The lush paddy fields of India
In the second of his series, BBC World Affairs Correspondent Mark Doyle analyses the state of food production across the globe.
On his farm just outside the Punjabi city of Ludhiana in northern India, Jagjit Singh Hara showed off his collection of old photos.
One of the farmer's most prized snaps is of him with the Norwegian-American agronomist Norman Borlaug, the man popularly known as The Father of the Green Revolution.
"Here we are when we were both young men," says Mr Singh Hara with smile.
"I said to him: 'Dr Borlaug, I want to put my hand in your pocket. But I don't want to take out the dollars, I want to take out the wheat seeds you have.'"
Punjab State, the breadbasket of India, is one of the places where the Green Revolution began. It more than doubled aggregate production here of wheat and rice.
India, a country that will probably soon overtake China as the most populous nation in the world, went from being a food-aid "basket case" to being largely self-sufficient in food.
Jagjit Singh Hara says India can feed the world
The benefits - and costs - of the Green Revolution in India are reflected in other parts of the developing world.
In Punjab, I was looking for clues about whether output could be boosted further to cope with the rising demand that will be required to feed a world population set to rise from 6.6 billion today to more than nine billion people by 2050.
Food output across the world increased considerably in the last four decades of the 20th Century, largely as a result of the intensive farming techniques introduced by the Green Revolution.
The new techniques involved distributing hybrid grain seeds - mainly wheat, rice and corn. The hybrids grow with a shorter stalk. This maximises the process of photosynthesis, which nourishes the grain because less energy goes into the stem.
The hybrid seeds were combined with the intensive use of fertilisers and irrigation.
Population v Production
After successfully being introduced in India, the Green Revolution was rolled out in other parts of Asia, Latin America and the Middle East. It was so successful in terms of production increases that it defied the gloomy Malthusian predictions of the 1960s, which said hundreds of millions would starve as population outstripped farm output.
The Revolution was a technological success.
"Before the 1960s, the population of India was multiplying like rats in a barn," said Jagjit Singh Hara, "but we didn't have the grain to feed them. After the Green Revolution, we doubled our yield and now we have proved that India can feed the world".
But the process has limits and they may have been reached. Population, on the other hand, has continued to rise in poor parts of the world.
The graph, compiled for the BBC by the UN Food and Agriculture Organization, shows that while yield per hectare has increased, the amount of land used for the major staple grains has remained fairly constant; this is because the amount of good farmland is finite.
Given the shortage of land suitable for growing more food, the obvious answer would be a new Green Revolution, or another hike in yields. But this may not be possible.
"The difficulty is that we are now pressing against the photosynthetic limits of plants," says the influential environmentalist Lester Brown of the Earth Policy Institute in the United States.
Brown draws an analogy with human performance on the running track;
"In the first modern Olympics in 1896, we were running the mile in under five minutes. By 1954, Roger Bannister had broken the four-minute mile. But now, more than half a century later, no-one is talking about a three minute mile."
Lester Brown: We are reaching the limits of what plants can do
"Plants are not that different from people in this sense", says Brown "You can get gains up to a point and then it becomes much more difficult - I don't know of any scientists who are predicting potential advances in grain yields that are comparable with those we saw in the last half century".
There are other limits to the Green Revolution.
Some of the poorer villagers I spoke to in rural Punjab said they had fallen into debt as they were unable to keep up with the rising cost of the inputs - fertilisers, irrigation pumps and regular fresh supplies of seed - which intensive agriculture requires.
One elderly man in the village of Lehragaga, Jasram Singh, sat on an old iron bedstead in his yard and recounted the unbearable pain he had suffered when two of his sons had committed suicide. They had fallen into debt, been forced to sell their land, and felt irreconcilable shame.
A local community activist, Jagdish Papra, said the case was typical of many families who had seen loved ones kill themselves because they could not keep up with the financial cost of inputs.
"In the old days we practiced subsistence agriculture and we felt a sense of control," said Papra. "Now everything is more complicated and lots of people are desperately in debt."
Amrita Chaudhry, an Agriculture Correspondent with The Indian Express newspaper, stood in a neat, almost manicured field of young green wheat;
"The balance sheet of the Green Revolution is that, yes, we are feeding the mouths. India no longer has to ask for food aid from other nations. But the fact is we are paying a very heavy price for agriculture at this present moment."
"Punjab is one of the biggest user of pesticides in India," Mr Chaudhry continued, "and they have leached into our subsoil water."
"There are health costs. We have had babies born blue because they are not breathing. Some of them have mental health problems. In the south-western belt, we have entire villages where each family has at least one or two cancer cases. All this is all because of this intensive agriculture that we have been doing."
In the final part of the series, I will be looking at how changing patterns of food consumption mean there are now more overweight people than hungry in the world.
For more information about food production and consumption tune to BBC World Service Radio on March 28, April 4 and April 11 to listen to the documentary series Feeding the World.