3.1. Red clover/grass mixture yields
The highest aboveground biomass of the red clover/ryegrass was obtained
for the first cut (4.58 t DM ha-1 on average during
2014‑2018); in comparison, the second and the third cuts yielded 2.98
and 1.49 t DM ha-1, respectively (Table 4). The
treatments used significantly affected the perennial ryegrass yields
during the five-year experiment. The soil amendments, i.e., straw and
biochar, significantly increased the productivity in comparison to that
of the CTR treatment. Even so, these differences were noticed only
during the first and second cut. For the first cut, a significant
difference was observed only between the CTR and any other treatment,
i.e., the MCTR and the soil with straw and biochar amendments. The plant
yield of the CTR was 3.69 t DM ha-1, whereas for other
treatments, the yields were 4.71 t DM ha-1 on average.
During the second cut, the CTR also resulted in the lowest yield (2.28 t
DM ha-1), but yield at the MCTR (2.66 t DM
ha-1) was at the same level. When comparing the
productivity of the plants from the soils with straw or biochar
amendments, the highest yield was observed for the WS treatment (3.48 t
DM ha-1). A significantly lower yield was obtained
from the WBL treatment (2.62 t DM ha-1) with wheat
biochar amendment at 2.25 t ha-1. During the third
cut, there were no significant differences between any treatments. The
aboveground biomass was 1.56 t DM ha-1. The
differences in the yields obtained during particular cuts also resulted
in significant differences between the treatments for the total annual
yields. The low values were characterized for CTR (7.42 t DM
ha-1) and MCTR (8.25 t DM ha-1). All
treatments amended with straw and biochar produced higher biomass, at
9.37 t DM ha-1 on average.