oats, which was followed by covered barley. On the other hand, naked oats had the smallest share in grain yield of mixtures containing it on both soils.


\* Covered barley + covered oats (CB + CO), Covered barley + wheat (CB + W), Covered barley + covered oats + wheat (CB + CO + W), Naked barley + wheat (NB + W), Covered barley + naked oats + wheat (CB + NO + W), Covered barley + covered oats (CB + CO), Covered barley + wheat (CB + W), Covered barley + covered oats + wheat (CB + CO + W), Naked barley + wheat (NB + W), Covered barley + naked oats + wheat (CB + NO + W).

**Table 5.** Yield sharing (%) of each partner in mixture on Haplic Arenosols (average 2013–2015).


\* Covered barley + covered oats (CB + CO), Covered barley + wheat (CB + W), Covered barley + covered oats + wheat (CB + CO + W), Naked barley + wheat (NB + W), Covered barley + naked oats + wheat (CB + NO + W), Covered barley + covered oats (CB + CO), Covered barley + wheat (CB + W), Covered barley + covered oats + wheat (CB + CO + W), Naked barley + wheat (NB + W), Covered barley + naked oats + wheat (CB + NO + W).

The grain yield of the studied mixtures was much higher on Albic Luvisols than on Haplic Arenosols, which was conditioned by weather conditions in studied years (Tables 6–8). On both these soils, there was a large variability in grain yield between mixture variants. Regardless of the soil quality, the highest grain yields were achieved with a mixture of hulled barley and covered oats at both sowing densities. On the better soil, similarly to it, the mixture of covered barley and wheat was yielded, but only at lower sowing density. On the poorer soil, higher yields were achieved by a mixture of barley with oats and wheat regardless of sowing density. On both soils, the lowest yields were recorded for mixtures of naked grain barley with wheat and of covered barley with naked oats and wheat. All types of mixtures differing in grain species' composition were yielded similarly under both sowing densities (insignificant differences between densities) (Tables 6 and 8).


**Table 6.** Yields of various spring cereal mixtures on Albic Luvisols.

\* Means not followed by the same letter are significantly different. \*\* Covered barley + covered oats (CB + CO), Covered barley + wheat (CB + W), Covered barley + covered oats + wheat (CB + CO + W), Naked barley + wheat (NB + W), Covered barley + naked oats + wheat (CB + NO + W), Covered barley + covered oats (CB + CO), Covered barley + wheat (CB + W), Covered barley + covered oats + wheat (CB + CO + W), Naked barley + wheat (NB + W), Covered barley + naked oats + wheat (CB + NO + W).

Comparison of means for grain yield, protein yield, and net energy yield by orthogonal contrasts depending on planting density proved that productivity of mixtures with covered barley depends on the sowing ratio and soil quality (Tables 7 and 9). In three mixture components, the difference of the sowing ratio of covered barley did not affect the grain yield, or yield quality. However, comparing the yields among two-component versus three-component mixtures indicates that covered barley significantly increases the productivity in higher crop density.



\* n.s.- not significant.


**Table 8.** Yield of various spring cereal mixtures on Haplic Arenosols.

\* Means not followed by the same letter are significantly different. \*\* n.s.- not significant, \*\*\* Covered barley + covered oats (CB + CO), Covered barley + wheat (CB + W), Covered barley + covered oats + wheat (CB + CO + W), Naked barley + wheat (NB + W), Covered barley + naked oats + wheat (CB + NO + W), Covered barley + covered oats (CB + CO), Covered barley + wheat (CB + W), Covered barley + covered oats + wheat (CB + CO + W), Naked barley + wheat (NB + W), Covered barley + naked oats + wheat (CB + NO + W).



n.s.- not significant.

Cereal species differed in terms of grain protein content covered by barley (11.4–11.9% d.m.), naked barley (12.4–12.7% d.m.), covered oats (11.1–11.5% d.m.), naked oats (13.3–13.7% d.m.), and wheat (13.7–14.4 d.m.). On poorer soil, a slightly higher protein content in grain (by 0.2–0.3% d.m.) was obtained. These data are not shown for individual components of each mixture.

On the better soil, the highest protein yields in grains were produced by mixtures of barley (covered or naked) with wheat, regardless of sowing density. Low protein yields were found in mixtures of covered barley with naked oats and wheat (especially under lower sowing density) and covered barley with covered oats under lower sowing density. On the poorer soil, higher protein yields

of mixtures of barley (covered or naked) with wheat and mixtures of covered barley with covered oats and wheat were found, but only at higher sowing density (Tables 6 and 8).

The highest yield of net metabolic energy on the compared soils was recorded for a mixture of naked barley with wheat under both sowing densities as well as for a mixture of covered barley with wheat under lower sowing density. On Haplic Aerosols, the mixture of naked barley with wheat under higher sowing density gave the highest yield of net metabolic energy, while both 3-component mixtures, under lower sowing density—the lowest (Tables 6 and 8).

The yield suppression ratio of individual components of mixtures were varied (Tables 10 and 11) depending on cereal species and soil quality. The highest yield suppression ratio in the mixtures was found for covered barley, which was followed by naked barley, covered oats, and naked oats. Wheat turned out to be the least competitive in the mixture stand. On the Haplic Aerosols, covered barley and naked barley were more competitive in the mixtures (Tables 6 and 8). Oats (covered and naked) responded in the opposite way as it was more competitive on the better soil (Albic Luvisols) than on the poorer soil (Haplic Arenosols). The competitiveness of wheat was similar on both soil types.


**Table 10.** Yield suppression ratio of the mixture components on the soil of Albic Luvisols.

\* Covered barley + covered oats (CB + CO), Covered barley + wheat (CB + W), Covered barley + covered oats + wheat (CB + CO + W), Naked barley + wheat (NB + W), Covered barley + naked oats + wheat (CB + NO + W), Covered barley + covered oats (CB + CO), Covered barley + wheat (CB + W), Covered barley + covered oats + wheat (CB + CO + W), Naked barley + wheat (NB + W), Covered barley + naked oats + wheat (CB + NO + W).

**Table 11.** Yield suppression ratio of the mixture components on the soil of Haplic Arenosols.


\* Covered barley + covered oats (CB + CO), Covered barley + wheat (CB + W), Covered barley + covered oats + wheat (CB + CO + W), Naked barley + wheat (NB + W), Covered barley + naked oats + wheat (CB + NO + W), Covered barley + covered oats (CB + CO), Covered barley + wheat (CB + W), Covered barley + covered oats + wheat (CB + CO + W), Naked barley + wheat (NB + W), Covered barley + naked oats + wheat (CB + NO + W).
