On 17th May 2016, Rothamsted Research celebrated the 160th Anniversary of the Park Grass Experiment. Below are some of my reflections on the occasion and on the utility of long-term experiments generally. 



The crime writer Agatha Christie was married to an archaeologist called Max Mallowan and she said of her husband: "An archaeologist is the best husband a woman can have. The older she gets the more interested he is in her."

That is exactly the point of long-term experiments: the older they get, the more interesting they become. Just like a good Agatha Christie, Park Grass is a perennial source of mystery and revelation. Agatha Christie published an extraordinary 100 works in her 85 years. Park Grass is at 300 and counting. 

It all began back in 1856, when John Bennet Lawes and Joseph Henry Gilbert devised an experiment to determine the effect different fertiliser applications have on hay yield.  Back then, hay was the red diesel of agriculture, fuelling the horses that did all the heavy work that tractors do today. It was not long before very significant yield increases were observed, especially on plots receiving nitrogenous fertiliser. 

Within a couple of years, Lawes and Gilbert also observed that different fertilisers encouraged the growth of different species. The botanical differences that arose were so large they said it looked as though the plots had been sown with different species.

As we know, adding N reduces biodiversity, but the new, exciting finding, recently published in the journal Nature by Jon Storkey and colleagues, is that the negative effect of N fertilisers on biodiversity is reversible. We never knew that!  For once it is good news for the environment, as these results suggest that semi-natural grasslands elsewhere that have lost species due to atmospheric nitrogen deposition may recover if nitrogen pollution is reduced.

Baron Justus von Liebig

Baron Justus von Liebig

Lawes and Gilbert achieve dramatic results so quickly that one may wonder why they didn't end the experiment after just a few years. One possibility is that Park Grass was a living demonstration of a novel fact that we now take for granted: plants get their nitrogen from the soil. Perhaps Park Grass was preserved as living proof that the god of agricultural chemistry of that time, Baron Justus von Liebig, was wrong to insist that plants get their nitrogen from the air.  The Baron was a major celebrity in Victorian times, and for two decades he stubbornly refused to accept that he was wrong. Such was his status that when he visited Britain, Liebig was invited to stay with Queen Victoria and Prince Albert at Balmoral.

Long-term experiments are one of the few tools we have that can help us cope with the scariest things about the future: the unknown unknowns. Park Grass has taught us many things that Lawes and Gilbert simply could not have conceived of in 1856.

The Park Grass Experiment began 3 years before Darwin published the Origin of Species, and yet it has provided us with superb examples of evolution and local adaptation in grasses. It was almost a century before Watson & Crick made the breakthrough that laid the foundation stone of molecular genetics, but now Park Grass is helping us understand the molecular mechanisms of adaptation to soil conditions. Soil bacteria, unknown to Victorian science, are critical to soil fertility, but only in the last 5 years has DNA sequencing revealed the incredible diversity of the microbial world and how it is altered by fertilisers.

So, here's to the unknown unknowns that will certainly be discovered in the next 160 years at Park Grass!

Silvertown, J. et al. (2006) The Park Grass Experiment 1856 - 2006: Its Contribution to Ecology. Journal of Ecology, 94, 801-814.

Storkey, J. et al. Grassland biodiversity bounces back from long-term nitrogen addition. Nature, doi:10.1038/nature16444 (2015).