American officials have stoked concerns over the reliability of Chinese crop data, in a report warning that the Asian nation's addiction to soybean imports is damaging efforts to grow the oilseed itself.

US Department of Agriculture staff, who have repeatedly cautioned that a subsidy system leads China's local authorities to over-report national grains production, have flagged the difficulty of obtaining reliable data on the biggest soybean-producing province.

 The 7.9m tonnes of 2009-10 soybeans that Heilongjiang farmers have marketed as of May 10, according to beancounters at the province's Grain Bureau, is bigger than the 5.9m-tonne harvest as estimated by the Heilongjiang Provincial Statistics Bureau.

"Area statistics are also contested, with estimates for 2009-10 planted area ranging from 3.9m to 4.7m hectares," the USDA said, as it outlined a cut to its forecast for China's soybean harvest this year.

Late sowing penalty

The comments come the day after China's grain think tank, the CNGOIC, raised questions among analysts by sticking to an estimate for the 2009-10 corn crop of 164m tonnes, significantly higher than other estimates, some of which have come in below 140m tonnes.

The USDA said that its revision, which puts China on course for a second successive year of falling soybean output, reflected in part cold weather which had reduced sowings by up to three weeks, notably in Heilongjiang, responsible for more than 40% of China's production of the oilseed.

"The planting delays could have an impact on soybean yields by shortening the growing season and exposing the crop to additional weather risks," the department said.

Vicious circle 

However, China's weak performance in soybeans also reflect the weak profitability from growing the crop, compared with those from corn or rice, despite the country's huge appetite for the oilseed which has made it the world's biggest importer.

Since 2001-02, when China produced more soybeans than it imported, domestic output has declined while shipments from abroad have near quintupled to 49.0m tonnes.

"The large imports have depressed domestic soybean prices, which in turn have led to lower planted area and production, thus increasing the need for additional imports," the USDA said.