By Sarah Murch BBC Two's Future of Food

Climate change, drought, population growth - they could all threaten future food supplies. But global agriculture, with its dependence on fuel and fertilisers is also highly vulnerable to an oil shortage, as Cuba found out 20 years ago.

Around Cuba's capital Havana, it is quite remarkable how often you see a neatly tended plot of land right in the heart of the city.

Sometimes smack bang between tower block estates or next door to the crumbling colonial houses, fresh fruit and vegetables are growing in abundance.

Some of the plots are small - just a few rows of lettuces and radishes being grown in an old parking space.

Other plots are much larger - the size of several football pitches. Usually they have a stall next to them to sell the produce at relatively low prices to local people.

Twenty years ago, Cuban agriculture looked very different. Between 1960 and 1989, a national policy of intensive specialised agriculture radically transformed Cuban farming into high-input mono-culture in which tobacco, sugar, and other cash crops were grown on large state farms.

Cuba exchanged its abundant produce for cheap, imported subsidised oil from the old Eastern Bloc. In fact, oil was so cheap, Cuba pursued a highly industrialised fuel-thirsty form of agriculture - not so different from the kind of farming we see in much of the West today.

But after the collapse of the Soviet Union, the oil supply rapidly dried up, and, almost overnight, Cuba faced a major food crisis. Already affected by a US trade embargo, Cuba by necessity had to go back to basics to survive - rediscovering low-input self-reliant farming.

City allotments

Oxen replaced tractors when Cuba became a low-fuel economy

With no petrol for tractors, oxen had to plough the land. With no oil-based fertilisers or pesticides, farmers had to turn to natural and organic replacements.

Today, about 300,000 oxen work on farms across the country and there are now more than 200 biological control centres which produce a whole host of biological agents in fungi, bacteria and beneficial insects.

Havana has almost 200 urban allotments - known as organiponicos - providing four million tonnes of vegetables every year - helping the country to become 90% self-sufficient in fruit and vegetables.

Alamo Organiponico is one of the larger co-operatives, employing 170 people, built on a former rubbish tip that produces 240 tonnes of vegetables a year.

There is a wide range of crops planted side by side and brightly coloured marigolds at the edges.

Car parks and rubbish tips have become vegetable plots

"We produce all different kinds of vegetables," says farmer Emilio Andres, who is proud of the fact that his allotment feeds the local community.

"We sell to the people, the school, the hospital, also to the restaurant and the hotel.

"It's important because it's grown in the city, it's fresh food for the people, it's healthy food, and it provides jobs for the people here too.

"We don't spray any chemicals. We only spray biological means like bastilos - a bacteria and fungus to kill the pests. And we use repellent plants like marigolds to keep away the pests.

"When I see all of these healthy crops, without too many pests, grown without any chemicals, it's amazing for me - I am making a contribution for the people that get healthy crops, healthy products."

Healthy diet

The organiponico uses raised beds filled with about 50% high-quality organic material (such as manure), 25% composted waste such as rice husks and coffee bean shells, and 25% soil.

A Western diet includes about three times as much food energy from animal products like meat and dairy

As well as marigolds, basil and neem trees are planted around the containers to keep the aphids and beetles at bay. Sunflowers and corn are also planted around the beds to attract beneficial insects such as ladybirds and lace wings. Sticky paper or plastic funnel-shaped bottles are positioned throughout the beds to trap harmful pests that do get into the garden.

And the methods work. Lettuce, tomatoes, peppers, squash, sweet potatoes, spinach, herbs and many other crops are grown in huge quantities and sold cheaply. Mangoes are 2 pence (3 US cents) a pound. Black beans 15p (25 cents) and plantain, just 12p (20 cents).

At the time of the oil shock, average calorie consumption in Cuba dropped by a third to dangerously low levels. Since then they have bounced back and Cubans eat just a little less than people in the UK.

The biggest difference is that a Western diet includes about three times as much food energy from animal products like meat and dairy.

The Cuban diet is much less fatty and requires less fuel to produce. A far less varied diet than in the West, it is also much healthier. The standard lunch for the farm workers is black beans, potatoes and rice.

Cuban agricultural researcher, Fernando Funes reckons the rest of the world has something to learn from the Cuban agricultural story.

"Well, do you have oil forever? And there also other considerations like global warming, nature conservation... the conventional way of farming generates a lot of damage to the environment and to human health.

"Developed countries as well as developing countries should pay a lot of attention to this kind of agriculture which takes care of land, people, environment and is also efficient and productive. You can combine both."

Find out more on BBC Two's Future of Food, Mondays 17, 24 & 31 August, at 2100 BST. All three episodes will also be available in the UK on BBC iPlayer .