The NFU has criticised Government plans to reduce the level of feed-in tariff (FIT) incentives paid to growers with large-scale solar photovoltaic installations.
The scheme was launched on 1 April 2010 to give renewable energy users payments for the excess electricity they produce and export back to the national grid.
The union said the revised tariffs were "ill-judged" and "extremely damaging" to the renewable energy sector.
NFU chief renewable energy adviser Dr Jonathan Scurlock said: "We are horrified to see solar electricity incentives snatched away from our farmers and growers, many of whom have invested substantial amounts of their own project development money in good faith.
"These are not adjustments to the scheme - this is an ill-judged 'slash-and-burn' decision that sends a damaging message to investors in UK renewable energy."
He added: "The fast-moving international solar industry will be driven from Britain and the Government will struggle to decarbonise power generation without the confidence of investors in land-based renewables. It is a ghastly strategic mistake."
The changes were announced by climate change minister Greg Barker following a review of FITs that found large-scale solar photovoltaic schemes no longer needed the same level of support because technology had become cheaper.
Barker said: "Taking a pro-active approach to changing tariffs will allow us to avoid the boom-and-bust approach we have seen in other countries and enable us to support more homes and community schemes and a wider range of technologies."
Solar installations producing 250kW-5MW per hour and stand-alone installations will have their payment rates reduced from 30.7p/kWh to 8.5p/kWh