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• Researchers found increasing application of fertilisers on agricultural grassland reduced flower numbers five-fold and halved the number of pollinating insects 
  
  
• With a trade-off in land management between yield and biodiversity, study highlights the need for financial incentives in UK and EU agricultural reforms to support biodiversity-friendly practices. 
  
  
• Scientists say fertiliser adjustments, such as limiting nitrogen, can maintain yields while benefiting pollinators and promoting sustainable landscapes. 

A new study by researchers at the University of Sussex and Rothamsted Research released today (Monday 20 January) has revealed the devastating impact that increased fertiliser use has on agricultural grasslands.  

The researchers examined the role of soil fertilisation on the diversity and number of pollinators and flowering plants at the world’s longest-running ecological experiment, Park Grass, Rothamsted, set up nearly 170 years ago, in 1856.  

Their findings, published in the journal npj Biodiversity, show that increasing application of fertilisers such as nitrogen, potassium and phosphorus, can reduce flower numbers five-fold and half the number of pollinating insects in agricultural grasslands. 

This is a critical moment for land use policy globally, with many countries including the UK and the European Union, currently undertaking significant green reforms of their agricultural policies. 

Almost a quarter of the Earth’s land area and almost half of the UK is agricultural grassland, areas where grasses or grass mixtures are used to feed livestock, support wildlife and maintain land resources in good condition.  Fertilisation of these areas has boosted food production but has come at the cost of environmental degradation and adverse effects on human health and welfare. 

Dr Nicholas Balfour, Post-Doctoral Researcher at the Laboratory of Apiculture and Social Insects at the University of Sussex, said:  

“Our results show significant biodiversity benefits from reducing fertiliser in agricultural grasslands.  

“While reduced yields are not typically thought of as a good thing, reducing grassland production intensity has the potential to realise many of the benefits of multifunctional landscape: benefiting pollinators, increasing resilience to extreme weather events, increased natural pest control, better soil health and air quality, and reduced soil erosion.  

“Our study suggests that the subsidies proposed in the forthcoming agricultural reforms are an economic necessity for sustainable and considered land stewardship that reduces fertiliser application and limits its negative consequences for biodiversity.” 

Dr Nicholas Balfour, Ciaran Harris and Professor Francis Ratnieks of the University of Sussex conducted a field study in Hertfordshire, England where they quantified and identified the flowering plants and the insect pollinators (bees, wasps, flies etc.) present across 18 paired fertiliser treatments at Park Grass.  

They found that reducing fertiliser application increased the numbers, species richness and functional diversity of both flowers and pollinating insects. 

They also identified a trade-off between flower and pollinator diversity and grassland yield. To maximise flowering plant species richness, and hence also pollinator species richness, a significant drop in fertility is required – but this will reduce yields. 

However, the study, funded by NERC, Rowse Honey Ltd., and the Elizabeth Creak Charitable Trust, did identify a potential solution looking at fertiliser adjustments. Their findings revealed that fertilising plots with all the major plant nutrients except nitrogen encouraged a high proportion of leguminous species. This approach not only preserved yields but also supported a greater number of pollinators, including bees. This could be a possible solution for conflicted landowners.  

Professor Francis Ratnieks, Emeritus Professor of Apiculture at the University of Sussex, said:  

“I visited Park Grass many years ago and realised the unique opportunity it provided to study the effect of fertilising grasslands on wild flowers and bees. Considering the current focus on fertiliser use, and the substantial declines in pollinator numbers over recent years, this study could not have come at a better time, as we seek to understand how landowners can best help bees and other pollinators through open grassland areas.” 

The authors' findings highlight the challenge of balancing competing priorities in farmland management. They emphasise the importance of financial incentives to help with yield losses and enhance biodiversity in agricultural grasslands. Achieving these benefits will require well-crafted policies that promote the sustainable stewardship of pastoral landscapes. 

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