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