<b>Long-term manuring decouples the soil nutrient cycles that it is intended to balance</b>

Organic amendments are widely promoted for soil fertility, yet whether repeated manure application keeps these cycles coupled—or decouples element pools, turnover rates and the mediating microbial genes—has never been jointly tested.

Here, using a 54-year field experiment that combined ¹⁴C, ¹⁵N, ³³P and ³⁵S isotope tracing with soil metagenomics, we show that farmyard manure decouples the cycling of carbon and nitrogen from that of phosphorus and sulphur. Manure increased soil carbon and nitrogen stocks, turnover rates and related enzyme activities, but depleted topsoil organic phosphorus and sulphur through enhanced mineralisation and lower or similar phosphorus and sulphur inputs, even though plant-available phosphorus and sulphur remained similar.