A growing number of urban farms are providing major benefits such as employment, fresh food and green space to local communities, a study has found.

But researchers have called for greater awareness of the value urban farms have for the often deprived areas in which they are situated, and more support as many face financial pressures.

The study, presented at the Royal Geographical Society's annual conference, examined a range of larger scale urban agricultural projects from schemes with poly-tunnels for growing crops to city farms with animals and petting zoos.

The number of urban farms, which are bigger than community gardens or allotments and typically occupy an area the size of a football pitch, have surged in recent years, the study's lead Dr Michael Hardman, from the University of Salford, said.

Many are adopting innovative technologies such as hydroponics to grow vegetable crops, utilising roof tops of city buildings, or running vegetable box schemes and other entrepreneurial ways to keep going.

But barriers remain, mainly around a lack of financial support and staffing, with those receive funding from local authorities are particularly at risk from financial pressures.

Funding for projects such as urban farms which are "seen as something that isn't vital to that area" is often the first thing to go in the face of the cuts councils are facing, Dr Hardman said.

The threat of development to farms which occupy valuable land in cities also casts a constant shadow.

But the farms - some of which have been going for more than 30 years - provide huge benefits to people who live near them, according to the study.

Dr Hardman said: "Not only are they enabling many, especially those from deprived areas, to access fresh produce through food box schemes and other initiatives, they are also providing jobs, apprenticeships and much valued green space.

"A growing number also contain animals, allowing city dwellers to reconnect with nature."

The study, which included soil testing, visits and interviews, also found food grown on city farms is safe to eat and the availability of produce had led many local residents to improve their diet.

"It's not going to change our food system, it's an add-on which can help supplement rural agriculture," he said, adding urban farms allowed people to see where their food comes from.

The research was commissioned by the Pendleton Cooperative, a group of housing developers, local authorities officials, residents and other local organisations who are considering an urban farm as part of regeneration plans for Salford.