Traditional family farms could soon disappear, National Farmers' Union President Tim Bennett has warned.
Farming is being squeezed by low food prices
The farmers' leader blames cheap food prices and the changes to the way European subsidies are calculated.
Mr Bennett told BBC News generations of agricultural experience could be lost, and the change could be devastating for the countryside.
European subsidies are moving in emphasis towards environmental stewardship and away from production.
Wildflower meadows and cover for ground-nesting birds are among the habitats that will be encouraged by Brussels.
But Mr Bennett and many others in farming are warning that only big farms can make a profit in an economy based around cheap food.
Organic and selling direct to the consumer through farmers' markets may offer possibilities for some farmers to make money, but there is only a limited amount of room, Mr Bennett says.
And unless traditional family farms find something else to do, many will have to stop farming.
If that happens, it will be a social tragedy for rural communities which will lose irreplaceable skills, the NFU boss says.
Shadow environment, food, and rural affairs minister, Oliver Letwin, told BBC News the face of the countryside had always been shaped by farming and was bound to change over coming decades.
And he said the move away from subsidies for production towards environmental stewardship was "a matter of consensus" and "inevitable".
But he suggested various measures to help more of the most efficient small farms survive, including making it easier for them to diversify, bringing in better food labelling to show consumers when food had been produced to British standards, and cutting down on bureaucracy.
"Beyond that, we have to understand as a matter of strategy over the next 10, 20, 30 years that the countryside of Britain is a national treasure," he said.