Floristic diversity, yield and forage quality: recent snapshots from a long-term alpine grassland fertilisation trial

A long-term fertilisation trial has been conducted in Zweisimmen, Switzerland since 1956. Eight fertilisation treatments, arranged in a randomised block design, include NPK, NP, PK, N, slurry (G), slurry with P (G-P), slurry with PK (G-PK) and a control (0). While past studies have focused on a subset of treatments (mainly NPK, NP, G and 0), the present study showcases the latest results for all treatments, examining effects on floristic diversity, dry matter yield (DMY) and forage quality. Botanical composition was assessed in 2021 while forage quality and DMY were analysed in 2023 and 2024. Forage quality and DMY were significantly influenced by fertilisation treatment and harvest date. The N treatment produced the lowest DMY and legume proportion as well as one of the lowest Shannon-Wiener Index values (H ′). Contrastingly, treatments containing P and K, particularly G-PK and PK, produced high DMY and legume proportions without significantly reducing H ′ when compared to the control. Further analysis of the complete, long-term dataset is necessary to determine if the effects reported in the present study are a result of recent or cumulative fertilisation. Such insights may support the development of management strategies that promote species richness and productivity in alpine agroecosystems.