Skip to main content

A new study of long-term data from a Hertfordshire pasture suggests that spring hay yields in southern England have already been reduced by more than a third due to changes to our climate and further declines are forecast as global heating accelerates.

The analysis by Rothamsted Research and the University of Reading is published today in the Journal of the Royal Society Interface. This research has revealed that yields of animal fodder from grassland have fallen by around 35% over the last century. The data were collected between 1902 and 2016 from the Park Grass long-term experiment at Rothamsted’s main site in Harpenden, Hertfordshire. The study forecasts that climate change will reduce spring hay yield by a further 20-50% between 2020 and 2080. 

An innovative statistical modelling approach was used to analyse the data. This takes into account unusual patterns of yield variability, but the wide forecast range for loss in yield is primarily due to uncertainty over future global greenhouse gas emissions. The model confirmed that warmer and drier autumns, winters and, within limits, springs in the twentieth and twenty-first centuries reduced yield. The optimum spring weather is colder and wetter than the conditions that we are generally seeing now and those we are expecting to see in the future. 

Dr John Addy, a statistician at Rothamsted Research and the study’s lead author said, “The precise response of spring hay yield to temperature and rainfall varied during the year but there is an optimum “Goldilocks” spring rainfall and temperature associated with the maximum level of yield. Changes in autumn and winter temperature had more of an effect on yield than autumn and winter rainfall.”

Managed grassland (rough grazing and pasture) is the UK’s largest crop by area at over 12 million hectares; it underpins a livestock sector worth over 13 billion GBP each year. Spring hay and silage is fed to livestock throughout the winter and in also in times of summer drought, as is the case this year. 

Professor Richard Ellis of the School of Agriculture, Policy and Development at the University of Reading added “The one hundred and fifteen years of results from the Park Grass experiment allow us to analyse the consequences of the previous year’s weather on yield. There is a substantial legacy effect in this perennial crop: if the weather in one year is poor for hay yield, then yield in the following year is also reduced to some extent and vice versa. This is highly relevant to the resilience of farming businesses.”

These projections are specific to the Park Grass site, but the design of the long-term experiment means that a range of grassland systems are studied. Plots on the site range from those with high fertilizer inputs, plots with only additions of farmyard manure and some plots with no additional inputs. The relative effect of climate change on yield was remarkably similar across all these contrasting treatments. 

“Many livestock farmers in the region have already responded to change - the increase in the area of forage maize over the past half century being but one example, but future investments in milk production from grass are more likely to favour the wetter and cooler regions of the UK” concludes Professor Ellis.



Rothamsted Research is the longest-running agricultural research institute in the world. We work from gene to field with a proud history of ground-breaking discoveries, from crop treatment to crop protection, from statistical interpretation to soils management. Our founders, in 1843, were the pioneers of modern agriculture, and we are known for our imaginative science and our collaborative influence on fresh thinking and farming practices.
Through independent science and innovation, we make significant contributions to improving agri-food systems in the UK and internationally. In terms of the institute’s economic contribution, the cumulative impact of our work in the UK was calculated to exceed £3000 million a year in 20151. Our strength lies in our systems approach, which combines science and strategic research, interdisciplinary teams and partnerships.
Rothamsted is also home to three unique resources. These National Capabilities are open to researchers from all over the world: The Long-Term Experiments, Rothamsted Insect Survey and the North Wyke Farm Platform.
We are strategically funded by the Biotechnology and Biological Sciences Research Council (BBSRC), with additional support from other national and international funding streams, and from industry. We are also supported by the Lawes Agricultural Trust (LAT).
For more information, visit; Twitter @Rothamsted 1Rothamsted Research and the Value of Excellence: A synthesis of the available evidence, by Séan Rickard (Oct 2015)


The Biotechnology and Biological Sciences Research Council is part of UK Research and Innovation, a non-departmental public body funded by a grant-in-aid from the UK government.
BBSRC invests in world-class bioscience research and training on behalf of the UK public. Our aim is to further scientific knowledge, to promote economic growth, wealth and job creation and to improve quality of life in the UK and beyond.
Funded by government, BBSRC invested £469 million in world-class bioscience in 2016-17. We support research and training in universities and strategically funded institutes. BBSRC research and the people we fund are helping society to meet major challenges, including food security, green energy and healthier, longer lives. Our investments underpin important UK economic sectors, such as farming, food, industrial biotechnology and pharmaceuticals.
More information about BBSRC, our science and our impact.
More information about BBSRC strategically funded institutes.


The Lawes Agricultural Trust, established in 1889 by Sir John Bennet Lawes, supports Rothamsted Research’s national and international agricultural science through the provision of land, facilities and funding. LAT, a charitable trust, owns the estates at Harpenden and Broom's Barn, including many of the buildings used by Rothamsted Research. LAT provides an annual research grant to the Director, accommodation for nearly 200 people, and support for fellowships for young scientists from developing countries. LAT also makes capital grants to help modernise facilities at Rothamsted, or invests in new buildings.