Over-use of fertilisers is a particular problem in China, where whole river systems are polluted and the soils degraded by intensive farming. But safeguards in Europe, including using only a small amount of fertiliser where needed, and providing catchment reed beds that filter out any runoff before it enters the river, have greatly reduced the problem there.
However, local fertiliser use has a global impact. Producing fertilisers also pollutes the atmosphere with climate-altering greenhouse gases. The Haber reaction requires burning fossil fuels, which emit carbon dioxide. And other potent greenhouse gases, including nitrous oxide, are also released while making or using fertiliser. Transporting fertiliser also releases significant carbon emissions, making it a dirty industry.
So what’s the answer? One school of thought advocates organic methods that use pre-industrial methods of soil enrichment, such as muck-spreading, for example, They are useful, environmentally sensitive and cheap, if time-consuming ways of improving depleted soils across the world, but they have their disadvantages.
Artificial fertilisers cannot replace lost organic matter (carbon) in soils – mulch is a useful way of restoring structural integrity and preventing fertilisers from washing out of soil immediately, but it uses valuable animal fodder or cooking fuel. As with all fertilisers, manure runoff can also pollute rivers and oceans with eutrophication (death by oxygen starvation). Making manure releases its own potent greenhouse gas – methane. Planting legumes that fix nitrogen can take up space in the field that many farmers would prefer to dedicate to cash crops.
But, perhaps most damningly, in the world’s poorest areas, the majority of farmers do not have a choice about whether to go organic or not – most farmers are working with poor soils, bad seeds and uncertain water supplies.
The truth is that it would be impossible to feed a growing global population using purely organic farming methods. And because organic farming is relatively inefficient (yields are on average 25% lower) compared to modern technological methods, vast new tracts of land would need to be used, which would further impact our forests and other ecological spaces.
We’re already seeing the effect of this Africa, where 75% of the continent’s farmland is degraded. While Asia and Latin America farmers increased yields by increasing productivity of existing fields, in Africa, they have extended their cultivated land through slash and burn. As a result, grain yields in most of Africa are around 1 tonne per hectare, whereas South Asia achieves 2.5 tonnes per hectare and East Asia makes 4.5 tonnes per hectare. With Africa’s population set to double by 2050 to two billion, this yield gap must be overcome.
Which leads to the other main school of thought – one that advocates industrial-scale methods with the efficiencies of synthetic tools.
Africans use less than one-tenth of the global average of fertiliser use – less than 10kg (22 lbs) per hectare compared to 140kg (309 lbs) per hectare in Latin America and South Asia. Very few African countries produce fertilisers, the majority are imported, and the cost of transportation is very high on the continent because of high fuel prices and terrible roads. As a result, African farmers pay as much as six times the global average price for fertiliser – when they can find it at all.
In the 1980s, the IMF and World Bank imposed conditions on development aid, preventing African governments from subsidising fertilisers. The cost of fertilisers have risen fourfold in the past few years because petrol prices have soared. Millions of African subsistence farmers survive on less than a dollar a day, so fertiliser is simply unaffordable. Without subsidies, farmers can’t afford bad years, they plant less and are crippled by debts from loans just to buy seeds.