The Effects of Spent Mushroom Substrate on the Yield and Nutritional Value of <i>Festulolium braunii</i> (K. Richt.) A. Camus

The aim of the experiment was to assess the effects of mineral and mushroom substrate nitrogen on the yield and selected parameters of <i>Festulolium braunii</i>. To this end, a two-year field experiment was conducted between 2017 and 2018. Spent mushroom substrate was applied at three levels (10, 15 and 20 Mg·ha⁻¹) and mineral nitrogen at four (30, 68, 105 and 180 kg·ha⁻¹). Mineral phosphorus and potassium were used at one level only, with 60 and 150 kg·ha⁻¹, respectively. The research also included the effects of the interaction between organic and mineral fertilizers and the determination of an optimal amount of nitrogen resulting in good-quality forage and a high yield. The plant used in the experiment was <i>Festulolium braunii</i>, an intergeneric hybrid of the Sulino variety. Treatment combinations significantly affected its yield, the content of total and digestible protein, as well as the energy values. For most forage parameters, the beneficial effects of mushroom substrate nitrogen and mineral nitrogen interaction were demonstrated, compared to the effects of mineral nitrogen applied on its own. The largest significant increase in the amount of biomass, was by 16% in comparison to plants treated with mineral fertilizers only (N₄PK); a significant increase in energy level (by 17%), was recorded for grass treated with 15 Mg·ha⁻¹ of mushroom substrate together with 68 kg·ha⁻¹ of mineral nitrogen (SMS₂ + N₂PK). The highest dose of nitrogen contained in mushroom substrate applied together with the smallest amount of mineral nitrogen (SMS₃ + N₁PK) resulted in the highest increase in total and digestible protein concentrations in the grass, 18% and 21% more, respectively, than in plants treated with mineral fertilizers only. The interaction of mineral and mushroom substrate nitrogen did not significantly affect the digestibility of the forage and its concentration of net energy of lactation (NEL).