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.