Obstacles to organic: A farmer in Bangladesh carries produce the traditional South Asian way - on his head. Image: Craig Meisner

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Can organic food feed the world? A recent study, published in the journal Renewable Agriculture and Food Systems provides new data that suggests it can. However, I have some grave reservations about this prospect that are based on my experience as a scientist and my time living and working with real farmers in developing nations.

The authors of this study assume the major stumbling blocks to organic farming feeding the world are low crop yields and insufficient quantities of approved organic fertilisers. However, I have lived and worked in Bangladesh – as a professor of Cornell University, covering agricultural research and development – for the last 25 years, and I believe that even if these problems could be surmounted, using organic farming to feed the developing world remains a pipe dream.

Green Revolution

Bangladesh is the size of England and Wales together, but with a larger population of about 140 million people. It has achieved remarkable progress in its food productivity, even achieving self-sufficiency in flood-free years (currently we are experiencing a particularly devastating flood). The basis of the Green Revolution that saved South Asia was not organics, but the use of a dwarfing gene to stop rice and wheat collapsing when they flourished, coupled with chemical fertilisers and irrigation systems.

Despite the burgeoning population, the Green Revolution of the 1960s is continuing today in South Asia with an increase in the use of hybrid rice and maize, conservation agriculture, deep placement of nitrogen in rice paddies, and many other exciting technologies.

Heavy burden

So, why won't the use of pure organics work in developing countries like Bangladesh?

Most supporters of the idea that organic farming can feed the world, assume that organic manures are cheap and available to all – even the poor. But this isn't often the case. I see cow dung in Bangladesh and all of South Asia as a valuable commodity. During my walks in the villages I see it collected largely by women and children and used as fuel. It's found in nearly every house, dried and formed into patties, to be sold or burned for cooking.

Straw is another organic source of nutrients, but that's not always available either. Rice and wheat straw is collected from the fields, and used for cattle feed or thatching for roofs. Even the stubble is used, which the poorest come and cut for fuel.

The authors of the study mentioned above – led by researchers at the University of Michigan in Ann Arbor, U.S. – have rightly assumed that organics can supply sufficient nutrients for plant growth. However, the quantities of organics required to sustain such productive growth makes it very difficult for the poor to handle. Organics whether farmyard manure, compost, or cow dung, contain moisture and are heavy and difficult to carry from the homestead to the fields by the growers.

For example, to raise a six-tonne rice crop in the peak season requires 100 kg of nitrogen. Because of monsoons and the fact that several metres of rainfall drains through the soil every three months, the amount of nitrogen it carries is low. Assuming we used good quality manure, there would be about 0.6 per cent nitrogen in the material; thus, requiring 17 tonnes per hectare to produce a six-tonne rice yield.

Can you imagine carrying 17 tonnes of manure, in repeated 50 kilogram loads, in a basket on your head? The lack of machinery to carry that material and the labour required to apply it, compounds the challenge.

Plus, there just simply isn't enough manure, or even plant biomass, available to apply 17 tonnes per hectare, for even a single annual rice crop across the whole of Bangladesh. That's enough of a problem, but when you consider there are actually two rice crops a year, the full scale of the problem becomes apparent!

Green manure

In answer to some of these problems, the new study proposes the use of a leguminous 'green manure' crop. These pulse crops fix nitrogen into the soil from the air through a symbiotic relationship with bacteria in their roots. They provide enough nitrogen for their own growth and more, and when ploughed under provide nitrogen for a subsequent crop too.

However for such a crop to be used in Bangladesh, it would have to take the place of a food crop, effectively halving the amount of food the land can provide. The cropping intensity in many developed countries is well over two crops per year, but I have seen as many as four to five crops per year in places that are elevated and flood-free.

Besides substituting for a food crop, green manure crops would also require cutting and ploughing under the soil. While ploughing technology has increased dramatically in the last decade in many developed countries, it is mostly the two-wheel tractors or roto-tiller types; thus making it a significant challenge to plough down any high-biomass green manure or crop residues into the soil.

Some propose a greater use of leguminous food crops to supply nitrogen for the proceeding cereal crop and where possible, growers would love to expand pulses. However, in South Asia, while the national pulse yields appear stable, switching to more of these crops is quite risky for individual farmers due to unseasonable rainfall, diseases, and poor growing environments.

Faced with a choice

So, to make compost effectively, one has to have surplus plant biomass and cow dung. For the poor who have limited land and animals, this is quite difficult.

Surveys I have conducted in Bangladesh clearly show that growers that do have the ability to add organics to their land are those who are richer and have larger land holdings and animals. The poor have to rely on purchased fertilisers, whether organic or chemical. When faced with a choice based on labour and expense, the poor choose the non-organic fertilisers.

Another recent study, published in Nature, revealed clearly what plant scientists have known for years — that plants take up some 20+ elements from the soil — whether it is from decomposing organics or chemical fertilisers. That study showed there was absolutely no difference in the biochemical make up of the plants grown in pure organics compared to fertilisers.

When I have asked growers in Bangladesh, most would love to be able to use more organics in their farming production. But due to the lack of availability and costs, organics are actually being used less each year.

Can organic agriculture feed the world? No, but most growers understand that it benefits the soil, and as such its use is is advocated as much as is possible. Unfortunately, for Bangladesh, and many developing countries, those possibilities are diminishing yearly as organics become less and less available and affordable.