Phosphorus and potassium requirements of a hay meadow of the Swiss Jura dominated by red fescue

Phosphorus (P) and potassium (K) inputs on grassland aim to maintain an appropriate botanical composition and to produce sufficient quantities of forage without harming the environment. Over a 13-year period, eight different levels of P and K fertilisation were applied on a low-intensive permanent grassland in the Swiss Jura. Rising inputs of P (between 0 and 26 kg P/ha/year) and K (between 0 and 116 kg K/ha/year) improved the availability of these elements in the soil. PK fertilisation had little influence on the botanical composition, but a significant and positive effect on the quantity of forage from the tenth year onwards. P and K content of the forage increased substantially with increasing inputs of these two elements. Based on the soil P content, the botanical composition, the quantity of forage and its P content, the annual P balance (inputs-removal) and the P nutrition index (PNI), an annual input between 9 and 17 kg P/ha/year can be considered as optimal for this type of grassland producing around 45 dt DM/ ha/year. The optimal dose of K is more difficult to determine, since it varies significantly depending on the indicator considered.