Image copyright Reuters The Campaign to Protect Rural England has called for a post-Brexit "revolution" in the way farming subsidies are handed out in England.
It argues too much money goes to large-scale farms and says assisting smaller, more diverse farms would help the countryside and rural communities.
At present, farmers get about £3bn a year in subsidies, with the biggest farmers receiving as much as £1m.
The National Farmers' Union said it was wrong to say all big farms were "bad".
The CPRE has set out its vision for the future of agriculture after the UK leaves the European Union in a paper titled New Model Farming.
Farmers currently receive subsidies and other payments under the EU's Common Agricultural Policy (CAP) - but will cease to get EU funding once the UK leaves the EU.
Ministers have promised to maintain EU levels of funding until at least 2020.
What could Brexit mean for farmers?
'Industrial farms'
The grants, which are given for owning land and also taking care of wildlife, can amount to up to 60% of some farmers' income.
Existing level of state aid needed to be justified, and there should be a shift away from giving money to "industrial farms", the CPRE report said.
Such large-scale farms damaged the environment and put smaller farmers out of business, it claimed.
Subsidies should instead be directed towards smaller farms, and land should be made available for new farmers to enter the market, it said.
The charity argued this would benefit the countryside, and help rural communities reconnect with farming.
The National Farmers' Union has welcomed the Treasury's promise to maintain EU levels of farming subsidies until 2020, saying it would give "longer-term confidence" for farming businesses.
Cate Le Grice Mack, from the CPRE, told BBC Radio 4's Today programme there had been "a huge decline" in biodiversity in the UK.
She said authorities needed to make sure we are "maximising the potential for our landscape - for food, but also for wildlife and biodiversity".
"What we are saying is __that farmers need encouraging and supporting and helping to actually improve the natural landscape.
"They are the people who can do it, they are the people with the skills, this is about encouragement and help."
Minette Batters, deputy president of the NFU - which has launched a month-long consultation of its members on post-Brexit farming policy - said the UK had "incredibly diverse farmers".
"What we cannot say is __that big is bad, or small is good", she said.
"The point is we have a very diverse food and farming landscape in this country that the consumer benefits from."
She added: "Farms doors are open, the public can see what is going on and I really do not think we have industrial farming."