Trade-offs between forage nutrition and ruminant carrying capacity in response to fertiliser application – Findings from the Park Grass long-term experiment (1860–2020)

Rothamsted Research’s Park Grass Experiment (PGE) has been running continuously since 1856, making it the longest-running grassland experiment in the world. Naturally regenerating grassland swards are grown in plots with varying applications of fertiliser including ammonium sulphate and sodium nitrate (at varying application rates), organic fertiliser, minerals (K, Mg, Na, P), and lime, which is mown twice a year. As the world’s most widely produced crop, grass is predominantly used to feed ruminants, however, the nutritional properties and carrying capacities of the PGE plots have not previously been quantified. Dried PGE herbage samples were taken from the Rothamsted sample archive at decade intervals from 1860 to 2020, representing a range of plot treatments. Proximate analysis and XRF elemental analysis were performed, and the data was used to estimate ruminant carrying capacity of plots based on metabolisable energy and crude protein requirements for production. Results showed that all fertiliser applications increased carrying capacity driven by yield increases. Fertiliser applications tended to reduce crude protein and increase cellulose and hemicellulose. Increased growth appeared to have a dilution effect on some essential minerals, particularly Ca, Mg, Mn, and P. In addition to the results presented, this study highlights the importance of long-term experimental studies in the agricultural and environmental sciences.