A large proportion of the British agricultural landscape is dominated by grasslands, used to graze livestock. Since livestock production is one of the mainstays of the British economy, these grasslands have been intensively managed in the past to increase productivity. However, they are today largely economically unproductive, ecologically degraded, dominated by a single grass species, and heavily reliant on fertilizer inputs to maintain productivity.
Increasingly, British farmers now seek to change their livestock rearing practices to promote sustainability and to mimic more natural systems that have enhanced productivity. In addition, they seek to improve the image and ecological impacts of livestock farming, which is put under increasing pressure to reduce greenhouse gas emissions and improve the quality of the British grassland habitats. One farmer group, the Pasture-Fed Livestock Association (PFLA), has set its own farming standards to include the promotion of diverse, species-rich pastures and the monitoring and maintenance of soil health.
A new study from researchers at the UK Centre for Ecology & Hydrology (UKCEH) has now compared the health of vegetation and soils in grassland plots across the U.K. that have been managed in different ways. They studied 940 large (200 m2) plots of grassland, including some from intensively-managed land with high levels of soil phosphorus and a predominance of a few sown pasture species, to others with lower soil phosphorus and a higher diversity of plant species.
These plots were sampled as part of the UKCEH Countryside Survey to assess relationships between key grassland sward and soil variables. The study also looked at how these variables changed over time as plots switched between different management protocols. In addition, comparable data on soils and vegetation were also collected from plots on 56 (mostly beef) farms managed according to PFLA criteria. The PFLA farm data was compared to the CS plot data to assess the impacts of PFLA management on soil and vegetation variables.
In particular, the researchers collected information on plant species diversity, plant height, soil invertebrate numbers, soil moisture, and soil levels of carbon, nitrogen and phosphorus.
The results, published in the journal Ecology Solutions and Evidence, show that high levels of phosphorus in soils are associated with low diversity of plant species. The presence of elevated phosphorus is indicative of fertilizer and slurry application, and it favors the growth of ryegrass (Lolium sp), which is a productive fodder species used for grazing livestock. In phosphorus-rich soils, ryegrass outcompetes other plant species, leading to generally low plant biodiversity.
The researchers also found that less intensively managed grasslands had greater plant species diversity, which was correlated with better soil health, such as increased levels of nitrogen and carbon, and a greater diversity of soil invertebrates, such as springtails and mites.
The plots on PFLA farms were found to have a greater plant diversity than was present in the CS plots – on average an additional six plant species inhabited the less intensively managed PFLA farm plots. These included different types of grasses and herbaceous flowering plants. In addition, grassland plants on these farms were often taller, meaning that they provided forage and breeding opportunities for a range on insects, including butterflies and bees.
Pasture-Fed Livestock Association grasslands did not yet show increased soil health, but the research indicated that this may be due to a time lag between increasing numbers of plant species and changes in soil health, particularly on farms which have been intensively managed in the past.
“We’ve shown for the first time, on land managed by farmers for production, that a higher diversity of plants in grasslands is correlated with better soil health,” said study lead author Dr. Lisa Norton, senior scientist at UKCEH. “This work also tells us that the Pasture-Fed Livestock Association members are on the right track to increase biodiversity, though it may take longer to see improvements in soil health.”
“Grassland with different types of plants able to grow tall and flower is associated with improved soil health measures, and is beneficial for creepy crawlies below and above ground. Having this abundance of life in our grasslands can in turn support small mammals and birds of prey, and farmers have told us that they are seeing voles and mice in their fields for the first time.”
“My hope for the future is that our grasslands can be managed less intensively – with all the improvements in plant and animal biodiversity and soil health that brings – but still remain productive for farmers.”
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