Substrate and Fertilization Used in the Nursery Influence Biomass and Nutrient Allocation in Fagus sylvatica and Quercus robur Seedlings After the First Year of Growth in a Newly Established Forest

This study evaluates the efficacy of innovative peat-free organic substrates and liquid fertilizers as alternatives to traditional peat substrates in the cultivation of Fagus sylvatica L. and Quercus robur L. seedlings in a newly established forest in Southern Poland. The experiment was conducted in a 2 × 2 × 4 experimental layout using a randomized complete block design, comprising eight treatments that combined four substrate types (three novel organic substrates and one peat-based control) with two types of fertilizers (solid and liquid). After one year of growth, biomass and nutrient allocation in the roots, shoots, and leaves of the seedlings were analyzed. The results showed that while solid fertilization enhances biomass accumulation, liquid fertilization supports more uniform growth across different substrates, particularly in oak seedlings. Also, peat substrates recorded the highest nutrient allocation. However, one novel substrate (R22) performed comparably, indicating its potential as a viable peat alternative. Significant interspecies differences were observed, with beech seedlings allocating more biomass to aboveground organs, while oak seedlings favored belowground nutrient allocation. These findings suggest that while peat substrates and solid fertilizers currently provide better outcomes, the innovative R22 substrate shows promise for sustainable forestry practices. Further refinement of the liquid fertilizer was recommended to enhance effectiveness.