Impact of pH on Grass-White Clover Growth and Nutritional Quality in Grassland Soils: A Long-Term Experiment Study in Scotland

The pH of grassland soils in Scotland is declining in large areas due to less frequent lime applications. Soil nutrient availability, grassland yield and crop diversity are highly influenced by soil pH values. The consequence of acidic soil on grassland nutritional quality have not yet been comprehensively assessed. Grass-white clover sward samples were collected in 2019-2021 from a long-term pH field experiment, Woodland’s Field in Aberdeen, Scotland. This experiment is part of the larger ACE platform in Aberdeen. This was an 8-course ley-arable crop rotation which included a pH gradient (4.5-7.5 at pH 0.5 increments) superimposed across each crop row resulting in 7 target values. Collected crop samples were separated into grass and clover, and analysed for impact of pH on yield, protein and digestibility. These were analysed in the 1st, 2nd and 3rd year grass-clover ley. White clover growth in the sward was inhibited at pH 4.5≤5.0. Increasing soil pH above 5 increased the clover presence from 0.1-14% to 33-58%, a 800-1650% increase in clover biomass. This significantly increased the nutritional quality of white clover in the sward. This was exhibited through greater percent nitrogen, crude protein content and proportion of more quickly digested fibre fractions. Increasing soil pH from 4.5 to 6.0 increased total sward (grass and clover) biomass yield by 122-282.1%. The positive impact of pH on nutritive qualities of white clover in the sward are likely to increase dry matter intake of grazing animals and therefore liveweight gain and/or milk production. A simple measure to increase human-available products. By not increasing soil pH out of a highly acidic range, there may be sward nutritional quality and overall biomass yield consequences that are easy to remediate.