Cutting nitrogen fertiliser use by farmers in half in some regions of China would substantially cut the country's greenhouse-gas emissions without damaging crop yields, says a new study.
The rampant overuse of nitrogen-based fertilisers by Chinese farmers to boost crop yields has caused widespread pollution: acidic soils and excess fertiliser flowing into rivers and water sources.
It has also dramatically increased China's emissions of nitrous oxide (N20) - the most potent of all greenhouse gases.
When applied to crops and plants, explains the study co-authored by Hanqin Tian
, from Auburn University in the US, nitrogen enters the soil and reacts with bacteria, which gives off N2O as a waste product. N2O is the third highest contributor to climate change behind CO2 and methane but is the most potent of the greenhouse gases as it absorbs the sun's radiation more readily.
“Farmers use these chemicals as they feel like it, or as they always have,” explained Xu Ming, director of the Pollution Prevention Office at the Ministry of Agriculture’s Agro-Environmental Protection Institute.
“The Ministry of Agriculture has standards for use, but if the standard says to use one bottle cap’s worth of pesticide the farmers will use three, just to make sure. But that’s just a waste.” In more closely regulated nations farmers aren’t allowed to apply pesticides themselves – certified companies need to be used. Although there are agricultural technology offices in China’s villages, there’s no way to monitor what the individual farmers are doing," he added.
Even more worryingly, Chinese agriculture has now become reliant on these chemicals.
“It’s become a natural phenomenon. The farmers know when to apply the pesticide. With green veg and Chinese olives if you don’t apply pesticide the whole lot gets eaten by insects,” said Xu.
However, Tian's study, published in the journal Environmental Research Letters
, estimates that crop yields of major crops (maize, rice, wheat, soybean and barley) would not be damaged by a major reduction in fertiliser use.
"Nitrogen fertiliser has become less efficient in recent years as the nitrogen input has surpassed nitrogen demands of plants and microbes. Excess nitrogen is not stimulating plant growth but leaving the system through leaching and nitrous gas emissions," says Tian.
"We need to advance education programmes to inform Chinese farmers of both the economic and environmental costs of excessive nitrogen fertiliser use. Effective management practices such as compound fertiliser use and optimised irrigation and tillage should be advanced to increase nitrogen use efficiency," he said.
As the world's biggest user of nitrogen fertiliser, China has the opportunity to not only reduce pollution, but also reduce its food security concerns from an over-dependence on expensive imputs, such as nitrogen fertiliser.