Swamped by fertiliser

01-12-2009 | David Oliver

China is the world's largest consumer and producer of fertiliser, tallying up around one-third of total global production and consumption.

Fertiliser usage has rocketed in the past 30 years to a point where China has gone from a deficit of nutrients to serious environmental concerns about the effects of over fertilisation.

Along with the huge increase in fertiliser use, grain yields have doubled in the past 30 years. A recent Science journal report showed that while crop yields had doubled, nitrogen usage had climbed by 271% in the corresponding period.

"Nutrient additions to many fields [in China] far exceed those in the United States and northern Europe - and much of the excess fertiliser is lost to the environment, degrading both air and water quality," the authors wrote.

A survey in 2003-2005 showed that in intensive agricultural regions of northern China up to 588kg/ha of nitrogen was being used annually, releasing 227kg/ha of excess nitrogen into the environment. Researchers showed that nitrogen applications could be cut in half without loss of grain yield or quality, in the process reducing nitrogen losses by more than 50%.

Dr Zhang Weifeng, a fertiliser specialist at the China Agriculture University in Beijing, says several factors contribute to overuse of fertilisers on grain crops (in China these include rice, wheat, maize, soybeans, potatoes and other grain crops).

Overuse is more of an issue with smaller farmers; larger farms tend to be more efficient.

"Firstly, small farmers on small plots care more about the production they will get off the land to feed their own household rather than the cost," Zhang says. "With the migration of young people to the cities many of these are older farmers who are set in their ways, who lack knowledge about new ideas."

With livestock moving into larger feedlots he says there is less manure, and what is available is more likely to be used on fruit and vegetable crops. Chinese crop varieties have been bred to stay standing, whereas varieties in other countries may collapse easily if over fertilised. Many Chinese farmers also practise a monoculture style of intensive cropping instead of putting a legume such as soybeans into their rotation.

And, Dr Zhang adds, "as farmers receive a range of subsidies these encourage overuse of inputs by making the price lower than they would normally be".

At the local level curbs are sometimes handed down by decree. This includes restrictions on farming practices around important reservoirs and lakes that have been affected by serious pollution. Fluctuating prices have also led to a drop in demand in 2009 of at least 10%. This may lead to a sustained reduction in fertiliser usage if farmers see that crop yields are maintained due to a build-up of nutrients in the soil.

A national programme of soil testing and fertiliser recommendation has been implemented.

Generally S levels are not a concern due to soil types and previous use of superphosphate. Another source of sulphur which is not a welcome development is from acid rain which adds S but also contributes to soil acidification. Micronutrient deficiencies are becoming an issue; zinc and iron are beginning to be added to some fertilisers.

Total production has climbed from 18.8 million tonnes in 1990 to over 58 million tonnes in 2007 according to China Agriculture Ministry statistics. In 2009 demand is forecast at 33.5 million tonnes of N, equivalent to 72 million tonnes of Urea. P demand is forecast at 10.5 million and K at 4.5 million tonnes.

Though there is an oversupply of nitrogen and phosphate fertilisers there is still a shortage of potassium. As production is higher than demand this has also led to China becoming a major player in the global fertiliser trade. In 2007, 11.75 million tonnes was imported and 14 million tonnes exported. In addition to potassium fertiliser, China is a net exporter of urea and ammonium phosphate. Coal remains the raw material of choice for urea production with 80% coming from this source and 20% coming from natural gas. This lignite coal-to-urea process is the same as that being proposed by Solid Energy and Ravensdown in Southland.

Subsidies have played a role in building industry capacity and creating demand. Fertiliser plants can enjoy cheaper prices for inputs such as coal, gas and electricity as well as preferential tax rates. At the farm level farmers get a general subsidy for grain crop production that takes into account the cost of fertiliser, seeds and chemicals. This general subsidy varies from province to province and can range from RMB40 per mu of land ($NZ120ha) up to RMB400 per mu ($NZ1200/ha) in wealthy provinces such as Zhejiang.

The run-up in global prices in 2008 led to concerns there would insufficient supply for the domestic market. In response, in April 2008 the government imposed a 100% export tariff on all fertiliser exports as well as some fertiliser related raw materials.

In September 2008 the export tariff for nitrogen fertiliser and synthetic ammonia was increased to 150%. After seeing world prices drop and reduced domestic demand the government announced earlier this year that all controls would be removed and market forces would determine prices.

While the government realises the environmental and economic cost of fertiliser overuse, food security is still the highest priority, especially at the local level, and ensuring a stable food supply takes precedence over any longer term costs. Therefore while efforts are being made to use fertiliser more efficiently, the emphasis will remain on ensuring there is adequate food for a growing population.

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