A Victorian experiment still running
In 1856, two scientists named John Bennet Lawes and Joseph Henry Gilbert began an experiment on 2.8 hectares of parkland at Rothamsted Research. The land had been permanent pasture for at least a century. Their initial goal was agricultural: to test how different fertilizers and manures affected the yield of hay. They divided the field into around 20 main plots and began applying specific, consistent treatments. Some plots received inorganic fertilizers like sodium nitrate or ammonium salts, others got farmyard manure, and one important plot was left completely unfertilized as a control.
Within just two years, Lawes and Gilbert noticed that the treatments were dramatically changing the types of plants growing in each plot. A study on hay yield became a long-term observation of ecological change. The same treatments have been applied annually ever since, providing an unbroken record of how nutrient inputs alter a grassland ecosystem. The plots are harvested for hay each June, which allows seeds to be returned to the soil, and a second cut is taken later in the year.
A patchwork of biodiversity
The long-term results are striking. The unfertilized control plot (Plot 3) maintains a high level of biodiversity, with 35 to 45 species of grasses, legumes, and other herbs. This plot is considered a baseline, showing the natural state of the meadow. Plots that receive heavy annual doses of nitrogen-based fertilizers have lost most of their species diversity. These plots are now dominated by just two or three competitive plant species that thrive on the excess nitrogen.
a major changes has been to the soil itself. When the experiment began, the soil pH was around 5.5. On plots treated with ammonium sulfate, the pH has dropped as low as 3.5 due to soil acidification. This acidic environment is toxic to most plant species and soil organisms like earthworms. In these plots, plant matter decomposes very slowly, leading to a buildup of an organic mat on the soil surface.
Since 1965, most of the original plots have been subdivided into four smaller sub-plots. Three of these receive applications of lime to maintain the soil pH at controlled levels of 7, 6, and 5, respectively. The fourth sub-plot receives no lime, allowing the acidifying effects of the fertilizers to continue. This allows scientists to separate the effects of the fertilizer nutrients from the effects of the soil pH changes they cause.