The Broadbalk Winter Wheat experiment was established in 1843 to better understand the impact of adding varying amounts of manure or man-made fertiliser on both wheat yields and the soil it was grown from. Still running today, the experiment has seen various additions and modifications to help maintain its relevance as farming and environmental awareness have evolved over the last 180 years. 

With new insights and rapid advancements in technology, and alongside an ever-growing store of soil, grain and straw samples, the world-famous experiment continues to inform the way we farm. 

In the wake of our recent Long Term Experiments conference, we asked a few of our experts to suggest seven key things Broadbalk has taught us:

How to feed the world

First up, Broadbalk has achieved its initial aim of showing us how good yields of wheat can be achieved from the same field for 180 years with either inorganic fertilizers or manure. At the time the experiment was set up, typical wheat yields were about 1 tonne per hectare. Today, we’ve reached yields that can exceed 12 tonnes through careful management ensuring that soil acidity, weeds and diseases do not compromise the experiment – whilst the introduction of short-straw cultivars in the late 1960s led to game changing increases in grain yield.

Much of the knowledge of how to successfully grow wheat, knowledge which we now take for granted, originally came from what Broadbalk taught us. But it’s important to remember the part wheat has played in the history of mankind, as increasing wheat yields played a large part in fuelling the rapid growth of European cities in the late 1800s, and the 1960s green revolution that transformed the developing world.

Soil carbon and climate change

Initially developed for the soil data from Broadbalk, the RothC model is now used the world over to simulate the dynamics of carbon in soils – including grasslands, woodlands, and even volcanic soils. Taking into account soil type, climate and plant cover, it successfully mimics the fate of carbon in soils over decades from small experimental plots right up to the global scale.

Our current understanding of how soils will affect, and be affected by climate change, is in large part, thanks to the RothC model, which wouldn’t have been possible without decades of soil samples collected from Broadbalk.

When not to use fertiliser

Data from Broadbalk was instrumental in stopping the routine application of nitrogen fertilizer in autumn by cereal farmers in the UK, as it was clearly demonstrated how inefficient (and harmful) this was, with most being lost to the air or soil. Separate analyses of the drainage water from Broadbalk also led to important developments in our understanding of soil phosphorus leaching, which results in excess fertiliser encouraging harmful algal blooms in freshwaters.

Broadbalk not only shows us the value of adding fertilisers but also the point at which we need to stop – where diminishing yield returns are not worth the financial cost or the environmental impacts. 

The impact of acid rain on soils

Excess nitrogen is considered one of the major drivers of global biodiversity loss. Many human activities release nitrogen and sulphur into the atmosphere, resulting in various types of pollution, including acid rain. Data from Broadbalk showed just how bad things had got in the 1980s, with over 40 kg of nitrogen deposited per hectare. Thankfully, with various measures implemented to reduce nitrogen pollution since, today that number is closer to what it was in the 1880s. Interestingly, a similar decline in sulphur pollution over recent decades has actually led to a deficiency in many agricultural soils.

The growing threat of weeds

On plots where herbicides have never been used, yield losses to weeds have been consistently increasing since the 1960s. Less than a third of the harvest was lost to weeds during the 1970s, but between 2005-2014, this had risen to more than half. This is due to weeds doing better than crops in a warming climate, coupled with a shift towards shorter crop varieties that get shaded out by the taller weeds. Many weed species have also benefited over this period from increased use of nitrogen fertilisers whilst many have developed resistance to herbicides.

Conversely, these same areas of Broadbalk which has never received any herbicides, provide a refuge for seven plant species that are rare, uncommon or declining nationally, including corn cleavers – one of the UK’s rarest plants. These two results further demonstrate the fine balancing act we face in feeding a growing population without harming the planet.

The first ever study into ‘rewilding’

Rewilding is very much in vogue at the moment, but rather than be a modern idea, its roots can actually be traced back 140 years. One end of Broadbalk field was fenced off in 1882 and allowed to naturally revert to woodland, becoming the ‘Broadbalk Wilderness’. A publication on this (by two of our first women scientists, Winifred Brenchley and Helen Adam, in 1915) recorded the succession of plants that recolonised the former cultivated land as it transitioned to woodland. The Wilderness has also subsequently demonstrated the capture of carbon in soil and biomass through rewilding, with as much organic carbon sequestered in the soil under trees as on the plots receiving 35 tonnes per hectare of manure annually. That’s not to mention the carbon captured in the trees themselves.

How to design experiments

Away from the field, many of the concepts of experimental design and the statistical tests used to analyse their results were developed at Rothamsted specifically to cope with the reams and reams of data coming from Broadbalk and the other long-term experiments.  From archaeology to zoology, the statistical methods developed for Broadbalk in the 1920s have transformed research in the experimental and social sciences, and ultimately, shaped our world.