John Watson, who has died aged 93, was a first-generation dairy farmer near Dartington, south Devon, driven by the writings of the environmental movement (particularly Rachel Carson’s Silent Spring and the Club of Rome Limits to Growth report) to resist chemical fertilisers, which he could see were depleting the soil, and become an early convert to organic farming.

He combined a life of the mind with a relentless will to action, believing that examples inspired others far more than words. In 1974 his farm, Riverford, was possibly the first in the country to open for tours, which demystified farming for visitors. Riverford later became a beacon for the organic dairy, meat and vegetable movement, selling direct to customers, as his children developed various sustainable businesses on the farm.

John was born in Woodford Green, then in Essex, the younger son of William Watson and Emily Halfhead. His father was a banker turned sugar grower in Trinidad, where John and his sister, Pamela, grew up. John was at Marlborough college when the second world war was declared in 1939, and, after having finished his education in Trinidad and Ontario, sailed back in time for his 18th birthday to join up.

After demobilisation from the army in 1946 and a two-year agricultural degree at Emmanuel College, Cambridge, in 1951 he took on the tenancy of Riverford, a derelict Church Commissioners’ farm. The following year he married Gillian Hickling; they had five children, Louise, Rachel, Ben, Oliver and Guy, who all became involved in the farm.

His idealism started as a belief in new technology and techniques, and Riverford became a demonstration farm for chemical products. But John sensed the land was running down and knew he needed to change, although it was expensive and risky, and many thought organic farming was for cranks.

John was a believer, yet his distinctive voice stopped him seeming too single-minded. On his retirement smallholding near Modbury he set about proving how little carbon was needed to live, by installing a mini wind turbine, waterwheel and solar panels. He created a local low-growth, utopian community, with a vegetable-growing co-operative feeding into the LETS (local exchange trading system) network. Days spent pressing apples, surrounded by children raising money for Oxfam, were his version of heaven: education for the greater good.

John, who was my uncle, communed with the sea as well as the land. A solo sailor in his junk-rigged boat, Sulaire, he went where the wind took him. He objected to planning a route and wasn’t a natural maintenance hand. Thus he would often be found moored in a creek waiting for a spare part, while reading intensely or painting a watercolour.

When 89, John said: “The older I get, the more I think about the future than the past.” Certainly the more he aged the more he flourished, his 70s and 80s being probably his most fulfilled years. He died with Wendell Berry’s Manifesto: The Mad Farmer Liberation Front next to his bed. He inspired a huge number of people through his example, his transparent integrity and his optimism.

His coffin was made by one of his sons from larches he planted on the farm 40 years ago, and painted with his life’s story by the whole family. His grave on the farm is next to Gillian’s, looking over the land he redeemed and across to Dartmoor.

Gillian died in 1998. John is survived by his children, 14 grandchildren and a great-grandchild.