The government should buy more British food for schools and hospitals, Sir Keir Starmer has said in a speech to the National Farmers Union (NFU).
The Labour leader also denied that his party was anti-countryside, calling the idea "more perception than reality".
International Trade Secretary Liz Truss said leaving the EU provided the chance to end "50 years of an anti-innovation" approach imposed by the bloc.
The NFU's conference was its first since the EU-UK post-Brexit trade deal.
The virtual get-together happened on the same day that Brussels asked for the full ratification of the agreement to be delayed until the end of April - to which the UK government agreed.
Some businesses have complained of more friction at borders and an increase in bureaucracy in recent weeks since the deal came into force, with the Britain leaving the European single market and customs union.
There are also concerns about trade between Northern Ireland and the rest of the UK.
But Ms Truss was keen to talk up the future of UK agriculture, telling NFU members it would continue to "lead the world in food and drink" and had quality and safety standards which were "second to none".
In a press conference afterwards, she admitted that there "continue to be issues to work through", but ministers would work to "make sure that trade continues to flow".
And Environment Secretary George Eustice said that following Brexit, farmers would be rewarded for "farming more sustainably, creating space for nature on their land, enhancing animal welfare and reducing carbon emissions".
During his speech, Sir Keir said more of the government's catering budget should go on British produce.
He also argued that money from his proposed Covid Recovery Bond scheme could go towards helping rural communities, for example by investing in long-term flood protection.
A 2014 government report said the public sector spent about ??2.4bn on food for schools, hospitals and the armed forces.
Sir Keir's appearance at the NFU conference was the first by a Labour leader since Tony Blair in 2008 and he used the opportunity to tackle perceptions of a "distance that has grown" between his party and rural communities.
He argued that Labour had strong connections to the countryside, citing its support for protecting British food standards.
Sir Keir said: "No party can claim to represent the country if we don't represent the countryside."