Multispecies swards and multiple soil functions: evidence from agricultural grasslands

Conventional agricultural grasslands are often made up of only one grassland species (i.e., perennial ryegrass), which usually require large amounts of nitrogen fertilizer. This can have negative effects on the environment. In this research, I explored whether growing different species of plants in grasslands could improve soil functions and reduce reliance on nitrogen fertilizers. I compared four types of grasslands: perennial ryegrass, permanent pasture, and two mixtures containing grasses, legumes, and herbs using field and greenhouse experiments. These were managed with chemical nitrogen fertilizer, cattle slurry, or a combination of both. The mixtures produced more yield and used nitrogen more efficiently than perennial ryegrass, mainly because of legumes which naturally fix nitrogen. The mixtures also contained more micronutrients which are important for livestock, such as zinc and selenium and supported fewer harmful plant-parasitic nematodes. However, these benefits reflect short-term effects and are associated with some trade-offs. Overall, the use of grassland mixtures could improve sustainability, but management decisions remain important.