The massive blast registered as a minor earthquake, leaving a hole which was 10 metres wide and four metres deep.
Residents of Ahlbach were woken by the blast at 4am on Sunday, which created a 1.7 Richter magnitude earthquake.
City spokesman Johannes Laubach told local paper Hessenschau: "We can be glad that the farmer was not in the field.
"With the former railway depot we were quite a bomb target at the end of the Second World War.”
The road near Ahlbach had also been used for the withdrawal of German soldiers.
Unexploded bombs are regularly found across Germany, with hundreds discovered annually.
In May 2015, 20,000 people were evacuated in Cologne after a one-tonne bomb was discovered in the city’s largest evacuation since the war.
In December 2011, almost half the population of Koblenz was evacuated in the country’s biggest bomb disposal operation since 1945.
A 1.8-tonne explosive and a smaller 125kg bomb were found in the riverbed of the Rhine after a drought.
In July 2010, three people died on a building site in Goettingen when a bomb was unearthed and exploded.