How the changing climate is affecting hay production

Data collected over more than a century at Rothamsted Research showed a fall of around 35% based on figures taken from between 1902 and 2016 from its Park Grass long-term experiment at Harpenden, Hertfordshire.

The study forecasts spring hay yields will continue to decline, reducing by a further 20-50% between now and 2080.

The study, carried out in conjunction with the University of Reading, used an innovative statistical modelling approach to analyse the data. This took into account unusual patterns of yield variability, but the wide forecast range for loss in yield is primarily due to the uncertainty over future global greenhouse gas emissions.

Reduced yields

The model confirmed that warmer and drier autumns, winters and, within limits, springs in the 20th and 21st centuries reduced yields. The optimum spring weather is colder and wetter than the conditions that are generally being seen in the south of England and those expected to be seen in the future.

Professor Richard Ellis, co-author in the School of Agriculture, Policy and Rural Development at the University of Reading, said the 115 years of results from the Park Grass experiment allowed the research team 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.

“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.”

Grazing and pasture

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

The 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 fertiliser inputs, plots with only additional farmyard manure and some plots with no additional inputs. The effect of climate change on yield was remarkably similar across all these contrasting treatments.

Dr John Addy, a statistician at Rothamsted Research and study 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.”

The research has been published in the Journal of the Royal Society Interface, here.