Halting China's fertiliser frenzy
Many nations can justifiably be envious of China's agricultural achievements - no famine for thirty years and only five per cent of food consumed is imported. Great leaps in production were achieved from the mid-1980s when fertilisers became readily available and subsidised. But from the mid-1990s onwards, while fertiliser use continued to rise, yields reached a plateau.
Weary from a weekend of soil workshops with a thousand apple farmers, Professor Tong Yanan is back at base at Yangling University in northern China. From a small set of labs and lecture rooms, with a loyal set of undergraduates, he is leading the campaign to get farmers across Shaanxi province to think carefully about which fertiliser they use, when and how. "There is much that farmers and advisors need to understand," he says. "Agricultural productivity is not the only measurement of success."
Yanan continues, "The law of diminishing returns is so evident here in China. China averages 240 kilograms of nitrogen per hectare but in Sweden it is 80kg/ha and in the United States, just 60 kg/ha. Over-use of fertiliser in China is one of the leading causes of surface and groundwater pollution."
Over-use of fertiliser
Tracing the fertiliser back to what farmers are doing in their fields in the province of Shaanxi, an area of three million hectares with a population of 35 million, has become Yanan's personal mission. "In a recent survey of 385 households, 85 per cent were found to have over-applied nitrogen on corn. I use this evidence all the time to convince other scientists, farmer advisors and government what is happening."
The soil type compounds the problem. In the Yangling area - in the southern plains of the province - the soils consist of 35 per cent clay, which helps to slow the passage of nitrates. But in other parts of the province such as the Loess Plateau in the north, where clay content is as low as five per cent, there is little to halt the leaching. With every passing month the nitrates move deeper through the soil. Once they reach two metres in depth, they are no longer available to plant roots. Nitrogen loss in Shaanxi province is calculated to be 22,000 tonnes per year - worth 244 million Chinese yuan (US$ 31.5 million).
Money wasted is only one facet of China's fertiliser crisis. In the 1990s, with support of European partners, Yanan began investigating nitrate levels in the water courses that feed from Shaanxi into the mighty Yellow river. Nitrate levels considerably exceeded the World Health Organisation (WHO) standards, posing a serious problem to river life and a health risk to people. But assessing the rate of over-use only determines the scale of the problem. For the problem to be addressed, it is essential that advice on best practice is disseminated. "Farmers often use their fertiliser in one application but we advise them to apply smaller correct doses three times during the cropping cycle," explains Yanan.
High value crops
Subsistence farmers on rain-fed land are not ostensibly the major culprits; it is on the irrigated plains where fertiliser use has risen fastest. The main targets for the new recommendations are farmers who grow high value crops such as fruit. With more money from the farm, farmers have more money to spend on inputs, so rising farmer affluence is coupled with greater wastage and pollution. Since the Chinese authorities permitted farmers to diversify into cash crops rather than staple crops for local consumption, millions of farmers have branched out into tree crops. Twenty five per cent of Chinese apples and 10 per cent of world apple production come from Shaanxi province, and the carefully managed, highly productive orchards stretch for hundreds of kilometres across the plains.
The task of reaching all these farmers is daunting even to an enthusiast like Yanan. "Yesterday a thousand farmers came to the meeting on improved production in apples. The more educated ones can understand the science of what I am saying. But for many it is hard to understand how fertiliser - the input they associate with more production - is now a problem." He concludes, "There are 27 million farmers to reach in this province alone, which is only one part of the Loess Plateau. Farmer training is a therefore a challenge and it can take many years to bring about change."
Date published: May 2007
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Professor Tong Yanan's work is being supported by the UK Department for International Development
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