Groningen (grōˈnĭng-ən) [key], province (1994 pop. 556,600), c.900 sq mi (2,330 sq km), NE Netherlands, bordering on Germany in the east and the North Sea in the north. Groningen is the capital of the province, which has both an agricultural and industrial economy. There is a fertile coastal strip; the interior consists largely of reclaimed fenland and peat bogs and is drained by numerous canals. Vast reserves of natural gas were discovered there in 1961. In 1536, Charles V, the Hapsburg ruler, added Groningen to his Netherlands possessions. During the revolt of the Netherlands against Spain, the nobles living in the province's countryside signed the Union of Utrecht in 1579. The capital, however, remained loyal to the Hapsburgs until 1594.