Each year, Chinese farmers apply around 600 kilogrammes of fertiliser per hectare. Fertiliser use surged from seven million tonnes in 1977 to 26.2 million tonnes in 2005. As a result, the average grain production on farmed land doubled in that time period.
Zhang Fusuo of the China Agricultural University in Beijing, who led the study, and his colleagues studied two typical "double-cropping" planting systems: the wheat–rice system in a region near Tai Lake in eastern China and the wheat–maize system in the North China Plain in the north-east.
Reporting in the Proceedings of the National Academy of Sciences, an American journal, the researchers showed that, as more fertiliser is applied, plants become less efficient at taking up nitrogen and more is lost into the environment. Depending on the crop, 20% to 50% leaked into air and groundwater.
Field experiments also showed that an optimal level of fertiliser — a third of the average amount applied by Chinese farmers — could maintain crop yields when properly managed. The study found, too, that the best yields were achieved when most of the fertiliser was applied later to seedlings, rather than at the time of planting.
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