It has run ever since.

The experiment set out in 1843 to assess the value of then-new inorganic fertilisers against farmyard manure and control plots with no additions.

After 166 years of continuous year-on-year plot trials, and the collection of more than 26,000 soil, straw and grain samples, the experiment provides a unique picture of agricultural development.

Typical wheat yields in the area in 1847 were around 1.2 tonnes per hectare. The first unfertilised control plots yielded around this level, and continue to yield much the same today.

Today’s best yielding wheat plots—those fertilised with inorganic NPK, or with manure boosted by inorganic nitrogen, and grown in a rotation—can now deliver up to 11-12 t/ha.

Yields over the past 160-odd years intermittently rose in response to new knowledge. Major steps forward included:

• Fallowing in the 1920s.

• Liming in the 1950s.

• Herbicides in the 1960s.

• A huge lift from high-yielding semi-dwarf wheat varieties, also in the 1960s - part of the Green Revolution spurred by major plant breeding breakthroughs.

• Fungicides in the 1970s.

All these, and the revolution in farm machinery productivity, have contributed to yields now accepted as normal.

The Broadbalk archives have also been used to map environmental pollutants, and to assess the effects of climate change over the past 166 years.

For more information, visit Rothamsted Research Station

* Matthew Cawood visited Rothamsted Research on a travel scholarship provided by the World Conference of Science Journalists.